05000416/LER-2012-007
| Grand Gulf Nuclear Station, Unit 1 05000 416 1 Of 4 | |
| Event date: | 07-19-2012 |
|---|---|
| Report date: | 09-14-2012 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4162012007R00 - NRC Website | |
A. Reportable Occurrence This Licensee Event Report (LER) is being submitted pursuant to 10 CFR 50.73(a)(2)(i)(B) as an operation or condition prohibited by Technical Specifications.
B. Description of Structure(s), System(s) and Component(s) In accordance with the Grand Gulf licensing basis and as stated in the Grand Gulf Final Safety Analysis Report (FSAR), the Standby Service Water (El IS:BI) system was designed to provide a continuous flow of cooling water to those systems and components necessary for plant safety either during normal operation or under abnormal and accident conditions. During accident conditions, the Standby Service Water (SSW) system must provide the cooling water necessary to allow the engineered safety features to perform their intended function.
C. Initial Conditions The reactor was in Mode 1 at approximately 100% pre-extended power uprate (EPU) power. Although the SSW system was administratively inoperable since 1987, there have been no passive failures which have challenged operability.
D. Description of Occurrence The operation or condition prohibited by Technical Specifications resulted from modifying the single passive failure criterion to restrict passive failures to pump seal leakage and valve packing failures for the SSW components from the Grand Gulf Nuclear Station (GGNS) Final Safety Analysis Report (FSAR) in 1987 without prior Nuclear Regulatory Commission (NRC) approval. The SSW system was administratively inoperable since 1987 when an inappropriately performed 10 CFR 50.59 evaluation was put in place to change the definition of a passive failure.
During the 2012 Component Design Basis Inspection (CDBI) at GGNS, the NRC reviewed the 10 CFR 50.59 safety evaluation performed for FSAR change dated August 18, 1987 per NPEFSAR 87/0067. This change affected FSAR Section 9.2.1 in removing detail for single passive failures for SSW components.
The inspection team noted that the responses to questions 1 and 2 in the evaluation provided justification (in part) from NUREG-0138 and SECY-77-439 for the "NO" responses. Justification concluded that no increase in probability of occurrence or consequences of an accident previously evaluated in the FSAR would occur. The "NO" responses allowed changes to be made without prior NRC approval.
U.S. NUCLEAR REGULATORY COMMISSIONNRC FORM 366A LICENSEE EVENT REPORT (LER)(9-2007)
CONTINUATION SHEET
Description of Occurrence (continued) NUREG-0138 and SECY 77-439 conclude that the implementation of the single failure criterion does not require significant ruptures of moderate energy piping subsequent to a Loss Of Coolant Accident (LOCA), as this combined event would be extremely unlikely. The 10 CFR 50.59 safety evaluation used the NUREG and SECY documents to justify making changes to FSAR Section 9.2.1. These changes revised the methodology for postulating single phase failures of the SSW system to state that credible passive SSW failures that can result in a loss of fluid post-accident, are limited to pump seal or valve seal leakage, not rupture of SSW system piping.
E. Cause of Occurrence The apparent cause for this issue is misapplication of industry documents that were used for justification in the 10 CFR 50.59 safety evaluation due to lack of understanding their applicability.
The NUREG-0138 document did not specifically address single passive failures for systems such as the SSW System at GGNS. These documents were based on single passive failures of Emergency Core Cooling Systems (ECCS). Therefore, it would be appropriate to respond with a "YES" answer to questions 1 and 2 in the safety evaluation which would have required prior NRC approval before these changes were made to the GGNS FSAR.
This issue is considered a latent human performance error from 1987.
F. Corrective Actions
A Request has been submitted to the NRC seeking approval of changes to the SSW passive failure methodology.
An extent of condition sample review of safety evaluations to identify any similar misapplication of industry documents such as a SECY or NUREG is being conducted.
G. Safety Assessment The event posed no threat to public health and safety as the SSW system was determined to be Operable with Compensatory Measures in place. Prior to implementation of the Compensatory Measures, there were no passive failures which challenged operability.
U.S. NUCLEAR REGULATORY COMMISSIONNRC FORM 366A LICENSEE EVENT REPORT (LER)(9-2007)
CONTINUATION SHEET
Safety Assessment (continued) Probabilistic Risk Assessment (PRA) determined that, when combined with the annual frequency associated with a large LOCA, as defined in PRA-GG-01-001S06, the likelihood of SSW failure during the 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> period after a LOCA is 7.95E-10/year for pipe ruptures.
Currently, GGNS utilizes flow differential instrumentation between the SSW discharge and return to detect leakages greater than 1200 gallons per minute (gpm). For leakages less than 1200 gpm, an Off Normal Event Procedure (ONEP) for low SSW basin level has been created.
Compensatory actions provide system leakage monitoring, make-up water addition instructions, and guidance for locating and isolating system leaks that would cause losses beyond evaporative losses.
The actions in the ONEP are adequate to maintain SSW A and SSW B operable by managing system inventory loss.
H. Additional Information
Since August 1987, the safety evaluation process has gone through many changes and improvements. Procedural guidance has evolved from a single site to a fleet process.
Significant improvements have been made to the training program for 10 CFR 50.59 Evaluations. Industry experience has improved the process through application of NEI 96-07, "Guidelines for 10 CFR 50.59 Evaluations." From review of process improvements since 1987, no additional improvements are identified from evaluation of this issue.
I. Previous Occurrences
There have been no previously identified revisions to the GGNS FSAR without prior NRC approval in which prior NRC approval was required due to similar misapplication of industry documents such as a SECY or NUREG. Additionally, there have been no passive failures that have challenged operability.