Title: DRIVEN%20SUBCRITICAL%20FISSION%20SYSTEMS%20USING%20A%20CYLINDRICAL%20INERTIAL%20ELECTROSTATIC%20CONFINEMENT%20(IEC)%20NEUTRON%20SOURCE
1DRIVEN 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, Australia 3Tsinghua University, Beijing,
China 4NPL Associates, Inc., Champaign, IL, USA
2Introduction 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.
3Flexible geometry offers new types of drive
configurations ---
Fig. 1 Spherical IEC Device
Fig. 2 Cylindrical IEC Device
4Cylindrical 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.
5Figure 3 Diagram of the C-device with calculated
ion trajectories and equi-potential surfaces
6IEC 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
7Vertical Cross-Section Showing C-device Modules
8Top Cross-Section View Shows C-Device Modules in
Channel Locations
9IEC Status
- Considerable research on the IEC concept has
already been carried out on a laboratory scale
1012 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 1014 n/s,
followed by a full demo unit at 1018 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.
10Flowchart of MCP Code used to scale up from
presnt low level devices
11Neutron Production Fits Reasonably Well With
Earlier Data
12Neutron source strength predictions
- Present experiments give 1010 DD n/s (1012 DT
n/s at 90 kV and 20 mA. - Extrapolation to 1014 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 lt10 kW. - Research focusing on power reduction.
- Further extrapolation to higher power systems
also promising.
13Near 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.
14Graphite Modulated Sub-critical System
- Figure presents the power obtained per unit
source as a function of the multiplication factor
k8. - assumed to be a cylindrical homogeneous reactor,
fueled by uranium dioxide. - The fuel enrichment is adjusted to give the
desired value of k8. - 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 .
15Figure 4 Power level per unit source (P/S) as a
function as a function of k? for two different
moderators
16Table 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) 3050
Source strength (neutrons/s) 1x1012
Power (kW) 1.2
17Summary
- 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).
18Future 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.
19Design RD 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 lt 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..
20Conclusions
- 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.