ML20206S709

Safety Evaluation on Util 850426 Response to Open Items Re Generic Ltr 81-14, Seismic Qualification of Auxiliary Feedwater Sys (Afws). Reasonable Assurance Exists That Afws Will Perform Required Safety Function Following SSE

ML20206S709
Person / Time
Site:	Point Beach
Issue date:	09/16/1986
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20206S689	List: ML20206S686 ML20206S709 ML20206S749
References
GL-81-14, TAC-43669, TAC-43670, NUDOCS 8609220351
Download: ML20206S709 (7)

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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SEISMIC QUALIFICATION OF THE AUXILIARY FEEDWATER SYSTEM POINT BEACH NUCLEAR PLANT UNITS 1 AND 2 Introduction Since~the accident at Three Mile Island, attention has been focused on the ability of pressurized water reactors to provide reliable decay heat removal. While it is recognized that alternate methods may be available to remove decay heat following transients or accidents, heat removal via the steam generators is the first choice for accomplishing a safe shutdown of the plant. Therefore, there should be reasonable E.ssurance that the auxiliary feedwater system (AFWS) can withstand the postulated safe shutdown earthquake (SSE).

To address this concern, the NRC developed and initiated Multiplant Action C-14, " Seismic Qualification of Auxiliary Feedwater Systems." The objective of this plan is to increase, to the extent practicable, the capability of those plants without seismically qualified AFWS to withstand earthquakes up to the SSE level. This program was implemented with the issuance of NRC Generic Letter 81-14 dated February 10, 1981.

Wisconsin Electric Power Company, licensee for Point Beach Nuclear Plant, Units 1 and 2 responde'd to Generic Letter 81-14 by letters dated July 16, 1981, May 4 and December 15, 1982, February 11, 1983, January 31 and December 4, 1984. The staff issued the results of its initial review on January 16, 1985 in the form of a status report with attached Technical Evaluation Report (TER) prepared by our contractor, Lawrence Livermore National Laboratory. The j

licensee responded to open items contained in the status report by letter dated April 26, 1985. Additionally, a site / corporate headquarters visit was conducted by members of the NRC staff and our consultant, Brookhaven National Laboratory on November 20, 1985 to resolve two areas of concern, the seismic resistance of the containment facade structures and the consequences of rupture of the non-seismic condensate storage tanks. Our review of the licensee's responses is the subject of this evaluation.

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4 Evaluation s

The enclosed TER was prepared for us by our consultant, Brookhaven National Laboratory, as part of our technical assistant contract program. The TER provides their technical evaluation of the licensee's conformance to the requirements of Generic Letter 81-14 with respect to two areas, the seismic resistance of the containment facade structures and the consequences of rupture of the non-seismic condensate storage tanks. We have reviewed our ~

consultant's technical evaluation and the additional information the licer3seE' submitted on April 26, 1985 to address the concerns in the staff's January;16, 1985 status report and attached TER. Our summary findings are described [ '

below. ,

Pumps and Motors The Point Beach Nuclear Plant auxiliary feedwater system utilizes two steam driven pumps and two electric motor driven pumps for the two units. Each

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unit has one steam driven pump and both units share the two electric motor driven pumps. The auxiliary feedwater pumps including the support systems are qualified to withstand the effects of the safe shutdown earthquake. The auxiliary.feedwater pumps are located in the control building which is aiso designed to withstand the effects of the safe shutdown earthquake.

Piping ', -

The licensee has stated that nine branch lines were not originally designed y to withstand the effects of a safe shutdown earthquake. These branch lines

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are identified by the numbers 20 through 28 and are described as follows:

1. Branch piping numbers 20 and 21 connect the AFWS to the Units 1 and 2 condensers respectively.

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2. Branch piping number 22 is a 1.5-inch connection between the AFWS and the waste and blowdown evaporator distillate processing system.

3. Branch piping number 23 is a 4-inch connection between the AFWS and the lM heating boiler feed pump.

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'4. Branch piping number 24 is a 2-inch diameter connection that provides a f source of water to the turbine plant chemical addition tanks.

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5. Branch piping number 24 is a 3-inch diameter connection between the AFWS

~; and the mixed bed demineralizer in the makeup water treatment system.

6. Branch piping numbers 26, 27 and 28 are condensate return lines that connect the steam heating condensate pumps to the AFWS.

In the submittal dated April 26, 1985, the licensee identified two

, seismically qualified isolation valves in series for each of the branch lines; therefore, we conclude that the non-seismic branch lines 20 through 28 are properly isolated from the AFWS.

The licensee also identified the 1.5-inch recirculation pipe for each of the four AFWS pumps and the discharge piping of each pump as not being adequately

, supported. The licensee modified these branch connections for each line in

,otder to provide seismically qualified connections up to the second isolation g valve in series.

Valves / Actuators The only valves in the AFWS that are not seismically qualified are the valves 3 that' isolate the nonseismic branch lines from the safety-related portion of

[% s the AFWS. These valves are addressed in the section on Piping.

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Power Supplies The components of the power supplies to the auxiliary feedwater system are qualified to withstand the effects of the safe shutdown earthquake. In order to qualify the AFWS power supply to withstand the effects of a safe shutdown earthquake, the licensee upgraded the battery racks and the cable conduits in

~ cubicles P38A and P38B to withstand the effects of the safe shutdown earthquake.

Water Sources The condensate storage tank, which is the primary water source of the auxiliary' feedwater system, is not qualified to withstand the effects of the safe shutdown earthquake. Each non-seismic tank contains 180 tons of water and is mounted on the roof of the diesel generator building with 3/4-inch diameter bolts. The proximity of the walls of the adjacent buildings preclude impact of these tanks on the diesel generator building roof from potential tipping (see Fig.1 BNL report). Concerns with regard to flooding of safety-related components and equipment were investigated and dismissed for all adjacent areas, except the air intake to the diesel generator building. Failure of the condensate storage tanks with subsequent induction of water into the air intake could direct the flow of water over the control panels of the diesel generators. The licensee has indicated mcdifications are in progress to protect the control panels from this concern. The licensee has agreed to report the completion of the modifications and provide

• a confirmatory analysis that the modifications adequately address the above Concern.

The service water system is a seismic Category I water source but must be manually switched over to provide water for the auxiliary feedwater system.

The licensee has installed an automatic pump trip on low suction pressure in the event of loss of the primary AFW source. An alarm is also annunciated

in the control room during loss of the primary AFW supply. fhe licensee has demonstrated that adequate time would be available to perform the manual switchover to the service water system following loss of the-condensate storage tanks during a seismic event. The staff finds this acceptable.

Initiation / Control System _s The licensee has reviewed the initiation / control system and initially identified the following components that are not designed to withstand the effects of a safe shutdown earthquake:

1. Conduits D0 1-2, 2-4001, 1-4000 and 1-4001;

2. Conduits above panels D12, D13 and D14;

3. Four safeguard motor control center (1832, 1842, 2B32 and 2B42).

In a submittal dated April 26, 1985, the licensr.e verified that the initiation / control system components have beer upgraded to withstand a safe shutdown. earthquake.

Structures The licensee has stated that the containment, auxiliary building (up to elevation 66'), the pipeways, and the control building were designed as seismic Category I structures. The licensee has also stated that the turbine building was seismically analyzed during original plant design and found capable of withstanding SSE loads.

-The facade structures are steel frame structures which enclose the containment building and house the Auxiliary Feedwater Pump Urive Steam and Main Steam lines between the Auxiliary Building, North and South Wing

and Containment Buildings at the Point Beach site. The facade structures include steel columns for vertical support, horizcntal steel members with attachment to the containment or auxiliary buildings and metal siding as an enclosure member (see Fig. 2 BNL report).

One AFW pump steam supply line for each unit branches off a main steam line at the containment structur'e exterior and is routed through the facade into the auxiliary building. The other steam supply line for each unit is routed from the facade through the north or south wing prior to entering the auxiliary building. There the two lines from either unit join and continue through the control building to the AFW pumps.

The facade structures were designed for a tornado wind load of 360 mph, assuming one third of the siding remaining intact. The liccrsee has determined that the shear loads resulting from the postulate seismic event (SSE) are smaller than those resulting from the postulated tornado event.

The staff and our consultant have audited these calculations and have found them acceptable. However, the staff and our consultant determined a need to evaluate these structures for the condition where the containment and auxiliary buildings moved out of phase during the seismic event. This analysis was performed by BNL utilizing the SAP V computer ccde, as documented in their TER (attached). The results indicate that the controlling stresses are small enough to preclude collapse of the facade structures during the SSE seismic event.

The auxiliary building central superstructure was originally designed for tornado wind loading consistent with the facade structures. However, the superstructure was additionally analyzed for seismic loads and found capable.

of withstanding an SSE. At least three sioes of the wing superstructures have been analyzec for SSE or designed for loads which can be reasonably expected to envelop SSE loads. However, even if the wing superstructures would not withstand an SSE, at least one steam supply line to an AFW

turbine-driven pump for each unit is routed through structures capable of withstanding SSE loads. Should the other steam supply lines be lost (considering the north and south wings as seismic Category III), the failed lines could be isolated, by closing valves IMOV-2020 and/or 2M0V-2019 from the control room. These valves are located in the auxiliary building central which is seismic Category I. Further, there is no loss of available steam to the supply lines considering loss of the main steam lines in the north or south wings since the main steam isolation valves are located upstream in the facade structures.

The staff finds that the design for the structures housing AFWS to provide adequate protection against a seismic event and is, therefore, acceptable.

Walkdown of AFWS System The walkdown conducted by the licensee was performed for both the seismically and non-seismically qualified components of the AFWS.

Conclusions Based on the licensee submittals, we conclude that the Point Beach AFWS provides a reasonable assurance that it will perform its required safety function following a safe shutdown earthquake.

Principal Contributors:

T. Colburn P. Hearn F. Rinaldi -

Date:

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