Nitride fuels

These fuels are compatible with stainless steel cladding. However, with carbide fuels prevention of carbon transport from the fuel to the cladding material or vice versa requires control of the chemical potential of carbon in the fuel (e.g., by using stoichiometric UC by stabilizing the fuel with addition of small amounts of Cr, V, or Mo or by Cr plating the pellets). Both carbide and nitride fuels have good compatibility with sodium but poor oxidation resistance. 

The selection of materials must also consider oxidation/reduction processes that occur in the absence of an aqueous electrolyte. Examples include sulfidation, destructive oxidation of alloys in air or steam at high temperatures, carburization, nitriding, fuel ash corrosion, and high-temperature hydrogen attack. 

For purposes of limiting the scope of the thesis, the reactor will use a directly coupled closed Brayton cycle for power conversion and will use highly enriched Uranium Nitride fuel. The sections of the thesis will be ... 

Johnson, C. E., Thermophysical and Mechanical Properties of Advanced Carbide and Nitride Fuels., ANL-AFP-26., June 1976. 

BRcore l even in sodium cooled reactor (on condition that higher density nitride fuel is used), in spite of elimination of both radial and axial fertile blankets. 

Studies made at the Institute for Physics and Power Engineering have confirmed the possibility of achieving BR = BRcore= 1 with typical for LMFRs volumetric fraction of nitride fuel in the core of sodium cooled 800-1600 MW(e) reactor, its core overall dimensions being much lower than those of lead cooled reactor [2.31]. 

Preliminary design study of lead cooled fast reactor with nitride fuel assemblies has been performed by the Japanese specialists to improve uranium resource utilization and transmutation of HLW nuclides. Plant size limitations caused by seismic resistance... 

The use of U nitride fuel and boron control rods in LCFR (BREST concept) will cause tritium formation as a result of triple fission on N-14 and B-10 nuclei. Tritium activity may reach 2.6-10 Bq/day, that is rather high value. Because of its penetration into the secondary circuit through SG tube walls, tritium release into the environment is possible. These assessments are thought to be performed not only by calculations but also using experimental studies. 

Experiments in the Phenix reactor (materials, transmutation of actinides, and irradiation of targets containing long-lived fission products), and in BOR-60 (transmutation of americium, nitride fuels). 

A lot of information has been accumulated on tested fuel. Results of tests of advanced nitride fuel core performed during almost 19 years are very important. Maximum burnup values achieved for different fuel compositions are as follows ... 

New fuel test(mixed-carbide fuel, nitride fuel)... 

Feasibility study of advanced nitride fuel has been conducted since 1986. PNC/JAERI irradiation test of nitride and carbide pins continues in Joyo since 1994. 

The highest Pu consumption rates can be achieved only if uranium is eliminated from the core. Nitride appears to be a possible non-uranium fuel material, and the performance of a core fuelled with pure PuN has been studied. AEA-T have studied the vaporisation behaviour of nitride fuels, surveyed the extant data on the physical and chemical properties of PuN and (U,Pu)N, and set up a calculational model of a nitride fuel pin. Preliminary results indicate that acceptable bumups can be achieved provided potential problems of fuel swelling can be solved. 

Many numbers of irradiation tests, such as for the nitride fuel and the carbide fuel, are now in progress. The creep test of fuel cladding material under irradiation with MARICOf Material Testing Rig with Temperature Control) was performed at the 29th duty cycle. 

Design study on a 1300MWe-size plant featured with passive safety using nitride fuel is underway at PNC. 

A critical experiment for nitride fuel FBR cores is in progress at Fast Critical Assembly (FCA) as a cooperative study between Japan Atomic Energy Research Institute and PNC. The first stage of the experiment, which consists of reaction rate and sample reactivity measurement in small area of nitride fuel, was completed on June 1994. The preliminary analysis showed the general prediction accuracy of the nitride fuel core seemed to be equivalent to that of the conventional oxide fuel cores. The second phase of the nitride fuel core experiment with enlarged region of nitride fuel is planned in 1996. 

Plutonium, instead of is a main contributor to the nuclear reactions in FRs where mixture of plutonium and uranium is used as fuel. Simple metallic fuel is a candidate to achieve better FR core performance than oxide fuel due to its higher fuel density, which has been employed in the LWR. Carbide and nitride fuels are also considered. 

Nitride fuel with BR 1, no uranium blanket, small reactivity variations with fuel burning (optimal BR 1.05), fuel composition designed to require no U, and Pu separation in reprocessing (merely addition of... 

For the properties of natural safety to be fully and consistently implemented, it is not only nitride fuel and lead coolant but also certain other options that should be translated into the reactor design, such as ... 

Differential neutron spectra were measured In center of a fast-spectrum molybdenum-reflected critical assembly using spherical proton-recoil detectors. The critical assembly was buiU to investigate geometrical variables and reactivity effects of-materials for a small, fast-spectrum conceptual reactor (lithium-cooled, U nitride-fueled). Measurements were made at Atomics Intemational where the critical asseimbly was designed, built, and operated. Calculations were made, at the NASA Lewis Research Center. 

The Criticality Implications of Pu-U Carbide and Pu-U Nitride Fuel Mixtures, S. R. Bierman, B. W. Howes. E. D. Oayton (BNW)... 

The principal R D issues associated with the LFR are related to fuels and materials. The technology for ferritic stainless steel and metal alloy fuel is reasonably well developed for temperatures up to 550°C. However, in the range of 750°C-800 C, the development of nitride fuels will be required. The development issues include fuel/clad compatibility as well as clad/coolant compatibility. The development of high-temperature structural materials will also be needed. 

Lead-bismuth cooled, using either traditional fuel, i.e., MOX or metal alloy fuel, or nitride fuel in steel cladding at moderate ( 550°C) temperatures and... 

Lead cooled, using nitride fuel at somewhat higher ( 600 C) temperature. 

The SSTAR (24) and STAR-LM (25) lead cooled reactor concepts are based on nitride fuel and use a higher core outlet temperature to drive a supercritical CO2 Brayton cycle at 550 to 600°C, with a potential to gain energy conversion efficiencies of 43% at these temperatures. Moreover, the outlet temperature on the cool side of the recuperator can lie in the range of 70 to 125°C with only weak influence on the efficiency. As the inlet to the compressor is just above 31°C, these conditions facilitate installation of bottoming cycles for district heating, seawater desalination, or process heat production, using the heat otherwise rejected in thermodynamic cycle (see Annexes XXII and XXIII). The supercritical CO2 Brayton cycle lacks an industrial experience base this non-conventional Bra)don cycle will require R D. 

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