Analysis of the Venting System of the Gas-Cooled Fast Breeder Reactor Fuel Element for Various Operating Conditions

Abstract

The fuel element concept of the gas-cooled fast breeder reactor (GCFR) is based on vented fuel pins to equalize pressure differences between the fission gas inside the fuel pin and the coolant. The fission products escaping from the fuel, mainly noble gases, are collected and swept separately from the primary coolant by a helium stream into a purification plant. Calculations were performed to estimate the activity release during normal operation, transient, and accident conditions for a 1000-MW(e) GCFR designed by Kraftwerk Union. The results show that during normal operation, only 0.8% of the total equilibrium noble gas activity in the core will be released into the purification plant. The most severe case for the activity release is a depressurization accident followed by the release of the whole fission gas inventory in the interstitial gas volume of the fuel pins of ∼5.3 × 10⁷ Ci (2.0 EBq). To adsorb this amount of fission gases in the low-temperature charcoal beds of the purification plant, a temporary refrigeration load of ∼173 kW is necessary. Using a purification plant with a refrigeration capacity of ∼50 kW and an equivalent storage of liquid nitrogen for auxiliary purposes, no significant extrapolation from the designed high-temperature gas-cooled reactor purification plants is necessary.