Study on the influence of source term release on accident consequences in severe accidents for small pressurized water reactor

In this paper, a small PWR with no pressure vessel external cooling system (ex-vessels) is used as the research object. It is found that for the small low burnup marine reactor without ex-vessels, the more core releases at an early stage, the later core damage occurs. Considering in the case of large break loss of coolant and loss of power accident, and the ORIGEN program is coupled with the MELCOR program is used as a severe accident process simulation tool. The significant parameters have been took into account, include core melting time, core damage rate, and lower head failure time, etc. It could be found through calculation that, for a certain reactor, in case of the reactor core meltdown happened, different released amount of source term will results in a difference of core heat release in the pressure vessel. For the small reactors without ex-vessels, the amount difference of source term release can reach 20%, and the lower head failure time can be delayed by 70%.