Theoretical and Experimental Analysis of Irradiated Thorium bundle from KAPS-2

Abstract

Thorium bundles were loaded in Indian PHWRs for initial flux flattening from KAPS Unit l onwards. The Post Irradiation Examination was carried out for one of the discharged bundles from KAPS- Unit 2, which had seen 508 FPDs. About five grams of the irradiated bundle were cut off from the edge pellet of the outer ring of the irradiated 19-rod thorium cluster, and was supplied for dissolution studies and separation of the uranium isotopes. The isotopic vector of the bred uranium was assessed by three different techniques by three different groups in BARC. The burnup analysis using the stable fission products like Nd-148 burnup monitors was also carried out. The various independent experimental analyses showed the amount of 232U to be about 490 ppm, which is nearly five times the originally predicted value by the ORIGEN-2 code (using the in built cross section library i.e. candunau.lib). A new set of effective one group cross sections for the nuclear reactions leading to the formation of 232U was generated and calculations were repeated with ORIGEN. Also the lattice code CLUB was used with old WIMS (1971) and the latest IAEA (WLUP) 172 group libraries, to directly evaluate the uranium vector. More refined data sets and calculation models are required to improve the results further.