ML20210P447

Application for Proposed Amend 150 to License DPR-54, Changing Tech Specs to Replace Phase Imbalance/Underpower Relay for Each Reactor Coolant Pump W/Undercurrent Relays. B&W Engineering Info Record 51-1164378-01 Encl.Fee Paid

ML20210P447
Person / Time
Site:	Rancho Seco
Issue date:	09/22/1986
From:	Julie Ward SACRAMENTO MUNICIPAL UTILITY DISTRICT
To:	Miraglia F Office of Nuclear Reactor Regulation
Shared Package
ML20210P451	List: ML20210P447 ML20210P513
References
JEW-86-358, TAC-63080, NUDOCS 8610060775
Download: ML20210P447 (11)

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$SMU= SACRAMENTO MUNICIPAL UTILITY DISTRICT O 6201 s Street, P.O. Box 15830. Sacramento CA 95852-1830,(916) 452-3211 AN ELECTRIC SYSTEM SERVING THE HEART OF CAllFORNIA JEW 86-358 September. 27 1986 DIRECTOR OF NUCLEAR REACTOR REGULATION ATTENTION FRANK J MIRAGLIA DIRECTOR PWR-B DIVISION U S NUCLEAR REGULATORY COMMISSION WASHINGTON DC 20555 DOCKET N0. 50-312 LICENSE N0. DPR-54 PROPOSED AMENDMENT N0. 150 In accordance with 10 CFR 50.90, the Sacramento Municipal Utility District proposes to amend its Operating License DPR-54 for Rancho Seco Nuclear Generating Station Unit No. 1.

Proposed Amendment No. 150 consists of replacing the phase imbalance /underpower relay for each Reactor Coolant Pump with undercurrent relays. Details of this proposed change are presented in Attachments I, II and III which are the Description of and Reasons for Proposed Changes, Safety Analysis and Bases for No Significant Hazards Determination, respectively.

Pursuant to 10 CFR 50.91 (b) (1), the Radiological Health Branch of the California State Department of Health Services has been informed of this proposed amendment by mailed copy of this submittal.

Enclosed is a check in the amount of $150.00 as required by 10 CFR 170.21,

" Schedule of Fees."

The District requests prompt review of this proposed amendment since it is planned, if approved, to implement this change before restart of the plant.

Should you require any further information with respect to this Proposed Amendment, please contact Mr. Ron W. Colombo at Rancho Seco Nuclear Generating Station Unit No. 1.

.E. WARD Subscribed and sworn to before me DEPUTY GENERAL MANAGER this & day of Stc6edf1986.

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ATTACHMENT I DESCRIPTION OF AND REASONS FOR PROPOSED CHANGE Proposed Amendment No. 150 consists of replacing the phase balance and power sensing relays used in the Reactor Coolant Pump motor monitors with undercurrent relays. The existing relays, manufactured by Wilmar Electronics, have been in service since 1971. These relays have been the source of continuous problems since their initial installation, resulting in frequent reportable occurrences and requiring many repairs, both by the manufacturer and by District personnel.

Because of these recurring problems, the District contracted Babcock & Wilcox to perform an engineering study to consider replacing the troublesome Wilmar phase balance /underpower relays with undercurrent relays manufactured by Brown Boveri (Model ITE-37).

The study noted that the Wilmar relays are unique to Rancho Seco, and that all other B&W PWRs utilize current sensing methods, two of which are similar'to that proposed for Rancho Seco. A copy of the B&W study (Document 51-1164378-00) is enclosed with Attachment II, Safety Analysis.

The proposed changes with respect to the Rancho Seco Technical Specifications affect Tables 3.5.1-1 and 4.1-1 as described below:

1. Table 3.5.1-1, Instruments Operating Conditions, Page 3-30a: Under Auxiliary Feedwater, changed Item 2 from: " Phase Imbalance /Underpower RCP:" to: " Undercurrent RCP:."

2. Table 4.1-1, Instrument Surveillance Requirements, Page 4-7b: Changed Item 48a from: " Phase Imbalance /Underpower RCP" to: " Undercurrent RCP."

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ATTACHMENT II SAFETY ANALYSIS i

Proposed Amendment No. 150 consists of replacing the existing phase imbalance /

underpower relays used in the Reactor Coolant Pump motor monitors with under-current relays. The existing relays, in use since their initial installation in 1971, have experienced numerous component failures and calibration problems resulting in many reportable occurrences.

At the request of the District, Babcock & Wilcox performed an engineering study of the proposed replacement (see enclosed B&W document 51-1164378-00),and concluded that the use of undercurrent relays instead of phase imbalance /

underpower relays will adequately perform the required function of monitoring i loss of electrical power to the Reactor Coolant Pump motors. The' District 4

has reviewed the B&W study and reaches the same conclusion.

On this basis, the District considers that the proposed changes will have no adverse effect on plant safety or-to that of the public.

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BWNP-20440 3 (8/85)

, , b [* ENGINEERING INFORMATION RECORD Safety Related:

Document identifier 51-1164378-01 Yes O No 3 i Title Study of Proposed Reolacement of Wilmar Relavs in the Reactor Coolant Puns

.ionitors at Rancho Seco Prepared by b 6 a I, I b'

• k ' ) Date 7-/7-Eb Reviewed by Aadv b- [5 * ~ Date 7-2/-%

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Remarks:

This report reviews the acceptability of a proposed design change to the Reactor Coolant Pump Monitors (RCPM) at Rancho Seco wherein Wilmar phase balance relays will be removed and the Wilmar underpower relays are replaced by undercurrent relays. An examination is made of RCPM designs at the other operating B&W plants, RCPM functional requirements, functional comparisons between the existing versus the proposed design, affected licensing documentation, and recommended design criteria. The s-report concludes that the proposed design change will allow the j RCPM to adequately perform its required function.

Revision 01 provides current relay setpoint recommendations and Technical Specification revision recommendations.

Page 1 of 7

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51-1164378-01 Page 2 of 7 i STUDY OF PROPOSED REPIACEMENT OF WILMAR REIAYS ,

IN THE REACTOR COOLANT PUMP MONITORS  !

B&W TASK 752 l l

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1.0 INTRODUCTION

l The Reactor Coolant Pump Monitors (RCPM) at Rancho Seco presently utilize Wilmar phase balance and power sensing relays to provide RCP status signals to the RPS and ICS.

Since installation, the Wilmar relays have experienced numerous component failures and calibration problems. To alleviate these problems, SMUD is considering eliminating l the phase balance relays and replacing the power sensing relays with undercurrent relays. Because B&W provided the functional requirements for the RCPMs, SMUD has requested that B&W review the acceptability of this proposed change. l l

2.0 DISCUSSION In preparing this report, the following items were examined:

(1) What' types of Reactor Coolant Pump Monitors are in use at the.other cperating B&W plants.

(2) What are the functional requirements for the RCPMs.

(3) How do the proposed undercurrent relays compara " -

functionally with the existing phase balance and power sensing relays for the purposes of meeting the functional requirements determined in (2) above.

(4) What effect, if any, does the proposed change have upon previous licensing documentation.

(5) Recommended design criteria applicable to the proposed design change.

The following is detailed discussion of each of these items.

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51-1164378-01 Page 3 of 7 2.1 Survey of Reactor Coolant Pump Monitors at Other Operatina B&W Plants Schematic diagrams of RCPM circuits for Oconee, TMI-1, Arkansas Nuclear One, Crystal River, and Davis Besse were examined to determine the methods used to monitor the RCP status. Two plants utilized current transducers in one phase of each RCP to provide a signal to a comparator which provided both undercurrent and, in one case, overcurrent trips to the RPS. The remaining plants utilized watt transducers to sense' motor power to determine RCP status.

Nonc of the plants su:icycd utilized phase balance relays in the RCPM signal to the RPS.

From the above survey, it can be concluded that the scheme proposed by SMUD to utilize undercurrent relays to provide RCP status information to the RPS would not be unique with respect to B&W plants, but rather that two plants already utilize schemes to provide RCP status based only upon motor current. ..

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2.2 Reactor Coolant Pumo Monitor Functional Recuirements The functional requirements for the SMUD RCP monitors are given in the SMUD Technical Specifications Section 2.3.1.B:

"The pump monitors prevent the minimum core DNBR from decreasing below the CHR correlation limit by tripping the reactor due to (a) the loss of two reactor pumps in one reactor coolant loop and (b) loss of one or two reactor coolant pumps during two pump operation. The pump moni* ors also restrict power level to 55 percent for one reactor coolant pump operation in each loop". Per SMUD USAR Section 14.1.2.6.1, a pump failure can occur from loss of electrical power, or a mechanical failure which is considered to be a <

locked rotor and is used as a bounding accident which covers also a separation of the pump impeller from the motor shz.ft.

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l 51-1164378-01 Page 4 of 7 The locked rotor analysis referred to in USAR Section 14.1.2.6.3 assumes that the RPS trips on overpower based on  ;

flow and imbalance. Therefore, because the trip due to loss of an RCP due to mechanical failures does not require pump status input, the RCPM is only required to monitor a loss of electrical power to the RCPs.

2.3 Functional Comparison Between Phase Balance and Undernower Relav Combination Versus Undercurrent Relav In order to determine the capability of undercurrent relays to perform tha role of the phase balance and underpower .

relays which they would replace in the RCPM, a comparison is made below of the function of each device.

A ' current sensing relay differs in function from a power sensing relay in that while both devices utiliza current magnitude as inputs, the power sensing relay also utilizes the additional inputs of voltage magnitude and phase angle between the current and the voltage, which is a measure of power factor.

Q From the three values of voltage, current and

[f power factor the power sensing relay derives a value for active power (watts). The undercurrent relay senses only the current magnitude, which for the full range of motor operation from stalled to no load speed, is not proportional to the motor power. However, for the normal RCP operating range from cold to hot reactor coolant conditions the power factor remains practically constant. Therefore, for this range, the current and power are relatively prrportional, provided that the voltage remains reasonably stable. Due to the proportionality between the current and power throughout the range of normal RCP motor operation, the undercurrent relay and the underpower relay behave in a similar manner in this range and either device can be set to trip outside of this range. Therefore, the undercurrent relay is an

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51-1164378-01 Page 5 of 7 adequate replacement for the underpower relay for the function which the underpower relay performs in the RCPM, which is to sense loss of power to the RCP motor.

The proposed design change would eliminate the phase balance relays from the RCPM. This change is acceptable on the

basis that the maximum possible phase imbalance, which occurs when one phase is open circuited, will result in a reduction in motor speed of only 8 RPM for cold loop conditions and 5 RPM for hot loop conditions (See Attachment I). This represents a maximum change in speed of 0.68% ,

which will have negligible affect on the DNBR referred to in Section 2.2.

1 2.4 Licensine Documentation Affected by the ProDosed Desian Chance Both the SMUD USAR. and Technical Specifications were reviewed for impact by the proposed design change. USAR Section 7.1 addresses the RCPMs as being " power monitors". '

L If the design change is incorporated, the RCPMs will no ,_j longer directly monitor pump power, therefore, the - USAR should be revised accordingly. Also, Table 7.1-2 in the USAR should be revised to delete the phase unbalance sensors. Similar changes are also required to the Technical Specifications Table 3.5.1-1, Auxiliary Feedwater Item 2, and Table 4.1-1, Item 48A. j 2.5 Recommended Desian Criteria 2.5.1 The design change should retain the single failure criterion of IEEE 279 to the extent that no single l

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51-1164378-01 Page 6 of 7 failure of an RCPM component will prevent the Reactor Protection System from fulfilling its protective functions when action is required. It is recommended that four relays be provided in the RCPM for each motor, one relay for each RPS channel.

2.5.2 Means should be provided for physical and electrical channel separation and isolation of the RPS circuit from non-IE circuits.

2.5.3 All equipment in the Class 1 portion of the RCPM and the RCPM cabinet should be seismically qualified.

2.5.4 Undercurrent relay trip setpoints should be established which will allow reliable sensing of loss of RCP motor electrical power without causing spurious actuations during normal RCP operation. The previous setpoint of 300 amperes recommended by B&W in a 8/20/71 letter from R.J. Cuffin to R.A. Horry is suitable for this purpose. .

_.1 2.5.5 The response time of the undercurrent relays should be

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examined to ensure that the maximum response time requirements imposed on the original equipment is not exceeded, and that the response time is not so short as to cause spurious actuations.

3.0 CONCLUSION

The design change proposed by SMUD to replace the Wilmar l phase balance and underpower relays in the RCPM with undercurrent relays will allow the RCPM to adequately perform its required function of monitoring loss of electrical power to the RCP motors.

[ ATTACHMENT 1 Sabccc'< & Vi!!co;; '

Mr. Roy A. Norry ECP Motor Single Fnasing Protection *

~ June 25, 1971 vill result in line currents on the re=aining two phases of 'approximately

-274-and.454 of rated current for the cold and hot loop conditions after slowdown. Since these currents are in the ran;;e of protection of the over- '

current relay, one could expect it to trip should the phase balance relay -

fail entirely. However, with the phase balance relay ' set for.25g ~ imbalance.,

4 e.wculd. .

e:epect.a.. trip-te'ocee:vithin the..5;second

- - . . - - . . . . a setting.

Since the unit is at speed prior to single phasing and the single phase -

line voltr.ge vill not dip below 92p d of rated voltage, then the unit vill not stall. The rate of change of speed from three phase to sin 6 1e operation is governed by the total rotating inertia of the system (phase including loop water), and the difference between the pu=p load curve and motor torque curves. -

The change in speed for 10700 HP steady state conditions from thr'ee p' nase to single phase operation 1s from 1176 to 1168 RE4.

For a hot loop HP of 8050, this change is from 1182 RPM to 1177 RR4.

Eas.ed--~bfebnelaying %cribe.J.,a* Mind- m nbject.ios to single. phase . opera ,

stion,Sor. a period. ef..five sec =ds before_.the. motor -is--removed from.the line.

Should an tte=pt be 'made to restart the.. unit with single phase power,-

adequate protection should' aga.in'be' afforded by the phase balance relay

_vs protection curve .0501-0199F.

Attached for your infor=ation is the 3W 1etter to A-C dated May 19, 1971.

Please advise if you have any further questions on this subject. .

. Very truly.yours, .

R. T. Schemer Project Manager ,

. J. Cuffia Project Engineer -

cc:

J. J.' Mattimoe - *

. 1 D. W. Harris , l 1

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ATTACHMENT III BASES FOR N0 SIGNIFICANT HAZARDS DETERMINATION Proposed Amendment No. 150 consists of replacing the phase balance and power sensir,9 relays used in the Reactor Coolant Pump motor monitors with undercurrent relays. The existing relays, manufactured by Wilmar Electronics, have been in service since 1971. These relays have been the source of continuous problems since tLn r initial installation, resulting in frequent reportable occurrences, and requiring many repairs both by the manufacturer and by District personnel.

Because of these recurring problems, the District contacted Babcock & Wilcox to perform an engineering study to consider replacing the troublesome Wilmar phase balance /underpower relays with undercurrent relays manufactured by Brown Boveri (Model ITE-37).

The study noted that the Wilmar relays are unique to Rancho Seco, and that all other B&W PWRs utilize current sensing methods, two of which are similar to that proposed for Rancho Seco.

The B&W concluded that the use of undercurrent relays instead of phase imbalance /

underpower relays will adequately perform the required function of monitoring loss of electrical power to the Reactor Coolant Pump (RCP) motors. The District has reviewed the B&W study and reaches the same conclusion.

The District has also reviewed the proposed change against each of the criterion of 10 CFR 50.92 and concluded that plant operation would not:

1. involve a significant increase in the probability or consequences of an accident previously evaluated. As indicated above, the engineering studies have concluded that the use of undercurrent relays will adequately acrform the same function of monitoring loss of power to the RCP motors as phasa imbalance /

underpower relays. Accordingly, the probability or consequences of an accident previously evaluated is not seen as being increased by the proposed change.

2. create the possibility of a new or different kind of accident from any previously analyzed. The use of undercurrent relays has been determined to provide an equivalent function to those of phase imbalance /underpower relays.

Therefore, any malfunction of the former, although expected to be significantly less frequent than the latter, is considered to have the same effect on plant operation. Thus, no new or different kind of accident from any previously analyzed is foreseen.

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3. involve a significant reduction in a margin of safety. Since engineering studies have determined that the proposed undercurrent relays will provide an equivalent function to the existing phase imbalance /underpower relays, it is concluded  !

that no margins of safety will be reduced.

Based on the above determinations, the District has concluded that there is reasonable assurance that the health and safety of the public will not be endangered by plant operation in the proposed manner. I l