05000275/LER-2012-005-01, Regarding Unanalyzed Condition Due to Nonconservative Change in Atmospheric Dispersion Factor
| ML13155A238 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 06/03/2013 |
| From: | Allen B Pacific Gas & Electric Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| DCL-13-062 LER 12-005-01 | |
| Download: ML13155A238 (7) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 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 |
| 2752012005R01 - NRC Website | |
text
Pacific Gas and Electric Company June 3,2013 PG&E Letter DCL-13-062 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 Barry S. Allen Site Vice President 10 CFR 50.73 Licensee Event Report 1-2012-005-01, Unanalyzed Condition due to Nonconservative Change in Atmospheric Dispersion Factor 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 References: 1.
PG&E Letter DCL-12-082, "Licensee Event Report 1-2012-005-00, Unanalyzed Condition due to Nonconservative Change in Atmospheric Dispersion Factor," dated August 31,2012.
- 2.
PG&E Letter DCL-13-034, "Expected Submittal Date for Licensee Event Report 1-2012-005 Supplement," dated April 1, 2012.
Dear Commissioners and Staff:
In Reference 1, Pacific Gas and Electric Company (PG&E) submitted a Licensee Event Report (LER) to the U.S. Nuclear Regulatory Commission (NRC) related to an unanalyzed condition involving a nonconservative change in atmospheric dispersion factor. In this LER, PG&E indicated that it would provide a supplemental report to explain the safety consequences of this event by April 1, 2013, following the completion of a safety consequences assessment.
In Reference 2, PG&E notified the NRC about the revised expected date for the associated supplemental LER 1-2012-005-01 based on a pending safety consequences assessment.
PG&E submits the enclosed supplemental LER which includes the completed safety consequences assessment.
PG&E makes no new or revised regulatory commitments (as defined by NEI 99-04) in this letter. All corrective actions will be implemented in accordance with the Corrective Action Program.
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
m u.s. Nuclear Regulatory Commission June 3,2013 I & Page 2 Sincerely,
~u.JdtJ2-fo ~~
Barry S. Allen Site Vice President J8L3/50497328 Enclosure PG&E Letter DCL-13-062 cc/enc:
Thomas R. Hipschman, NRC Senior Resident Inspector Arthur T. Howell, III, NRC Region IV James T. Polickoski, 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 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 5
- 4. TITLE Unanalyzed Condition due to Nonconservative Change in Atmospheric Dispersion Factor
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED MONTHi DAY I I
DAY I FACILITY NAME DOCKET NUMBER YEAR YEAR I SEQUENTIAL I REV MONTH YEAR Diablo Canyon, Unit 2 05000-323 i
NUMBER NO.
07 1 05 1 2012 2012 -
005 -
01 06 03 1 2013
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10CFR§: (Check all that apply) 1 D 20.2201(b)
D 20.2203(a)(3)(i)
D 50.73(a)(2)(i)(C)
[8] 50.73(a)(2)(vii)
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)(I)
D 20.2203(a)(4)
[8] 50.73(a)(2)(ii)(B)
D 50.73(a)(2)(viii)(B)
- 10. POWER LEVEL D 20.2203(a)(2)(i)
D 50.36(c)(I)(i)(A)
D 50.73(a)(2)(iii)
D 50.73(a)(2)(ix)(A)
D 20.2203(a)(2)(ii)
D 50.36(c)(l)(ii)(A)
D 50.73(a)(2)(iv)(A)
D 50.73(a)(2)(x) 100 D 20.2203(a)(2)(iii)
D 50.36(c)(2)
D 50.73(a)(2)(v)(A)
D 73.71(a)(4)
D 20.2203(a)(2)(iv)
D 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)
[8] 50.73(a)(2)(i)(B)
[8] 50.73(a)(2)(v)(D)
SpecifY in Abstract below or in LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET u.s. NUCLEAR REGULATORY COMMISSION
- 2. DOCKET
- 6. LER NUMBER
- 3. PAGE 3 OF 5 YEAR I
SEQUENTIAL I REV. NO NUMBER 05000-275 2012 005 01 between July 5 and July 11,2012. The delay was due to personnel errors in communicating the concern to control room licensed operators for evaluation. Preliminary dose calculations, using the originally-licensed methods, concluded the CR operator dose limit of 30 Rem thyroid would be exceeded following a large-break loss-of-coolant accident (LBLOCA). Plant operators had already entered Technical Specification (TS) 3.7.10, "Control Room Ventilation System (CRVS)," Condition B, which states: "One or more CRVS trains inoperable due to inoperable CRE boundary in MODE 1,2,3, or 4," due to preplanned maintenance on a Unit 1 CRVS subtrain. Since plant operators had already completed Action B.1, "Initiate action to implement mitigating actions immediately," and Action B.2, "Verify mitigating actions ensure CRE occupant exposures to radiological hazards will not exceed limits, and CRE occupants are protected from smoke and chemical hazards within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />," because of the preplanned maintenance, operators reevaluated the mitigating actions (i.e., availability of self-contained breathing apparatus and staging of potassium iodide) that were already in place and found them to be adequate. However, Action B.3, "Restore CRE boundary to OPERABLE status,"
had not yet been completed.
On July 26,2012, at 1152 PDT, PG&E established new compensatory actions to restrict allowable emergency core cooling system (ECCS) leakage and containment [NH] leakage, and declared the CRE operable after completing a prompt operability assessment (POA) that concluded the CR operator dose limit of 30 Rem thyroid following a LBLOCA would not be exceeded under accident conditions with the compensatory actions in place. The POA additionally identified the fuel handling accident analyses also used the MH methodology XlQs. Compensatory actions were established to prohibit fuel movement until the issue was resolved.
Emergency planning models and offsite dose analyses do not rely on the XlQs derived from MH methodology and are not impacted by this incorrect analysis change. Therefore, this condition is limited to the CR post-accident dose for both Units 1 and 2.
After further investigation into the adequacy of the original analyses, on August 28,2012, PG&E identified additional release pathway XlQ's that had not been correctly modeled in the original analyses and could affect the CR operator dose following a LBLOCA or a fuel handling accident. At that time, PG&E evaluated this condition and concluded that the previously established compensatory measures adequately addressed these errors.
However, based on further analysis of the conditions described above PG&E subsequently concluded that the CRVS would not have been capable of performing its safety function of mitigating the CR operator dose consequences of a LBLOCA or a fuel handling accident.
In December 2012, PG&E completed CRVS modifications, performed tracer gas in-leakage testing for the CRVS, and established additional compensatory measures involving the auxiliary building ventilation system to ensure CRE/CRVS remain capable of satisfying GDC 19 limits following a LBLOCA. In January 2013, PG&E established compensatory measures involving the CRVS and fuel handling building ventilation system prior to fuel movement to ensure the CRE/CRVS remain capable of satisfying GDC 19 limits.
C. Status of Inoperable Structure, Systems, or Components That Contributed to the Event None.
FORM 366 (10-2010)
D. Other Systems or Secondary Functions Affected
None.
E. Method of Discovery
PG&E discovered this incorrect change to the XlQs during a licensing basis review ofUFSAR Chapter 15, Section 15.5, "Environmental Consequences of Plant Accidents."
F. Operator Actions
On July 11 and August 28,2012, plant operators entered TS 3.7.10, "Control Room Ventilation System (CRVS),"
Condition B, and implemented mitigative actions as directed by TS Actions B.l and B.2.
G. Safety System Responses None.
III. Cause of the Problem The incorrect change of the XlQs was determined to have been caused by inadequate design control processes in 1986, whereby the analysis change was made without evaluating the change in accordance with 10 CFR 50.59 to determine whether prior NRC review and approval was required.
IV. Assessment of Safety Consequences
The effect of a nonconservative change in XlQ methodology on operator actions modeled in the probabilistic risk assessment (PRA) would have an insignificant impact on the calculated core damage frequency and large early release frequency. Although the revised methodology indicates CR operator dose could have been greater than 30 REM in 30 days, given the existing operator procedural guidance and mitigating actions the incremental dose increase to CR operators within the 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> PRA mission time would not impair the operator's ability to perform risk significant, post-accident functions. This event resulted in no personnel injuries, no offsite radiological releases, and no damage to safety-related equipment. There were no challenges to plant safety.
V. Corrective Actions
- 1) PG&E will revise the accident analyses which used the MH XlQs and incorporate the revised analyses into the DCPP licensing basis.
- 2) PG&E will complete its licensing basis verification project that is reviewing, validating, and revising the current DCPP licensing basis. This project was initiated in 2010. This project identified the problem described in this licensee event report (LER).
FORM 366 (10-2010)
VI. Additional Information
A. Failed Components None.
B. Previous Similar Events
LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET U.S. NUCLEAR REGULATORY COMMISSION
- 2. DOCKET
- 6. LER NUMBER
- 3. PAGE 5 OF 5 YEAR I
SEQUENTIAL I REV. NO NUMBER 05000-275 2012 005 01 On September 12,2011, at 1745 PDT, operators declared the Units 1 and 2 CRE boundary inoperable and entered TS 3.7.10, "Control Room Ventilation System (CRVS)." This was due to discovery of inadequately-documented CRE in-leakage test data. At 2257 PDT on September 12,2011, PG&E made an 8-hour nonemergency report under 10 CFR 50.72(b)(3)(ii)(B). Human error affected the interpretation of test results and led to the nonconservative determination of zero in-leakage in 2005. Plant staff verified that administrative controls were in place to maintain post-loss-of-coolant accident ECCS leakage at a rate that would ensure that CR operator doses would not exceed GDC 19 limits. PG&E performed an assessment of the testing and revised procedures to specify separate acceptance criteria for each of the tested CRVS configurations in accordance with Regulatory Guide 1.197. (Reference LER 1-2011-007-01)
On November 3,2011, at 1550 PDT, PG&E determined that the DCPP CRVS had a design vulnerability; whereby, unfiltered air supplied to the control room could exceed the flow rates used in the licensing-basis analysis of DBA consequences. PG&E discovered this vulnerability during performance ofCR in-leakage testing required by TS Surveillance Requirement 3.7.10.5. On November 3,2011, at 2051 PDT, PG&E made an 8-hour nonemergency report under 10 CFR 50.72(b)(3)(ii)(B). (Reference LER 1-2011-008-00)
C. Industry Reports None.
FORM 366 (10-2010)