Assessment of Scaling of Pressurized Water Reactor Emergency Core Coolant Bypass Flow Tests

Abstract

The Emergency Core Coolant (ECC) is injected in the reactor cold legs to flow down the downcomer and to cool the hot core during a Large Break Loss of Coolant Accident. The ECC flows down in the downcomer before reaching the core entrance. The delivery of ECC to the core is critical to the safety. The portion of ECC not delivered to the core is bypassed to the break. Linearly scaled small test facilities have been designed to determine ECC delivery rates for the Nuclear Power Plants (NPP). However, based on the data, it is concluded that linearly scaled small facilities do not capture the phenomena of the NPP. In the small facilities the liquid distribution facilities is a combination of pure film and liquid slugs. In the full scale facilities the ECC flows as a column beneath the cold legs almost unaffected by the pressure of the gas. In addition, the correlation recommended by the USNRC for NPP based on scaled facilities underpredicts the ECC delivery rate when compared to the data from Upper Plenum Test facility which is a full scale test facility.It is recommended that the ECC bypass phenomena experiments be performed in full scale facilities.

This work was performed under the auspices of the U.S. Nuclear Regulatory Commission