|Point Beach Nuclear Plant Unit 1|
|Reporting criterion:||10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded|
|2662017003R00 - NRC Website|
|Person / Time|
Document Control Desk, Office of Nuclear Reactor Regulation
|Download: ML17347A773 (3)|
comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
Description of the Event:
At 0404 CST on October 30, 2017, with Unit 1 in MODE 3 for refueling activities, a boric acid indication downstream of 1CV-309B, 1P-1B RCP Labyrinth Seal 1DPT-124 Upper Root Valve was identified as a through-wall flaw. The flaw location on the root valve [RTV] to DPT [PDT] instrument tubing welded joint [PSF] was within the RCS [AB] pressure boundary.
The root valve to DPT instrument tubing welded joint has been repaired and returned to service.
This 60 day licensee event report is being submitted in accordance with the requirements of 10 CFR 50.73(a)(2)(ii)(A) for any event or condition that results in the condition of the nuclear power plant, including its principal safety barriers, being degraded. The material defect in the primary coolant system could not be found acceptable in accordance with ASME Section XI, IWB-3600, "Analytical Evaluation of Flaws" or ASME Section XI, Table IWB-3410-1, "Acceptance Standards.
Cause of the Event:
The most likely cause of the degraded barrier was crater cracking at a weld stop point in the root valve to instrument tubing welded joint.
Analysis of the Event:
Maintenance activities identified a through-wall flaw downstream of the root valve to the RCP Labyrinth Seal DPT instrument tubing welded joint. The condition was discovered during reactor startup activities after the reactor had been shut down for several weeks for a planned refueling. The labyrinth seal serves as a buffering interface, to limit the exchange of reactor coolant from the seal portion of the RCP. The RCP Labyrinth Seal DPT instrument provides performance information only of the buffer interface. The through-wall flaw was within the RCS pressure boundary.
The through-wall flaw in the welded joint was most likely the result of crater cracking at a weld stop point. The flaw has been corrected. Adequate heat removal capability for the reactor was provided by two separate engineered safety feature system trains.
The root valve to DPT instrument tubing welded joint has been repaired and returned to service. RCS pressure boundary systems and components will continue to receive repetitive visual examinations on predetermined frequencies in accordance with existing programs.
The event was determined to be of very low safety significance. The flaw location was on small bore piping. There was no loss of any safety systems, structures or components needed to shut down the reactor, maintain safe shutdown conditions, remove residual heat, control the release of radioactive material or mitigate the consequences of an accident. There was no impact on the health and safety of the public as a result of this condition.
There have not been similar events of this degraded condition in the past three years.
Component Failure Data:
None Point Beach Nuclear Plant Unit 1 05000266
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