Measurement and evaluation of corrosion products deposition distribution in the experimental fast reactor JOYO

Aoyama, Takafumi ; not registered; Sumino, Kozo ; Saikawa, Takuya*

The Corrosion Product (CP) is the major radiation source in the primary cooling system of an LNFBR plant. It is important to characterize and predict the CP behavior to reduce the personnel exposure dose due to CP deposition. The CP measurement was carried out in the Experimental Fast Reactor JOYO during the 11th annual inspection period when the accumulated reactor thermal power reached about l43GWd. The CP deposition density was measured using a pure germanium detector. The plastic scintillation fiber (PSF) was applied for the gamma-ray dose rate distri bution measurement and compared with the thermoluminescence dosimeter (TLD). The major results obtained by the CP measurements in JOYO are the follows: (1)The major CP nuclides deposited in the primary cooling system are Mn and CO. Mn is the dominant isotope and it tends to deposit in the cold leg region. On the other hand, Co deposits mainly in the hot leg region. The deposition density of Mn is about seven times as much as that of Co in the cold leg region and twice in the hot leg region. (2)The deposition densities of Mn and Co, and the gamma-dose rate were decreased from the last data in the previous annual inspection period mainly due to the short operation time and the longer cooling time. (3)The continuous gamma-ray dose rate distribution up to 10m can be measured by using the PSF in a few minutes. The PSF is suitable to measure the gamma-ray dose rate distribution in the maintenance work area where it is narrow and the mixture of gamma-ray sources from primary pipings and components. The data base of detailed gamma-ray dose rate distribution was greatly extended by the PSF.