ML20196B480

Forwards Response to GL 98-02, Loss of Rc Inventory & Associated Potential for Loss of Emergency Mitigation Functions While in Shutdown Condition

ML20196B480
Person / Time
Site:	Prairie Island
Issue date:	11/24/1998
From:	Sorensen J NORTHERN STATES POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
GL-98-02, GL-98-2, NUDOCS 9812010109
Download: ML20196B480 (13)

Text

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Northern States Power Company

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Prairie Island Nuclear Generating Plant 1717 Wakonade Dr. East l

j Welch, Minnesota 55089 i

l November 24,1998 10 CFR 50.54(f)

Generic Letter 98-02 U S Nuclear Regulatory Commission i

Attn: Document Control Desk Washington, DC 20555 PRAIRIE ISLAND NUCLEAR GENERATING PLANT l

Docket Nos. 50-282 License Nos. DPR-42 l

50-306 DPR-60 Response to GL 98-02:

Loss of Reactor Coolant inventory and Associated Potential for Loss of i

Emergency Mitigation Functions While in a Shutdown Condition 7

/

On May 28,1998, the Nuclear Regulatory Commission issued the referenced generic letter to request that addressees (1) assess the susceptibility of their residual heat removal (RHR) and emergency core cooling (ECCS) systems to common-cause failure as a result of reactor coolant system (RCS) draindown while in a shutdown condition, and (2) submit certain information, pursutat to 10 CFR 50.54(f), concerning their findings regarding potential pathways for inadvertent RCS draindown and the suitability of surveillance, maintenance, modification, and operating practices and procedures regarding configuration control during reactor shutdown cooling.

1 Addressees were specifically required to perform (within 180 days):

(1) an assessment of whether the plant emergency core cooling system includes certain design features, such as common rump suction header, which can render the systems 1

i susceptible to common-cause failures; and if this susceptibility is found, (2) prepare, with consideration of plant specific design attributes, a description of j

features of the Appendix B quality assurance program that provide assurance that the safety-related functions of the RHR system and ECCS will not be adversely affected by i

activities conducted at hot shutdown.

( }.[. I d 9812010109 981124 C PDR ADOCK 05000202 P

PDR E

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NORTHERN STATES POWER COMPANY November 24,1998 Page 2 '-

- The attachment to this letter provides the required response for the Prairie Island

' Nuclear Generating Plant. In this letter we have made one new Nuclear Regulatory

- Commission commitment indicated by the text in italics. Please contact Jeff Kivi (651-388-1121)if you have any questions related to this letter, t

~ =1 Joel P. Sorensen Plant Manager -

Prairie Island Nuclear Generating Plant c: Regional Administrator-Region Ill, NRC u

Senior Resident Inspector, NRC j

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NRR Project Manager, NRC J E Silberg l

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Affidavit,

i Attachments: Response to Generic Letter 98-02 i

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UNITED STATES NUCLEAR REGULATORY COMMISSION NORTHERN STATES POWER COMPANY PRAIRIE ISLAND NUCLEAR GENERATING PLANT DOCKET NO.

50-282 50-306 GENERIC LETTER 98-02: Loss of Reactor Coolant Inventory and Associated Potential for Loss of Emergency Mitigation Functions While in a Shutdown Condition Northern States Power Company, a Minnesota corporation, with this letter is submitting information requested by NRC Generic Letter 98-02.

This letter contains no restricted or other defense information.

i NORTHERN STATES POWER COMPANY BY Joei P. Sore'nsen Plant Manager Prairie Island Nuclear Generating Plant On this 2M day of Alo V W bW

/ 9 7 ? before me a notary public in and for said County, personally appeared Joel P. Sorensen, Plant Manager, Prairie Island Nuclear Generating Plant; and being first duly sworn acknowledged that he is authorized to execute this document on behalf of Northern States Power Company, that he knows the contents thereof, and that to the best of his knowledge, information, and belief the statements made in it are true and that it is not interposed for delay.

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DAL.E M. VINCENT 30TARY Pustc.WinNE8074 "M AccUNIY

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Response to Generic Letter 98-02 i

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Attachment November 24,1998 l

Page 1 RESPONSE TO GENERIC LETTER 98-02 Statement of Susceptibility Prairie Island Nuclear Generating Plant (PINGP) Units One and Two have suction piping that is common to both the Safety injection (SI) and the Residual Heat Removal

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(RH) systems, and are, therefore, considered to be susceptible to the potential of steam voiding affecting both the high head and low head portions of the ECCS.

l Evaluation of Susceptibility Five potential flow paths from the Reactor Coolant System (RCS) to either the RH or Si 4

systems, and then to the common ECCS suction piping were identified:

1. From the RCS hot legs RH suction supplies to the RWST

2. From the RH discharges to the reactor vessel or an RCS cold leg

3. From the Si discharges to the RCS cold legs and reactor vessel

4. From the Chemical and Volume Control System -(VC) letdown line to the RH system and then to the common ECCS suction piping

5. From the RH discharge to the SI pump suction One flow path from the RH discharge to the Containment Spray pump suctions was also identified. The CS suction from the RWST and mini-flow recirculation piping is i

separate from the piping that is common to the ECCS pumps. None the less, this flow path was also evaluated.

Each of these five potential flow paths was evaluated for:

passive barriers in place to prevent flow such as, check valves or Motor Operated e

Valves (MOV's) that are norrnally closed with their power supply breakers locked open electrica! interlocks to prevent critical MOV operation e

applicability of ASME Section XI testing to the critical valves in the flow path activities conducted at temperatures above cold shutdown that could affect the e

l position of critical MOV's the availability of valve position indication on the main control board for the critical e

MOV's applicability of the PINGP independent verification program to the critical MOV's administrative controls, management expectations and operator training regarding e

procedure compliance g198-02. DOC

Attachment November 24,1998 Page 2 operator training on the activities conducted at temperatures above cold shutdown e

that could affect the position of critical MOV's applicability of the PINGP process that controls the bypassing of interlocks e

applicability of the PINGP process that controls the positioning of certain ECCS e

valves and electrical supply breakers Recults of Evaluations Evaluations for the PINGP concluded that flow paths one, two, three and four have extremeiy robust defenses, such that steam voiding of the common ECCS suction piping through these flow paths is not credible. The PINGP evaluation further concluded that flow path five has robust defenses, such that steam voiding of the common ECCS suction piping through these flow paths is highly unlikely. The robustness of a barrier in MOV testing procedures is being enhanced to improve the overall robustness of the defenses for flow path five.

Summary of Individual Evaluations Flow path one -from the RCS hot legs RH suction supplies to the RWST:

When the RH system is not in service to cool the RCS (lined up for safeguards operation), flow path one would require leakage, equivalent to a 2 inch diameter pipe, through two normally closed MOV's plus reverse flow, also equivalent to a 2 inch diameter pipe, through one check valve in order to affect the common ECCS suctions. The MOV's and check valves are functionally tested in accordance with the PINGP ASME Section XI in service testing program. These MOV's have valve position indication on the main control board. These MOV's and their associated power supply breakers are also included in the PINGP Independent Verification program.

When the RH system is being used for shwlown cooling, flow path one would require leakage, equivalent to a 2 inch diameter pipe, through one normally closed MOV plus reverse flow, also equivalent to a 2 inch diameter pipe, through one checi. valve in order to affect the common ECCS suctions. Therefore, it is concluded that steam voiding of the common ECCS suction piping through this flow path is not credible.

Flow path two - from the RH discharges to the reactor vessel or an RCS cold leg: When the RH system is not in service to cool the RCS (lined up for safeguards operation), flow path two would require reverse flow (leakage),

equivalent to a 2 inch diameter pipe, through either four check valves in series or through one normally closed MOV and three check valves in series in order to affect the common ECCS suctions. The check valves are leak tested in g198-02. Doc

-.- = _

Attachment November.24,1998 i

Page 3 accordance with the PINGP ASME Section XI in service testing program. The MOV has valve position indication on the main control board. The MOV and its power supply breaker are included in the PINGP Independent Verification program.

l l

When the RH system is being used for shutdown cooling, flow path two would l

require leakage, equivalent to a 2 inch diameter pipe, through one normally l

closed MOV plus reverse flow, also equivalent to a 2 inch diameter pipe, through one check valve in order to affect the common ECCS suctions. Therefore, it is j

concluded that steam voiding of the common ECCS suction piping through this flow path is not credible.

l Flow path three -from the Si discharges to the RCS cold legs and reactor vessel: Flow path three would require reverse flow (leakage), equivalent to a 2 inch diameter pipe, through either four check valves in series or through one normally closed MOV and four check vaives in series in crder to affect the common ECCS suctions. The MOV has two independent vaive position indications on the main control board. The MOV is included in the PINGP l

Independent Verification program. Therefore, it is concluded that steam voiding I

of the common ECCS suction piping through this flow path is not credible.

Flow path four - from the Chemical and Volume Control System (VC) l l

letdown line to the RH system and then to the common ECCS suction l

piping: Flow path four contains the letdown orifices, which are less than 2 inches in diameter and, therefore, need not be considered per the guidance of l

the Generic Letter. Additionally, flow to the RH suctions would require reverse l

flow (leakage), equivalent to a 2 inch diameter pipe, through two check valves in series in order to affect the common ECCS suctions. Therefore, it is concluded that steam voiding of the common ECCS suction piping through this flow path is l

not credible.

Flow path five - from the RH discharge to the SI pump suction: This flow path is used neither during power operation nor during hot shutdown. When RH is in service for shutdown cooling, flow path five would require that three conditions to exist simultaneously on one train of ECCS for steam binding in the i

common Si suctions to occur. These conditions are: (1) high RH heat exchanger j

outlet temperature, (2) RH to Si suction cross-connect valve open, and (3) SI suction MOV open.

Each RH to Si suction cross-connect MOV is interlocked such that the MOV cannot be opened unless its associated Si suction MOV is closed and RCS pressure is <210 psig (nominal). Each cross-connect MOV normally has its gl98-02. DOC 4

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Attachmint November 24,1998 Page 4 power supply breaker locked open. Open/ closed valve position indication for the cross-connect MOV's is available on the main control board and is functional when the breakers are closed. Separate valve OPEN indication is also provided on main control board. Standing operating procedures or maintenance procedures control operation of these valves. Operators are trained in use of the operating procedures and procedure compliance. The maintenance procedures that may operate these valves are associated with MOV testing and inservice testing. These maintenance procedures are typically performed during a refueling outage and are implemented via the Work Order process. The Work Order process requires isolations and other initial conditions to be specified and reviewed prior to approval. The Outage Planning Group schedules the work.

j The barriers in place to prevent the three conditions from existing simultaneously are sufficiently robust that steam voiding of the common ECCS suction piping through this flow is highly unlikely. MOV testing Work Order procedures for these MOV's are being converted to repetitive task Work Orders. This will eliminate the need to write new work orders each time a valve is to be tested,.

thus insuring consistency in work orders from outage to outage, which will further insure that conditions that could lead to steam binding will be precluded.

The CS suction from the RWST and mini-flow recirculation piping: This flow path is separate from the piping that is common to the ECCS pumps. This flow path is neither used during power operation nor used at hot shutdown. Flow through this path wculd require reverse flow (leakage) equivalent to a 2 inch diameter pipe through a check valve and through the normally closed cross-connect MOV. Each cross-conneci valve normally has its power supply breaker locked open. Open/ closed valve position indication for the cross-connect valves (located on the main control board)is functional when the breakers are closed.

l The check valves are functionally tested in accordance with the PINGP ASME Section XI in service testing program. The 2 inch manual valves in the mini-flow I

recirculation lines are normally blocked and tagged closed and are on the plant's independent verification list. Due to the robustness of the barriers in this flow path plus the fact that the piping connections to the RWST are separate from the ECCS suction piping it is concluded that steam voiding of the common ECCS l

suction piping through this flow path is extremely unlikely.

1 g198-02. Doc n'

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Attachment November 24,1998 Page 5 RH Pump Nae.

Notes TRAIN B Notes To RWST 1,2,3.4.57,8,9 1.2.4.5.7,8,9 k

d.5.6.7 St Note 7 RCS p a. yen,K -A w m k

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NJtes Notes Note 7 1,2,5,.4.5,7,8,9 1,2.4,5,7,8,g 4.5,6.7 TRAIN A RH Pump Notes 1 This valve is rKrmally closed dunng pcmer operation 2 This valw is interlocked to prewnt opening if RCS pressure >425psig 3 The breaker for this vane is normally locked open 4 This valw is on the independent vanfication hst 5 This valw has position indication on the main control board when breaker is closed 6 This vale has additional vale position indication on the main contrd board 7 This valw is included in the ASME XI IST program (functx:nalty tested) 8 This value's associated power supply breaker is on the independent venfication hat 9 This valw automatically closes if RCS pressure >600psig FLOW PATH ONE - FROM RCS HOT LEGS THROUGH RH TO RWST SlfAPLIFIED DIAGRAM 9198-02 DOC l

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Attachment November 24,1998 Page 6 From Si Accursddw To RWST Nan'=

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2 This imho e interlocked to prowent opening i RCS pressure >425ps 0 il j 3 The treeker far trus waive is namisNy lacked open To St Pump 4 The valve is on theindependent verfmetson hat

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Suctions 5 The vehe has position indmetusi on tha man contrd board when treeker is

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system ' V3 7 The weNo is includeo in tie ASME 10 IST program (functonefy tested) g 8 The vehe's esaN power s@ trusker is on the independed varication bst

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Punps Notes aL JL 1 This veno as normally closed dimng power operation From RH Heat 2 TNs veno is interlocked to prevent opening K RCS pressure >425psig 3 The tweaker for this veno is normany locked open Exchangers j

4 TNs vane is on the independait vertfication list 5 TNs veno has posihon indicaban on the main contrd board when trNiker is i

closed 6 This wilve has adcstional vane position indcation on the mant contrd board 7 This veNe is induded in the ASME XI IST program (functionally tested)

B TNs ##s associated pcwur supply breaker is on tie kulependait verification list 9 TNs veNe is included in lhe ASME Xi IST program (leak tested)

FLOW PATH THREE - FROM St COLD LEG INJECTION LINES THROUGH St TO RWST SIMPLIFIED DIAGRAM g198-02. DOC

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Attachment November 24,1998 Page 8 To RWST and St Pumps Notes E]

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9198-02. DOC I

Attachment November 24,1998 Page 9 Notes 1 A,5.0,7,0 From RWST w

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3 The breaker for this valve is normally locked open 4 This valve is on the independent verification list

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6 This valve has additional valve position indication on the main control s valve is included in the ASME XI IST program (functionally t.

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pump suction valve is closed j

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