efda european fusion development agreement efda csu garching s.ciattaglia, page 1/25 overview of...

EFDA CSU Garching S.Ciattaglia, page 1/25

EFDA EUROPEAN FUSION DEVELOPMENT AGREEMENT

OVERVIEW OF SAFETY OF EUROPEAN FUSION POWER PLANT DESIGNS

Annual Meeting on

Nuclear Technology

May 10 - 12, 2005

Nuremberg

S.Ciattaglia, aL.Di Pace, W.Gulden, P.Sardain, bN.Taylor

EFDA Close Support Unit, S&E Field, Garching GermanyaENEA Fusion Technologies, Frascati (Rome), Italy

bEuratom/UKAEA Fusion Association, Culham Science Centre, Abingdon, UK



Outline

•Introduction

•Power Plant Conceptual Studies

•Safety analysis

•Environmental impact

•Radioactive wastes

•Achievements and open points

•Conclusions



Introduction

From 1990 to 2000 a series of studies on safety, environmental and economic potential of fusion power

• potential to provide inherent safety and favourable environmental features, to address global climate change and gain public acceptance

• the cost of fusion electricity likely to be comparable with that from other environmentally responsible sources of electricity generation

Further progress on experiments and R&D• Substantial advances in the understanding of fusion plasma physics

and in the development of more favourable plasma operating regimes, • Progress in the development of materials and technology.



Introduction (2)

PPCS (Power Plant Conceptual Studies)• A comprehensive design study for commercial fusion power plants

performed from mid 2001 to mid 2004, to serve as a better guide for the further evolution of the fusion development programme.

• Focussed on four (+1) power plant models, named PPCS A to PPCS D plus model AB, spanning a range from relatively near-term concepts, based on limited technology and plasma physics extrapolations, to a more advanced conception.

• They differ from one another in their size, fusion power and materials compositions, and these differences lead to differences in economic performance and in the details of safety and environmental impacts.

• The study was carried out with the help of a large number of experts from both the European fusion research community and its industrial partners.



Power Plant Conceptual Studies

Objectives

• Demonstration of:• Credibility of fusion power plant design• Safety and environmental advantages of fusions power• Economic viability of fusion power

• Set of requirements issued by industry and utilities• Safety• Operational aspects• Economic aspects

• Economic safety and environmental analyses of these models were made



Schematic diagram of a tokamak fusion power plant

Breeding Blanket

Poloidal Field Coil

Toroidal Field Coil

Power Conversion System

Supply Electric Power to the Grid

Heating &Current drive

IsotopeSeparation

PumpingD+T+ashes

Breeding Blanket

Poloidal Field Coil

Toroidal Field Coil

Power Conversion System

Supply Electric Power to the Grid

Heating &Current drive

IsotopeSeparation

PumpingD+T+ashes

Vacuum

Vessel



General layout



Key parameters

• 1500 MWe

• Fusion power is determined by efficiency, energy multiplication and current drive power

• Given the fusion power, plasma size mainly driven by divertor considerations



PPCS main elements

• All the models PPCS A to D are based on the tokamak concept as the main line of fusion development proceeding through JET, the world’s largest and most advanced operating machine, that is provides the basis for the plasma physics of ITER, under design finalisation.

• Two main elements:

• Blanket:

• Takes the energy of the energetic neutrons produced by the fusion process

• Neutrons absorbed by Li atoms to produce the fuel, tritium.

• Divertor

• for exhausting from the plasma chamber the fusion reaction products, mainly helium, and the associated heat power



Plants main features

Model A Model B Model C Model D

Fusion Power (GW) 5.0 3.6 3.4 2.5

Blanket Gain 1.18 1.39 1.17 1.17

Plant Efficiency 0.31 0.36 0.44 0.6

Bootstrap Fraction 0.45 0.43 0.63 0.76

Padd (MW) 246 270 112 71

H&CD Efficiency 0.6 0.6 0.7 0.7

DV Peak load (MW.m-2) 15 10 10 5

Average neutron wall load 2.2 2.0 2.2 2.4

Major Radius (m) 9.55 8.6 7.5 6.1

Structural material Eurofer Eurofer Eurofer SiC/SiC

Coolant Water Helium LiPb/Helium LiPb

Breeder LiPb Li4SiO4 LiPb LiPb

TBR 1.06 1.12 1.15 1.12

Structural material CuCrZr W alloy W alloy SiC/SiC

Armour material W alloy W alloy W alloy W alloy

Coolant Water Helium Helium LiPb

Conversion Cycle Rankine Rankine Brayton Brayton

Bla

nke

tD

V



PPCS A and PPCS B

• Limited extrapolations in plasma physics performance compared to the design basis of ITER.

• Blankets• based, respectively, on the “water-cooled lithium-lead” and the “helium-cooled

pebble bed” concepts, using of a low-activation martensitic steel

• Divertors• water-cooled divertor is an extrapolation of the ITER design and uses the

same materials. • helium-cooled divertor, operating at much higher temperature, requires the

development of a tungsten alloy as structural material. • Balance of plant

• model A based on PWR technology, which is fully qualified• model B relies on the technology of helium cooling, the industrial development

of which is starting now, in order to achieve a higher coolant temperature and a higher thermodynamic efficiency of the power conversion system



Model A

BlanketEurofer as structural materialWater as coolant LiPb as breeder and neutron multiplier

OutboardModulea 20˚ sector



Model A: Water-cooled Divertor

High temperature Dv Low temperature Dv



Model B: He-cooled divertor

Divertor concept using helium as coolant and W as structural material Peak load of 10 MW/m2 necessity to optimize the heat exchange



PPCS Models C and D

• PPCS C and D are based on successively more advanced concepts in plasma configuration and in materials technology

• The objective is to achieve even higher operating temperatures and efficiencies

• Their technology stems, respectively, from a “dual-coolant” blanket concept (helium and lithium-lead coolants with steel structures and silicon carbide insulators) and a “self-cooled” blanket concept (lithium-lead coolant with a silicon carbide structure)

• In PPCS C the divertor is the same concept as for model B• In PPCS D, the divertor is cooled with lithium-lead like the blanket. This

allows the pumping power for the coolant to be minimised and the balance of plant to be simplified.



Model C : DC Blanket Scheme and main Features



EU Fusion Programme development needs

• ITER operation• optimisation of low activation martensitic steels, • development of tungsten alloys, and their testing in IFMIF, as armour

material• development of the more advanced materials envisaged in the PPCS• development of blanket modules, to be tested in ITER• development of divertor systems, capable of combining high heat flux

tolerance and high temperature operation with sufficient lifetime in power plant conditions

• development and qualification of maintenance procedures by remote handling

• A DEMO power plant study has been lunched: a study to give guidance to the ITER-accompanying programme in plasma physics and technology



PPCS Safety analysis

• Aim• Critical design review and relevant recommendations in order to• Demonstrate that no design-basis accident and no internally

generated accident will constitute a major hazard to the population

outside the plant perimeter, e.g. requiring evacuation.

• Technique adopted

• Functional Failure Mode and Effects Analysis methodology to find out

representative accident initiators• a plant functional breakdown for the main systems. • a FFMEA for each lower level function

• Two design-basis accidents and two beyond design basis accidents

chosen and analysed in detailed for both Plant Model A and B



Safety analysis (2)

• Fusion Reactors will produce and contain radioactive materials that require careful management both during the operation (avoiding release in normal and accident conditions) and after decommissioning

• Main radioactive mobilisable inventories• tritium in the in-vessel components and in the fuel cycle• activated materials (dust originating from plasma-PFC interaction and

corrosion products)

• Energies that can mobilise the above inventories during accident conditions• decay heat• electromagnetic energy• chemical energy



SOURCE TERMS

ASSESSMENT

Normal working conditions Occupational dose

PIERASBAS

Thermodynamic transients Aerosols and H3 transport

Containments Release from the plant DCF

Overall Plant AnalysisFMEA

Radioactive waste Identification&classificationOperational&Decomm waste

Management•On-site•Recycling•Final disosal

Effluents

PST

PST EST

DCF

man*Sv/y

dose/sequence to MEI

frequency*dose

Quantity and waste categories

mSv/y

General fusion safety analysis approach



PPCS safety analysis has benefited by the main conclusions of ITER safety analysis

• A comprehensive analysis of off-normal events and failures and combination of failures

postulated to critically verify the design • Source Terms: 1 Kg of tritium, 100 Kg of Be and W dust, 200 Kg of carbon dust• ORE design target: < 0.5 person Sv/y• Energies definition: magnetic, • Protection/Mitigation systems definition (VV suppression tank, plasma shutdown, HVAC

systems and capability of dust and tritium filtering• Low decay heat at shutdown (360 ºC is PFC Tmax after 9hr from the plasma shutdown in case

of LOCA in-vessel)• Radioactive releases for all accident events below the project release guidelines (relevant doses

~ average annual natural background dose) • Hypothetical events (all cooling systems or common cause failure damaging both vacuum vessel

and cryostat): no evacuation, (<50 mSv). PFC Tmax ~ 650 ºC

Safety analysis (4)



• PPCS source terms

• Energies• Decay heat• Magnetic

• Activation

• ORE

• ?• Sarebbe dadare di dati/assunzinifate

Safety analysis (4)



• Bounding accident sequences: complete unmitigated loss of cooling; no safety systems operation; conservative modelling.

• Temperature transients: example opposite - Model A after ten days.

• Maximum temperatures never approach structural degradation.

Safety Analysis (5)



Bounding Temperature Accident Analysis

Plant Model A

Plant Model B

T

T



Specific activity of the mid-plane outboard

first wall in four Plant Models

Activation of tokamak structures and components



Safety Analysis (7)

The most challenging scenario in terms of environmental release:

“Loss of flow in one primary cooling loop with consequential in-vessel LOCA (Model B)”.

• Parametric analyses on the building leakage rate from Expansion Volume;

• Possibility to operate an Emergency Detritiation System to reduce environmental releases



Safety Analysis - Model B Loss of flow in one primary cooling loop with consequential in-vessel

LOCA

Reference building leakage rates Pressure inside VV, EV and PS

Complete mobilisation of 10 kg of dust &1 kg-T in the VV.

Elevated environmental releases due to building leakage rate considered: (75%/d); 58 g-T, 109 g of W, 346 g of SS dusts.

Parametric analyses• Lower leakage rates: 1%, 10%; • One cylindrical (H= 40.0 m; D= 46.0 m) concrete structure surrounding the

EV, and having a thickness of 0.4 m, externally insulated.

ECART results



Environmental Impact (1)

• Environmental source terms• activated dust/ corrosion products• tritium

• During normal operation• negligible release (doses to the most exposed individual less than 1%

of the natural background level),• ALARA principle is applied for public and workers

• No emission of any of the greenhouse gases

• Conservatively assumed

• a mobilisation fraction of 100 % for the dust at the beginning of the

accident sequence,

• 90% as HTO for T

• worst atmosphere conditions



Model B• Ex-vessel LOCA + in-vessel LOCA (Containment response and environm. release)

Total dust deposited

Total dust airborne

VV

TCHS

Dust in compart. T in the compart.Dust to the Env.

0.2 g

0.6 g

24 h

24 h

For 7-day T release assume a linear release with the slope of 1•10-8 kg/s. At 7 days T released = 5.4 g.

T to the Env.



Model A ex-vessel LOCA results

Pressure in TCWS vault, ST and DT

TCWSST

DT

7-day ACP release <1 mg

7-day T release <3 mg

ACP

T



Bounding accident sequences for Models A and B: complete unmitigated loss of cooling; no safety systems operation; conservative modelling

Mobilisation; transport within the plant; release and transport in environment; leading to:

Conservatively calculated worst case doses to the MEI from worst case accident:

MODEL A: 1.2 mSv MODEL B: 18.1 mSv

Comparable with typical annual doses from natural background.

Model C and Model D worst case doses (analyses undergoing) expected to be lower (abbiamo dei risultati???)

Environmental Impact (4)



Radioactive Wastes (1)

The fusion radioactive waste is characterised by low heat generation density and low radiotoxicity compared to fission plant waste. Therefore recycling may be a viable option.

Storing the fusion radioactive materials for 50-100 years on the plant allows reduction of radioactivity level waste masses

Table 2 – Classification of fusion radioactive waste.

Activated material classifications Contact dose

rate after 50 y

(mSvh-1)

Decay heat per

unit volume after

50 y (Wm-3)

Clearance

index after 50 y

[5]

PDW, Permanent Disposal Waste (Not

recyclable)

>20 >10 >1

CRM, Complex Recycle Material 2-20 1-10 >1

SRM, Simple Recycle Material <2 <1 >1

NAW, Non Active Waste (to be cleared) <1



For ALL the Models:

Activation falls rapidly: by a factor 10,000 after a hundred years

Significant contribution to SRM and CRM from operational wastes

Potentiality to have no waste for permanent repository disposal

Also tritiated + activated wastes

Wastes from model B




NAWSMR

CMRPDW

D

C

BA

0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

80,000

90,000

Tonnes

Radioactive material category

Power Plant model

Figure 2 - Masses of the material after 100 years decay

D

C

B

A




NAWSMR

CMRPDW

D

C

BA

0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

80,000

90,000

Tonnes

Radioactive material category

Power Plant model

Figure 1 - Masses of material after 50 years decay

D

C

B

A





If no recycling is planned

• the amount of waste to be disposed after 100 years, is equal to the CRM+SRM amounts. They don’t require a deep geological repository.

• Suitability and capability analyses of the final waste repositories in a few EU countries to store the PPCS wastes are undergoing (Konrad and Gorleben in Germany, SFR and SFL 3-5 in Sweden, CSA in France, El Cabril and DGR in Spain).

• First results, limited to Model B and German conditions, indicate that the fusion reactor waste can be al disposed in Konrad. For a few ones, detritiation is necessary to meet the relevant limits



Achievements and open points

Comprehensive safety analysis of PPCS has showed• “No evacuation” criteria met with margin also in case of severe

accidents (bounding accidents analysis and consequences)• Intrinsic-passive safety features of nuclear fusion plants confirmed

• Lack of operating experience• Reliability of prototypes • PFCs erosion/deposition and transport in SOL• Tritium retention and distribution in the tokamak • Detritiation techniques• ORE minimisation

• Quantity of operational waste• Tritiated + waste disposal



Conclusions (1)

• The four PPCS conceptual design for commercial fusion power plants

differ in their dimensions, gross power, and power density

• All models meet the overall objectives of the PPCS (design, safety,

economics)

• Plasma performance only marginally better than the design basis

of ITER is sufficient for economic viability of fusion reactors

• Conceptual design of a helium-cooled divertor capable of

tolerating a peak heat load of 10 MW/m2

• Definition of a maintenance concept capable of delivering high

availability (75%)

• A first commercial fusion power plant - accessible by a “fast track”

route of fusion development - will be economically acceptable,

with major safety and environmental advantages



Conclusions (2)

• R&D is needed• Materials

• Validation of Eurofer• Use of ODS

• Temperature• Welding

• Tungsten as structural material• SiC/SiC

• He cooled divertor• Integration and technology issues

• Attachment system and access to collectors



Conclusions (3)

The safety and environmental attractiveness of fusion power has been confirmed

Bounding accident sequence analyses driven by internal events have revealed no surprise: “no evacuation criteria” is met

• Bounding accident sequence analyses driven by external events have to be completed

• Model B LOFA + in-vessel LOCA i provides the largest environmental source terms

• Wastes amount are significant

• There is the potentiality to have no need of permanent disposal waste after 100 years from shutdown if recycling is applied

efda european fusion development agreement efda csu garching s.ciattaglia, page 1/25 overview of...

Documents

commercial fusion power

power plant models

fusion development programme

environmental analyses

environmental impacts

inherent safety

details of safety

overview of safety