Fuel IRT-4M is at the reactor in two modifications: a six-tube and eight-tube fuel cells. The fuel consists of concentric square tubes connected by the lower and the upper head. Absorbers of the control rods or other channels (such as terminal of the pneumatic tube post) can be placed into six-tube fuel cells. IRT-4M fuel layer consists of a dispersion of Al and UO2, enriched to 19.7 % of U-235. The fuel layer is coated on both sides with pure aluminium with thickness of 0.31 mm. Producer of the IRT-4M fuel is the NZCHK company located in Novosibirsk (the Russian Federation).
Eight-tube IRT-4M fuel element
Because of the small power level of the reactor, fuel remains physically fresh, i.e. with no measurable burn-up. Specifically, the reactor burns less than 0.01 grams of U-235 for 1 year. Due to the negligible fuel burn-up there is no chance that a fuel damage may cause releasing of significant quantities of radioactive materials. Only local contamination may arise, but it can be easily handled by reactor staff. In the case of fuel element damage (during manipulations or by corrosion during the long stay in the water) there is a hermetic stainless steel case, into which the damaged element is placed and then is stored in the standard transport cask until the final disposal. Such manipulation was examined in the emergency exercises.
In autumn 2005, the reactor was converted from high-enriched fuel to low-enriched fuel. The main objective was to replace the older type of fuel IRT-3M with enrichment of 36 % U-235 by the fuel type IRT-4M with enrichment of 19.7 % U-235, so the internationally recommended treshold of low-enriched uranium was achieved. The exchange of the fuel took place within the framework of RERTR (Reduced Enrichment for Research and Test Reactors) programme. The exchange was performed in direct cooperation with the U.S. Department of Energy, the Russian manufacturer of fuel NZCHK, the International Atomic Energy Agency and Russian organization SOSNY, which took over the IRT-3M fuel.
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