05000275/LER-2011-008-01, Control Room Ventilation System Design Vulnerability
| ML13025A166 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 01/24/2013 |
| From: | Allen B Pacific Gas & Electric Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| DCL-13-004 LER 11-008-01 | |
| Download: ML13025A166 (8) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(8) 10 CFR 50.73(a)(2)(ii)(8) 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 |
| 2752011008R01 - NRC Website | |
text
Pacific Gas and Electric Company January 24, 2013 PG&E Letter DCL-13-004 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 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 Licensee Event Report 1-2011-008-01, Control Room Ventilation System Design Vulnerability
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. 80th 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)(8) and 10 CFR 50.73(a)(2)(ii)(8). 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, Baf!.jen S-. ¥--
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 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2013 (10-2010)
, the NRC may digits/characters for each block) not conduct or sponsor, and a person is not required to respond to, the information collection.
- 3. PAGE Diablo Canyon Power Plant, Unit 1 05000-275 1
OF 7
- 4. TITLE Control Room Ventilation System Design Vulnerability
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED YEAR I SEQUENTIAL I REV FACILITY NAME DOCKET NUMBER MONTH DAY YEAR NUMBER NO.
MONTH DAY YEAR Diablo Canyon, Unit 2 05000-323 FACILITY NAME DOCKET NUMBER 11 03 2011 2011 - 008 -
01 01 24 2013
- 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)(i)(C)
D 50.73(a)(2)(vii) 1 D 20.2201(d)
D 20.2203(a)(3)(ii)
D 50.73(a)(2)(ii)(A)
D 50.73(a)(2)(viii)(A)
D 20.2203(a)(1)
D 20.2203(a)(4)
[(] 50.73(a)(2)(ii)(B)
D 50.73(a)(2)(viii)(B)
D 20.2203(a)(2)(i)
D 50.36(c)(1)(i)(A)
D 50.73(a)(2)(iii)
D 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL D 20.2203(a)(2)(ii)
D 50.36(c)(1)(ii)(A)
D 50.73(a)(2)(iv)(A)
D 50.73(a)(2)(x)
D 20.2203(a)(2)(iii)
B 50.36(c)(2)
D 50.73(a)(2)(v)(A)
D 73.71(a)(4) 100 D 20.2203(a)(2)(iv) 50.46(a)(3)(ii)
D 50.73(a)(2)(v)(B)
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)
[(] 50.73(a)(2)(i)(B)
D 50.73(a)(2)(v)(D)
Specify in Abstract below or in
B. Event Description
On November 3,2011, at 1550 PDT, operators determined that the DCPP CRVS had a design vulnerability whereby control room pressurization airflow could bypass the supply filter if neither CRVS booster fan in the train was operating. This would allow as much as 800 cubic feet per minute of unfiltered air to be delivered to the control room following an accident that resulted in initiation of the CRVS pressurization mode. Operators would have corrected this condition within 30 minutes after initiation of a safety injection by manually selecting and starting the train's redundant subtrain in accordance with existing, proceduralized actions specified in DCPP Emergency Operating Procedure (EOP) E-O, "Reactor Trip or Safety Injection," Appendix E, "ESF Auto Actions, Secondary and Auxiliaries Status."
Pacific Gas and Electric Company (PG&E) had not previously included this 30 minutes of unfiltered air supply to the control room in the analysis of record. This design vulnerability could have potentially resulted in operator dose greater than analyzed. Plant staff verified that all components and redundant components in each ventilation train were operable, and established configuration controls to ensure operator dose would continue to meet regulatory limits as a compensatory measure to restore operability. These compensatory measures assured both trains would remain available to operators even in the event of a single failure of an operating train. At 2051 PDT on November 3, 2011, PG&E made an 8-hour non-emergency report (see NRC Event Notification 47414) under 10 CFR 50.72(b)(3)(ii)(B).
PG&E noted that SR 3.7.10.5 TS bases stated "Temporary analytical methods may also be used as compensatory measures to restore operability. Options for restoring the CRE boundary to operable status include changing the licensing basis DBA consequence analysis, repairing the CRE boundary, or a combination of these actions." On December 1, 2011, PG&E declared the CRE operable after implementing compensatory measures and performing surveillance testing in the most limiting configuration permitted with the compensatory measures in place, demonstrating the capability of the compensated CRE boundary to ensure operator doses remain below regulatory limits.
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 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 CR VS equipment from the opposite train in operation does not satisfy the requirements for performing SR 3.7.10.5." PG&E subsequently concluded that because the inleakage 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.
YEAR
- 6. LER NUMBER
- - r SEQUENTIAL I I NUMBER 2011 -
008 REV NO.
01 4
- 3. PAGE OF 7
In December 2012, after modifying the CRVS, PG&E satisfactorily completed inleakage testing on the CRVS using a single CRVS train, successfully demonstrating acceptable inleakage in the most limiting configuration with a single CRVS train operating. Operators declared the CRE 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
This situation applies to both Units 1 and 2 when the CRVS pressurization mode is required. However, the CRVS trains remained capable of performing their normal ventilation functions.
E. Method of Discovery
PG&E discovered this design vulnerability during performance of Surveillance Test Procedure (STP) M-57, "Control Room Ventilation System Tracer Gas Test," to satisfy TS SR 3.7.10.5.
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
Plant staff verified that all components and redundant components in each ventilation train were operable, and established configuration controls to ensure operator dose would continue to meet regulatory limits. Operations issued an Operations Standing Order instructing operators to enter TS 3.7.l0.A any time a CRVS supply fan or a booster fan is not available as a compensatory measure to restore and maintain operability. PG&E had also previously revised STP M-87, "Operational Leak Inventory ofECCS Systems Outside Containment Likely to Contain Highly Radioactive Fluids Following an Accident," to limit post-Ioss-of-coolant-accident emergency core cooling system (ECCS) leakage. These actions ensured operator doses would be maintained less than the Final Safety Analysis Report accident analysis results for the highest unfiltered air inleakage rate reported in STP M-57 as well as mitigating the consequences of a potential 800 scfm of filter bypass flow.
G. Safety System Responses None.
III. Cause of the Problem PG&E first identified and documented this design vulnerability in 1991 in a nonconformance report. Human error on the part of a Technical Review Group (root cause evaluation team) in 1991 to eliminate the design vulnerability YEAR
- 6. LER NUMBER I
SEQUENTIAL T NUMBER I 2011 -
008 REV NO.
01 5
- 3. PAGE OF 7
was the apparent cause of this issue in that the team focused on managing the consequences of the design vulnerability rather than eliminating it (see Section VI.B, "Previous Similar Events," of this licensee event report).
The cause of incorrectly declaring the CRVS operable was that the bases for SR 3.7.10.5 were unclear and subject to multiple interpretations that PG&E clarified via consulting industry experts versus requesting that NRC clarify the intent.
IV. Assessment of Safety Consequences
PG&E modeled the potential dose to control room operators using the as-found condition of SOO scfm bypass flow, measured CRE unfiltered in-leakage of 51 scfm and ECCS leakage of 0.42 gallons per minute, and concluded that the dose to control room operators would not have exceeded 5-rem whole body dose or its equivalent to any part of the body (calculated over 30 days) if one subtrain in each train was started within 30 minutes. ECCS leakage over the past 3 years has remained less than 0.14 gpm. PG&E's review of CRVS configuration for the past 3 years confirmed that at least one subtrain in each CRVS train was functional and available to operators at all times.
This event did not result in failure of equipment or a 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 implemented modifications to eliminate the design vulnerability.
PG&E performed testing of the CRVS in an alignment as clarified by the NRC's TIA 2012-0S following CRVS modification. Control room operators exited TS 3.7.10, Condition B, on December 20,2012.
PG&E will revise the SR 3.7.10.5 bases, and the in-leakage test to address the NRC's clarification in its TIA 2012-0S. 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 None
B. Previous Similar Events
PG&E first identified and documented this design vulnerability in 1991 in Nonconformance Report DCO-91-EN-N02S.A PG&E Technical Review Group determined that a postulated single, active failure of one of the redundant booster fans or booster fan dampers in the CRVS could potentially cause the CRVS to be outside its design basis, as there was neither an alarm to notify control room operators of the failure nor an automatic switchover to the unaffected redundant CRVS train. In this situation, the potential existed for an undetected failure of a booster fan or damper during the pressurization Mode 4, resulting in infiltration of unfiltered airborne radioactivity into the control room. To correct the deficiency, PG&E installed ribbon-type streamers on the CRVS booster fan recirculation duct registers in the control room to enable control room operators to diagnose booster fan or its inlet damper status. Procedural guidance was provided in EOP E-O to instruct the operators how to use the streamers to verify the proper operation of the booster fans while CRVS was in Mode 4.
C. Industry Reports None Control Room
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