Leakage limits for inflatable seals of sodium cooled fast breeder reactor

•All possible types/modes of gas escape covered.•Limits include simultaneous contributions from bypass and permeation leakage modes.•Leakage of radioactive cover gas with fission products assumed.•Possibility of sodium frost deposition in sealed gap considered.•Cover gas activity decay during fuel handling and relative importance of types/modes of leakage considered for realistic results and simpler seal design.

Estimation and stipulation of allowable leakage for inflatable seals of 500 MWe Prototype Fast Breeder Reactor is depicted. Leakage limits are specified using a conservative approach, which assumes escape of radioactive cover gas with fission products across the seals in bypass and permeation modes and possibility of sodium frost deposition in sealed gaps because of permeation leakage of inflation gas. Procedures to arrive at the allowable leakages of argon cover gas (normal-operation/fuel-handling: 10−3/10−2 scc/s/m length of seal) and argon inflation gas (10−3 scc/s/m length of seal) is described.