ML20207L299

Safety Evaluation Supporting Amend 205 to License DPR-69

ML20207L299
Person / Time
Site:	Calvert Cliffs
Issue date:	03/08/1999
From:	NRC (Affiliation Not Assigned)
To:
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ML20207L293	List: ML20207L291 ML20207L299
References
NUDOCS 9903180067
Download: ML20207L299 (8)

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UNITED STATES s-NUCLEAR REGULATORY COMMISSION WAsM:NOToN, D.C. 20006 0001

• g SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. POR TO FACILITY OPERATING LICENSE NO. DPR-69 BALTIMORE GAS AND ELECTRIC COMPANY CALVERT CLIFFS NUCLEAR POWER PLANT. UNIT NO. 2 4

DOCKET NOS. 50-317 AND 50-318

1.0 INTRODUCTION

By letter dated July 20,199C as supplementM by letter dated December 4,1998, and December 23,1998, Baltimoie Gas and Electnc Company (BGE), the licensee for the Calvert Cliffs Nucicar Power Plant requested an amendment to Operating License No. DPPA9 by incorporating the changes to the Technical Specification (TS) Bases for TS 3.8.2 for Calvert Cliffs Unit 2.- The purpose of this change is to allow BGE to provide attemate cooling to the Unit 2 emergency diesel generators (EDGs) during their replacement of the Unit 2 service water (SRW) heat exchangers in the 1999 refJeling outage since the normal SRW cooling would be unavailable. The licensee is proposing to provide the 2A EDG with cooling water from the Unit 1 SRW system and to provide the 2B EDG with cooling water from an independent extema! cooling system during the replacement work. Due to the altamate Unit 2 EDG cooling conficarations, the licensee requested a one-time change to the description of an operable EDG while Unit 2 is in Modes 5 and 6 in the Bases for TS 3.8.2. The December 4, 1998, and December 23,1998, letters provided clarifying information that did not change the initial proposed no significant hazards consideration determination.

2.0 EVALUATION The SRW system at Calvert Cliffs is a closed system that uses plant domineralized water to remove heat from turbine plant components, blowdown recovery heat exchangers, containment air coolers, spent fuel pool cooling (SFPC) heat evchangers, and the EDG heat exchangers. There are a total of three SRW pumps for each unit. For each unit, two pumps are powered from a different 4 kV engineered safety features (ESF) bus. The third pump can be powered from either 4kV ESF bus. During normal operation, both subsystems are in service and fully redundant to assure the safe operation rad shutdown of the plant. During the 1999 refueling outage on Unit 2, each Unit 2 SRW system will be modified to replace the two existing shell and tube SRW heat exchangers with four new plate and frame heat exchangers (two per train) that have an increased thermal performance capability.

The EDGs are designed to provide a dependable onsite power source capable of starting and supplying the essential loads necessary to safely shut down the plant and maintain it in a safe shutdown condition under all conditions. Unit 2 has two EDGs (2A and 28) and Unit 1 has one EDG (1B) that relies on the SRW system to provide cooling water. The other EDG (1 A) on

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Unit 1 is air-cooled. In order to minimize the impact on operable or operating plant equipment 9903180067 POR ADOCA 18 P

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• Pom the Unit 2 SRW equipment removal and replacement activities, and to minimize testing and plant system configuration evolutions, the licensee proposed to replace the heat exchangers on both of the SRW subsystems at the same time. However, sitemate cooling water must be available to the Unit 2 EDGs.

During this replacement, Unit 1 would continue at full power operation and Unit 2 would be in either Mode 5, Mode 6, or defueled. The shutdown unit is required to have an EDG operable in accordant.a with TS 3.8.2 in Modes 5 and 6 to perform refueling and feel movement operations. Although the TSs only require one EDG to be operable in Modes 5 and 6, the 2B EDG provides power to shared systems and Unit 2 components credited in the updated final safety analysis report for Unit 1 events. The Control Room Emergency Ventilatim System (CREVS), the Control Room Emergency Temperature System (CRETS), the hycogen analyzers and the spent fuel pool cooling (SFPC) system are systems that are snared between units, and the Unit 2 motor-driven auxiliary feedwater pump is credited in the TSs as being able to mitigate a Unit i loss of feedwater event. The 2B EDG provides emergency power to the No.12 CREVS, the No.12 CRETS, the No. 6519 Hydrogen Analyzer, the No 12 SFPC pump, the Unit 2 motor-driven auxiliary feedwater pump, and the Nos. 21 and 24 battery chargers. The 2A EDG provides emergency power to the Nos. 22 and 23 battery chargers.

Thus, the operations of bo'h the 2A and 2B EDGs are important to both units. Therefore, the licensee has proposed to provide an attemate cooling water supply in which the 2A EDG would be provided with cooling water from the Unit 1 SRW system and the 28 EDG would be provided with cooling water from an independent extemal cooling system. Accordingly, a temporary TS Bases change to the description of an operable EDG while Unit 2 is in Modes 5 and 6 and to support Unit 1 continued operation was proposed. If the conditions of the TS

- Bases are not met, the appropriate action statements would be entered.

The replacement work on Unit 2 is expected to take approximately 40 days. Unit 1 would continue at full power operation during the refueling outage. Also, the non-safety-related plant air compressors, which require SRW for cooling, can be used to supply air to either Unit 1 or Unit 2. To ensure that compressed air is available during the outage, a temporary diesel air compressor would be connected to the Unit 2 non-safety-related compressed air system, which could also be cross-connected to 'Jnit 1 in the event of a loss of air pressure. A second, temporary diesel air compressor in m:aual start would be installed as a back-up.

There is an increase in tta probability of a malfunction due to the use of an independent extemal cooling system that is non-safety-related and unprotected from seismic or tomado events.' Also, the reliance of a Unit 2 EDG on Unit 1 SRW resuhs in the increase of the probability of a malfunction. Since these SRW lineups affsci the probability of a maKunction for other equipment that rely on SRW du.ing an ou*ege, the licensu has requested approval of the unreviewed safety questions (USQs) discussed below.

2.1 2A EDG C;oled by No.12 SRW Subsystem The licensee has proposed to provide attemate cooling water to the 2A EDG by connecting the No.12 SRW subsystem using existing piping and spool pieces. The spool pieces would meet i

or exceed the requirements for temperature and pressure of the SRW piping and be installed as Seismic Category 1. The additional heat load on the No.12 SRW subsystem would not adversely impact its ability to provide cooling to the normally connected safety-related loads.

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in order to preserve the capability of the No. ii

'W subsystem to support its normally connected loads under loss-of-coolant accident (LO) conditions on Unit 1, the licensee plans to place a limit on the ultimate heat sink temperature which would require the removal of the 2A EDG from the No.12 SRW subsystem if the limit is exceeded.

The first USQ is due to the realignment of the Unit 1 No.12 SRW subsystem to cool the Unit 2 2A EDG in addition to its normal alignment to cool the Unit 1 1B EDG. This alignment would rely on two existing control valves (one to each EDG) to function properly in order to provide adequate SRW flow to both EDGs. If one of the valves should fail open, it may result in insufficient SRW flow or increased SRW temperatures since the two EDGs would share the same cooling water supply. This is an increase in the probability of a malfunction because the operability of an EDG relies on both control valves performing property. The licensee concluded that this is an acceptable condition because the control valves and their air supply are safety-related and would be performing their design function. The control valves would not be modified by the temporary configuration and would not require any operator action. Based on its review, the staff found that the probability of malfunction due to the reliance of the EDGs on an additional SRW control valve would increase slightly, but is acceptable for the limited time requested.

The second USQ for this temporary configuration is a condition in which the Unit 2 2A EDG is dependent on the Unit 1 1B EDG for cooling water. The 18 EDG provides the emergency power source for the SRW pump that would provide cooling to the 2A and 1B EDGs. The probability of a malfunction for the 2A EDG has increased since it now depends on the operability of the 1B EDG. There is no electricalinterdependence between the two EDGs. In this configuration, the No.12 SRW subsystem pump would only be fed from the 1B EDG. If

' the 1B EDG was lost, then the No.12 SRW subsystem would be lost (due to a loss of power to its associated pump), which would lead to a loss of cooling to the 2A EDG, and a failure of the diesel to function. The licensee concluded that this is an acceptable condition because the 1B EDG is safety-related and is proven reliable through testing. Additionally, the 1B EDG would not be operated in a different manner, it would not re quire any additional operator actions, and the type of malfunction is similar to what is currently postulated (i.e., loss of SRW cooling resulting in a failure of an EDG). Based on its review, the staff found that tha probability of malfunction of the 2A EDG due to its dependence on the opera'.>ility and SRW cooling from the 1B EDG would increase slightly, but is acceptable for the limited time requested.

2.2 Connection of 2B EDG to Temporary Cooling System The third USQ is for a temporary cooling system for the 2B EDG that would replace the cooling i

provided by SRW. The normal supply of cooling water for the 2B EDG is safety-related and is seismically designed. The proposed temporary cooling system is not safety-related,

,eismically designed, or tomado-missile protected, which increases the probability of a malfunction since it is more likely to fail than a safety-related, protected system. It consists of a cooling tower and its associated pumps, piping, and controls. The cooling tower is a skid-mounted, mechanical draft coolirig tower rated for approximately 1015 million BTU /hr. It is constructed of stainless and galvanized steel, and it has three fans to provide the airflow

, through the cooling tower. Makeup water is provided from a pre treated water tank and is gravity-fed into the cooling system. Part of the piping for the pre-treated water tank is underground. The cooling system loads would be energized at time, t=0 seconds, when the I

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4 generator breaker is closed to ensure that the cooling system would be available upon start of the 2B EDG.

The events that would most likely cause the temporary cooling system to fail would be seismic events and severe weather. The licensee concluded that the use of the temporary cooling system is acceptable since significant seismic events are not probable in this area of the east coast and severe weather is not highly probable during the time that the temporary cooling system would be in use. The licensee stated that the cooling tower would have two pumps to improve its reliability and it would be positioned close to the auxiliary building with the makeup piping mostly underground to help protect the cooling tower and its piping from severe weather events.

Based on its review, the staff found that the probability of malfunction of the temporary cooling system would increase slightly, but is acceptable for the limited time requested since the probability of natural phenomenon affecting the system is low, the licensee has taken both physical and reliability measures to prevent severe weather from affecting the system, and because the 2B EDG would continue to operate as before without any operator action required for the cooling tower to perform its function.

The fourth USQ exists because the piping from the proposed cooling tower to the 2B EDG would not be safety-related and could rupture, causing a flood in the 2B EDG room, which would increase the probability of a malfunction due to the increased probability of flooding in the room. The licensee evaluated the flooding that could possibly occur due to a failure of ;he non-safety-related, non-seismic, temporary cooling water piping to the 28 EDG. The licenae concluded that if the entire contents of the cooling system were introduced into the room, the subsequent flood height would be enveloped by other postulated flooding events and would not impact safety-related components in the room. Based on its review, the staff found that the probability of malfunction due to the increased probability of flooding in the 2B EDG room would increase slightly, but the consequences of a flood would be acceptable since the ECG room is enveloped by other postulated flooding events which do not impact safety-related components within the room.

2.3 ElectricalPower The offsite power system for Calvert Cliffs consists of three 500 kV transmission lines that meet in a common switchyard, and a separate 69 kV transmission line that connects to 13 kV buses. The three 500 kV lines are independent of each other and are mounted on weather-resistant towers along a single right-of-way. The 69 kV transmission line comes into a separate substation on the site along a different right-of-way and is buried for n,ost of its length on BGE property.

To reduce the possibility that maintenance activities could contribute to a loss-of-offsite power (LOOP), the licensee proposed to restrict activities on three of the four offsite transmission lines until the Unit 2 EDGs are retumed to their normal configuration. In a phone conversstion with the licenses on October 23,1998, the staff informed the licensee that this was not acceptable and required that no maintenance be performed on any transmission line or in the switchyard to avo!d any transient that could create a LOOP to the plant and unnecessarily ci allenge the EDGs. Subsequently, in a letter dated December 4,1998, the licensee agreed j

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to restrict work in the switchyard and on all of the transmission lines during the replacement of the Unit 2 SRW system heat exchangers.

The licensee anticipates that all of the work on the SRW heat exchanger replacements will be completed in March and April, before the time of the year when tomados and hurricanes are at their highest frequency for the Calvert Cliffs site. The above will prevent the possibility of

. losing offsite power due to bad weather. The licensee also stated that prior to removing each associated train of the SRW system from service, both Unit 2 EDGs will have been removed j

from service, mooified, tested and retumed to operable status.

Additionally, Calvert Cliffs has a station blackout (SBO) EDG OC, which is electrically isolated

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from the ESF buses by two breakers in series and a Class 1E disconnect switch. The SBO EDG allows for manual alignment to any one safety-related train in either unit via a Class 1E ESF bus. To ensure that backup power is available to any of the safety-related buses, the licensee stated that the SBO EDG will not be taken out-of-service for planned maintenance and will remain available to be connected to any of the safety-ralated buses during the repair period.

Based on the above, the staff concludes that the above measures taken by the licensee would minimize the possibility of losing offsite power during the replacement of the SRW system heat exchangers, and is acceptable.

2.4 Risk Assessment The licensee performed a quantitative probabilistic safety assessment (PSA), and qualitative assessment, of the risk aspects for the planned SRW heat exchanger replacement. The

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licensee's assessment considered the risk impact on Unit 1 which will remain at power during the work, and on the shutdown Unit 2. Ultimately, the new SRW heat exchangers are expected to decrease risk due to decreased unavailability. A potential decrease of approximately 1.4E-5/yr in the baseline Core Damage Frequency (CDF), based on decreased SRW heat exchanger unavailability estimates, was estimated by the licensee.

f The Calvert Cliffs PSA model baseline CDF from both intemal and extemal events is 3.1E-04/yr. Given the attemate cooling ccafigurations, the licensee conservatively estimated that the incremental conditional core damage probability (ICCDP) over a 40.25 day work evolution period to be 4.75E-6 for Unit 1. This estimate is based on the Unit 2 2A and 2B EDG unavailability for cooling supply modification and other work such as inspections, the 2A EDG

. cooling dependency on both the 1B EDG and the No.12 SRW subsystem, and the 2B EDG cooling dependency on the cooling tower. When temporary diesel air compressors at Unit 2 are considered in the updated Calvert Cliffs PSA model, the ICCDP is estimated to be appronmately 1.3E-6. The staff believes the ICCDP for this TS amendment request is reasonably low since the request is for one-time nnly and the licensee will have a number of measures in place to minimize risk during the Unit 2 work as discussed below. Furthermore, the SRW heat exchanger replacement is expected to result in a significant risk benefit.

Based on the Calvert Cliffs PSA model, risk insights indicate that a dual Unit LOOP is an important consideration while the planned work is in progress. The licensee's Unit 1 risk assessment of he impact of the Unit 2 work indicates that dual Unit LOOP events caused by a I

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hurricane and a Unit 2 steam generator feedwater turbine pump fire are dominant risk l

contributors. Calvert Cliffs has four offsite power feeds: three 500kv lines and one 69kv line.

Loss of all three 500 kV lines will result in a dual Unit LOOP. The frequency of a dual Unit LOOP in the Calvert Cliffs PSA model is relatively high. Accordingly, the licensee has taken steps to decrease the likelihood of a LOOP during the SRW heat exchanger replacement work. These steps include restricting maintenance on all four offsite transmission lines, and performing the Unit 2 work during favorable weather conditions in March and April 1999, when l

cold weather effects on transmission lines are minimel. Furthermore, since the licensee does not have direct control over Chalk Point, which is operated by Potomac Electric Power Company (PEPCO) and provides power to one of the 500 kV transmission lines, the licensee is requesting of PEPCO that no testing or maintenance on the transmission line be performed during the SRW heat exchanger replacement work. A similar request is being made to Southem Maryland Electric Cooperative, which provides 13 kV power from a 69/13kV substation.. These practices decrease the likelihood of a LOOP, and, therefore risk to the Units 1

during the planned work evolution.

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in addition to restricting maintenance on all four offsite transmission lines, the licensee will take the following measures to further reduce risk during SRW heat exchanger replacement work: (1) no outage maintenance will be performed on EDG 2A during reduced inventory periods at Unit 2, (2) SBO Diesel Generator OC will not be taken out-of-service and will remain available to be connected to any of the safety-related buses, and (3) a temporary diesel air compressor will be connects:) to the Unit 2 non-safety-related compressed air system, which can also be cross-connected o Unit 1 in the event of a loss of air pressure. A second, temoorary diesel air compressor in manual start will be installed as a back-up.

The staff's review of the dominant CDF accident sequences, given the altemate cooling configurations, finds that the Calvert Cliffs PSA model permits a detailed probabilistic assessment of the risk associated with this one-time TS amendment. Further, the staff finds that the licensee has gained important detailed insights of the risk to Unit 1 associated with the Unit 2 work. Insights from the dominant accident sequences generated by the Calvert Cliffs PSA model indicate that the decay heat removal role of the auxiliary feedwater (AFW) system is important during the Unit 2 work. Insights further indicate that the risk to Unit 1 is greatest during periods when the No.12 SRW header is taken out-of-service and 2B EDG is using the cooling towu, and also when the 2B EDG is out-of-service and the 2A EDG is using the No.12 SRW header.

Due tc the Unit 2 SRW Pump Room doors being open during the SRW heat exchanger replacement, the potential exists for a flood to propagate into the auxiliary building which contains safe shutdown equipment. The staff finds that the licensee performed a thorough analysis of this flooding concem, and evaluated actions to minimize risk to both Units from flooding during the work evolution period.

The licensee's risk evaluation process for Unit 1 work uses procedure MN-1-202,

• Conduct of Plant Work Control." Proposed tests and maintenance evolutions are evaluated for potential i

degradation of components and the potential for increases in initiating event prcbabilities.

Further, potential plant configurations are evaluated with the Calvert Cliffs PSA model. Thus, the staff notes that prior to and during the work evolution period at Unit 2, the licensee has a process in place to evaluate the Uret i risk on an on-going basis.

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.a-y 7-At the shutdown Unit 2, SRW heat exchanger work is not planned during periods of high decay heat and periods of reduced reactor coolant system inventory, which are potentially risk significant plant operational states. To address shutdown risk, the licensee performed a j

qualitative assessment of the plant operational states impacted by the work. At all times at least one of the Unit 2 EDGs will be operable, but with degraded reliability due to the attemate i

cooling configurations for these diesels. During reduced inventory, both Unit 2 EDGs are planned to be available. In addition, the SBO EDG OC will be available, the reliability of which is not impacted by the planned Unit 2 work. Also, as discussed above offsite power will be protected. Furthermore, the licensee evaluates the outage schedule, and any subsequent changes, to ensure minimum essential equipment is available per procedure NO 103, " Conduct of Lower Mode Operations." Thus, while performing this work, the staff notes that the licensee will take steps to keep reliable e' site and onsite power available and will i

continuously evaluate shut down risk and 'ake necessary actions to minimize risk.

1 The staff finds that the potential benefit of the new SRW heat exchangers, the PSA insights, the measures established to minimize risk, and the licensee's risk evaluation processes

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support the licensee's one-time TS amendment.

Based on the above, the staff concludes that approval of the licensee's application for amendment, based on the potential benefit of the new SRW heat exchangers coupled with the licensee's risk evaluation and measures established to minimize risk and increase the availability of the EDGs during the replacement of the Unit 2 SRW heat exchanger replacement, is appropriate. Therefore, the !:censee's request for a one-time TS change to the Unit 2 Aases for TS 3.8.2 is acceptable.

3.0 STATE CONSULTATION

in accordance with the Commission's regulations, the Maryland State official was notified of the proposed issuance of the amendment. The State official had no comments.

4.0 ENVIRONMENTAL CONSIDERAliON

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l The amendment changes a requirement with respect to installation or use of a facility component located within the restricted aren as defined in 10 CFR Part 20. The NRC staff has determined that the amendment involves no significant increase in the amounts, and no

. significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure. The Commission has previously issued a proposed finding that the amendment involves no significant hazards consideration, and there has been no public comment on such finding (63 FR 45523).' Act ordingly, the amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(g). Pursuant to 10 CFR 51.22(b) no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendment.

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5.0 CONCLUSION

The Commission has concluded, based on the considerations discussed above, that: (1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public.

Principle Contributors: V. Ordaz D. O'Neal O. Chopra Date: March 8,1999

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