Application of the post-BT standard to future BWR licensing assessment

The core of light water reactors has been so as not to cause boiling transition during both normal operation and transient phenomena as a means to guarantee the integrity of fuel. This is one restriction for maintaining the fuel integrity. However, research in recent years has shown that the boiling transition itself does not directly affect the fuel integrity rather it is the increased fuel cladding temperature. Based on these facts, a standard that includes the criteria and evaluation method of fuel integrity after boiling transition was made by the Standards Committee of Atomic Energy Society of Japan. If this standard is applied to the present boiling water reactors, the operational limited minimum critical ratio (OLMCPR) can be decreased during the end of cycle. If this standard is applied to plants to be built from now on, there are possibilities to rationalize the facilities, to uprate and to reduce the workload of control room operators. (author)