05000275/LER-2012-003, Regarding Low Temperature Overpressure Protection System Inoperable Due to Human Performance Error
| ML12220A165 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 08/06/2012 |
| From: | Welsch J Pacific Gas & Electric Co |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| DCL-12-072 LER 12-003-00 | |
| Download: ML12220A165 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 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)(8) |
| 2752012003R00 - NRC Website | |
text
Pacific Gas and Electric Company August 6, 201 2 PG&E Letter DCL-12-072 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Docket No. 50-275, OL-DPR-80 Diablo Canyon Unit 1 James M. Welsch Station Director 10 CFR 50.73 Diablo Canyon Power Plant Mail Code 104/5/ 502 P. O. Box 56 Avila Beach, CA 93424 805.545.3242 Internal: 691.3242 Fax: 805.545.4234 Internet: JMW1@pge.com Licensee Event Report 1-2012-003, "Low Temperature Overpressure Protection System Inoperable due to Human Performance Error" Dear Commissioners and Staff; Pacific Gas and Electric Company (PG&E) is submitting the enclosed Licensee Event Report in accordance with 10 CFR 50.73(a)(2)(v)(D), for a human performance event that rendered the low temperature overpressure protection (LTOP) system inoperable. On June 7, 2012, at 0129 PDT, PG&E declared both trains of the L TOP system inoperable when the vital 120 VAC Distribution Panel (PY) PY13 was de-energized due to an electrical maintenance technician inadvertently opening the incorrect breaker. Plant staff immediately recognized the error and the technician closed the PY13 supply breaker, thereby re-energizing Panel PY13, returning one train of L TOP to service.
PG&E makes no new or revised regulatory commitments (as defined by NEI 99-04) in this report.
This event did not adversely affect the health and safety of the public.
Sincerely,
~~L,jA..~
James M. Welsch Interim Site Vice President wrl8/50488907 Enclosure cc:
Diablo Distribution cc/enc:
Elmo E. Collins, NRC Region IV Michael S. Peck, NRC Senior Resident Inspector Joseph M. Sebrosky, NRR Senior Project Manager INPO A member of the STARS (Strategic Teaming and Resource Sharing) Alliance Callaway. Comanche Peak. Diablo Canyon. Palo Verde. San Onofre. South Texas Project. Wolf Creek
NRC FORM 366 (10-2010) u.s. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2013 LICENSEE EVENT REPORT (LER)
(See reverse for required number of digits/characters for each block)
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 1. FACILITY NAME Diablo Canyon Power Plant
- 4. TITLE
- 2. DOCKET NUMBER 05000-275
- 3. PAGE 1 OF 5 Low Temperature Overpressure Protection System Inoperable due to Human Performance Error
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED YEAR
/SEQUENTIALI REV MONTH DAY NUMBER I NO.
YEAR FACILITY NAME DOCKET NUMBER MONTH DAY YEAR FACILITY NAME DOCKET NUMBER 06 07 2012 2012 - 003 -
00 08 06 2012
- 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 SO.73(a)(2)(i)(C)
D SO.73(a)(2)(vii)
D 20.2201(d)
D 20.2203(a)(3)(ii)
D SO.73(a)(2)(ii)(A)
D SO.73(a)(2)(viii)(A)
D 20.2203(a)(1)
D 20.2203(a)(4)
D SO.73(a)(2)(ii)(8)
D SO.73(a)(2)(viii)(8) 5 D 20.2203(a)(2)(i)
D SO.36(c)(1)(i)(A)
D SO.73(a)(2)(iii)
D SO.73(a)(2)(ix)(A)
- 10. POWER LEVEL D 20.2203(a)(2)(ii)
D SO.36(c)(1)(ii)(A)
D SO.73(a)(2)(iv)(A)
D *SO.73(a)(2)(x) o D 20.2203(a)(2)(iii)
B SO.36(c)(2)
D SO.73(a)(2)(v)(A)
D 73.71(a)(4)
D 20.2203(a)(2)(iv)
S0.46(a)(3)(ii)
D SO.73(a)(2)(v)(8)
D 73.71(a)(5)
D 20.2203(a)(2)(v)
D 50.73(a)(2)(i)(A)
D 50.73(a)(2)(v)(C)
D OTHER D 20.2203(a)(2)(vi)
D 50.73(a)(2)(i)(8)
[(] SO. 73(a)(2)(v)(D)
Sp~cify in Abstract below or In closure and returned one train ofLTOP back to operable within nine minutes. This condition resulted in a Safety System Functional Failure for Unit 1LTOP.
On June 7, 2012, at 0856 PDT, PG&E made an 8-hour non-emergency report of the event (Reference NRC Event Notification 48002) under 10 CFR 50.72(b)(3)(v)(D).
C. Status ofInoperable Structures, Systems, or Components That Contributed to the Event None.
D. Other Systems or Secondary Functions Affected
The control room ventilation system (CRVS) and the fuel handling building [BLDG] ventilation system (FHBVS) realigned to their safeguards alignments, as expected, due to the de-energization of associated radiation monitors [MON]
(RM) RM-26 and RM-59.
E. Method of Discovery
The control room received multiple alarms related to the loss ofPY13.
F. Operator Actions
Operators declared both trains of the L TOP system inoperable when the technician inadvertently de-energized vital 120 VAC panel PY13. Plant staff immediately recognized the error and the technician closed the PY13 supply breaker, thereby re-energizing Panel PY13, restoring the functionality of one train ofLTOP.
G. Safety System Responses The CRVS swapped to its safeguards alignment after RM-26 alarmed due to loss ofPY13. The FHBVS swapped to its safeguards alignment after RM-59 lost power due to loss ofPY13. Both the CRVS and FHBVS responded appropriately.
DCPP operators reset the associated RM after verifying that it responded solely because power to PY13 was lost.
III. Cause of the problem A. Apparent Cause Electrical Maintenance (EM) supervisors have not consistently reinforced self-checking standards.
B. Contributing Cause
YEAR G. LER NUMBER I
SEQUENTIAL I NUMBER 2012 -
003 REV NO.
00 4
- 3. PAGE OF 5
(l) EM allowed use of a troubleshooting plan which did not meet work instruction quality standards as described in DCPP Procedure, AD7.DC8, "Work Planning," in that specific component identifiers and sign-offs for each step were not provided.
(2) EM allowed use of a troubleshooting plan without establishing robust barriers on adjacent equipment to prevent mis-operation.
IV. Assessment of Safety Consequences
The potential for over pressurizing the reactor vessel is greatest when the RCS is water solid. During this event, the RCS loops were not filled and the RCS was thus not water solid. During Mode 5 (Cold Shutdown with all reactor vessel head closure bolts fully tensioned), TS Limiting Condition for Operation 3.4.12, "Low Temperature Overpressure Prote,ction System," provides RCS overpressure protection by limiting coolant input capability to the RCS andhaving adequate pressure relief capacity. The LCO specifies that no safety injection pumps, and only one centrifugal charging pump, are capable of injecting into the RCS, and all of the accumulator discharge isolation valves are deactivated in the closed position. Considering the plant conditions at the time of this occurrence, it is not credible that enough mass or heat energy could be injected into the RCS to cause a low temperature overpressure event while the LTOP system was incapable of actuating for less than 5 seconds.
V. Corrective Actions
DCPP performed an Apparent Cause Evaluation of this occurrence and developed the corrective actions described below.
A. Corrective Actions
(l) Perform a "Skills Assessment" for EM personnel to ensure human performance verification standards and the use of robust barriers are clearly understood and can be successfully demonstrated. A remediation plan will be developed for those workers that cannot demonstrate the knowledge and proficiency of the standard.
(2) Counsel EM supervisors on expectations for reinforcement of self checking, correct component verification (CCV),
and the use of robust barriers and establish supervisor commitment and accountability.
(3) Revise DCPP Procedure MAl.DC10, "Troubleshooting," Revision 12, to provide direction that troubleshooting plans will comply with station work instruction and documentation quality standards as described in DCPP Procedure AD7.DC8, "Work Planning," and to specify the use of robust barriers.
VI. Additional Information
A. Failed Components None.
B. Previous Similar Events
On February 28, 200S, maintenance workers began work on Unit 2 Main Steam (MS) Lead Check Valve MS-2-2066 in error. Workers were assigned to perform a check valve inspection on Valve MS-2-106S. As workers completed work on MS-2-42, the workers were then ready to work on Valve 2-MS-1068, which was said to be adjacent to MS-2-42. There were two valves in the area, MS-2-106S, and MS-2-2066, both with insulation removed. All the valves in the area no longer have any operator valve identification (OVID) tags. The workers assumed which valve to work on by deducing that the removed insulation and staged rigging over Valve MS-2-2066 identified the correct valve. Subsequently, the workers began disassembling the wrong valve. On February 29, 200S, a worker obtained the OVID drawings, and identified that the valve in progress was MS-2-2066, not MS-2-106S. The worker immediately notified the supervisor.
On May 16,2011, as part of the 230kV Startup System Reliability Upgrade Project, PG&E was making a physical modification to the 12kV startup relay board panel (RU). During cutting of the RU with a reciprocating saw, the 230kV Line Differential Relay 287 actuated and sent a trip signal to the Unit 1 Startup Transformer 11 output breaker to the Unit I Startup bus and to the Unit 2 startup Transformer 21 output breaker (cleared at the time) to the Unit 2 startup bus.
On May 27, 2011, while performing function testing of Unit 2 Relay 87UT2I, technicians inadvertently began testing on Unit 1 Relay 51187 UTI I, initiating a trip signal for the Unit 1 Startup Transformer 11 hi-side circuit interrupter and output supply breaker to the Unit I startup bus.