Progress, Challenges, and Opportunities for Converting U.S. and Russian Research Reactors A Workshop Report (2012) / Chapter Skim
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3 Reactor Conversion Case Studies
3 Reactor Conversion Case Studies
Pages 61-88
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From page 61... ...
Because of the uniqueness of many research reactors, conversion studies 1 "Neutronics" refers to an analysis of the neutron flux throughout the core, which entails analysis of fission and neutron capture events caused by absorption of neutrons by the reactor core, scattering of the neutrons, and losses of the neutrons from the reactor.
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From page 62... ...
research reactor conversions are summarized in this chapter: • Paul Wilson (University of Wisconsin) reported on the successful conversion of the University of Wisconsin research reactor (UWNR)
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From page 63... ...
total fuel assembly power and core power distributions; and (2) axial and radial power distributions in the maximum power fuel assembly; • Shutdown margins as a function of fuel burnup; and • Key reactivity parameters, including (1)
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From page 64... ...
. However, the reduction in the number of fuel assemblies resulted in a slightly reduced core lifetime following conversion.7 Thermal/hydraulic Analysis The thermal/hydraulic analysis focused on the behavior of the highpower channel at steady state, low-power pulse, and high-power pulse.8 The analysis yielded estimates of: • Coolant flow rate; and • Temperatures at the fuel centerline, the axial/radial temperature profile, and the minimum departure from nucleate boiling ratio (DNBR)
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From page 65... ...
conversion from HEU to LEU fuel. Fuel elements are shown in red, and beryllium reflector elements are shown in grey.
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From page 66... ...
Accident Analysis The potential for a fission product release under accident conditions was analyzed for a maximum hypothetical accident consisting of cladding failure in the high-power fuel assembly (25 kW) after continuous full-power operation.
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From page 67... ...
For example, experimental research is ongoing to better understand natural circulation heat transfer in TRIGA-relevant conditions, and the fresh LEU core provides a wide variety of benchmark data for continuing to improve analytical capabilities. Massachusetts Institute of Technology Reactor Thomas Newton MITR is a 6 MW research reactor that is currently operating using aluminide (UAlx)
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From page 68... ...
Fuel elements are shown in red, beryllium reflector elements are shown in grey, and white boxes are bitmap empty positions. SOURCE: Austin (2010)
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From page 69... ...
MITR has not yet been converted to LEU fuel because an appropriate fuel has not yet completed development and qualification. In fact, MITR's unique fuel assembly design and highly compact core complicate conversion.
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From page 70... ...
The results of the neutronic and thermal-hydraulic analyses have been used to design an LEU fuel for this reactor. The LEU fuel assembly will contain more plates and use a thinner fuel meat (0.51 mm for UMo LEU fuel versus 0.76 mm for HEU fuel)
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From page 71... ...
Two challenges are foreseen in the mixed-core transition: Power peaking is generally higher in new LEU elements, and steady-state HEU and LEU margins to ONB decrease with an increasing number of LEU fuel elements in the mixed 13 This is the relationship between the pressure drop and the conditions in the flow channel such as mass flow rate. 14 This is the relationship between the conditions in the flow channel at the time when there is net vapor generation.
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From page 72... ...
These improved capabilities have resulted in an optimized LEU fuel design for the MITR reactor. Oak Ridge: High Flux Isotope Reactor David Cook HFIR currently operates at 85 MW -- following a derating from 100 MW in the early 1990s because of embrittlement of the reactor pressure vessel -- using a U3O8-Al dispersion fuel that is 93 percent enriched in uranium-235.
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From page 73... ...
The inner fuel element contains 171 fuel plates, and the outer fuel element contains 369 fuel plates. The fuel plates, are involute-shaped, and the fuel meat is radially contoured along the involute -- the fuel distribution is peaked in the center and thinner on the edges to suppress power peaking (see Figure 3-6)
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From page 74... ...
The inner fuel element, shown on the left, will Figure dramatically asymmetric than the outer fuel element, shown on be more 3-6.eps the right, although both fuel elements are noticeably asymmetric.
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From page 75... ...
. Current calculations indicate that essential neutron fluxes as well as fuel-cycle length can be preserved using UMo monolithic LEU fuel if the reactor power is increased from 85 to 100 MW.
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From page 76... ...
. LEU Fuel Design and Testing There are remaining fuel development and fabrication challenges associated with producing the UMo monolithic LEU fuel that will be required to convert HFIR: • Fuel development is still under way, and the results will affect the final LEU fuel design.
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From page 77... ...
However, as noted in Chapter 1, in December 2010 the U.S. and Russian governments agreed to initiate feasibility studies to analyze the conversion potential of the following six Russian research reactors that are currently operating with HEU fuel:18 1.
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From page 78... ...
It has a maximum thermal neutron flux at the experimental positions of 5 × 1014 n/cm2-s. Its primary mission is to test experimental fuel assemblies and fuel rods under normal, abnormal, and accident conditions.
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From page 79... ...
Each fuel assembly consists of four cylindrical fuel tubes arranged concentrically (see Figure 3-8)
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From page 80... ...
Under this scenario, the annual fuel consumption for LEU would be four times higher than for HEU, but the number of fuel assemblies used would decrease by a factor of approximately 1.75. Overall, it appears that the quality of the core can be improved by using UMo dispersion LEU fuel and changing the fuel meat thickness.
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From page 81... ...
with 90 percent enriched HEU fuel. The 60-cm-high IR-8 reactor core contains 16 IRT-3M fuel assemblies with a beryllium reflector.
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From page 82... ...
Similar to the MIR.M1 reactor, two options were initially considered for transitioning to LEU: the IRT-3M assemblies with UMo dispersion LEU fuel, and IRT-4M fuel assemblies with UO2 fuel. The IRT-4M assemblies were determined to be inadequate to maintain the needed neutron fluxes because the 3 gU/cm3 uranium density in the UO2 fuel is too low.
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From page 83... ...
The use of UMo dispersion LEU fuel results in a harder neutron spectrum compared to HEU fuel, which could create problems for silicon doping applications as well as for the production of radiopharmaceuticals. Another issue of concern is the potential for higher fuel costs for LEU relative to HEU.
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From page 84... ...
In particular, it is important to MEPhI to address the following issues in converting to LEU fuel: • Ensure that safety parameters will continue to conform to existing regulations. The radiation safety parameters for IRT are set to be stricter than for many other research reactors because of the public tours.
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From page 85... ...
MEPhI staff has determined that high-density UMo dispersion LEU fuel will be necessary to successfully convert the IRT reactor, as is the case for most of the other Russian reactors discussed in this chapter. However, staff
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From page 86... ...
Efforts in Russia are focused on the development and qualification of UMo dispersion LEU fuel with densities of more than 5 gU/cm3. Argonne National Laboratory has been working closely with the Bochvar Institute to develop and qualify UMo dispersion LEU fuel for use in Russian research reactors.
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From page 87... ...
of IRT MEPhI Research Reactor Conversion. Presentation to the Research Reactor Conversion Symposium.
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