NPL-97-0751, Special Rept:On 971023,low Temp Overpressure Protection Sys Operation Occurred.Caused by Starting Reactor Coolant Pump w/water-solid Reactor Coolant Sys.Operating Personnel Will Be Briefed on Event

Special Rept:On 971023,low Temp Overpressure Protection Sys Operation Occurred.Caused by Starting Reactor Coolant Pump w/water-solid Reactor Coolant Sys.Operating Personnel Will Be Briefed on Event

ML20199J009
Person / Time
Site:	Point Beach
Issue date:	11/21/1997
From:	Dante Johnson WISCONSIN ELECTRIC POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NPL-97-0751, NPL-97-751, NUDOCS 9711280022
Download: ML20199J009 (3)

Text

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.q Wisconsin

. Electnc POWER COMPANY -

Point Beoch Nuclear Pkint (920) 755 2321 6610 Nuclear Rd., Two Rtvers. WI $4241

NPL 97-0751 November 21,1997 Document Control Desk '

U.S. NUCLEAR REGULATORY COMMISSION Mail Station PI-137 Washington, DC 20555 1.adies/ Gentlemen:

- DOCKET 50-266 LOW TEMPEllATURE OVERPRESSUIE JULOIECTION. SYSTEM OPERATIQ3 EQINT IlEACll NUCLIL\R PLANT. UNIT 1

'On October 23,1997, an evolution being performed at the Point Beach Nuclear Plant, Unit 1, resulted in the operation of the Low Temperature overpressure Protection System. This occurrence resulted in the momentary p lifting of Pressurizer Power Operated Relief Valve (PORV) 431C which was aligned fbr operation in the low tempermure overpressure protection mode in accordance with Technical Specification 15.3.15.

Attached is a special report for this occurrence as required by Technical Specification 15.6.9.2.C. This Specitication requires a special report to the NRC in the event that the evaluation of the occurrence determines that an overpressurization incident could have occurred had the Low Temperature Overpressure Protection System not been operable. As required by Specification 15.6.9.2.C, this report describes the circumstances .

initiating the transient and corrective actions identified to prevent recurrence. This report summarizes a root cause evaluation of this occurrence and recommended corrective actions.

New commitments that have not been previously docketed are identified ' italics.

If you have any questions regarding the event and our report, please contact us.

Sincerely, r[ % h/r Douglas F. Johnson Manager - Regulatory Services & Licensing 4{b;7

/

Attaclunent 9711290022 971121 PDR ADOCK 05000266.

cc: NRC Resident inspector IE,5EER,l,REl.l ,

. NRC Regional Administrator A muw.,awww twoavatar

Attachment to NPL 97-0751 ,

• ' Page1 DOCKET 50-266-LOW TEMPERATURE OVERPRESSURE J PROTECTION SYSTEM OPERATION-POINT BEACH NUCLEAR PLANT, UNIT I At approximately 1230 on October 23,1997, Unit I operators were in the process of completing OP 4A, "Fihing and Venting Reactor Coolant System." OP 4A directed the operators to OP 4B, " Reactor Coolcnt Pump Operation," to start a reactor coolant pump (RCP). OP-4B has two sections for starting an RCP. OP-4B contains separate directions for starting an RCP dependent on whether the Reactor Coolant System (RCS) loops have previously been filled and vented and for when starting an RCP is necessay for filling and venting an RCS loop. In this case the RCS loops were filled and vented. Unit I was at approximately 350 psig primary pressure,127 F primay temperature, with the RCS in a water-solid condition.

' Between 1230 and 1349, preparations were made to start the pump. These preparations included a pre- '

job briefinvolving the Unit 1 Control Operator, Operating S'ipenisor, third Reactor Operator, Duty Operating Supervisor and was observed by the Duty Shift Supervisor (DSS). The briefing identified that plant conditions necessary for the RCP start were different than previously experienced by the operating crew. The operating crew had started an RCP prior to this event with the plant solid , but it was directly after filling and venting of the RCS with the water in the reactor vessel and loops at approximately the same temperatures. In the existing plant conditions, the water in the reactor vessel was at approximately 127'F and the steam generator temperatures were approximately 70 F. During the brief, the Duty Operating Supervisor noted that approximately three weeks prior, this same evolution, performed by a different crew, resulted in a pressure increase requiring aggressive action by the operator to prevent an f

- overpressure condition. Initial primary pressure for this earlier evolution was approximately 325 psig.

Pressure peaked at approximately 390 psig during this earlier evolution.

At approximately 1349, "A" RCP was started. RCS pressure began to decrease as expected due to cooling of the RCS due to lower temperature water in the Steam Generators. The Unit 1 Control Operator took action to control the pressure decrease by throttling RCS letdown and raising charging pump speed. Primary pressure decreased to approximately 340 psig, and then began to rapidly increase due to reactor coolant pump discharge pressure and charging flow into the water solid RCS exceeding letdown flow by approximately 50 gpm. The control operator, noting the pressure increase, took action to increase letdown flow and decrease charging to control the pressure transient. During this time, the position indication light for RC- 431C flashed on indicating that the PORV had opened and was confirmed _by an associated computer alarm. Pressure was observed by the operating crew to peak between 405 psig and 415 psig. Computer data indicates that the PORV remained open for less than I second.

A calculation performed for this occurrence concluded that, absent operator action to mitigate the pressure increase and absent LTOP actuati in, RCS pressure would hwe reached a level exceeding applicable 10 CFR 50, Appendix G limits within approximately 15 seconds. hierefore, this report is being provided pursuant to Technical Specification 15.6.9.2.C.

The Low Temperature Overpressure Protection System (LTOP) at PBNP utilizes the two installed PORVs. The PORVs are made operational for low pressure relief by utilizing a dual setpoint where the

l Attachment to NPL 97 07,51 Page 2

• low pressure circuit is energized and de-energized by the operator with a keylock switch depending on plant conditions. LTOP made of operation is required to be enabled and operable when RCS temperature is less than 355'F. The PORV lin setpoint during LTOP operation is 415 psig (s; 440 psig is required by th( Technical Specifications). RilR system relief valves are also available to limit RCS pressure when the RilR system is aligned for shutdown cooling.

The root cause evaluation performed for this occurrence determined that the root cause of this event was starting the reactor coolant pump with a water solid reactor coolant system at 350 psig and misoperation of the charging and letdown systems. We concluded that the operating crew did not have a complete undetstanding of the magnitude of the pressure transient expected resulting in an overaggressive response to the pressure decrease immediately following the RCP start.

Contributing to this occurrence were procedure inadequacies. OP 411," Reactor Coolant Pump Operation," does not provide clear guidas:e on minimum RCS pressure required to start an RCP with the RCS solid. OP 4 A," Filling and Venting Reactor Coolant System," requires RCS pressure to be between 325 psig and 400 psig prior to starting an RCP OP 4B states that the 325 psig minimum pressure for starting an RCP is not applicable during oti.ut than fill and vent operations, but has the operator check pressure gicater than 325 psig immediately aner starting the pump. If the pump had been started at less than 325 psig, and .hcre had been no misoperation of the charging and letdown systems, it is likely that the LTCP operation muld have been prevented.

The following corrective actions are being taken:

4

1. By March 13,1998, operatin); personnel will be briefed on this event. The briefing willinclude how to idennfy abnormal evem precursors and will reinforce the need to maintain a questioning  ?

attitude.

2. OP-4B, " Reactor Coolant Pump Operation, " will be revised by December 13,1997.

3. Licensed operators will be provided training on reactor coolant pump operations in solidplant conditians with various loop and steam generator temperature differences and on control of the chemical and volume control system during solidplant conditions. Training v 31 be completed by March 15,1998, l

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