ML20062F145
| ML20062F145 | |
| Person / Time | |
|---|---|
| Site: | Fort Calhoun  |
| Issue date: | 11/29/1978 |
| From: | Reid R Office of Nuclear Reactor Regulation |
| To: | Short T OMAHA PUBLIC POWER DISTRICT |
| References | |
| NUDOCS 7812150076 | |
| Download: ML20062F145 (6) | |
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November 29, 1978 Docket No.: 50-285 Mr. Theodore E. Short Division Manager - Production Operations Omaha Public Power Olstrict 1623 Harney Street Omaha, Nebraska 68102
Dear Mr. Short:
RE: CONTAINMENT PURG!NG DURING NORMAL PLANT OPERATION A number of events have occurred over the past several years which directly relate to the practice of containment purging during nomal plant operation. During recent months, two specific events have occurred which have raised several qLestions relative to potential failures of automatic isolation of the large diameter purge pene-trations which are used during power operation. On July 26, 1978, the Northeast Nuclear Energy Company reported to the NRC such an event at Millstone Unit No. 2, a pressurized water reactor located in New London County, Connecticut. On September 8, 1978, the Public Service Electric and Gas Company reported a similar event at Salem Unit No.1, a pressurized water reactor located in Salem County, New Jersey.
During a review of operatin orocedures on July 25, 1978, the licensee discovered that.since May 1 1978, intemittent containment purge operations had been conducted at Millstone Unit No. 2 with the safety actuation isolation signals to both inlet and outlet redundant containment isolation valves (48 inch butterfly valves) in the purge inlet and outlet penetrations manually overridden and inoperable.
The isolation signals which are required to automatically close the purge valves for containment integrity were manually overridden to allow purging of containment with a high radiation signal present.
The manual override circuitry designed by the plant's architect / engineer defeated the high radiation signal and all other isolation signals to these valves. To manually override a safety actuation signal, the operator cycles the valve control switch to the closed position and then to the open position. This action energized a relay which blocked the safety signal and allowed manual operation independent cf any safety actuation signal. This circuitry was designed to permit reopening these valves after an accident to allow manual operation of certain safety equipment.
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On September 8,1978, the staff was advised that, as a matter of routine, Salem Unit No. I has been venting the containment through the containment ventilation system valves to reduce pressure.
In certain instances this venting has occurred with the containment high particulate radiation monitor isolation signal to the purge and pressure-vacuum relief valves overridden. Override of the containment isolation signal was accomplished by resetting the train A and B reset buttols. Under these circumstances, six valves in the containment vent and purge systems could be opened with a high particulate isolation signal present.
This override was performed after verifying that the actual containment particulate levels were acceptable for venting. The licensee, after further investigation of this practice, determined that the reset of the particulate alarm also bypasses the containment isolation signal to the purge valves and that the purge valves would not have auto-matically closed in the event of an emergency core cooling system (ECCS) safety injection signal.
These events and information gained from recent licensing actions have raised several concerr.s relative to potential failures affecting the purge penetration valves which could lead to a degradation in containment integrity 6nd, for PWR's, a degradation in ECCS performance.
Should a loss-of-coolant accident (LOCA) occur during purging there could be insufficient containment backpressure to assure proper operation of the ECCS. As the practice of containment purging during normal operation has become more prevalent in recent years, we have required that applicants for construction permits or operating licenses provide test results or analyses to demonstrate the capability of the purge isolation valves to close against the dynamic forces of a design basis LOCA.
Some licensees have Technical Specifications which p ohibit purging during plant operation pending demonstration of isolation valve operability.
In light of the above, we request that you provide within 30 days of receipt of this letter your commitment to cease all containment purge during operation (hot shutdown, hot standby, startup and power operation) or a justification for continuing purging at your facility. Specifically, provide the following information:
1 (1) Propose an amendment to the plant Technical Specifications based upon the enclosed model Technical Specification, or j
(2)
If you plan to justify limited purging, you must propose a Technical Specification change limiting purging during operation to 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> per year as described in the enclosed Standard Review Plan Section 6.2.4, Revision 1.
Your justification must include a demonstration (by test or by test and analysis similar to that required by Standard Review Pian 3.9.3) of the ability of the containment isolation valves to close under I
postulated design basis accident conditions. Within thirty days of receipt of this letter, you are requested to provide a schedule for completion of your evaluation justifying i
continuation of limited purging during power operation.
(3)
If you plan to justify unlimited purging you need not propose a Technical Specification change at this time. You must, however, provide the basis for purging and a schedule for responding to the issues relating to purging during normal operation as described in the enclosed Standard Review Plan Section 6.2.4, Revision 1, and the associated Branch Technical Position CSB 6-4 As discussed in these documents, purging during normal operation may be permitted if the purge isolation valves are capable of closing against the dynamic forces of a design basis loss-of-coolant accident. Also, basis for unlimited rurging must include an evaluation of the impact of purging during operation on ECCS performance, an evaluation of the radiological consequences of any design basis accident requiring containment isolation occurring during ;u operations, and an evaluation of containment purge and isolatte atrumentation and control circuit designs. Within thirty days of saceipt of this letter, you are requested to provide a schedule for completion of your evaluation justifying continuation of unlimited purging during power operation.
pending completion of the NRC staff review of the justification for continued purging in (2) or (3) above, you should commit to either cease purging or limit purging to an absolute minimum, not to exceed 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> per year.
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. I The staff believes that both the Millstone and Salem events resulted from lack of proper management control, procedural inadequacies, and possible design deficiencies.
While the containment atmosphere was properly sampled and the purging (venting) discharges at both facilities were within regulatory requirements, the existing plant operating procedures approved by the licensee's management did not adequately address the operability of the purge valves and the need for strict limitations on (or prohibition of) overriding a safety actuation closure signal.
The requirements for valve operability were not discussed and the related Technical Specifi-cations were not referenced in the procedures. Design deficiencies probably contributed to the events as the safety actuation bypass condition is not annunciated nor is a direct manual reset of the safety actuation signal available. Consequently, we have developed the position specified below to assure that the design and use of all override circuitry in your plant is such that your plant will have the protection needed during postulated accident conditions.
Whether or not you plan to justify purgin;. you should review the design of all safety actuation signal circuits which incorporate i
a manual override feature to ensure that overriding of one safety actuation signal does not also cause the bypass of any other safety actuation signal, that sufficient physical features are provided to facilitate adequate administrative controls, and that the use of each such manual override is annunciated at the system level for every system impacted. Within thirty days of receipt of this letter, you are requested to provide (1) the results of your review of override circuitry and (2) a schedule for the development of any design or procedural changes imposed or planned to assure correction of any non-conforming circuits. Until you have reviewed circuitry to the extent necessary to verify that operation of a bypass will affect no safety functions otner than those analyzed and discussed on your docket, do not bypass that i
signal. Our Office of Inspection and Enforcement will verify that
you have inaugurated administrative controls to prevent improper i
manual defeat of safety actuation signals as a part of its regular inspection program.
l Sincerely, l
G;2&/wm Robert W. Reid, Chief Operating Reactors Branch #4 Division of Operating Reactors
Enclosures:
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Model Technical l
Specification 2.
Standard Review Plan 3.
Branch Technical Position CSB 6-4 cc: w/e.7 closures i
See next page i
Omaha Public Power District cc:
Margaret R. A. Paradis LeBoeuf, Lamb Leiby & MacRae 1757 N Street, N. W.
Washington, D. C.
20036 Blair Public Library 1665 Lincoln Street Blair,fiebraska 68008 e
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STANDARD REVIEW PLAN OFFICE OF NUCLEAR REACTOR REGULATION e...e SECTICN 6.2.s CCNTA!WENT !5CLAT!GN Sv5 FEM Riv!Fw Rf5PON5!BIL!f!ES Primary - Containment Systems Branch (C$8)
Secondary - Accident Analysis Branen ( AAB)
Instrumentation and Control System Branch (ICSB)
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- echanical Engineering Branch (PEB)
Structural Engineering Branch (SEB)
- eactor Systems Sranch (R58)
Power Systems Branch (PSB)
I, AREAS CF 4Ev!fW The design oDjective of the containment isolation system is to allow the normal or emer-gency passage of fluids through the contatnment boundary while preserving the aDility of the boundsry to prevent or limit tre escape of fisston products that may result f rom postulated accidents. Imts $RP secticn. therefore. 15 concerned alth the isolation of fluid systems antcn penetrate the contatement boundary, including the oesign and testing requirements for isolation barriers and actuators. Isolation barriers inc h.de valves, closed piping systems dod blind flanges.
The CSS revtews tf.e information presented in the applicant's safety analysis report (SAR) regarding containment isolation provisions to assure conformance with trie requirecents of General Cesign Crtteria 54, 55, 56 and 57.
The C58 review covers the following aspects of containment isolation:
t.
'ne design of centainment Italation provtsions, including.
s.
The numcer and location of isolation valves, i.e., the isolation valve arrange-ments and the physical location of Isolation valves witn respect to the conta t r.pe n t.
O The sctuation and control features for isolatton valves.
c.
De posittons of isolation valves f or normal plant operattng conditions (includ*
ing bhutdown). post-accident conditiCns, and in the event of valve operator comee failures.
L Pe valve sctuation signsis.
e, Ire bests for selection of closure tites of isolation valves.
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The mechanical redundancy of isolation devices.
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The acceptability of closed piping systems inside containment as isolation barriers.
2.
The protection provided for containment isolation provisions against loss of function from missiles, pipe anip, and earthquakes.
3.
The environmental conditions inside and outside the containment that.ere considered in the design of isolation barriers.
4 The design criteria applied to isolation barriers and piping.
5.
The provisions for detecting a possiole need to isolate remote-manual controlled systems, such as engineered safety features systems.
6 The design provisions for and technical specifications pertaining to operability and leakage rate testing of the isolation barriers.
7.
The calculation of containment atmosphere released prior to isolation valve closure for lines that provide a direct path to the environs.
PSB has primary responsibility for the qualifiestion test program for electric valve operators, and the IC$3 nas primary responsibility for the qualification test program for tne sensing and actuation instrumentation of the plant protection system located both inside and outside of containment. The MEB has review responsibility for the qualffica-tion test program to demonstrate the performance and reliability of containment isolation valves. The WEB and SE3 have review responsibility for mechanical and structursl design j
of the containment isolation provisions to ensure adequate protection against missiles, pipe whip, and earthquates. The AA8 reviews the radiological dose consequence analysis for the release of containment atmosobere prior to closure of containment isolation valves in lines that provide s direct path to the environs. The RSS reviews the closure time for containment isolation valves in lines that provide a direct path to the environs, with respect to the predtetion of onset of accident induced fuel failure.
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!!. ACCEPTANCE CRITE4!a The general design criteria sstablish requirements for isolation barriers in lines pene-trating the prieary Containment boundary. In general, two isolation barriers in series l
are required to assure that the isolation function is satisfied assuming any single active failure in the containment isolation provisions.
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l The design of the containment isolation provisions will be acceptable to CSB if the following criteria see satisfied:
1.
General Design Criteria 55 and 56 require that lines that penetrate the primary cen-tainment ootodary and either are part of the reactor coolant pressure boundary or det. I 6.2.4*2
connect directly to the containment atmosphere should be proviced =tth isolation valves as follows:
One locked closed isolation valve 1/ inside and one locked closed isolatton a.
valve outside containment; or D.
One automatic isolation valve inside and one locked closed isolation valve out-side containment; or One locked closed Isolation valve inside and one automatic isolatinn valveU c.
outside containment; or OneautomaticisolationvalveinsideandoneautomaticisolationvalveU d.
outside contair: ment, 2.
General Design Criterion 57 requires that If nes that penetrate the primary contain-ment boundary ard are neither part of the reactor coolant pressure boundary nor connected directly to the contalement atmosphere snould De provided with at least one locked closed, remote-manual, or autcmatic isolation valve outside containment.
3.
Ibe general design criteria permit containment isolation provisions for lines pene-trating the primary containeent boundary that dif fer f rom the esplicit requireeents of General Design Celterta 55 and % if the basts for acceptanility is defined.
Following are guidelines for acceptable alternate containment isolation provisions for certain classes of lines; a.
Regulatory Cutoe 1.11 descriDes acceptaDie contairment isolation provisions for instrument lines. In addition, instrument lines that are closed Doth inside and outside containment, are designed to witnstand the peessure and temcerature conditions following a loss-of-coolant Jccident, and are destgred to eithstand dynaM c effects, are acceptable without isolation valves.
D.
Containment isolatton provisions for lines in eagineered safety features or engtmeered safety feature-related systems may ' nc lude remote-manu.51 valves, out provistans should ce made to detect poss1 Die leakage fece these lines outstce containment, c.
Containment isolation provisions for lines in systems needed for safe shutdown of the plant (e.g., licuid poison system, reactor core isolation cooling system, and isolation condenser system) may incluce remote-sanual valves, Dut provision snculd te 1 Lade to detect Dossible teamage from these 11n45 outstde conta kment, hLXaeoclosed isolation valves are defired as sealgd clCsed Dsrriers (see item II.3.f),
{/4 simDI4 CheCW valde is not normally an.aCCeptaDie autcmatic isolation salve for this Ao01tcation.
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d.
Containment isolation provisions for lines in the systems identified in items b and c rormally consist of one isolation valve inside and one isolation valve outside containment. If it is not practical to locate a valve inside contain-ment (for example, the valve may be under water as a result of an accident),
l both valves may be located outside containment. For this type of isolation valve arrangement, the valve nearest the containment and the piping bet.een the containment and the valve should be enclosed in a leak tignt or controlled leakage housing.
If, in lieu of a housing, conservative design of the piping and valve is assumed to preclude a breach of piping integrity, the design should conform to the requirements of SRP section 3.6.2.
Design of the valve and/or the piping compartment should provide the capaDility to detect leakage from the valve shaft and/or bonnet seals and terminate the leakage, e.
Containment Italation provisions for lines in engineered safety feature or engineered safetf feature-eelated systems normally consist of two isolation valves in series. A single tsolation valve will be acceptable if it can be j
shown that the system relinoility is greater with only ore isolation valve in ths line, the system is closed outside containment, and i single active failure can be accommodated =1th only one isolation valve in the lire.
The closed system outside containment should be protected from missiles, designed to seismic Category I standards, classified Safety Class 2 (Ref. 5), and should have a design tempersture and pressure rating at feast e3ual to that for the containment. The closed system outside containment should be lean tested, unless it can be shown that the system integrity is being maintained during normal plant cperations. For this type of isolation valve strangement the valve is located outside containment, and the piping bet =een the containment and the valve should be enclosed in a leak tight or controlled leakage housing.
If, in lieu of a housing, conservative design of the piping and valve is assumed to preclude a breach of piping integrity, the design snould conform to the reoutrements of $RP section 3.6.2.
Cesign of the valve and/or the piping compartment should provide the capability to detect leakage from the valve shaft and/or bonnet seals and terminate the leakage.
f Sealed closed barrters may be used in place of autcoatic isolation valves.
Sealed closed barriers include blind flanges and sealed closed isolation valves
-nich e.ny be closed manual valves, closed remote-manual valves, and closed automatic valves =hich remain closed after a loss-of-coolant accident. Sealed closed isolation valves should be under administrative control to assure that they cannot be inadvertently opened. Administrative control includes mechanical devices to seat or lock the valve closed, or to prevent power frcm Deing suc-plieJ to the valve acerator.
g.
4ellef valves may be used as isoistion valves provided the relief set point is greate* than 1.5 times the contatnment design pressure.
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! solation valves outside containment should be located as Close to the contairment as practical, as required by General Design Criteria $5. 56, and 57.
l 5.
The position of an isolation valve for normal and shutdown plant operating conditions and post-accident conditions depends on the fluid system function. If a ffuld system does not have a post-accident function, the isolation valves in the lines should be automatically closed. For engineered safety feature or engineered lafely feature-related systems, isolation valves in the lines may remain open or be opaned.
i The position of an isolation valve in the event of power failure to the valve operator should be the " safe" position. Normally this position would be the post accident valve position. All power-operated isolation valves should have positfor indication in the main control room.
j 6.
There should be diversity in the parameters sensed for the initiation of containment jeoIation.
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System lines.nicn provide an ooen path from the containment to the environs should be equipped with radiation monttors that are capable of isolating these lines upon a high rsdiation signal. A high radiation signal should nct be cc.isidered one of the diverse containment isolation parameters.
8.
Containment isolation valve closure times shculd be selected to assure espid isola-I tion of the containment following postulated accidents. The valve closure time is the time it takes for a power coerated valve to be in the fully closed position af ter the actuator power has reached the operator asseenly; it does not include the time to reach actuation signal setpoints or instrument delay times, which should be considered in determining the overall time to close a valve. System design capa-bilities snould be considered in establishing valve closure times. For lines which provide an ocen path f rom the containment to the environs; e.g., the containment i
purge and went lines, isolation valve closure times on the order of 5 seconds or less may be necessaey. The closure times of these valves should be established on the basis of minimizing the release of containment atmosphere to the environs, to ritigate the offstte esdiological consecuences, and assure that emergency core cooling system (ECCS) ef'ectiveness is not degraded by a reduction in the centalement bacsoressure. Analyses of the radiological consecuences and the effect on the contaireent bactoressure due to the release of containment atmosphere should be l
t provided to justify the selected valve closure time. Additional guidance on the design and use of containment purge systems which may be used during the normal plant operating modes (i.e., startup, power operation, mot standby and hot shutdown) is crovided in Branch Technical Position CSS 6-4 (Ref. 9).
For plants under review for operating licenses or plants for enich the Safety Evaluation Report for construc-tion permit spolication.as issued prior to July 1,1975, the methods described in Section 3, Items S.I..
a, b, d, e. f, and g, 8.2 througn B.4, and S.S.b. c, and d of Branch fechnical Position 6 4 should te isolemented. For trese plants, BTP Items l
S. I.c and 9.5.a. regarding the size of the purge system used during normal plant coeration and the justification Dy acceptable dose consequence analysis, may oe 6.2.4-5 Rev. 1 J
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valved if the applicant commits to limit the use of the purge system to less than 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> per year. nile the plant is in the startup, power, hot standby and hot shutdown modes of operations. This commitment should te incorporated into the Technical Specifications used in the operation of the plant.
9.
The use of a closed system inside containment as are of the isolation barriers will be scceptable if the design of the closed system satisfies the following requirements; a.
The system does not communicate with either the reactor coolant system or the Containment 5tmosphere, b.
fhe system is protected against iissiles and pipe.nio.
c.
The system is designated seismic Category I.
d.
The system is classified Safety C'. ass 2 (Ref. 5).
e.
The system is designed to withstand temperatures at least equal to the contain-ment uesign temperature.
f.
The system is designed to withstand the enternal pressure fece the containment structural acceptance test.
g.
The system is designed to withstand the loss-of-coolant accident transient and envirCnment.
Insofar as CSB is concerned with the structural design of containment internal structures and piping systems, the prntection of isolation barriers against loss of function fece missiles, pipe.nio, and earthquakes will be acceptable if isolation barriers are located tenind etssile barriers, pipe nic was considered in the design of pipe restaa1nts and the location of piping penetrating the containment, and the isolation barriers, including the piping tatween isciation valves, are designated seismic Category I, i.e., designed to withstand the effects of the safe shutdown earthquare, as recommended by Regulatnry Guide 1.29.
10.
The oesign c-iteria apolted to components performing a containment isolation functicn, l
including the isolation barrters and the piping bet.een them, or tre Diping bet.een the centatreent and the outtrmost isolation carrier, are accectacle if:
l Group B cuality stancards, as defined in Regulatory Gaide 1.26 are acclied to a.
tSe ;ompo ents, unless the service function dictates that Group A quality standards be a: plied.
I b.
The ccmponents are designated seismic Category I, in accor$4nce with Regulatcry Gwide 1.29.
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11.
The design of the containment isolation system is acceptable if provisions are mace to allow the operator in the main control room to know enen to isolate fluid systems f
that are equipped with remote manual isolation valves. Such provisions may include instruments to measure fina rate, sump water level, temperature, pressure, and radiation level.
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4 12.
Provtsions should be mace in tne aesign of the containment isolation system for l
t operaDility testing of the containment isolation valves and leakage rate testing of the isolation barriers. The isolation valve testing program should be consistent with that proposed for other engineered safety features. The acceptance criteria
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for the leakage rate testing program for containment isolation barriers are presented i
in SRP section 6.2.6.
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For those areas of review identifieo in subsection 1 of this SRP section as being the i
responsibility of other branches, the acceptance criteria and their methods of application are contained in the SRP sections corresponding to those branches.
!!!. REv!EW PROCEDURES The procedures cesCribed below provide guidance on review of the Containment Isolation T
system. The reviewer selects and emchasizes material frcm the review procedures as may be accropriate for a particular case. Portions of the review may be done on a generic basis for aspects of containment isolation common to a class of containments, or by accoting the results of previous reviews of plants with essentially the same containment isolation provisions.
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I Upon request from the primary reviewer, the secondary review branches will provice input for the areas of review stated in subsection 1.
The primary reviewer obtains and uses such inout as required to sssure that this review procedure is C0molete.
i The CSB determines the acceptability of the containment isolation system by comparing the
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system design criteria to the design recuirements for an eagineered safety feature. The l
'2uality standards and the seisatc cesign classification of the containment isolation oro-visions, incluotng the piping cenetrating the contairment, are comoared to Regulatory Guices 1.25 and 1.29, rescectively.
7 The CSB also ascertains that no single fault can prevent isolation of the containment.
This is acccmolished by revisning the containment isolation provisions for each line j
penetrating the containment to cetermine that two isolation barriers in series are provided, and in conjunction with tre P58 by reviewirg the power sources to the valve operators.
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i The C58 reviews tne info mation in the SAR justifying containment isolation provisions l
F antch Jiffer from tne explicit requirecents of General Cesign Criteria 55, 56 ana 57.
The Cta judges the acceptability of tnese containment isolation orovisions cased on a comcarison with tne acceptance criteria given in suosection II.
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4 The C58 reviews the position of isolation valves for normal and shutdown plant operating conditions, post-accident conditions, and valve operator power failure conditions as listed in the SAR. The position of an isolation valve for each of the above Conditions depends on the system function. In general, power-operated valves in fluid systems which j
do not have a post-accident safety function should close automatically. In the event of power failure to a valve operator, the valve position should be the position of greater safety, which is normally the post-accident position. However, special cases may arise and these will be considered on an individual basis in determining the acceptability of the prescribed valve positions. The C58 also ascertains from the SAR that all power-operated Isolation valves have position indication capability in the main control room.
i The CSB reviews the signals obtained from the plant protection system to initiate contain-ment isolation. In general, there should be a diversity of parameters sensed; e.g.,
abnormal conditions in the reactor coolant system, the secondary coolant system, and the contairmoot. <hich generate containment isolation signals. Since plant designs dif fer in 1
this reges N many dif ferent coebinations of signals f rom the plant protection system are used to initiate containment isolation, the CSB considers the arrangement proposed on an individual basis in determining the overall acceptability of the containment isolation signals.
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j The C58 reviews isolation valve closure times. In general, valve closure times should be less than one minute, regardless of valve size. (See the acceptance criteria for valve closure times in subsection !!.) Valves in Ifnes that provide a direct path to the l
environs, e.g., the containment purge and ventilation system lines and main steam lines for direct cycle plants, may have to close in times muc't shorter than one minute. Closure times for these valves may be dictated by radiological dose analyses or ECC5 performance considerations. The C58 will recuest the AA8 or R58 to review analyses justifying valve closure times for these ulves as necessary.
The CSB determines the acceptabilitf of the use of closed systems inside containment as isolation barriers by comparing the system designs to the acceptance criteria specified in subsection II.
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The ufB and SEB have review responsibility for the structural cesign of the containment internal structures ned ofping systems, inclucing restraints, to assure that the contain-ment isolation provisons are adequately protected against missfies, pipe = hip, and earth-cuakes. The CSB determines that for all containment isolation provisions, missile pro-tection and protection against loss of function from pipe wnlo and eartnquakes were desf n Considerations. The CSB reviews the system drawings (=nich should show the loCa*
Q tions of missile barriers relative to the Containment isolation provisions) to determine that the isolation provisions are protectea from missiles. The CSS also reviews the design Criteria ADD 1ed to the containment isolation provisions to determine that protec*
I tion sqainst dynamic effects, such as pipe wniD and earthquakes, =4s Considered in the design. The CSS will request the WEB to review LPe design adecuaCy of p10174 and valves for eniCn Conservative design is assumed to preclude possible DreaC9 of system integrity in Iteu of croviding a less tight a.ousing.
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Systems having a post accident safety function may have remote-manual isolation valves in the lines penetrating the containment. The CSC reviews the provisions made to detect leakage from these lines outside containment and to allow the operator in the main control room to isolate the system train should leakage occur. Leakage detection provisions may include instrumentation for ceasuring system flow rates, or the pressure, temperature, j
radiation, or water level in a-eas outside the contairment such as valve rooms or engi-l neered safeguards areas. The C58 bases its acceptance of the leakage detection provisions des 6ribed in the SAR on the capacility to detect leakage and identify the lines that I
should be isolated.
The CSB determines that the containment isolation provisions are designed to allow the isolation barriers to be individually leak tested. This information should be taDulated in the safety analysis report to facilitate the CSB review.
l The CSB determines from the descriptive information in the SAR that provistens have been mace in the design of the containment isolation system to allow perlooic coerability test'ng of the power-operated isolation valves and the containment isolation system. At the operating license stage of revtew, the CSB determines that the content and intent of proposed technical specifications pertaining to operability and leak testing of contain-i ment isolation equipment is in agreement with requirements developed by the staf f.
IV.
EVAleATIcN FINDINGS The information provided and the CSS review should support ccncluding statements similar to the following, to be included in tne staff's safety evaluation report:
"The scope of review of the containment isolation system for the (plant name) has included schematic drawings and descriptive information for the isolation provisions for fluid systems which penetrate the containment boundary. The review has also included the applicant's prooosed design bases for tne containment isolation provi-sions, and analyses of the functional capaDility of the contairment isolation system.
"The basis for the staf f's acceptance has been the confermance of the containment isolation provisions to the Commission's regulations as set forth in the General Cesign Criteria, and to acclicaDie regulatory guides, staff technical positions, and f
industry codes and standards. (Special prcDiess or exceptions tnat the staf f takes to specific containment isolation provisions or the functional capacility of the containment isolation system should be discussed.)
"The staff concludes that the containment isolation system cesign conforms to all i
aoplicaele regulations, guides, staff positions, and industry cedes and standards, i
and is BCceptaDle."
L 3EFEDENCES 1
10 CFR Part 50, Apoendix A. General Cesign Criterion 54, " Piping Systems Penetrating Containment."
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10 CFR Part 50, Appendia A General Design Criterion 55, " Reactor Coolant Pressure Boundary Penetratirg Containment."
3.
10 CFR Part 50, Appendin A, General Design Criterion 56, " Primary Containment Isolation."
4 10 CFR Part 50, Appendia A, General Design Criterion 57, " Closed System Isolation valves."
5.
Regulatory Guide 1.141, " Containment Isolation Provisions For Fluid Systems."
6.
Requiatory Guide 1.11. " Instrument Lines Genetrating Primary Reactor Containment."
7.
Regulatory Guide 1.26, " Quality Group Classifications and Standards for Water,
Stean, and Radioactive-Waste-Containing Components of Nuclear Fower Plants."
8.
Regulatory Guice 1.29,
- Seismic Design Classification."
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9.
Branch Technical Position CSB 6-4, " Containment Purging During Normal Plant Opera-tions,' attached to this SRP section.
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Branen Technical Position CSB 6 4 t
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s CCNTA!W8ENT PURGING OURING NORMAL PLANT OPERATIONS
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A.
BACKGROUNO This branch technical position pertains to system lines which can provide an as n path l
0 from the containment to the environs during normal plant operation; e.g., the,su ge and vent lines of the containment purge system. It supplements the position t( e in SRP f
sectisn 6.2.4.
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While the containment purge system provides plant operational flesibility, its design must consider the importance of minimizing the release of containment atmosphere to the environs following a postulated loss-of-coolant accident. Therefore, plant designs must not rely on its use on a routine basis.
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f The need for purging has not always been anticipated in the design of plants ano there-
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fore, design criteria for the containment purge system have not been fully developed.
The purging esperience at operating plants varies consiceraoly from plant to plant. Some plants do not purge ouring reactor operation, scoe purge intermittently for shcrt periods and some purge continuously.
The containment purge system has ceen used in a variety of ways, for enamole, to alleviate
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certain operational proolems, such as excess air leakage into the contair: ment free pneumatic l
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controllers, for reducing the atreorne activity within the containment to facilitate i
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personnel access during reactor power operation, and for controlling the contatnment pressure, teepersture and relative humidity. However, the purge and vent lines provide i
an open path from the containment to the environs. Should a LOCA occur during containment I
j purging when the reactor is at power, the calculated accident doses should be within l
10 CFR 100 guideline values.
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The sizing of the purge and vent lines in most plants has been Dased on the need to
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control the containment stmospeere during eefueling coerations. This need has resulted j
j in very large lines penetrating the containment (about 42 inches in diameter). Since i
these lines are normally the only ones provided that mill permit some deg*ee of control
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over the containment atmosphere to facilitate personr.el access, some plants have used l
i them for containment purging during normal plant operation. Urder such conditions, calculated accident doses could De significant. Therefore, the use of these large contain-sent purge and ver.t lines should ce restricted to cold shutdown conditions and refueling operations, t
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The design and use of the purge and went lines should be based on the premise of achieving acceptable calculated offsite radiological consequences and assuring that emergency core cooling (ECCS) effectiveness is not degraded by a reduction in the containment backpressure.
Purge system designs tnat are acceptable for use on non-routtrco b;;is during normal plant operation can be achieved by providing additional purge anc =ent lines. The 512e of these lines should be limited such that in the event of a loss-of-coolant accident, assuming the purge and vent valves are open and subsequently close, the radiological consequences calculated in accordance with Regulatory Guides 1.3 and 1.4 would not exceed the 10 CFR 100 guideline values. Also, the maaimum time for valve closure should not esceed five seconds to assure that the purge and went valves would be closed before the onset of fuel failures following a tCCA.
The size of the purge and went lines should be about eignt inches in diameter for PkR plants. This line size may be overly conservative from a radiological viewpoint for the Mark III EnR plants and the HTGR plants because of containment and/or core oesign features.
'merefore, larger line sizes may be justified. However, for any proposed line size, the a:plicant must demonstrate that the radiological consequences following a loss-of-coolant accident would be within 10 CFR 100 guideline values. In summary, the acceptability of a specific line size is a function of the site meteorology, containment design, and radio-logical source term for the reactor type; e.g., BhR, P%R or HTGR.
B.
80ANCH TECHNICAL POSITION The system used to ourge the containment for the reactor operational modes of power oceration, startup, hot standby and hot shutdown; i.e., the on-line purge system, should te indepenoent of the purge system used for tne reactor operational modes of cold shutdown and refueling.
1 The on-llre purge system should be designed in accordance with the following criteria:
The per*ormance and reliability of the purge system isolation valves should be a.
consistent with the operability assurance program outlined in MES Branch Tech-
"i nical Position "EB-2, Pump and valve Ocerability Assurance Program. (Also see SRP Section 3.9.3.)
The Jesign basis for the valves and actuators snould j
include the buildup of containment pressure for the LOCA brear spectrum, and the purge line and went line flows as a function of time uD to and during valve closure.
O The numoer of purge and vent lines that may te used should be limited to one surge line and one vent line.
The size of the purge and vent lines should not exceed acout eight inches in c,
diameter unless detailed justification for larger line sizes is provided.
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The containment isolation provisions for tne purge system lines should meet the standards approcriate to engineered safety features; i.e., quality, redundancy, testability and other appropriate criteria.
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Instrumentation and control systems provided to isolate the purge system lines should be independent and sctuated my diverse parameters; e.g., containment pressure. safety injection actuatio% and containment radiation level. If energy
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f is required to close the valves at ' east two diverse sources of energy sn&,1 De I
provided, either of wnich can af fect the Isolation function.
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Purge system isolation valve closure times including instrumentation delays.
should not exceed five seconds.
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Provisions should be saae to ensure that isolation valve closure will not ce prevented by debris.nich could potentially Decome entrained in the escaping air and steam,
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The purce system should not be relied on for temperature and humidity control within i
the containment.
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Provisions should be made to minimize the need for purging of the containment by providing containment atmosonere cleanup systems within the containment.
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4 Provisions should be maoe for testing the availanility of the isolstion function and l
the leamage rate of the isolation valves, individually, during reactor operation.
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The following analyses should be cerformed to justify the containment purge system
-l design:
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An analysis of the radiological consequences of a loss-of-coclant accident.
l The snalysis should be doce for a soectrum of treak sizes. and the instrumenta-r tion and setpoints that will actuete the vent and purge valves closed should be icentified. The source term used 4n the radiological calculations should be cased on a calculation unde
- the terms of Appendix ( to cetermine the entent of fuel failure ard the concomit.snt release of fission products, and the fission product activity in the primary coolant. A pre emisting f odice spike should be
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l constdered in determining primary coolant activity. The volume of containment j
in.nich fission products are mined should De justified. and the fission products
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from the above sources should be assumed to be reieased through the open purge valves during the maximum interval eecuired for valve closure. The radiological f
consecuences snould ee within 10 CFR 100 guiceline values.
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An analysis.nich cemons ates the acceptability of the provisions made to j
protect structures and safety-related equicsent; e.g.,
fans, filters and duct-i
.ork, located beyond the purge system isolation valves against loss of function from the environment created by the escaping air and steam, h
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An analysis of the reduction in the containment pressure resulting from the partial loss of containment atmosphere during the accident for ECCS backpressure determination.
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The allowable leak rates of the purge and vent isolation valves should be specified for the spectrum of design basis pressures and flows against which the valves must close.
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6.2.5-14
CONTA!NMEtlT SYSTEMS CONTAINMENT VENTILATION SYSTE!i (OPTIONAL *)
LIMITING CONDITIOt1 FOR OPERATION i
3.6.1.8 The containment purge supply and exhaust isolation valves shall be closed.
APPLICABILITY: MODES 1, 2, 3, and 4.
ACTIO!1:
With one containment purge supply and/or one exhaust isolation valve open, close the open valve (s) within one hour or be in at least fiOT STA'CBY within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in COLD SHUTDOWN within the follcw-ing 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />.
SURVEILLAt;CE RECUIRE!1ENTS 4.6.1.8 The containment purge supply and exhaust isolation valves shall be detemined closed at least once per 31 days.
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l CONTAlfiMENT SYSTEMS BASES 3/4.6.1.8 CONTAINMENT VENTILATION SYSTEM The containment purge supply and exhaust isolation valves are 4
required to be closed during plant operation since these valves have not been demonstrated capable of closing during a (LCCA or steam.line break accident). Maintainirig these valves closed during plant operations ensures that excessive quantities of radioactive materials will not be released via the containment purce system.
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