Analysis of an advanced test reactor small-break loss-of-coolant accident with an engineered safety feature to automatically trip the primary coolantpumps

A new engineered safety feature that automatically trips the primary coolan t pumps following a low-pressure reactor scram was recently installed in th e Advanced Test Reactor (ATR). The purpose of this engineered safety featur e is to prevent the ATR's surge tank, which contains compressed air, from e mptying during a small-break loss-of-coolant accident (SBLOCA). If the surg e tank were to empty, the air introduced into the primary coolant loop coul d potentially cause the performance of the primary and/or emergency coolant pumps to degrade, thereby reducing cove thermal margins. Safety analysis p erformed with the RELAP5 thermal-hydraulic code and the SINDA thermal analy zer shows that adequate thermal margins ave maintained during an SBLOCA wit h the new engineered safety feature installed. The analysis also shows that the surge tank will not empty during an,SBLOCA even if one of the primary coolant pumps fails to trip.