ML19305F248

Safety Evaluation Re Degraded Grid Voltage Protection for Class IE Power Sys at Facility.Proposed Design Mods & Changes to Tech Specs Are Acceptable

ML19305F248
Person / Time
Site:	Rancho Seco
Issue date:	12/04/1980
From:	Office of Nuclear Reactor Regulation
To:
References
TAC-10968, NUDOCS 8101080204
Download: ML19305F248 (3)

Text

,

ENCLOSURE i

SAFETY EVALUATION RANCHO SECO NUCLEAR GENERATING STATION, UNIT 1 DOCKET NO. 50-312 DEGRADED GRID VOLTAGE PROTECTION FOR THE CLASS 1E POWER SYSTEM i

'I NTO JUCTION AND'

SUMMARY

,y The criteria and staff positions pertaining to degraded grid voltage protection were transmitted to Sacramento Municipal Vtility District. (SMUD) by NRC generic' l

1etter dated June 3,1977.

In response to this, by letters dated July.19,1977.-

June 20,1978, August l',1980 and September 22, 1980, the licensee propused -

ertain design modifications and changes to the Technical Specifications. ' A l

detailed review and technical evaluation of these proposed modifications and changes to the Technical Specification was performed by Lawrence Livermore Laboratory (LLL), under contract to the NRC, and with general supervision by NRC staff. This work is reported by LLL in a report, " Technical-Evaluation of the Proposed Design Modifications and Technical Specifications Changes on Grid Voltage Degradation (Part A) for the Rancho Seco Nuclear Generating Plant" (attached). We have reviewed this technical evaluation. report and concur in its conclusions that the proposed design modifications and' Technical. Specification changes are acceptable.

Proposed Changes and Evaluation Criteria The following design modifications and Technical Specification changes were proposed by SMUD:

a.

The existing undervoltage protection is integrated into one loss of voltage and degraded voltage protection scheme. The 1roposed scheme

. will consist of three undervoltage relays, and will be arranged in a

~

2-out-of-3 coincident logic. The setpoint is selected such that it will take 12 seconds to trip for 90.6% of nominal bus voltage and less than one second upon complete loss of voltage.

b.

The licensee has proposed changes to the plants Technical Specifications.

These include addition of trip setpoint, limiting conditions for operation and surveillance requirements associated with the design modifications.

The present design blocks the undervoltage trip load shedding feature on the Class 1E buses when the diesel generators are supplying these buses.

If the diesel generator circuit breaker is tripped, the load-shedding logic circuitry will be automatically reinstated.

l l

The criteria used by LLL in its technical evaluation of the above proposed changes include GDC-17. " Electric Power Systems," of Appendix A to 10 CFR 50; j

IEEE Standard 279-1971, " Criteria for Protection Systems for Nuclear Power Generating Stations;" IEEE Standard 308-1974, " Class lE Power Systems for Nuclear Power Generating Stations," and the staff positions defined in NRC generic letter to SMUD dated June 3,1977.

CONCLUSIONS We have reviewed the Lawrence Livermore Laboratory's Technical Evaluation Report and concur in its findings that (1) the proposed modifications will protect the Class 1E equipmenh and systems from a sustained degraded voltage I

of the offsite power source,.and (2) the proposed changes to the Technical

-- Specifications meet the criteria for periodic testing of protection systems and equipment.

Therefore, we conclude that the proposed design modifications and changes to the Technical Specification are acceptable.

9 l

1

'l

4 l

UCID.18690 i

i r

3 TECHNICAL EVALUATION OF THE PROPOSED DESIGN MODIFICATI0"S At0 TECHNICAL SPECIFICATION CHANGES ON GRID VOLTAGE DEGRADATION (PART A)

FOR THE RANCHO SECO NUCLEAR GENERATING PLANT Robert L White October 1980

\\

x

....b na " - /

.. - * ' - u.. ;

.1-,

i..

VD g{h N ig*,Nd%.,[(. fit % k* iM,h.l;..

'NQ Qi"?$7g%D

'A F

f

,gg%. 4, ;ge, g

A

+

e

..... y,...

_.y,_,

'.. + -. t

p y

• y w s This is sa informal report intended primarDy for brsernal or theited external distribet6pa.

.y JEA'Y.

NY.

The opinnuns and coh stated are those of the author sad sney or may not be those

~

4

%V

.y 4#

of thelaborenary.

u l

.[* :7 This work was supported by the United States Nuclear Reguistory Comunksine moder g

a hiemorandam of Understandingv'ith the United States Department of Energy.

g-

.,,,, i * ;

2:n%? y ".

C pr' v.

g, 3 '.,;. A,...'.19..C.,

. ll;.ya

$2', t }7: ' f e4.;;);.

r..

Lpi.kle@,7.v).u. : ;:;" l.: ~., *...2.Riki '... :e ~

^*

~~

P, :'v.n

~

* ~

• t+' *

'^.

.F r,

,. c.. *,.., -.

-x,, Q.;a.; * '

t.

.* ' g

,,,ll"

,.4*

+

'.,,_**,.?',..$...,.f '

.. a

.< i%v. r.,y,.;y:.st;a..,.

. q.!

~

l

.s

.. r n, l

• y e

.1.

[

~

1 aa.m2

. em A'n

,,J

..y.

> - n j

i 2

1 I

ABSTRACT,-

l 1

)

1 This report documents the' technical' evaluation of the proposed 4

design modifications and Technical Specification changes for protection of Class lE equipment.from grid voltage degradation for. the Rancho.Seco Nuclear Generating Plant. The review criteria are based ~on several' IEEE standards and the Code of Federal Regula'tions. The evaluatibn, 5

compares the submittals made by the. licensee with the NRC staff. positions

)

and the review criteria and presents the reviewer's. conclusion.on the.

q acceptability.of the proposed system.

es e m Sa***

it

+%a,.

s I

l l

• r

.%.s.

aMA.,.a*

.eA_.p 1

1 1

i I

i

.J.-

i iii _

l l

~

1 1

FOREWORD m..

i I

This report is supplied.as part of'the Selected Electrical, Instrumentation, 'and Control Systems' 1ssues : (SEICSI)' Program 'being -

conducted for the U. S. Nuclear Regulatory Com:aission, Office' of.' Nuclear 3

Reactor Regulation, Division of Operating Reactors, by Lawrence Livermore National ~ Laboratory, Engineering Research. Division of the Electronics Engineering Department.

)

]

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 A-0231.

l f

'i i

c I

'I J

v i

~.. -. _.,

- i TABLE OF CONTENTS P

i A

P_a ge -

f 1.

INTRODUCTION.

.1' 2.

DESIGN BASIS CRITERIA 3-3..

EVALUATION 5

3.1.

Existing Undervoltage Protection..

51 3.2 Modifications.

5 3.3 Discussion'.-.-

6 3.3.1 NRC Staff Position 1:

Second Level of Under-voltage or Overvoltage Protection with a Time Delay 6

3.3.2 NRC Staff Position 2:

Interaction of Onsite

-Power Sources with Load Shed Feature...

8 3.3.3 NRC Staff Poof. tion 3:

Onsite Power Source Testing

.~

9 3.4 Technical Specifications 9

j l

4.

CONCLUSION 11 1

J REFERENCES 13-

)

l i

i vii j

l

+

1 n 77 7.,7 g-

~

~

4 TECHNICAL EVALUATION REPORT PROPOSED DESIGN MODIFICATIONS AND TECHNICAL SPECIFICATION CHANGES ON GRID VOLTAGE DEGRADATION FOR THE, RANCHO SECO NUCLEAR GENERA' ting PLANT -

(Docket No. 50-312)

Robert L. White Lawrence Livermore National Laboratory, Nevada 1.

INTRODUCTION-By letter dated June 3, 1977 JRef.-1], the U. S. Nuclear Regulatory-Commission (NRC) requested the Sacramento Municipal Utility District to

' assess the susceptibility of the Rancho Seco Nuclear Generating Plant Class 1E electrical equipment to sustained degraded voltage conditions at offsite power sources and to the interactic-between the-offsite and onsite emergency power systems.

In addition, the NRC requested that the licensee compare the current design of the emergency power systems at the plant facilities with

)

the NRC staff positions as stated in the June 3,1977 letter (Ref.1], and i

that the licensee propose plant modifications, as necessary,-to meet the.

.I NRC staff positions, or provide a detaile'd analysis which shows that the facility design has equivalent capabilities and protective features.- Further, the NRC required certain Technical Specifications be incorporated into all facilities' operating licenses.

By letters dated August 1,1980 (Ref. 2], June 20,1978 (Ref. - 3),

July 19, 1977 [Ref. 4], and September 22, 1980.[Ref. 5],-Sacramento Municipal i

Utility District proposed certain design modifications and additions to the licensee's Technical Specifications.

The design modifications include the installation of a degraded voltage protection system for the Class 1E

-1 ~

.-m,.~

,.,.--:,,,,., ~

..w,,

~1,.

I j

s equipment. The proposed additions to the Technical Specifications are in regard to the relay setpoints, calibrations, system tests,.and surveil-lance requirements associated with the proposed voltage protection system.

The purpose of this report is to evaluate the licensee's proposed design modifications and Technical Specification changes and to determine that they meet the criteria established by the NRC for the protection of Class 1E equipment from a grid voltage degradation.

+

e f

o k

l i

i i

1 a

1

-)

- 1 j

2.

DESIGN BASIS CRITERIA

. i t

6 The-design basis criteria that were applied in determining the i

B acceptability of the system modification to protect theLClass lE equipment from degradation of grid voltages are as follows:

i (1) General Design Criterion 17. (CDC.17), "Eleatric Power-Systems," of Appendix A, " General Design Criteria'for.

- i Nuclear Power Plants," in the-Code of Federal Regulations; Title 10, Part 50 (10 CFR.50) [Ref. 6].

(2) IEEE Standard 279-1971, " Criteria for Protection Systems.

for Nuclear Power Generating Stations" [Ref. 7}.

(3) IEEE Standard 308-1974, " Class lE Power Systems for-Nuclear Power Generating Stations" [Ref. 8).

(4) NRC Staff positions as stated in a letter' dated June'3, 1977:

5

[Ref. 1].

O I

i l

l l

i i

1

' I I

- 1 i

I 3.

EVALUATION l

3.1 EXISTING UNDERVOLTAGE PROTECTION The Rancho Seco Nuclear Generating Plant has 'two' 4160-volt and i

two 480-volt Class 1E buses.- The existing undervoltage protection design uses a single undervoltage relay on each'4160-volt Class 1E b'us..

If the' voltage drops below.3534 volts (85% of 4160 volts), the 'undervoltage relay.

will energize a set of load-shedding' relays.

The load-shedding relays i

initiate the disconnection of the emergency 4160-volt buses from the'off-l site source, load shed the emergency 4160-volt' buses, start' the emergency L

)

diesel generators, and provide an enabling signal for the load-sequencing timing circuit. When the emergency diesel generator reaches the required voltage it is connected to the emergency buses and load-sequencing will be-gin automatically, if a safety injection (SI) signal exists.

H The existing Rancho Seco design complies with _ NRC Staf f Position 2

^~~

requiring the system to automatically prevent' load' shedding of the emergency buses once the onsite souces are supplying power to all sequenced loads on l

the emergency buses.

The present design will also reinstate the load-shedding feature if the emergency diesel generator breakers are tripped..

j 3.2 MODIFICATIONS a

The licensee has proposed a design change to establish an automatic degraded voltage protection circuitry.

The modification consists of incorpo-c

.n._n,.-

e w

rating the existing underveltage pretection_e: heme with a degreded voltage protection scheme.

The proposed scheme will consist _ of 3 undervoltage relays monitoring each 4160-volt emergency bus. The 3 undervoltage ' relays

~..

will be arranged in a 2-out-of-3 coincident logie with a setpoint of 3771 volts + 38 volts (90.6% of 4160 volts) with a time delay of?l2 seconds'

' + 1.2 seconds.

There will be only one loss of voltage-degraded voltage pro-tection system.

The relays are of the inverse time-voltage type. Upon complete loss of voltage the undervoltage relays will trip in less.than one r

- i second.

The licensee has provided proposed Technical Specification changes to document relay setpoints, surveillance requirements, limiting conditions t

for operation, and diesel generator test procedures for the proposed. changes-l c

as presented in this evaluation.

i 3.3 DISCUSSION This section presents a statement on the NRC staff position from their June 3, 1977 letter (Ref. 1] followed by an evaluation of the licensee's design.

3.3.1 NRC Staff Position 1: Second Level of Undervoltage or Overvoltage Protection with a Time Delay

- s

'~

This position is to be met by the licensee meeting certain criteria. Each criterion has been evaluated against the licensee's E

proposal and is addressed below.

(1) "The selection of voltage and timeLsetpoints shall be determined from an analysis of the voltage requirements of the safety-related loads at all onsite system distri-bution levels."

1

-r

-r+,

y

,m,r

-n, w

s 2-*

-u n---

- -++

r---

~

8 The licensee's proposed-degraded voltage setpoint is

' {

3771 volts + 38 volts (90.6% of 4160 volts). The proposed time-delay'setpoint is 12 seconds + 1.2' seconds.

The licensee's analysis shows that.this setpoint.and,

-time delay are ' satisfactory for both 4000-volt and 460-volt Class 1E loads and for relays.contactors, j

and other components whose functional performance would 1

-be~ inadequate because of undervoltage.

(2) "The voltage protection shall include coincidence logic to preclude spurious trips of the offsite power sources."

The proposed modification lfor degraded voltage protection

-incorporates a 2-out-of-3' coincidence logic. Each_4160-volt 1 Class lE bus 1will. have 3 phase-to phase undervoltage ' relays.

The logic will initiate al signal to. trip the circuit breakers t

from the offsite source when 2 of the 3 independentLinput,

channels are actuated.

(3) "The time delay selected shall be. based. on the following.

conditions."

(a) "The allowable time delay,' including margin, shall-not exceed the maximum time delay'that is assumed-in the FSAR accident analysis."

The proposed time delay of 12 seconds +-1.2 seconds-i does not exceed the maximum time delay that'is assumed in the FSAR accident. report.

(b) "The time delay shall minimize the effect of short-duration disturbances from reducing the. availability of the of fsite power sources."

The licensee's proposed time delay of 12 seconds-f

+ 1.2 seconds is long enough to override any grid disturbances of short duration.

This has been con-1 firmed by testing.

(c) "The allowable time duration of a degraded voltage condition at all distribution system levels shall not result in failure of safety systems or components."

i A review of the licensee's voltage analysis indicates that the time delay will not cause any.failureLof any1

- }'

equipment connected to and associated.with the Class lE-emergency power system.

(4)."The undervoltage monitors shall automatically initiate the:

disconnection of offsite power sources whenever the voltage setpoint and time delay limits have'been exceeded."

.M-4*-

Wap%*

-y**.

-w-4

.%,.,w.e ne gy,.

r

...m.-

~

The 2-out-of-3 coincident logic. circuitry will automatically initiate the oisconnection of.offsite power sources when-ever the voltage degrades below the. voltage 'setpoint for a period of time. exceeding the proposed time delay.

(5) "The voltage monitors shall be designed'to satisfy the.

requirements of 1EEE Standard 279-1971."

The licensee states that the degraded voltage monitors were designed to satisfy the requirements of.IEEE Standard 279 and IEEE Standard 603.

(6)

"The Technical Specifications shall include limiting conditions for operations, surveillance. requirements,

trip setpoints.with minimum and maximum limits, and allowable values. f or the second-level voltage protec-tion monitors."

The licensee has provided proposed Technical Specifica-tion changes to document voltage setpoints, surveillance requirements, limiting conditions.for operation,'and.

~

diesel generator test procedures for the degraded voltage protection system.

3.3.2 NRC Staff Position 2: Interaction of Onnite Power Sources with Load-Shed Feature The second position requires the system to be designed to prevent i

automatic load shedding of the emergency buses once the onsite sources are

~

supplying power to all sequenced loads.

If an adequate basis can be pro-vided for retaining the load-shed feature,'the licensee must assign maxi-i

^-

mum and minimum values to the setpoint of the. load-shed. feature.

These setpoints must be documented in the Technical Specifications.

The load--

~'

~ '

shedcing feature must also be reinstated if the onsite source supply breakers I

are tripped.

i The present design for Rancho Seco meets NRC Staf f Position 2.

An auxiliary "b" contact from the diesel generator circuit' breaker is used to prevent load-shedding when the emergence diesel generator is energizing r

---+m y

..,,p.y...

c.

the Class 1E buses.

If the diesel generator. circuit _ breaker is tripped,

-the load-shedding logic circuitry will be automatically. reinstated..

3.3.3 NRC Staff Position 3: ~ Onsite Power' Source Testing e

4

-The third position requires that certain test requirements.be 1.

included in the Technical Specifications.- These tests are to ... demonstrate the full functional operability.and.in' dependence of the onsite power sources at least once per 18 nonths during shutdown." The tests are to simulate ~

loss of offsite power in conjunction with a safe'ty-injection actuation sig--

nal and to simulate interruption and subsequent,reconnection of onsite power sources. These tests will verify the proper o'peration of th'e load-she'd system, the load-shed bypass circuitry, and that there"is no adverse' interaction between the onsite and offsite power sources.

The licensee states that Rancho Seco will meet Position 3 with a test of the system by simulating a loss of offsite power.in conjunction with a SI signal. The test sequence will be bus de-energization, load shedding, voltage restoration, and load sequencing.

The operating time on' emergency onsite power will be at least 5 minutes.

The licensee will also interrupt the emergency diesel generators while they are supplying.the Class 1E buses-

~

to test the re nstatement of the load-shedding circuitry,'the load-shedding operation and then upon re-energization of the emergency buses'by the onsite power source, test the load-sequencing circuitry.

3.4 TECHNICAL SPECIFICATIONS The changes proposed by Sacramento Municipal Utility District. to the Rancho Seco Nuclear Generating Plant's Technical Specifications reflect the proposed design modifications.

Specifically,-the proposed changes:.

sr-(1) Include'the trip setpoints for the degraded voltage-protection sensors.and the1 associated time delays with tolerances (3771. volts + 38' volts (90.6% of

' 4160 volts]and'12 seconds [1.2 seconds)..

(2) Provide the required coincidenceLlogic (2-out-of-3).-

(3) Incorporate action statements.regarding. limiting condi-tions for operations when the number of operable channels for degraded voltage protection is reduced.

j

- ~

(4) - Provide the instrument surveillance requirements for channel check, channel calibration, and channel func-tional test.

(5) Provide the surveillance requirements to demonstrate atn least once per 18 months'that the loss of offsite power in conjunction with a safety actuation signal will pro--

vide the sequence.of Class 11E bus de-energization, load

-ahedding, voltage restoration, and load sequencing.

t

,i.. j. ;

.r--~<~,;

i l

~

1

..-- ~.

1

=

gb."

"..n e -

Y e

~

l I

I i

, ~

• --- -' * '*w Tt ei'M T

4 9'r=-=*T N e-E g

• r W

-IW"f

u-#f 5

?

ETTP 3

b' I

'E

'ir ak

• M_-

e e=t

a-4 CONCLUSION Based on the information provided by Sacramento !!unicipal Utility District, it has been determined that the proposed modifications to Rancho Seco Nuclear Generating Plant comply with NRC Staff Position 1.

All of the staff's requirements and design basis criteria have been met.

The modifica-tions will protect the Class lE equipment from a sustained degraded voltage condition of the offsite power source.

The present design complies with Position 2 and will prevent load-shedding when the Class IE buses are being energized by the onsite emergency source.

The design also prevents adverse interaction of the offsite and onsite emergency power systems.

The proposed changes to the Technical Specifications and the j

method of testing the logic circuitry have been reviewed and found to comply with Position 3.

Accordingly, we recommend that the NRC approve the proposed design modifications and Technical Specifications.

r i

t REFERENCES i

1.

NRC letter (R. W. Reid) to Sacramento Municipal Utility District

. J. J. Mattimoe), dated June 3, 1977.

(

i 2.

Sacramento Municipal Utility District letter (J. J. Mattimoe) to NRC (R. W. Reid), dated August 1, 1980.

3.

Sacramento Municipal Utility District letter (J. J. Mattimoe) to~

NRC (K. R. Goller), dated June 20,.1978.

4.

Sacramento Municipal Utility District letter (J. J. Mattimoe) to imC 4

(R. W. Reid), dated July 19, 1977.

5.

Sacramento Municipal Utility' District letter (W. C. Walbridge). to NRC :

(R. W. Reid), dated September 22, 1980.

i 6.

Code of Federal Regulations, Title 10, Part 50 (10 CFR 50), General Design Criterion 17 (GDC 17), " Electric Power Systems" of _ Appendix' A

" General Design Criteria for Nuclear Power Plants."

7.

IEEE Standard 279-1971, " Criteria for Protection Systems for Nuclear Power Generating Stations."

l l

8.

IEEE Standard 308-1974, " Criteria for Class 1E Power Systems for j

Nuclear Power Generating Stations."

i i

I 1

s r

e !

. -.,. -