ML20067C235

Technical Evaluation Rept on Monitoring of Electric Power to Reactor Protection Sys for Monticello Nuclear Generating Plant, Supporting Amend 12 to License DPR-22

ML20067C235
Person / Time
Site:	Monticello
Issue date:	07/16/1982
From:	Selan J LAWRENCE LIVERMORE NATIONAL LABORATORY
To:	NRC
Shared Package
ML20067C231	List: ML20067C227 ML20067C233 ML20067C235 ML20067C238
References
CON-FIN-A-0250, CON-FIN-A-250 UCID-19145, NUDOCS 8212090023
Download: ML20067C235 (9)

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TECUMCAL :' VALUATION REPORT ON THE

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A.aBable from: P.stional Technical Information Senice - U.S. Department of Commerce

$285 Port Roya! Road - Springfield. VA 22161 - 56.00 per copy - (Microtiche $3.54)

ABSTRACT This report documents the technical evaluation of the monitoring of electric power to the reactor protection system (RPS) at the Monticello Nuclear Generating Plant. The evaluation is to determine if the proposed design modification will protect the RPS from abnormal voltage and frequency conditions which could be supplied from the power supplies and will meet certain requirements set forth by the Nuclear Regulatory Commissicn.

The proposed design modifications will protect the RPS from sustained abnormal voltage and frequency conditions from the supplying sources.

FOREWORD Tiiis report is supplied as part of the Selected Electrical, Instrumentation, and Control Systems Issues Program being conducted for the 'J. S. N iclear Regulatory Commission, Office of Nuclear Reactor Regulation, Division of Licensing, by Lawrence Livermore National Laboratory.

The U. S. Nuclear Regulatory Commission funded the work under the authorization entitled " Electrical, Instrumentation and Control System Support," B&R 20 19 04 031, FIN-A0250.

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TABLE OF CONTENTS Page 1.

INTRODUCTION.

1 2.

DESIGN DESCRIPTION 2

3.

EVALUATION 3

4.

CONCLUSION 4

S REFERENCES S

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TECHNICAL EVALUATION REPORT ON THE MONITORING OF ELECTRIC POWER TO THE REACTOR PROTECTION SYSTEM

& THE MONTICELLO NUCLEAR GENERATING PIANT (Docket No. 50-263)

James C. Selan Lawrence Livermore National Laboratory, Nevada 1.

INTRODUCTION During the operating license review for Hatch 2, the Nuclear Regulatory Commission (NRC) staff raised a concern about the capability of the Class lE reactor protection system (RPS) to operate af ter suffering sustained, abnormal voltage or frequency conditions from a non-Class lE power supply. Abnormal voltage or frequency conditions could be produced as a result of one of the following causes: combinations of undetected, random single failures of the poser supply components, or multiple failures of the power supply components caused by external phenomena such as a seismic event.

The concern for the RPS power supply integrity is generic to all General Electric (GE) boiling water reactors (BWR) MARK 3's, MARK 4's, and MARK 5's and all BWR MARK 6's that have not elected to use the solid state RPS design. The staff therefore pursued a generic resolution. Accordingly, GE proposed a revised design, in conceptual form, for resolution of this concern [Ref. 1].

The proposed modification consists of the addition of two Class lE " protective packages" in series between each RPS motor-generator (M-C) set and it's respective RPS bus, and the addition of two similar packages in series in the alternate power source circuit to the RPS buses.

Each protective package would include a breaker and associated overvoltage, undervoltage and underfrequency relaying. Each protective package would meet.the testability requirements for Class lE equipment.'

With the protective packages installed, any abnormal output type failure (undetectable random or seismically caused) in either of the two RPS' M-G sets (or the alternate supply) would result in a trip of either one or both of the two Class IE protective packages. This tripping would interrupt the power to the ef fected RPS channel, thus producing a scram signal on that channel, while retaining full scram capability by means of the other channel.

Thus, fully redundant Class lE protection is providad, bringing the overall.,

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RPS design into full conformance with General Design Criteria (GDC)-2 (Ref. 2],

cnd GDC-21 [Ref. 3] (including IEEE-279 [Ref. 4] and the Standard Review Plan [Ref. 5]).

The NRC staff reviewed the proposed GE design and concluded t hat the modification was acceptable [Ref. 6], and should be Laplemented in conformance with the applicable criteria for Class lE systems.

The NRC requires that the components of the RPS not be exposed to unacceptable electric power of any sustained abnormal quality that could damage the RPS.

This involves providing means to detect any overvoltage, undervoltage, or underfrequency condition that is outside the design limits of the RPS equipment and to disconnect the RPS from such abnormal electric power before damage to the RPS can occur. The equipment which performs these functions must satisfy the single failure criterion and be reismically qualified. The NRC issued a generic letter [Ref. 7] to all operating BWR's requesting the licensees to submit design modification details and Technical Specifications for post implementation review.

By letters dated November 1,1980 [Ref. 8], April 24,1981 [Ref. 9],

Karch 23,1982 [Ref.10], and May 17,1982 [Ref.11], Northern States Power Company (NSP), the licensee, submitted design modifiestion details regarding the monitoring of electrical power to the RPS at the Monticello Nuclear Generating Plant.

The purpose of this report is to evaluate the licensee's submittal with respect to the NRC criteria and present the reviewer's conclusion on the cdequacy of the design modifications to protect the RPS from abnormal voltage and frequency conditions.

2.

DESIGN DESCRIPTION The licensee has proposed to install the GE designed " electrical protection assembly" (CE No. 914E175) to monitor the electric power in each of the three sources of power (RPS M-G sets A and B, and the alternate cource) to the RPS.

Each assembly consists of two identical and redundant packages. Each package includes a circuit breaker and a monitoring module.

When abnormal electric power is detected by either module, the respective circuit breaker will trip and disconnect the RPS from the abnormal power source.

The monitoring module detects overvoltage, undervoltage, and underfrequency conditions and provides a time-delayed trip when a setpoint is exceeded.

i 3.

EVALUATION The NRC stated several requirements that the licensee must meet in their design modification to monitor the power to the RPS. A statement of these requirements followed by an evaluation of the licensee's submittals is as follows:

(1)

"The components of the RPS shall not be exposed to unaccept-able electric power of any sustained abnormal quality that could damage the RPS."

The monitoring module will detect overvoltage, undervoltage, and underfrequency conditions with the following setpoints.

The chosen setpoints are within the ratings of the RPS components and thus ensure their protection from sustained abnormal power:

Nominal voltage 116 volts, 60 Hz nominal C_nfition Setpoint Time Delay Overvoltage

< 128 volts

.10 second Undervoltage

> 104 volts

.10 second Underfrequency

>, 57 Hz

.10 second (2) " Disconnecting the RPS from the abnormal power source shall be automatic."

The monitoring module will automatically disconnect the RPS buses f rom the abnormal power supply af ter the set time delay chould the parameters setpoints be exceeded.

(3)

"The power monitoring system shall meet the requirements of IEEE 279-1971, GDC-2 and ODC-21."

The monitoring packages meet the Class 12 requirements of IEEE 279, the single failure criteria of GDC-21, and the seismic qualifications of GDC-2.

(4)

" Technical Specifications shall include ~ limiting conditions of operation, surveillance reqqirements, and trip setpoints.",

The licensee submitted draft Technical Specification changes which included limiting conditions for operation when the number of operable monitoring syste.as is less than required and surveillance requirements which included a functional test, channel calibration and verification of the trip se t point s..

a 4.

CONCLUSION Based on the information submitted by Northern States Power Company for the Monticello Nuclear Generating Plant, it is concluded that:

(1) The proposed setpoints of the relays in the two protective packages to be installed in series, in each of the power sources to the RPS buses, will automatically protect the RPS components from sustained abnormal overvoltage, under-voltage, and underfrequency conditions outside the design limits of the RPS components.

(2) The protective packages meet the requirements of Class lE equipment (IEEE 279), single failure criteria (GDC-21), and seismic qualification (GDC-2).

(3) The proposed time delay before circuit breaker tripping.

will not result in damage to components of the RPS or prevent the RPS from performing its safety functions.

(4) The following minimut a nd maximum limits to the trip setpoints, limiting conditions for operation (LCO), and surveillance requirements, to be included in the Technical Specifications, will protect the RPS components from sustained abnormal power:

(a) Overvoltage

< 128 volts, time delay <.10 second Undervoltage 2; 104 volts, time delay <.10 second Underfrequency 2; 57 Hz, time delay <.10 second (b) An inoperable power monitoring system be restored in 30 minutes or remove the source associated with the inoperable power monitoring system. One package may be inoperable, as necessary for testing and maintenance, not to exceed S hours per =onth.

(c) A functional test at least once per 6 months and a channel calibration once per operating cycle to determine the oper-ability of the protective instrumentation including simulated automatic actuation, tripping logic.,- output circuit breaker tripping, and verification of the netpoints.

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REFERENCES 1.

General Electric Company letter, MFN 408-78 (G. G. Sherwood) to NRC (R. S. Royd), dated October 31, 1978.

2.

General Design Criteria-2 (GDC-2), " Design Bases for Protection Against Nattral Phenomena," of Appendix A, " General Design Criteria for Nuclear Power Plants," in the Code of Federal Regulations, Title 10, Part 50 (10 CFR 50).

3.

General Design Criteria-21 (GDC-21), " Protection System Reliability and Testability," of Appendix A, " General Design Criteria for Nuclear Power Plants," in the Code of Federal Regulations, Title 10, Part 50 (10 CFR 50).

4.

IEEE Std. 279-1971, " Criteria for Protection Systems for Nuclear,Pbwer Generating Stations."

5.

NUREG-75/087, " Standard Review Plan for che Review of Safety Analysis Reports for Nuclear Power Plants."

6.

NRC me.orandum from Faust Rosa to J. Stolz, T. Ippolito, and G.1,ainas, dated February 19, 1979.

7.

NRC letter to Operating BWR's, dated September 24, 1980.

8.

NSP letter (L. O. Mayer) to NRC, dated November 12, 1980.

9.

NSP lette r (L. O. Mayer) to NRC, dated April 24, 1961.

10.

NSP letter (L. O. Mayer) to NRC, date ' March 23, 1982.

11.

NSP letter (L. O. Mayer) to NRC, dated May 17, 1982.

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