ML19289C208
| ML19289C208 | |
| Person / Time | |
|---|---|
| Site: | Farley  |
| Issue date: | 11/28/1978 |
| From: | Schwencer A Office of Nuclear Reactor Regulation |
| To: | Barton A ALABAMA POWER CO. |
| References | |
| NUDOCS 7812140364 | |
| Download: ML19289C208 (6) | |
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'g UN!TED STATES i_
4 NUCLEAR REGULATORY COMMISSION
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%.~....p November 28, 1978 Docket No. 50-348 Alabama Power Company ATTN:
Mr. Alan R. Barton Senior Vice President Post Office Box 2641 Birmingham, Alabama 35291 Gentlemen:
RE: CONTAINMENT PURGING 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 normal plant operation. During recent months, two specific events have occurred which have raised several questions 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 operating procedures on July 25, 1978, the licensee discovered that since May 1, 1978, intermittent 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 of 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 buttons. 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 perfomed after verifying that the actual containment particulate levels were acceptable for venting. The licensee, after further investigation of this practice, detemined 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 infomation gained from recent licensing actions have raised several concerns relative to potential failures affecting the purge penetration valves which could lead to a degradation in containment integrity and, for PWR's, a degradation in ECCS perfomance. Should a loss-of-coolant accident (LOCA) occur during purging there could be insufficient containment backpressure to assure proper operation of the ECCS. Ae the practice of containment purging during nomal 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 prohibit 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:
e (1) Propose an amendment to the plant Technical Specifications basad upon the enclosed model Technical Specification, or (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 Plan 3.9.3) of the ability of the containment isolation valves to close under 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 ccntinuation 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 r?ay 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 purging 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 purge operations, and an evaluation of containment purge and isolation instrumentation and control circuit designs. Within thirty days of receipt 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.
-4 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 tne 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 purging, you should review the design of all safety actuation signal circuits which incorporate 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 other than those analyzed and discussed on your docket, do not bypass that signal. Our Office of Inspection and Enforcement will verify that
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6 L you have inaugurated administrative controls to prevent improper L
nanual defeat of safety actuation signals as a part of its regular f
inspection program.
Sincerely, Original signec By A. Schwencer, Chief Operating Reactors Branch #1 Division of Operating Reactors
Enclosures:
1.
Model Technical Specification 2.
Standard Review Plan 3.
Branch Technical Position CSB 6-4 cc: w/ enclosures See next page DISTRIBUTION Docket File NRC PDR Local PDR ORB 1 Rdg A. Schwencer C. Parrish Project Manager /, f u w M. Mlynczak W. Russell I&E (3)
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Ruble A. Thomas, Vice President Southern Services, Inc.
Post Office Box 2625 Birmingham, Alabama 35202 George F. Trowbridge, Esquire Shaw, Pittman, Potts & Trowbridge 1800 M Street, tJW Washington, D.C.
20036 John Bingham, Esquire Balch, Bingham, Baker, Hawthorne, Williams & Ward 600 tiorth 18th Street Birmingham, Alabama 35202 Edward H. Keiler, Esquire Keiler & Buckley 9047 Jefferson Highway River Ridge, Louisiana 70123 George S. Houston Memorial Library 212 W. Vurdeshaw Street Dothan, Alabama 36301
a NUREG-75/087
& **%e U.Se NUCLEAR REGULATORY COMMISSION
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STANDARD REVIEW PLAN
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OFFICE OF NUCLEAR REACTOR REGULATION CCNTA!WENT ISOLATIuN SYSTEM SECTICN 6.2.4 REVIEW RESPONSIBILITIES Primary - Containment Systems Branch (CSB)
Secondary - Accident Analysis Brarch (AAS)
Instrumentation and Control System Branch (ICSB) l Mechanical Engineering Branch (MES)
Structuval Engineering Branch (SEB)
Reactor Systems Branch (R$8)
Power Systems Branch (PSB)
I.
AREAS OF REVIE%
The design objective of the containment isolation system is to allow the normal or emer-gency passage of fluids througn the contatement boundary ohile preserving the ability of the boundary to prevent or limit the escace of fission products that may aesult from This SRP section, therefore, is concerned eith t*:e isolation of postulated accidents.
fluid systems =nich penetrate the containment boundary, ircluding the design and testing reoutrements for isolation barriers and actuators. Isolation barriers include valves, closed oiping systems, and blind flanges.
The CSB reviews the information presented in the applicant's safety analysis report (SAR) regarding containment isolation provisions to assure conformance with the requirements of General Cesign Criteria 54, 55, 56 and 57.
The CSB review covers the following aspects of containment isolation:
1 The design of containment isolation orovisions, including:
The numoer and location of isolation valves, i.e.
the isolation valve arrange-a.
ments and the physical lccation of isolation valves with respect to the containment.
The actuation and control features for isolation valves.
D.
The positions of isolation valves for ncrmal clant coersting conditions (incluo-c.
ing shutdown), post-accident conditions, and in the event of valve operator power failures.
d.
The valve actuation signals.
The basis for selection of closure times of isolation valves.
e.
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The mechanical redundancy of isolation devices.
g.
The scceptability of closed piping systems inside containment es isolation barriers.
2.
The protection provided for containment isolation provisions against loss of function from missiles, pipe whip, and earthquakes.
3.
The environmental conditions insice and outside the containment that.ere consicered in the design of isolation barriers.
4 The design criteria applied to isolation barriers and piping.
5.
The provisions for detecting a possible need to isolate remote-manual-controlled systems, such as engineered safety features systems.
6.
The design provisions for and technical spec ications pertaining to operability and leakage rate testing of the isolwtion barrie-s.
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 qualification test program for electric valve operators, and the ICSS has primary responsibility for the qualification test program for the sensing and actuation instrumentation of the plant protection system located both inside and outside of co'tainment. The MES has review responsibility for the qualifica-n tion test program to demonstrate the performance and reliability of containment isolation valves. The MES and SEB have review responsibility for mechanical and structural cesign l
of the containment isolation provisions to ensure acequate protection against missiles, Dice whip, and earthquakes. The AAB reviews the radiological dose consequence anthsis for the release of containment atmosobere prior to closure of containment isolation valves in lines that provide a 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 rescect to the prediction of anset of accident induced fuel failure.
!!. ACCEPTANCE CRITERIA The general design criteria establish requirements for isolation barriers in lines pene-trating the primary centainment boundary. In general, two isolation barriers in series are required to assure that the isolation function is satisfied assuming any single active failure in the containment isolation provisions.
The design of the containment isolation provisions will be acceptable to CSB if the following criteria are satisfied:
1.
Generai Design Criteria 55 and 56 require that lines that penetrate the primary con-tainment boundary and eitner are part of tne reactor coolant pressure boundary or Rev. 1 5.2.4-2
connect directly to the containment atmosphere should te provided with isolation valves as follows:
Cne locked closed isolation valveM nside and one locked closed isolation i
a.
valve outside containment; or b.
One automatic isolation valve inside and one locked closed isolation salve out-sice containment; or One locked closed isolation valve inside and one automatic isolation valve $'
c.
outside containment; or One automatic isolation valve inside and one automatic isolation valvd d.
outside containment.
2.
General Design Criterion 57 recuires that lines that aeneirate the primary contain-ment Downdary and are neither part of the reactor coolant pressure boundary nor connected directly to the containment atmosphere should be provided with at least one locked closed, remote-manual, or automatic isolation valve $ outside containment.
3.
The general design criteria oermit containment isolation provisions for lines pene-trating the primary containment boundary that differ from the esplicit requirements of General Design Criteria 55 and 56 ff the basis for acceptability is defined Following are guidelines for acceptaDie alternate containment isolation provisions for certain classes of lines:
Regulatory Guide 1.11 describes acceptable containment isolation provisions for a.
instrument lines. In addition, instrument lines that are closed both inside and outside containment, are designed to withstand the c' essure and temperature conditions following a loss-of-coolant accicent, and are designed to withstand dynamic effects, are acceptable without isolation valves.
D.
Containment isolation provisions for lines in engineered safety features or engineered safety feature-related systems may include remote-manul <alves, but provisions should be made to detect possible leakage from these lines outside containment.
c.
Containment isolation provisions for lines in systems needed for safe shutdown of the plant (e.g., liquid poison system, reactor core isolation cooling system, and isolation condenser system) may include remote-manual valves, but provision should be made to detect possible leakage from these lines outside containment.
F Locnea closed isolation valves are defined as sealed closed carriers (see 'tes II.3.f).
E/A simple check valve is not normally an accepta01e automatic isolation valve for this apDlication.
6.2.4-3
d.
Containment isolation provisions for lines in the systems icentified in items 0 and c nor ally 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 enample, the valve may be under water as i result of in accident).
l Doth valves 94y be located outside containment. For this type of (solation valve arrangement, the valve nearest the containment and the ;1 ping tetween 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 should conform to the requirements of SRP section 3.6.2.
Design of the valve and/or the piping compartment should provide the capability to detect leakage from the valve shaf t and/or bonnet seals and terminate the leakage, Containment isolation provisions for line in engineered safety feature or e.
engineered safety feature-related systems normally consist of two isolation valves in series. A single isolation valve will be acceptaDie if it can be j
shown that the system reliability is greater with only one isolation valve in the line, the system is closed outside containment, and a single active failure can be accommodated with only one isolation valve in the line. The closed system outside containment shoulc be protected frem missiles, designed to seismic Category I standards, classified Safety Class 2 (Ref. 5), and should have a design temperature and pressure rating at least equal to that for the containment. The closed system outside containment should be leak tested, unless it can be shown that the system integrity is being maintained during normal plant operations. For this type of isolation valve arrangement the valve is located outside containment, and the piping between 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 picing and valve is assumed to preclude a breach of piping integrity, the design should conform to the requirements of SRP section 3.6.2.
Oesign of the valve and/or the picing compartment should provide the capability to detect leanage frem the valve shaft and/or bonnet seals and terminate the leakage.
E Sealed closed barriers may be used in place of automatic isolation valves.
Sealed closed barriers include blind flanges and sealed closed isolation valves wnich may be closed manual valves, closed remote-sanual valves, and closed automatic valves wnich 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 seal or lock the val,e closed, or to prevent power from being suo-plied to the valve operator, g.
Relief valves may be used as isolation valves provided the relief set point is greater than 1.5 times the containment design pressure.
Rev. 1 6.2.4-4
4 Isolation valves outside containment should be located as close to the containment as practical, as required by General Design Criteria 55, 56, and 57.
5.
The position of an isolation valve for normal and shutdown plant opersting conditions and post-sccident conditians depends on the fluid system function. If a fluid system does not have a post-accident function, the isolation valves in the lines should be automatically closed. For engineered safety feature or engineered safety feature-related systems, isolation valves in the lines may remain open or be opened.
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 position Indication in the main control room.
6.
There should be diversity in the parameters sensed for the initiation of containment isolation.
7.
System lines wnich provide an open path from the containment to the environs should be eouipped with radiation sonitors that are capable of isolating these lines upon a high radiation signal. A high radiation signal should not be considered one of the diverse containment isolation parameters.
8.
Containment isolation valve closure times should be selected to assure rapid isola-tion of the containment following postulated accidents. The valve closure time is the time it takes for a power operated valve to be in the fully closed position af ter the actuator power has reached the operator assembly; it dets not include the time to reach actuation signal setpoints or instrument delay times, which should be cor.. Aered in determining the overall time to close a valve. System design capa-bilities should be considered in establishing valve closure times. For lines which provide an open path from the containment to the environs; e.g., the containment purge and vent lines, isolation valve closure times on the order of 5 seconds or less may be recessary. The closure times of these valves should be estaDlished on the basis of sinimizing the release of containmeG atmosohere to the environs, to sitigate the offsite radiological consecuences, and assure that emergency core cooling system (ECOS) effectiveness is not degraded by a reduction in the containment backaressure. Analyses of the radiological consecuences and the effect on the containment backpressure due to the release of containment atmosphere should be provided to justify the selected valve closure time. Additional guidance on the design and use of containment purge systems which say be used during the normal plant operating modes (i.e., startup, power operation, hot stancby and hot shutdown) is provided in Branch Technical Position 058 6-4 (Ref. 9).
For plants under review for ocerating licenses or plants for which the Safety Evaluation Report for construc-tion permit application was issued prior to July 1,1975, the methods oescribed in Section 3. Items 3.1., a, b, d, e, f, and g, 9. 2 through 3.4, and 3. 5.b. c, and d of Branch Technical Position 6-4 should be implemented. For these plants, BTP Items B.I.c and B.S.a. regarding the size of the purge system used during normal plant ocerstion and the justificatrion by acceotable dose consecuence analysis, may be 6.2.4-5 Rev. I
waived if the applicant commits to limit the use of the purge system to less than ?0 hours0 days <br />0 hours <br />0 weeks <br />0 months <br /> per year wnile the plant is in the startup, pc er, hot stanoby and hot shutscwn modes of operations. This commitment should te incorporated into the Technical Specifications used in the cperation of tne plant.
9.
The use of a closed system inside containment as one of the isolation barriers will be acceptable if the design of the closed system satisfies the following requirements:
a.
The systes does not communicate eith either the reactor coolant system or the containment atmosonere.
b.
The system is protected against missiles and pipe.nto.
c.
The system is cesignated teismic Category I.
d.
The system is classified Safety Class 2 (Ref. 5).
The system is designed to withstand temperatures at least equal to the contain-e.
ment design temperature, f.
The system is designed to withstand the external pressure from the containment structural acceptance test.
g.
The system is designed to withstand the loss-of-coolant accident transient and enyironment.
Insofar as C58 is concerced with the structural design of containtrent internal structures and piping systems, the protection of isolation barriers against loss of function frem missiles, pipe ship, and earthquakes will be acceptable if isolat on barriers are located behind missile barriers, pipe whip was considered in the design of pipe restraints and the location of piping peretrating the containment, and tre iso'ation barriers, including the piping between isolation valves, are designated seismic Category I, i.e., designed to withstand the ef fects of the safe shutacwn earthquane, as recomrnended by Regulatney Guide 1.29.
10.
The design criteria applied to components performing a containment isolation function, l
including the isolation barriers and the piping between them, or the piping between the containment and the outermost isolation barrier, are acceptable if:
l a.
Group B Quality standards, as defined in Regulatory Guide 1.26 are applied to the components, unless the service function dictates that Group A auality standards be applied.
b.
The components are designated seismic Category I, in accordance with Regulatory Guide 1.29.
Rev. 1 6.2.4-6
11.
The design of the containment isolation system is accept 3 Die if provisions are made to allow the operator in the main control race to cow nnen to isolate fluid systems that are eQuipDed with remote manual isolation val +es.
Such provisions may include cate, su o =ater level, temperature, pressure, and instruments to measure flow m
radiation level.
12.
Provisions should be made in the cesign of the containment isolation system for l
ccersoility testing of the centainmert isolation valves and leakage rate testing of the isolation barriers. Th5 isolation valve testing program should be consistent with that proposed for other engineered safety features. The acceptance criteria for the leakage rate testing program for contatnatnt isolation barriers are presented in SRP section 6.2.6.
For those areas of review identified in subsection 1 of this SRP secticn as ceing the resconsibility of other branches, the acceptance criteria and their methods of application are contained in the SRP sections corresponding to those branches.
III. REVIEW 900CEDURES The precedures described below provide guidance on resiew of the containment isolation system. The reviewer se ects and emanasizes material from the review procedures as may be acoropriate for a particular case. Portions of the review may te done on a generic basis for aspects of containment isolation common to a class of containments, or by adopting the results of previous reviews of plants with essentially the same containment isolation provisions.
UDon request from the primary reviewer, the secondary review Dranches will provide irput for the areas of review stated in subsection 1 The primary revie er octains and uses such frcut is recuired to assure that this review procedure is comolete.
The CSB determines the acceptability of the containment isolation system of ccmcaring the system design criteria to the design requirements for an engineered safety feature. The aual.ty standards and the seismic design c!assification of the contairment isolation cr--
msions, incluaing the piping penetrating the containment, are compared to Regulatory Guides 1.25 and 1.29, respectively.
The CSB also ascertains that no single fault can prevent isolation of the containment.
This is acc0mplished by reviewing the containment isolation provisions for each line penetrating t5e containment to determine that two isolation barriers in series are provided, and in conjunction with the DSB by reviewing the power sources to the valve ocerators.
l The CSB reviews the information in the SAR justifying contairment isolaticn provisions
.hicn differ from the explicit requirements of General Design Criteria 55, 56 and 57.
The CSB judges the acceptanility of these containment isolation provisions cased on a comoarison witn the acceptance criteria given in suosection II l
Rev-I 5.2.2.7
The C58 reviews the position of isolation valves for normal and snutdewn 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 aoove conditions depends on the system function. In general, power-ocerated valves in fluid systems which 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 De 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 tne acceptability of the prescribed valve positions. The CSB also ascertains f rom the SAR that all power-operated isolation valves have position indication capability in the sain control room.
The C58 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 tne containment, which generate containment isolation signals. Since plant designs differ in this regard and sany dif ferent combinations of signals from the plant protection system are ased to initiate containment isolation, the CSB considers the arrsngement proposed on an individual basis in determining the overall acceptability of the containment isolation signals.
The CSB 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 lines 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, n.ay have to close in times much shorter than one minute. Closure times for these valves may be dictated by radiciogical dose analyses or ECCS performance considerations. The CSB will request the AAB or RSB to review analyses justifying valve closure times for these valves as necessary.
The CSB determines the acceptability of the use of closed systems inside containment as isolation barriers by comparing the system designs to the acceptance criteria specified in subsection !!.
l The wES and SEB have review responsibility for the structural design of tre contairment internal structures and piping systems, including restraints, to assure that the contain-ment isolation provisons are adeauately protected against missiles, pipe wnip, and earth-quakes. The CSB determines that for all containment isolation provisions, missile pro-tection and protection against loss of function from pipe whip and earthquakes were design considerations. The CSB reviews the system drawings (which should snow the loca-tions of sissile barriers relative to the containment isolation provisions) to determine that the isolation provisions are protectea from missiles. The CSS also reviews the design criteria applied to the containment isolation provisions to dete mine that protec-tion against dynamic ef fects, such as pipe whip and earthauakes, was considered in the cesign. The CSB will re9aest the MES to review the design adecuacy of oiping and valves for which conservative design is assumed to precluds cossible breach of system integrity in lieu of providing a leak tight housing.
Rev. I 6.2.4-d
Systems having a post-accident safety function may have remote-manual isolation valves in the lines penetrating the containment. The CSS reviews the provisions made to detect leakage fece 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 say include instrumentation for measuring system flow rates, or the pressure, temperature, radiation, or water level in areas outside the containment such as valve rooms or engi-nee-ed safeguards areas. The CSS bases its acceptance of the leakage detection provisions described in the SAR on the capaoility to detect leatage and identify the lines that should De isolated.
The C58 determines that the containment isolation provisions are designed to allow the isolation barriers to be individually leak tested. This information should be tabulated in the safety analysis report to factittate the CSS review.
The CSB determines from the descriptive information in the SAR that provisions have been made in the design of the containment isolation system to allow periodic operability testing of the power-coersted isolation valves and the contairment isolation system. At the operating license stage of review, the CSB determines that the content and intent of proposed technical specifications pertaining to opera 0111ty and leak testing of contain-ment isolation equipment is ia agreement with requirements developed by the staff.
IV.
EVALUATICN FIN 0fMGS The information provided and the CSB review should support concluding statements similar to the following, to be included in the 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 anich penetrate the containment boundary. The review has also included the aoplicant's proposed design bases for the containment isolation provi-sions, and analyses of the functional capability of the containment isolation system.
"The basis for the staff's acceptance has been the conformance of tre containment isolation provisions to the Commission's regulations -ss set forth in the General
{
Cesign Criteria, and to applicable regulatory guides, staff technical ocsttions, and l
industry codes and standards. (Special problems or exceptions that the staff takes to specific containment isolation provisions or the functional cacability of the containment isolation system should be discussed.)
"The staf f concludes that the containment isolation system design conforms to all applicaole regulations, guides, staf f positions, and industry codes and standards, and is acceptacle."
V.
REFERENCES 1.
10 CFR Part 50, Appendix A, General Design Criterion 54, " Piping Systems Penetrating Containment."
5.2.4-9 2ev. !
2.
10 CFR Part 50, Appendix A. General Design Criterion 55,
- Reactor Coolant Pressure Sounoary Penetrating Contairanent."
3.
10 CFR Part 50, Acceadim 4. Genersi Design Criterien 56, "Detmary Containment Isolation."
4.
10 CFR Part 50, Accendix A, General Design Criterion 57, " Closed System Isolation Valves.*
5.
Regulatory Guide 1.141, " Containment Isolation Provisions For Fluid Systems."
6.
Regulatory Guide 1.11, " Instrument Lines Penetrating Primary Reactor Containment."
7-Regulatory Guide 1.25, " Quality Group Classifications and Standards for water,
Steam, and Radioactive-Waste-Containing Components of Nuclear Power Plants."
3.
Regulatory Guide 1.29, *5eismic Design Classification.*
9.
Branch Technical Position CSB 6-4, "Contairment Purging Ouring Normal Plant Opera-tions," attached to this SRP section.
l Rev. 1 6.2.4-10
Branch Technical Position CSB 6-4 CCNTAINMENT PURGING OURING NORMAL PLtNT CPERATICNS A.
BACKGRCUND This branch technical position pertains to system lines which can provide an open path from the containment to the environs during normal plant operation; e.g., the purge and vent lines of the containment purge system. It supplements the position taken in SRP section 6.2.4.
While the containment purge system provides plant operational flexibility, its design must co9 sider the importance of minimizing the release of containment atmosphere to the environs following a postulated loss-of-coolant accident. Therefore, plant designs must not *ely on its use on a routine basis.
The need for purging has not always been anticipated in the design of plants, and there-fore, design criteria for the containment purge system have not been fully developed.
The purging experience at operating plants varies consideraDly from plant to plant. Some plants do not purge during reactor operation, some purge intermittently for short periods and some purge continuously.
The containment purge system has been used in a variety of ways, for example, to alleviate certain operational problems, such as excess air leakage into the containment from pneumatic l
controllers, for reducing the aircorne activity within the containment to facilitate personnel access during reactor power operation, and for controlling the containment pressure, temperature and relative humidity. However, the purge and vent lines orovide an open patn frorr the containment to the environs. Should a LCCA cccur during containment purging when the,eactor is at power, tne calculated accident coses shculd be within 10 CFR 100 guideline values.
The sizing of the purge and vent lines in most piants has been based on the need to control the containment atmosphere during refueling operations. This need has resulted in very large lines penetrating the containment (acut 42 inches in diameter). Since these lines are normally the only ones provided that 'will pemit some degree of control over the containment atmosphere to facilitate personnel access, some plants have used thes for containment purging during nnemal plant operation. Under such conditions, calculated accident doses could De significant. Therefore, the use af these large contain-ment purge and vent lines should ce restricted to cold shutdown conditions and refueling toerations.
E'*-
I 6.2.4-11
The design and use of the purge and vent ifnes should be based on the premise of achieving acceptable calculated offsite radiological consequencas and assuring that emergency core cooling (ECCS) effectiveness is not degraded ey a reduction in the containment tackaressure Durge system designs that are accepta01e for ase on non-routine basis during norma; plant operation can be achieved by providing additional purge and vent lines. The size of these lines should be limited sucn that in the event of a loss-of-coolant accident, assuming the purge and vent valves are open and suosequently 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 maximum time for valve closure should not exceed five seconds to assure that the purge and vent valves would be closed before the onset of fuel failures following a LOCA.
The size of the purge and vent lines should be about eight inches in diameter for PWR plants. This line size may be overly conservative from a radiological viewpoint for the Mark III BWR plants and the HTGR plants because of containment and/or core design features.
Therefore, larger line sizes may be justified. However, for any proposed line size, the applicant 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., BWR, PWR or HTGR.
8.
BRANCH TECHNICAL POSITION The system used to purge the containment for the reactor operational modes of power operation, startuo, hot stancby and hot shutdown; i.e., the on-line Durge sy*tes, should be independent of the purge system used for the reactor operational modes of cold shutdown and refueling.
1.
The on-line purge system should ce designed in accordance with the following criteria:
a.
The performance and reliacility of the ourge system isolation valves should be consistent with the ooeracility assurance program outlined in MES Branch Tech-nical Position MEB-2, Pua.s and valve Operability Assurance Program. (Also see SRP Section 3.9.3.)
The design basis for the valves and actuators snould j
include the buildup of containment pressure for the LOCA break spectrum, and the purge line and vent line flows as a function of time up to and during valve
- closure, b.
The numoer of purge and vent lines that may be used should be limited to one purge line and one vent line.
c.
The size of the purge and vent lines should not exceed about eight inc9es in diameter unless detailed justification for larger line sizes is provided.
Re v. 1 5.2.4-12
d.
The containment isolation provisions for the purge s,vstem lines should meet the standards appropriate to engineered safety features; i.e., Quality, redundancy, testability and other appropriate criteria.
Instrumentation and control systems provided to isolate the purge system lines e.
should be independent and actuated Dy diverse parameters; e.g., containment pressure, safety injection actuation, and containment radiation level. If energy is required to close the valves, at least two diverse sources of energy shall be provided, either of wnich can affect the isolation function.
f.
Purge system isolation valve closure times, including instrumentation delays, should not exceed five seconds, g.
Provisions should be made 'o ensure that isolation valve closure will not ce prevented by deDris wnich could potentially become entrained in the escaping air and steam.
2.
The purge system should not be relied on for temperature and humidity control within the containment.
3.
Provisions should be made to minimize the need for purging of the containment by providing containment atmosphers cleanup systems within the containment.
4 Provisions should be made for testing the availability of the isolation function and the leakage rate of the isolation valves, individually, during reactor operation.
5.
The following analyses should be performed to justify the containment purge system design:
a.
An analysis of the radiological Consequences of a loss-of-coolant accident.
The analysis snould De done for a spectrum of break sizes, and the instrumenta-tion and setpoints that will actuate the vent and purge valves closed should be identified. The source term ased in the radiological calculations should be based on a calculation under the terms of Appendix K to determine the extent of fuel failure and the concomitant release of fission products, and the fission product activity in the primary coolant. A pre-existing iodine spike should be considered in detersining primary coolant activity. The volume of containment in which fission products are mixed should be justified, and the fission products from the above sources should be assumed to be released through tne open purge valves during the maximum interval required for valve closure. The radiological consecuences should be witnin 10 CFR 100 guidelire values.
b.
An analysis which demonstrates the acceptability of the provisions made to protect structures and safety-related ecuipment; e.g.,
fans, filters ano duct-work, located beyond the purge system isolation valves against loss of function from the environment created by the escaping air and steam.
6.2.4.13 Rev. l
4 An analysis of the reduction in the contairment pressure resulting from the c.
partial loss of containment atmospnere during the accident for ECCS backpressure determination.
d.
The allowa01e leak rates of the purge and vent isolation valves should be spectfled for the spectrum of design basis pressures and flows against nich the valves aust C1.ase.
lev. 1 6.2.4-14
i CONTAINMENT SYSTEMS CONTAINMENT VENTILATION SYSTEM (OPTIONAL *)
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LIMITING CONDITION FOR OPERATION 3.6.1.8 The containment purge supply and exhaust isolation valves shall i
be closed.
APPLICABILITY: MODES 1, 2, 3, and 4.
ACTION:
1 With one containment purge supply and/or one exhaust isolation valve open, cloca the open valve (s) within one hour or be in at least HOT STANDBY 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 follow-ing 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />.
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, SURVEILLANCE RECUIREMENTS 4.6.1.8 The containment purge supply and exhaust isolation valves shall be detenained closed at least once per 31 days.
CCNTAINMENT SYSTEMS BASES 3/4.6.1.8 CONTAINMENT VENTILATION SYSTEM The containment purge supply and exhaust isolation valves are required to be closed during plant operation since these valves have not been demonstrated capable of closing during a (LOCA or steam line break accident). Maintaining 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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STS B 3/4 6-4 1