ML20151T730

Responds to Re Appeal of NRC Position on Plant ATWS Sys Instrument Diversity.Implementation of Unit 1 ATWS Rod Insertion Should Not Be Slowed to Resolve Issue & Extension of Time to Comply W/Rule for Unit 2 Granted

ML20151T730
Person / Time
Site:	Brunswick
Issue date:	08/08/1988
From:	Murley T Office of Nuclear Reactor Regulation
To:	Eury L CAROLINA POWER & LIGHT CO.
References
TAC-59075, TAC-59076, NUDOCS 8808170227
Download: ML20151T730 (4)

Text

,__ _ _- _

o#s' <

', ~. ; *l A'J G 8 1938 r

Docket Nos.: 50-325 and 50-324 i Mr. Lynn W. Eury.

Senior Vice President Operations Support .

Carolina Power & Light Company .

P. O. Box 1551 Raleigh, N. C. 27602

SUBJECT:

DIVERSITY BRUNSWICK UNITSREQUIREMENT 1 AND 2 (TAC NOS. 59075OF ANC ATWS 59076 RULE (10 CFR 50.62 l The purpose of this letter is to respond to your letter dated May 11, 1988 regarding your appeal of the staff position on the Brunswick ATWS system instrument diversity. We have reviewed your submittal and the BWROG Jure 28,  ;

1988 letter supporting your position. We met with your staff on July 19, 1988 to review major transient events which could lead to an ATWS and the equipment available to respond to such an event. Durin Rosemount analog transmitter trip unit (ATTU)g theboard.

circuit meeting, we also examined a Your fundamental application" exists position, between explained the reactorintrip oursystem meeting,(was that "diversity of RTS)andARIATTUs. That  ;

is, although the same type circuit boards are used in the ARI system and the RTS, diversity of application is provided by setting two internal switches so that the ARI is energized to trip while the RTS is de-energized to trip. Since i both-boards are made by Rosemount and are virtually identical, we conclude that the application of different energization states is not sufficient to minimize the potential for ccmon cause failures in the ARI and RTS ATTUs.

Your submittal also contends that functional diversity is achieved within the reactor trip system channels. Even if a comon cause failure of the ATTVs in the ARI system and the RTS were to occur, a scram signal would be initiated by ,

at least one other channel in the RTS which does not use an ATTU. Based on your July 19, 1988 presentation on the loss of feedwater event assuming failed I ATTUs, the only scram signal that may occur for that event is the APRM Downscale t~

Trip (setpoint at 3% power level). The staff does not believe that APRM downscale trip provides acceptable diversity for the postulated ATWS because the -

core would have to be significantly voided to reach the downscale trip. A level i of protection, comparable to that provided by the ATTUs, would be necessary for i, a diverse signal. Therefore, we conclude that functional diversity within the [

' RTS instrument channels is not sufficient to minimize the potential for comon *

l. cause failures. t i

I g ,

)

8800170227 seosos PDR L

P ADOCK 05000324 pg [

l

E o

Mr. Lynn W. Eury AUG S W 13W We, therefore, conclude that the Brunswick ATWS design is not in compliance with the requirements of the ATWS Rule (10 CFR 50.62) in that the ARI system is not diverse (from the reactor trip system) from sensor output to the final actuation device. It was learned during the meeting that compatible circuit boards are available which are manufactured by a different vendor, and are fully qualified as a replacement for the Rosemount ATTVs. If the alternate boards were used in the ARI system, sufficient diversity would exist between the ARI system and the RTS. Such a modification appears reasonable and practicable. We believe that the ARI system as designed and implemented at Brunswick Unit 2 provides a diverse logic design which addresses the major contributors to common cause failure in the RTS and is therefore acceptable until the modification can be made during the next refueling outage. Another alternative, permitted by the provisions of 10 CFR 50.12, would be to request an exemption from 10 CFR 50.62. We do not recomend this option.

Implementation of the ARI system on Unit 1 should not be slowed to resolve this issue, because there is a clear safety benefit even with the Rosemount ATTVs.

t!e expect the current as-designed system to be installed now. We will agree to an extension of time to fully comply with the ATWS Rule, as with Unit 2, until not later than the end of the next refueling outage.

Sincerely, Original Signed by, a m s E. itirleY Thomas E. Murley, Director Office of Nuclear Reactor Regulation cc: D.N. Grace (BWROGChairman)

DISTRIBUTION:

Central Files SICB RF T. Murley T. Martin L. Shao G. Lainas A. Thadani S. Newberry J. Mauck H. Li D. Lynch  ;

Oi SVarga

RPR AD SRXB: DEST

• C A GL as WHodges SW 7/)(j/88 07/3 /88 07/25/8 07/J /88 y .>

• SEE PREVIOUS CONCURRENCE M

SICB: DEST

• SICB: DEST

• SICB: DEST

• SAD:DiST* A .

HLi:bl JMauck SNewberry AThadani T,prtin T.urley 07/22/88 07/22/88 07/22/88 07/25/88 07g /88 0T/4{ /88 Og7g/88 0FFICIAL RECORD COPY

F

~ . .

Mr. Lynn W. Eury Brunswick Steam Electric Plant Carolina Power & Light Company Units 1 and 2 cc:

Mr. P. W. Howe Mr. J. L. Harness Vice President Plant General Manager Brunswick Nuclear Project Brunswick Nuclear Project P. O Box 10429 P. O. Box 10429 Southport, North Carolina 28461 Southport, North Carolina 28461 Mr. R. E. Jones, General Counsel Mr. H. A. Cole Carolina Power A Light Company Special Deputy Attorney General P. O. Box 1551 State of Nortn Carolina Raleigh, North Carolina 27602 Post Office Box 629 Raleigh, North Carolina 27602 Mr. Mark S. Calvert Associate General Counsel Mr. Robert P. Gruber Carolina Power & Light Company Executive Director ,

Post Office Box 1551 Public Staff - NCUC Raleigh, North Carolina 27602 Post Office Box 29520 Raleigh, North Carolina 27626-0520 Mr. Christopher Chappell, Chairman Board of Comissioners Mr. E. E. Utley Post Office Box P49 Senior Executive Vice President Bolivia, North Carolina 28422 Power Supply and Engineering &

Construction Mrs. Chrys Baggett Carolina Power & Light Company State Clearinghouse Post Office Box 1551 Budget and Management Raleigh, North Carolina 27602 116 West Jones Street Raleigh, North Carolina 27603 Resident inspector U. S. Nuclear Regulatory Comission Star Route 1 Post Office Box 208 Southport, North Carolina 28461 Regional Administrator, Region !!

U. S. Nuclear Regulatory Commission 101 Marietta Street, Suite 2900 Atlanta, Georgia 30323 Mr. Dwayne H. Brown. Chief Radiation Protection Branch Division of Facility Services N. C. Department of Human Resources 701 Barbour Drive Raleigh, North Carolina 27603-2008

DISTRIBUT!0tl FOR LTR TO HR. LYNN EURY DATED AUGUST 8, 1988 l Docket file. ,

'NRC POR Local PDR P021 r/f SICB r/f T. Murley (12G18)

T. Hartin (12G18)

5. Varga (14E4)

L. Shao (8E2)

A. Thadani (7E4)

G. Lainas E. Adensam P. Anderson B. Buckley '

B. Mozafart W. Hodges (8E23)

5. Newberry (7E12)

J. Hauck (7E12)

H. Li (7E12)

OGC E. Jordan (HNBB 3302)

B. Grimes (9A2)

ACRS (10) ,

- _ _ _ _ _ _ - _ _ _ _ _ _ _ _ _ . _ _ _ _ _ ___ ____-_