South Texas Project (STP) unit 1 restarted last month, after the US Nuclear Regulatory Commission (NRC) announced that the South Texas Project Nuclear Operating Company had completed all necessary actions for the restart, following repairs to pipes in the bottom of the reactor vessel.

On April 12, while unit 1 was shut down for a refuelling outage, STP staff discovered leaks in two of the 58 pipes where instruments penetrate the bottom of the reactor vessel.

NRC began a special inspection at the reactor on 5 May to review the circumstances of the discovery, the licensee’s root cause analysis and the adequacy of the licensee’s repairs. The repair involved removal of the lower portion of the damaged pipe, replacing it with a new pipe that has improved resistance to corrosion, and welding it to the outside of the reactor vessel wall. NRC staff concluded that the repair was acceptable regardless of the cause of the leakage, which is still under investigation. The inspection of the reactor was featured in last month’s edition of NEI on page 32.