05000275/LER-2011-007-02, Inadequate Control Room Envelope Testing Due to Inadequately-Documented In-leakage Test Data
| ML13025A165 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 01/24/2013 |
| From: | Allen B Pacific Gas & Electric Co |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| DCL-13-003, OL-DPR-80, OL-DRP-82 LER 11-007-02 | |
| Download: ML13025A165 (7) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(i)(8) 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(ii)(8) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(v)(8) 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(viii)(8) 10 CFR 50.73(a)(2)(ix)(A) 10 CFR 50.73(a)(2)(x) |
| 2752011007R02 - NRC Website | |
text
Pacific Gas and Electric Company January 24, 2013 PG&E Letter DCL-13-003 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Docket No. 50-275, OL-DPR-80 Docket No. 50-323, OL-DPR-82 Diablo Canyon Units 1 and 2 Licensee Event Report 1-2011-007-02 Barry S. Allen Site Vice President 10 CFR 50.73 Diablo Canyon Power Plant Mail Code 104/6 P. O. Box 56 Avila Beach, CA 93424 805.545.4888 Internal: 691.4888 Fax: 805.545.6445 Diablo Canyon Power Plant - I nadequate Control Room Envelope Testing Due to Inadequately-Documented In-leakage Test Data Dear Commissioners and Staff; Pacific Gas and Electric Company (PG&E) submits the enclosed Licensee Event Report (LER) supplement regarding control room envelope (CRE) in-leakage testing. Both Units 1 and 2 are affected by this issue. PG&E is submitting this LER supplement in accordance with 10 CFR 50.73(a)(2)(i)(B) and 10 CFR 50.73(a)(2)(ii)(B). This supplement includes PG&E's actions following the NRC's review of Diablo Canyon's CRE testing documented in NRC Task Interface Agreement 2012-08. It also includes additional cause and corrective actions.
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, 0<7 s-. 4tL Barry S. Allen wrl8/50428146 Enclosure cc/enc:
Elmo E. Collins, NRC Region IV Thomas R. Hipschman, NRC Senior Resident Inspector Joseph M. Sebrosky, NRR Senior Project Manager INPO Diablo Distribution 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)
- 1. FACILITY NAME Diablo Canyon Power Plant, Unit 1
- 4. TITLE
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 2. DOCKET NUMBER 05000-275
- 3. PAGE 1 OF 6 Inadequate Control Room Envelope Testing Due to Inadequately-Documented In-leakage Test Data
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED MONTH DAY Diablo Canyon, Unit 2 05000-323 YEAR YEAR I SEQUENTIAL I REV MONTH DAY NUMBER I NO.
YEAR FACILITY NAME DOCKET NUMBER FACILITY NAME DOCKET NUMBER 09 12 2011 2011 - 007 -
02 01 24 2013
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply) 1
- 10. POWER LEVEL 100 D 20.2201 (b)
D 20.2201 (d)
D 20.2203(a)(1)
D 20.2203(a)(2)(i)
D 20.2203(a)(2)(ii)
D 20.2203(a)(2)(iii)
D 20.2203(a)(2)(iv)
D 20.2203(a)(2)(v)
D 20.2203(a)(2)(vi)
D 20.2203(a)(3)(i)
D 20.2203(a)(3)(ii)
D 20.2203(a)(4)
D 50.36(c)(1)(i)(A)
D 50.36(c)(1)(ii)(A)
D 50.36(c)(2)
D 50.46(a)(3)(ii)
D 50.73(a)(2)(i)(A)
[(] 50.73(a)(2)(i)(8)
D 50.73(a)(2)(i)(C)
D 50.73(a)(2)(ii)(A)
[(] 50.73(a)(2)(ii)(8)
D 50.73(a)(2)(iii)
D 50.73(a)(2)(iv)(A)
D 50.73(a)(2)(v)(A)
D 50.73(a)(2)(v)(8)
D 50.73(a)(2)(v)(C)
D 50.73(a)(2)(v)(D)
D 50.73(a)(2)(vii)
D 50.73(a)(2)(viii)(A)
D 50.73(a)(2)(viii)(8)
D 50.73(a)(2)(ix)(A)
D 50.73(a)(2)(x)
D 73.71(a)(4)
D 73.71(a)(5)
D OTHER Specify in Abstract below or in
B. Event Description
YEAR I
SEQUENTIAL I NUMBER 2011
- 007 REV NO.
02 3
OF 6
On September 12,2011, at 1745 PDT, operators declared the Units 1 and 2 CRE inoperable and entered TS 3.7.10.
This was due to discovery of inadequately-documented CRE in-leakage test data. Plant personnel reviewing the test report (dated February 3, 2005) for the common CRE identified that three of the four ventilation alignments tested had values of in-leakage greater than zero standard cubic feet per minute (SCFM). However, Pacific Gas &
Electric (PG&E) had concluded that these results were adequate to show that the CRE had no unfiltered in-leakage, and had provided this information to the NRC in PG&E Letter DCL-05-042, "Control Room Envelope In-leakage Test Results Relative to Generic Letter 2003-01, 'Control Room Habitability,'" dated April 22, 2005.
At 2257 PDT on September 12,2011, PG&E made an 8-hour nonemergency report (NRC Event Notification 47258) under 10 CFR 50.72(b)(3)(ii)(B). On September 13,2011, plant personnel verified that administrative controls were in place to maintain post loss-of-coolant accident (LOCA) emergency core cooling system (ECCS) leakage at a rate that would ensure operator doses were maintained less than the Final Safety Analysis Report (FSAR) accident analysis results for the highest in-leakage rate reported in the test.
On October 18, 2011, plant staff further identified that inadequate information was available in the report to conclude that the limiting condition for testing (where only one train of the CRVS was functioning) would result in zero SCFM in-leakage into the CRE. This was contrary to Regulatory Guide (RG) 1.197, Revision 0, May 2003, "Demonstrating Control Room Envelope Integrity at Nuclear Power Reactors." PG&E updated Event Notification 47258 on September 16, and October 18,2011.
In November 2011, PG&E established compensatory measures that assured both trains would remain available to operators even in the event of a single failure of an operating train. These compensatory actions were taken to address a design deficiency (described in LER 1-2011-008-01). PG&E reperformed the CRE in-leakage test with one unit in CRVS pressurization mode and the other unit in recirculation mode. This was the most limiting operator-dose consequence configuration, with the compensatory measures in place, ensuring that both CRVS trains will be available following a DBA. Four test phases were performed using each of the CRVS subtrains for pressurization. A fifth phase test used the most limiting of the subtrains, along with a supply flowpath to the Technical Support Center (TSC). During the testing, several deficiencies were found and were repaired through plant processes. PG&E completed the test on November 8, 2011. The results of the CRE in-leakage testing showed the following:
Test Phase In-leakage by Pitot (SCFM)
In-leakage by Tracer (SCFM) 1 30 29 2
19 18 3
51 41 3*
16 14 4
23 26 5**
36 45
- Phase 3 was repeated with two identified sources of in-leakage temporarily corrected.
- Phase 5 repeated the phase with the highest measured in-leakage (phase 3) with the TSC portion of the ventilation system operating.
YEAR
- 6. LER NUMBER I
SEQUENTIAL I NUMBER 2011 -
007 REV NO.
02 4
- 3. PAGE OF 6
The maximum in-leakage test result of 51 SCFM was 1 SCFM higher than that given in PG&E Letter DCL-11-127, "Control Room Envelope Testing," dated December 2,2011, as the test results reported in DCL':'11-127 were based on a contractor test report. PG&E later identified the inaccurate value, and the contractor revised its test report to correct the value to 51 SCFM. This error was entered into DCPP's corrective action program.
On October 1,2012, PG&E declared the CRE inoperable to modify the CRVS to eliminate the design vulnerability. On November 28,2012, PG&E received the NRC's Task Interface Agreement (TIA) 2012-08, "Final Response to Task Interface Agreement 2012-08, Diablo Canyon Power Plant, Unit 1 and 2 - Request Office of Nuclear Reactor Regulation's Review of Operability Issues Associated with Technical Specification 3.7.10,
'Control Room Ventilation System,'" dated November 20,2012. The TIA concluded that DCPP's CRE had not been restored to operable status because PG&E "has not changed the licensing basis DBA or repaired the CRE boundary or performed a combination of these... Further, SR 3.7.10.5 requires testing the CRE in-leakage with the CRVS in the design basis accident configuration to verify the operability of the CRE boundary. Operation of CRVS equipment from both trains is not credited in the current licensing basis as part of the design basis configuration. Performing the in-leakage test with CRVS equipment from the opposite train in operation does not satisfy the requirements for performing SR 3.7.l0.5." PG&E subsequently concluded that because the in-leakage was performed with both trains operating, the SR had not been performed as required, nor had it ever been performed as required. Therefore, DCPP had been in violation of this TS since the issuance of License Amendments 201 and 202 for DCPP Units 1 and 2, regardless of the in-leakage flow rates obtained.
In December 2012, after modifying the CRVS, PG&E satisfactorily completed in-leakage testing on the CRVS using a single CRVS train, successfully demonstrating acceptable in-leakage in the most limiting configuration with a single CRVS train operating. Operators declared theCRE operable on December 20,2012.
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
PG&E investigations in response to questioning from the NRC Senior Resident Inspector about the 2005 CRE in-leakage testing led to the discovery of inadequate testing.
On November 28,2012, PG&E received the NRC's TIA 2012-08, which clarified the compensatory measures acceptable to the NRC that would allow declaration of operability following in-leakage test failure. Consequently, PG&E recognized that the CRE had been incorrectly declared operable, contrary to the requirements of TS 3.7.10.
F. Operator Actions
YEAR
- 6. LER NUMBER I
SEQUENTIAL I NUMBER 2011
- 007 REV NO.
02 5
- 3. PAGE OF 6
Following the September 12,2011, assessment of the 2005 test data, operators completed TS 3.7.10 Required Actions B.1 and B.2 within the respective completion times, and implemented administrative controls to maintain post LOCA ECCS leakage at a rate that would ensure operator doses were maintained less than the FSAR accident analysis results for the highest in-leakage rate reported in the test.
G. Safety System Responses None.
III. Cause of the Problem PG&E performed an Apparent Cause Evaluation to determine the apparent cause for concluding that the 2005 test demonstrated no unfiltered in-leakage. The evaluation determined that human error (a mental mindset) in the interpretation of test results led to a nonconservative determination of zero leakage.
The cause of incorrectly declaring the CRVS operable was that the bases for SR 3.7.10.5 were unclear, and PG&E clarified via co,nsulting industry experts versus requesting that NRC clarify the intent of the SR Bases.
IV. Assessment of Safety Consequences
PG&E reviewed ECCS leakage outside containment over the past 3 years, and concluded that actual ECCS leakage had been controlled to ensure that CR operator dose did not exceed General Design Criterion 19 (1971) limits. The CRVS has remained capable of performing its safety function. This event did not result in radiological release to plant personnel or the public. Therefore, this event did not adversely affect the health and safety of the public.
V. Corrective Actions
PG&E revised CRVS testing procedures to specify separate acceptance criteria for each of the tested configurations in accordance with RG 1.197. Plant procedure modifications assure that testing is conducted in the alignment that would result in the greatest consequence to CR operators during a DBA. PG&E also had an outside contractor perform an independent assessment of the CRE in-leakage test configuration. The contractor reviewed the requirements ofRG 1.197 and DCPP's CRVS design, and determined that the testing alignments used in plant procedures conform to RG 1.197 requirements.
PG&E performed testing of the CRVS in an alignment as clarified by the NRC's TIA 2012-08 following CRVS modification. CR operators exited TS 3.7.10, Condition B, on December 20,2012.
PG&E will revise the SR 3.7.l0.5 bases, and the in-leakage test, to address the NRC's clarification in its TIA 2012-08. PG&E revised the DCPP Current Licensing Basis Determination procedure to provide guidance to seek NRC clarification on issues that may involve difference in NRC and industry perspective.
VI. Additional Information
A. Failed Components All components functioned as designed.
B. Previous Similar Events
There are no examples of previous similar events at DCPP. 6