ML20154A538

Forwards Rev B to EE-12-0013, Integrated Sys Study of CRD Mechanism Rod Position Instrumentation & Temp Prediction for CRD Mechanism Motors, Per 871204 Meeting

ML20154A538
Person / Time
Site:	Fort Saint Vrain
Issue date:	05/06/1988
From:	Warembourg D PUBLIC SERVICE CO. OF COLORADO
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
Shared Package
ML20154A543	List: ML20154A538 ML20154A545 ML20154A550
References
P-88152, TAC-61601, NUDOCS 8805160044
Download: ML20154A538 (11)

Text

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2420 W. 26th Avenue, Suite 1000, Denver, Colorado 80211 May 6, 1988 Fort St. Vrain Unit No. 1 P-88152 ,

U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555 Docket No. 50-267

SUBJECT:

Control Rod Drive (CRD) Rod Position Indication Instrumentation

REFERENCE:

(1) NRC Memorandum, Heitner to Calvo (NRC), dated December 15, 1987 (G-87445) l (2) PSC letter, Warembourg to Calvo, l

dated April 7, 1988 (P-88121)

Gentlemen:

As a followup to our site meeting of December 4,1987 (Reference 1), Public Service Company of Colorado (PSC) is transmitting as Attachments 1 and 2 to this letter the Control Rod Drive (CRD) Rod PositionIndication(RPI)Instrumentationevaluation. Also, based on commitments set forth in Reference 2, please find enclosed in Attachment 3 PSC's evaluation of the Control Rod Drive Motor (CRDM) service temperature projection which incorporates the results of the most recent core testing.

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P-88152 Page 2 May 6, 1988 If you have any questions on either of these subjects, please contact Mr. M. H. Holmes at (303) 480-6960.

Very truly yours, b A f}(tass M k D.W.Warembourg, Manage)-

Nuclear Engineering Division DWW:CRB/dvd Attachments cc: Regional Administrator, Region IV ATTN: Mr. T. F. Westerman, Chief Projects Section B Mr. Robert Farrell Senior Resident Inspector Fort St. Vrain

Attachment 1 to -

P-88152 l Page 1  !

l ATTACHMENT 1 I CRD ROD POSITION INDICATION INSTRUMENTATION l BACKGROUND FSV Rod Position Indication (RPI) Instrumentation deficiencies

.were originally identified in Reference 1. In response to these NRC  !

concerns, PSC performed an Integrated Systems Study and submitted  !

recommended corrective actions in Reference 2 to resolve the CRD RPI [

concerns. In this-response, PSC comitted to the following actions: .

(1) replacement of the full-in/ full-out limit switches with proximity limit switches; (2) replacement of the existing potentiometers with improved potentiometers which are appropriately designed and l qualified for the life and service condit, ions to be experienced. l NRC's subsequent review of PSC's evaluation and proposed I corrective actions (Reference 7) indicated that PSC's solutions were i not adequately supported, r'ssulting in a general misunderstanding l between PSC and NRC. l l

To resolve the misunderstandings, PSC proposed (Reference 4) an j onsite technical meeting te discuss the original NRC concerns. This [

meeting was conducted on December 4, 1987, and results of this meeting are reported in Reference 5. The purpose of this letter is to provide an updated PSC evaluation of CRD RPI Instrumentation.  ;

DISCUSSION i f

The Integrated Systems Study for CRD RPI has been revised to i resolve remaining concerns identified in the NRC Technical Evaluation  !

Report (Reference 3) and has been included as Attachment 2 to this letter. PSC's resolution of specific NRC concerns identified in {

References 1 and 3 are contained in Enclosure 1 to Attachment 1. {

v CONCLUSIONS l l

Conclusions reached as a result of this revised study remain the same  :

as those presented to the NRC in December, 1987. These conclusions  !

are as follows:

(1)CRD RPI Instrumentation (continuous and limit switch) currently [

installed at FSV is acceptable to meet operability requirements i imposed by the FSAR and FSV Technical Specifications, when i operated in accordance with current aaministrative limits.  !

Improved maintenance and surveillance requirements support  ;

operational conditions. j (2) PSC will continue to pursue the corrective actions identified  !

below to further improve the reliability of CRD RPI [

i Instrumentation, i

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Attachment 1 to

-P-88152-Page 2 PSC ACTIONS:

Short Term Corrective Actions Previously Implemented and Results:

The following practices have 'been implemented to improve overall reliability of the CRD RPI:

(1) Continuous Rod Position Indication (Potentiometers):

Imposition of administrative limits on operators (which prevent overdriving of the control rods past the full-in positiori) has resulted in N0 potentiometer failures since the CRDM incidents of 1984; no addTtional short term actions are deemed to be necessary for these potentiometers pending implementation of long-term corrective action.

(2) Full-in/ Full-out Limit Switchas:

(a) All full-in/ full-out limit switches were replaced following the multiple limit switch failures in 1984; (b) As a result of improved maintenance, surveillance and N0 failures of full-in/ full-out limit operations switches havepractices, been e Eierienced since the CRDM incidents of 1984. Operator awareness of moisture ingress concerns and subsequent moisture reduction in the PCRV since 1984 have also contributed to the reduction in CRD RPI problems, Long-Term Corrective Actions:

The following activities will be implemented as improvements intended to further improve CRD RPI reliability:

(1) Continuous Rod Position Indication (Potentiometers):

(a) PSC will replace existing 10-turn dual element potentiemeters with 15-turn dual element potentiometers, which will significantly reduce the possibility of breakage of the potentiometers due to overdriving the CRDM's, These new potentiometers will be procured to specifications which will ensure that the materials are suitable for the service conditions to which they will be exposed ud will have suitable service life for their intended application.

Appropriate quality standards will be applied to the procurement of these potentiometers to satisfy their design function.

(b) Replacement of existing 10-turn dual element potentiometers with 15-turn dual element potentiometers will begin following completion of qualification analyses and type testing. This replacement is not expected to begin until after the 4th refueling and will be performed sequentially on CRDM's in the region being refueled during each subsequent refueling outage,

Attachment 1 to  :

P-88152 Page 3  ;

i (2) Full-in/ Full-out Limit Switches:

i (a) To reduce mechanical wear between the limit switch shaft and i guide tube, reduced angle cams will be installed to actuate the limit switch shaft roller, per the manufacturer's recommendations. This replacement will be performed  :

sequentially on CRDM's in the region being refueled during each subsequent refueling outage and is not expected to ,

begin until after the 4th refueling.

(b) Limit switches will continue to be replaced (like-for-like);

replacement is intended to reduce the likelihood that 4

mechanical wear or corrosion on the limit switch shaft will result in mechanical failure of the limit switch.

Replacement of limit switches will be performed sequentially  ;

on CRDM's in the region being refueled during each refueling outage, commencing with the upcoming 4th refueling, ,

(c) PSC will continut to evaluate design improvements or replacement indication which will improve the reliability of RPI full-in/ full-out indication. Proximity switches which meet suitable quality and service requirements will be evaluated to determine if replacement in desirable.

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Attachment I to P-88152 Page 4

References:

(1) NRC letter, Denton to Walker, dated October 16, 1984 (G-84392)

(2) PSC letter, Warembourg to Berkow, dated August 15,1986(P-86522)

(3)NRCletter,HeitnertoWilliams,datedJuly 31,1987(G-87262)

(4) PSC letter, Warembourg to Calvo, dated September 3,1987 (P-87307)

(5) NRC Memorandum, Heitner to Calvo (NRC), dated December 15, 1987 (G-87445) i

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r Encicssre 1 to Attachment 1 )

P:ge 1 ENCLOSURE 1 NRC R0D POSITION INDICATION CONCERNS CONTROL R00 INSTRLMENTATION ANOMALIES: PSC RESPONSE:

(NRC Letter, Denton to Walker, dated 10/16/84 (G-84392))

Actions Prior to Restart (following 1984 CRDM incident):

1. To prevent CRDM damage and to protect rod position Plant operating procedure 50P 12-01 has baen potentiometers and limit switches, plant procedures implemented which provides precautions regarding the-

! should be changed to prevent overdriving the CRDM potential damage to the CRD RPI resulting from I past the full-in limit (yo-yo-ing). overdriving the control rod drives. Since.the implementation of these administrative controls, there have been no failures of the potentiometer shafts. Additionally, heavy emphasis is plcced on this issue during initial operator. training and operator requalification training.

2. Periodic surveillances of rod position potentiometers This concern has been addressed by compliance and switches should be developed and implemented in with Interim Technical Specifications 3.1.2 and interim procedures and be proposed for inclusion in 3.1.3, as implemented by supporting surveillances.

the plant technical specifications. This Additional guidance is also contained in 50P 12-01 surveillance should include verification of limit which directs operators to ensure that accurate and I

switch operability and confimation that redundant RPI is available.

redundancy has not been lost.

Long-Tem Actions:

3. Damage due to ciertravel should be precluded by PSC intends to proceed with their long-tem corrective installation of a positive mechanical stop or by action to replace the 10-turn dual element potentiometers providing sufficient clearance to prevent damage, with 15-turn dual element potentiometers. To' resolve the overtravel as it relates to potentiometer damage, the.

installation of a mechanical stop was evaluated and determined to be not feasible.

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Enclosure I to Attachment 1 Page 2 4 An appropriate, independent and definitive means As reported to the NRC in PSC letter, Gahm to Johnson, of verification of control rod full-in position dated 7/31/87 (P-85262), PSC has modified and strengthened should be provided because the installed rod position the requirements specified in SOP 12-01. Surveillance it,strumentation can be inadequate to verify control Procedure SR-TE-9-X (Inserted Rod Position Indication) roo oosition. In the present form, Watt-meter of the is specified to be used to accurately establish shim Msting motor is considered inadequate to verify (wattmeter test)' full-in rod position for control full insertion of control rods. It is therefore rod pairs with inoperable position indication per concluded that the Watt-meter method be refined or an FSV Interim Technical Specifications.

alternate method be developed to achieve sufficient resolution of rod position and then formalized into a plant procedure.

5. Conduct an integrated systems study to resolve RPI The previous 1**"grated systems study has beer revised maintenance and operability questions. to incorporate coments received during the NRC onsite technical visit in December 1987.

CRDM ROD POSITION INDICATION INSTRUMENTATION TECHNICAL EVALUATION:

(NRC Letter, Heltner to Williams, dated 7/31/87 (G-87262))

1. The contribution of corrosion of the full-in limit Effects of corrosion and mechanical eroston have switches was not evaluated. been evaluated in the revised integrated systems study. It has been determined that H moisture ingress events which occurred during or before 1984 resulted in corrosion of metallic surfaces of the potentiometers and the limit switches.

Increased operator awareness of the consequences H and causes of moisture ingress into the core has resulted in significantly reduced core moisture levels, and therefore reduced corrosion.

Erosion was also noted to be a problem with the limit switches due to the steep cam angle, thereby causing frictional forces to be present between the limit switch actuating shaft and the guide cylinder.

Both erosion and corrosion concerns have been ~!

to Attochment 1 Page 3 reduced by the one-time replacement of all limit switches following the CRDM incident, and the continuing program of regional limit switch replacement during region refueling. Replacement of existing cam actuators with reduced angle cams will further reduce the likelihood of limit switch failure.

2. The design of the replacement targets for the As discussed during the December 1987 onsite full-in/ full-out limit switches did not consider technical meeting, there is not a credible mechanism the potential for damaging the rod position for the replacement targets (or limit switch actuating potentiometers when the control rods are overdriven. cams) to mechanically interfere with the position potentiometer shaft.

3. The failure of the slack cable limit switches As discussed during the December 1987 onsite was not eva?uated. technical meeting and addressed in the discussion of limit switch failures in the revised integrated systems study, there have been no failures associated with the slack cable limit switches; ac* - .on of the slack cable limit switch during 1984 was proper indication of a failed CR0M cable.

6. The specification for the replacement rod position The specification for the replacement rod position potentiometers did not include all the potentiometers has been prepared and incorporated environmental conditions that the components into a PSC engineering evaluation to ensure could be exposed to and did not define how the that the replacement potentiometers will be potentiometers would be qualified. suitably qualified for the service conditions and operating requirements that they are expected to experience. Qualification will include appropriate consideration of the temperature qualification plan previously provided to the NRC in PSC letter, Warembourg to Calvo, dated 4/7/88 (P-88121).

5. The proposed replacement instruments that are important As discussed during the December 1987 onsite technical to safety (full-in limit switch and rod position meeting, the CRD RPI potentiometers and limit potentiometer) did not comply with the quality switches are non-safety relatrd components.

Enciostre 1 to Attcchment 1 Pcge 4 standard and instrumentation requirements of GDC 1 Therefore, requirements of GDC 1 and 13 are not and 13 of Appendix A to 10 CFR 50. directly applicable. PSC will take suitable precautions to ensure that replacement components will be manufactured and qualified to withstand the service conditions and operating requirements to which they will be exposed.

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l Attachment I to P.88]Sg