For the scenario of boil-off in the spent fuel pool (SFP) initiated with loss of pool cooling, when the pool water level drops below the top of the spent fuel (SF), the steam is heat up by the upper uncovered part of the SF and becomes super-heated. The cladding temperature mainly depends on the steam temperature before it rises up to the oxidation heating dominate bound. For an ideal adiabatic condition without radial heat transport, the steam temperature only depends on the decay heat proportion between the evaporation section (water covered part) and supper heating section (uncovered part), not on total decay heat or decay time. It can be easily deduced that for one SFP stored with different decay time SFs, if the axial decay heat profiles are same, the SFs' outlet steam temperatures are identical. Thus, four kinds of axial decay heat profiles with peak heat at upper, lower, middle parts of and uniform along the SFs are applied to investigate the effect on the steam and cladding temperatures in adiabatic condition with RELAP5/MOD3.3 code. The calculation results are showed and discussed. Obviously, SFs with upper peak decay heat suffered the worst deficient cooling and could burn at a much higher water level.
