Progress, Challenges, and Opportunities for Converting U.S. and Russian Research Reactors A Workshop Report (2012) / Chapter Skim
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2 Challenges and Opportunities Associated with Conversion
2 Challenges and Opportunities Associated with Conversion
Pages 21-60
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From page 21... ...
• Panel 2.2: Other technical challenges associated with conversion featured presentations on ageing and obsolescence, regulatory challenges, and challenges posed by research reactors that cannot be converted. • Panel 2.3: How challenges associated with previously converted reactors were overcome featured presentations on approaches for overcoming the conversion challenges identified by the other panels in this session.
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From page 22... ...
3 As noted in Chapter 1, there are two additional HEU-fueled research reactors in the United States (NTR General Electric and TREAT; see Footnote 20 in Chapter 1) that appear to be convertible using current-type LEU fuels.
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From page 23... ...
UMo Dispersion LEU Fuel Initial irradiations of fuel elements containing UMo dispersions resulted in the formation of interaction layers between the UMo and Al particles and the development of porosity and distortion (pillowing)
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UMo Monolithic LEU Fuel Fuel plates under development for high-performance U.S. reactors consist of a UMo alloy foil ("U-10Mo Foil" in Figure 2-1)
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Cherepnin Most Russian research and test reactors use HEU fuels consisting of UO2-aluminum dispersions fabricated as thin-walled tubular elements of various enrichments and configurations. A Russian program was started in the 1990s to further reduce the enrichment of fuel used in Russian-origin research reactors that are located outside of the Russian Federation.
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From page 26... ...
The 19.5 percent enriched fuel will be used in the Russian-origin MARIA research reactor in Poland. The transition to these LEU fuel assemblies has proceeded using the same fabrication technologies and equipment for producing HEU fuel.
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From page 27... ...
IRT-4M square fuel assembly, and (right) MR tubular fuel assembly.
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From page 28... ...
U.S. Viewpoint on Core Modifications John Stevens The conversion of a research reactor from HEU to LEU fuel can result in performance penalties in the reactor, primarily arising from the reduced density of uranium-235 and absorption of neutrons by uranium-238.
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From page 29... ...
An LEU fuel is considered to be acceptable for conversion when it meets the following criteria: • Qualified: the fuel assembly has been successfully irradiation tested and is licensable. • Commercially available: The fuel assembly is available from a commercial manufacturer.
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The LEU fuel contains slightly more uranium-235 than the HEU fuel it replaced to ac count for the increased neutron absorption by uranium-238.
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From page 31... ...
However, by increasing the thickness of the fuel meat by 0.1 millimeters, the conversion goal could be met using only 13 fuel assemblies, a savings of 4 assemblies. Additionally, by changing the locations of some of the beryllium reflector blocks, designers were able to increase neutron flux densities in key locations in the reactor core to better suit experimental needs.
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From page 32... ...
The reactor is planned to be converted using a 19.75 percent enriched UMo dispersion LEU fuel. However, integrating a burnable poison into these fuel plates will be difficult owing to the high-volume fraction of UMo in the dispersion.
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From page 33... ...
As illustrated by the following three examples, for some Russian research reactors there are no developed LEU fuel elements that would enable conversion with acceptable consumer characteristics. Moreover, some Russian research reactors are approaching the ends of their operating lives, and there is a need to consider whether to shut down these reactors or modernize them.
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From page 34... ...
These studies indicate that conversion would result in some consumer and economic penalties compared to HEU fuel: neutron flux densities in the fuel and reflector regions would decrease by 20-30 percent and 10-20 percent, respectively, and the number of fuel elements in the core would increase by 2-4 elements.9 The economics of conversion will depend on the cost of LEU fuel elements and their reprocessing compared to the costs for HEU fuel elements.10 However, there would be no unacceptable changes in safety characteristics, and fuel burnups would not change. IVV-2M (Institute of Nuclear Materials, Zarechny)
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From page 35... ...
) provided a description of several Russian research reactors at RIAR and their missions (Svyatkin et al., 2011)
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AR is automatic regulating rod. FIGURE 2-6 Schematic illustration of the WWR-M reactor core.
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, compare reactor performance with HEU and LEU fuels, and calculate key safety parameters. • Operational and safety analyses to demonstrate that the transition from HEU to LEU fuel can be done safely and without interrupting normal 11Service lifetimes of LEU fuel assemblies can be increased if the uranium-235 loadings are higher than comparable loadings in the HEU fuel.
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From page 38... ...
The final LEU fuel assembly design can be selected once these studies are completed. Some high-performance reactors may require fuel-design optimization and possibly facility-specific mitigation measures to address any performance penalties arising from conversion.
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In the case of highperformance reactors or reactors with unique designs, iterative collaborations among facility operators, fuel designers, and conversion analysts are essential to optimize fuel and core design and minimize performance impacts. Descriptions of Russian Research Reactors A.L.
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In particular, new LEU fuel compositions can be examined for applications in high-flux reactors. The reactor can also be used for training.
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From page 41... ...
The experimental applications could be expanded to include advanced reactor and fuel cycle research. AGEING AND OBSOLESCENCE OF RESEARCH REACTORS Two presentations on understanding and addressing the ageing and obsolescence of research reactors were given by Panel 2.2 speakers: H.-J.
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From page 42... ...
As the result of this expert meeting, the IAEA initiated the development of a database on research reactor ageing. This database is intended to address ageing as a technical and safety issue and explicitly excludes reactor conversion to LEU fuel.
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This will involve the reconfirmation of research reactor operator contacts, updates to the content of templates, and fresh approaches to the research reactor operators who did not provide information in 2009.
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There have been a total of 80 research reactors constructed by the Soviet Union, including the following 15 reactors that were constructed in foreign countries: • VVR-S (2-10 MW power) : Constructed in East Germany, Czechoslovakia, Romania, Poland, Hungary, and Egypt between 1957 and 1961.
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From page 45... ...
Eleven research reactors besides F-1 have been constructed at the Kurchatov Institute: • RFT: Channel graphite reactor; initial power 10 MW, later upgraded to 20 MW; began operations in 1957 and was partially demolished in 1962. • VVR-2: Pool-type reactor; initial power 0.3 MW, later upgraded to 3 MW; began operations in 1954 and was dismantled in 1983.
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From page 46... ...
The neutron flux density in the reflector was 5 × 1014 n/cm2-s. This reactor was used to work out the structure of active zones of nuclear reactors and test 400 fuel assemblies and more than 8,000 fuel rods for VVER, RBMK, ACT, high-temperature, and naval reactors.
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From page 47... ...
The USNRC does not get involved directly in these fuel development activities, but it does have the responsibility for approving LEU fuels for use in USNRC-licensed reactors. USNRC approval of new LEU fuels is based on information submitted by DOE, including: • Results of LEU fuel development and testing.
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Regulation of Research Reactor Conversions When regulatory requirements for conversion became effective there were 26 HEU-fueled civilian research reactors in the United States under the regulatory authority of the USNRC. Most of these reactors were being operated by universities.
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The regulations also require reactor licensees to replace HEU fuel with LEU fuel acceptable to the Commission in accordance with an approved schedule. To be acceptable to the Commission, LEU fuel must (1)
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• Reactor accidents: The licensee should reanalyze the HEU Safety Analysis Report accidents using LEU fuel to determine the impacts from conversion. Particular concerns include changes in power per fuel element, fission product inventory, and reactivity.
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The federal codes and standards provide general safety provisions for each type of atomic energy facility, for example, nuclear power plants, research reactors, icebreaker reactors, and nuclear fuel cycle facilities. These codes and standards also provide specific provisions for activities at these facilities including siting, construction, operation, and decommissioning.
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From page 52... ...
• 30 critical assemblies • 12 subcritical assemblies The average operation age of the research reactors is 24 years, but 17 reactors have been operating for more than 30 years. ROSTEXNADZOR is just beginning to develop regulations for the conversion of research reactors in the Russian Federation.
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From page 53... ...
protect high-priority nuclear and radiological materials from theft and sabotage. GTRI's Reactor Conversion Program is focused on converting civilian research reactors worldwide to operate on LEU fuel.
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research reactors (ATR and its critical assembly, HFIR, MITR, MURR, and NBSR) that cannot be converted until a new LEU fuel is developed.
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Although GTRI policy is to take all reasonable steps to convert facilities and reduce the use of HEU, there may be some facilities that are not feasible to convert. For example, a feasibility study for a particular reactor might indicate that conversion is not feasible because LEU fuel assembly criteria are not satisfied and a unique fuel development effort is not technically or economically feasible.
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This fuel used in these assemblies is not self-protecting22 and therefore poses special security concerns. Converting these facilities to LEU fuel cannot be accomplished without sacrificing the current mission.
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B Myasoedov commented that he expected the role of research reactors to grow in the future to support the development of more complex reactor designs for nuclear power plants, including those based on fast reactor designs; for radiopharmaceutical production; and for analytical methods (such a neutron activation analysis)
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From page 58... ...
This fuel is a potential replacement for the tubetype fuel that is now being used in Russian research reactors. The recent agreement between DOE and Rosatom to assess the feasibility of converting six Russian research reactors could play an important role in assessing the potential utility of this LEU fuel.
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From page 59... ...
The recent agreement between DOE and Rosatom to assess the feasibility of converting six Russian research reactors is an important step for eliminating HEU use in Russian research reactors. It is important that the Russian Federation and the United States serve as an example to countries by reducing the enrichments of their research reactors to lower levels.
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From page 60... ...
Presentation to the Research Reactor Conversion Symposium.
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