doe ff hybrid ws gaithersburg md 9/09 driven subcritical fission systems using a cylindrical...

DOE FF Hybrid WS Gaithersburg MD 9/09

DRIVEN SUBCRITICAL FISSION SYSTEMS USING A CYLINDRICAL INERTIAL

ELECTROSTATIC CONFINEMENT (IEC) NEUTRON SOURCE

Miley G. H., Thomas R., Takeyama Y., Wu L., Percel I., Momota H., Hora H2., Li X. Z3. and P. J. Shrestha4

1University of Illinois, Urbana, IL, USA 2University of New South Wales, Sydney, NSW, Australia3Tsinghua University, Beijing, China4NPL Associates, Inc., Champaign, IL, USA


Introduction – IEC driven subcritial systems

The IEC is already a commercial fusion neutron source at low levels!!

Replaced Cf-252 in neutron activation analysis at: Ore mines in Germany Coal mines in USA

In these cases ease of licensing, long lived “target” (plasma), on-off capability, simplicity of construction (low cost), compactness, low maintenance requirement, flexibility in neutron spectrum (2.54 or 14 MeV), ease of control gave the IEC the “edge”. The features can carry over to a driver for a hybrid.

Possibility of small size/power opens door to several near term applications = university training and research facilities.

ICONE-10 April 2002, Arlington, Virginia

Flexible geometry offers new types of drive configurations ---

Fig. 1 Spherical IEC Device Fig. 2 Cylindrical IEC Device


Cylindrical IECs

Cylindrical IECs offer many advantages for the present sub-critical reactor system .

The prototype cylindrical IEC version , C-device, is a particularly attractive.

Deuterium (or D-T) beams in a hollow cathode configuration give fusion along the extended colliding beam volume in the center of the device = a line-type neutron source.


SIMION

Figure 3 Diagram of the C-device with calculated ion trajectories and equi-potential surfaces


IEC Modular Cylindrical Design Advantage

Accelerator approaches to date have used an accelerator spallation-target system.

The large size and cost of the accelerator remain an issue. Also, the in-core target system poses significant design and engineering complications.

The IEC fits in fuel element openings of the sub-critical core assembly. This provides a distributed source of neutrons

Replaces both the accelerator system and spallation-target by by multiple modular sources assembly.

Provides flexibility in core design and in flux profile control.

Small IEC units can be produced at a lower cost than the accelerator

Vertical Cross-Section Showing C-device Modules

Top Cross-Section View Shows C-Device Modules in Channel Locations


IEC Status Considerable research on the IEC concept has already been

carried out on a laboratory scale 10*12 n/s neutron driver for low power sub-assemblies . (student labs or research assemblies)

A key remaining issue for power reactors or actinide burners is concerns the ability to scale up to the high neutron rates required using the small volume units that are envisioned. Requires an intermediate prototype at ~ 10*14 n/s, followed by a full demo unit at 10*18 n/s. Modular design allows testing on single small units – speeding this development up.

Engineering issues include materials development (common to other drivers), blanket (here= “core”) design, rad hardening of the high-voltage components.

Flowchart of MCP Code used to scale up from presnt low level devices

GETDATA:

Reads user inputs

DEFBINS:

Defines bins and meshes

INITIALIZE:

Initializes all variables

POISOLVE:

Finds potential distributionn

CALCFIELD:

Calculates electric field vectors

MARGINAL:

Generates CDFs for sampling

Iterations< Max Iterations?

yes

no

Species=1

Species Nspecies?

yes Trials=0 Trials< Nhist?

yes

Species=Species+1 no PARTICLESOURCE: Sample initial particle properties.

Weight> Minweight?

Trials= Trials+1

no

In Electrode?

yes

MOVE: Moves particle

no

Collision? no

SCORECOLL: Score collision

BNDTRANS:

Handle electrode collisions

yes

yes

DENSCALC:

Convert weight data to real particle data

MARGINAL:

Generates CDFs for sampling

POISOLVE:

Finds potential distributionn

CALCFIELD:

Calculates electric field vectors

Iterations= Iterations+1

Stop

Transport Loop

no

Neutron Production Fits Reasonably Well With Earlier Data

1.00E+2

1.00E+3

1.00E+4

1.00E+5

1.00E+6

1.00E+7

1.00E+8

0 10000

20000

30000

40000

50000

60000

70000 Applied Voltage (V)

Sp

her

ica

l-E

qu

ival

ent

Ne

utr

on

Yie

ld

(Neu

tro

ns

/sec

on

d)

10 mA equivalent MCP 20 mA equivalent MCP 40 mA equivalent MCP 80 mA equivalent MCP 10 mA, 4.3-cm Sperical 10 mA, 4.1-cm Spherical 20 mA, 4.1-cm Spherical 10 mA, 5-electrode C-device 20 mA, 5-electrode C-device 40 mA, 5-electrode C-device

Neutron source strength predictions

Present experiments give 10*10 DD n/s (10*12 DT n/s at 90 kV and 20 mA.

Extrapolation to 10*14 n/s (prototype research reactor goal) at 100 kV requires 0.3 A or 30 kW input.

With improved potential profile control, might be reduced to <10 kW.

Research focusing on power reduction. Further extrapolation to higher power systems

also promising.


Near Term Use in Low Power

Research Reactors or Teaching Labs

Present experimental IEC devices are close to neutron yields required of this application.

Calculations for a representative graphite moderated subassembly next.


Graphite Modulated Sub-critical System

Figure presents the power obtained per unit source as a function of the multiplication factor k∞.

assumed to be a cylindrical homogeneous reactor, fueled by uranium dioxide.

The fuel enrichment is adjusted to give the desired value of k∞.

the fraction of core volume occupied by the fuel fixed at 5%.

the graphite-moderated system can deliver 1 kW of power with a source of 1012 neutrons/sec at Keff =0.99

Specifications summarized in Table .


1.E-15

1.E-14

1.E-13

1.E-12

1.E-11

1.E-10

1.E-09

1.E-08

1.E-07

0.5 0.6 0.7 0.8 0.9 1

k

P/S

(W/ n

eutro

n s

-1)

Water

Graphite

Figure 4 Power level per unit source (P/S) as a function as a function of k for two different moderators


Table 1: Parameters for a 1 kW graphite- moderated sub-critical system.

Fuel UO2 (0.5% U-235)

Moderator material Graphite

Moderator volume fraction

95%

Multiplication factor 0.97

Radius (cm); Height (cm) 30;50

Source strength (neutrons/s)

1x1012

Power (kW) 1.2


Summary A 1-kW IEC driven graphite moderated

research reactor appears attractive from a cost and safety point of view.

Also, existing experimental IEC devices very close to the target of 1012 n/s.

This is consistent with the source levels in Garching II research reactors (Cf-252 neutron source with 4x109 neutrons/sec).


Future Driven Reactor Designs vs Accelerator Target designs

Designed to ensure safety against criticality and loss-of-cooling accidents as is done in the conventional accelerator-target designs.

But important differences exist in the method used . Accelerator designs use a passive beam “shut-off” device

based a combination of thermocouple readings and a melt-rupture disk in the side-wall of the beam guide tube.

The IEC uses a temperature sensitive fuse in the in-core electrical circuit to shut down the high-voltage.

A melt rupture disk on the IEC wall is added as backup to spoil the IEC vacuum.

A very rough conceptual design for a 1000 MWe plant has been developed. The reactor core employs distributed IEC units as in the low power subcritical applications. Very important here for flux profile control.


Design & R&D Comments

Cylindrical IEC units occupy multiple fuel channels. = a distribute d neutron source and modular source design.

15 units stacked in each channel in preliminary design for 1000Mwe unit. Selected to optimize neutron profiles in both the radial and vertical

directions This “distributed source” design is to be contrasted to a central core

spallation target (STET) Waste heat from IEC is deposited on the large area hollow electrodes and

removed by coolant flow around the fuel channels. A keff < 0.97 requires ~1018 n/s per IEC ( vs present experimental values of

~1012 D-T n/s) – MCR calculations indicate feasible. Since IEC scaling involves velocity space increasing the yield does not

require a significant increase in unit size. Instead, higher beam currents and improved ion recirculation are key; other

special crucial issues include high-voltage stand-offs that are “radiation hardened”. Material development, etc. are common issues to other drivers.

These issues can be studied starting from a simple small unit, allowing a rapid development cycle..


Conclusions An alternative to the standard driven reactor accelerator-

spallation target design is proposed which employs IEC neutron sources which can be in a central location or distributed across a number of fuel channels. Such a modular design has distinct advantages in reduced driver costs, plus added flexibility in optimizing neutron flux profiles in the core. The basic physics for the IEC has been demonstrated in small-scale laboratory experiments, but a scale-up in source strength is required for ultimate power reactors.

However, the IEC source strength is already near the level required for low power research reactors or for student sub-critical laboratory devices. This application would be advantageous since the safety advantages of these reactors should enable a next generation of research reactors to be constructed quickly, meeting the educational and research needs facing us as there is a rebirth of interest in nuclear power.

doe ff hybrid ws gaithersburg md 9/09 driven subcritical fission systems using a cylindrical...

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