Calculation of tritium release from driver fuels into primary coolant of research reactors

Increasing of tritium concentration in the primary coolant of the research and test reactors during operation had been reported. To check the source for tritium release into the primary coolant during operation of the JMTR and the JRR-3M, the tritium release from the driver fuels was calculated by MCNP6 and PHITS. It is clear that the calculated values of tritium release from fuels are as about 107 and 106 Bq for the JMTR and JRR-3M, respectively, and that calculated values are about 4 order of magnitude smaller than that of the measured values. The JMTR is a tank type, and the JRR-3M is a pool type research reactor. The primary coolants are light water, in which the coolant temperature is lower than 50ºC. These results show that the tritium release from fuels is negligible for both the reactors. In the calculations of tritium release rates into the water by PHITS, a gaussian triton energy by ternary fissions of 235U.