ML20005E685

LER 89-031-00:on 891206,08 & 15,RWCU Sys Isolations Occurred.Caused by Design Deficiency & Deficiency in Leak Detection/Differential Flow Circuitry Setpoint &/Or Time Delay.Leak Detection Thermocouples relocated.W/900105 Ltr

ML20005E685
Person / Time
Site:	Perry
Issue date:	01/05/1990
From:	Hegrat H, Kaplan A CLEVELAND ELECTRIC ILLUMINATING CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-89-031, PY-CEI-NRR-1117, NUDOCS 9001100106
Download: ML20005E685 (5)

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r E* iTHELCLEVELAND; ELECTRIC ILLU911NATING COMPANY .

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' P.O. BOX. 97 5 , PERRY, OHIO 44061 ; 5 ' TELEPHONE (216) 269 3737' 5- ADDRESS 10 CENTER ROAD FROM CLEVELAND: 479 1200 A . TELEX: 241599 :

ANSWERBACK: CEI PRYO -

. Al Kaplan; Serving The Best Location h the Nation k PERRY NUCLEAR POWER PLANT

( YCE PRESIDENT : r y L i

.. NUCLEAR GROUP '

January 5~ 1990 PY-CEI/NRR-1117 L' b

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U.S. Nuclear Regulatory Commission-g-  : Document Control Desk l l g. ~ Washington,..D.C. . ~20555' r

Perry Nuclear Power Plant;

_ Docket No.'50-440

~.l LER 89-031

Dear Sir:

. . . 1 Enclosediis Licensee Event Report 89-031 for the ' Perry Nuclear Power Plant.

'Verytruly.yours{

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Al Kaplan.  ;

Vice President <

Nuclear Group I*

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Enclosure:

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Design Limitations Result in High Differential Flow and High Differential Temperature Reactor Water Cleanup System Containment Isolations tyENT DAff (Si LER NURABER 461 REPORT DAf t 171 OTMER F ACILITIES terv0LV4D let MONTH DAY YEAR YtAR -

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The cause of the December 6 and December 15, 1989 events was a design deficiency.

An engineering evaluation has determined that the location of leak detection thermocouples outside of the RWCU pump rooms resulted in excessive differential temperature readings during normal operation. As a result, increases in l differential temperature caused by minor ventilation or system fluctuations resulted in unnecessary RWCU System containment isolations. The cause of the l December 8, 1989 event is a previously identified design deficiency in the leak l detection / differential flow circuitry setpoint and/or time delay during RWCU system startup.

In order to prevent recurrence of the differential temperature isolations, leak detection thermocouples have been relocated to enhance the validity of differential temperature measurement. A comprehensive evaluation of potential RWCU system design changes and operating procedure revision is being performed to prevent l unnecessary system containment isolations due to indicated high di'ferential flow.

A supplemental report will be provided upon completion of this evaluation and l determination of appropriate corrective action.

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0l 0 0l2 or 0 l4 YtXT M mese apen e #sen.gst, ese espesasi NRC perm W W HM On December 6, 1989, at approximately 1034, and on December 15, 1989, at approximately 1725, Reactor Water Cleanup (RWCU) [CE] System containment isolations occurred due to high differential temperature in the RWCU Pump' Room ventilation. Da December 8, 1989, at approximately 2225, an RWCU System containment isolation occurred due to indicated high differential flow. At the  !

times of the events, the plant was in Operational Condition 1 (Power Operation) l at approximately 100 percent of rated thermal power. The Reactor. Pressure Vessel

[RPV) was at saturated conditions at approxinintely 1000 psig.

Prior to the December 6, 1989 event, RWCU was in operatian and the Auxiliary Building Ventilation System was using the "B" Supply and Exhaust fans. The Equipment Area Differential Temperature Recorder points, which monitor RWCU Pump Room 1 and 2 differential temperatures, were bypassed due to differential temperatures exceeding alarm setpoints; as a result, operators were monitoring the temperatures every 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />. At approximately 1034, during the performance of control room surveillance activities, an RWCU Pump Room 2 differential temperature switch [TDS] caused a temperature signal spike when the operator was taking his reading. This resulted in an inboard containment isolation of the RWCU System. At approximately 1059, after verifying that no steam leak existed, operators returned both RWCU pumps to service, and shifted ventilation Supply and Exhaust fans to reduce differential temperature.

Prior to the December 8, 1989 event, the RWCU system was shut down for maintenance. At approscimately 2225, while starting RWCU pump A, suction flow exceeded discharge flow by more than the 68 gpm setpoint for longer than the 45 second delay time, which resulted in an RWCU system containment isolation due to I high differential flow, despite efforts by the operators to manually trip the pump prior to exceeding the time delay setpoint. On December 9, 1989, at approximately 0255, the RWCU system was restarted with no further difficulty.

4 Prior to the December 15, 1989 event, the RWCU system was h service when both r Auxiliary Building Ventilation supply fans tripped on lov temperature resulting l in a high differential temperature in RWCU pump room 2 and subsequently an outboard RWCU system containment isolation at approximately 1725. The loss of ventilation had caused the RWCU pump room temperature to increase enough to exceed the dif ferential temperature setpoint but not the arabient temperature setpoint. At approximately 1745, operators closed the inboard RWCU system containment isolation valves. Investigation revealed the ventilation supply plenum roughing [FLT] filters to be covered with snow. The snow was removed and at 1840 a supply fan was restarted. At approximately 1955 RWCU was returned to service and at approximately 2200 all Auxiliary Building Ventilation supply plenum roughing filters were replaced.

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" TII*c"a N T YiEe Te*EeTbE'6 and December 15, 1989 events was a design deficiency.

A temperature survey of the RWCU pump room area revealed that temperature inside i the pump rooms were within the normal expected range and that the ventilation system inside the rooms was operating properly. Further engineering evaluations determined that the high differential temperatures (close to setpoint) were due to the location of installed leak detection system thermocouples. The location of the thermocouples outside the pump rooms resulted in an excessive indication of ventilation system differential temperature under normal operating conditions, j Additionally, as a result of previous operational problems, a 1 second time delay had been installed in the leak detection temperature trip circuitry to eliminate unnecessary isolation caused by spikes when temperatures are being read. During .

the December 6 event, with the pump room differential temperature very close to j the trip setpoint, the time delay was insufficient to prevent the signal spike from causing a spurious isolation signal. The actual differential temperature did not exceed the trip setpoint.

During the December 15, 1989 event, a severe snow storm was in progress resulting in snow intrusion into the Auxiliary Building Ventilation System and the resulting trip of system supply fans on low temperature. Because the Pump Room differential temperatures were approaching trip setpoints due to the design characteristics described above, the interruption of the Auxiliary Building Ventilation caused the trip setpoints to be exceeded before operator action could ,

be implemented to restore flow.

The cause of the December 8, 1989 event is a previously identified design deficiency in the leak detection / differential flow circuitry setpoint and/or time delay during RWCU system startup. Although several design improvements have been made, it is still difficult to obtain consistent and accurate flow measurment, for leak detection purposes, during dynamic startup conditions. This is due to i' the wide range of flows, process fluid temperatures, other system parameters and plant conditions present during RWCU system startups.

The RWCU system is used to control reactor water chemistry, reduce reactor water i inventory during startup and shutdown, and minimize temperature gradiente when y recirculation pumps are not operating. An RWCU containment isolation occurring at high reactor power will allow reactor coolant conductivity to slowly increase until the system is returned to service. The RWCU pump rooms differential temperature instrumentation is part of the Leak Detection system, designed to isolate the RWCU containment penetrations should an RWCU system leak develop in the RWCU pump room. Since no system leakage or actual RWCU Pump Room high differential temperature conditions existed and the system responded as designed, the events on December 6 and December 15, 1989 are not considered to be safety significant.

The Differential Flow portion of the Leak Detection System compares RWCU suction 1

flow to both the flow returning to the reactor vessel and blowdown flow to radwaste or the main condenser. All three flows are summed to generate an indication of differential flow. An RWCU high differential flow signal indicates the suction flow entering the system is not being discharged via normal flow paths (reactor vessel, and blowdown to radwaste or main condenser). This could N.C Penn 306A (6491 I i

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0l 0 q4 0F 0l4 TEXT W nesse apose a soesseel, var sessener N#C 7e= JmeU qth be the result of a line break in the RWCU system. High differential flow of greater than 68 gpm for a duration of 45 seconds generates an isolation signal from the Leak Detection System. The 45 second time delay normally allows for system flow transients when changing operational configurations. Since no RWCU high differential flow existed due to a leak and the systems did respond as designed to the high indicated differential flow, the December 8, 1989 event is not considered to be safety significant.

Other events involving RWCU System Containment 1solations due to high differential flow have been discussed in LER's89-025, 88-039,88-013, 88-002 and i 87-074. Other events involving RWCU System Containment Isolations due to high differential temperature or Auxiliary Building Ventilation System problems have been discussed in LER's88-010 and 89-004.

After the December 6, 1989 event, operators were instructed to bypass the leak detection isolation logic when performing channel checks on the temperature instrumentation until design improvements could be implemented. A design modification was developed and implemented to change the locations of the thermocouples monitoring temperatures outside of the pump rooms, improving the validity of differential temperature instrumentation measurements without j compromising the ability to detect actual leakage conditions. Additionally potential improvements to prevent snow intrusion for the Auxiliary Building Ventilation System supply plenum are being investigated.

To prevent recurrence of the event on December 8, 1989, a setpoint/ time delay change is being evaluated; however, this would necessitate changes to Technical Specifications. Because significant progress has been made over the last few years on reducing the number of spurious RWCU isolations due to differential flow 4 signals, and because the most recent events have occurred during system startup, a comprehensive evaluation of potential corrective actions is being performed.

These potential solutions include system design modifications and operating

( procedure revisions in addition to the previously mentioned Technical Specification changes. A supplemental report will be provided upon completion of this evaluation and determination of appropriate corrective actions.

Energy Industry Identification System Codes are identified in the text as [XX].

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