ML20205N365

Safety Evaluation Accepting IPE of External Events Submittal

ML20205N365
Person / Time
Site:	Catawba
Issue date:	04/12/1999
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20205N350	List: ML20205N347 ML20205N365 ML20205N379
References
REF-GTECI-***, REF-GTECI-057, REF-GTECI-103, REF-GTECI-131, REF-GTECI-147, REF-GTECI-148, REF-GTECI-A-45, REF-GTECI-NI, REF-GTECI-SC, TASK-***, TASK-057, TASK-103, TASK-131, TASK-147, TASK-148, TASK-57, TASK-A-45, TASK-OR GL-88-20, NUDOCS 9904160256
Download: ML20205N365 (10)

Text

p nay

[b t UNITED STATES g ,g NUCLEAR REGULATORY COMMISSION t WASHINGTON, D.C. 20555-0001

,o

• • ..+

STAFF EVALUATION REPORT BY THE OFFICE OF RESEARCH INDIVIDUAL PLANT EXAMINATION OF EXTERNAL EVENTS (IPEEE) SUBMITTAL CATAWBA NUCLEAR POWER STATION UNITS 1 AND 2 DUKE ENERGY CORPORATION. ET AL DOCKET NOS. 50-413 AND 50-414

1.0 INTRODUCTION

On June 28,1991, the NRC issued Generic Letter (GL) 88-20, Supplement 4 (with NUREG-

.1407, " Procedural and Submittal Guidance") requesting all licensees to perform individual plant I examinations of external events (IPEEE) to identify plant-specific vulnerabilities to cevere accidents and to report the results to the Commission together with any licensee-determined improvements and corrective actions, in a letter dated June 21,1994, the licensee, Duke Power Company (DPC, recently renamed Duke Energy Corporation), submitted itu :PEEE for Catawba Nuclear Station to the NRC.

The staff contracted with Energy Research, Inc. (ERI) to conduct a completeness and reasonableness " Step 1" review of the licensee's IPEEE submittal and its associated documentation in May 1995 and sent a request for additional information (RAl) to the licenree on September 15,1995. The licensee responded to the RAI on November 17,1995. Based on the results of the review, the staff concluded that the aspects of seismic events, fires, and high-winds, floods, and other exterc al events (HFO) were adequately addressed. The review findings are summarized in the evaluation section below. Details of the contractor's findings are presented in the technical evaluation report attached to this staff evaluation report.

In accordance with explicit requests in Supplement 4 to GL 88-20 and its associated guidance in NUREG-1407, the licensee provided information to address the resolution of these five issues:

Fire Risk Scoping Study (FRSS) issues; Generic Safety issue (GSI)-57, " Effects of Fire i Protection System Actuation on Safety-Related Equipment;" GSI-131, " Potential Seismic Interaction involving the Movable In-Core Flux Mapping System Used in Westinghouse Plants;"

GSI-103, " Design for Probable Maximum Precipitation (PMP);" and Unresolved Safety issue (USI) A-45, " Shutdown Decay Heat Removal Requirements." The staff's findings regarding these issues are included in this SER. The licensee also addressed USl A-17," Systems Interactions in Nuclear Power Plants," but, as discussed in the evaluation below, this issue has been resolved separately from the IPEEE. The licensee did not propose to resolve any additional USIs or GSis as part of the Catawba IPEEE.

ENCLOSURE 9904160256 990412 DR ADOCK 05

}43

~

2.0 EVALUATION The Catawba Nuclear Station is a two-unit, Westinghouse 4-loop pressurized-water reactor (PWR) located about 13 miles from Charlotte, North Carolina. The plant was designed to a seismic acceleration level of 0.3g PGA (peak ground acceleration) anchored to a Newmark spectral shape similar to NUREG/CR-0098. With respect to the seismic IPEEE, Catawba is assigned to the focused-scope seismic review category in NUREG-1407. The licensee used seismic probabilistic risk assessment (PRA) methodology to address the seismic aspects of the IPEEE. For fire events, the licensee has provided an updated analysis of its Level 3 PRA and performed a walkdown. For the analyses of other external events, the licensee used the progressive ';creening procedure as described in NUREG-1407.

2.1 Core Damaae Freauency (CDF) Estimate The licensee used a seismic PRA to perform the seismic IPEEE. In addition, the licensee performed walkdowr,s to confirm the PRA results. The licensee estimated that the CDF due to seismic events is about 1.6x104/ reactor-year (RY). Regarding the fire analysis, the licensee estimated that the CDF due to fire events is about 4.7x104/ RY. The licensee also estimated that the contribution to CDF from tornadoes is about 2.6x104/RY. The CDF due to intemal events is about 5.8x104/RY, including internal flooding. )

2.2 Dominant Contributors Seismic events contribute about 69% of the total CDF. Many of the dominant sequences involve a loss of offsite power (LOOP) event followed by a failure of the emergency diesel generators (EDGs). At low ground acceleration, EDG failures are due to random start, run, or maintenance failures. At ground acceleration levels above 0.5 g, the EDG failures are mostly seismic failures.

Internal fire events contribute about 20% of the total CDF. The dominant fire sequences are related to fires in the control room, cable spreading room, and the component cooling room. A sensitivity analysis also identified the turbine building, which was previously screened out, as another dominant fire risk location.

With respect to HFO, the licensee identified that the dominant HFO contributors to CDF are tornado events which make up about 11 percent of the CDF. The tornado-initiated sequences l are non-recoverable LOOP sequences, followed by failures of EDGs.

The licensee's'IPEEE assessment appears to have examined the significant initiating events and dominant accident sequences.

2.3 Containment Performance The licensee has conducted seismic walkdowns which included componentt required for containment performance both inside and outside the conicbment. In addition, the licensee performed a screening analysis of containment penetrations to determine if their failures could lead to significant release pathways. However, the assessment failed to note the susceptibility

3-of the hydrogen mitigation system to seismically related failures for seismically induced SBO scenarios. In general, the licensee's containment performance analyses for seismic events appeared to have considered important severe phenomena and are consistent with the intent of Supplement 4 to GL 88-20.

With respect to assessing the impact of fires on containment performance, the licensee noted that the analysis of containment performance for the fire sequences is identical to the analysis of containment performance for other events where containment safeguards are assumed not to be available, in addition, the licenseo performed a walkdown which did not result in the identification of any additional fire-related containment failure modes. The licensee's containment performance analyses for internal fire events appeared to have considered important severe phenomena and are consistent with the intent of Supplement 4 d GL 88-20.

2.4 Generic Safety Issues As a part of the IPEEE, a set of generic and unresolved safety issues (USI A-45, GSI-131, GSI-103, GS!-57, and the Sandia Fire Risk Scoping Study (FRSS) issues) were identified in Supplement 4 to GL 88-20 and its associated guidance in NUREG-1407 as needing to be addressed in the IPEEE. The staff's evaluation of these issues is provided below.

1. USI A-45," Shutdown Decay Heat Removal (DHR) Requirements" The licensee determined that the CDF due to a failure of DHR systems for external initiators did not change significantly as a result of the IPEEE analysis. The staff finds that the licensee's USI A-45 evaluation is consistent with the guidance provided in Section 6 3.3.1 of NUREG-1407, and therefore, the staff considers this issue resolved.

2. GSI-131, " Potential Seismic Interaction involving the Movable In-Core Flux Mapping System Used in Westinghouse Plants

The licensee stated that this issue was addressed by the addition of restraints during construction and that the restraints are adequate to prevent seismic interaction and breach of the pressure boundary. The staff finds that the licensee's GI-131 evaluation is consistent with the guidance provided in Section 6.2.2.1 of NUREG-1407, and therefore, the staff considers this issue resolved.

3. GSI-103, " Design for Probable Maximum Precipitation" The license 2 has assessed GSI-103 and pro, an analysis of water buildup on the roof of plant structures as a result of Probable Maximum Precipitauon (PMP). In addition, the licensee has assessed the effects of site flooding as a result of PMP. The staff finds that the licensee's GSI-103 evaluation is consistent with the guidance provided in Section 6.2.2.3 of NUREG-1407, and therefore, the staff considers this issue resolved.

I

4. GSI-57,' Effects of Fire Protection System Actuation on Safety-Related Equipment" The licensee performed walkdowns to investigate the potential effects on safety-related equipment due to water discharge from sprinkler heads and fire hoses. The walkdown for

~

each fire area concluded that there are no areas in which the potential for water spray or migration from fire suppression activities created an unacceptable risk to plant safety. The staff finds that the licensee's GSI-57 evaluation is consistent with the guidance provided in EPRl's FIVE which was accepted by the NRC staff, and therefore, the staff considers this issue resolved.

5. Fire Risk Scoping Study issues The licensee has addressed the fire risk scoping study issues (fire-induced alternate shutdown / control room panel interaction (Section 4.8.7 of IPEEE); seismic-fire interactions (Section 4.8.6 of IPEEE); effects of fire protection system actuation on safety-related

)

equipment (Section 4.8.5 of IPEEE); smoke control and manual fire-fighting effectiveness (Section 4.8.4 of IPEEE); and adequacy of fire barriers (Section 4.8.8 of IPEEE)). Based on the results of the IPEEE submittal review, the staff considers that the licensee's process is capable c identif ,ing potential vulnerabilities associated with these FRSS isst .d therefore, the staff considers these issues resolved.

In addition to those safety issues discussed above that were explicitly requested to be evaluated in Supplement 4 to GL 88-20, four generic safety issues were not specifically identified as issues to be resolved under the IPEEE program; thus, they were not explicitly discussed in Supplement 4 to GL 88-20 or NUREG-1407. However, subsequent to the issuance of the generic letter, the NRC evaluated the scope and the specific information requested in the generic letter and the associated IPEEE guidance and concluded that the plant-specific analyses being requested in the iPEEE program cou'd also be used, through a satisfactory IPEEE submittal review, to resolve the external event aspects of these four safety issues. The following discussions summarize the staff's evaluation of these safety issues at Catawba.

1. GSI-147, " Fire-Induced Alternate Shutdown / Control Room Panet Interactions" Catawba has a standby shutdown system (SSS) which is located in the plant yard and is physically independent of the control room. The SSS controls, and instrumentation are physically protected from fires in other plant areas by fire barriers and electricallf protected from malfunction due to fire effects by optical isolators. The licensee concluded that there is no pote'ntial risk to plant safety due to control systems interactions for SSS controls.

Based on the results of the IPEEE t omittal review, the staff considers that the licensee's process is capable of identifyir.g potential vulnerabilities associated with this issue. On the basis that no vulnerability :ssociated with this issue was identified in the IPEEE submittal, the staff considers this issue resolved.

2. GSI-148, " Smoke Control and Manual Fire-Fighting Effectiveness" The licensee's IPEEE submittal contains information addressing this issue (i.e., the effect of smoke and misdirected suppressica was accounted for in the w lkdown (Sections 4.0.4

and 4.8.5 of IPEEE)). Based on the results of the IPEEE submittal review, the staff considers that the licensee's process is capable of identifying potential vulnerabir.ies associated with this issue. On the basis that no vulnerability associated with this issue was identified in the IPEEE submittal, the staff considers this issue resolved.

3. GSI-156, " Systematic Evaluation Program (SEP)"

Since Catawba is not a SEP plant, GSI-156 does not apply to Catawba.

4. GSI-172, " Multiple System Responses Program (MSRP)"

The licensee's IPEEE submittal contains information directly addressing the following

, external events-related MSRP issues: effects of fire protection system actuation on safety-related equipment (Sections 4.8.5 and 4.8.6 of IPEEE), seismically induced spatial and functional interactions (Section 3.1.2.3 of IPEEE), seismic-fire interactions (Section 416 of IPEEE), non-safety-related control system / safety-related system dependencies (Section 3.1.2.3 of IPEEE), effects of flooding and/or moisture intrusion on non-safo:/ related and safety-related equipment (Secticn 5.2 of IPEEE), seismically induced fire suppression system actuations (Sections 4.8.5 and 4.8.6 of IPEEE), seismically induced flooding (Section 3.1.2.3 of IPEEE), seismically-induced relay chatter (Sections 3.1.2 and 3.1.6 of IPEEE), evaluation of an earthquake greater than the SSE (Section 3 of IPEEE), and smoke control and manual fire-fighting effectiveness (Section 4.8.4 of IPEEE). Based on the fact that no vulnerabilities were identified, the staff considers these MSRP issues resolved.

In addition, the staff considers that the following MSRP issues are resolved for Catawba for the reasons given below:

(i) Regarding the effects of hydrogen line ruptures, the submittal did not explicitly discuss hydrogen lines and tanks in the fire assessment. However, the submittat did state that the licensee examined locations of flammable or combustible gas piping for seismic / fire interaction.

(ii) Regarding the IPEEE-related aspects of common cause failures associated with human errors, human errors occurring as part of recovery actions during certain fire scenarios were addressed in Section 4.6 of the IPEEE. With respect to the seismic events, the licensee incorporated operator recovery actions in the fault tree analysis; however, the licensee did not provide details on how to assign human error probabilities for the operator recovery actions (Section 3.1.5 of IPEEE).

Based on the overall results of the staff's IPEEE submittal review, the staff considers that the licensee's process is capable of identifying potential vulnerabilities associated with GSI-172. On the basis that no potential vulnerability associated with this issue was identified in the IPEEE submittal, the staff considers the IPEEE-related aspects of this issue resolved.

The licensee also addressed another issue that was not specifically required as a part of the IPEEE review as requested in Supplement 4 to GL 88-20 or NUREG-1407. This issue is

.6-USl A 17, " Systems Interactions in Nuclear Power Plants." This issue has been resolved in a separate evaluation from the IPEEE program as indicated in NUREG-0933, "A Prioritization of Generic Safety issues." No other specific USIs or GSis were proposed by the licensee for resolution as part of the Catawba IPEEE.

2.5 P' ant Safety Features. Potential Vulnerabilities. and imorovements The licensee did not report any unique safety features at the plant.

The licensee defined an "unduely significant sequence" as a vulnerability. The licensee dd not identify any potential severe accident vulnerabilities related to seismic, fire, or HFO events.

With respect to seismic events, the licensee developed and implemented the following plant improvements (Table 3-3 of IPEEE):

1. Add spacers and dummy batteries and stiffen side rails on the diesel generator battery racks.

2. Relocate an instrument to avoid a potential seismic interaction with adjacent piping.

3. Replace a valve to eliminate seismic spatial interaction between valve 2RN225 and nearby spent fuel cooling line.

With respect to fire events, the licensee developed the following plant improvements:

1. A fire in a diesel generator load sequencer could cause load shed of a 4,160 volt bus. A procedure enhancement has been made by placing additionalinstructions in the pre-fire IM for the ETB switchgear area.

2. A plant modification was being implemented to replace reciprocal air compressors with centrifugal compressors. The cables for the newly installed instrument air compressors would be routed so that sufficient redundancy for fire would exist.

3. Missing door bolts have been reinstalled in the auxiliary shutdown panel National Electrical Manufacturers Association 4 cabinets.

The licensee did not identify any HFO improvements based on the findings of its IPEEE HFO analysis. -

3.0 CONCLUSION

S On the basis of the above review findings, the staff notes that: (1) the licensee's IPEEE is complete with regard to the information requested by Supplement 4 to GL 88-20 (and associated guidance in NUREG-1407), and (2) the IPEEE results are reasonable given the Catawba design, operation, and history. Therefore, the staff concludes that the licensee's IPEEE process is capable of identifying the most likely severe accidents and severe accident vulnerabilities, and therefore, that the Catawba IPEEE has met the intent of Supplement 4 to

7-GL 88-20. In addition, the resolution of specific generic safety issues have been discussed in this SER.

It should be noted that the staff focused its review primarily on the licensee's ability to examine Catawba for severe accident vulnerabilities.~ Although certain aspects of the iPEEE were explored in more detail than others, the review was not intended to validate.the accuracy of the licensee's detailed findings (or quantification estimates) that underlie or stem from the examination. Therefore, this SER does not constitute NRC approval or endorsement of any IPEEE material for purposes other than those associated with meeting the intent of Supplement 4 to GL 88-20 and the resolution of specific generic safety issues discussed in this SER.

Attachment:

Technical Evaluation Report Principal Contributors: E. Chow A. Rubin Date: April 12, 1999

)

Attachment CATAWBA NUCLEAR PLANT UNITS 1 AND 2 INDIVIDUAL PLANT EXAMINATION OF EXTERNAL EVENTS (IPEEE)

TECHNICAL EVALUATION REPORT i

j l

3 Attachment CATAWBA NUCLEAR PLANT UNITS 1 AND 2 INDIVIDUAL PLANT EXAMINATION OF EXTERNAL EVENTS (IPEEE)

TECHNICAL EVALUATION REPORT

)

Attachment  !

CATAWBA NLICLEAR PLANT UNITS 1 AND 2 INDIVIDUAL PLANT EXAMINATION OF EXTERNAL EVENTS (IPEEE)

TECHNICAL EVALUATION REPORT