ML20127E800

Ro:On 850131,full Reactor Scram Occurred.Caused by Operator Opening Instrument Isolation Valve on Jet Pump PDI-42-IR005. Shifts Notified That Valving on Racks to Be Done by or W/Instrument & Controls Technicians

ML20127E800
Person / Time
Site:	Limerick
Issue date:	05/01/1985
From:	Ullrich W PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC
To:	Murley T NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
References
CON-#285-952 NUDOCS 8505200214
Download: ML20127E800 (7)

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F PHILADELPHIA ELECTRIC COMPANY 2301 MARKET STREET P.O. BOX 8699 PHIL.ADELPHIA. PA.19101 1215)848-4000 May 1, 1985 Docket No. 50-352 Dr. Thomas E. Murley, Administrator Region I

.U.S. Nuclear-Regulatory Commission 631 Park Avenue King of Prussia, PA 19406

Dear Dr. Murley:

The purpose of this letter is to inform you of events which occurred at the Limerick Generating Station on Unit No.1 on Although these January 31, 1985 following a full reactor scram.

events were not considered to be reportable under 10 CFR 50.73, the following information (including the information concerning the. reactor scram which was previously submitted to the NRC in Licensee Event Report > 85-021-00) is provided due to the interest expressed by the Resident Inspector. These events were reviewed during NRC Combined Inspection 50-352/85-11 and 52-353/85-03.

Reference:

Docket No. 50-352 Event Date: January 31, 1985 Facility: Limerick Generating Station P.O. Box A, Sanatoga, PA 19464 Description of the Event:

1985, at approximately 8:05 p.m., with Unit No.1 On January 31, in the startup condition and at 3.5 percent power, while an operator was returning'the Jet Pump Developed Head Instrument, PDI-42-IR005, to service, a full scram occurred (no other safety systems actuated). An Unusual Event was declared at about 8:09 Investigation p.m. due to the unplanned reactor shutdown.the scram occurred when the opera indicated that The scram signals instrument isolation valve on PDI-42-IR005.

were reset-by 8:ll p.m..

the operators noted that 34 of the 185 Following the scram, control rods did not display a green full-in light on the full kDj52OO214 850501 S ADOCK 05000352 PDR

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Dr. Thom2c E.LMurley May 1,_1985 Page 2 core display panel or indicate full-in on the Rod Sequence Control System (RSCS) panel. However, all but control rod 42-27 were indicated to be at position 00 on the four-rod display and

.on the process computer. No position indication was available for control rod 42-27 which had been at position 08 prior to the scram because the rod position indication system was showing a data fault for_this rod. Using indications svailable on the RSCS panel, the operators determined that the rod had inserted to at least position 04. To obtain full-in indications and to verify that control rod 42-27 was fully inserted, the mode switch was placed in Refuel and the operator applied a manual insert signal to each rod which lacked its full-in indication. No rod withdrawals were performed while the mode switch was in the Refuel position. For each selected rod except 42-27, the rod briefly inserted beyond position 00, the full-in indication was obtained on both the full core display and the RSCS panel and the rod settled back to position 00 as expected. Technicians then determined that the data fault for rod 42-27 was caused by the reed switches for position 00 and 06 being closed at the same time.

While the rod position indication problem was being resolved, other operators were in the process of isolating steam flows from the reactor such as those for the steam seal evaporator and the steam jet air ejectors by aligning steam from the auxiliary boiler to these components. Other pathways of steam flow from the reactor at the time of the scram included one reactor feed pump turbine, a partially open bypass valve and the main steam line-drains. Because the cooling effects of the steam flow from the reactor coolant system exceeded the reactor decay heat, a higher than expected cooldown rate developed after the scram.

The main steam isolation valves (MSIVs) were closed at 8:42 p.m.

to slow the_cooldown rate. The reactor coolant system water temperature had decreased at a rate of about 113 degrees F per hour while the MSIVs were open.

On January 31, 1985, at about 9:05 p.m. , the Unusual Event was terminated since the cause'of the scram had been identified and the reactor coolant system cooldown rate had been decreased.

Conscouences of the Event:

As a result of the pressure transient on the RPS instrumentation sensing lines, the reactor protection system functioned as designed. Even though the 34 control rods did not indicate full-

.in on the full core display or the RSCS, the process computer and the four-rod display did indicate that all rods were at position 00 (fully inserted), excluding rod 42-27 which did not indicate position 00 due to a failed position indicating probe. The failure of the full-in indication on the full core display or the

Dr. Th: ag E. Murlcy May 1, 1985 Page 3 RSCS did not present a safety concern since there was sufficient indication that the rods were full-in as shown on the process computer and-four-rod display. Subsequent to resetting the scram, those rods that were not indicating full-in were driven in using normal' drive pressure (manual insertion) and a full-in green light indication was restored on both the full core display and the RSCS panel. Full shutdown was achieved since all control rods had fully inserted.

Analysis of the effects of the cooldown rate on the reactor pressure. vessel concluded that this event, in which the reactor coolant exceeded the 100 degrees F/hr. cooldown rate, was less severe than the design shutdown flooding event and therefore should be considered as an additonal shutdown cycle.

Cause of the Event:

Instrument PDI-42-IR005 had been blocked out-of-service to reverse the high and low pressure sensing line connections which were reversed during initial installation. As a result of the work to correct the sensing line connections, the process legs between the instrument isolation valves and the instrument rack isolation valves were not completely filled with liquid. While in the process of clearing the equipment tag-out block, the plant operator, with authorization from the licensed control operator, opened the instrument isolation valve, filling the instrument process line and momentarily causing a pressure reduction in the process line to other instruments on the same instrument rack.

The momentary pressure reduction affected level transmitters LT-42-lN080A and B which initiated a reactor scram signal based on perceived low reactor water level. The low level signals from LT-42-1N080A and B properly generated a full scram signal.

There are three separate reed switches which are used to provide full-in indications to various readout locations for each control rod. The position 00 reed switch (S-00) provides indication to the four-rod display and the process computer. Reed switches S-51 and S-52 are located approximately 0.38 in and 1.26 in.

respectively, above the S-00 switch and either one would provide full-in indication to the full core display and to RSCS.

Investigation indicated that the magnetic coupling between the control rod maanet and the reed switches was insufficient to maintain either S-51 or S-52 closed.

The identification of the unacceptoble cooldown rate (approximately 13 degrees F/hr. above the Tech. Spec. limit) was delayed due to the unavailability in the control room of the proper surveillance procedures normally used to monitor cooldown/hentup rates. Furthermore, clarification was needed regarding the heatup and ecoldown rate limits in Technical

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p. : .

TDrspThimaclE.$Murley1 May 1, 1985 Page:4

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SpecificationsLto identify whether the limits applied to. reactor th  ; coolant' system l temperatures or to' reactor vessel-metal is temperatures.'

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l Corrective' Actions: _

l' r , ,

Instrument.and Controls Technicians are trained with respect-to-

the proper. method for. returning _ instrumentation 1to'. service.- Each1 shift'has been notified that any: valving-to be-done on instrument racks should be done by an Instrument and-Controls Technician or-

.byLan operator with an I&C Technician in attendance.

Additionally, the process.of backfilling and venting instrument-L , process lines performed by I&C technicians has been formalized by written'andrapproved' procedure RT-ll-00467.

'Th'e position = indicating _ probe on control rod'42-27:was replaced.

Procedures were implemented in order to guide the operators

reaction.to a loss of full-in rod position indications following; a' scram.- A memorandum was. issued to'each operating shift discussing-these procedures.

~

. A PORC Technical Specification Position was developed regarding the interpretation of the heatup and cooldown rate limits; checks of'both coolant temperature _and vessel metal temperatures are. required. A Technical Specification Amendment Request will be submitted subsequent to the issuance of the Full Power License for the purpose of clarification in accordance with the PORC

<  ? position. LAn Operator Aid was. posted with the post-scram TRIP procedure cautioning the operators to be aware of high cooldown Erates.after scrams from low decay heat condition and prescribing

.a planned course of~ action for dealing.with these situations.

Additionally, a new simulator scenario was established to train

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the operators in scrams from low decay heat conditions.

Previous Similar Occurrences

None.

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,4. i. :

Dr.-Thorac _E. Murlcy' -

May:1, 1985 Page 5

-If'you require anE further information, please do not

-hesitate to contact-us.

F_

Very truly yours, ff W.-T. Ullrich Superintendent Nuclear Generation Division cca J. T. Wiggins, Senior. Site Inspector See Service List L

4

i cc: Judge Helen F. Hoyt Judge Jerry Harbour Judge Richard F. Cole Troy B. Conner , Jr. , Esq.

Ann P. Hodgdon, Esq.

Mr. Frank R. Romano Mr. Robert L. Anthony Ms.'Phyllis Zitner Charles W. Elliott, Esq.

7.ori G. Ferkin, Esq.

Mr. Thomas Gerusky Director, Penna. Emergency Management Agency Angus Love, Esq.

David hersan, Esq.

Robe r t J . Sugarman, Esq.

Martha W. Bush, Esq.

' Spence U. Perry, Esq.

Jay M. Gutierrez, Esq.

Atomic Safety & Licensing Appeal Board Atomic Safety & Licensing Board Panel Docket & Service Section (3 Copies)

James Wiggins Timothy.R. S. Campbell d

l January 16, 1985 l

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