ML20094B808
| ML20094B808 | |
| Person / Time | |
|---|---|
| Issue date: | 11/24/1975 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| References | |
| NUREG-75-087, NUREG-75-087-06.2.4, NUREG-75-87, NUREG-75-87-6.2.4, SRP-06.02.04-02, SRP-6.02.04-2, NUDOCS 9511010295 | |
| Download: ML20094B808 (14) | |
Text
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U.S. NUCLEAR REGULATORY COMMISSION
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STANDARD REVIEW PLAN OFFICE OF NUCLEAR REACTOR REGULATION er SECTION 6.2.4 CONTAINMENT ISOLATION SYSTEM REVIEW RESPONSIBILITIES Primary - Containment Systems Branch (CSB)
Secondary - Accident Analysis Branch (AAB)
Electrical. Instrumentation and Control System Branch (EICSB)
Mechanical Engineering Branch (MEB)
Structural Engineering Branch (SEB) 1.
AREAS OF REVIEW The design objective of the containment isolation system is to allow the normal or emergency passage of fluids through the containment boundary while preserving the ability of the boundary to prevent or limit the escape of fission products from postulated accidents.
This plan, therefore. is concerned with the isolation of fluid systems which penetrate the containment boundary, including the design and testing requirements for isolation barriers and actuators. Isolation barriers include valves. closed piping systems. and blind flanges.
The CSB reviews the information presented in the applicant's safety analysis report (SAR) regarding containment isolation provisions. The CSB review covers the following aspects of containment isolation:
1.
The design of containment isolation provisions. including:
a.
The number and location of ist ation valves. i.e.. the isolation valve arrangements and the physical location of isolation valves with respect to the containment, b.
The actuation and control features for isolation valves, The positions of isolation valves for nonnal plant operating conditions (including c.
shutdown), post-accident conditions, and i'. the event of valve operator power
- failures, d.
The valve actuation signals, e.
'The basis for selection of closure times of isolation valves, f.
The mechanical redundancy of isolation devices.
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The acceptability of closed pipiag systems inside containment as isolation barriers.
2.
The protection provided for containment isolation provisions against loss of function from missiles, pipe whip, and earthquakes, v
3.
The environmental conditions inside and outside the containment that were considered.
in the design of isolation barriers.
4.
The design criteria applied to isolation barriers and piping.
1 i
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 specifications pertaining to operability and i
leakage rate testing of the isolation barriers.
EICSB has review responsibility for the qualification test program for electric valve operators, and the sensing and actuation instrumentation of the plant protection system that is located both inside and outside of containment; The MEB has review responsibility for the qualifications test program to demonstrate the perfonnance and reliability of contain-ment isolation valves; The MEB and SEB have review responsibility for the structural design of tne containment isolation provisions to ensure adequate protection against missiles, pipe whip, and earthquakes.
II. ACCEPTANCE CRITERIA The general design criteria establish requirements for irolation barriers in lines pene-
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trating the primary containment 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 follow-ing criteria are satisfied:
1.
General Design Criteria 55 and 56 require that lines that penetrate the primary con-tainment boundary and either are part of the reactor coolant pressure boundary or connect directly to the containment atmosphere should be provided with isolation valves as follows:
One locked closed isolation valveU nside and one locked closed isolation valve i
a.'
outside containment; or 1/ Locked closed isolation valves are defined as sealed closed barriers (see item II.3.f).
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One automatic isolatien valve inside and one locked closed isolation valve out-side containment; or.
2 One locked closed isolation valve inside and one automatic isolation valve ]
c.
outside containment; or 4
2 d.
One automatic isolation valve inside and one automatic isolation valve ] outside containment.
4 2.
General Design Criterion 57 requires that lines that penetrate the primary containment boundary and are neither part of the reactor coolant pressure boundary nor connected j
directly to the containment atmosphere should be provided with at least one locked
[
closed, remote-manual, or automatic isolation valve]outside containment.
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3.
The general design criteria permit containment isolation provisions for lines penetrat--
i ing the primary containment boundary that differ from the explicit requirements of General Design Criteria 55 and 56 if the basis for acceptability is defined. Fol-
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lowing are guidelines for acceptable alternate containment isolation provisions for certain classes of lines:
1 a.
Regulatory Guide 1.11 describes acceptable containment isolation provisions for instrument lines. In addition, instrument lines that are closed both inside and l
outside containment, are designed to withstand the pressure and temperature conditions following a loss-of-coolant accident, and are designed to withstand dynamic effects, are acceptable without isolation valves, b.
Containment isolation provisions for lines in engineered safety features or engineered safety feature-related systems may include remote-manual valves, 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 i
should be made to detect possible leakage from these lines outside containment.
d.
Containment isolation provisions for lines in the systems identified in items b and c normally consist of one isolation valve inside and one isolation valve outside containment. If it is not practical to locate a valve inside containment (for example, the valve may be under water) both valves may be located outside containment. For this type of isolation valve arrangement, the valve nearest the containment and the piping between the containment and the valve should be enclosed in a leak-tight or controlled leakage housing, or additional conser-vatism should be used in the design of this section of piping.
M simple check valve is not nomally an acceptable automatic isolation valve for this applica-A tion.
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Ctntainment isolation provisions for lines in Engin1ered safety feature or
, engineered safety feature-related systems normally consist of two isolation valves in series. A single isolation valve outside containment will be acceptable if it can be 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 y
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 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 is being maintained during normal plant operations, f.
Sealed closed barriers may be used in place of automatic isolation valves.
Sealed closed barriers include blind flanges and sealed closed isolation valves which may be closed manual valves, closed remote-manual valves, and closed auto-matic valves which remain closed after a loss-of-coolant accident. Sealed closed isolation valves should be under administrative control to assure that they can-not be inadvertently opened. Administrative control includes mechanical devices to seal or lock the valve closed, or to prevent power from being supplied 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.
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 operating conditions and post-accident conditions 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 beithe 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.
Containment isolation valve closure times should be selected to assure rapid isolation of the containment following postulated accidents. System design capabilities 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.
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isolation value closure times on the order of 5 seconds or less may be necessary. The closure times of these values should be established on the basis of minimi2ing tho re-l lease of containment atmosphere to the environs, to mitigate the offsite radiological consequences, and assure that emergency core cooling system (ECCS) effectiveness is not degraded by a reduction in the containment backpressure. Analyses of the radiological consequences and the effect on the containment backpressure due to the release of con-l tainment atmosphere should be provided to justify the selected valve closure time.
Additional guidance on the desigin and use of containment purge systems is provided in l
l Branch Technical Position CSB 6-4 (Ref. 9).
8.
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
- l a.
The system does not communicate with either the reactor coolant system or the containment atmosphere.
b.
The system is protected against missiles and pipe whip, c.
The system is designated seismic Category I.
d.
The system is classified Safety Class 2 (Ref. 5).
l e.
The system is designed to withstand temperatures at least equal to the containment design temperature.
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f.
The system is designed to withstand the external pressure from the containment l
structural acceptance test.
g.
The system is designed to withstand the loss-of-coolant accident transient and i
environment.
Insofar as CSB is concerned with the structural design of containment internal struc-tures and piping systems, the protection of isolation barriers against loss of function from missiles, pipe whip, and earthquakes will be acceptable if isolation barriers are I
located behind missile barriers, pipe whip was considered in the design of pipe re-straints and the location of piping peaetrating the containment, and the isolation barriers, including the piping between isolation valves, are designated seismic Cate-gory I, i.e., designed to withstand the effects of the safe shutdown earthquake, as recon 1 mended by Regulatory Guide 1.29.
9.
The design criteria applied to components performing a containment isolation function, including the isolation barriers and the piping between them, or the piping between the containment and the outermost isolation barrier, is acceptable if:
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 quality standards be applied.
6.2.4-5 11/24/75 l
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b.
The componInts are designated seismic Category 1, in accordance with Regulatory Guide 1.29.
- 10. The design of the containment isolation system is acceptable if provisions are made to allow the operator in the main control room to know when to isolate by remote-manual means fluid systems that have a post-accident safety function. Such provisions may include instruments to measure flow rate, sump water level, temperature, pressure, and radiation level.
- 11. Provisions should be made in the design of the containment isolation system for opera-bility 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 for the leakage rate testing program for containment isolation barriers are presented in Standard Review Plan 6.2.6.
III. REVIEW PROCEDURES The procedures described below provide guidance on review of the containment isolation sys-K tem. The reviewer selects and emphasizes material from the review procedures as may be appropalate 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 adopting the results of previous reviews of plants with essentially the same containment isolation provisions.
The CSB determines the acceptability of the containment isolation system by comparing the system design criteria to the design requirements for an engineered safety feature. The quality standards and the seismic design classification of the containment isolation pro-visions, including the piping penetrating the containment, are compared to Regulatory Guides 1.26 and 1.29, respectively.
l The CSB also ascertains that no single fault can prevent isolation of the containment.
This is accomplished by reviewing the containment isolation provisions for each line penetrating
- the containment to detennine that two isolation barriers in series are provided, and in conjunction with the EICSB by reviewing the power sources to the valve operatorb.
l The CSB reviews the information in the SAR justifying containment isolation provisions which differ from the explicit requirements of General Design Criteria 55, 56 and 57. The CSB judges the acceptability of these containment isolation provisions based on a comparison with the acceptance criteria given in Section II.
The CSB reviews ti,e position of isolation valves for nonnal 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 do not have a post-accident safety function should close automatically. In the event of power failure 6.2.4-6 l
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l to a talve operator, the value position should be the position of grecter 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 CSB also ascertains from the SAR that all power-operated isolation valves have position indication capability in the main control room.
The CSB reviews the signals obtained from the plant protection system to initiate contain-l 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 containment, which generate containment isolation signals. Since plant designs differ in this regard and many different combinations of signals from the plant protection system are used to initiate containment isolation, the CSB considers the arrangement proposed on an individual basis in detemining the oserall acceptability of the containment isolation signals.
l 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 i
closuretimesinSectionII.) Valves in lines that provide a direct path to the environs, j
e.g., the containment purge and ventilation system lines and main steam lines for direct cycle plants, may have to close in times much shorter than one minute. Closure times for these valves may be dictated by radiological dose analyses or ECCS performance considerations.
Supporting analyses justi.fying valve closure times for these lines should be provided in the safety analysis report for the CSB and AAB review.
l The CSB determines the acceptability of the use of closed systems inside containment as I
isolation barriers by comparing the system designs to the acceptance criteria specified in Section II.
The MEB and SEB have review responsibility for the structural design of the containment internal structures and piping systems, including restraints, to assure that the containment isolation provisions are adequately protected against missiles, pipe whip, and earthquakes.
The CSB determines that for all containment isolation provisions, missile protection and protection against loss of function from pipe whip and earthquakes were design considerations.
The CSB reviews the system drawings (which should show the locations of missile barriers relative to the containment isolation provisions) to detemine that the isolation provisions are protected from missiles. The CSB also reviews the design criteria applied to the containment isolation provisions to determine that protection against dynamic effects, such as pipe whip and earthquakes, was considered in the design.
Systems having a post-accident safety function may have remote-manual isolation valves in the lines penetrating the containment. The CSB reviews the provisions made to detect leakage from these lines outside containment and to allow the operator in the main control room tn isolate the system train should leakage occur. Leakage detection provisions may 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 engineered safeguards areas. The CSB bases its acceptance of the leakage detection provisions described in the SAR on the capability to detect leakage and identify the lines that should be isolated.
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The CSB detemines 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 facilitate the CSB review.
The CSB determines from the descriptive information in the SAR that provisions have been made in the design or me containment isolation system to allow periodic operability testing of the power-operatec isolation valves and the containment isolation system. At the opera-ting license stage of review, the CSB deter 1 nines that the content and intent of proposed technical specifications pertaining to operability and leak testing of containment isolation equipment is in agreement with requirements developed by the staff.
IV. EVALUATION FINDINGS 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:
"6.2.4 Containment Isolation System Thescopeofreviewofthecontainmentisolationsystemforthe(plantname)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 proposed design bases for the containment isolation provisions, and analyses of the functional capability of the containment isolation system.
"The basis for the staff's acceptance has been the conformance of the containment isolation provisions to the Comission's regulations as set forth in the general design criteria, and to applicable regulatory guides, staff technical positions, and industry codes and standards. (Special problems or exceptions that the staff takes to specific containment isolation provisions or the functional capability of the containment isolation system should be discussed.)
"The staff concludes that the containment isolation system design conforms to all appli-cable regulations, guides, staff positions, and industry codes and standards, and is acceptable."
V.
REFERENCES 1.
10 CFR Part 50, Appendix A, General Design Criterion 54, " Piping Systems Penetrating Containment."
2.
10 CFR Part 50, Appendix A General Design Criterion 55, " Reactor Coolant Pressure Boundary Penetrating Containment."
3.
10 CFR Part 50, Appendix A General Design Criterion 56, " Primary Containment Isolation."
4.
10 CFR Part 50, Appendix A General Design Criterion 57, " Closed System Isolation Valves."
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5.
ANSI N271 (Draft, November 1974) " Containment Isolation Provisions," American National Standards Institute.
6.
Regulatory Guide 1.11. " Instrument Lines Penetrating Primary Reactor Containment."
7.
Regulatory Guide 1.26. " Quality Group Classifications and Standards for Water, Steam,
and Radioactive-Waste-Containing Components of Nuclear Power Plants," Revision 1.
8.
Regulatory Guide 1.29. " Seismic Design Classification," Revision 1.
9.
Branch Technical Position CSB 6-4, " Containment Purging During Normal Plant Operations,"
attached to this plan.
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- Branch Technical Position CSB 6-4 I
l CONTAINMENT PURGING DURING NORMAL PLANT OPERATIONS A.
BACKGROUND 1
This branch technical position pertains to system lines which can provide an open path from j
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 t6 en in Standard Review plan 6.2.4.
j j
i While the containment purge system provides plant operational flexibility, 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.
The need for purging has not always been anticipated in the design of plants, and therefore, design criteria for the containment purge system have not been fully developed. The purging experience at operating plants varies considerably from plant to plant. Some plants do not purge during reactor operation, some purge intermittently for short periods and some purge continuously.
l The containment purge system has been used in a variety of ways, for_ example, to alleviate l
certain operational probelms, such as excess air leakage into the containment from pneumatic controllers, for reducing the airborne activity within the containment to facilitate person--
nel access during reactor power operation, and for controlling the containment pressure, temperature and relative humidity. However, the purge and vent lines provide an open path from the containment to the environs. Should a LOCA occur during containment purging when the reactor is at power, the calculated accident doses should be within 10 CFR 100 guide-line values.
The sizing of the purge and vent lines in most plants 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 (about 42 inches in diameter). Since these lines
.are normally the only ones provided that will permit some degree of control over the con-tainment atmosphere to facilitate personnel access, some plants have used them for contain-ment purging during normal plant operation. Under such conditions, calculated accident doses could be significant. Therefore, the use of these large containment purge and vent lines should be restricted to cold shutdown conditions and refueling operations.
The design and use of the purge and vent 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.
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Purga system designs that are acceptable for use on non-routine basis during normal plant operation can be achieved by providing additional purge and vent lir.es. The size 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 cal-culated 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 demonstiate 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 radiological source term for the reactor type; e.g., BWR, PWR or HTGR.
B.
BRANCH TECHNICAL POSITION The system used to purge the containment for the reactor operational modes of power opera-tion, startup, and hot standby; i.e., the on-line purge system, should be independent of the purge system used for the reactor operational modes of hot shutdown, cold shutdown, and refueling.
1.
The on-line purge system should be designed in accordance with the following criteria:
a.
The performance and reliability of the purge system isolation valves should be consistent with the operability assurance program outlined in MEB Branch Technical Position MEB-2 Pump and Valve Operability Assurance Program. (Also see Standard j
ReviewPlan3.9.3.) The design basis for the valves and actuators should 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.
I b.
The number 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 inches in diameter unless detailed justification for larger line sizes is provided.
d.
The containment isolation provisions for the purge system lines should meet the standards appropriate to engineered safety features; i.e., quality, redundancy, testability and other appropriate criteria, e.
Instrumentation and control systems provided to isolate the purge system lines should be independent and actuated by diverse parameters; e.g., containment 6.2.4-11 11/24/75
i pressure, safety injection actuation, and containmsnt 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 which 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 to ensure that isolation valve closure will not be prevented by debris which 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 pro-viding containment atmosphere 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 should be done for a spectrum of break sizes, and the instrumentation and setpoints that will actuate the vent and purge valves closed should be identi-fied. The source term used 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 determining 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 the open purge valves during the maximum interval required for valve closure. The radiological consequences should be within 10 CFR 100 guideline values, b.
An analysis which demonstrates the acceptability of the provisions made to protect structures and safety related equipment; e.g., fans, filters and ductwork, located beyond the purge system isolation valves against loss of function from the environ-ment created by the escaping air and steam, c.
An analysis of the reduction in the containment pressure resulting from the i
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 isolction valves should be specifiQd for the spectrum of design basis pressures and flows Ggainst which the valves must close.
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