Experimental fast reactor "JOYO" the 4th annual inspection report; The dose rate distribution on the surface of the primary cooling system piping

Maeda, Yukimoto*; not registered; not registered; not registered; not registered; not registered; not registered

Experimental Fast Reactor "JOYO" started its operation at 100MWt after finishing the core conversion work. On December 2, 1983, JOYO finished the second duty cycle at 100Mwt, and subsequently the 4th annual inspection was begun. Since the maintenance work in the underfloor such as inspection of overflow EMP is conducted near the primary pipings and equipments, the radiation exposure by the maintenance is problem for the man rem saving. As the maintenance work in the underfloor is necessary to keep integrity of equipments, it is important to obtain the dose rate distribution on the surface of the primary cooling system pipings for decreacing the radiation exposure. This report describes the results of measurement of the dose rate on the surface of the primary cooling system pipings with sodium drained which was conducted before starting the 4th annual inspection. The measurement was conducted the first time after starting the Mark-II operation, and we would like to use the obtained data for designing the future reactors by continueing the measurement. The results are as follows: (1)The dose rate was increased all over and the trend of increasing was almost same as last time. (2)The increase of dose rate on the surface of the large components such as primary main pumps and intermediate heat exchangers (IHX) was remarkably high, especially on the surface of IHX(B). (3)The dominant nuclides were Mn and Co, and the contribution of Na was small.