ML20029B097

LER 91-006-00:on 910202,inboard Isolation Valves Closed on RWCU Delta Flow High Signal During Removal of RWCU Filter from Svc.Caused by Personnel Error.Sys Operating Instruction Being revised.W/910301 Ltr

ML20029B097
Person / Time
Site:	Perry
Issue date:	03/01/1991
From:	Hegrat H, Lyster M CENTERIOR ENERGY
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-91-006, LER-91-6, PY-CEI-NRR-1327, NUDOCS 9103050416
Download: ML20029B097 (4)

Text

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. _ CENTE PERRY NUCLEAR POWER PLANT Mail Address-Michael D Lyster-PO BOX 97 -

10 CENTER ROAD PERRY, OHIO . 44081

. PERRY OHIO 44081 VICE PRESIDENT . NUCLEAR (216) 259 3737._

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March 1, 1991 PY-CE1/NRR-1327 L t

U.S. Nuclear Regulatory Commission l Document Control Desk .

Washington, D.C.- 20555 l Perry Nuclear Power Plant Docket-No. 50-440 LER 91-006  !

Dear Sir:

i Enclosed is Licensee Event Rcport 91-006 f or the Perry Nuclear Power Plant.

Sincerely, o

, AL Michael D. yster 'l

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Enclosure:

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] vis n,,,, tuserto sven,wo= oA ris 7 =o l l l a sf uCT ,t , Am ,. . . . . . -. M.,. w r .~. n si On February 2, 1991, at 1230, Reactor Water Cleanup (RWCU). Inboard lsolation Valves closed on a RWCU Delta Flow High signal during removal of a RWCU filter from service.

l The root cause of this event is personnel error,_ inadequate knowledge. The t System Operating Instruction specified that the operator throttle the bypass l valve to maintain the appropriate RWCU inlet flow during filter shutdown operations. While attempting to follow the instruction, the operator was f monitoring other related instrumentation in addition to the RWCU inlet flow and the bypass valve was opened too far. When flow exceeded the calibrated range af I the instrument, the Leak Detection system could no longer accurately determine differentin' flow, and an artificial differential flow signal was initiated.

Because the instruction did not provide appropriate limitations for system flow during this operation, procedural inadequacy la considered to be a contributing _

factor.

To prevent recurrence, the System Operating Instruction is being revised to provide the necessary guidance for control of system flow during filter operations. The inetrument and Controls support engineer is discussing this i event and the associated procedural changes with all onshift operators.

I Additionally this event will be discussed with all licensed operators during their requalification training. <

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9l 1 0l2 0F 0 l3 nxt es -. -,.a .== aac e r: wm on February 2,1991, at 1230, Reactor Water Cleanup (RWCU) (CE) Inboard Isolation Valves (ISV) closed on a RWCU Delta-Flow liigh signal f rom the Division II Leak Detection System (IJ). At the time of this event the plant was in Operational Condition 1 (Power Operation) and the Reactor Pressure Vessel (RPV) was at saturated conditions with a reactor pressure of 1026 psig.

On February 2 operators were attempting to remove RWCU A filter (FLT) f rom service in accordance with System Operating Instruction (S01-G33) " Reactor Water Cleanup System (Unit 1)". The Plant Operator van decreasing flow for the A

- filter at the local panel; while the Control Room Operator was throttling tha bypass valve, IC33F044, to maintain system flow with two pumps running. When the I "RWCU Delta Flow liigh Timer Run" alarm came in, the dif ferential flow on the Division II Leak Detection indicator was reading approximately 70 gpm, while the ,

Division I indicator was reading approximately 60 gpm. The Control Room operator was instructed to close the isolation valves and did so with three seconds remaining on-the timer. Ilowever, the valves did not sufficiently reduce the flow differential in time to reset the timer and at 1230 a Division II isolation signal on high differential flow was initiated. In accordance with approved operating instruction, the Control Room Operator restored the system following the inolation. At 1335 RWCU B pump was started and at 1340 RWCU A pump was started.

The root cause of this event is personnel error, inadequate knowledge. S01 G33 directs the operators to maintain RWCU flow within normal parameters while removing the filter from service._ This is accomplished by throttling open the filter bypass valve from the control room to compensate for decrease in system flow as the filter is locally removed from service. In this event, the operator was attempting'to follow the approved instruction; however,-he initially over-compensated for the reduction in filter flow, increasing system flow to above the maximum indicated rauge on control panel instrumentation, while waiting

,,. for further reduction of filter flow. With the flow instruments sensing flow

above their normal calibrated range, a false dif ferential flow signal was generated, resulting in a system isolation. Procedural inadequacy is considered

.to be a contributing factor for this event, in that S01-033 did not provide appropriate limitations for system flow during this operation.

The RWCU system. is used to control reactor water chemistry, redace reactor water inventory during the startup and shutdoan, and minimize temperature gradients when the recirculation pumps are not operating. A RWCU containment isolhtion occurring at high reactor power will allow reactor coolant conductivity to slowly increase until the system is returned to service. The differential flow portion of the Leak Detection System compares RWCU suction flow to both the flow

. returning to the reactor vessel and blowdown flow to radwaste or the main i condenser. All three flows are summed to generate an indication of differential flow. A RWCU high differential flow signal indicates the suction flow entering the system.is not being discharged via normal flow paths. This could be the -

result of a line break in the RWCU system. liigh dif ferential flow of greater than 68 gpm for a duration of 45 seconds generates an isolation signal from the Leak Detection System. The 45 second tima delay normally allows for system flow

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0 10 0 13 0F 0 l3 rut = = . w - nae w asaw nn transients when changing operational configurations. Since no RWCU high differential flow existed due to a leak, and because the systems did respond to the high indicated differential flow as designed, the February 2, 1991 event is not considered to be safety significant.

Other events involving RWCU system containment isolations due to high differential flow have been discussed in LER's89-025, 88-039,88-013, 88-002 and 87-074 No RWCU isolations have bcen experienced at steady state powt.r while removing a filter.

To prevent recurrence, S01-033 la being revised to provide the necessary guidance for control of system flow during filter operations. The Instrument and Controls support engineer is discussing this event and the associated procedural modifications with all onshift operators during shift briefings. Additionally this event will be discussed with all licensed operators during their requalification training 4.

Energy Industry Identification System Codes are identified in the text as (XX).

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a N'.C Fesset 30EA 14499

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