05000389/LER-2010-002, Regarding Manual Reactor Trip Due to Moisture Separator Re-heater Safety Valve Lift
| ML101730558 | |
| Person / Time | |
|---|---|
| Site: | Saint Lucie  |
| Issue date: | 06/14/2010 |
| From: | Richard Anderson Florida Power & Light Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| L-2010-118 LER 10-002-00 | |
| Download: ML101730558 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(viii)(B) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(ix)(A) 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3892010002R00 - NRC Website | |
text
0 Florida Power & Light Company, 6501 S. Ocean Drive, Jensen Beach, FL 34957 FIPL June 14, 2010 L-2010-118 10 CFR 50.73 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D.C. 20555 Re:
St. Lucie Unit 2 Docket No. 50-389 Reportable Event: 2010-002 Date of Event: April 15, 2010 Unit 2 Manual Reactor Trip Due to Moisture Separator Re-heater Safety Valve Lift The attached Licensee Event Report 2010-002 is being submitted pursuant to the requirements of 10 CFR 50.73 to provide notification of the subject event.
- - r Aichard L. Anderson Site Vice President St. Lucie Plant RLA/dlc Attachment an FPL Group company
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 08/31/201(
(9-2007)
Estimated burden per response to comply with this mandatory collection request: 50 hours5.787037e-4 days <br />0.0139 hours <br />8.267196e-5 weeks <br />1.9025e-5 months <br />. Reported lessons learned are incorporated into the licensing process and fed back to industry. Send comments regarding burden estimate to the Records and FOIA/Privacy Service Branch (T-5 LICENSEE EVENT REPORT (LER)
F52), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by internet e-mail to infocollectsenrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503.. If a means 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.
- 3. PAGE St. Lucie Unit 2 05000389 1
OF 4
- 4. TITLE Unit 2 Manual Reactor Trip Due to Moisture Separator Re-heater Safety Valve Lift
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
[
- 8. OTHER FACILITIES INVOLVED SEQUENTIAL REV FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR NUMBER NON MONTH DAY YEAR I 1FACILITY NAME DOCKET NUMBER 04 15 2010 2010 -
002 00 06 14 2010[
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR§: (Check all that apply)
El 20.2201(b)
El 20.2203(a)(3)(i)
El 50.73(a)(2)(i)(C)
[I 50.73(a)(2)(vii) 1E 20.2201(d)
El 20.2203(a)(3)(ii)
El 50.73(a)(2)(ii)(A)
[I 50.73(a)(2)(viii)(A)
El 20.2203(a)(1)
El 20.2203(a)(4)
El 50.73(a)(2)(ii)(B)
El 50.73(a)(2)(viii)(B)
El 20.2203(a)(2)(i)
El 50.36(c)(1)(i)(A)
El 50.73(a)(2)(iii)
E3 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL El 20.2203(a)(2)(ii)
[: 50.36(c)(1)(ii)(A)
Z 50.73(a)(2)(iv)(A)
El 50.73(a)(2)(x)
[: 20.2203(a)(2)(iii)
El 50.36(c)(2)
El 50.73(a)(2)(v)(A)
El 73.71(a)(4) 100%
El 20.2203(a)(2)(iv)
El 50.46(a)(3)(ii)
El 50.73(a)(2)(v)(B)
El 73.71 (a)(5)
El 20.2203(a)(2)(v)
El 50.73(a)(2)(i)(A)
[E 50.73(a)(2)(v)(C)
El OTHER El 20.2203(a)(2)(vi)
El 50.73(a)(2)(i)(B)
El 50.73(a)(2)(v)(D)
Specify in Abstract below or in =
Description of the Event On April 15, 2010, St. Lucie Unit 2 was operating in Mode 1 at 100% power when the Unit was manually tripped due to premature lifting of the 2B Moisture Separator Re-heater (MSR) safety valve [EIIS:SN].
The Unit initially commenced a rapid down power evolution as a result of the lifting safety valve followed by a manual reactor trip at approximately 95% power. All control element assemblies (CEA)
[EIIS:AA] fully inserted on the trip and all systems functioned as designed; the plant was stabilized at normal operating temperature and pressure in Mode 3.
A non-emergency notification to the NRC was made due to manual reactor protection system (RPS) [EIIS:JD] and auxiliary feedwater (AFW) system actuations [EIIS:BA].
Cause of the Event
An investigation of the 2B MSRV failure modes was conducted both onsite and at the Vendor's facility to determine the cause of this event. Vendor disassembly and inspection of the pilot valve identified the pilot valve spring was broken and made of corrosion resistant (CR) alloy steel.
All other attributes of the valve were judged to be in good to excellent condition.
Visual examination of the failed spring revealed extensive pitting on the outer surface and brittle-like fractures with no evidence of plastic deformation.
FPL Metallurgist's review of the spring condition concluded that these features indicated the causative failure mechanism of the high strength alloy steel spring was hydrogen embrittlement.
The direct cause of the premature MSRV lift was the failure Of the spring in the pilot valve due to corrosion and hydrogen embrittlement induced by long term exposure to a marine atmospheric environment.
Discussions with the Vendor concurred with the assessment of hydrogen embrittlement as the primary cause of pilot valve spring failure. Additionally it was identified that the Vendor has been replacing the alloy steel springs with Inconel since 2008 for applications of 400 degrees F or greater. Currently, based on a business decision, the Vendor is utilizing the Inconel springs in all applications irrespective of temperature.
This change in pilot valve spring materials and vulnerability of the (CR) alloy steel pilot valve springs had not previously been communicated to PSL Engineering.
At the request of FPL, a previous expedited refurbishment of the failed valve was completed using a spare pilot valve without an Inconel pilot valve spring. The valve was tested SAT, shipped to PSL, and reinstalled on the 2B MSR which subsequently failed. Investigation has identified that either a replacement of the as-found pilot spring with a new spring or a thorough disassembly and inspection of the spare pilot valve could have identified a degraded spring condition. Thus not refurbishing the valve in accordance with ASME Code requirements was also considered a contributing cause to the valve failure.
Based on a review of the PM Program for the MSR Safety Valves, the program was considered to be less than adequate. The inspection and overhaul program did not provide sufficient detail to ensure an adequate inspection and repair of pilot valves were in accordance with ASME Section VIII requirements, or reference of the National Board Inspection Code (NBIC),
Part 3 Repairs and Alterations Section S7-14.3 "Pilot Operated Safety Valves."
The LTA organizational focus on the repair and refurbishment of Critical 1 components is also considered a cause in the failure of
the spring in the pilot valve as critical 1 components should require an inspection to assess the parts condition and suitability for repair/refurbishment.
Analysis of the Event
In accordance with NUREG 1022, Rev.
2 10 CFR 50.73(a) (2) (iv) (A); any event or condition that resulted in manual or automatic actuation of any of the systems is reportable and requires Licensee Event Report (LER).
Analysis of Safety Significance The failure mode (broken pilot valve spring) identified for valve 2B is applicable to all eight MSR safety valves for both Unit 1 and 2.
The valves were setpoint tested and certified in accordance with the Vendor's program.
Although the cause of the premature MSRV lift was failure of the spring in the pilot valve due to corrosion induced by long term exposure to a marine atmospheric environment, a review of industry and station OE has not identified this as a high probability or a high frequency event.
Given that the MSRs and their safety valves are classified as Non-Nuclear Safety (NNS) components in the secondary plant, and based on the satisfactory inspection of all other valves in the extent of condition population and all plant systems actuated to perform their design safety function, with no radiological events occurring, this event had no impact on the health and safety of the public.
Corrective Actions
The corrective and supporting actions are entered into the Site Correction Action Program (CAP).
Any changes to the proposed actions will be managed under CAP.
Corrective'Actions
- 1. All eight safety valves were sent to the Vendor and the pilot valve springs replaced with either Inconel or new CR alloy springs which is an acceptable alternative to Inconel.
- 2.
The replacement MSR safety valves for both units will be procured with pilot valve spring materials that are not susceptible to hydrogen embrittlement and that design drawings reflect the spring materials.
- 3.
PSL Engineering will prepare and track to completion CRNs to insert notes for the design drawings of (existing) MSR safety valves which identify that all future replacements of CR alloy steel pilot valve springs will be with Inconel pilot valve springs.
- 4. Detailed Engineering requirements (including ASME Code requirements) and documentation content and distribution requirements for refurbishment of the
MSR safety valves will be incorporated in the stock code information for the MSRs.
- 5.
PSL Engineering (Training) will revise Corporate Nuclear Engineering Procedure ENG-002 to include a module focused upon the importance of procedures and processes for the procurement, storage, inspection, maintenance, testing, repair and refurbishment of Critical Components.
- 6.
PSL Engineering (Mechanical) will revise PMs and stock code information for those Critical 1 and 2 valves with springs subject to hydrogen embrittlement as necessary to address periodic inspection and replacement of the springs to preclude valve failure.
Similar Events
A review of condition reports since 2000 identified no instances of MSR safety valve failures at PSL.
Failed Components
- 1. 18" x 22" (inlet x outlet) Model 13906/143-1(2) Consolidated Turbine Reheater Pilot Operated Safety Valve Type 13900-2, PSL SC#227760-4, marketed by Dresser Valve.