Blind problem exercise on modelling of PHWR fuel at extended burnup

Abstract

The current discharge burnup of PHWR bundles is about 7000 MWd/TU. It is proposed to extend the discharge burnup beyond 15 000 MWd/TU. The behaviour of fuel pins at extended burnup is not fully understood with respect to fission gas release, pellet clad interaction and cladding corrosion. Computer codes capable of predicting PHWR fuel performance at such high burnup are required to check the adequacy of current design to withstand the high burnup and to investigate the effect of possible design changes for achieving this burnup. Validation of codes is required before they can be used. A blind problem exercise was organised on PHWR fuel modelling to investigate the predictive capability of existing codes for their application at extended burnup and to identify areas of improvement. The blind problem for this exercise was based on a PHWR fuel bundle irradiated in Kakrapar Atomic Power Station-I (KAPS-I) up to about 15 000 MWd/TU and subjected to detailed post-irradiation examination in the hot cells facility at PIED, BARC. Eleven computer codes from seven countries including India participated in this exercise. The participants provided blind predictions of fuel temperature, fission gas release, internal gas pressure and other performance parameters for the fuel pins. The predictions were compared with the experimental PIE data which included fuel temperature derived from fuel restructuring, fission gas release measured by fuel pin puncturing, internal gas pressure in pin, cladding oxidation and fuel micro-structural data. The details of the blind problem, and an analysis of the results of blind predictions by the codes vis-a-vis measured data are provided in this paper.