ML20010E315
| ML20010E315 | |
| Person / Time | |
|---|---|
| Site: | Peach Bottom  |
| Issue date: | 08/21/1981 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20010E314 | List: |
| References | |
| NUDOCS 8109030325 | |
| Download: ML20010E315 (2) | |
Text
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ENCLOSURE
[f( pKfig )h UNITED STATES j
NUCLEAR REGULATORY COMMISSION j
.y WASHINGTON. D. C. 20555 a
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SAFETY EVALUATION REPORT PEACH BOTTOM UNITS 2 AND 3 OVERRIDE OF CONTAINMENT PURGE ISOLATION AND OTHER ENGINEERED SAFETY FEATURE ACTUATION SIGNALS Introduction Instances have been reported at nuclear power plants where the intended automatic closure of containment purge / ventilation valves during a postulated accident would not have occurred because the safety acutation signals were inadvertently overridden and/or blocked, due to design deficiencies.
These instances were determined to constitute an Abnormal Occurrence (#78-5). As a followup action, NRR' issued a generic letter requesting each licensee to take certain actions.
Evaluation The enclosed report (1183-4161) was prepared for us by EG&G, San Ramon, as part of our technical assistance contractor program.
The report provides their technical evaluation of the design compliance with NRC-provided criteria.
The contractor's evaluation conc'udes:
(1) that with the exception of the potential re-opening of certain s tives upon " Reset," the primary containment isolation system (PCIS) circuit d, sign meets the staff's criteria; (2) that the acceptability of the CAC/ CAD system is.beyond the scope of the contractors charter; and (3) that the other ESF systems audited meet the staff's criteria.
Further, the contractor recommended incorporation of design changes to provide manual actuation of PCIS at the systems level.
The potential re-opening of PCIS valves upon " reset" of the system logic was reviewed as part of the TMI Lessons Learned program and appropriate plant modifications were made.
The changes made as part of Lessons Learned have made the design acceptable.
The design provision that allows override of the PCIS in order to operate the SGTS or the provide access to a recombiner can only be used when the reactor Mode switch is out of the Run mode. The SGTS and reccmbiner are other ESF systems.
Keylock switches are provided and their use is automatically annunciated.
We. conclude that reasonable precautions have been provided, and that these overrides are acceptable on the basis of safety objectives.
8109030325 810821 PDR ADOCK 05000277 I
. The contractor recommended the installation of system-level actuate features for the PCIS. The Peach Bottom plants were designed and licensed i
prior to the advent of IEEE standard 279-1971.
The earlier version (trial-use standard of 1968) required manual actuation features but did not require them to be at the systems level.
The Peach Bottom plant design does include manual actuation 7eatures for the PCIS. While systems-level manual actuation features are desirable, the design satisfies the standards in effect at the time of licensing and thus is acceptable as is.
Based upon recent information (reference: fiay 26 andJ ay 27, 1981 telephone conference between J. T. Beard (flRC) and Wes Bowers and Dave Helwig of Phliadelphia Electric Co.), the licensee has re-confirmed his earl er i
statements that the radiation monitoring equipment provided for SCIS actuation does not measure the containment (i.?., drywell) atmosphere or the exhaust therefrom.
Therefore, the present plant design does not comply with Criterion #4 of this review.
Conclusio n Based upon our review of the contractor's report, as discussed above, and upon information provided by the licensee, we conclude that, with one exception, the electrical override aspects of the containment purge isolation system and of other ESF systems meet the staff's criteria and are therefore accep table.
To satisfy the one exception, the licensee must provide appropriate instru-mentation such that all containment purge and vent isolation valves will receive an automatic closure signal on containment high radiation.
Dated: Aunust 21, 1901 l
dECc6 1183-4161 August 1980 Encrey Mearurements Group Len hemon Operations i
-i TEC!'! lC!.L EVALUATION OF THE ELECTnlCAL, INSTRUh.ENTATION, AND CONTROL DESIGN ACCECTS OF THE OVECC:DE OF CONTAINT.~.ENT PURGE VALVE ISCLATION
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AND OTHER ENGINEECED SAFETY FEATURE SIGNALS FOR THE PEACH COTTOM NUCLEAR POWER STATION, b
UNITS 2 AND 3
"(Dock.ts 50 277 AND 50 278)
.r by D. B. Hackett/B. Kountanis i
Approved for Publication Q
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J. R. Racosevic Depart:nent Manager
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This document is UNCLASSIFIED L1 i
a:n'2: % B e4 h
" Nicnolas EAraderick Department Manager
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,f Contr.ct No. DE.ACOS-76 NVQ 1183.
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. a, ABSTRACT
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..j This report documents the technical evaluation of the electrical, instrumentation, and control design aspects of the override of containment
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purge valve isolation and other engineered safety feature signals for the
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Deach Bottom nuclear power station, Units 2 and 3.
The review criteria are I
based on IEEE Std-279-1971 requirements for the safety signals to all purge
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FOREWORD
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N This report is supplied as part of the Selected El ectrical,
Instrumentation, and Control Systems Issues (SEICSI) Program being con-ducted for the U.S.
Nuclear Regulatory Co:r:ni ssion, Office of Nuclear Reactor Regulation, Division of Operating Reactors, by Lawrence Livermore National Laboratory, Field Test Systems Division of the Electronics
.a Engineering Depa tment.
The U.S. Nuclear Regulatory Commission funded the work under an authorization entitled "El ectrical, Instrumentation and Control System Support," B&R 20 19 04 031, FIN A-0231.
j The work was perfonned by EG&G, Inc., Energy Measurements Group, San Ramon Operations, for Lawrence Livermore National Laboratory under U.S.
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Department of Energy contract number DE-AC08-76NV01183.
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TABLE OF CONTENTS Page
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INTRODUCTION.
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2.
EVALUATION OF PEACH BOTTOM NUCLEAR POWER STATION, UNITS 2 AND 3 3
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--s 2.1 Review Criteria 3
2.2 Containment Ventilation Isolation Circuits q
Design Description 4
2.3 Containment Ventilation Isolation System Design Evaluation.
6 2.4 Other Engineered Safety Feature System Circuits 8-l 3.
CONCLUSIONS.
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TECHNICAL EVALUATION OF THE ELECTRICAL, INSTRUMENTATION, AND CONTROL DESIGN ASPECTS
--n 0F THE OVERRIDE OF CONTAINMENT PURGE VALVE ISCLATION AND OTHER ENGINEERED SAFETY FEATURE SIGNALS FOR
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THE PEACH BOTTOM NUCLEt'l POWER ST/. TION, UNITS 2 AND 3 (Dockets 50-277 and 50-278)
D. B. Hackett/B. Kountanis
'_.y EG&G, Inc., Energy Measurements Group, San Ramon Operations
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INTRODUCTION Several instances have been reported where automatic closure of the containment ventilaticr/ purge valves would not have occurred because the safety actuation signals were either manually overridden or blocked l
during nomal plant operations.
These events resulted from procedural inadequacies, design deficiencies, and lack of proper management controls.
g These events also brought into question the mechanical operability of the containment isolation valves themselves.
These events were determined by the U.S. Nuclear ' Regulatory Commission (NRC) to be an Abnormal Occurrence l'
(#78-5) and were, accordingly, reported to the U.S. Congress.
1 As a follow-up on this Abncmal Occurrence, the NRC staff is reviewing the electrical override aspects and the mechanical operability e
aspects of containment purging for all operating power reactors.
On y
November 28,197E, the NRC issued a letter entitled " Containment Purging f
During Nomal Plant Operation" [Ref.1] to all boiling water reactor (BWR) k and pressurized water reactor (PWR) licensees.
In a letter [Ref. 23 dated January 2,1979, the Philadelphia Electric Company (PEC), the licensee for
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the Peach Bottom nuclear power station, Units 2 and 3, replied to the NRC generic letter.
The evaluation of other engineered safety feature (ESF) systems was submitted in response to IE bulletin 79-08 [Ref. 3].
The i,'
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licensee met [Ref. 43 with the NRC in Washington, D.C., on August 24, 1979, to discuss this issue further.
Additional information [Refs. 6 and 7]
dated August 8,1979 and April 16, 1980, was received and evaluated.
This document addresses only the electrical, instrumentation, and control (EI&C) design aspects of the containment ventilation isolation (CVI) and other ESFs.
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2.
EVALUATION OF PEACH BOTTOM NUCLEAR POWER STATION, UNITS 2 AND 3 2.1 REVIEW CRIlERIA
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The primary intent of this evaluation is to determine tnat tne following NRC staff criteria are met for the :,afaty signals to all ESF
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equipment:
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Criterion no.1 - In keeping with the requirenients of General Design Criteria 55 and 56, the overriding
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one type of safety actuation signal (e.g., radiation) should not cause the blocking of any other type of y c safety actuation signal (e.g.,
pressure) for those c.
valves that have no function besides containment i sol ation.
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(2)
Criterion no. 2 - Sufficient physical features (e.g.,
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keylock switches) are to be provided to facilitate
_J adequate administrative controls.
(3)
Criterion no. 3 - A system-level annunciation of the cverridden status should be provided for every safety
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system impacted when any override is active. (See R.G.
1.47).
Incidental to this review, the following additional NRC design e-.s criteria were used in the evaluation:
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(1)
Criterion no. 4 - Diverse signals should be provided to initiate isolation of the containment ventilation system.
Specifically, containment high radiation, il safety injection actuation, and containment high r.,
pressure (where containment high pressure is not a portion of safety injection actuation) should auto-matically initiate CVI.
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- The following definition is given for clarity of use in this evaluation:
i Override:
The signal is still present, and it is blocked in ld order to perfonn a function contrary to the signal.
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(2)
Cri terion no. 5--The instrumentation and control s
systems provided to initiate the ESF should be de-signed and qualified as safety-grade equipment.
(3)
Cri terion 10. 6--The overriding or resetting
Criterion 6 in this review applies primarily to other related ESF systems because implementation of this criterion for containment isolation has been reviewed by the Lessons Learned Task Force, based on the recc-
'atf or.s in NUREG-0578 Section 2.1.4.
Automatic valve repositioning upon reset may be acceptable when containment isolation is not ' involved; consideration will be given on a case-by-case basis.
Acceptability would be dependent upon system function, design intent and suitable operating procedures.
2.2 CONTAINMENT VENTILATION ISOLATION CIRCUITS DESIGN DESCRIPTION Each unit at Peach Bottom Nuclear Power Station, Units 2 and 3, has two ESF trains which can cause isolation of the containment ventilation system, and which are labeled Primary Containment Isolation System (PCIS) on these units.
One train controls the inboard containment ventilation / purge isolation valves, and the other train controls the outboard isolation valves.
The initiating contacts for each train are described below:
I (1)
Automatic contacts (all one-out-o f-two, taken twice logic)
(a) Reactor building vent exhaust high radiation (reactor zone).
(b) Reactor building vent high radiation (refueling floor).
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(c) High drywell pressure.
(d) Low reactor water level.
- The following definition is given for clarity of use in this evaluation:
Reset:
The signal has come and gone, and the circuit is being cleared to return it to the normal condition. {
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Manual Contacts (a) None at the system l evel.
(Isolation may be accomplished by the individual PCIS valve manual
'k-swi tches.)
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The relays for each of the monitored plant conditions have con-
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tacts in each of the two trains that :ontrol the PCIS valves.
Each train
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is powered by a different electrical bus.
The PCIS circuits contain a y
reset switch, which functions as defined in this report.
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Li Several 2-inch-diameter isolation valves, hich bypass the large ventilation valves, are utilized by th2 Containment Atmospheric Control System (CAC) and the Containment Atmospheric Dilution System (CAD) to control the containment during normal plant operations and postaccident f*
operations, respectively. These valves (2509, 2510, 2513, 2514, and 2523),
which go to the flammable gas recombiner and standby gas treatment systems, F.
have a designed electrical override capability.
The override circuit b
contains an interlock to prevent its operation if the reactor is in the "run" mode. The override switch is a keylock switch with the key ontrol-led by the shift supervisor. The overridden condition is annunciated.
k When a monitored plant condition calls for isolation, electric power is removed from the slave relays (e.g.,16A-K23).
The slave relay contacts open to remove electric power from the soler.oid valves, causing the isolation valves to close.
- q 64 The PCIS valve solenoid valves must remain energized in order f1r the isolation valve to be kept open.
The slave relay circuit contains a seal-in contact to maintain electric power to the solenoid valve as lone as a PCIS signal is not present.
With a PCIS signal present, the valves will not remain open and cannot be opened by their manual switch (with the ex-ception of the five valves in the bypass circuit described above).
k The PCIS signal cannot be cleared until the initiating condi-tion (s) is cleared.
When all initiating conditions are cleared, pressing I-1 lh w
the PCIS reset button will restore power to the soleaoid valve circuits.
Pressing the PCIS reset butten will also clear a bypass conditicil on the CAC and CAD system valves 2509, 2510, 2513, 2514, and 2523 f f one exists.
The manual isolation valve switches are pistol-grip hanc.le, maintained-contact type (GE type SSM SW).
Hence, once electr'*c power is restored to the solenoid valve circuits, any isolation valve with its switch in tne "open" position will automatically reopen.
Incidental to this review, we have noCJ that the PCIS circuits do not contain 1 system-level manual isolation switch.
To manually isolate the PCIS valves, each of their individual manual switches must be turned to "close."
2.3 CONTAINMENT VENTILATION ISOLATION SYSTEM DESIGN EVALUA In response to this issue, on an interim basis, the 18-inch con-tainment ventilation / purge isolation valves at Peach Bottom nuclear power station, Units 2 and 3, are currently tagged shut. To facilitate their use prior to the completion of the NRC review, mechanical stops are being purchased, and the air pressure will be adjusted to limit the valves to a partial open position on an interim basis.
The PCIS actuation system has a reset switch but does not have an override capability.
However, the CAC/ CAD systems have a postaccident bypass capability for five 2-inch valves as discussed in Section 2.2.
Since, +he CAC/ CAD systems are designed to control and/or mitigate the containment atmosphere following an accident, their evaluation has not been included becausc it is beyond the scope of criterion 1.
Therefore, we conclude that NRC staff criterion no.1 is satisfied for the PCIS system except that no detennination has been made for the CAC/ CAD system.
The CAC/ CAD system bypass has a keylock switch with proper admin-istrative control, as well as annunciation of the bypass condition.
We conclu4 that NRC staff criteria nos. 2 and 3 ara satisfied..
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The containment isolition automatic actuation signal is formed by
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We conclude that NRC staff
.a criterion no. 4 is satisfied.
-- J Judging from the information provided by the licensee during the 1
August 24, 1979, meeting [Ref. 4] with the NRC and the " Submittal of Envi-ronmental Qualifications" [Ref. 73 dated April 16, 1980, the radiation-
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monitoring equipment at the Peach Bottom Nuclear Power Station, Units 2 and
_.3,j 3, is designed and qualified as safety-grade equipment.
We conclude that
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NRC staff criterion no. 5 is satisfied.
' _,1 When all initiating isolation conditions have been cleared, the PCIS actuation signal can be reset.
Upon resetting, ar.y of the isolation valves with their manual switch in the "cpen" position will automatically reopen.
This condition does not satisfy criterion 6.
In addition, if the p_g
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- However, evaluation of the CAC/ CAD system is beyond the scope of criterion 6 and no n
evaluation has been made.
The PCIS circuits do not contain a system-level manual isolation m.
6 switch as specified in the 1971 revision of IEEE Std-279.
However, the g
switch was not included in the design because the date of these units Q
precedes the 1971 revision.
The addition of a manual isolation switch would provide a quick and efficient means for the operators to isolate the
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containment in an emergency.
The work involved would be to install the
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switch in the control panel and connect the associated wiring to the PCIS
>q logic circuits.
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i 2.4 OTHER ENGINEERED SAFETY FEATURE SYSTEM CIRCUITS The licensee submitted an evaluation of other ESF systems in response to IE bulletin 79-08 [Ref. 3].
In order to audit the other ESF systems, we have reviewed the core spray system.
Based on sube.ittals for this system, we conclude that the NRC criteria are satisfied.
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CONCLUSIONS I
.d The EI&C design aspects of containment purge valve isolation and
.-. u the core spray systems for the Peach Bottom Nuclear Power Station, Units 2 and 3, were evaluated using those design criteria stated in Section 2 d of
_j this report.
t We conclude that, with one exception, the PCIS cir;dit design
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meets the NRC staff criteria. This exception (based on review of available
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drawings) is that under certain conditions the PCIS valves could a.ito-b matically reopen. The evaluation of the CAC/ CAD system is beyond the scope l
of this review.
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Based on our audit, we conclude that the other ESF systems meet the NRC staff criteria.
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The PCIS circuits do not contain a system-level manual isolation switch as specified in IEEE Std-279-1971.
We recomend that a manual y
system-level isolation switch be incorporated.
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..t REFERENCES c.1 1.
NRC/00R letter (A. Schwencer) to P EC, " Containment Purging During Nonnal Plant Operation," dated November 28, 1978.
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PEC letter (S.
L.
Dal troff) to NRC (Thomas A.
Ippolito), Dockets 50-277 and 50-278, (no title), dated January 2,1979.
I 3.
PEC reply to IE Bulletin 79-08, (J.
W.
Gallagher) to NRC (B.
H.
?j Grier),"Re: IE Bulletin 79-08", dated April 25, 1979.
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4.
PEC meeting with the NRC in Washington, D.C., on " Containment Purging During Nennal Plant Operation", August 24, 1979.
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U.S. Nuclear Regulatory Comission, Standard Review Plan, " Containment Isolation System," NUREG 75/087, Rev.1, Section 6.2.4.
mg 6.
PEC reply to IE Bulletin 79-08 (S. L.
Daltroff) to NRC (Boyce H.
I Gri
-), Dockets 50-277 and 50-278 (no title), dated August 8,1979.
f 7.
PEC letter (W. M. Alden) to NRC (Richard Clark), Dockets 50-277 and 50-278 (Submittal of Environmental Qualifications), dated April 16, jj 1980.
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