05000306/LER-2015-003, Regarding Turbine/Reactor Trip - Low Bearing Oil Pressure
| ML15217A019 | |
| Person / Time | |
|---|---|
| Site: | Prairie Island  |
| Issue date: | 08/05/2015 |
| From: | Davison K Northern States Power Co, Xcel Energy |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| L-PI-15-066 LER 15-003-00 | |
| Download: ML15217A019 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| 3062015003R00 - NRC Website | |
text
(l Xcel Energy~
U S Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Prairie Island Nuclear Generating Plant Unit 2 Docket 50-306 Renewed License No. DPR-60 L-PI-15-066 10 CFR 50.73 Licensee Event Report (LER) 50-306/2015-003-00. Unit 2 Turbine/Reactor Trip-Low Bearing Oil Pressure Northern States Power Company, a Minnesota corporation, doing business as Xcel Energy (hereafter "NSPM"), encloses Licensee Event Report (LER) 50-306/2015-003-00, Unit 2 Turbine/Reactor Trip-Low Bearing Oil Pressure Summary of Commitments This letter contains no new commitments and no changes to existing commitments.
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Kevin Dav;s:T Site Vice President, Prairie Island Nuclear Generating Plant Northern States Power Company-Minnesota Enclosure cc:
Administrator, Region Ill, USNRC Project Manager, Prairie Island Nuclear Generating Plant, USNRC Resident Inspector, Prairie Island Nuclear Generating Plant, USNRC Department of Commerce, State of Minnesota 1717 Wakonade Drive East
- Welch, Minnesota 55089-9642 Telephone: 651.388.1121
ENCLOSURE LICENSEE EVENT REPORT 50-306/2015-003-00 3 pages follow
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150*0104 EXPIRES: 01/31/2017 (01-2014)
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 6. LER NUMBER
- 3. PAGE YEAR I SEQUENTIAL I REV NUMBER NO 3 OF 3 2015 003 0
failure. Additionally, as there is no evidence that 2T0-303 has previously been disassembled, changes in gasket thickness from original configuration during reassembly is also not a probable cause for the failure.
The piping and welds for the section of piping from check valve 2T0-303 to the downstream orifice were replaced due to the poor quality of welds. Additional inspections will be performed on other welds in the turbine oil reservoir to ensure similar conditions do not exist.
SAFETY SIGNIFICANCE
This event did not challenge nuclear safety as all plant systems responded as designed. The automatic reactor trip occurred as designed because of the automatic turbine trip. There were no radiological, environmental, or industrial impacts associated with this event. The health and safety of the public and site personnel were not at risk at any time during this event.
CAUSE
Poor weld quality reduced the strength of the welded connection resulting in a broken weld at the connection of the main oil pump discharge to the high pressure seal oil supply. This resulted in a diversion of oil flow from the bearing oil supply piping. The poor weld quality combined with the normal stresses that occur in an operating system over the life of the plant led to the failure of the weld.
CORRECTIVE ACTION
Perform weld repair, internal Unit 2 turbine oil reservoir piping. Complete (Work Order 524416-06).
Inspect piping connections in the Unit 2 Turbine Oil Reservoir to determine if the fit up is appropriate and inspect welds for cracks (CA 1482090-11).
Inspect piping connections in the Unit 1 Turbine Oil Reservoir to determine if the fit up is appropriate and inspect welds for cracks (CA 1482090-12).
PREVIOUS SIMILAR EVENTS
None.