ML20038C635
| ML20038C635 | |
| Person / Time | |
|---|---|
| Site: | Point Beach  |
| Issue date: | 07/31/1981 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20038C632 | List: |
| References | |
| NUREG-0800, NUREG-0800-06.02.04, NUREG-800, NUREG-800-6.02.04, SRP-06.02.04, SRP-6.02.04, TAC-44877, TAC-44878, NUDOCS 8112110320 | |
| Download: ML20038C635 (16) | |
Text
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NUREG-0800 (Formerly NUREG.75/087) pa arc
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=fj U.S. NUCLEAR REGULATORY COM
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OFFICE OF NUCLEAR REACTOR REGULATION 6.2.4 CONTAINMENT' ISOLATION SYSTEM REVIEW RESPONSIBILITIES Primary - Containment Systems Branch (CSB)
Secondary - None I.
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 that may result from postulated accidents.
This SRP section, therefore, is con-cerned with the isolation of fluid systems which penetrate the containment boundary, including the design and testing requirements for isolation barriers and acttrators.
Isolation barriers include valves, closed piping systems, and blind flanges.
The CSB review of the applicant's safety analysis report (SAR) regarding contain-ment isolation provisions covers the following aspects:
1.
The design of containment isolation provisions, including:
a.
The number and location of isolation 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 isolction valves for normal plant operating conditions c.
(including shutdown) postaccident conditions, and in the event of valve i
operator power failures.
i d.
The valve actuation ' signals.
3 l
e.
The basis for selection of closure times of isolation valves.
l f.
The mechanical redundancy of isolation devices.
opCK05000266 2O 811123 D
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Rev. 2 - July 1981 l
PDR USNRC STANDARD REVIEW PLAN Star.dard review plans are prepared for the guidance of the Office of Nuclear Reactor Regulation staff responsible for the review of rpplications to construct and operate nuclear power plants. These documents are made available to the public as part of the Commission's policy to inform the nuclear industry and the general public of regulatory procedures and policies Standard review plans are not substitutes for regulatory guides or the Commission's regulations and compliance with them is not required. The standard review plan sections are keyed to the Standard Format and Content of Safety Analysis Reports for Nuclear Power Plants.
Not all sections of the Standard Format have a corresponding review plan.
Published standard review plans will be revised periodically, as appropriate to accommodate comments and to reflect new inf orma-l tion and emperience.
ed and should be sent to the u.S. Nuclear Regulatory Commission.
i g.
The acceptability of closed piping systems inside containment as isolation barriers.
2.
The protection provided for containment isolation provisions against loss of function of missiles, pipe whip, and earthquakes.
3.
The environmental conditions inside and outside the containm'ent that were considered 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 r mote-manual-controlled systems, such as engineered safety features systems.
l 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 l
closure for lines that provide a direct path to the environs.
CSB will coordinate other ' branch evaluations that interface with the overall review of the containment isolation system, as follows:
The Mechanical Engineering Branch (MEB) will review the system seismic design and quality group classification as part of its primary review responsibility for SRP Sections 3.2.1 and 3.2.2, respectively. The Structural Engireering Branch (SEB) and the MES will review the mechanical and structural Jesign of the con-tainment isolation system as part of their primary review responsibilities for SRP Sections 3.8 and 3.9, respectively, to ensure adequate protection against l
a breach of integrity, missiles, pipe whip, jet impingement and earthquakes.
The Instrumentation and Control Systems Branch (ICSB), as part of its primary responsibility for SRP Section 7.5, will evaluate the actuation and control features for isolation valves.
The Equipment Qualification Branch (EQB), as part of its primary review responsibility for SRP Sections 3.10 and 3.11', will t
evaluate the qualification test program for electric valve operators, and sens-ing and actuation instrumentation of the plant protection system located both inside and outside of containment; and the operability assurance pnagram for l
containment isolation valves.
The Accident Evaluation Branch (AEB), as part of its primary review responsibility for SRP Section 15.6.5, will review the radiological dose consequence analysis for the release of containment atmo-sphere prior to closure of containment isolation valves in lines that provide a direct path to the environs.
The Reactor Systems Branch (RSB), as part'of l
its primary review responsibilities for SRP' Section 15.6.5, will review the l
closure time for containment isolation valves in lines that provide a direct l
path to the environs, with respect to the prediction of onset of accident-induced fuel failure.
The review of proposed technical specifications, at the operating
~
license stage of review, pertaining to operability and leakage rate testing of the isolation barriers, and the closure time for containment isolation valves, is performed by the Licensing Guidance Branch (LGB), as part of its primary review responsibility for SRP Section 16.0.
For those areas of review identified above as being reviewed as part of the primary review responsibility of other branches, the acceptance criteria necessary for the review and their methods of application are contained in the referenced SRP section of the corresponding primary branch.
6.2.4-2 Rev. 2 - July 1981
II. hCCEPTANCE CRITERIA
- The CSB will accept the containment isolation system design if the relevant requirements of General Design Criteria 1, 2, 4, 16, 54, 55, 56, and 57 and Appendix K to 10 CFR Part 50 are met. The relevant requirements are as follows:
General Design Criteria 1, 2, and 4 as they relate to systems importut 1.
to safety being designed, fabricated, erected, and tested to quality standards' commensurate with the importance of the safety function to be performed; systems being designed to withstand the effects of natural phenomena (e.g., earthquakes) without loss of capability to perform their safety functions; and systems being designed to accommodate postulated environmental conditions and protected against dynamic effects (e.g.,
missiles, pipe whip, and jet impingement), respectively.
General Design Criterion 16 as it relates to a system, in concert with 2.
the reactor containment, being provided to establish an essentially leak tight barrier against the uncontrolled release of radioactivity to the environment.
General Design Criterion.54, as it relates to piping systems penetrating 3.
the containment being provided with leak detection, isolation, and contain-ment capabilities having redundant and reliable performance capabilities, and as it relates to design provision incorporated to permit periodic oper-ability testing of the containment isolation system, and leak rate testing of isolation valves.
4.
General Design Criteria 55 and 56 as it relates to lines that penetrate the primary containment boundary and either are part of the reactor coolant pressure boundary or connect directly to the containment atmo-sphere being provided with isolation valves as follows:
l inside and one locked closed One locked closed isolation valve a.
is'olation valve outside containment; or One automatic isolation valve inside and one locked closed isolation b.
valve outside containment; or One locked closed isolation valve inside and one autcmatic isolation c.
~~
valve 2 outside containment; or z
One automatic isolation valve inside and one automatic isolation valve d.
outside containment.
General Design Criterion 57 as it relates to lines that penetrate the primary 5.
containment boundary and are neither part of the reactor coolant pressure boundary nor connected directly to the containment atmosphere being provided with at least one locked closed, remote-manual, or automatic isolation valve 2 outside containment.
ILocked closed isolation valves are defined as sealed closed barriers (see Item II.3.f).
2A simple check' valve is not normally an acceptable automatic isolation valve for this application.
6.2.4-3 Rev. 2 - July 1981 9
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- 6. " Appendix K to 10 CFR Part 50 as it relates to the determination of the extent of fuel failure (source term) used in the radiological calculations.
Th2 General Design Criteria identified above established requirements for the I
d; sign, testing, and functional performance of isolation barriers in lines penetrating the primary containment boundary and, in general, required that twa isolation in series be used to assure that the isolation function is main-toined assuming any single active failure in the containment isolation provisions.
However, containment isolation provisions that differ from the explicit require-ments of General Design Criteria 55 and 56 are acceptable if the basis for the difference is justified.
Sp;cific criteria necessary to_ meet the relevant requirements of the regulations identified above and guidelines for acceptable alternate contair. ment isolation provisions for certain classes of lines are as follows:
Regulatory Guide 1.11 describes acceptable containment isolation provisions a.
for instrument lines.
In addition, instrument lines that are closed both inside and 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 feature or engineered safety feature related systems may include remote-manual valves, but provisions shculd be made to detect possible leakage from these lines outside containment.
Containment isolation provisions for lines in systems needed for safe c.
shutdown of the plant (e.g., liquid poison system, reactor core isolation cooling system, and isolation condenser system) may include remote-manual valves, but provisions 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 as a result of an accident).,-both valves may be located outside containment.
For this type of isolation valve arrar.gement, the valve nearest the con-tainment and the piping between the containment and the valve should be enclosed in a leak-tight or controlled leakage housing.
If, in 1.ieu of a housing, conservative design of the piping and valve is assumed to pr'eclude a breach of piping integrity, the design should conform to 'he requirements of SRP Section 3.6.2.
Design of the valve and/cr the piping compartment should provide the capability to detect leakage from the valve shaft and/or bonnet seals and terminate the leakage.
Containment isolation provisions for lines in eng'neered safety feature e.
or engineered safety feature related systems normally consist of two isolation valves in series.
A single isolation valve 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 system outside containment should be protected from missiles, designed to seismic Category I standards, classified Safety 6.2.4-4 Rev. 2 - July 1981
~
Class 2 (Ref. S'), 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 contain-ment, 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 piping and valve is assumed to preclude a breach of piping integrity, the design should conform to the require-ments 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 l
bonnet seals and terminate the leakage.
f.
Sealed closed barriers may be used in place of automatic isolation valves.
I Sealed closed barriers include blind flanges and sealed closed isolation valves which may be closed manual valves, closed remote-manual valves, and closed automatic valves which 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. Administra-tive 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 :.he relief setpoint is greater than 1.5 times the containment design pressure.
h.
Item II.E.4.2 of NUREG-0737 and NUREG-0718 requires that systems penetrat-ing the containment be classified as either essential or nonessential.
Regulatory Guide 1.141 will contain guidance on the classification of essential and nonessential systems.
Essential systems, such as those des-cribed in items b and c, may include remote-manual containment isolation valves, but provisions should be made to detect possible leakage from the lines outside containment.
Item II.E.4.2 of NUREG-0737 and NUREG-0718 also rei uires that nonessential systems be automatically isolated by the l
containment isolation signal.
i i.
Isolation valves outside contaiment should be located as close to the con-tainment as practical, as required by General Design Criteria 55; 56, and 57.
j.
In meeting the requirements of General Design Criteria 55 and 56, upon l
loss of actuating power, automatic isolation valves should take the posi-tion that provides greater safety.
The position of an isolation valve for normal and shutdown plant operating conditions and postaccident condi-tions depends on the fluid system function.
If a fluid system does not have a postaccident function, the isolation valves in the lines should be automatically closed.
For eng'neered safety features or engir,aered 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 l
failure to the valve operator should be the " safe" position.
Normally this position would be the postaccident valve position.
For lines equipped with motor-operated valves, a loss of actuating power will leave the affected valve in the "as is" position, which may be the open position; however, redundant isolation barriers assure that the isolation function for the line is satisfied.
All power operated isolation valves should have position indication in the main control room.
6.2.4-5 Rev. 2 - July 1981 e.
9
4 k.
To improve the reliability of the isolation function, which is addressed in General Design Criterion 54, Item II.E.4.2 of NUREG-0737 and NUREG-0718 requires that the containment setpoint pressure that initiates containment isolation for nonessential penetrations be reduced to the minimum value
[
compatible with normal operating conditions.
1.
There should be diversity in the parameters sensed'for the initiation of s
containment isolation to satisfy the requirement 'of General' Design Cri-terion 54 for reliable isolation capability.
m.
To improve th'e reliability of the isolation function, which is addressed i
in General Design Criterion 54, system lines which provide an cpen path l
from the containment to the environs (e.g., purge and vent lines which I
are addressed in Item II.E.4.2 of NUREG-0737 and NUREG-0718) should be equipped with radiation monitors that are capable of isolating these' x
l lines upon a high radiation signal.
A high radiation signal should not i
be considered one of the diverse containment' isolation parameters. +
l n.
In meeting the requirements of General Design Criterion 54 the. performance i
capability of the isolation function should reflect the importance to i
safety of isolating system lines.
Consequently, containment isolation i
valve closure times should be selected to assure rapid' isolation 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 X
position after the actuator power has reached the operator assembly; it J.
does not include the time to reach actuation signal setpoints or instrtr-s ment delay times, which should be considered in determining the overall V:
l time to close a valve.
System design capabilities should be considered in establishing valve closure times.
For lines which provide an open path i
from the contaiment to the environs; e.g., the containment purge and vent l
lines, isolation valve closure times on the order of 5 seconds or less may be necessary. The closure times of these valves should be established on the basis of minimizing the release of containment atmosphere to the environs, to mitigate the offsite radiological consequences, and asi;ure that emergency core cooling system (E'CCS) effectiveness is not degraded by a reduction in the containment backpressure. Analyses of the radio-l logical consequences and the effect on the containment backpressure due I
to the release of containment atmosphere should be provided to justify _
the selected valve clo~s~ure time.
Additional guidance on the design and use of coz-ainment purge systems which may be used during the normal plant operating modes (i.e., startup, power operation, hot standby and hot shut-down) is provided in Branch Technical Position CSB 6-4 (Ref. 13).
For plants under review for operating licenses or plants for which the Safety Evaluation Repor;t fo'r construction permit application was issued prior to l
July 1, 1975, the methods described in Section B, Items B.1.a, b, d, e, I
g, f, and g, B.2 through B.4, and B.S.b, c, and d of Branch Technical Posi-tion CSB 6-4 should be. implemented.
For these plants, BTP Items B.1.c and B.5.a, regarding the size of the purge system used during normal plant operation and the justification by acceptable dose consequence analysis, l
may be waived if the applicant commits to limit the use of the purge sys-tem to less than 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> per year while the plant is in the startup, power, hot standby and hot shutdown modes of operations.
This commitment should be incorporated into the Technical Specifications used in the operation of the plant.
6.2.4-6 Rev. 2 - July 1981
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c JItek. II.E'.4.2 of NUREG-0737 anLNUREG-0718 requires tha't containment purge 4
valves that do not satisfy the operability criteria set forth in Branch
~
s Techrticd) Position CSB'6-4 orsthe Staff Interim Position of October 23,
- 4
's 1979)un be sealed closed a5' defined in SRP Section 6.2.4, Item II.3.f
,during ope' rational conditjens % 2, 3 and 4.
Furthermore, these valves
, must be verified to be do5ed at'least every 31 days.
(A copy of the Staff =Interin Position aopears as Attachment 1 to Item II.E.4.2 in s
- H.
. NUM.G-073K) ~ ' ;
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The ine of Ec1'o ed system;inside containmelit as one of the isolation
'i ' barriers wil] be u ceptable~if the design of the closed system satisfies thefollogingrequirements:
The 'cystem does r.ot communicate with#either the reactor coolant sys-1.
tem or the'containmqnt atmosphere.
2.
JhEjfstem is prctected against missilas and pipe whip.
~
h 2
4 s
3.
The cy tem i's' designated seismic Category I.
1 t
-s A.
4.
The system is cla'ssified Safety Class 2 (Ref. 12).
5.
The system is designad to withstand temperatures at least equal to the containment design temperature.
w 6.
The system is designed to withstand the external pressure from the containment structure acceptance test.
s 7.
The system is designed to withstand the loss-of-coolant accident tran-
,sient and environment.
Insofar a's CSB is concerned with the st:uctural design of containment inter-na".vtructures 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 located behind missiles barriers, pipe whip was considered in the design of pipe restraints and the loca-J tion of piping penetrating the containment, and the isolation barriers,
\\
including the piping between isolation valves, are designated sei'smic Cate-gory I, i.e., designe_d,to withstand the effects of the safe shutdown earthquake, as recommended by Regulatory Guide 1.29.
,r f.' '
In meeting the requirements of General Design Criteria 1, 2, 4 and 54, appropriate reliability and performance considerations should be included Cin the design of isolation barriers to reflect the importance to safety
?
of ass'oring their integrity; i.e., containment capability, under accident conditions.
The design criteria applied to components performing a contain-ment isolation function, including the isolation barriers and the piping between them, or the piping between the containment and the outermost isolation barrier, are acceptable if:
1.
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.
2.
The components are designated seismic Category I, in accordance with Regulatory Guide 1.29.
6.2.4-7 Rev. 2 - July 1981
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 mi.s-sile barriers relative to the containment isolation provisions) to determine 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 earth-quakes, was considered in the design.
The CSB will request the MEB to review the design adequacy of piping and valves for which conservative design is assumed to preclude possible breach of system integrity in lieu of providing a leak tight housing.
Systems having a postaccident safety function (essential systems, as defined in Regulatory Guide 1.141) 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 anc'to allow the operator in the main control room to isolate the system train should leakage occur.
Leakage detection provisions may include instrumentation for mea'suring 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.
The CSB 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 facilitate the CSB 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 perio-dic operability testing of the power-operated isolation valves and the ccntainment isolation system.
At the operating license stage of review, the CSB determines that the content and intent of proposed technical specifications pertaining to operability and leak testing of containment isolation equipment is in agree-ment with requirements developed by the staff.
The CSB verifies that the design of the control system for automatic contain-ment isolation valves is sucn that resetting the isolation signal will not result in the automatic reopening of containment isolation valves, and that ganged reopening of isolation valves is not possible.
IV.
EVALUATION FINDINGS l
The information provided and the CSB review should support concluding state-ments similar to the following, to be included in the staff's safety evaluation report:
The staff concludes that the containment functional design is accept-l able and meets the requirements of General Design Criteria 1, 2, 4, 16, 54, 55, 56, and 57 and Appendix K to 10 CFR Part 50.
The con-clusion is based on the following: [The reviewer should discuss each item of the regulations or related set of regulations as indicated.]
1.
The applicant has met the requirements of (cite regulation) with respect to (state limits of review in relation to regulation) 6.2.4-10 Rev. 2 - July 1981
by (for each item that is applicable to the review state how it was met and why acceptable with respect to'the regulation being discussed):
a.
meeting the regulatory positions in NUREG
.and/or Regulatory Guide (s) b.
providing and meeting an. alternative method to regulatory positions in Regulatory Guide
, that the staff has reviewed and found to be acceptable; c.
meeting the' regulatory position in BTP d.
using calculational methods for (state what was evaluated) that have been previously reviewed by the staff and found acceptable; the staff has reviewed the impact parameters in this case and found them to be suitably conservative or performed independent calculations to verify acceptability of their analysis; and/or e.
meeting the provisions of (industry standard number and title) that have been reviewed by the staff and determined to be appropriate for this application.
2.
Repeat discussion for each regulation ci~ted above.
V.
IMPLEMENTATION i
The following is intended to provide guidance to applicants and licensees regarding the NRC staff plans for using this SRP section.
Except in those cases in which the applicant proposes as acceptable alterna-tive method for complying with specified portions of the Commission's regulations, the method described herein will be used by the staff in its evaluation of conformance with Commission regulations.
Implementation schedules f.or conformance to parts of the method discussed herein are contained in the referenced regulatory guides and NUREGs.
VI.
REFERENCES 1.
10 CFR Part 50, Appendix A, General Design Criterion 1, " Quality Standards and Records."
2.
10 CFR Part 50, Appendix A, General Design Criterion 2, " Design Bases for Protection Against Natural Phenomena."
3.
10 CFR Part 50, Appendix A, General Design Criterion 4, " Environmental and Missile Design Basis."
4.
10 CFR Part 50, Appendix A, General Design Criterion 16, "Co.ntainment Design."
5.
10 CFR Part 50, Appendix A, General Design Criterion 54, " Piping Systems Penetrating Containment."
6.2.4-11 Rev. 2 - July 1981
~
6.
10 CFR Part 50, Appendix A, General Design Criterion 55, " Reactor Coolant Pressure Boundary Penetrating Containment."
7.
10 CFR Part 50, Appendix A, General Design Criterion 56, " Primary Contain-ment Isolation."
8.
10 CFR Part 50, Appendix A, General Design Criterion 57, " Closed System Isolation Valves."
9.
Regulatory Guide.l.11, " Instrument Lines Penetrating Primary Reactor Con-tainment."
10.
Regulatory Guide 1.26, " Quality Group Classifications and Standards for Water, Steam, and Radioactive-Waste-Containing Components of Nuclear Power Plants."
11.
Regulatory Guide 1.29, " Seismic Design Classification."
12.
Regulatory Guide 1.141, " Containment Isolation Provisions for Fluid Systems."
13.
Branch Technical Position CSB 6-4, " Containment Purging During Normal Plant Operation," attached to this SRP section.
14.
10 CFR Part.100, " Reactor Site Criteria."
15.
10 CFR Part 50, Appendix K, "ECCS Evaluation Models."
16.
NUREG-0737, " Classifications of TMI Action Plan Requirements."
17.
NUREG-0718, " Licensing Requirements for Pending Application for Construc-tion Permits and Manufacturing License."
6.2.4-12 Rev. 2 - July 1981
Branch Technical Position CSB 6-4 CONTAINMENT PURGING DURING NORMAL PLANT OPERATIONS A.
BACKGROUND 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 lines associated with the containment purge-and vent systems.
It supplet 3ts the position taken in SRP Section 6.2.4.
While the containment purge and vent systems provide plant operational flexibility, their designs 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 their 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.
There is similar disparity in the need for, and use of, containment vent systems at operating plants.
Containment purge systems have been used in a variety of ways; for example, to alleviate certain operational problems, such as excess air leakage into the containment from pneumatic controllers, for reducing the airborne activity within the containment to facilitate personnel access during reactor power operation, and for controlling the containment pressure, temperature and relative humidity.
Containment vent systems are typically used to relieve the initial containment pressure buildup caused by the heat load imposed on the containment atmosphere during reactor power ascension, or to periodically relieve 'the pressure buildup due to the operation of pneumatic controllers.
However, the purge and vent lines provide an open path from the contaiment 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 Part 100 guidelines values.
The sizing of the purge lines in most plants have 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 containment atmosphere to facilitate personnel access, some plants have used them for containment 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 and they must be sealed closed in all other operational modes.
l 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 contaiment backpressure.
Purge system designs that are acceptable for use on a nonroutine basis during normal plant operation can be achieved by providing ' additional purge lines.
l 6.2.4-13 Rev. 2 - July 1981
The size of these lines should be limited such that in the event of a loss of-coolant accident, assuming the purge valves are open and subsequently close, the radiological consequences calculated in accordance with Regulatory Guides l
1.3 and 1.4 would not exceed the 10 CFR Part 100 guideline values.
Also, the maximum time for valve closure should not exceed five seconds to assure that the purge valves would be closed before the onset of fuel failures following a LOCA.
Similar concerns apply to vent system designs.
The size of the purge lines should be about eight inches in diameter for PWR I
plants.
This line s'ize 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 Part 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 systems used to purge the containment for the reactor operational modes of power operation, startup, hot standby and hot shutdown;. i.e., the on-line purge system, should be independent of the purge system used for the reactor opera-tional modes of cold shutdown and refueling.
1.
The on-line purge system should be designed in accordance with the following criteria:
a.
General Design Criterion 54 requires that the reliability and perfor-l t
mance capabilities of containment isolation valves reflect the impor-tance of safety of isolating the systems penetrating the containment boundary.
Therefore, the performance and reliability of the purge system isolation valves should be consistent with the operability assurance program outlined in Branch Technical Position MEB-2, " Pump, and Valve Operability Assurance Program." (Also see SRP Section 3.10.)
The design basis for the valves and actuators should include the build-up of containment pressure for the LOCA break spectrum, and the supply line and exhaust Tine flows as a function of time up to and during valve closure.
b.
The number of supply and exhaust lines that may be used should be limited to one supply line and one exhaust line, to improve the reliability of the isolation function as required by General Design Criterion 54, and to facilitate compliance with the requirements of Appendix K to 10 CFR Part 50 regarding the containment pressure used in the evaluation of the emergency core cooling system effectiveness and 10 CFR Part 100.egarding offsite radiological consequences.
c.
The size of the lir.es should not exceed about eight inches in diameter, unless detailed justification for larger line sizes is provided, to improve the reliability and performance capability of the isolation and containment functions as required by General Design Criterion 54, and to facilitate compliance with the requirements of Appendix K to 10 CFR Part 50 regarding the containment pressure used in evaluating the emergency core cooling system effectiveness and 10 CFR Part 100 regarding the offsite radiological consequences.
6.2.4-14 Rev. 2 - July 1981
l' 54, the containment isolation h uld meet the standards appro-As required by General Design Criterionprovisi i.e., quality, redundancy, test-to reflect the importance to d.
priate to engineer.ed safety features; ability and othe General Design Criterion 56 estab-i barriers in purge system safety of isolating these lines.lishes explicit requirements i
function, which is addressed!
lines.
To improve the reliability of'the isolationin G tion and control systems 1
should be independent and i
provided to isolate the purge system l nes e.
level. Furthermore, actuated by diverse parameters; e.g., co i t least two diverse sources injection actuation, and containment radiat onf which ca if energy is required to close the valves, a of energy shall be provided, either o function.
including instrumentation Purge system isolation valve closure times, facilitate comp 7
delays, should not exceed five seconds, to10 i
l consequences.
f.
tially become entrained Provisions should be made to ensure thatnot be t
g.
in the escaping air and steam.
temperature and humidit.y The purge system should not be relied on for control within the containment.
d for purging of the contain-2.
Provisions should be made to minimize the neee cleanu h
ment by providing containment atmosp er 3.
ilability of the isolation ment.
lves during reactor Provisions should be made for testing the avafu 4.
to justify the containment operation.
The following analyses should be performed f a loss-of-coolant 5.
purge system design:
f break sizes, An analysis of the radiological consequences oThe The source term used in thed o and the instrumentation and setpoints t a a.
accident.
valves closed should be identified.
tent of fuel failure and the radiological calculations should be base and the fission product terms of Appendix K to determine the exconcom The volure t activity.
activity in the primary coolant.
are mixed should be justified, l
be considered in determining primary coo an l
sources should be assume t
of containment in which fission produc s and the fission products from the abovebe rele required for valve closure.
l s
within 10 CFR Part 100 guideline va ue.
bility of the provisions An analysis which demonstrates the acceptalated equipm l
made to protect structures and safety-re b.
Rev. 2 - July 1981 6.2.4-15
filters, and ductwork, located beyond the purge system isolation valves against loss of-function from the environment reatad by the escaping air and steam.
An analysis of the reduction in the containment pressure resulting c.
from the partial loss of containment atmosphere during the accident for ECCS backpressure determination.
d.
The maximum allowable leak rate of the purge isolation valves should be specified on a case-by-case basis giving appropriate. consideration to valve size, maximum allowable leakage. rate for the containment (as defined in Appendix J to 10 CFR Part 50), and where appropriate, the maximum allowable bypass leakage fraction for dual containments.
I m+
~
6.2.4-16 Rev. 2 - July 1981
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