Diversified Reactor Level Measurement System in the Boiling Water Reactor of Olkiluoto

This study investigated the feasibility of a new reactor water level measurement system for the Boiling Water Reactor (BWR) of the Olkiluoto Nuclear Power Plant (NPP). The operation of this new system is based on a different physical principle than the existing ones. It is capable of indicating low or high water levels in the downcomer and of initiating the related safety functions. This diversified system is designed to operate under Design Extension Cases (DEC), in which in addition to an Anticipated Operational Occurrence (AOO) a Common Cause Failure (CCF) occurs in the preliminary level measurement system, thus when a conventional system cannot execute its safety function. The target of this study was to analyze the most relevant AOOs, where Diversified Level Measurement System (DLMS) is needed for bringing the NPP to a controlled state1.