Preliminary Study of Influence of Severe Accident Mitigation Countermeasures to In-Vessel Release of Fisson Products

During the severe accident in a nuclear power plant, large amounts of fission products release with accident progression, which includes in-vessel release and ex-vessel release. Mitigation of release of fission products is the need of alleviating radiological consequence in severe accident. Mitigation countermeasures to in-vessel release of fission products are studied, including feed-bleed in primary loop, feed-bleed in secondary loop and cooling of ex-vessel. Representative high pressure melt accident of station blackout is chosen, and different entry condition of countermeasures is assumed. The results show that: (1) Feed-bleed in primary loop is an effective countermeasure to mitigate in-vessel release of fission products. With early time to implement the countermeasure, in-vessel release fraction of fission products is low. (2) Feed-bleed in secondary loop is also an effective countermeasure to mitigate in-vessel release of fission products. Low in-vessel release fraction of fission products is produced with early time of countermeasure implemented. (3) Cooling of ex-vessel is not an effective countermeasure to control in-vessel release of fission products, the in-vessel release fraction in this case is almost equal to base case that uses none countermeasure.