A behavioural study of fission products released into the helium coolant of the PBMR with special emphasis on Fresco-II and Spatra codes

Abstract

The fission products release rates into the helium coolant for the PBMR reactor, and their plate-out (sedimentation) were numerically calculated. These were done using the well known FRESCO-II and SPATRA codes respectively for both normal and upset operational conditions. It was found that for the Ag-ll0m, under normal operating conditions , the release rate is higher than, for example, for Cs-134, Sr-9 0 , I-131. The release of Ag-ll0m is comparably high due to i t s fast diffusion in the fuel element components and bad retention on graphite. On the other hand the plate-out calculation show that Cs- 137 has a higher plate-out. This is expected since it has strong chemisorption by the fuel element graphite. Moreover, it was found that more activity is obtained in the recuperator of reactor than in any other secondary part of the reactor. Finally, the two codes were linked for the purpose of producing a single consolidation code. The results show to be reliably reproduced and to be in agreement with the previously calculated ones.