Measurement and evaluation of radioactive corrosion product behavior in primary sodium circuits of JOYO (II)

not registered; Chatani, Keiji; not registered ; not registered; not registered

The radioactive corrosion product (CP) deposition density and gamma dose rate have been measured along the primary sodium circuits in Experimental Fast Reactor "JOYO" during every annual inspection and the CP behavior analysis code "PSYCHE" has been verified with measurement data in order to contribute the reduction of exposure dose of plant personal. The deposition density is measured by using a pure germanium detector system and determined by multiplying count rates by conversion factor. Gamma dose rate is measured with CaSO thermoluminescence dosimeters (TLD). This report presents measurement results during the 9th annual inspection and the evaluation results for all data measured so far. The results on this study are summarized as follows: (1)Major CP nuclides deposited along the primary sodium circuits are Mn and Co. Mn is most dominant isotopes. Amounts of deposited Mn is about twenty times as much as those of Co. (2)Mn is deposited mainly on the cold leg pipings between the outlet of the intermediate heat exchanger (IHX) and the inlet of the reactor vessel. Co is deposited mainly on the hot leg pipings between the outlet of the reactor vessel and the inlet of IHX. (3)The buildup of Mn is saturated at 44.5 EFPY. The averaged dose rate of the pipings is saturated at about 1.5mSV/h. The dose rates of IHX and primary sodium pump are about 1.5 mSv/h and 2.1 mSv/h, respectively. The dose rate distributions around IHX and primary sodium pump show the peaks at the stagnant part of the flow and at the turbulence part. (4)Calculation by "PSYCHE" and measurement are compared. Calculation-to-measurement ratio is 1.2 for the CP deposition density and 1.5 for the dose rate. It can be said that the features of the CP behavior in the primary circuit of "JOYO" is made clear. The more effort will be required for the evaluation of CP behavior for subassemblies such as outer reflectors, clearness of ...