ML20094D774

Informs of Control Rod & CRD Insp & Testing in Response to NRC 840709 Insp.Major Power Consumption & Scram Verification of All 37 CRD & Orifice Assemblies Completed & Insp Underway.Plan for Further Action Described

ML20094D774
Person / Time
Site:	Fort Saint Vrain
Issue date:	07/18/1984
From:	Lee O PUBLIC SERVICE CO. OF COLORADO
To:	Johnson E NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
References
P-84221, TAC-55294, NUDOCS 8408080520
Download: ML20094D774 (5)

Text

{{#Wiki_filter:, w, N.f t PUBLIC SERVICE COMPANY OF COLORADO 1-OENVER, COLORADO 80201 - 80X 840 P. O. 16805 WCR 19 1/2, Platteville, Colorado 80651 O OSCAR R. LEE O e July 18, 1984 Fort St. Vrain Unit #1 P-84221 3g@m0MM V Mr. E. H. Johnson, Chief jl O Reactor Project Branch 1 n 3 01984 Region IV \\ Nuclear Regulatory Commission. ~y d 6. 611lRyan Plaza Drive, Suite 1000 iArlington, TX 76011 F

SUBJECT:

PSC Actions in Response To NRC Evaluation of Fort St. Vrain u

Dear Mr. Johnson:

.This letter is to provide you with a summary of PSC actions to date with respect to centrol rod drive inspections and to inform you of f future control rod inspections and testing as well as planned actions (

in the other areas addressed in the NRC inspection conducted the week of July 9,'1984.

Motor power consumption profiles have been obtained and scram verifications have been made for all 37 control rod drive and orifice assemblies- (CRD0A's) resident in the core on June 23, 1984. We have completed our examination of the control rod drives from Regions 7 and 14, and are currently in the process of examining the control rod drive from Region 10. Testing and inspection of the two CRDOAs recently examined consisted of.the following: 1) Overall visual inspections of the CRDOAs in the "as found" condition. 2) Collection - of free rotational torque data from the 200 Assembly gaar train and the motor-brake assemblies. 3): Disassembly and visual inspection of the motor-brake assemblies including one motor rotor bearing from each of the CRDOAs. 4) Disassembly and visual inspection of the Region 7 CRD0A 200 Assembly gear train. I 0 0 p*&520840718==og g L

F, jf .y b Z e y = Testing'has also been performed on a spare CRDOA motor-brake assembly to establish the sensitivity of the brake to moisture with .s sensitivity being detected. ~ Motor. power ' consumption profiles and scram time data for the 37 .CRDOAs were compared-to historical data. No significant differences were noted, and all data were within design expectations. Overall visual examinations of the CRD0As, thus far, have revealed evidence of min'or oxidation of the carbon steel components, previous

moisturs condensation,.and

-small quantities of unidentified particulate matter. No indications that the CRD0As had experienced excessive temperatures were noted. Free rotational torque data 'obtained from the-200 Assemblies and the motor-brake assemblies -showed no evidence of unacceptable performance, but variations were

observed in the. individual motor rotor bearings.

These variations -were not significant to the operability of the CRD0A. The specific visual examinations of the CRDOA subassemblies showed no evidence of excessive wear, pitting,. improper lubrications, gear misalignment, or -other conditions which could have resulted in CRDOA inoperability. A: review of historical inf'ormation and design documents has revealed noLcorrelation between the CRD0As that failed to scram and the CRD0A

1. F" removal / replacement activities during the third refueling, or their purified helium purge flow supplies (subheaders). A correlation was 9

. observed,- however,-relative to the specific circumstances prevailing at the. time of the June 23, 1984 incident and those which prevailed ( during the only other similar event. This similar event' occurred on ~ February 22, 1982, ~ and-was reported to the NRC via Reportable g.. ,0ccurrence.-No.'82_-007. In both events, high moisture levels in-the ' primary. coolant led to icing of the helium purification train low temperature gas-to gas heat exchanger which resulted in a temporary loss of train flow and hence a loss of purge flow to ~ he CRD0A t penetrations. ' Additionally, operational data taken prior to each event established that affected withdrawn CRDOAs were operable to 1 - l scram before the above conditions existed. y L l Based on. the information

above, we believe that further

? -investigations 'should concentrate on potential failure modes- / associated with these coincident conditions. It is anticipated that 7_ _in.vestigation results will dictate that immediate corrective actions t - be :taken to shutdown the reactor whenever high moisture levels

(limiting dewpoint temperature to be determined) are coincident with

~ !c. loss'of.CRDOA' purge flow. 3

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.-<,w- ~ a: 99j. h%l l k ' ', >p y 31;.,. Qi (@r$k'f *%. p s 4 ?' ,_ &q, ,.g -3 ' g..- 2.~W: n9[f, 4 %; 33MI,3 p-. (W1thire'shect;to.an;immediate-planLof action, PSC intends to pursue

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• the~following:

';qm g' " ll)' _ (Co.ntinue. zinvestigations.into :. the. effects of purge flow loss 7 coincident:withhighfprimarycoolantmoisturelevels, 1 J _ n.2)! Coritin'ue< to' collectSparticul' ate. matter found in the CRDOA te: nE . subassemblies,;and analyze it. for. constituent parts. (NOTE: -7 y 4:: c:Succe'ssful: analysis; is! contingent upon sufficient particulate C F' beingiavailable for collection), a w m~ p ^ }*'g [3)( lDisasse Ele ?and. inspect 1 the motor-brake ' assemblies of the s remaining four.CRD0As.that' failed to. scram' on June _ 23,- 1984 _ L(Regions.6,:10,125, Land 28), ... x ? 14)? : Disassemble.~and'. inspect the CRD0A 200 Assembly gear train from Region'25,- c. ~ w. i _'5)f d Functionally itest-:one---30 weight-percent' and one 40 weight , W t ly~ T - ' percent -reserve' shutdown hopper, ~ g@"O O; .N,.. - L.6)" *Performlia~ physical examination.~of-the Reserv'e Shutdown material ?

m. "

gj ';d i_ ~ subsequent.to; testing, ,i , Q M __ 17)1 cClean. disassembled. components 'of _the-CRDOA~s ' inspected, as-6? ~ h12A _

appropriate,Husingl wet or" dry; wiping, nitrogen blowdown, or L h (alcoholisolutionmethods.

u . w W% ~ %'8')):Performz a test'to determine the back EMF generated during ~ scram ~ c gw s "; ;for all'37.CRD0As,- .m sfpg 19))2 Perform: ate'sttodetermine-the.sensitivityofthemotor' bearing. "", f Eassembly~to moisturecrelative to free rotational torque, 1 i^ /10)JPerform.aitestto!determinetheeffectsofexercisingaCRD0Ato ~ ,i,s m cascertain.the.self clearing characteristics of the assembly, x. w & 'w '

11)(iDisassembleand'inspectthemotor-brake

assembliesoftwoCRD0As.

,i :: I-Iwhich properly 3 scrammed on~ June 23, 1984. In addition, one of gy ' ~ Cits-200 Assembly l gear train; .the iselected ECRDOAs will undergo disassembly and inspection of M w +- l f l:'

k, snQf 0.

? G:q' }i r' 4 - ~ I)i,'-- T i e

ff??l a c M e It.'is PSC's. position that. inspection of additional CRD0As to those

planned would_not' provide aay more significant information relative

to identifying the mechanism for the affected CRDOAs failing to scram and would not improve.the performance of the CRD0As.

This position is based:on the.following:

1), Inspections to date. have not revealed any CRD0A physical abnormalities which could have resulted in a loss of scram

' function. 2)' Motor-power consumption profiles for all 37 CRD0As subsequent to .the_ event illustrate that they are functioning properly and well within design expectations. 3)~ Free _ rotational torque data taken before and after disassembly 'and cleaning of the inspected CRDOA 200 Assembly have revealed no significant changes in performance. -4) Scram Lverification data for all 37 CRDOAs taken subsequent to + the event are well within FSAR limits. This suggests that no x - physical. degradationfis present which would inhibit the CRD0A's scram functions. 5)~ Since-all_ withdrawn CRD0As had_been verified operable prior to this event (and the same was true with respect to.the February ~ 22, J1982 event), abnormal degradation of the CRD0As is not indicated as the failure mechanism. The event appears to be due primarily to the specific plant conditions that existed at the time: _ high primary coolant moisture levels coincident with a C ~ . loss of CRD0A purge flow, _It must be emphasized that this position is founded on experience to s date'..If. future. findings suggest the'need for further testing and . _ inspections, PSC will reassess this position. With respect to remaining CRDOA issues, prior to startup, PSC commits to: i l)~. Evaluate a CRD0A-preventive maintenance program for future ~ .refuelings,

2)L Develop a surveillance test to assure that Control Rod Drive

. motor temperatures (for.those with installed instrumentation) will be monitored in conjunction with the weekly rod drop test c throughout the. remainder of Cycle 3 whenever power levels are 'above 30%. aL'

V. n. = p,f.f.,' j', g;b l J,' ' '. .}; m . %m x.n h m 43); lEvaluateithe' adequacy of the weekly rod drop test to demonstrate @J '; ,"' CRDOA. operability. ~- 4 % l ~ Regarding sother ' subjects discussed with the NRC the week of July 9, 4.1984,.PSC provides_the following:- wr ~ _ 4 1 ii)- (Moisture.: Ingress Committee modification recommendations will be j evaluated and ! finalized. An' ~ installation. schedule will be ~ '. developed:and1 submitted in. future correspondence, w. . I ^s.. s a = k,2) L ' ~PSC"lfrecognizes the need to. upgrade the Fort St. Vrain Technical _' Specifications _and, as indicated in' discussions-held with the P. .NRC rfully. intends <to' submit all_ upgrade revisions by the end of T ~

1985. iPreliminary schedule. estimates'. indicate, -however, that

. lthe'lNRC ' recommended submittal date_of. January 1, 1985, is not ^ feasible.- lA proposed schedule for this activity _will be ,7 m - isubmitted as~soon as it is: developed. !3)5 lA yachedule~ for'. evaluating ~ improvements 'in :the conduct of

operations'and maintenance activities will be submitted prior.to

.v M 1startup. -{, fy j-believe -that.'this'information provides an up to date summary of E 'ouricurrent knowledge and planned a_ctions associated with those items _ e (discussed twith-thel. NRCTduring theJinspection conducted the week of J-L July _ 9,, '-19 8 4. .f As indicated previously, we are performing our P O.4 longineering; evaluations ~ concurrent with our CRDOA inspection program 'with~thelintent of providing a final report as soon as possible upon - ~ ) completion of' - the' iiispection program. If'you have any questions or .requ re.ifurther-clarifications, please contact Mr. Don Warembourg at i i N.(303);785-2223. 4 D,. 3 Very truly yours, 4 ~ y 7 j -0.-R. Lee Vice President, ( g Electric Production V ' 4 s Q 'ORL/djm. z ',. df N _{. ur -:l> .'k l- ,e -f 4 't g, .c ,.t T =.h c I 4 s _}}