United States Nuclear Regulatory Commission - Protecting People and the Environment

RPV Bottom Head Issues

On April 12, 2003, during a visual examination of the instrument penetrations located at the reactor vessel lower head at South Texas Project Unit 1(STP-1), a small amount of white residue was discovered around the circumference of two instrument penetrations. Susbsequent analysis of this residue revealed the presence of boron and lithium, indicating that this residue had originated from the reactor coolant system. The licensee repaired the instrument penetrations and committed to implementing monitoring programs at STP-1. After reviewing the licensee’s activities, the NRC staff concluded that the licensee had taken all actions necessary to ensure a safe restart and operation of STP-1. The licensee has restarted STP-1.

As a result of the events at STP-1, the NRC staff issued Bulletin 2003-02, "Leakage from reactor pressure vessel lower head penetrations and reactor coolant pressure boundary integrity," on August 21, 2003.

In 2006, the following NUREG was developed which includes the responses from the licensees to the NRC Bulletin 2003-02. NUREG-1863, “Review Responses to NRC Bulletin 2003-02-Leakage from Reactor Pressure Vessel Lower Head Penetrations and Reactor Coolant Pressure Boundary Integrity.”

Page Last Reviewed/Updated Monday, April 18, 2016