ML20212D071

Safety Evaluation Re GL 88-20, Individual Plant Exam for Severe Accident Vulnerabilities

ML20212D071
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Site:	Callaway
Issue date:	09/14/1999
From:	NRC (Affiliation Not Assigned)
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NUDOCS 9909220275
Download: ML20212D071 (7)

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1 4 e areog g k UNITED STATES g j 2

NUCLEAR REGUL.ATORY COMMISSION WASHINGTON, D.C. 2066H001 i

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STAFF EVALUATION REPORT BY THE OFFICE OF NUCLEAR REACTOR REGULATION INDIVIDUAL PLANT EXAMINATION OF EXTERNAL EVENTS (IPEEE) l UNION ELECTRIC COMPANY CALLAWAY PLANT. UNIT 1 DOCKET NO. 50-483 l

1.0 INTRODUCTION

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

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1407, Procedural and Submittal Guidance) requesting all licensees to perform individual plant examinations of external events (IPEEE) to identify plant-specific vulnerabilities to severe accidents from external events and to report the results to the Commission together with any licensee-determined improvements and corrective actions. Union Electric Company (the licensee) responded to the GL for Callaway Plant, Unit 1 (Callaway) in letters dated December 18,1991, October 27,1992, June 30,1995, and February 2 and October 30,1996. In the letters of December 18,1991, and October 27,1992, the licensee provided their schedule and the IPEEE techniques to be used. In the letter dated June 30,1995, the licensee submitted the results of its IPEEE review for Callaway.

The staff contracted with Energy Research, Inc. to conduct a completeness and reasonableness " Step 1" review of the licensee's June 30,1995, submittal and sent a letter request for additional information (RAl) to the licensee on November 20,1995. The licensee responded to the RAI by letters of February 2 and October 30,1996. Based on the results of I the review, the staff concluded that the aspects of seismic; fires; and high winds, floods, transportation and other external events 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 (TER) (Enclosure 3).

1 in accordance with Supplement 4 to GL 88-20, the licensee provided information to address the l resolution of the following:

1 Unresolved Safety issue (USI) A-45, " Shutdown Decay Heat Removal Requirements,"

Generic Safety issue (GSI) -103, ' Design fcr Probable Maximum Precipitation (PMP),"

GSI-131,

• Potential Seismic Interaction involving Movable In-Core Flux Mapping System l Used in Westinghouse Plants,"

GSI-57,

• Effects of Fire Protection System Actuation on Safety-Related Equipment," and Sandia Fire Risk Scoping Study (FRSS) issues. l l

ENCLOSURE 2 9909220275 990914 PDR ADOCK 05000483 P PDR l

1 These issues were explicitly requested in Supplement 4 to GL 88-20 and its associated guidance ir* NUREG-1407. Staff and contractor review findings regarding these issues are included in this SER. The licensee did not propose to resolve any additional USIs or GSis as part of the Callaway IPEEE.

2.0 EVALUATION The Callaway Plant is a single unit Westinghouse four-loop pressurized-water reactor (PWR),

with a power output of 3565 MWt. The site is located in Callaway County, Missouri, approximately 80 miles west of St. Louis. The plant is on a plateau approximately 300 feet above the Missouri River (which is about 5 miles to the south of the plant). Callaway received its full power license in October 1984.

The licensee performed a focused-scope seismic margin assessment generally consistent with NUREG-1407. The contribution to piant core damage frequency (CDF) from seismic events was not estimated by the licensee since the seismic margin approach was used. A probablistic risk assessment (PRA) quantification for fire events that utilized the Electric Power Research institute's (EPRI) Fire induced Vulnerability Evaluation (FIVE) methodology was performed. The licensee evaluated the other extemal events (HFO) using the progressive screening approach from NUREG-1407 and GL 88-20, Supplement 4. Callaway was designed to the 1975 standard review plan (SRP) criteria, and hence, the HFO evaluation focused on any changes in the plant design or operation that occurred since the plant's operating license was issued. The contribution to CDF from HFO was not estimated, since no significant plant changes had occurred since licensing, and the contribution to CDF was considered by the licensee to be negligible.

The licensee used the Nuclear Energy Institute (NEI) 91-04 severe accident closure guidelines to identify vulnerabilities. Based on these guidelines, the licensee did not identify any potential vulnerabilities associated with seismic, fire or other extemal events; thus, no improvements related to external events were considered necessary by the licensee for Callaway.

2.1 Core Damaae Frecuency Estimates As noted, the licensee did not estimate s seismic core damage frequency (CDF) contribution, since the seismic margin approach was used. The analysis indicated that the overall high confklence of low crobability of failure (HCLPF) capacity for Callaway is at least 0.3g, the

- review level earthquake (RLE) value for the plant. The CDF contribution from HFO events was considered to be negligible. A quantification for fire events, that used the EPRI FIVE l

methodology, indicated that the contribution to plant CDF from fire was 8.9E-6/ reactor year

- (RY). The licensee estimated that the overall CDF due to intemal events was about 5.8E-5/RY.

2.2 Dominant Contributors As indicated above, the seismic margin analysis results indicated that the overall HCLPF plant capacity was at least equal to the RLE (0.3g) and that there were no weak components.

Specifically, all of the components on the plant's safe shutdown equipment list (SSEL) had HCLPFs in excess of the RLE. For fire events. the licensee reported that the main contributors to the fire-related CDF were the control room and the two emergency safety features

sw;;;.Near rooms. As indicated, the contributor to CDF from the HFO-related events was not estimated since this contribution was judged to be insignificant.

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

2.3 Containment Performance The licensee has assessed containment performance under seismic conditions at Callaway by investigating containment integrity during seismic events, specifically focusing on the ruggedness of containment isolation equipment to protect against containment bypass .

(including the potential for a unique seismic-caused containment bypass), and containment cooling systems. The licensee evaluated fires both inside and outside of containment and found them to be of little significance primarily because of the reactor coolant pump oil ] l collection design and the separation of redundant electrical cables. None of the fires outside of containment were found to adversely effect the containment functions.

The licensee's containment performance analyses for seismic and intemal fire events appears I

to have considered important severe phenomena and are consistent with the intent of Supplement 4 to Generic Letter 88-20.

4 2.4 Generic Safety issues As a part of the IPEEE, a set of unresolved and generic safety issues (i.e., USl A-45, GSI-131, GI-103, GSI-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 for Callaway is provided below.

1. USl A-45, " Shutdown Decay Heat Removal Requirements" This issue was addressed in Section 3.2.1 of the Callaway June 30,1995, IPEEE submittal for the seismic area and in Section 4.3.1 for fire. During the seismic margins assessment, the licensee evaluated the primary and attemate success paths which included decay heat removal as one of the safety functions required to mitigate the effects of a seismic event, including a small break loss-of-coolant accident (LOCA). The evaluation included the support systems for the heat exchangers, pump seal cooling and pump room cooling for i the component cooling water (CCW) and essential service water (ESW) systems needed l for decay heat removal. These systems were considered during the seismic prescreening evaluation and in the walkdown phases of the review. Spatial systems interactions were included, j i

Regarding the fire aspects of USl A-45, the licensee used the same modelin its IPEEE evaluation as was used in the individual plant examination (IPE) which included the entire array of heat removal capabilities for the plant. Bleed and feed cooling was used, and the dominant core damage scenarios were used to demonstrate the modeling of decay heat removal. The effect of Thermo-Lag was concluded to be inconsequential to the ,

assessment. '

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i The staff finds that the lice 43ee's evaluation of USI A-45 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 has reported that a seismic analysis pertaining to the interaction of the movable in-core flux mapping system indicated that the restraints for the flux mapping system were initially not adequate. Accordingly, the size and strmgth of the bolts and plates comprising the assembly were increased during a refueling outage in 1987. The staff finds that the licensee's GSI-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 licensee made refarence to its Final Safety Analysis Report (FSAR) for this issue in its June 30,1995 (Section 5.2.2), and February 2 and October 30,1996, IPEEE submittals.

In Section 2.4.2.3 of the FSAR, the licensee reports that Callaway has a roof drain system, and a surface collection system with drainage ditches to direct runoff away from the plant.

The licensee concluded that the new probable maximum precipitation (PMP) criteria will not have any adverse impact on Callaway due to the roof design and the ground drainage system. The staff finds that the licensee's GSI-103 evaluation is consietent with the guidance provided in Section 6.2.2.3 of NUREG-1407 and, therefore, the staff considers this issue resolved.

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4. GSI-57,

• Effects of Fire Protection System Actuation on Safety-Related Equipment" I The licensee has assessed the impact of inadvertent actuation of fire protection systems on safety systems which is also one of the issues identified in the FRSS. The June 30, i 1995, IPEEE submittal addressed this issue in Section 3.2.3. The staff finds that the )

licensee's GSI-57 evaluation is consistent with the guidance provided in FIVE methodology  ;

that was accepted by the NRC staff and, therefore, the staff considers this issue resolved.  !

5. Fire Risk Scoping Study issues j in Section 4.3.5 of the June 30,1995, IPEEE submittal, the licensee has explicitly addressed the FRSS issues which are also discussed in Section 2.2.13 of the enclosed TER. The licensee stated in its submittal that it has not identified any unacceptable risks or outliers at Ca!!away due to the FRSS issues. The staff finds that the licensee's evaluation is consistent with the guidance provided in NUREG-1407 and, therefore, the staff considers these issues resolved.

In addition to the safety issues discussed above that were explicitly requested in GL 88-20 Supplement 4, the following 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 GL, the NRC evaluated the scope and the specific information requested in the GL and the

5-associated IPEEE guidance, and concluded that the plant-specific analyses being requested in the IPEEE program could also be used, through a satisfactory review of the IPEEE submittals, to resolve the external event aspects of these four safety issues. The following discussions summarize the staff's evaluations of the external event aspects of these safety issues at Callaway.

1. GSI-147," Fire-induced Alternate Shutdown / Control Room PanelInteractions" The licensee's June 30,1995, IPEEE submittal contains a discussion addressing this issue in Section 4.3.5.5 ' on FRSS lssues. In the discussion, the licensee stated that Callaway has a safe shutdown facility that is independent of the control room and auxiliary shutdown panel. Based on the results of the IPEEE submittal review, the staff considers that the licensee's process is reasonable and is capable of identifying potential vulnerabilities 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.

2. GSb148, " Smoke Control and Manual Fire-Fighting Effectiveness" The licensee's June 30,1995, IPEEE submittal contains information addressing this issue in Section 4.3.5.4. The licensee addressed this issue and concluded that the Callaway fire protection systems and procedures provide adequate assurance that manual fire fighting effectiveness will not be significantly degraded from smoke and other fire effects. Based on the results of the iPEEE submittal review, the staff considers that the licensee's process is capable of identifying potential vulnerabilities associated with this issue. On the basis that no vulnerability associated with this issue was identified in the IPEEE subminal, the staff considers this issue resolved for Callaway.

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

The plant is not a SEP plant.

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

The licensee's June 30,1995, IPEEE submittal contains information directly addressing the i following external-event-related MSRP issues: l Effects of fire protection system actuation on safety-related and non safety-related equipment (Section 3.2.3); l Seismicaliy induced fire suppression system actuation (Section 3.2.3); l Seismically induced fires (Section 4.3.5.1);

Effects of hydrogen line rupture (Sections 4.3.5.1,4.6.2, and 4.6.3);

• . IPEEe-related aspects of common cause failures associated with human errors, recovery actions for certain seismic scenarios (Section 3.1.2.5),

• ' - lPGEE-related aspects of common cause failures associated with human errors, recovery actions for fire scenarios (Section 4.2.2);

- Non safety-relsted control system / safety-related system dependencies (Section 3.2.4);

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Effects of flooding and/or moisture intrusion on non safety-related and safety-related equipment (Section 3.2.3);

Seismically induced spatial interactions (Section 3.2.4);

Seismi: ally induced flooding (Section 3.2.3);

Seismically induced relay chatter (Section 3.1.4.4); and Evaluation of earthquake magnitude greater than safe shutdown earthquake (Section 3.1.3).

Based on the overall results of the 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 the issue to be resolved for Callaway.

No other specific USis or GSis were proposed by the licensee for resolution as part of the Callaway IPEEE.

2.5 Unioue Plant Features. Potential Vulnerabilities. and irr.orovements In Section 7 of its June 30,1995, IPEEE submittal, the licensee reported a number of unique safety features at the p! ant. Several features are reported to enhance the ability to maintain core cooling following an extemal event. These features include the existence of intermediate-head safety injection pumps in addition to the high-head centrifugal charging pumps; the ability, by design, of either (or both) residual heat removal (RHR) trains to provide suction to erther or both trains of the charging and safety injection pumps; and the ability to supply the auxiliary feedwater (AFW) system from the ESW system thus eliminating a dependency on the condensate storage tank. Regarding fire, the plant is stated to be extensively compartmentalized with three-hour fire barriers, and the control room has two separate cable spreading rooms.

The licensee stated that it utilized guidance given in EPRI documents NP-6041-SL and NP-6041 in its evaluation of seismic vulnerabilities and EPRI-TR-100370 in evaluating fire vulnerabilities using the EPRI FIVE approach. In Section 7 of its IPEEE submittal, the licensee stated that no fundamental weaknesses or vulnerabilities with regard to extemal events were identified during its evaluation. This section did, however, discuss a number of improvements that had been implemented in the seismic area as a result of the walkdowns that were done as a part of the IPEEE review. These improvements include:

Bolting of several motor control centers to the walls to eliminate spatial interaction, Installation of shear pins found missing in several AFW pump foundations,

. Removal of loose equipment behind the control room, and Relocation of chain hoists in the ECCS pump rooms, the CCW pump rooms, and the AFW pump rooms to avoid contact with the pumps.

The licensee state that these improvements are intended to improve plant safety and reduce the potential for seismic severe accident vulnerabilities at Callaway. The licensee did not identify any vulnerabilities in the fire area as a result of the IPEEE process; however, some updates in the accident management plans for fire events were identified and discussed in l l

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Section 4.2.3 of the submittal. These plan updates involved fire-induced hot short failures, and fire-induced loss of containment penetration room cooling. The licensee stated that these updates will be included in the SAMG process. No vulnerabilities or needed improvements were identified in the HFO area. In a conference call of August 18,1999, the licensee stated that the updates have been completed.

3.0 CONCLUSION

S On the basis of the above findings, the staff concludes that: (1) the licensee's IPEEE is complete with regard to the information requested by Supplement 4 to GL 88-20 and the associated guidance in NUREG-1407, and (2) the IPEEE results are reasonable given the Callaway design, operation, and history. Based on this, the staff concludes that the licensee's IPEEE process is capable of identifying the most likely severe accidents and severe accident vulnerabilities for extemal events, and, therefore, that the Callaway IPEEE has met the intent of Supplement 4 to GL 88-20 and the resolution of specific generic safety issues discussed above in this SER.

It should be noted that the staff focused its review primarily on the licensee's ability to examine Callaway for severe accident vulnerabilities. Although certain aspects of the iPEEE were explored in more detail than others, the review was . tot intended to validate the accuracy of the licensee's detailed findings (or quantification estimates) that underlie or stemmed from the examination. Therefore, this SER does not constitute NRC approval or endorsement of any Callaway 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 above in this SER.

Principal Contributors: B. Hardin A. Rubin J.Chen Date: