Progress in the preparation of Indian experimental benchmarks on thorium irradiations in PHWR and KAMINI reactor

Full text: Indian nuclear programme envisages extensive utilization of thorium for power production in the coming decades. Identical loading of thorium bundles was used in KAPS-1 and 2, KAIGA-1 and 2 and RAPS-3 and 4 to attain flux flattening in the initial core. The thorium oxide used is about 400 kg in all the 35 bundles put together in a reactor. The bundles loaded in KAPP-1 and 2 have already been discharged from the core. Samples were obtained from one of the irradiated ThO2 bundles and have been analyzed experimentally by alpha spectrometry for 232U and by thermal ionization mass spectrometry for 233U, 234U, 235U and 236U by two different groups from FRD and FCD in BARC. The previous analyses by two teams gave a factor of 6 to 8 under-prediction in the production of 232U. The discrepancy was traced to be due to the fact that the effective one group values of cross sections for isotopes of thorium fuel cycle and the use of assumptions in the ORIGEN code are not applicable to the irradiation of thorium in our PHWRs. New results of sensitivity of different modeling approaches such as single cell versus super cell model and treatment of (n, 2n) process (pseudo-fission versus explicit) to prediction of isotopic contents of urania were obtained. India is actively participating in this IAEA-CRP to share our information and to benefit from the developments related to the use of thorium around the world. India recognizes the importance of new and improved nuclear data in the design of advanced reactors such as INPRO project of the IAEA. Within the scope of the CRP, the following two deliverables from India are envisaged in a focused manner: Thorium Irradiation experiments and burn up measurements in PHWRs. In the 2nd CRP Meeting, the exact numerical values of specifications of geometry and irradiation history of the irradiated Thoria bundles for KAPS2 PHWR were presented. All the available experimental results of Post Irradiation Examination including burn-up monitors were presented. KAMINI experimental benchmark: Considerable data has already been released to the IAEA. Further work is underway to prepare international quality description of the benchmark, with quality such as in the state-of-art NEA Nuclear Science Committee document. For instance, a detailed MCNP Modeling is being performed by P. Mohanakrishnan et al., and by C.P. Reddy et al. at IGCAR, Kalpakkam. The future plans for further refining of benchmarks and scope of activities and contributions were outlined. Collaborative efforts with other countries such as Korea are helpful as benchmarking exercise is new to India. (author)