05000346/LER-2016-007, Regarding Pressurizer Code Safety Valve Setpoint Test Failures
| ML16236A240 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 08/22/2016 |
| From: | Boles B FirstEnergy Nuclear Operating Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| L-16-223 LER 16-007-00 | |
| Download: ML16236A240 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 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)(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)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(i) |
| 3462016007R00 - NRC Website | |
text
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RrstEnergy Nuclear Operating Company Brian D. Boles Vice President, Nuclear August 22, 2016 L-16-223 ATTN: Document Control Desk United States Nuclear Regulatory Commission Washington, D.C. 20555--0001
Subject:
Davis-Besse Nuclear Power Station, Unit 1 Docket Number 50-346, License Number NPF-3 Licensee Event Report 2016-007 5501 North State Route 2 Oak Harbor, Ohio 43449 10 CFR 50.73 419-321-7676 Fax: 419-321-7582 Enclosed is Licensee Event Report (LER) 2016-007, "Pressurizer Code Safety Valve Setpoint Test Failures." This LER is being submitted to provide written notification in accordance with 10 CFR 50. 73(a)(2)(v)(D) and 10 CFR 50. 73(a)(2)(i)(B).
There are no regulatory commitments contained in this letter or its enclosure. The actions described represent intended or planned actions, are captured in the DBNPS Corrective Action Program, and are described for information only. If there are any questions or if additional information is required, please contact Mr. Patrick J. McCloskey, Manager -
Site Regulatory Compliance, at (419) 321-7274.
Sincerely, Brian D. Boles Enclosure: LER 2016-007-00 cc: NRG Region Ill Administrator NRG Resident Inspector NRR Project Manager Utility Radiological Safety Board
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- 3. PAGE Davis-Besse Nuclear Power Station, Unit 1 05000 346 1 OF 4
- 4. TITLE:
Pressurizer Code Safety Valve Setpoint Test Failures
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED I
SEQUENTIAL I REV FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR NUMBER NO.
MONTH DAY YEAR 05000 FACILITY NAME DOCKET NUMBER 06 21 2016 2016 -
007 00 08 22 2016 05000
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR§: (Check all that apply)
D 20.2201(b)
D 20.2203(a)(3)(i)
D 50.73(a)(2)(ii)(A)
D 50.73(a)(2)(viii)(A) 1 D 20.2201 (d)
D 20.2203(a)(3)(ii)
D 50.73(a)(2)(ii)(B)
D 50.73(a)(2)(viii)(B)
D 20.2203(a)(1)
D 20.2203(a)(4)
D so.73(a)(2)(iii)
D 50.73(a)(2)(ix)(A)
D 20.2203(a)(2)(i)
D 50.36(c)(1)(i)(A)
D 50.73(a)(2)(iv)(A)
D 50.73(a)(2)(x)
- 10. POWER LEVEL D 20.2203(a)(2)(ii)
D 50.36(c)(1)(ii)(A)
D 50.73(a)(2)(v)(A)
D 73.71(a)(4)
D 20.2203(a)(2)(iii)
D so.36(c)(2)
D 50.73(a)(2)(v)(B)
D 73.71(a)(5)
D 20.2203(a)(2)(iv).
D so.4s(a)(3)(ii)
D 50.73(a)(2)(v)(C)
D 73.77(a)(1) 100 D 20.2203(a)(2)(v)
D 50.73(a)(2)(i)(A)
[8] 50.73(a)(2)(v)(D)
D 73.77(a)(2)(i)
D 20.2203(a)(2)(vi)
IX! 50.73(a)(2)(i)(B)
D 50.73(a)(2)(vii)
D 73.77(a)(2)(ii) l 1 0~f\\,:3*,~;Stf::;'yn1&1*~";~;
- * ' "i./ii,;;.
D 50.73(a)(2)(i)(C)
D OTHER Specify in Abstract below or in
==CAUSE OF EVENT==The root cause of this event is that the PSVs as-found allowable range of+ 1/- 3 percent does not provide a sufficient margin to accommodate for PSV setpoint variance. This is also similar to \\he contributing cause identified for the 2011 failure at the DBNPS (reference Previous Similar Events Section below).
ANALYSIS OF EVENT
While both valves had as-found setpoints that exceeded the TS allowable value, the highest out-of-tolerance setpoint was 34 psig higher than the TS allowed value.
Both PSVs lifting at a value higher than allowed by TS may result in exceeding accident analysis RCS pressure limits. Therefore, the transients described in the Updated Safety Analysis Report (USAR) that can produce an RCS over-pressurization were reviewed with *respect to the out-of-tolerance PSV setpoints. This review concluded that both valves would have performed their design function if they would have operated at their respective out..:of-tolerance lift pressures.
The PSVs are modeled in the DBNPS Probabilistic Risk Assessment (PRA) in two ways: a PSV fails to close after opening, or one or more PSVs fail to open upon demand. Failure of a PSV to close after opening results in a small loss of cooling accident. Failure of all relief capability (both PSVs and the Power Operated Relief Valve) to open could result in a transient over-pressurization of the RCS, resulting in the inability to inject cooling water. Failure of one or both PSVs to open limits the ability to successfully cool the plant using feed and bleed cooling, since iii some cases, the PSVs can be used as the RCS discharge path for this 00 cooling method. A review of the PRA concluded that neither failure mode (failure to re-close, failure to open) are impacted by the identified condition. Thus, there is no impact on PRA and no increase in Core Damage Frequency (CDF). The condition of having the two PSVs lift at pressures slightly above the allowed setpoint does not result in* any increase in \\CDF. Therefore, this issue had very low safety significance. Additionally,
- this issue did not prevent the PSVs from fulfilling their design safety function.
Reportability Discussion:
NUREG-1022, Event Reporting Guidelines, states that discrepancies found in TS surveillance tests are normally assumed to occur at the time of the test unless there is firm evidence, based on a review of relative information, to indicate the discrepancy occurred earlier. The NUREG provides an example that multiple safety valve testing failures is an indication that the discrepancies may well have arisen over a period of time and did not occur just at the time of discovery. Evaluation of the PSV test history and potential failure modes for the PSV did not identify any information that would allow a conclusion that the valves were operable while the plant was operating in Mode 1, 2 or 3, as required by TS LCO 3.4.10. Therefore, this condition (two PSVs exceeding the TS allowed setpoint) is reportable as a Licensee Event Report (LER) per 10 CFR
- 50. 73(a)(2)(i)(B) as an operation or condition prohibited by the plant's TS based on the above guidance from NUREG-1022.
Additionally, because it was concluded that both PSVs were inoperable during a portion of the past operational cycle, this condition is also reportable, in accordance with NUREG-1022 guidance, per 10 CFR 50.73(a)(2)(v)(D) as an event or condition that could have prevented fulfillment of a safety function needed to mitigate the consequences of an accident. As described in the "Analysis of Event" section above, the PSVs ANALYSIS OF EVENT (Reportability Discussion continued):
YEAR 2016
- 3. LER NUMBER SEQUENTIAL NUMBER 007 wpuld have performed their USAR accid~nt mitigation design safety function if they would have operated at their respective out-of-tolerance lift pressures.
CORRECTIVE ACTIONS
Completed Actions:
During the Nineteenth Refueling Outage concluding in May 2016, two PSVs were installed in place of the removed valves as part of planned preventive maintenance activities. The installed valves, i.dentical to the REV NO.
00 removed valves, had As-Left set pressures of approximately 2495 psig for bo!h PSVs.
Scheduled Actions:
As discussed in the cause analysis section above, setpoint drift cannot be eliminated; however, actions can be taken to minimize or reduce drift. Therefore, changes will be made to the PSV testing procedure(s) to provide actions for improving valve repeatability by establishing more restrictive PSV main spring requirements and requiring three (3) consecutive lifts as part of as-left testing.
Extensive industry operating experience research from this event's evaluation, coupled with the previous DBNPS LER 2011-001 discussed below, has shown that a prudent action to address the root cause* is to propose a License Amendment R_equest to change ~he TS 3.4.10 limit from less than or equal to 2525 psig to less than or equal to 2575 psig to facilitate the ASME acceptance criteria of+/- 3 percent for as-found testing.
rhe industry operating experience review from this event's evaluation indicates the DBNPS is an exception in not having changed the DBNPS TS licensing basis to the curre.ht ASME +/- 3 percent as-found test criteria.
PREVIOUS SIMILAR EVENTS
DBNPS LER 2011-001, "Pressurizer Code Safety Valve Setpoint Test Failures," was submitted on March 11, 2011, to document an occurrence where both PSVs removed during the Sixteenth Refueling Outage in Spring of 2010 had exceeded the TS allowed value with the highest out-of-tolerance setpoint of 10 psig higher than the required value. As discussed above in the cause analysis section, the causes were the same or similar to this event. The same [direct] cause of the 2011 test failure was determined to be setpoint drift, and the contributing cause was similar to this event's root cause. Additionally, the operating experience review from the 2016 test failure, suggest other licensees have changed their TS acceptance criteria. The
- 2011 corrective action focused on PSV testing improvements, such as establishing a strictly adhered to as-left test tolerance requirement, which was shown to be effective in testing performed following the Seventeenth Mid-Cycle Outage and the Eighteenth Refueling Outage.