1. 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 H 2., Li X. Z 3. and P. J. Shrestha 4 1 University of Illinois, Urbana, IL, USA 2 University of New South Wales, Sydney, NSW, Australia 3 Tsinghua University, Beijing, China 4 NPL Associates, Inc., Champaign, IL, USA

2. DOE FF Hybrid WS Gaithersburg MD 9/09 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.

3. ICONE-10 April 2002, Arlington, Virginia Flexible geometry offers new types of drive configurations --- Fig. 1 Spherical IEC DeviceFig. 2 Cylindrical IEC Device

4. DOE FF Hybrid WS Gaithersburg MD 9/09 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.

5. DOE FF Hybrid WS Gaithersburg MD 9/09 Figure 3 Diagram of the C-device with calculated ion trajectories and equi-potential surfaces

6. DOE FF Hybrid WS Gaithersburg MD 9/09 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

7. Vertical Cross-Section Showing C- device Modules

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

9. DOE FF Hybrid WS Gaithersburg MD 9/09 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.

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

11. Neutron Production Fits Reasonably Well With Earlier Data

12. 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.

13. DOE FF Hybrid WS Gaithersburg MD 9/09 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.

14. DOE FF Hybrid WS Gaithersburg MD 9/09 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 10 12 neutrons/sec at K eff =0.99 Specifications summarized in Table.

15. DOE FF Hybrid WS Gaithersburg MD 9/09 Figure 4 Power level per unit source (P/S) as a function as a function of k  for two different moderators

16. DOE FF Hybrid WS Gaithersburg MD 9/09 Table 1: Parameters for a 1 kW graphite- moderated sub-critical system. FuelUO 2 (0.5% U-235) Moderator materialGraphite Moderator volume fraction95% Multiplication factor0.97 Radius (cm); Height (cm)30;50 Source strength (neutrons/s)1x10 12 Power (kW)1.2

17. DOE FF Hybrid WS Gaithersburg MD 9/09 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 10 12 n/s. This is consistent with the source levels in Garching II research reactors (Cf-252 neutron source with 4x10 9 neutrons/sec).

18. DOE FF Hybrid WS Gaithersburg MD 9/09 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.

19. DOE FF Hybrid WS Gaithersburg MD 9/09 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 k eff < 0.97 requires ~10 18 n/s per IEC ( vs present experimental values of ~10 12 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..

20. DOE FF Hybrid WS Gaithersburg MD 9/09 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.