ML20206R893

Turbine Bldg Hazards Discovered by IPEEE, Presented 980510-15 in San Diego,Ca at 6th Intl Conference on Nuclear Engineering,ICONE-6

ML20206R893
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Issue date:	05/10/1998
From:	Ornstein H NRC OFFICE FOR ANALYSIS & EVALUATION OF OPERATIONAL DATA (AEOD)
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l 6th International Conference on Nuclear Engineering ICONE4 May 10-15,1998 San Diego, California ICONE-6-6399 TURBINE BUILDING HAZARDS DISCOVERED BY AN IPEEE Dr. H.L. Omstein Office for Analysis and Evaluation of Operational Data U.S. Nuclear Regulatosy Commission Mail Stop T-4 A9 Washington, D.C. 20555 USA Telephone: (301) 415-7574 FAX: (301) 415-6359 e-mail: hio@nrc. gov ABSTRACT in February 1997 Commonwealth Edison Company submitted the results of their integrated Plant Evaluation of Extemal Events (IPEEE) for Quad Cities Units 1 and 2 nuclear power plants. The IPEEE found that the core damage frequency for each unit was about SE-03 per reactor year. The licensee's analysis found that most of the risk was attributed to fires in the turbine building.

Upon receipt of this information, the U.S. Nuclear Regulatory Commission (NRC) met with the licensee to discuss the results of the analysis and the licensee's plans to reduce the risk from the recently found turbine building fire hazards.

Subsequent to the initial meeting, the NRC pe' formed a walkdown of the Quad Cities plant and met with Commonwealth Edison Company la d!! cuss short-and long-term action which could be taken to reduce the risk from the hazards described in the IPEEE.

The Quad Cities turbine building experience described in this paper demonstrates the importance and the strengths of the IPEEE program (i.e., the licensee's IPEEE discovered long-standing turbine building hazards which were dominant risk contributors, and the use of the IPEEE results enabled the licensee to take corrective action).

This paper presents details of the plant configuration, quantifications of risk in the turbine building areas, and the corrective actions being taken by the licensee to reduce the risk from the turbine building hazards.

I 9905210009 990329 PDR ORG IECCN PDR 9365Zloo o?

6th International Conference on Nuclear Engineering

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ICONE4 May 10-15,1998 San Diego, California introduction Supplement 4 to the U.S. Nuclear Regulatory Commission's (NRCs) Generic Letter (GL) 88-20,

' Individual Plant Examination of Extemal Events for Severn Accident Vulnerabilities -

10 CFR 50.54(f)" June 1991 (Ref.1), requested each U.S. commercial nuclear plant to perform an Individual Plant Examination of Extemal Events (IPEEE). The purpose of the IPEEEs was to identify potential vulnerabilities that were not known previously. Guidance for the utilities' examinations was provided in NUREG-1407, " Procedural and Submittal Guidance for Individual i

Plant Examination of Extemal Events (IPEEE) for Severe Accident Vulnerabilities," June 1991 (Ref. 2) which accompanied Supplement 4 to GL 88-20. In accordance with the GL supplement and the NUREG, the licensees for each U.S. commercial nuclear power plant examined seismic events, extemal fires, extemal flooding, the effects of high winds, transportation accidents, and accidents at nearby facilities. Although the IPEEEs focused on extemal events, the GL supplement also required the licensees to examine plant initiated (intemally generated) fires.

This paper provides information about the IPEEE that found significant risk from intemally generated fires (primarily in the turbine building) at the Quad Cities Nuclear Power Plants.

The Quad Cities Nuclear Station is located in Illinois along the Mississippi River. It has two 769 megawatt electric (MWe) boiling-water reactors (BWRs). The reactors were designed by the General Electric Company, and the architect-engineer was Sargent and Lundy. Quad Cities Unit 1 began mmmercial operation in 1972 and Quad Cities Unit'2 began commercial operation in 1973. The Quad Cities units are mirror images of each other. The reactor building and the turbine building are shared by both units 1 and 2. The south half of the turbine building houses the main turbine, generator, exciter, condenser, feedwater heaters, foodwater and condensate pumps, the condenser circulating water system and electrical switchgear for unit 1. The main control room which contains equipment and panels for both units is located adjacent to the south wall of the turbine building. Within the control room, the equipment and panels for each unit are located in distinctively defined separate areas. Because the control room is located at the south end of the turbine building, extensive power, instrumentation, and control cabling from both units are routed along the length of the turbine building. (As noted later, this feature gives rise to the cables' vulnerability to combustibles in many rooma/ areas along the length of the turbine building).

Discussion in February 1997 Commonwealth Edison Company submitted the results of their IPEEE for Quad Cities Units 1 and 2 nuclear power plants (Ref. 3). Commonwealth Edison's analysis found that at the Quad Cities Nuclear Power Station earthquakes, high winds, transportation and nearby facility accidents, and extemal fires did not pose significant risk of severe accidents.

However, the IPEEE analysis found that most of the risk of severe accidents at the Quad Cities Nuclear Power Station was attributed to intomal fires, primarily those in the turbine building.

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.s 6th International Conference on Nuclear Engineering ICONE-6 May 10-15,1998 San Diego, California The IPEEE results indicated that the core damage frequencies (CDFs) for Quad Cities Units 1 and 2 were about 5.4E-03 and 5.2E-03 per reactor year respectively. Turbine building fire hazards accounted for 85 percent and 87 percent of the CDF for units 1 and 2 respectively.

The service building fires accounted for 10 percent and 11 percent of the CDF for units 1 and 2 respectively. Reactor building fires accounted for 5 percent and 2 percent of the CDF for units 1 and 2 respectively.

After reviewing the IPEEE, the U.S. NRC held a meeting with Cornmonwealth Edison Company staff at U.S. NRC headquarters on March 31,1997, to discuss the Quad Cities IPEEE. Table I, i

" Core Damage Frequencies of Major Initiators or Contributors," contains some of the results of the Quad Cities Unit 1 IPEEE. Table i also includes a list of the areas in the turbine building which were found to have major contributions to CDF at Quad Cities Unit 1. The contributions to CDF nt Quad Cities Unit 2 are similar but not identical to those listed in Table i for Quad Cities Unit 1.

PLACE TABLE I HERE 4

In addition to presenting details of the IPEEE at the March 31,1997, meeting, the licensee indicated that it had implemented an interim altemate shutdown method (IASM) on Unit 1.*

The licensee estimated that implementation of the IASM would reduce the CDF from turbine building fire hazards by about a factor of six. (Unit 2 was shut down at the time the licensee indicated that an IASM would be implemented on unit 2 prior to restart which was estimated to be early in May 1997.)

The IASM is described in Quad Cities Station 10 CFR 50.59 Safety Evaluation Number SE-97-024 dated February 'k3,1997. As noted in that safety evaluation, the IASM provides "a means of cooling the reactor core in the event of loss of emergency core cooling system and feedwater systems and the 125 VDC system due to a severe turbine building fire. This altemate shutdown system [lASM] consists of adding an isolation valve on each of the RHR

[ residual heat removal] system and FP [ fire protection) systems, a fire hose to be connected between the two valves, and a portab;e 125 VDC supply for the automatic depressurization system valves to depressurize the reactor. The method uses the fire pumps to inject river water into the reactor through the RHR system via the fire hose. The only permanent changes to the plant are the addition of the two isolation valves.... All other equipment required for the IASM will be pre-staged in an appropriate location."

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6th laternational Conference on Nuclear Engineering ICONE-6 May 10-15,1998 San Diego, California On April 29-30,1997, a U.S. NRC assessment team consisting of representatives from the NRC's Office of Nuclear Reactor Regulation (NRR), the Office for Analysis and Evaluation of Operational Data (AEOD), the Office of Nuclear Regulatory Research (RES), and Region lil visited the Quad Cities station to review the plant areas associated with the more significant fire vulnerabilities and review the provisions of the lASM. At the March 31,1997, meeting and again during discussions at the Quad Cities station on April 29-30,1997, the licensee stated that the implementation of the IASM reduced the plant risk (reduction of the CDF) by about a factor of six. During the April 29-30,1997, assessment, Commonwealth Edison Company

> provided the U.S. NRC with details of the design of the IASM. The IASM design (at that time) required depressurization of the reactor coolant system to below about 200 psi to enable diesel-driven fire pumps to provide makeup water to the reactor.

Although the U.S. NRC assessment team viewed the IASM as a positive compensatory measure, the team was concemed with several of the IASM's weaknesses:

1. Implementation ' f the IASM required reactor coolant system depressurization (about o

200 psi) to enable the diesel-driven fire pumps to inject water into the core. As a result of the depressurization (blow down), the reactor core could become completely uncovered.

2. Fuel cladding temperatures would heat up to about 1800 'F followed by thermal shocking caused by the intra 4*an of cold, dirty, Mississippi River water.

3. The diesel driven fire pumps that would be used as part of the IASM did not have a history of high reliability (e.g., both fire pumps were inoperable for 5 months in 1996 due to zebra mussels).

4. Weaknesses in emergency lighting in the reactor building area where operators perform manual wiring tie-in of the attemate control power supply to the automatic depressurization system valves.

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Because of these weaknesses, the U.S. NRC assessment team suggested that the licensee revisit the adequacy of the IASM.

The U.S. NRC assessment team did not agree with the licensee's anaiysis of fires in the motor-generator (MG) areas (unit 1 and 2 MG set oil fire in which sets 1 A and 2B are located in an open compartment). Each MG set contains 1200 gallons of oil. The plant design has a water curtain between the MG sets. The functions of the water curtain are to: (1) provide fire separation between the unit 1 and unit 2 equipment and post-fire safe shutdown equipment, and (2)to allow operators to take actions associated with post-fire safe shutdown electrical bus manipulations in the event of a fire on either side of the water curtain.

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6th International Conference on Nuclear Engineering ICONE-6 May 10-15,1998 San Diego, California j

l The U.S. NRC assessment team indicated that because of the radiant heat energy and smoke i

which would result from the high temperature MG set oil fires, the water curtain is not capable l

of providing its intended function. Consequently, the U.S. NRC assessment team believes that the CDF for the MG set oil fire is significantly higher than the licensee's estimate. (ltem K on Table 1.)

The U.S. NRC assessment team concluded that based on the as-built conditions at the plant, the Quad Cities IPEEE fire analysis was not viewed as overly conservative. Therefore, the U.S.

i NRC assessment team recommended that the licensee expedite its review and implementation of plant modifications to reduce the risk from the fire hazards covered by the IPEEE.

The U.S. NRC assessment team made six additional recommendations which are noted below (most of which have since been implemented by the licensee):

1. Enhanced compensatory measures (e.g., roving 15 minute fire watches).

2. Enhanced administrative controls (e.g., strict controls over combustibles and hot work).

3. Improved staging of specialized fire fighting equipment which may be needed to combat a fire (e.g., locate foam fire fighting agents and application equipment, spare breathing air cylinders, etc., in adjacent fire safe areas).

4. Construct a passive fire barrier

• between the MG sets to shield sensitive electrical components in the area from fire (e.g., radiant and convective heat), and protect operators who are required to perform safe shutdown related actions in this area.

5. Develop and implement administrative controls that maximize the operability of site (common) specific post-fire safe shutdown systems when one unit is operating and the other is shutdown.

6. Consider a long term fix focused on developing a post-fire safe shutdown methodology / system that is unit specific and does not rely on the nonfire affected unit to support its implementation.

Within 30 days, the licensee constructed a seismically qualified 17' by 30' concrete block wall to provide the needed separation.

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6th International Conference on Nuclear Engineering ICONE-6 May 10-15,1998 San Diego, California At the April 29-30,1997, meeting the licensee provided the U.S. NRC with a list of" Global Issues" to which it attributed the unexpectedly high contribution that turbine building fire hazards had to the plants' overall risk. Those " Global Issues" are:

1. Use of Combustible Cables (non-lEEE 383 cables) which would result in fires "becoming severe more often."

2. Placement of redundant divisions of important and/or safety related equipment or cabling in the same areas (without adequate separation or protection).

3. Reliance upon a complex method for achieving safe shutdown which requires the use of opposite unit equipment during an Appendix R event.

In the U.S. NRC assessment team's report on the April 29-30,1997, site visit to the Quad Cities Station (Ref. 4), the team concluded that:

a major contributor to the fire vulnerabilities is the normal post-fire safe shutdown method (for fires in general plant areas) which relies on the utilization of equipment / systems from the nonfire affected unit. On the basis of its review of the Quad Cities fire protection program, the staff had accepted this shutdown method.

The staff also accepted a method which relied heavily on a large number of manual operator actions (e.g., load shedding; manual valve lineups; manual operation of pumps from load centers) and a number of exemptions from the technical requirements of Appendix R. It appears that these factors also contribute to the fire vulnerabilities that exist at Quad Cities.

On May 12,1997 (Ref. 5), the licensee notified the U.S. NRC that in following up (the U.S. NRC assessment team's] concems about water curtains in the vicinity of MG sets, it found that the water curtains could not be relied upon to perform as it had assumed in its Appendix R analysis.

On July 29,1997 (Ref. 6), the licensee notified the U.S. NRC that as follow-up to the IPEEE for Unit 2, it found a significant deficiency (i.e., cable relied upon for safe shutdown during some turbine building fires is located in a fire area of concern and it could be damaged by the same fire). The licensee concluded that procedural steps which covered providing power to various components needed to bring the plant to a safe shutdown condition were inadequate.

On August 26,1997 (Refs. 7 and 8), the licensee found that procedures for 9 of 16 Quad Cities safe shutdown paths did not contain adequate directions for the tripping and removal of breakers. In addition, the procedures were in conflict with the site's Fire Protection Report.

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6th international Conference on Nuclear Engineering ICONE 6 May 10-15,1998 San Diego, California Reference 8 indicated that these procedural deficiencies which resulted in the unavailability of safe shutdown equipment caused the " instantaneous risk" to be about three times the " base

.CDF."

As a result of the aforementioned fire protection issues, the licensee shut down Quad Cities Unit 2 on September 27,1997, and Quad Cities Unit 1 on December 20,1997. The licensee intends to restart the plants after correcting the major fire protection deficiencies that were discovered by the IPEEE and the subsequent fire protection reviews.

Conclusions The Quad Cities turbine building experience described in this paper demonstrates the importance and the strengths of the IPEEE program, that is:

1. The licensee's IPEEE discovered long-standing turbine building / fire hazards which were dominant risk contributors, and, i

2. The IPEEE has enabled the licensee to focus attention on the risk significant areas and initiate corrective action accordingly.

References

1. U.S. Nuclear Regulatory Commission, Generic Letter 88-20, Supplement 4, " Individual Plant Examination of Extemal Events for Severe Accxient Vulnerabilities - 10 CFR 50.54(f),"

June 28,1991.

2. U.S. Nuclear Regulatory Commission, " Procedural and Submittal Guidance for Individual Plant Examination of Extemal Events (IPEEE) for Severe Accident Vulnerabilities,"

NUREG-1407, June 1991.

3. Kraft, E.S., Jr., Commonwealth Edison Company, Letter ESK-97-029, letter to U.S. Nuclear Regulatory Commission, " Quad Cities Nuclear Power Station Units 1 and 2 Final Report -

Individual Plant Examination of Extemal Events (IEEE), Generic Letter 88-20, Supplement 4, NRC Docket Numbers 50-254 and 50-265," February 17,1997.

4. Madden, P., U.S. Nuclear Regulatory Commission, memorandum to S. West, " Site Visit to Quad Cities Nuclear Power Station, Units 1 and 2, Review of Plant Areas identified by the IPEEE as Fire Vulnerabilities and the Interim Altemate Shutdown Method," June 10,1997.

5. U.S. Nuclear Regulatory Commission, Event Notification 32317," Multiple Fire Protection System Actuations Could Cause System Failures," May 12,1997.

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6th International Conference on Nuclear Engineering ICONE-6 May 10-15,1998 San Diego, California

6. U.S. Nuclear Regulatory Commission, Event Notification 32697, " Plant Safe Shutdown Cable Used During a Fire Could be Damaged by that Fire," July 29,1997.

7. U.S. Nuclear Regulatory Commission, Event Notification 32820. " Discovery that a Postulated Fire Affecting Non-Safe Shutdown Load Cables Could Result in the Loss of Busses Needed to Power Safe Shutdown Loads," August 26,1997.

8. Commonwealth Edison Company, Licensee Event Report 254/97-021, Quad Cities Unit 1, September 25,1997.

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2 Table i " Core Damage Frequencies of Major Initiators or Contributors" j

Areas Within the Turbine Buliding Having Major initiators l

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or Contributors to Core Damage Frequency at Quad Cities Unit 1 (Unit 2 has a similar set)

A. Unit 1 Reactor Feed Pumps CDF = 3 x 5.84E-04 per pump (3 pumps [1 A,1B,1C])

(Total CDF for this sequence is 1 F50-03)

(Oil Fire) l B. Both Units' Air Compressors CDF = 5.32E-04 I

(Common Area Oil Fire)

C. Both Units' Turbine Oil Reservoirs CDF = 2.99E-04 l

(Common Area Oil Fire)

D. Both Units' Computer Room CDF = 2.05E-04 (Common Area Self-Ignited Cable Fire)

E. Unit 1 Turbine Building Ground Floor Busses CDF = 2 x 1.31E-04 (2 busses [ 11,12])

(Total CDF for this sequence is 2.62E-04)

(Electrical Cabinet Fire)

F. Unit 2 Turbine Building Mezzanine Busses CDF = 2 x 1.21E-04 (2 busses [13,14])

(Total CDF for this sequence is 2.42E-04)

(Electrical Cabinet Fire) i G. Auxiliary Electrical Room CDF = 1.06E-04 (Common Area Electrical Cabinet Fire)

H. Unit 1 Battery Charger Switchgear Room CDF = 8.16E-05 (Transient / Welding Fire) 1.

Unit 1 Battery Charger Foom CDF = 8.16E-05 l

(Transient / Welding Fire)

J. Unit 2 Reactor Feed Pumps CDF = 3 x 7.88E-05 (3 pumps [2A,2B,2C])

(Total CDF for this sequence = 2.36E 04)

(Oil Fire)

K. Units 1 and 2 Motor / Generator Sets CDF greater than 1.69E-05 (Housed in a common room)

(2 motor-generator sets [1 A,2B])

(Oil Fire) l l