ICONE19-43236 Analysis of Natural Circulation Characteristics in Spent Fuel Storage Pool

With the rapid development of nuclear power, there is a great lot of spent fuel removed from reactor every year. Because of its high radioactivity and decay heat, how to safely dispose of it has became an important problem. There are two methods for interim storage of spent fuel, one is the dry storage and the other is wet storage. But before interim storage the spent fuel unloaded from reactor should be put into the spent fuel storage pool in plant for several years. Whether a spent fuel storage system is intact or the outer main cooling system is failure, there will be a natural circulation in the whole spent fuel storage pool. The understanding of its characteristics is very significant to system security. In this paper, RELAP5 code is used as the research tool to study a spent fuel storage pool. And then corresponding nodalizations are established to discuss various thermal hydraulic characteristics of the entire pool with natural circulation, including the flow and temperature distribution when coolant pump is in normal operation and the flow and temperature history when the pump is failure. In addition, the paper also discusses the effect of different location of cooling system drain pipe on natural circulation in the pool. The results show that: the decay heat of spent fuel can be perfectly removed when cooling system is on normal condition; furthermore, when coolant pump is failure, the decay heat can be absorbed by pool water utilizing the natural circulation in pool, which is enough to remove the decay heat for a long time before boiling, and the time need by pool water to reach boiling from steady state is about 17 hours. Finally, the effect of the location of cooling system drain pipe on natural circulation is significant and some suggestions are given. The paper can be a reference of design and optimization for spent fuel storage pool and has important engineering significance.