05000323/LER-1917-001, Regarding Relief Valve Leakage Resulting in Inoperable Pressurizer Power Operated Relief Valve
| ML17276B863 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 10/03/2017 |
| From: | Welsch J Pacific Gas & Electric Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| DCL-17-085 LER 17-001-00 | |
| Download: ML17276B863 (6) | |
| 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)(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)(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) |
| 3231917001R00 - NRC Website | |
text
Pacific Gas and Electric Company October 3, 2017 PG&E Letter DCL-17-085 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Docket No. 50-323, OL-DPR-82 Diablo Canyon Power Plant, Unit 2 James M. Welsch Vice President, Nuclear Generation Diablo Canyon Power Plant Mail Code 104/6 P. 0. Box 56 Avila Beach, CA 93424 805.545.3242 Internal: 691.3242 Fax: 805.545.4884 10 CFR 50.73 Licensee Event Report 2-2017-001-00. Relief Valve Leakage Resulting in Inoperable Pressurizer Power Operated Relief Valve
Dear Commissioners and Staff,
Pacific Gas and Electric Company (PG&E) submits the enclosed Licensee Event Report (LER) regarding leakage on a relief valve, resulting in an inoperable pressurizer power operated relief valve. PG&E is submitting this LER in accordance with the following:
10 CFR 50. 73(a)(2)(i)(B), as an operation or condition which was prohibited by the plant's Technical Specifications, and 10 CFR 50. 73(a)(2)(v)(A & D), as an event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to shut down the reactor and maintain it in a safe shutdown condition, and mitigate the consequences of an accident.
PG&E makes no new or revised regulatory commitments (as defined by NEI 99-04) in this report. All corrective actions identified in this letter will be implemented in accordance with the Diablo Canyon Power Plant Corrective Action Program.
This event did not adversely affect the health and safety of the public.
Sincerely,
~~
jy1 e/4609/50934243 Enclosure cc/enc:
Scott A. Morris, NRC Region IV Administrator (Acting)
Christopher W. Newport, NRC Senior Resident Inspector Balwant K. Singal, NRR Senior Project Manager IN PO Diablo Distribution A member of the STARS Alliance Callaway
- Diablo Canyon
- Palo Verde
- Wolf Creek
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 03/31/2020 (04-2017) httQ://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1 022/r3/)
the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 3. PAGE Diablo Canyon Power Plant, Unit 2 05000323 1 OFS
- 4. TITLE Relief Valve Leakage Resulting in Inoperable Pressurizer Power Operated Relief Valve
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED SEQUENTIAL FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR REV MONTH DAY YEAR NUMBER NO.
05000 07 29 2017 2017
- - 001
- - 00 10 03 2017 FACILITY NAME DOCKET NUMBER 05000
- 9. OPERAllNG MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §:(Check all that apply) 1 D 20.2201 (b)
D 20.2203(a)(3)(i)
D 50.73(a)(2)(ii)(A)
D 50.73(a)(2)(viii)(A)
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 50.73(a)(2)(iii)
D 50.73(a)(2)(ix)(A)
D 20.2203(a)(2)(i) 0 50.36(c)(1)(i)(A)
D 50.73(a)(2)(iv)(A)
D 50.73(a)(2)(x)
- 10. POWER LEVEL 0 20.2203(a)(2)(ii) 0 50.36(c)(1 )(ii)(A)
~ 50.73(a)(2)(v)(A)
D 73.71(a)(4)
D 20.2203(a)(2)(iii) 0 50.36(c)(2)
D 50.73(a)(2)(v)(B)
D 73.71(a)(5) 100 D 20.2203(a)(2)(iv) 0 50.46(a)(3)(ii)
D 50.73(a)(2)(v)(C)
D 73.77(a)(1)
D 20.2203(a)(2)(v)
D 50.73(a)(2)(i)(A)
~ 50.73(a)(2)(v)(D)
D 73.77(a)(2)(i)
D 20.2203(a)(2)(vi)
~ 50.73(a)(2)(i)(B)
D 50.73(a)(2)(vii)
D 73.77(a)(2)(ii)
D 50.73(a)(2)(i)(C) 0 OTHER Specify in Abstract below or in NRC Form 366A
- 12. LICENSEE CONTACT FOR THIS LER LICENSEE CONTACT lfLEPHONE NUMBER (lndude Area Code)
!Jim Morris
~05-545-4609
- 13. COMPLETE ONE UNE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT
CAUSE
SYSTEM COMPONENT MANU-REPORTABLE
CAUSE
SYSTEM COMPONENT MANU-REPORTABLE FACTURER TOEPIX FACTURER TOEPIX D
LK RV Anderson y
Greenwood Crosby
- 14. SUPPLEMENTAL REPORT EXPECTED
- 15. EXPECTED MONTH DAY YEAR D YES (If yes, complete 15. EXPECTED SUBMISSION DATE) lXI NO SUBMISSION DATE ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines)
During an investigation of a nitrogen leak inside the Unit 2 containment, Nitrogen Accumulator Relief Valve (R V)
RV-355 was found to be leaking. The leak caused the pressure in the back up nitrogen accumulator supply to Power Operated Relief Valve (PORV) PCV-455C to decrease to a level that made the PORV inoperable. Based on a review of the trend data for nitrogen usage in the containment, it is conservatively assumed that RV-355 had been degraded since December 1, 2016, rendering the PORV inoperable for longer than permitted by Technical Specifications.
The presumptive cause was inadequate instructions provided in plant procedures for placing a new nitrogen bottle in service. These instructions did not provide a sequence that assures system pressure transients are mitigated. This may have caused excessive pressure excursions resulting in multiple lifts ofRV-355 which resulted in damage to the RV 0-ring seat and a nitrogen leak path.
Corrective actions include replacing RV-355 and revising procedures to provide instructions on placing nitrogen supply bottles in service to maintain back pressure and minimize pressure transients on the nitrogen system.
This event did not affect the health and safety of the public.
NRC FORM 366 (04-2017)
I. Reportable Event Classification
This event is reportable pursuant to the following criteria:
YEAR 2017 SEQUENTIAL NUMBER 001 REV NO.
00 10 CFR 50.73(a)(2)(i)(B), Any operation or Condition which was prohibited by the plant's Technical Specifications 10 CFR 50.73(a)(2)(v)(A & D), Any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to shut down the reactor and maintain it in a safe shutdown condition, and mitigate the consequences of an accident.
II. Plant Conditions
~t the time of the event, Diablo Canyon Power Plant (DCPP) Unit 2 was in Mode 1 (Power Operation),
operating at 100 percent power.
III. Problem Description
~- Background (The DCPP Unit 2 pressurizer is equipped with three Power Operated Relief Valves (PORVs), two safety-related (PCV-455C and PCV-456) and one non safety-related (PCV-474). The pressurizer maintains Reactor Coolant System (RCS) pressure and volume through the surge line during operation, and limits pressure changes during
~ransients. During plant load reduction or increase, reactor coolant volume changes are accommodated in the rressurizer via the surge line, pressurizer sprays and/or heaters, and the PORVs. The PORVs are normally operated by instrument air. When instrument air is isolated, the backup nitrogen supply provides the motive force to operate the PORVs. The safety-related PORVs and associated backup nitrogen accumulators are credited to mitigate the Feedwater Line Break (FLB) event, the Spurious Safety Injection (SSI) event, the Steam Generator Tube Rupture (SGTR) event and the Low Temperature Overpressure Protection (LTOP) event.
An FLB event generates a Safety Injection (SI) signal and Phase A containment isolation signal, which isolates instrument air and nitrogen supply to the containment. The backup Nitrogen accumulator is therefore credited to
!Provide an adequate capacity to cycle the PORV at least 300 times following a FLB event. This provides adequate time for the operators to take action to terminate the Emergency Core Cooling System (ECCS) injection flow and re-establish a bubble in the pressurizer.
The safety-related PORVs and operator actions are credited to mitigate the SSI event for pressurizer overfilling.
If the pressurizer overfills, the pressurizer PORVs are available to relieve water inventory from the RCS, as Page 2 of 5 (04-2017)
U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 3/31/2020 LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET (See NUREG-1 022, R.3 for instruction and guidance for completing this form http://www. nrc.qov/readinq-rm/doc-collections/nuregs/staff/sr1 022/r3/)
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 3. LER NUMBER YEAR Diablo Canyon Power Plant, Unit 2 05000323 2017 SEQUENTIAL NUMBER 001 REV NO.
00 long as nitrogen is available from the DCPP Design Class I backup nitrogen accumulators (instrument air is not available).
The safety-related PORVs are credited to open and depressurize the RCS as part of the SGTR event.
When an LTOP transient occurs, a pressurizer PORV opens until the pressure returns to acceptable limits.
~- Event Description On July 28, 2017, at 1206 PDT, with DCPP Unit 2 operating at 100 percent power, an Alert notification was declared due to low oxygen levels inside the containment. The cause of the low oxygen level was a nitrogen leak inside the containment. The nitrogen source was isolated and the containment atmosphere was restored to
~ormal conditions. The Alert notification was terminated on July 28, 2017, at 1819 PDT. During an investigation of the nitrogen leak inside the containment, RV-355 was found to be leaking. The leak caused the tpressure in the back up nitrogen accumulator supply to PORV PCV-455C to decrease to a level that made the PORV inoperable.
Based on a review of trend data for nitrogen usage in the containment, it is conservatively assumed that RV-355 had been degraded since December 1, 2016, rendering the PORV inoperable for longer than permitted by Technical Specifications. Technical Specification 3.4.11.B requires an inoperable PORV to be restored to operable within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. Therefore, the event is reportable as an event or condition prohibited by Technical Specifications. In addition, because the other safety-related PORV PCV-456 had been declared inoperable for L.esting multiple times since December 1, 2016, this event is reportable as an event or condition that could have prevented the fulfillment of a safety function.
C. Status of Inoperable Structure, Systems or Components That Contributed to the Event None.
D. Other Systems or Secondary Functions Affected
None.
E. Method of Discovery
~uring an investigation of the nitrogen leak inside the containment, RV-355 was found to be leaking. The leak caused the pressure in the back up nitrogen accumulator supply to PORV PCV-455C to decrease to a level that made the PORV inoperable. Page 3 of 5 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 3/31/2020 (04-2017)
LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET (See NUREG-1 022, R.3 for instruction and guidance for completing this form http://www. nrc. gov /readi ng-rm/doc-collectio ns/n u reg s/staff/sr1 022/r3/)
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 3. LER NUMBER,
Diablo Canyon Power Plant, Unit 2 05000323
f. Operator Actions
YEAR 2017 SEQUENTIAL NUMBER 001 Operators declared PCV-455C inoperable and entered Technical Specification 3.4.1l.B on July 29, 2017, at 0457 PDT. RV-355 was replaced and Technical Specification 3.4.1l.B was exited on July 30, 2017, at 1533 PDT.
G. Safety System Responses None.
~V. Cause of the Problem REV NO.
00 The presumptive cause was inadequate instructions provided in plant procedures for placing a new nitrogen supply bottle in service. These instructions did not provide a sequence that assures system pressure transients are mitigated. This may have caused excessive pressure excursions resulting in multiple lifts ofRV-355 which
~esulted in damage to the RV 0-ring seat and a nitrogen leak path.
IV. Assessment of Safety Consequences
OCPP assessed the Unit 2 risk significance of the inoperability ofPCV-455C using Probabilistic Risk
~ssessment and the Significance Determination Process. The assessment concluded that the PORV would be available for the most risk significant functions. An incremental conditional core damage probability associated
~ith this event was estimated to be less than 1.0E-06.
[VI. Corrective Actions A. Immediate Actions
- 1. Relief Valve RV-355 was replaced on July 29, 2017.
B. Other Corrective Actions
- 1. Plant procedures will be revised to provide instructions for placing nitrogen supply bottles in service to lminimize pressure transients on the nitrogen system. Page 4 of 5 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 3/31/2020 (04-2017)
LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET (See NUREG-1 022, R.3 for instruction and guidance for completing this form http://'I/>N>JIN. n rc.gov/readi nq-rm/doc-collections/n u regs/staff/sr1 022/r3/)
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 3. LERNUMBER Diablo Canyon Power Plant, Unit 2 rv11. Additional Information lA,. Failed Components Component:
Model:
Relief Valve 951282ME 05000323 Manufacturer: Anderson Greenwood Crosby
B. Previous Similar Events
Internal Operating Experience YEAR 2017 SEQUENTIAL NUMBER 001 A similar event occurred on January 5, 2000, while DCPP Unit 2 was at 100 percent power. A failure of RV-355 caused nitrogen pressure to decrease rapidly, resulting in PORV PCV-455C being inoperable.
RV-355 was replaced and PCV-455C was returned to service.
REV NO.
00 Page 5 of 5