A Subcritical Testbed for Fast Neutron Irradiation of Novel Fuels and Cladding in Fast Reactors
- Niowave, Inc., Lansing, MI (United States)
- Univ. of Michigan, Ann Arbor, MI (United States)
- Purdue Univ., West Lafayette, IN (United States)
- Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
To support experimentation and demonstration with novel fuels and materials for next generation nuclear reactors, it was proposed to develop an electron linac driven, subcritical testbed using a hybrid fast/thermal core configuration that provides a fast reactor like environment with 1E15 n/cm2s fast flux level for fast neutron irradiation tests. The 1E15 n/cm2s fast flux level will provide the essential high material-damage rate of ~20 dpa/yr in ~100 cm3 region to provide sufficient volume for testing reactor materials. In Phase I, two candidate core designs were developed that shows the feasibility of the concept and called HYbrid Subcritical Testbed (HYST). The HYST-I concept was devised by performing parametric studies to reduce the required fuel loading, fission power, and electron beam power level to yield the targeted flux level. The general Monte Carlo code, MCNP6, was used to perform reactor physics calculations on a cylindrical homogenized-region models. Starting from a reference thermal-spectrum cylindrical core design, a fast-spectrum region was introduced in the center and parametric studies determined the trends of fission power and critical mass of 235U as a function of the inner fast region size. The promising candidate HYST-I core design consists of inner fast core, 4 cm in radius (H/D=1.0), surrounded by an outer thermal core of 9.8 cm thickness. The total uranium loading is 6.2 kgU (19.75 wt.% enriched uranium) and requires 7.2 MW of fission power to reach 1015 n/cm2s fast neutron flux. The fast flux was boosted and thermal flux was significantly suppressed in the fast core. The HYST-II concept was developed such that the reactivity swing was minimized and the neutron energy spectrum in the fast core is similar or harder than that of a fast reactor. Starting with a reference fast core design, systematic parametric studies were performed using computer codes: MC2-3, DIF3D, and MCNP6. A reference fast core design was developed with 46% fuel volume fraction and 1050 kg loading of 19.75 wt.% enriched uranium, which can produce the targeted flux level at a 22 MW total fission power. Subsequently, using the same LEU fuel and LBE coolant, the outer region of the reference fast core was replaced with a moderated thermal region to reduce the required fuel loading. Through detailed parametric studies, a promising candidate HYST-II core design was obtained with an active core height of 59.4 cm and a radial core size of 20.0 cm, including a LBE filled test chamber of 2 cm radius, a fast region of 5 cm thickness, and a thermal region of 13 cm thickness. The total LEU fuel loading was reduced to 86 kg (i.e., 17 kg of 235U) with a comparable total fission power (~22 MW) requirement. Preliminary fuel cycle analyses on the candidate HYST-II core design showed a ~7% reactivity loss over a 45 day fuel cycle. This large reactivity change was controlled by, adding a burnable poison plate, which contains ZrB2 of natural boron and Gd-157 enriched Gd2O3, to the thermal region. The core multiplication factor was maintained around 0.97, with a maximum variation less than 1%. About 2% margin to criticality was left at the cold shutdown state. In addition to the core design studies, the superconducting electron linac driven neutron source converter was studied in stand-alone with an LBE target that is bombarded by monoenergetic electron beams. A neutron spectrum similar to the 235U fission spectrum was produced by the linac-based neutron converter. The power of a 40 MeV electron beam required to produce 21.71 MW fission power in the HYST-II core was estimated to be around 2.6 MW for a core multiplication factor of 0.97. The relatively small uranium loading and low fission power requirement to reach the targeted fast flux level, a significant gain was obtained by utilizing the hybrid fast/thermal core configuration. The HYST-I concept will provide the basis of building and operating a small-scale low-power demonstration system (in Phase II) that provides data on the engineering design aspect of the system, thermomechanical characteristics of the design, and neutronics data for code development.
- Research Organization:
- Niowave, Inc., Lansing, MI (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- SC0017733
- OSTI ID:
- 1429266
- Type / Phase:
- STTR (Phase I)
- Report Number(s):
- DOE-NIOWAVE-0017733-1
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS
36 MATERIALS SCIENCE
Hybrid fast/thermal subcritical testbed
Fast reactor
Thermal reactor
Fast neutron irradiation
Core design
Reactor physics study
Material irradiation damage
Superconducting electron linac
Accelerator-based neutron source
MC2-3, DIF3D, and MCNP6