05000275/LER-2011-008, Regarding Control Room Ventilation System Design Vulnerability

Regarding Control Room Ventilation System Design Vulnerability

ML120040128
Person / Time
Site:	Diablo Canyon
Issue date:	01/03/2012
From:	Becker J Pacific Gas & Electric Co
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
PG&E Letter DCL-12-001 LER 11-008-00
Download: ML120040128 (6)

LER-2011-008, Regarding Control Room Ventilation System Design Vulnerability

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 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)(8) 10 CFR 50.73(a)(2)(viii)(8) 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)(8) 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)(8)
2752011008R00 - NRC Website

text

Pacific Gas and Electric Company January 3, 2012 PG&E Letter DCL-12-001 James R. Becker Site Vice President Diablo Canyon Power Plant Mail Code 104/6 P. O. Box 56 Avila Beach, CA 93424 805.545.3462 Internal: 691.3462 Fax: 805.545. 6445 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555~0001 10 CFR 50.73 Docket No. 50-275, OL-DPR-80 Docket No. 50-323, OL-DPR-82 Diablo Canyon Units 1 & 2 Licensee Event Report 1-2011-008-00 Diablo Canyon Power Plant - Control Room Ventilation System Design Vulnerability

Dear Commissioners and Staff:

Pacific Gas and Electric Company is submitting the enclosed Licensee Event Report in accordance with 10 CFR 50.73(a)(2)(ii)(B) regarding a design vulnerability in the control room ventilation system for both units.

There are no new or revised regulatory commitments in this report.

This event did not adversely affect the health and safety of the public.

mlpy/50438661 Enclosure cc/enc:

Elmo E. Collins, NRC Region IV Michael S. Peck, NRC Senior Resident Inspector Alan B. Wang, NRR 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 Unit 1 05000 275 1

OF 5

4. TITLE Control Room Ventilation System Design Vulnerability

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 Diablo Canyon Unit 2 05000 323 FACILITY NAME DOCKET NUMBER 11 03 2011 2011 -

8 -

0 01 03 2012 05000

9. OPERATING MODE

11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply) 1 o 20.2201 (b) o 20.2203(a)(3)(i) o 50.73(a)(2)(i)(C) o 50.73(a)(2)(vii) o 20.2201(d) o 20.2203(a)(3)(ii) o 50.73(a)(2)(ii)(A) o 50.73(a)(2)(viii)(A) o 20.2203(a)(1) o 20.2203(a)(4)

[(] 50.73(a)(2)(ii)(8) o 50.73(a)(2)(viii)(8) o 20.2203(a)(2)(i) o 50.36(c)(1)(i)(A) o 50.73(a)(2)(iii) o 50.73(a)(2)(ix)(A)

10. POWER LEVEL D 20.2203(a)(2)(ii) o 50.36(c)(1)(ii)(A) o 50.73(a)(2)(iv)(A) o 50.73(a)(2)(x) 100 o 20.2203(a)(2)(iii) o 50.36(c)(2) o 50.73(a)(2)(v)(A) o 73.71(a)(4)

D 20.2203(a)(2)(iv) o 50.46(a)(3)(ii) o 50.73(a)(2)(v)(8)

D 73.71(a)(5)

D 20.2203(a)(2)(v)

D 50.73(a)(2)(i)(A) o 50.73(a)(2)(v)(C)

D OTHER o 20.2203(a)(2)(vi) o 50.73(a)(2)(i)(8) o 50.73(a)(2)(v)(D)

Specify in Abstract below or in

6. LER NUMBER I

SEQUENTIAL I NUMBER 008 REV NO.

00

3. PAGE 3

OF 5

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. At 2051 PDT on November 3, 2011, PG&E made an 8-hour non-emergency report (reference NRC Event Notification 47414) under 10 CFR 50.72(b)(3)(ii)(B).

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 vulnerability during performance of Surveillance Test Procedure (STP) M-57, "Control Room Ventilation System Tracer Gas Test," to satisfy TS Surveillance Requirement 3.7.10.5.

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 3.7.10.A any time a CRVS supply fan or a booster fan is not available. 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 are 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 the 800 sefm 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 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," ofthis LER).

IV. Assessment of Safety Consequences

LICENSEE REPORT (LER) u.s. NUCLEAR REGULATORY COMMISSION CONTINUATION SHEET

2. DOCKET

6. LER NUMBER YEAR 05000 275 2011 I

SEQUENTIAL I NUMBER REV NO.

008

... 00

3. PAGE 4

OF 5

PG&E modeled the potential dose to control room operators using the as-found condition of 800 scfm bypass flow, tested CRE unfiltered in-leakage of 51 sefm 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.

V. Corrective Actions

PG&E will implement actions to eliminate the design vulnerability.

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-N028. 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 tnttrumenl sat;::~rd ISSP5Room)

LICENSEE EVENT REPORT (LER) u.s. NUCLEAR REGULATORY COMMISSION CONTINUATION SHEET

2. DOCKET p. LER NUMBER YEAR 05000 275.

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