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JW3-FT-5.12 FUS-TN-SA-SE-R-86

ENTE PER LE NUOVE TECNOLOGIE, L'ENERGIA E L'AMBIENTE

Associazione ENEA-EURATOM sulla Fusione

FUSION DIVISIONNUCLEAR FUSION TECHNOLOGIES

JW3-FT-5.12

Proposal for experimental determination of

radiological hazards of JET dusts and flakes.

Outcome from a literature survey

L. Di Pace(11)

Deliverables 2 and 3

(1) Thermonuclear Fusion Division

Via E. Fermi 45, I-00044, Frascati (Rome), Italy

e-mail:[email protected]

Rev. 0 October 2003
mailto:[email protected]:[email protected]


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Fusion Technology Task Force at JET

Reference: Fusion Technology Task Force at JET

JET/Technology Workprogramme 2003

Task JW3-FT-5.12

Task Title:Literature review of the spread of activated or tritiated dust and

of its biological damage and experimental determination of the radiation

hazards due to dust/flakes at JET

Subtask Title: Literature study

Deliverables No. 2 and 3

Document: Proposal for experimental determination of radiological

hazards of JET dusts and flakes. Outcome from a literature

survey

Level of

confidentiality

Free distribution Confidential Restricted distribution

Author(s):Luigi Di Pace, ENEA C: R: Frascati, Italy

Date:14 November 2003

Distribution list: C. Grisolia (FT at JET Task Force Leader, CEA Cadarache, France)

P. Coad (FT at JET Deputy Task Force Leader, UKAEA, Culham, UK)

W. Gulden (EFDA CSU Garching Field Co-Ordinator, Germany)

R. Lsser (EFDA CSU Garching Field Co-Ordinator, Germany)

E. Eriksson (EFDA CSU Garching FT Responsible Officer, Germany)

S. Ciattaglia (EFDA CSU Garching, Germany)

G. Piazza (EFDA CSU Culham FT Responsible Officer, UK)

S. Rosanvallon (EFDA CSU Culham FT Responsible Officer, UK)

B. Patel (JET HP and Env. Monitoring GL, UKAEA, Culham, UK)

D. Campling (Operator representative, JET, UKAEA, Culham, UK)

J. Doncel (CIEMAT (EISS Vandellos), Madrid, Spain)

P: Garin (CEA (EISS Cadarache), Cadarache, France)

M. Samuelli (ENEA FUS, C.R. Frascati, Italy)

A. Pizzuto (ENEA FUS-TEC, C.R. Frascati, Italy)

M. T. Porfiri (ENEA FUS-TEC, C.R. Frascati, Italy)

T. Pinna (ENEA FUS-TEC, C.R. Frascati, Italy)Abstract:

Revision No: 0 Changes:

Written by: Reviewed by: Approved by:

Luigi Di Pace Maria Teresa Porfiri Aldo Pizzuto


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TABLE OF CONTENTS

TABLE OF CONTENTS ............................................................................................................................................ .3ACRONYMS AND SYMBOLS ..................................................................................................................................4

1. INTRODUCTION ....................................................................................................................................................52. TRITIATED DUST & FLAKES IN JET .................................................................................................................6

3. TRITIATED DUST & FLAKES PHYSICAL PROPERTIES ......................................................................... ....114. TRITIATED DUST & FLAKES RADIOLOGICAL PROPERTIES ................................................. ........ .........17

4.1 T dust inhalation and uptake mechanisms ........................................................................................... ........ ....175. IN VITRO EXPERIMENTS ................................................................................................................................. .20

5.1 In vitro experiments results .......................................................................................................................... ....205.2 Comparison and discussion of the in vitro experiments results .......................................................................28

6. CONCLUSIONS ....................................................................................................................................................42REFERENCES ...........................................................................................................................................................45


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ACRONYMS AND SYMBOLS

AMAD = Activity Median Aerodynamic Diameter

AMD = Activity Median DiameterBe = Beryllium

C = Carbon

CMD = Count Mean Diameter

DAC = Derived Air Concentration

D-T = Deuterium-Tritium

DTE1 = Deuterium Tritium Experiment 1

EFDA = European Fusion Development Agreement

ENEA = Ente per le Nuove tecnologie, lEnergia e lAmbiente

FW = First Wall

HRTM = Human Respiratory Tract Model

HTO = Tritium OxideICRP = International Commission on Radiological Protection

IVC = In Vessel Component

JET = Joint European Torus

NRPB = National Radiological Protection Board

OBT = Organically Bound Tritium

PFC = Plasma Facing Components

PI = Pellet Injector

SAF = Self Absorption Factor

T = tritium

TFTR = Tokamak Fusion Test Reactor

UKAEA = United Kingdom Atomic Energy AuthorityVV = Vacuum Vessel


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1. INTRODUCTION

The present report deals with the literature review of biological damage due to tritiated dust;

experimental determination of radiation hazards due to dust/flakes at JET.The aims of the JET Fusion Technology Task JW3 FT 5.12 are:

Literature study of physical parameters which determine the spread of tritiated dust,

flakes and other materials (metal tritides, catalysts, molecular sieves, etc.) in air and of

their biological effects after incorporation;

Experimental study of physical parameter which determine the distribution of dust and

flakes in the atmosphere, their incorporation, the tritium dissolution in the in vitro and in

vivo experiments.

The part of this task appointed to ENEA, defined as goal a) [1

] is mainly focused on thefollowing deliverables:

D2 Perform a literature study of:

the spread of tritium contaminated or activated dust in air, especially of tritiated

carbonaceous, and of the materials (flakes, dust etc.) created in JET;

the biological effect of incorporated tritiated dust and tritiated particles, e.g. of metal

tritides, especially focusing on uranium molecular sieve and catalysts; the behaviour of

tritiated carbonaceous particulates (flakes) after incorporation.

D3 Summarise and discuss the results found in the literature in a report and especially

address missing and/or available information of the quantities to be determined under

goal b).

The goal b) [1], appointed to UKAEA, deals with the experimental determination of the radiation

hazards due to dust/flakes at JET.

The present report deals with Deliverable 3. Deliverable 2 was covered by the report [2].


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2. TRITIATED DUST & FLAKES IN JET

The generation of dust and of loosely adhered deposits in experimental tokamaks is due to the

erosion of C/Be FW by plasma/wall interaction, disruptions and evaporation, combined withdeposition on the FW through diffusion, surface saturation and co-deposition with carbon (see

Figure 1 [3]).

Figure 1 - Plasma wall interaction mechanisms leading to dust formation [3]

Co-deposition is the dominant process for tritium uptake by carbon if this is used in the tokamak

plasma facing components. Unlike implantation, which is a relevant mechanism for all metals,

co-deposition has only been found significant for carbon thus far. The mechanism of Tritium co-

deposition with carbon is shown in Figure 2.

The JET experience showed the production of significant quantities of tritiated dust and flakes

during D-T campaigns and the related build-up of carbon flakes on the cooler shadowed surfaces

of the divertor structure [4

]. Same phenomena were observed during the tritium campaign inTFTR [5].

.

Redepositionflux

Net erosionflux

Normal flux Disruption flux

Net erosion Net erosion

Wall Wall

Sputter

Re-deposit

Re-deposit

Evaporate

Vapor shield

Flakes, debris(>100 m)

Dust(


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Figure 2 - Mechanism of Tritium Co-Depositing with Carbon [6]

During the DTE1 phase of the D-T campaigns in JET about 35 g-T were used that left gram

quantities of T associated with flakes and dust deposits.

As a matter of fact, 6.2 g-T was estimated to be still inside the JET vacuum vessel (VV) at the

end of D-T campaigns. After recovery,


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considering the breathing rate of a reference worker (ICRP Publication 66 1994) [8, 9] 1.2 m3/h, it

would be sufficient nine hours ofexpositionexposure to get about 20 mSv, that is the limit for

individual dose set by ICRP. Furthermore, the data provided in [4] about the tritium

concentration in glove box handling the tritiated dusts from JET, 30,000 DACHTO, (DACHTO =Derived Air Concentration for HTO that is 8 x 105 Bq/m3), gives the idea of the radiological

concerns linked to JET dust and flakes.

It is evident the need for protection measures, already in place and used extensively during the

manned access. Furthermore, the release of dust to atmosphere is a possible route for public

exposure.

The study of radiological features of dust and flakes is thus important in order to use the

appropriate dose conversion factor both for worker safety and public safety.

Intake of tritium as a particulate can yield a dose quite different to intake of the same quantity

HTO. From the available data it appears the intake of tritiated dust could lead to larger dose than

HTO. [10,11]

In 1999 during the Pellet Injector (PI) shutdown, a manned access was done inside the JET

Torus. Measurements were carried out by personal (portable) cascade impactor.

A cascade impactor consists of a series of jet orifices of diminishingdecreasing diameter, and

impactor stages. The air stream is induced to change direction sharply and particles with enough

inertia to leave the air stream impact on the collecting surfaces. A back-up filter collects any

particle small enough to escape the last impactor stage. Figure 3 depicts a portable cascade

impactor.

Figure 3 Eight Stage Personal Impactor (JET) [4]


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Another tool way used to collect dust is by vacuum cleaning, although the efficiency of pick-up

is variable. The tool used is the cyclone. It consists of a case in a shape of truncated cone where

air is made to spiral downwards, subjecting the aerosol particles to a centrifugal force whichcauses larger particles to impact on the walls, whilst smaller particles pass to a back-up filter.

See in Figure 4 the remotely operated vacuum cleaner with an in-line cyclone dust collection

system adopted in JET to collect dust and flakes for analysis.

Figure 4 Remotely operated dust collection vacuum cleaner used in JET [4]

As a matter of fact during the JET remote tile exchange shutdown (1998), vacuum cleaning

ll d 150 f d d fl k

Cyclone


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Particle size distribution (aerodynamic diameter) of the cyclone collected dust from the JET

divertor tiles is shown in Figure 5 [4]. It was also possible to correlate activity with the particle

size.

Collection of dusts by vacuum cleaning is also feasible, although the efficiency of pick-up is

variable. As a matter of fact during the remote tile exchange shutdown (1998), vacuum cleaning

collected 150 g of dusts and flakes.

Figure 5 - JET collected dust size distribution

Factors such as the aerodynamic diameter determine the mobility of such materials in the

respiratory tract and describe the extent for deposition, and for inhalation intake. With low

values of the aerodynamic diameter, there is a greater likelihood for the material to remain

airborne in the human respiratory tract or be distributed further down into the lungs. Particlesbelow 10 m are classed as respirable aerosols.Presence also of sub micron particles implies small settling velocities, and increasing likelihood

of deposition at the alveolar region of the lung if inhaled. That increases the likelihood that

particles may remain in the body for a long time or even to be subjected to macrophage action in

the lung. Basically, the macrophage action is operated by white blood cells that roam the body

tissues engulfing foreign organisms, removing dead cells, and stimulating the action of other

immune system cells.

In addition to particulate dusts, flakes have been found in JET. Flaking is a mechanism also

observed in TFTR on carbon tiles, leading to a progressive detachment of particles having sizes

greater than ~ 100 m. They can easily disintegrateinto smaller particles.

Particulate Size Distribution

0

5

10

15

20

25

30

0 5 10 15 20 25 30 35 40

Particulate Size (Aerodynamic Diameter) m

Count(%
http://www.aidsmap.com/main/glossary.asp?lett=W&Explanation=blankhttp://www.aidsmap.com/main/glossary.asp?lett=W&Explanation=blank


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3. TRITIATED DUST & FLAKES PHYSICAL PROPERTIES

Particle size is an important parameter in the deposition pattern of particles in the human

respiratory tract and for the self-absorption factor. Self-absorption factor (SAF), is the fractionof beta particles that escapes from a particle.

Usually the particle size distribution can be expressed as a log-normal distribution with a

distribution density function.

The log-normal distribution is given by the following:

[1]

where the count mean diameter (CMD), is the particle size for which half the total number of

particles are larger and half smaller.the diameter where 50% of the particle number exceeds the

value, and g is the geometric standard deviation (GSD).The GSD org is given by:

where N is the number of particles.

Other size dependent values used to characterize the particle size distribution are listed as

follows.

Surface area diameter DMVS, also referred to as the mean volume-surface diameter or the

Sauter diameter. This diameter is useful in relating dust specific surface area, defined further on,

to the physical size distribution.

By using the count based methods of particle size distribution measurements, the following

relation is given to determine the DMVS.

[2]

where:ni = number of particles in a distribution bin;

di = midpoint diameter of bin [micron].

For particles having a log-normal distribution, the volume to surface ratio is the mean volume-

surface diameter or the Sauter diameter.

( )

=

2

2

ln2

)ln(lnexp

ln2

1)(

gg

CMDd

ddf

D

n d

n d

ii

i

ii

i

MVS =

3

2

( ) 2

1

lnlnln

=

N

CMDdnig


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i

i

i

i

i

i

mn

An

S

=SP


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Another important size dependent value is the specific surface area given in general by the ratio

of the total external surface of all particles divided by the sum of the mass of all particles:

[3]

For a mono-disperse spherical powder, the specific surface area Ssp (m2/g) is given by:

[4]

where:

d = diameter of a mono-disperse aerosol [m]; = density [kg/m3].

For a poly-disperse spherical powder, the specific surface area is given by Hinds [ 12]:

[5]

considering the equation [2], it is possible to write:

[6]

where:

DMVS = surface area diameter [m];

= density [kg/m3].

For a poly-disperse powder with irregular shape, a general form of equation is used for the

specific surface area:

[7]

where:

DMVS

= surface area diameter [m];

= density [kg/m3].

[ ][ ] 336

26

3

2

1010

10

8/3/4

=

dN

dNSsp

310

6

=

dSSP

3106

=MVS

spD

3

MVS

10

=D

kSsp

3

3

2

108/3/4

=

i

i

i

i

i

i

spdn

dn

S


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k is the surface area shape factor, for a sphere k = 6.

The factor k has been calculated for a number of different geometrical shapes, shown in Table 1

Error: Reference source not found[13

].

Table 1 - Surface area shape factors (k-factors) for different shapes

Shape Axial ratio k

sphere 1:1:1 6.00

ellipsoid 1:2:4 7.57

cylinder 1:1:1 6.86

cylinder 1:1:2 7.21

cube 1:1:1 7.44

parallel-piped 1:4:4 9.38flake 1:10:10 24.0

The shape factors listed in Table 1 are only based on geometric considerations. The influence of

the density and of surface porosity as well as the bulk porosity is discussed in paragraph 5.2

where measures of specific surface area carried out on TFTR dust correlated by with the

measured surface area diameter DMVS may lead to determine values for k of few hundreds that do

not have physical implication. The values of k obtained in that case starting from measured

values of spS andDMVS by using relationship [7] should be meant to indicate the available surface

area rather than a strict deviation from spherical dense material.

Measured metallic dusts are generally spherical and with a mass density close to theoretical

density. The graphitic dust investigated in some tokamaks (TFTR, Alcator C-mod and DIII-D)

has been measured and specific surface areas greater than predicted by the particle size

measurements have been found. That is believed to be due to the multi-faceted nature of

graphite dusts, in addition to suspected surface connections.

As shown in Figure 6, all the graphite measurements lie above the calculated theoretically dense,

spherical surfaces. On the other hand, all the mechanical powders with spherical shape (steeland aluminium), agree with the corresponding calculated, theoretically dense, spherical particle

surface areas (see Figure 7).


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Figure 6 - Specific surface area vs. surface area diameter (DMVS) for different graphite

powders and for theoretical graphite dense sphere

Figure 7 Specific surface area vs. surface area diameter (DMVS) for different metallic

powders and for theoretical stainless steel and for aluminium

The graphitic dust investigated has measured specific surface areas greater than what is predicted

by the particle size measurements. Or the other way round: the diameter calculated from particle

size distribution is greater then DMVS , which is calculated based on specific area measurements.

This discrepancy is believed to be due primarily to the multi-faceted nature of graphite, and to alesser extent to the suspected surface connected porosity of graphitic dusts.

S=6/( DMVS) x103 [m2/g]

0,01

0,1

1

10

100

0,1 1 10 100

DMVS [micron]

S[m2/g]

theoretical stainless steel theoretical aluminumCA 304 Stainless steel 718 Inconel316 SS (10 m sieve) Al (5 - 15 m sieve)

S=6/( DMVS) x103 [m2/g]

0,01

0,1

1

10

100

0,1 1 10 100

DMVS [micron]

S[m2/g]

theoretical graphite dense sphereCrushed POCO Graphite

Aldrich graphiteDIII-D dustTFTR measurements


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Continuing the analysis of the different diameter used to represent a particle size distribution we

have:

projected area diameter (dpa) = diameter of an irregular particle calculated by measuring theprojected area corresponding to a circle having an equivalent area (see Figure 8).

Figure 8 Dust particle projected area diameter

volume equivalent diameter (dve) = diameter of a sphere with the same volume of the particle

dust, simply given by the following equation.

[8]

Other important physical properties for the particle distributions are:

aerodynamic equivalent diameter (dae) that is the diameter of a unit density sphere having the

same settling velocity of non-spherical particle.

[9]

where:

is the dynamic shape factor (the dynamic shape factor is used to account for the effect of the shape on the settlingof the particle), is the density, 0 is the density 1, and C is the slip correction factor. The ratio C(dve)/C(dae) is

close to 1 for particles > 1 m particles.Activity Median Diameter (AMD) is defined such as the half of the aerosol radioactivity is

i t d ith ti l h i D < AMD [D b d d d d ]

dpa

36 V

dve

=

( )( )aeve

veaedC

dCdd

=

0


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Activity Median Aerodynamic Diameter (AMAD) is defined such that half of the radioactivity

in an aerosol is associated with particles with an aerodynamic equivalent diameter (dae) greater

than the AMAD [4].

It characterizes the mobility of a dust and describes the extent for deposition in the respiratorytract and for inhalation intake.

Considering a log normal distribution where it is possible to assume uniform density and specific

activity for all particles, the radioactivity is also log-normally distributed with the same

geometric standard deviation g. The activity median diameter (AMD) is given by the followingequation [14]:

AMD = CMD exp [3 (lng)2] [10]

where the count mean diameter (CMD) could be referred to volume equivalent dve or

aerodynamic equivalent diameter dae. In the former case we would refer to the activity median

diameter, in the later case to the activity median aerodynamic diameter (AMAD).

The self absorption factor (SAF), which is a size dependent physical property influences the

dust radiological properties.

It is well known that tritium beta emission is low, hence there is absorption of beta particles

within the dust. To take into account this phenomenon in order to correctly calculate (predict)

doses due to tritiated dust particles, the following parameters have been defined [10]:

SAF is the fraction of beta rays escaping their absorber, in our case the carbon basedparticle;

SAF is the fraction of beta energy escaping the particle.


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4. TRITIATED DUST & FLAKES RADIOLOGICAL PROPERTIES

As written above, the intake of T as a particulate can yield a dose quite different to the intake of the same quantity of

HTO. For this reason it is important to determine the biological effect of incorporated tritiatedparticles.

The amount of T exchanged into body fluids and hence the dose delivered will depend on:

the deposition of tritiated particles in the respiratory tract and lungs, as a function of: the chemical composition, the aerodynamic diameter, particle motion and lung air-flow pattern governed by breathing rate and route of intake,

the rate of clearance of the dust particle from the respiratory tract by particle transport and by

absorption into blood, the dissolution rate of T from the dust particle, and the activity present in the dust particle.

For this reason it is important to determine the biological effect of incorporated tritiated particles.

4.1 T dust inhalation and uptake mechanisms

As written above, measurements performed during the JET 1999 shut down showed that the

value of AMAD was ~ 4 m. This value is in the range of the respirable aerosols (


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Figure 9 On the left; fractional deposition of particles in the different respiratory tract region

for a reference light worker. On the right is displayed the respiratory tract model

defined in the new ICRP model

In detail the human respiratory system is divided, according to the new ICRP model in fiveregions, as shown in Figure 9 on the right:

2 extra thoracic: ET1 (anterior nose), ET2 (posterior nose, larynx, pharynx and mouth), ,

and

3 thoracic: BB (bronchial), bb (bronchiolar) and AI (alveolar-interstitial).

The human respiratory system is represented in Figure 10.

Figure 10 The human respiratory system (left), the lungs (right)

Material deposited in the anterior nasal passage (ET1) is removed in ~ 1 day. The remaining

airways of the head and of the neck (ET2) are covered by a fluid lining, which is cleared to the

pharynx and swallowed. The time scale for this is a few minutes.

Much of the material deposited in the bronchial (BB) and bronchiolar (bb) regions is clearedrapidly (few hours) by mucus, while smaller particles than a few m can stay longer.Human experimental data show that in the alveolar interstitial (AI) region there is about 80%

retention at 50 days and 50% at 1 year.

Because small dust particles are retained in the alveoli for years, the dissolution of tritium

adsorbed on, and absorbed into, the dust particle is an important factor in the calculation of the

dose and the dose conversion factor. The process of dissolution takes place mostly in the AI

region.

The clearance of a material from an organ or a tissue may take place by particle transport or

absorption.

In general, the absorption phenomena is a two-stage process: dissolution + uptake. Dissolution

is the dissociation (leaching?) of (dust?) particles into material (is this the same material?


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confusing! or is it the body fluids?) that can be absorbed into blood and hence body fluids, and

the uptake is the absorption into blood of soluble or dissociated particles . The clearance rates

associated with both stages can be time-dependent.

In vitro tests to reproduce the relevant phenomena occurring during dissolution, have alreadybeen performed [15], but the related effects in human organs are not easily extrapolated due to

varying physico-chemical effects such as macrophage action occurring in the lung, which can be

material specific.


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5. IN VITRO EXPERIMENTS

In vitro dissolution tests have been conducted by the U.K. National Radiological Protection

Board (NRPB) for JET to better define properties of JET tritiated C/Be dusts [15].The overall range of JET particle size was not determined before the in-vitro test, but it is known

to be large, extending from sub-micron particles to large friable flakes with geometric diameter

in excess of 100 micron. The dust were collected from the surfaces of the poloidal limiter tiles

(recovered in the remote tile exchange shut down in 1998), and separated the particles into two

broad size ranges identified simply as coarse and fine to be subjected to tritium dissolution

tests in a lung serum simulant. The particle consists of carbon (> 98%) and is similar in

appearance to soot. (I believe not knowing the size distribution of the two samples is a serious

limitation of the study one that should be noted in the conclusions of this report)

The chemical composition of the lung serum simulant used for the in vitro experiments is similarto that widely used for in vitro dissolution studies in general.

Two different procedures were adopted to simulate the dissolution.

The first consisted in preparing small quantity (aliquot) of suspension containing the dust, put

them in small tubing (Visking seamless cellulose tubing, 2.4 nm pore size, 19 mm inflated

diameter; BDH, Poole, Dorset). The tubing was soaked in lung fluid simulant for 24 hours

before use. The prepared tubing was cut into lengths of 1.5 cm and 1 ml of suspension with

particles was put in it. The tubing was sealed and suspended in 300 ml of serum simulant inside

a 500 ml screw-capped plastic bottle. The bottle in turn was then suspended in shaking water at

37 C and timed to shake alternate hours over the duration of the study. At predetermined

intervals (1, 2, 3, 7 and 14 days) the simulant was removed from the bottle for analysis and

replaced by fresh simulant. (I believe the short duration of these experiments is another serious

limitation of the study, which should be noted in the conclusions of this report)

The second one, centrifuge tube method, was devised to allow bioavailability to be assessed at

earlier times (less than 1 day). This was deemed necessary because of the high (who believes, or

believed, this? even if it was believed to be true before, it is not true now)perceivedprobability

of a rapid early dissolution. 1 ml suspension of freshly prepared particles was added to 20 ml of

serum simulant in a 25 ml tube for centrifuge. Then mixing and the treatment as the previous

method were carried out. At predetermined time (5 and 30 min, 1 and 2 hours, and 1, 2, 5, and 7

days) the tubes were removed from the water bath, and centrifuged at 1000 rpm for 5 min. Then

a sample of 1 ml of supernatant liquor was taken for the analysis.

5.1 In vitro experiments results

Ideally, the total tritium content of the particles would have been assayed for each individual

aliquot (?) analysis (first method) and centrifuge tube experiment (second method), and the

fractional dissolution rate determined using this information. However, problems encountered

recovering carbon particles from the dialysis bags and centrifuge tubes, and the high tritium

activity made it impossible. Therefore the values (what does values refer to? Tritium

concentration in the simulant?) obtained for the small volume (10 l) sample aliquots, dispensedat the start, were used in all calculations. The mean (simulant?) T activity for the fine particle

i i l l d b 6 6 / l f h i l 4 / l


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The fraction of T remaining in carbon particles is shown in Figure 11.

The related detailed data are given in Table 2..

this figure tells me that there is a lot of scatter in the experimental results, which does not show

up in Figure 12.

Figure 11 Fractional retention of tritium in carbon particles [15]

Table 2 - Fractional retention of T in coarse and fine particles [ 15]

Coarse particles

Days 0.003 0.02 0.04 0.08 1 2 5 7 14

Fraction 0.957 0.9536 0.9499 0.9482 0.9248 0.9231 0.907 0.9002 0.8809

SD x 10-3 3 5 5 4 17 17 19 20 19

No. of aliquots 3 3 3 3 6 6 6 6 3

Fine particles

Days 0.003 0.02 0.04 0.08 1 2 5 7 14

Fraction 0.9967 0.9970 0.9966 0.9968 0.9960 0.9957 0.9938 0.9928 0.9920

SD x 10-3 1 0.6 1.2 0.8 2.1 2.4 4 5.1 1.6

No. of aliquots 3 3 3 3 6 6 6 6 3

SD = standard deviation

The graph ofFigure 11 has been translated in logarithmic scale as far as the x-axis is concerned

(see Figure 12).


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The coarse particle data have been fitted with a two-component exponential law describing the

retention fraction. The best fit was obtained with a fraction of ~ 5 % dissolving rapidly at a rate

characterised by a time constant of 500 d-1 (approximate half-life of 2 minutes) the remainder

(99.7 %) dissolves at a rate characterised by a time constant of 6.310-3

d-1

(half-life of 110 days).(see Figure 12, red curve).

It is important to note that we dont know the particle size distribution of the sample. For a

sample of uniform particle size, dissolution theory tells us that the process is exponential and

there is a single rate constant. Therefore, mass of undissolved dust (m) = mo exp(-t). Because

the dust sample used in the JET experiments was not characterized, with respect to particle size

distribution, it is not possible to say how many rate constants there would have been, as m = moi

exp(-it), where subscript i refers to a specific particle size. This is why I said earlier that, not

knowing the particle size distribution of the sample is a severe limitation of the experiment.

(Keep in mind that, from a dose perspective, it is only the fine particles that are of interest, as

they are the ones that are trapped inside the AI. That is, dust particles of ten micron or less).

The fine particles data has a similar trend, but the fraction dissolving rapidly at a dissolution

rate with a time constant of ~ 500 d-1 is lower (0.3%), the remainder (99.7 %) dissolves at a rate

with a time constant of 3.610-4 d-1(half-life of 1925 days). The change in the dissolution trend is

not marked in the blue curve ofFigure 12 due to the scale.

Same comment applies to the fine particles.

Figure 12 - Fractional retention of tritium in JET carbon particles in time logarithmic scale

T retention fraction

0,8

0,85

0,9

0,95

1

0,0001 0,001 0,01 0,1 1 10 100

time [days]

Coarse particles

Fine particles


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Using the material specific dissolution values (see Table 3) with the relationship [11], the fine

particles were assigned to type S (rather than type M) as at 180 days the fraction retained is more

than the amount that would be retained for a hypothetical material with a constant absorption rate

of 0.001 d-1

(= ln2/t1/2; t1/2=ln2/; t1/2 = 0.693/0.001 700 days) (see Figure 13).

Table 3 - Provisional dose coefficients for tritiated dust (Sv per Bq) and ALI for a reference

worker with a dose limit of 20 mSv per year [15]

Particle size Rapid fraction

(fr)

Rapid rate (sr)

[s-1]

Slow rate (ss)

[s-1]

Type Gut uptake

factor (f1)

Dose conversion

factor

[SvBq-1]

ALI (20 mSv)

[MBq]

HTO

Coarse 0.05 500 6.00E-03 type M 0.1 2.60E-11 769

Fine 0.003 500 3.40E-04 type S 0.01 9.90E-11 202

ICRP 68 vapour n.a. 1.80E-11 1111

OBT (organically

bound tritium)

Coarse 0.05 500 6.00E-03 type M 0.1 2.80E-11 714

Fine 0.003 500 3.40E-04 type S 0.01 9.90E-11 202

ICRP 68 vapour n.a. 4.10E-11 488

The fitting equation of tritium retention fraction for coarse particles can be written as follows:

RC-JET(t) = 0.05 exp(-500t) + (0.95) exp(-6.00E-03t) [12]

The fitting equation of tritium retention for fine particles can be written as follows:

RF-JET(t) = 0.003 exp(-500t) + (0.997) exp(-6.00E-03t) [13]

You need to show how the dose conversion factor was calculated. The only check I can perform

is the following: the biological half-life of HTO is ten days and the DCF is 1.80E-11. the

biological half-life of the fine dust sample is 1925 days. Therefore, the DCF for the fine dust

should be 192.5 times that for HTO. If you then assume that the gut uptake factor f1 is 0.01, then

the DCF for fine dust should be 1.92 times that for HTO, or 3.46E-11. as I dont have a copy of

ICRP 71, I cannot verify the gut uptake factor f1. I am of the opinion, however, that the gut

uptake factor f1 does not depend on the dissolution rate (F, M, S), but is a function solely of the

element. For example, for carbon it is 1.0, for silicon 0.01, for aluminium 0.01 and beryllium

0.005. also, for HTO and OBT the gut uptake factor f1 is 1.0. it would appear from this that

tritiated carbon dust is far worse than tritiated beryllium dust, given the same tritium

concentration on both.


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Figure 13 - Coarse and fine particle retention vs. particles vs. material adsorbed in moderate

way (M) and in slow way (S)

From the graph ofFigure 13, it is clear that the coarse particle fall in the M region (moderate

dissolution region) while the fine are in the slow region.

Using the data summarised in and taking into account the recommendations in the ICRP 71 [16]

for the environmental exposure to assume for the gut uptake factor f1 a value of 0.1 for the

inhalation of the type M tritium and a value of f1 of 0.01 for the inhalation of the type S tritium,

provisional dose conversion factor were calculated. They are summarised in Table 3 together

with the data used to derive the dose conversion factors.

The results suggest that, except for a very small initial fraction, T is dissolved very slowly from

the carbon particles. The initial faster dissolution is less than 5% and it was already present at

the time of the first measurement suggesting the hypothesis of tritium dissolution into the serum

simulant medium just during the preparation of the particle suspension. Same behaviour was

found in analogous in vitro dissolution tests carried out on TFTR dust using a lung serum

stimulant [14].

Furthermore, as the biokinetic of the absorbed T is unknown the calculations were performed

assuming the dissolved tritium was available as HTO and organically bound tritium (OBT).

The dose coefficients, shown in Table 3 are intended as provisional and to be confirmed by in

vivo experiments [15]. I repeat, again, these DCFs should not be considered even provisional

given the flawed nature of the experiments and the lack of a complete analysis of same. For

example, how does self-absorption impact the DCFs you calculated? Moreover, given that we

dont have any good in-vitro experiments, why would anyone rush to do in-vivo experiments? I


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Furthermore, another outcome from the JET dust in vitro experiments [15], is to recommend a

more accurate analysis of the physico-chemical attributes of the particles, such as size, porosity

and chemical composition as a priority, and to confirm dissolution kinetics, gut uptake factor and

the biokinetic behaviour of the absorbed tritium by studies with animals. Understanding of howit really works the dissolution of T into body fluids is one of the key points that need to be

investigated by the in vivo experiments.

From another reference [9] it was outlined that at present there is insufficient information

available to model the factors involved in dissolution and uptake, in order to predict the rates of

absorption for specific materials. In vitro dissolution measurements cannot yet be used with

confidence to predict the absorption rate of a material in vivo, although they do have practical

applications, e.g. to determine the fraction that is absorbed rapidly. Material-specific

absorption rates thus need to be based on reliable in vivo human or experimental animal data.

Some in vivo experiments carried out by intra-tracheal instillation of metal tritides (Zr, Ti) in rats

has shown slow clearance rates from the rat lung. The radiation dose was estimated to be an

order of magnitude larger than those calculated for HTO [10].

That needs to be confirmed in the case of carbonaceous tritiated particles (e.g. JET case) by in

vivo experiments. The same advice was given in the reference [14] about the in vitro

experiments carried out on TFTR dust about the necessity to integrate the in-vitro experiments

with that in-vivo on animals.

The TFTR carbon tritide size distribution was obtained through a measure over 250 particles.

The experimental measures are fitted through a log-normal distribution with CMD related to the

volume equivalent diameter equal to 1.23 m and the geometric standard deviation g equal to

1.72 [14]. The CMDae and the geometric standard deviation related to the aerodynamic

equivalent diameter have been calculated starting from the geometric diameter using equation

[9]. The value of CMDae = 1.72 m and g = 1.72 has been determined assuming the dynamicshape factor in equation [9] = 1.5. Assuming = 1.0 the following values have been

calculated CMDae = 1.89 m and g = 1.71.The activity aerodynamic particle size distribution was also measured by a cascade impactor.

The impactor data showed a wider size distribution than the data obtained starting by TEM data.

The activity median aerodynamic diameter (AMAD) of the impactor sample was 6.75 micron (g= 2.98) which is larger than TEM data of 4.48 micron (g = 1.71) calculated by equation [10],

correlating the count mean diameter (CMD) and the AMAD.

The tritium dissolution rate from the in vitro-experiments on TFTR dust is shown in Figure 14,

for in vitro dissolution rate over 110 days [14].


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This graph shows clearly why the JET experimental period of 14 days is totally inadequate to be

used for calculating DCFs.

Figure 14 - The fractional dissolution rate of tritium from carbon tritide particles in simulated

lung fluid by in vitro experiments on TFTR dust [14]

The fractional dissolution rate values are in the range of 10 -1 to 10-3/day during first few days and

then it decreases to 10-3 to 10-4/day.

The correlated fitted function DR(t) was expressed as a sum of three decay exponential functions:

DR(t) = 0.251 exp(-9.57 t) + 2.08 10-3 exp (-0.141 t) + 4.26 10-4 exp(-4.02x10-3t) [d-1] [14]

Other in-vitro experiments carried out on metal tritides including titanium tritide and erbium

tritide have been carried out [17]. The experiments dealt with the assessment of the dissolution

rates on titanium tritide particles in a simulated lung fluid. Particles with mean sizes of 103

micron (coarse) and 0.95 micron (fine) were used. Differently from the JET dust in-vitro

experiments [15], the results showed that the coarse particles dissolved much more slowly than

the fine particles. The dissolution model considered to interpret the tritium dissolution

experiments was based on a diffusion model based on the diffusion of a gas in a semi-infinite

solid medium. Based on that, the dissolution rate in terms of accumulated fraction (f ) can be

expressed as a function of time [18]:

[15]

where V/S is the volume-to-surface ratio of the particle, D is the diffusion coefficient of tritium

in the particle and t is the time. For particles having a log-normal distribution the volume-to-

surface ratio is the mean volume-surface diameter (see page 10).

tD

S

Vf

= 2


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The photomicrograph of titanium tritide particles revealed non irregular shapes for coarse

particles (CMD = 103 micron) and less irregularity for the smaller ones (CMD 1 micron).The results of dissolution tests showed that for the coarse particles the amount of tritium

dissolved (as HT and HTO) in the lung serum simulant in about 1 month was only 5.1 0.5 %.On the other hand the fraction of tritium dissolved in the same time period for the fine particles

was much higher (57 1.7 %). The cumulative dissolution fraction got from the experiments for

the fine particles is in a good agreement with relationship [15] related to diffusion model,

whereas the one obtained for the large particles did not agree.

For the coarse particles showed a slow dissolution rate of < 0.5 %/day, with the tritium fractional

retention curve R(t) given as a single decay curve (with d in days):

RC Ti tritide = exp(-1.9210-3 t) [16]

The dissolution half time was calculated to be 361 days.

For the small particles the dissolution rate was assessed to be 2 %/day, with the tritium fractional

retention curve expressed, like those derived for JET in-vitro experiments, to be a two-

component decay curve:

RF Ti tritide = 0.24 exp(-0.71 t) + 0.76 exp(-2.0910-2 t) [17]

That is in agreement with the JET dust in-vitro experiments at least for the type of curve (two-

component decay curve). One-component, two-component, three-component it doesnt matter.

It is all experimental scatter and is representative of the particle size distribution. The greater the

range of particle size the larger the scatter. What is important, however, is that these

experiments contradict the JET experiments i.e., the dissolution rate is higher for the fine

particles! This is the opposite of the JET results. Therefore, how does one resolve these

seemingly contradictory results?

5.2 Comparison and discussion of the in vitro experiments results

The comparison of the three different in-vitro experiments, presented in the previous paragraph

related to JET dust [15], TFTR dust [14], and titanium tritide [17], can provide importantoutcomes for any new planned in-vitro experiments on JET dust.

The first outcome is the different behaviour in the tritium dissolution rate comparing the titanium

tritide dissolution experiments with those carried out on the JET dust.

Both experiments were carried out on two different classes of size, in detail:

Ti tritide: 1st group with CMD = 0.95 m, 2nd group with CMD = 103 m;

JET dust: 1st group classified as fine, 2nd group classified as coarse.

As written previously, it was not possible to classify the JET dust used for the in-vitrodissolution experiments from the size point of view.


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Comparing the dissolution rate results, expressed in fraction of tritium dissolved per day (see are

the points on this graph experimental points, or just plotting points for the curve? If the latter

they should be removed to eliminate ambiguity. Same comment applies to the other graphs.,

with time in linear scale, and Figure 16 with time in logarithmic scale), it is possible to note, asalready written in paragraph 5.1, that the behaviour of JET dust differs from titanium tritide

particles and from what expected from the theory. The dissolution rates for both JET and

titanium tritide particles have been obtained by deriving the equation providing the tritium

fractional retention; equations [12], [13] for JET dust, and [16] [17] for titanium tritide.

Smaller particles should have a larger dissolution rates as the specific surface area per unit of

volume is larger. Comparing titanium tritide and JET dust tritium dissolution rates, it is evident

the difference between the two type of particles and the different behaviour of coarse versus fine

particles. Dissolution rate for JET coarse particles is of the order of 5.5E-3 day -1, larger than the

one for the fine particles (3.4E-4 day -1) of about one order of magnitude. Both values are

reached quite soon as shown in Figure 15, while that is not true for titanium tritide particles.

Does this not raise questions about the validity/acceptability of the JET experimental procedure?

There is an appearance of artificiality in the JET graph, whereas the other looks more normal.

The tritium dissolution rate measured for titanium tritide is larger in the case of fine particles; in

the range 1.86E-1 day-1 (at the beginning) and around 1E-2 day-1 after 10 days up to the end of

experiment (30 days), while the related value for coarse particles is about 1.9E-3 day-1 (see

Figure 16). I recommend deletion of figure 16, as dissolution is an exponential process, and

therefore, only understood when the results are plotted in a semi-log graph (not log-log). In this

latter case (larger titanium tritide particles), a constant tritium dissolution rate is reached almost

immediately.

The second outcome, linked in such a way to the first, is a possible explanation for the different

behaviour of the JET dust tritium dissolution rate. This clarification originates from the

correlation between the specific surface area spS , (expressed in m2/g) and the particle

dimensions that has been analysed. As shown in Figure 6, the specific surface area spS , for

theoretical graphite dense spheres decreases with the increase of the surface area diameter,

coincident with the diameter in the case of mono-disperse spherical powder (see equation [4]).

The relationship providing the surface area diameter spS versus the surface area diameter DMVS,

given in the case of a poly-disperse spherical powder or for a poly-disperse powder with

irregular shape is given by equation [7], already reported at page 12:

[7]

Where k = 6 for spherical powder.

3

MVS

10

=D

kSsp


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are the points on this graph experimental points, or just plotting points for the curve? If the latter

they should be removed to eliminate ambiguity. Same comment applies to the other graphs.

Figure 15 Tritium dissolution rate for Ti tritide in-vitro experiments [17] and for JET in vitroexperiments [15], time in linear scale


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Fi

gure 16 - Tritium dissolution rate for Ti tritide in-vitro experiments [17] and

for JET in vitro experiments [15], time logarithmic scale


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The equation [7] shows that, according to theory, the specific surface area decreases increasing

the dust (particle) size.

The correlation between specific surface area versus the surface area diameter for dense carbon

particles with different shapes (different k), including spherical particles, shown in Figure 17, iscompared with experimental measurements carried on TFTR carbon dust [13]. It is possible to

observe that for TFTR carbon dust, the related specific surface area is positioned above the

theoretical line for graphite dense particles. A possible explanation for that may be due to the

multi-faceted shape of graphite particles in addition to the surface connected porosity [13] that

increase the surface area, in addition to the bulk porosity that reduces the apparent density that is

one of the term of equation [k]. Both increase of term k and decrease of term r in equation [7] go

in the same direction to increase the specific surface area related to spherical dense particles.

Furthermore the specific surface area for TFTR dust, even if the experimental points are few and

quite scattered, does not show a marked decrease for larger particle size, suggesting the idea that

increasing the size, the shape factor k increases or the apparent density decreases. As matter of

fact, increasing the surface area diameter DMVS of TFTR dust, linked through equation [2] to

geometric dimensions, and starting from particle size distribution measurements, the

experimental points are intersected by lines with increasing k (see Figure 17) assuming to keep

constant the dust particle density.

As written in reference [13], where data ofFigure 17 are taken from, the k values fitting the

experimental points do not represent physically the actual shape of dust, because it is believed

there is a significant amount of surface area due to surface connected porosity in many of the

materials collected from tokamaks. So, it would be preferable to use the fitting k to indicate the

available surface area rather than a strict deviation from spherical dense material.

As already written, another factor increasing the specific surface area, regardless of the surface

porosity, is the bulk porosity. The straight lines ofFigure 17, calculated for a theoretical carbon

density of 1800 kg/m3, move upward in case of lower density. Figure 18 shows the same lines of

Figure 17 in the case of apparent carbon density equal to 900 kg/m3, one half of the theoretical

value.

These considerations suggest that increasing the size, the TFTR dust particles are remarkably

irregular in shape with along with an increase of porosity (surface and bulk).

How can these evidences concerning TFTR dust be correlated with JET dust?

As far as the dust of larger size is concerned it is possible to draw the existence of a similaritybetween TFTR dust and JET dust, taking into account the same type of material (carbon)

composing the dust, and the same type of process (flaking) observed on the plasma vessel tiles

[19, 4]. Hence, considering the measurements of the specific surface area done on TFTR dust

[13] versus particle size (surface area diameter DMVS), it would be not too far from the reality to

assert that JET coarse dust particles have a similar behaviour to those of TFTR. In other

words, in the case of JET coarse dust, the larger specific surface area than what expected from

the theory, due to irregular shape (flake size is in the range of 100 m), and the existence of bulkand surface porosity might justify the larger tritium dissolution rates than what measured for fine

particles. The coarse dust is not of interest from a dosimetry perspective, as it is well above the10 micron cut-off. This should be noted in the conclusions of this report. Furthermore, it has


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been made the hypothesis [15] of fast tritium dissolution in the serum simulant medium just

during the preparation of the particle suspension.

Figure 17 Carbon dense ( theoretical =1800 kg/m3) particles specific surface area versus surface

area diameter

Figure 18 - Carbon porous ( apparent = 900 kg/m3) particles specific surface area versus surface

area diameter


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In order to verify the hypothesis made of a similar behaviour of JET and TFTR dust it is

important to compare the TFTR in-vitro tritium dissolution experiments [14] with those carried

to JET dust [15].

As written in the previous paragraph, the tritium dissolution rate has been determined over aperiod of 110 days (see Figure 14). The comparison with the tritium dissolution rates determined

for JET dust is presented in Figure 19 (logarithmic time scale) and (linear time scale).

Figure 19 Comparison of tritium dissolution rates determined for TFTR and for JET

carbonaceous dust (fine and coarse), using logarithmic time scale

The comparison shows a fair agreement between JET fine dust and TFTR dust, taking also into

account the different procedures adopted during the in-vitro experiments. I DISAGREE! The

behaviour of the TFTR dust is closer (very close) to that of the titanium dust, taking into accountthat titanium dust is less reactive than carbon dust. This confirms again the anomalous results of

the JET experiments. If one looks at , where the time scale is linear and the dust tritium

dissolution rate for the JET has been extrapolated to a time scale of 100 days (the JET in-vitro

tests lasted only 14 days), the agreement seems to be more fair. In view of all that you have seen

and done, how is it possible to justify extrapolating the JET data to 100 days? Please think about

technical credibility. You have tried very hard to justify the validity of the JET results, but in

doing so you have demonstrated the obvious the JET results are anomalous due to a possible

flawed experimental procedure I believe this is the main conclusion of the study. The data

speak for themselves! The trend of the tritium dissolution rate for JET fine dust is similar to that

measured for TFTR dust, both tending in the long term (few days) to a value of ~ 3E-3 day -1 (see

).


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Integrating the equation [14], related to the dissolution rate determined by in-vitro tritium

dissolution rates for TFTR, the following relationship has been obtained for the tritium fractional

retention of TFTR dust:

RTFTR(t) = 0.853 - 0.251/(-9.57) exp(-9.57 t) - 2.08 10-3/(-0.141) exp (-0.141 t) -

- 4.26 10-4/(-4.02x10-3) exp(-4.02x10-3t) [18]

The comparison between tritium fractional retention for TFTR dust, given by equation [18], with

the one related to JET, given by equations [12] and [13] is shown in .

Figure 20 - Comparison of tritium dissolution rates determined for TFTR and for JET

carbonaceous dust (fine and coarse) using linear time scale


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Figure 21 - Comparison of tritium fractional retention determined for TFTR and for JET

carbonaceous dust (fine and coarse)

The tritium fractional retention for JET fine particles and TFTR dust is almost coincident for

the first minutes (see Error: Reference source not found).

The comparison anyway cannot be complete, as there are no information in reference [14] about

the in-vitro procedure adopted for TFTR dust and, at the same time, precise information about

the JET dust used in the in-vitro experiments is not available.

As written before, the tritiated TFTR dust used for in vitro experiments have an activity median

aerodynamic diameter (AMAD) value equal to 6.75 micron (g = 2.98), the analogous value forJET fine dust used in the in-vitro experiments is not known, but it might be reasonable to assume

a value in that range for the so called fine dust.

So, it might possible, on a preliminary basis, to assume that JET fine particles, might be in the

range of AMAD 5-7 micron. Why do you want to stick out your neck??? If that is the case,

why are the results in figure 21 so different?

From other experimental evidences it was observed that both TFTR [5, 19] and JET [4] dust of

larger size have irregular shapes in a form mostly defined as flakes,. That can be considered

another important proof to the existence of a similar behaviour between TFTR and JET dust as

far as the tritium uptake and dissolution are concerned. It would be interesting to compare

tritium dissolution rates measurements from in-vitro test for larger size dust particles if related

TFTR data were available.

Another topic of discussion suggested by the outcomes of the in-vitro experiments on JET dust[15] is related to the distribution of the tritium inside the dust particles. That derives from the

d f t t iti di l ti i th i l t di j t d i th ti f th


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particle suspension in the case of JET coarse particles, suggesting the hypothesis of superficial

distribution of tritium on those particles.

In general, diffusion of tritium into the bulk material is not expected to play a major role. Results

from TFTR showed very low bulk concentrations at a position 2 mm below the plasma facingsurface of the graphite tiles (0.4 atomic ppm). Recent investigations of divertor tiles of ASDEX

Upgrade and JET have shown that deuterium is mostly retained in the carbon deposits on the

surface of graphite, beryllium and tungsten tiles. [20]. That could induce to think that even in

dust a non homogeneous distribution on tritium might occur, with larger concentration on the

outer layers of carbon dust particles. On the other side the production of dust is from phenomena

such as: erosion of C/Be FW by plasma/wall interaction, disruptions and evaporation combined

with deposition on the FW through diffusion, surface saturation and mostly important co-

deposition with carbon.

All these phenomena involve the very external surface of plasma facing components, hence the

dust, especially the smaller ones should have a quite homogeneous tritium distribution, while the

larger ones (with size similar to flakes) might have a non-homogeneous distribution.

On this subject, it would be interesting to determine the tritium distribution in the dust, only

possible through indirect method. One possible way to have an idea of tritium distribution into

dust could be to perform an evaluation of the beta particles emitted or of the beta energy emitted

from a sample of dust of the same size or belonging to the same log-normal distribution (same

CMD). Then using the equation provided in reference [10], related to the correlation of the

average beta activity measured in the particles with the particle size distribution assuming the

hypothesis that the specific activity of the particle and its composition and density are constant

across the particle size.

This relationship is simply represented by [10]:

[19]

where A is the average beta activity measured on a population of tritiated particles and 0A is

the average beta activity in the particle, and d is the characteristic diameter for self absorption

of beta particles. .

[20]

The mean escape factor of beta particles, SAF , for a log-normally distributed particle is then:

qdSAF = )(

( )q

d

= 0AA

( )

( )

=2

2

ln2

q-3-4.5

expCMD gq

d


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( )

( )

q

gq

= 2

2

ln2

q-3-4.5

expCMD [21]

where and q are constants by fitting numerical values ofSAF into the power function using anon-linear curve-fit procedure

So comparing the average beta activity obtained from a direct measure on the particle size

distribution with the one obtained from equation [19] introducing the value of the average beta

activity in the tritiated particle 0A , could be a good way to have an idea of the shift of theactual tritium distribution from homogeneity.

An idea of a possible shifting from an homogeneous distribution of tritium comes from a simplecalculation starting from experimental data.

Considering the following assumptions:

T concentration in the dust = 1000 GBq/g-dust (close to the maximum value found in

JET dust of ~ 1.3 TBq/g);

constant T/C atomic ratio for co-deposited layer = 0.3 [21], [22];

spherical shape of the dust;

homogeneous distribution of tritium starting from the external surface toward the centre,

till to the thickness x,

it has been calculated the ratio between the thickness x of particle with constant tritium

concentration, considering the given T/C ratio, and the particle radius r.

Table 4 summarize the spreadsheet used to calculate the ratio x/r.

Table 4 Thickness of tritium at constant concentration in a spherical particle

Tritium average specific activity in dust 1000 [GBq/g]T/C ratio 0.3 [ - ]Tritium Specific Activity 3.58E+14 [Bq/g]

Carbon atom weight 12 [g/mole]Carbon density C 1800 [kg/m3]Tritium atom weight 3 [g/mole]Tritium average concentration in dust CT 2.79E-03 g-T/g-dust

Carbon density C 1.8 [g/cm3]Carbon molar density 1.5E+05 [mole/m3]Carbon molar density 0.15 [mole/cm3]Carbon atom concentration 9.03E+22 [atoms/cm3]Tritium atom concentration 2.71E+22 [atoms/cm3]Tritium molar density 0.045 [mole/cm3]

Tritium density (in dust) T 0.135 [g/cm3]

CT4/3R3

c =4R2

xTx/R = CT /3*( C/ T) 1.24E-2


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Once determined the tritium density in the dust T (relative to the layer where T and C are in theratio defined as input), it is possible to calculate the thickness of the tritium layer by the

following simplified equation (that is valid for low values of x):

CT4/3R3C =4R2xT [22]

That, solved versus x/R, gives:

x/R = CT /3( C/ T) [23]

Using the input values, reported in blue in Table 4, the ratio x/R is quite low (1.24E-2); the

thickness where the tritium is homogeneously distributed according to the atomic ratio T/C = 0.3

is just bit more than 1% of the particle radius.

shows the value x/r for different values of tritium concentration dust and different values of T/C,

according to the simplified equation [23].

Figure 22 Relative thickness of the tritium layer versus tritium average specific activity and

T/C

The equation (of the 3rd order) to be solved to obtain exact x/R values is of the following one:

CT4/3R3C = 4/3[R3-(R-x)3] T [24]


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That after the required expansion and simplifications gives:

Tx[x2-3Rx+3R2] - CCTR3 = 0 [25]

Equation [25] can be further simplified as it follows:

R3[T(x/R)3-3T( x/R)2+3T(x/R)- CCT = 0 [26]

It provides for larger values of CT and lower values of T/C, larger values for x/R than the

simplified equation as shown in for the case with T/C = 0.02

Figure 23 - Relative thickness of the tritium layer versus tritium average specific activity for T/C

= 0.02 using simplified equation [24] and exact equation [25]

In order to have an homogeneous distribution of tritium in the dust particle it is necessary to have

a tritium specific activity of 1 TBq/g and an atomic ratio of T/C equal to 3.73E-3, that seems to

be quite low compared with values reported in the literature for carbon co-deposited layers.

These calculations try to demonstrate that, considering the tritium specific activity measured in

the JET dust, and taking into account the typical values of atomic ratio between T and C in

carbon dust, it might be justified a superficial distribution or a not homogeneous distribution of

tritium.


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In order to conclude the report, it would be important to summarize some guidance for the next

in-vitro experiments to be carried out on JET dust.

As no such related information were provided for the past JET dust in-vitro experiments, it

would be important:1) to define the dust size class more rigorously, providing the count mean diameter value

and the standard deviation and the related aerodynamic mean diameter, even through semi-

empirical relationships, as those given by equations [8], [9] and [10].

2) to determine the specific surface diameter, as demonstrated through the consideration

made before is an important parameter to know for a better understanding and interpretation

of the in-vitro experiments results. The surface specific area can be measured using the

method adopted by INEEL [13], consisting in a Micromeritics ASAP2010 Porosimetry

Instrument [23, 24, 25].

This instrument uses a Kr or N2 gas adsorption method to measure the specific surface area.

3) to perform some beta radiation measurements on dust samples (size log-normally

distributed) to be compared to the one obtained by equation [19] introducing the value of the

average beta activity of the tritiated particle 0A , in order to have an idea of the shift of theactual tritium distribution from homogeneity.

The dust to be sampled for the next in-vitro experiments should include two or three different

size classes. The first class should have a value of the count mean diameter CMD 1 m, thatis in the range of the reference diameter of the ITER dust particles assumed to be 0.5 m [26], thesecond class with CMD around 5 m and the third with CMD > 20 m. from a dosimetry

perspective, the third would not be very useful. If that would be too burdensome or time-

consuming, the selection might be restricted to the smallest and the largest size class. from a

dosimetry perspective, the third would not be very useful. In order to separate the different size

classes, it might be possible to use the same approach adopted at FZK Karlsruhe based on

analysing sieves, but the capacity of sampling arrives down to 20 micron [27]. In order to have

finer dust it is would be possible make it by milling a coarse one, e.g. with a ball mill, but it is

likely that this operation might disturb the tritium distribution on the particle surface and

influence the in-vitro dissolution experiments. Hence the sampling for dimension (expressed as

CMD) lower than 20 micron should use different means than analysing sieves. A possible

method to discriminate dust with an aerodynamic equivalent diameter in the range of 1 m to 10m is using a personal air sampler [28]. This sampling device has been developed to include asize-selective sampling head which is actually a miniature, single stage centripeter. It is also

known as the lung model sampler because it separates aerosol particles into two size fractions,

one of which corresponds to dust which would be deposited in the pulmonary region of the lung

according to the ICRP Publication 30 respiratory tract model. An annular impactor is arranged so

that, in general the smaller particles deposit on the central area of the filter whilst the larger

particles deposit on the outer annular ring of the filter. The particle size range that it measures is

restricted to 1 m to 10 m, dae, because of its small size. This is precisely the range of

interest!!!!


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6. CONCLUSIONS

Large quantities of dust and flakes have been produced during the operation of experimental

tokamaks especially during D-T phases (e.g. JET and TFTR). Not a conclusionThe related measurements carried out so far on dust and flakes showed a large T concentration in

dust and flakes. Not a conclusion

Larger radiological effects and dose for particulates (tritiated dust and flakes) intake than for a

similar HTO intake may be foreseen. That is a consequence of the large T content and the

expected longerand largerbiological retention. As a matter of fact in vivo experiments carried

out by instillation of metal tritides (Zr, Ti) in rats have showed slow clearance rates from the rat

lungs. Consequently, the radiation dose was estimated to be an order of magnitude larger than

those calculated for HTO).

A dedicated in vitro experiments using lung serum simulant were carried out by the NationalRadiological Protection Board(NRPB) have not been conclusive and demonstrate significant

anomalies when compared to other available data. on dust collected during the 1998 shut-down

of JET showed the dissolution rate of tritium from particles can be fitted by is a two-stage

exponential relationship: fast dissolution rate of a limited fraction (up to 5%),very slow

dissolution rate of the remainder. Similar behaviour was found in analogous in vitro dissolution

tests carried out on TFTR fine dust using a lung serum simulant.

In both cases, it has been outlined the need to verify the T dissolution rates from carbonaceous

dust derived from in vitro experiments using a lung serum stimulant by in vivo experiments.

Collect all the comments I made in the text that should go in the conclusions and put them here.

The following are not conclusions.

I REPEAT, IT WOULD BE IRRESPONSIBLE AND UNETHICAL TO RECOMMEND IN-

VIVO EXPERIMENTS BEFORE ADDITIONAL IN-VITRO EXPERIMENTS ARE

PERFORMED AND THE RESULTS UNDERSTOOD. THIS HAS TO BE THE KEY

CONCLUSION OF THIS REPORT.

Other in-vitro experiments carried out on titanium tritide particles divided in two size classes

(CMD 1 micron and CMD = 103 micron), have been analysed. The different nature of thetritide material, in this case a metallic one, has lead to different results, in terms of dissolution

rates. What is evident, comparing the titanium tritide results with those from JET tritiated dust is

the different behaviour of the dissolution rate for smaller and larger particles. In the case of JET

dissolution rate for coarse particles is of the order of 5.5E-3 per day, larger than the one for the

fine particles (3.4E-4 day) of about one order of magnitude lower (3.4E-4 per day) while for

tritium tritide particles, the tritium dissolution rate is larger in the case of fine particles as it

should be according to theory.

The comparison between JET fine particles tritium dissolution tests with the analogous tests

performed on TFTR shows a fair agreement, also taking into account the same type of dust base

material (carbon). Furthermore, both TFTR and JET dust of larger size have irregular shapes ina form mostly defined as flakes.


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Assuming the existence of a similarity between TFTR and JET dust, it is possible to try to justify

the larger tritium dissolution rates measured on the JET coarse particles during the in-vitro

experiments on the base of some measurements performed on TFTR dust. The specific surface

area for TFTR dust, even if the experimental points are few and quite scattered, does not show amarked decrease increasing the particle size, as it should be according to theory. That would

suggest the idea that increasing the size, the shape factor k increases and also the porosity (bulk

or superficial) increases. All these parameters increase the surface area for exchanging tritium

with the serum simulant.

Another issues has been discussed: that related to a possible not homogeneous distribution of

tritium on JET carbonaceous dust and a possible indirect way to verify that.

In vitro experiments for JET dust/flakes may be repeated to correlate T dissolution behaviour

with particulate size (the experiments described in the present report were based on a raw

classification between coarse and fine).

In detail for the next in-vitro experiments, it would be important:

to define the dust size class more rigorously, providing the count mean diameter value and the

standard deviation and the related aerodynamic mean diameter, even through semi-empirical

relationship, as those given by equations [8], [9] and [10].

to determine the specific surface diameter, as demonstrated through the consideration made

before is an important parameter to know for a better understanding and interpretation of the in-

vitro experiments results. The surface specific area can be measured using the method adopted

by INEEL [13], consisting in a Micromeritics ASAP2010 Porosimetry Instrument [23, 24, 25].

This instrument uses a Kr or N2 gas adsorption method to measure the specific surface area.

to perform some beta radiation measurements on dust samples (size log-normally distributed) to

be compared to the one obtained by equation [20] introducing the value of the average beta

activity of the tritiated particle0A , in order to have an idea of the shift of the actual tritium

distribution from homogeneity.

to determine as far as possible the chemical composition of dust in addition to C and H.

The dust to be sampled for the next in-vitro experiments should include two or three different

size classes. The first class should have a value of the count mean diameter CMD 1 m, thatis in the range of the reference diameter of the ITER dust particles assumed to be 0.5 mthe second class with CMD around 5 m and the third with CMD > 20 m.

For the next future, it is recommended that a more accurate analysis of the physic-chemical

attributes of the particles, such as size, porosity and chemical composition would be considered

as a priority, and that dissolution kinetics, gut uptake factor and the bio-kinetic behaviour of the

absorbed tritium would be confirmed by studies with animals;

While waiting for the in vivo experiments, some in vitro experiments using JET dust/flakes may

be proposed. The idea is to repeat the previous experiments with the aim to correlate Tdissolution behaviour with particulate size.


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The answer required to the present literature survey whether further experiments are required and

in case which ones, is then affirmative.

The exact type of in-vivo experiments will be defined in collaboration with UKAEA as one of

the outcomes of the task, and presented in a form a proposal for the next JET FT Task activities.


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REFERENCES


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1 EFDA JET Technology Workprogramme 2003, Task Summary of the JET Task Fusion

Technology JW3-FT-5.12, September 2002

2 L. Di Pace, Literature Review on radiological hazards of JET dusts and flakes, FUS-TN-SA-

SE-R-74, Rev. 0, July 2003

3 S. J. Piet and G. Federici, ITER White Paper on Integrated Picture of In-Vessel Tritium and

Dust, ITER IDoMS S 81 RI 13 96-06-28 W 1.4, July 21, 1996

4 B. Patel, et al., Radiological Properties of Tritiated Dusts and Flakes from the JET Tokamak,

Culham, JET

5 C. H. Skinner, C. A. Gentile, M. M. Menon, R. E. Berry Flaking of co-deposited hydrogenated

carbon layers in the TFTR limiter, Nuclear Fusion, Vol. 39, No.9, pp. 1081-1085, 1999

6 ITER GSSR Generic Site Safety Report VOLUME III RADIOLOGICAL AND ENERGY

SOURCE TERMS, ITER G 84 RI 3 01-07-13 R1.0, March 2001

7 R. Lsser et al. JET Fusion Technology R&D for Wastes from Fusion Facilities, Workshop

W53: Experience in the Management of Wastes from Fusion Facilities, Culham, UK, 25-

26/03/2003

8 International Commission on Radiological Protection (ICRP),Human Respiratory Tract Model

for Radiological Protection, Publication 66, Ann. ICRP. 24(1/3) (Oxford: Elsevier Science) (1994)

9 M. R. Bailey, The New ICRP Model for the Respiratory Tract, Radiation Protection

Dosimetry, Vol. 53, Nos 1-4, pp 107-114 (1994)

10 R. F. Kropf, Y. Wang, and Y. S. Cheng, Self-Absorption of Tritium Betas in Metal Tritide

Particles, Lovelace Respiratory Research Institute, Albuquerque, NM, USA, March 1998

11 Y. S. Cheng*, M. Burton Snipes*, Y. Wang* and H. Nian Jow, Biokinetics and Dosimetry of

Titanium Tritide Particles in the Lung, *Lovelace Respiratory Research Institute, Albuquerque,

NM, USA, and Sandia National Laboratory, Albuquerque, NM, USA, September 1998

12 W. C. Hinds, Aerosol Technology, Properties Behavior, and Measurements of Airborne

Particles, p. 80 John Wiley and Sons. New York, NY, 1982

13 W. J. Carmack, et al., Tokamak Dust Particle Size and Surface Measurements , INEEL, June

1998, preprint submitted to Journal of Fusion Engineering

14 Y. S. Cheng et al., Characterization of Carbon Tritide Particles in a Tokamak Fusion Reactor,

Princeton Plasma Physics Laboratory PPPL, USA15 A. Hodgson, E. R. Rance, P. G. D. Pellow and G. N. Stradling, In vitro Dissolution of Tritium

Loaded Carbon Particles from the JET Tokamak,National Radiological Protection Board, Chilton,

Didcot, Oxon OX11 0RQ, UK, NRPB-DA/1/2002, March 2002

16 International Commission on Radiological Protection (ICRP),Age-dependent Doses to

Members of the Public from Intake of Radionuclides: Part 4 Inhalation Dose Coefficients,

Publication 71, Ann. ICRP. 25(3/4) (Oxford: Elsevier Science) (1995)


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17 Y. S. Cheng*, A. R. Dahl* and H. Nian Jow, Dissolution of Metal Tritides in a Simulated

Lung Fluid, *Lovelace Respiratory Research Institute, Sandia National Laboratory,

Albuquerque, NM, USA, June 1997

18 Jost W., Diffusion in solids, liquids, and gases, New York: Academic Press; 1960

19 C. H. Skinner, C. A. Gentile, M. M. Menon, R. E. Berry, Flaking of co-deposited

hydrogenated carbon layers in the TFTR limiter, Nuclear Fusion, Vol. 39, No.9, pp. 1081-1085,

1999

20 C. H. Skinner, C. A. Gentile, J. C. Hosea, D. Mueller, J. P. Coad, G. Federici, R. Haange,

Tritium experience in large tokamaks: Application to ITER (Report on the IEA Workshop held at

Princeton New Jersey, USA, 16 18 March 1998), Nuclear Fusion Volume 39, Number 2,

February 1999

21 ITER Early Safety and Environmental Charecterization Study ESECS, Draft Working version,

ITER EDA S81 RE 95-06-01 W1.1, June 1995

22

Federici, G., et al, "Preliminary Assessment of the Tritium Inventory and Permeation in thePlasma Facing Components of ITER," Fusion Technology 1994, Elsevier Science Publishers,

(18th Symposium on Fusion Technology), 1995

23 S. V. Gorman, W. J: Carmack, and P. B: Hembree, CMOD Dust Particulate Characterization,

INEEL ITER EDF # ITER/US/97/TE/SA-17, August 1997

24

k-shape factors

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