In 700 MWe PHWRs, after refueling the reactor channel, spent fuel bundles from heavy water to light water environment takes place in air i.e. dry transfer operation between Fuelling Machine (FM) and the Mobile Transfer Machine (MTM) through Fuel Transfer (FT) port. During dry transfer operation, the spent fuel bundles will remain in air medium without any forced cooling for a short duration of time. Due to decay heat of spent fuel bundles and absence of forced cooling, the spent fuel bundle temperature rises during the dry transfer operation. During normal operation, spent fuel dry transfer operation gets completed within specified time limit. However during off-normal conditions when time exceeds the predefined limit, forced air cooling can be considered to ensure cooling of bundles and to maintain spent fuel bundle temperature below limiting clad temperature.
3D CFD analysis has been carried out in order to assess the increase in bundle temperature with time, during off-normal conditions with provision of cooling air flow for dry transfer operation. From the results of the study, maximum temperature has been observed at the central pin, near the end of the fuel bundle pair (in air flow direction). Significant reduction in maximum temperature is observed when the radiation heat transfer mechanism is incorporated in the study.