ML20106C046
| ML20106C046 | |
| Person / Time | |
|---|---|
| Site: | Cooper  |
| Issue date: | 09/28/1992 |
| From: | Horn G NEBRASKA PUBLIC POWER DISTRICT |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GL-92-04, GL-92-4, NSD921014, NUDOCS 9210060030 | |
| Download: ML20106C046 (8) | |
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mmm,a m:ymy-, =m.m NSD921014 September 28, 1992 Nuclear Regulatory Comniission At t etit i on : Document Control Desk Washington, DC 20555
Subject:
Response to NRC Generic Letter 92-04 Resolution of the Issues Related to
" Reactor Vessel Water Level Instrumentation in BVR's" Cooper Nuclear Station NRC Docket 50 298, DPR-46 Centlemen:
NRC Generic Letter (CL) 92 04,-Resolution of the Issues Related to " Reactor Vessel Water Level Instrumentation in BWR's", was issued on August 19, 1992. The Generic Letter contains requested actions and reporting requirements regarding the adequacy of, and corrective actions for BWR water level instrumentation with respect to the effect of noncondensi* ole gases on system operation.
As requested by the Generic letter, attached is the Nebraska Public Power District's (District) response to the requested actions contained in the NRC Ceneric Letter 92 04. This response is submitted under on h '.. accordance with the provisions of 10 CFR 50.54(f).
Please contact me at this office if you have any questions.
Sincarol n-W C.pt. llorn Nucient Power Group Manager CRil/tj a : CL92 -04 Attachment ec:
NRC Regional Office Region IV Arlington, TX NRC Resident Inspector Cooper Nuclear Station I
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NSD921014 Page 2 September 28, 1992 STATE OF NEBRASKA )
)ss PlATTE COUNTY
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R. llorn, bei first duly sworn, deposes and says that he is an authorized
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representative of the Nebraska Public Power District, a public corporation and political subdivision of the State of Nebraska; that he is duly authorized to submit this response on behalf of Nebraska Public Power District; and that the stat.aoents, contained horcin are true to the best of his knowledge and belief.
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NEBRASKA PUliLIC POWER DISTRICT'S RESPONS4 TO CENERIC LETTER 92-04 RESOLUTION OF "HE ISSUES RELATED 10 "REAC*iOR VESSEL VATER El, INSTRUMFFMTION IN BWRs" M ; wj
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on August 19, 1997, tr NRC i stawd Gene ric Letter 92 M, Resolution of the issuca 45 celated to "Reac t or Vessel Wat e r level Inst rumentat lon in hWRs.. " The Generic Letter required licensee's to provide a written response to t l.e following requentec' act ions
, n.
by Septembe r 2 7, 1992. Tht, following in the Nebranka l'uhlic Power District's Response d f4 to those requested actions.
p PtrtuLnLfs1.intw pote Tt tal 'evel indication errors f rom the of f ects of noncondensible 8
1.
In light o gas, each licennee should determine a.
The in of potential 1cve' indication errors on the natic
-identt syntem ponse during all
,u.
Ing basin transientn ans c
12SLOESL.
The BWR Owners' Group (BWROC) provided to the NRC and each of tbn member 2
utilities a report which addresses the satNty impact of poten.ini wa cl level indication errorn on automatic system response during all llennaing hanic transients and accidents.
The analysis basis is contained .
Section f2.0, Safsly l Ell 3112. of tia r eport and is summart.'ed in SectAna 2.2, I'lant_r;xingnnu t o Pomtulated Accideilt _Ecat11!IinL. It t> the Nebraska Public Power District's (District) position tha, the inioimation in tac BWROG report is applIcahic to the design of Cooper Nuclent Stat. ion (CNS).
This conclusion is baned on our review of the report and the evaluation made by General Electric an contained in Att achment 2 t o the report.
The Dist rict recop,niten t hat there ara dif f erencen between the designs of BWR plants and systems; however, our revlaw of the report and the conclusions reinforce CNS's general understanding th ' t.he basic plant response to design basis trannfsnts and accident events is nufficiently similar to obviate the ne e.1 for adM tional plant unique 4 tailed re analysin Additionally, the CNS design incorporates featuren that are more conservative than those ev..iunted in the BWROG report, including the initiation of automat ic nafety syst em actuation f or Emergency Core Cooling Systems (ECCS) from hot leg instrumc* ation. and a qualified system for backfilling reactor water level indication cold reference legs (flow diagram enclosed au Figure 1 to the Attachmont).
The CNS ECCS automatic initiation sJgnals originate from inscrumentation that utilize hot 4
i BWROG Report, "BWR Reactor Vassel Water, e l Instrumentation", Revis ion 1, Aug':s t 2 8, 1992.
Attachment to.
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NSD921014 Page 2 of 5 (Yarway) reference legs. These Yarway instruments provide the signals for Diesel Cenerator start, HPCI/RCIC start. Core Spray inj ection,. RHR' LPCI inj ec tion, ADS initiation, Reactor Recirculation Purrp Trip, AR1 initiation, and also provido Group 1 and 7 isolations as described in the CNS Technical Specifications. As such, the CNS ECCS actuation would not be affected by the potential noncondensible' gas phenorranon in the cold references legc.
These Yarway indicators / switches are located on local instrument racks at CNS and can he accessed and monitored depending on the-circumstances surrounding the transient or accident event. The qualified system for backfilling reactor water level indication cold reference legs uses the Core Spray System to inj ect water into the divisional cold reference 1er,.
This design and approval' was to eliminate flashing and 2
boil-off of water from cold reference legs in response to NUREC 0737, item II.F.2.
Ilowever, this system could be used to backfill the "old reference legs during potential water level indication errora caused by noncondensible gas buildup in the cold reference legs during depressurization events, b.
The impact of potential level indication errors on operator's short and long term actions during and after all lie;nsing basis accidents and transients; BESPONSE:
9 The BWROG report addresses, b) Section 6.9, Operator Responses, the operator actions that could be anticipated in asponse to potential water level indication errors. An evaluation was conducted that verified ~that 1
CNS is conservatively bounded by the BWROG report, Further reviews have verified that station procedures provide for proper short and long term operator actions during all licensing basis accidents end transients.
These procedures include instructions for responding to indeterminate water level indications, including reactor vessel flooding (EOPs).
Additionally, CNS operators have procudures available for their use that allow backfilling of the cold referenca legs of water level instrunentation.
These procedures, 4.6.1 " Reactor Vessel Water Level Indication", and (EOP) 5.8.19 " Reference Leg inj ect! = en", are r_ tallable for-the operator to assure the recovery of any instrt aentation that may have lost water level indication.
These procedures have been augmented by special guidance and training as detailed in 2.b below, c.
The impact of potertial level dication errors on. operator : actions prescribed in emergency operating procedures or other affected procedures not covered in (b).
2 Letter from J.M. Pilant (NPPD) to D.B. Vassallo (USNRC) dated May 31, 1985 NPPD, Cold Reference Leg Modifications to Comply with NRC Generic Letter 84 23.
3 Lottar from D.B. Vassallo (NRC) to J.M. P11 ant (NPPD) dated-August 21,.
_1985, NRC Safe.ty Evaluation Report (SER) Inadequate Core Cooling Instrumentation.
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NSD921014 Page 3 of 5
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'RESPONS11 As stated in-Section 6.9 of the BVROC recqn*, and addressed :in the BWHOC '
letter', and as discussed in response 1.b above, _ plant operators have adequate information in the present CNS procedures, as augmented by the additional guidance and training detailed in 2,b below. CNS will continun-to. follow any tecommendations provided by th-Emergency Procedure i
Committee (EPC) for implementation of additionW guidance-addressing '
potential water level indication errors. These,)ossible recommendations will take into recount the information from the BWROG program of analysis and testing regardfug this iss ss detailed in the BWROG letter'.
2.
Based upon the results of (1), above, each licensee should notify rle-ICC of short term actions taken, such as:
a.
Perirdic monitoring of level -instrumentatica system leakage;
RESPONSE
llistorical data of reactor depressurization events at CNS have been examined for the possible effects of noncondensible gases on reactor water level indications, Evaluation of this data determined that reactor water level indication anomalies potentially attributable to noncondensible gases, occurring during normal depressurization, are limited to less than-5 inches and only occur at recctor' pressures less than 100 psig.
These-anomalies in reactor water icvel instrumentation do not present a concern to the safe ty ot operation of the plant.
Additionally, _
enhanced-maitoring of reactor water lwel indications was utilized during7 two recent normal reactor depressurizations.
"h enhanced monitoring has not indictted any reactor water level inaication anomalies potentially a tributable to noncondensible gas pheaomenon above reactor pressures of-100 !aig. Below reactor pressures of 100 psig CNS has noticeo some minute a:,omalics that could be attributable to noncondensibles however, these minute anomalies were less than 5 inches difference betwee,. divisional:
instruments and presented no safety or operational concern to the plant.
The District will continue this enhanced monitoring of reactor water level instrumentation until this issue is resolved.
Reactor Pressure Vessel water level reference leg sensing -lines, both inside and outside containment, have been examined for proper configuration,. A five foot horizontal run'of tubing at an instrument rack was found bent downward (sagging) and was replaced during a recent plant
-shutdown.
Methods, ' procedures, and training for monitoring reactor water -_ level instrumentation system leak. age were evaluated and found to be thorough and' x
effective.
-These include procedures that require instrument; rack inspections during reactor startup and routine inspections following all instrument-valve manipulations (e.g.,
during monthly surveillances).
Personnel perfoutr.g these inspections are ' VT-2 qualified and receive additional training that ensures that they are aware of the need and
- Letter form BWROC to USNRC dated September 24, 1992, " Reactor Vater Level Instrumentation".
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reason for checking for leaks. ' Additionally, other activities._such as radiation control practices, management, supervisory,-system engineers, and - operator t'ours' contribute to ensuring that leaks are identified.
Leaks found are documented and tracked to ensure that corrective action is timely and comprehensive.
Together, these activities are considered a maj or element contributing to the apparent lack of the; maj or noncondensible gas phenomenon in reactor water level indication at-CNS.
b.
Implementation of procedures and operator training to assure that potential level errors will not result in improper actions;
RESPONSE
CNS personnel are currently trained in the me of CNS procedures'4.6.1-
"u.cactor Vessei Water 1.evel Indication" and (EOP) 5.8.19 " Reference Leg Inj ec tion" to assure che recovery of any instrumentation that may have lost water level indication. Personnel are also trained in the use of the EOPs that instruct the operator to reflood the vessel in the event that-water level is indet rminate.
Additionally, operators have been provided training (in the form-of tailgate sessions) and written guidance that: 1) describes the theory and postulated e f fec ts of noncondensible gases in reactor water-level instrument reference legs, 2) addresses how existing procedures provide guidance to ensure that proper. operator actions are taken-in response to the effects of the phenomenon, and 3) identifies the instruments, and their functions, that are potentially effected.
3.
Each licensee should provide its plans and schedule for corrective actions, including _ any propcsed hardware modifications necessary to ensure _ the _ level instrumentation system design is of high functional reliability for long, tc a operation; RESPONSfd The District endorses the BVP.00 plans originally provided in the BWROG 1etter to 5
the NRC on Aubust 12, 1992. - The District also reaffirms support of the BWROG plans by endorsing the BWROC letter of September 24,_1992*.
If the BWROG program indicates that modifications and/or procedure changes are necessary, the District will review such modifications and/or procedures changes ;against the current CNS' configurat n such as the Core Spray cold refere ce leg injection,-'and ECCS act -, tion -
the reactor water hot (Yarway) reference legs.
If the District determines. 4t additional modifications and/or procedure changes are necessary after this review, a schedule and description for _ such modifications and/or procedure changes'will be provided at that-time.
The District believes that hardware and procedure modifications should_ not be implemented at this time, until a better understanding of the. underlying phenomenon and its significance relative to the performance of reactor water level instrunentation systems can be determined.
Once this determination has 5 Letter from SWROG to USNRC dated August 12, 1992, "BWROG_ Reactor Water Level Instrumentation Long Term Action Plan";
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Attaciunent to NSD921014 Page 5 of 5 I
been made, - the - District will evaluate potential alternatives to resolve this issue, and will review such modifications and/or procedures changes'against the current-CNS configuration, such as the Core Spray cold reference leg injection, and ECCS actuation off the reactor water hot (Yarway) reference legs.
SUMMARY
The District recognizes the importance of reliable water level instrwoentation to.
confirm plant safety, and has taken interim actions to assure safe operation af CNS.
2 Based on the BWROC assessment of the issue, the BWROG is able to conclude, and the NRC has indicated crucurrence, that a substantial safety hazard does not exist. In Generic 1.ctter 92 04, the NRC has indicated that it would like the schedule for long term.
S actions defined in the BWROC letter to be accelerated. The Dist rict believes that the proposed schedule recognizes the need to resolve this issue as soon as possible, and that the schedule is realistic.
In closing, the District wishes to emphasize the fact, that CNS has r.ot noticed this phenomenon of noncondensible gases in reactor level cold reference legs occurring during normal operation of the plant.
CNS has noticed through review of historicol data of reactor deprest.urization events, indication anomallet potentially attributabic to noncondensible gases, llowever, these indication anomalies were limited to less than 5 inches and only occurred at reactor pressuies less than 100 psig.
Furthermore, enhanced monitoring of reactor water level indications were utilized during two r cent normal reactor depre.isurizations at CNS. This enhenced monitoring has not indicated any reactor water level indication anomalies potentially attributable to noncondensible gas pheno.nenon above reactor pressures of 100 psig.
Below inactor pressures of 100 psig CNS has notfeed some minute anomalies that could be attributable to noncondens!bles however, these minute anomalies were less than 5 inches difference between divisional instruments and present no safety or operational concern to the plant.
Additionally, the CNS design is somewhat unique in that.CNS ECCS initiation signals transpire from instrumentation that utilize hot (Yarway) reference legs. These Yarway instruumnts provide the simais for Diesel Generator start, llPCI/RCIC start, Core Spray inj ec t!' n, RllR 1ECI inj t ADS init lation, Reactor Recirculation Pump Trip, ARI initiation, and also provide Group i and 7 isolations as described in the CNS Technical Spec i f 4 catic ns.
As such, the CNS ECCS actuatiLn would not be affected by noncondensible gas phenomenon found in the cold references legs.
'These Yarway-indicators / switches are located on local instrument racks at CNS and can be accessed and nonitored depending on the ci vewns tances surrounding the transient or accident event.
CNS also has available for immediate operator use a qualified system for.
backfilling reactos: ', ster level ludicatiors cold reference 1 cgs. This systen uses the Core Spray System to inject water into the divisional cold reference legs, and has been approved by the NRC. This system could be used to backfill the cold reference legs during potential water level indication errors :aused by noncondensible gas buildup in the cold reference legs during depressurizatio events.
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