ML20029B236
| ML20029B236 | |
| Person / Time | |
|---|---|
| Site: | Wolf Creek  |
| Issue date: | 02/28/1991 |
| From: | Bailey J, Mike Williams WOLF CREEK NUCLEAR OPERATING CORP. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| LER-90-025, LER-90-25, NO-91-0074, NO-91-74, NUDOCS 9103060269 | |
| Download: ML20029B236 (10) | |
Text
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W9LF CREEK NUCLEAR OPERATING CORPORATION John A. Dailey Vwo Presittent Orwratons February 28,1991 ho 91-0074 U. S. Nuclear Regulatory Coenission ATTN: Document Control Desk Hail Station P1-137 Washington, D. C. 20555
Subject:
Docket No. 50-482: Licensee Event Report 90-025-01 Gentlemen:
The attached Licensee Eveut Report (LER) is being submitted pursuant to 10 CFR 50.73 (a)(2)(1) and 10 CFR 50.73(a)(2)(vil).
Very truly yours, M w NJO M -
J John A. Bailey Vice President Operations JABlaem Attachment cci A. T. Howell (NRC) v/a R. D.' Martin (NRC), w/a a D. V. Pickett (NRO), w/a H. E. Skov (NRC), v/a e
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On December 23,1990 at 1230 CST, it was detennined that the/ccmon minhuum flow path return line for the Safety Injection (SI) punpa to the Refueling-Water Stc, rage Tank (RWST) was frozen. Previous actions to investigate
- problans with the freeze protection systan were unsuccessful in preventing developnant of this condition._ 'Ihe two SI punps were declared inoperable with this return line frozen and entry was modo into 'nxinical Specification 3.0.3. 'Ihe punps were returned to operable status at 1757 CST.
A fault.y Ambient hgweture Switch for_ the RWST heat trace systen provented the heat trace from activating and was subsequently replaced. In addition, administrative controlo did not sufficiently recognize the safety significance of flow through this line and the need to ensure flow capability._ Additional guidance has been provided. .Also, ineffective conmunications between Operations. personnel and Electrical Maintenance
, personnel prevented. thorough evaluation of the RWST heat trace trouble alarm. '1he'need for effective ccnunications has:been reiterated- to plant pusonnel. his supplemnt provides conclusions regarding the safety significance of this event. ,
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0l1 0l2 or 0p TEXT Ilf esore gas.e a mpuest use e#Urner hec 1mkl6A si11h Cn Deceber 23,: 1990 at 1230 CST, it ws determined that the ccrmrm mininum ficw path return line -(i.e., recirculatica line) for Safety Injection (SI) punps [BQ-P] PD101A and PEM01B to the Refueling Water Storage 'fank (RWST)
[BP 'IK] was frozen. Since a recirculation flow path nust be present to prevent punp lamage'during extended SI pump cperatton when the Reactor
, Coolant System (AB] pressure is above the shutoff head of the pumps the two >
SI punps were declared in-mhle. Technical Specification 3.5.2 requires that,two independent Bnergency Core Cooling System (ECCS) subsystes be ,
q=mble and provides actions in the event that one ECCS subsystan is inoperable. %e sinultaneous inoperability of both SI pumps placed the plant in a ccmdition prohibited by the plant's Technical Specifications and rest:lted in an entry into 'Itchnical Specificaticm 3.0.3. W erefore, this corriiticn is being reported pursuant to 10 CFR 50.73(a)(2)(1). It'is also considered reportable under 10 CFR 50.73(a)(2)(vii) as a single condition lwhich caused two independent trains to becczne inoperable in-a single syste.
DESCRIPTIGE W E75tf ,
'Ihe Control Rom received freeze protection trouble alarms for the .
Danineralized Water Storage Tank (KC-TK] and the Condensate Storage Tank
-[KA-TK) on Decaiser 20 and 21, 19 @. Control Rom Annunciator AIR-55F,
" Freeze Protection Trouble",= is illuminated when the ;tamature of the tank's heat traced piping falls below a ncuninal-35_ degrees Fahrenheit. 'he.
Freeze Protection' Panel breakers were verifled-to be closed per Alarm Response p ucadure AIR 00-055F. Ebllowing discussions between Control Pmu~
personnal ard Electrical Maintenance personnel-the current flow in thc heat '
trace as verified for the affected circuits to confirm proper operation.
-On Dei _u fer 21,1990 at 2045 CST, the Control Rom received a freeze protection trouble"alann for the RHST. Discussions ware held with
' Electrical Maintenance concerning the capabilities of the heat trace
- a l a ma . - Control Rocm perscnnel were unaware that a crew change had occurred within the Electrical Maintenance organization since their last_ cliscussions concerning troubleshooting of the' freeze protection systen. Consequently.
Control' Rocm pm.mausel were not explicit in their request for current:
measurements and the conversation was instead focused on the "reflash"
- capabilities of the alarm. ,It was concluded that if an alarm on the heat trace circuit were in ~a -" locked .in" condition and a breaker feeding .the heat trace-were to trip, a "reflash" would not occur on the locked in alann.
'Iherefore, Operations personnel then began to check the circuit breakers approximately every four hours to ensure that the heat trace circuits were operating properly for all outside tanks.-
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Oli 01 3 or 0 l9 TEXT 4 more spece a revues 4 vae ##eorW MC #sre .kili4's311h Cn Dy=he 23,1990 at 0007 CST, an attempt was nade to add water to the RWST because of a low level alam. '1he level was substantially above the required Technical Specification mininum level. '1he flow path involved the return line to the RWST, which also provides a flow path for Safety Injection punp recirculation flow [ Figure 1). When this attmpt to fill the RWST failed, an investigation was starte:! to detemine the cause. It was learned that an open work request existed to repair Isolation Valve BGV0193 (CB-ISV). 'Ihis valve isolates the Chmical and Vol'une Control Systm (CB) frm the Refueling Water Storage System (BP). 'Ihe proble description on the work request incilcated that the valve stat and diaphragm had esparated.
Believing that this mndition would prevent flow thru.gh the valve, the faulty isolation valve was identified as the reason that flow oculd not be .
established to the RWST. Because RHST level us still substantially above '
mininum level, it was riae f rini at that time to wait until dayshif t to have the proble with Isolation Valve DGV0195 further evaluated.. . During the Shift Turnover,.this event was discussed as well as the need to confirm
.p w operation of freeze protection circuits.
The dayshift crew proceeded with the investigation of the itens that were discussed during the Shtft 'nirnover. It was deirinel to try to fill the RWST using an alternate flow path and to have Electrical Maintmance-verify the operation of the heat trace circuits. At 1139 CST the dayshift crew attenpted to fill the RWST through an alternate flow path, which did not ,
require flow through,Isolatim Valve BGV0195, utilizing fuel Pool Cleanup Punps (DA-P] PEC02A and PECO2B At 1145 CST, Electrical Maintenance detamined that the heat tracing on the RWST return line had a faulty ambient tenperature; switch and no current existed in the heat tracing. -
-- After the atterpt to fill the RWST through-the alternate flow path failed, the RWST return line was detaminct! to be fIczen and therefore unable to fulfill its function as a# recirculation line fo2. both SI pumps. _A -
recirculation flow path nust be present to prevent punp damage during extended SI punp operatim when the Reactor Coolant Systen (AU) pressure is.
above the shutoff head of the punps. At-1230 CST both SI pungs were -
declared inopamble and Technical Specification 3.0.3 was entered.
Both SI punps were placed in " pull-te ':ck" at 1250 CST to prevent an autmatic start and subsequent de . 2cause of a potential shutoff head candition. The Shift Supervisor-assigned an operator to operate the SI punps under appropriate circumstances.
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, t; Activities were initiated to thaw the RWST return line in order to obtain-the use of the SI punp's recirculation-line. A junper was installed across i the inoperable Ambient '1wperature Switch to provide power to -the heat -
trace. A tmporary heat source was also used on the frozen-section of the -
pipe. In' conjunction with_the_ external heat being applied, the Fuel Pool-Cleanup Punps were used to provide internal pressure to the blockage. At 1600 CST, the plant declarad a' Notification of Unusual Event and bogan to reduce power to conply with Technical Specification 3.0.3. -
Flow was established to the RWST frcm the Fuel Pool Cleanup Punps at 1702 CST. Reactor power was etabilized at apptuximately 65 percent while verifying SI punp recirculation flow. _ Recirculation flow for SI punp Pm01A was verified at 1735 CST per surveillance procedure STS m-100A and =
Technical Specifications 3.0.3 was exited.- 'Ibchnical- Specification 3.5.2 was then entered for having one ECCS subsystem inoperable arri the Notification of Unusual Event was tecninated. Ibliowing the verification of .
recirculationJ for SI pump Pm01B at 1757 CST per surveillance procedure S'Is m-100B, the RWST was placed in continuous recirculation through its return -
- line to assure minirun flow capability and Technica1' Specification 3.5.2 was -
. exited. -.At 2235 CST, Reactor power was restored to 100 percent. -Electrical U Maintenance was also instructed to verify the current flow in all heat trace
- circuits every four hours to confirm proper operation. A review was 2
conducted;to determine-if there were other similar punp arrangements in .
which a heat traced line could freeze and prevent recirculation capabilities.
of the.puup and'none were found. A new Ambient Tenperature Switch was subsequently installed _to replace the taporary junper at 1340 CST on ,
N W r 24, 1990. Js Hotsr CAUSE Am opmuCTIVE ACTIGE
'Ihere are several factors that led-to the freezing of the RhBT return line which also serves as the recirculation line'for both SI pumps.- A faulty-
-.anibient tampamture switch for the' RHST heat trace system prevented the heat' trace frun activating when the external tecperature dropped below 40 degrees Fahrenheit. Although the exact cause of the failure could not be detennined, corrosion of the internal mechanism is thought to be a major Econtributor. :In order to ensure proper operation of'the AmbientItmperature Switches and the low Tuperature Alart Switches,_ they will be calibrated _in the fall of each year to ensure that the heat trace circuits and alaras are activated at.the proper temperature.
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011 01 5 N O l9 nn m .,-.. ,*.-, - m , - oir, In addition, administrative controls did not sufficiently recognize the safety significance of flow through this line and the need to ensure flow capsbility. Wis Idcensee Event Report has been included in Operations Required _ Reading to ensure that all licensed personml are cognizant of the details of this event. Also, additional training will b3 provided as part of licensed requalification training to licensed personnel reiterating the safety significance for f1w through the line and anphasizing that imwxilate operator actions are necessary when freeze protection alams are received.
Wie additional training will be canpleted by March 29, 1991. me subject wi]1 also be included in the recurring training file to be evaluated for inclusion in subsequent requalification training cycles.
Also, ineffective connunications between Operations personnel and Electrical Maintenance personnel prevented the RWST heat tracing frun being thoroughly evaluated when its alam was received. Control Roca personnel were unaware that a crw chango had occurred within the Electrical Maintenance organization since their last discussions concerning troubleshooting of the i freeze protection system. Consequently Control Roan personnel were not explicit in their request for current masurments and the conversation was i instead focused on the "reflash" caphilities of the alam. We need for effective cannunications will be discussed in group meetings for Operations and Naintenance personnel. We need for effective connunications ms discussed in a group meeting held by Instrumentation and Controls on January 18, 1991. mis-subject will also be incitr3ed in the requalification training mentioned above for licensed personnel. . Wese canmunication needs were reiterated to plant personnel through a . letter from the Director Plant Operations.
Alam Response procedure ALR 00-0SSF, " Freeze Protection Trouble", '
instructed the operators to verify that the pcwer supply breaker, the heater circuit breakers, and the control circuit bruaker for the affected Freeze Protection Panel 'are closed. he heat trace circuits were believed .to be operational when the circuit breakers were closed. mis procedure has been revised to provide more concise instructions when a freeze protection trouble alarm is received in the Centrol Rocm. Wese instructions include a provision to have Electrical Maintenance check heat trace current flow daily to verify proper operation when a freeze protection trouble alam is .
activated. Also, this pusdure instructs the operators to initiate flow through piping that can be placed in recirculation (incitriing RWST) if tauperature control cannot be restored. Procedure SIN GP-001, " Plant Winterization", has been revised to include provisions to put the RWST in
, continuous recirculation through its . return line to assure minimum flow l capability of the SI pump recirculation line.
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Follcwing a review of possible design enhancamnts to the heat traco systan, several unhancatents have been identified that could hiprove its ruliability and naintainability. %e ackiition of pilot lights at the ends of the heat tracing tape would allow the operator to positively verify that power is available to the tape as well as verifying that no discontinuities exist on the hast trucing tape. Also, the aditticn of an Auto-Manual cwitch would allow the operator to by-pass the existing ambient tanporaturn thentostat to establish power to the heat tracing tape. %ese design enhancerents will be implemonted by the end of Refuel V.
M11TTKNAI. IdFUMMPION At the time of the event, the plant was in Mode 1, Power Operation, at approximately 100 percent Reactor power. Power was reduced to approxinately 65 percent before subsequently returning to 100 percent Reactor power.
%e faulty Airbient Ruperature Switch was nanufactured by United Electric Company, Mcdel Number NC-1A.
%ere have been no pnwlous similar occurrences, gFFRY SICMTFICMCP. T. WMP he functional nxIuirements of the safety injection pumps to mitigate the consequences of design basis accidents (DBAs) were reviewal and the Updated Safety Analysis Report (USAR) licensing basis analyses were evaluated to assess the impact of the frozen recirculation line. Specifically, the analyses associated with the postulated prinary and secondary systan pipe ruptures were exantined. Se following sections surmarize the evaluations l performed for the affected safety analyses.
Evaluation of SI pump failure because of extendo1 operation at shutoff head has c'etennined that such failure would not occur until over two minutes of operation. If Reactor Coolant Pressure were to drop below shutoff head in the first two minutes, the SI pumps would not be danaged.
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011 0l 7 or 0l9 sw w. w. . w ~ w w .w u n n Secondary Systan Pire Rupture Events ib credit has been taken in the analysis of these secondary systan pipe break cvents in the USAR for the operation of the intoutrxiiate head safety injection pumps. Werefore, potential SI punp damage, because of shutoff head situations, resulting from the frozen recirculation f1w pipe has no impact on the analysis results calculated for the Feedline Break and Ste mline Break events.
Prinary Systan Pire Rupture Events Steam Generator Tube Rupture (SGIR):
For the analyzed SGIR scenarios, a shutoff head situation will exist for_ an extended tinn period, which will result in SI punp damage and reduction of total SI flw. However, SI punp f1w is not required to ensure adequate Reactor Coolant Systan inventory. Milng the SI punp flw leads to naintaining a higher prinary to secondary pressure differential and consequently a higher break f1w reste for a longer tino period. % erefore, SI pump damage caused by a shutoff head condition during a postulated SGIR evers would result in less severe consequences with respect. to the offsite dose releanes and the nnrgin to overfill.
Luge Break Ioss of Ccolant Accident (IDCA):
Shutoff head cxanditions will not exist for the SI pumps during the bloviown phase of the large break IOCA as the Reactor Coolant Systan (RCS) will depressurize to the SI pump discharge pressure over a very sixart tian period. W erefore, the frozen recirculation flow line of the SI pumps would not result in pump danage should a large break IOCA have occurred during that tinn period. For-these reasons, the frozen pipe would not advercely affect the calculated peak e'inMng tanperature (ICP) for a' postulated large break IOCA.
Small Break IOCA:
We review of the currently analyzed break sizes for vb1f Creek Generating Station concluded that the shutoff head conditions would not eedst for nore than two minutes (duration to SI punp damage) should a break in the range of a 1.75 to 6 inch diannter line occur.
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011 018 M 019 nx, a _ m ~ nec o. uu ,mn For annll htmk IOCA's with break sizes betwen 3/8 and 1.75 inches, the evaluation indicated the RCS pressure would rumin higher than the SI punp shutoff head for note than 2 minutos af ter SI actuation. A frozen rocirculation line could result in the SI punps sustaining damgo and failing if allowed to operate for nore than the allowable two minutes at the shutoff head. Ikuwer safe shutdown and core subcooling would still be established with the centrifugal charging and maidual heat rmoval aystm pumps. Aktitionally, an assessnmt of thu PCf based upon sensitivity sttritos denenstrated that the 10 CFR 50.46 ICP 11mtt would not have been violatcd.
In the event that the SI punps were danagol because pressuru meined higher than the cut-in pressure for the very anall breaks, the high pressure hot leg injection capability would have been lost. Ilowever, for breaks in this size range, core subcool.k ; would be established by the cooldown, and the mergency operating procedures would be exited prior to the nood for switchover of the ECCS to hot leg recirculation node. In addition, once the depressurization to the Residual Iloat Rmoval (RHR) (BP) cut-in prussure was accomplished, hot leg injection frun the RHR pung (BP-P] would Imvo bean a.allable, if needed, t'or break sizes of 3/8 inch or loss, the Chcznical and Voluno Control Systm is capable of naintaining pressuru and inventory in the RCS, '1horefore, the SI pumps are not requirrd to reach a safe shutdown for these casos.
Based on the above ruview, this event did not significantly jeopardize enfo oporation of the plant nor poso a threat to the health and safety of the public.
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