05000275/LER-2012-005, Regarding Unanalyzed Condition Due to Nonconservative Change in Atmospheric Dispersion Factor
| ML12248A036 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 08/31/2012 |
| From: | Welsch J Pacific Gas & Electric Co |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| DCL-12-082 LER 12-005-00 | |
| Download: ML12248A036 (7) | |
| 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)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(i) 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)(i)(B), Prohibited by Technical Specifications |
| 2752012005R00 - NRC Website | |
text
Pacific Gas and Electric Company August 31,2012 PG&E Letter DCL-12-082 James M. Welsch Station Director 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 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 and 2 Licensee Event Report 1-2012-005-00, Unanalyzed Condition due to Nonconservative Change in Atmospheric Dispersio~ Factor
Dear Commissioners and Staff:
Pacific Gas and Electric Company (PG&E) submits the enclosed Licensee Event Report (LER) regarding the discovery of a nonconservative historical change in the control room ventilation system atmospheric dispersion factor methodology on July 5, 2012. PG&E is submitting this LER in accordance with 10 CFR 50.73(a)(2)(i)(8), 10 CFR 50.73(a)(2)(ii)(8), 10 CFR 50.73(a)(2)(v)(D),
and 10 CFR 50.73(a)(2)(vii). PG&E will submit a supplemental LER explaining the safety consequences of this issue following completion of our assessment.
This LER also mentions a related issue identified on August 28, 2012 (Event Notification 48246), that PG&E is still investigating. PG&E will either withdraw that notification or submit a separate LER to the NRC for the August 28, 2012, issue based on the outcome of its investigation.
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,
~AWLL-James M. Welsch Interim Site Vice President 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 Document Control Desk August 31,2012 I & Page 2 PG&E Letter DCL-12-082 wrl8/6980/50497328 Enclosure cc/enc:
Elmo E. Collins, NRC Region IV Dean H. Overland, NRC Senior Resident Inspector Michael S. Peck, 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 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 YEAR ISEQUENTIAL I REV FACILITY NAME DOCKET NUMBER MONTH DAY YEAR NUMBER NO.
MONTH DAY YEAR Diablo Canyon, Unit 2 05000-323 FACILITY NAME DOCKET NUMBER 07 05 2012 2012
- 005
- 00 08 31 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 50.73(a)(2)(i)(C)
[(] 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)
[(] 50.73(a)(2)(v)(D)
Specify in Abstract below or in between July 5 and July 11,20.12. 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.
As a result of further investigation into this issue, on August 28, 2012, PG&E identified additional release pathways that could affect the CR operator dose following a LBLOCA (see Event Notification 48246). Consequently, PG&E declared the CRE inoperable and established mitigative actions in accordance with TS 3.7.10, Actions B.l and B.2. Accordingly, PG&E has concluded that, pending reanalysis, the CRVS would not have been capable of performing its safety function of mitigating the CR operator dose consequences of a LBLOCA. PG&E will either withdraw that notification or submit a separate licensee event report (LER) on the August 28,2012, issue based on the outcome of its investigation.
PG&E has not completed reanalysis of the fuel handling accidents. PG&E conservatively assumed that the CR operator dose limits would be exceeded, pending reanalysis of the fuel handling accidents. Therefore, PG&E has concluded that, pending reanalysis, the CRVS would not have been capable of performing its safety function of mitigating the consequences of a fuel handling accident for past fuel handling activities. PG&E has implemented a compensatory measure prohibiting fuel movement inside the fuel handling building (FHB) [ND] and inside the containment until this issue is resolved.
C. Status ofInoperable Structure, Systems, or Components That Contributed to the Event None.
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, as previously discussed in Section B, "Event Description."
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
To be provided in a supplemental LER.
V. Corrective Actions
- 1) PG&E will revise the accident analyses which used the MH X/Qs 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 where found to be necessary. This project was initiated in 2010. This project identified the problem described in this LER.
- 3) Additional corrective actions will be addressed and reported in a supplemental LER as necessary.
A. Immediate Corrective Actions
Operators reviewed the mitigating actions in place for adequacy to assure that CR operator dose would remain acceptable following a LBLOCA. PG&E has implemented' a compensatory measure prohibiting fuel movement inside the FHB and inside the containment and revised operational restrictions on ECCS leakage and containment leakage.
VI. Additional Information
A. Failed Components None.
B. Previous Similar Events
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-LOCA 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 RG 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 design basis accident consequences. PG&E discovered this vulnerability during performance of control room 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.