Technetium transmutation in thin layer coating on PWR fuel rods

Abstract Based on the EFTTRA-T2 experiment results, we study the transmutation characteristics of pressurized water reactors (PWR) after coating a thin layer of Tc-99 on the fuel rods. Our calculation shows that for the same Tc-99 loading amount, the effect on the PWR k eff after coating Tc-99 on the PWR fuel rods is much less than that of the homogeneous addition of Tc-99 to uranium dioxide nuclear fuel. If we just coat 0.2λ c (0.0065 mm) thickness Tc-99 on PWR fuel rods, the total Tc-99 coating amount is about 291.37 kg, this is approximately equivalent to the 4 PWR Tc-99 annual outputs, and the system k eff merely decreases to 0.98530. Loading Tc-99 to the PWR is equivalent to introducing extra poisons to PWR system to control excess reactivity, some control poisons like boric acid concentration in primary coolant or burnable poison rods in fuel assemblies are needed to be removed to keep the reactor in criticality. As Tc-99 coating thickness increases from 0.05λ c to 0.2λ c , no matter which substitution pattern is used, B16→12 or C16→12, the system k eff variations are almost the same and can return to criticality again after removing corresponding burnable poison rods from fuel assemblies. For coating 0.15λ c or 0.2λ c thickness on the fuel rods of PWR, the system k eff is slightly below the criticality either in B16→12 or C16→12 substitution pattern, we may reduce the concentration of the boric acid slightly to let the system in criticality again. Our calculation results indicate that the optimal coating thickness of Tc-99 on PWR fuel rods is probably between 0.15λ c to 0.2λ c , i.e. 0.00488–0.0065 mm.