ML19221A984
| ML19221A984 | |
| Person / Time | |
|---|---|
| Issue date: | 03/31/1979 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| References | |
| NUREG-75-087, NUREG-75-087-06.2.3, NUREG-75-87, NUREG-75-87-6.2.3, SRP-06.02.03, SRP-6.02.03, NUDOCS 7907120130 | |
| Download: ML19221A984 (11) | |
Text
NUREG 75/087
.?p.e ag%o U.S. NUCLEAR REGULATORY COMMISSION 4' '
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STANDARD REVIEW PLAN
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OFFICE OF NUCLEAR REACTOR REGULATION 9
SECTION 6.2.3 SELCNDARY CONTAINMENT FUNCTIONAL DESIGN WEVIEW RESPCNSIBILITIES Primary - Containment Systems Branch (CSB)
Secondary - Accident Analysis Branch ( AAB)
Auxiliary Systems Branch (ASB)
Analysis Branch (AB) 1.
ARFAS OF REVIEW The CSB reviews the information in the applicant's safety analysis report (SAR) con-cerning the functional capability of the secondary containment system.
The secondary containment system includes the outer containment structure of dual containment plants and the associated systems provided to mitigate the radiological consequences of postu-lated accidents. The secondary contain' rent structure and suppr.rting systems are pro-vided to collect and process radioactive material that may leak from *.be primary contain-ment following an accident. The supporting systems maintain a negative pressure within the secondary containment and process this leakage.
Plant areas and systems contiguous to the secondary containment which also collect and process radioactive material that may leak f rom the primary contairment following an accident are reviewed by the CSB in the same manner as the secondary containment.
The CSB review of the functional capability of the secondary containment system of du3l contaircent designs includes the follcwing points:
1.
Analyses of the pressure and temperature response of the secondary containment to a loss-of-coolant accident w; thin the primary containcent.
2.
Analyses of the effect of openings in the secondary containment on the capability of the depressurization and filtration system to accomplish its design objective of establishing a neg3tive pressure in a prescribed time.
3.
Analyses of the pressure and temperature response of the annular region between the primary and secondary containment to a high energy line rupture within the secondary containment.
4.
The functional design criteria applied to guard pipes surrounding high energy lines within the secondary containment.
USNRC STANDARD REVIEW PLAN
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5.
Analyses of any primary containment leakage paths that bypast the secondary containment.
6.
The design provisions for periodic leakage testing of secondary containmert bypass leakage paths.
7.
The proposed technical specifications pertaining to the functional capability of the seconoary containment system and the leakage testing of bypass leakage paths.
8.
Analyses of the pressure response of the secontaty containmer.t resulting from inad-vertent depressurization of the primary contaiament when there is vacuum r elief from the secondary containment.
The AAB reviews the design requirements and the periodic inspection and operability test program for the depressurization and filtration systems, from the standpoint of assuring that the systems and system components are functionally capable of depressurizing the secondary containment. The fission product removal capability of the secondary contain-ment supporting systems is. eviewed by the AAB under SRP Section 6.5.3.
l The AB is responsible for determining tl.e acceptability of the mass and energy release data used in the analysis of the secondary containment pressure response to postulated high energy line breaks, as described in SRP Sections 6.2.1.3 and 6.2.1.4.
The ASB has responsibility for reviewing analyses of pipe reptures postulated to occur in auxiliary areas or other areas outside primary containment that serve as the second-ary containment, i.e., in areas other than the annular region formed by the secondary containment.
II.
ACCEPfANCE CRITERIA 1
Analyses of the nressure and temperature response of the secondary containacnt to a loss of-coolant accident occurring in the primary containment should be based on the following guidelines:
a.
Heat transfer f rom the priraary to secondary containment should be considered.
(1) Heat transfer from the primary containment atmasphere to the primary con-tainment structure should be calculated using conservative heat transf er coefficients such as those provided in Branch Technical Positinn CSB 6-1 (Ref. 4).
(2) Conductive heat transfer through the primary containment structure 2nd convective heat transfer to the secondary containment atmosphere should be considered.
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(3) Radiant heat transfer to the secondary containment should be considered.
l b.
Adiabitic boundiry conditions should be assumed for the surface of the second-ary containment structure m posed to the outside environment.
c.
The compressive effect of primary containment expansion on the secondary con-tainment atmosphere should be considered.
d.
Secondary containment inleakago should be considered.
e.
No credit should be taken for secnndary containment outleakage.
f.
Secondary containment response analyses should be based on the assumption of loss of offsite power and the most severe single active failure in the emer-gency power system (e.g., a diesei gener_ ar failure), in the primary contain-ment heat removal systems, in the core cooling systems, or in the secondary containmont depressurization and filtration system. Any delay, due to system design, in actuating the secondary containment depressurization and filtratian system should be considered.
g.
Heat loads generated within the secondary containment (e.g., equipment heat loads) should be considered.
h.
fan performance characteristics should be considered in evaluating the depres-surization of the secondary containment.
High energy lines passing through the secondary containment should be provided with guard pipes. Design criteria for guard pipes are given in SRP Section 3.6.2.
If guard pipes are not provided, analyses should be provided which defhonstrate that both the primary containment structure and the secondary containment structure are capable of withstanding the effects of a high energy pipe rupture occurring inside the secondary containment without loss of integrity.
3.
The fraction of primary containment leakage bypassing the secondary containment and escaping directly to the envirr.iment should be specified. Branch Technical Position (BTP) CSB 6-3 (Ref. 3) provides guidance for identifying the leakage paths to the l
environment which may bypass the secondary containment. The periodic leakage rate testinq program for measuring the fraction of primary conta6 ment leakage that may directly bypass the secondary containment and other contiguous areas served by ven-tilation and filtration ystems should be described.
4.
The negative pressure differential to be maintained in the secondary containment and other contiguous plant areas should be no less than 0.25 inches (water) when compared with adjacent regions, under all wind conditions up to the wind speed at which diffusion becomes great enough to assure site boundary exposures less than 7 'l )
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those calculated for the design basis accident even if exfiltration occurs. If the l
leakage rate is in excess of 100% of the volume per day, a special exfiltration analysis J,ould be performed.
5.
The secondary containment depressurization and filtration systems should be capable l
of maintaining a uniform negative pressure throughout the secondary containment, as well as ott.er areas served by the systems.
6.
Provisions should be madt in the design of the secondary containment system to permit inspection and monitoring of functional capability. The determination of the depressurization time, the secondary containment inleakage rate, the uniformity l
of negative pressure throughout the secondary containment and other contiguous areas, and the potential 10r exfiltration hould be included in the preoperational and periodic test programs pursuant to General Design Criterion 43.
l 7.
All openings, such as ersonnel doors and equipment hatches, should be under adminis-trative control. These openings should be provided with position indicators and alarms having readout and alccm capability in the main control room.
The effect of open doors or hatches on the functional capability of the depressurization and filtration systems should be evaluated and confirmatory preoperational tests conducted.
Some plants may have only portions of the pr. mary containment enclosed, rather than having a recondary containment structure or shield building that completely encloses the primary containment. These enclosed a'eas are areas into which the primary containment would most likely leak, and they may be equipped with air filtration systems. Quantitative credit cannot be given for the holdup effect of these encle areas or for the air filtration systems, to mitigate the radiological consequences of a postulated accident, unless the magnitude of unprocessed leakage can be ade-quately demonstrated. Quantitative credit for leakage collection in a partial-dual containment will be reviewed on a case-by-case basis.
8.
The eternal design pressure of the secondary containment structure should provide an adequate margin above the maximum e>pected external pressure.
for those areas of review identified in subsection I of this SRP section as beir.g the responsibility of other branches, the acceptance criteria and their methods of applica-tion are contained in the SRP sections correspcnuing to those bianches.
III. REVIEW PROCEDURES The procedures described below provide guidance on the review of the secondary contain-ment system.
The reviewer selects and emphasizes material f rom the review procedures as may be appropriate for a particular case. Portions of the review may be done on a generic basis for aspects of scondary containment functional design common to a class of plants, or by adopting the results of previous reviews of similar plants.
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Upon request from the primary reviewer, the secondary review branches will provide input for the areas of review stated in subsect.icn I.
The primary reviewer obtains and uses such input as required to assure that this review procedure is complete.
CSB reviews the analytical mocels used and the assumptions made in the analyses of the pressure and temperature response of the secondary containment to loss-of-coolant acci-dents in the primary containment. In general, CSB determines that the analyses conserv-atively preJict the secondary containment pressure response.
In so doing, CSB compares the analyses to the guidelines in subsection II.
If considered necessary, CSB performs confirmatory analyses of the pressure and temper-ature response of the secondary containment for loss-of-coolant accidents within the primary containment and for high energy line (e.g., steam line and feedwater line) rupturts occurring within the annular region formed by the secondary containment. The analyses are done using the CONTEMPT-LT computer code (Ref. 2).
Upon request by the C$B the AB will evaluate the acceptability of the mass and energy release rates resulting from postulated pipe ruptures under SRP Sections 6.2.1.3 and 6.2.1.4.
It should be roted that, for the analysis of the pre 3sure and temperature response in the secondary containment for loss-of-coolant accidents within the primary containment, the present version of the CONTEMPT-LT only has the capability of calculating the pressure in the secondary containment up to the time the depressurization systems are actuated. The code is being improved to permit the calculation of the pressure response for the entire course of an accident.
The analysis will be based on the guidelines given in subsection II, and code input data obtained from the SAR.
CSB determines that the secondary containment design pressure is not exceeded and that the depressurization time is consistent with that assumed in the AAB analysis of the radiological consequences of the accident. In addition, CSB deter-mines that the primary containment external desigr, pressure is not exceeded.
CSB determines that all direct leakage paths have been properly identified, and from a review of the proposed leakage testing program that provisions have been made in the design of the plant to measure the fraction of total primary containment leakage that bypasses the secondary containment. The acceptability of the leakage testing program is considered in SRP Section 6 2.6.
CSB advises AAB of any inadequacies in the applicant's f
direct leakage assumptions used in the radiological analysis. At the operating license stage of review, CSB reviews technical specificati m which specify the surveillance requirements for leakage testing of the secondar containment bypass leakage paths.
y CSB reviews analyses of the capability of the secondary containment system to resist exfiltration under post-accident conditions. If the secondary containment leakage rate is in excess of 100% of the volume per day, CSB advises AAB in order that they may perform a special exfiltration analysis. CSB reviews the preoperational and periodic inservice testing programs to assure that testing will be done to verify the exten'. of e x f i l t ra *. i o n.
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CSB reviews the proposed secondary containment system testing program and the surveil-lance requirements ir the technical specifications (operating license stage) to assure that tests will be periodically conducted to verify that the prescribed negative pres-sure can be uniformly maintained throughout the secondary containment. CSB also reviews the testing program and surveillance requirements to assure that tests will be periodic-ally conducted to verify the secondary containment design inleakage rate and to verify the analysis of the depressurization of the secondary containment.
CSB reviews the proposed technical specifications to assure that adequate administrative control will be exercised over the secondary containment openings, such as personnel access doors and equipment hatches. CSB determines from the descriptive information in the SAR that all doors and hatches are provided with position indicators having readout and alarm capability in the main control room.
The CSB will ascertain that normally opt n doors were considered in the analyses of the functional capability of the secondary containment system.
IV.
EVALUATION FINDINGS The reviewer verifies that sufficient information has been provided and that his evalua-tion supports conclusions of the following type, to be included in the staff's safety evaluation report:
"The scope of review of the functional design of the secondary containment systen, for the has included plan and elevation drawings, system drawings, and descriptive information. This system is provided to control the atmosphere within the secondary containment and contiguous areas.
The review has included the appl:
Cant's propos'd design bases and analyses of the functional capability of the secondary containment system.
"The basis for the staff's acceptance has been the conformance of the functional design and design bases to the Commission's regulations as set forth in the General Design Criteria, and to applicable guides and staff technical positions. (Special problems of exceptions that the staff takes to the design or functional capability of structures or systems should be discussed.)
"The staf f concludes that the secondary containment system design conforms to all applicable regulations, guides, staff positions, and industry codes and standards, and is acceptable."
V.
REFERENCES 1.
10 CFR Part 50, Appendix A, General Design Criterion 43, " Testing of Containment Atmosphere Cleanup Systems."
2.
R. J. Wagner and L.
L. West, "CCNTEMPT-LT Users Manual," Interim Report 1-214-74-12.1, Aerojet Nuclear Company, August 1973.
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3.
Branch Technical Position CSB 6-3, " Determination of Bypass Leakage Paths in Dual Containment Plants," attached to this SRP section.
4.
Branch Technical Position CSB 6-1, " Minimum Containment Pressure Model for PWR ECCS Performance Evaluation." 6ttached to SRP Section 6.2.1.5.
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BRANCH TECHNICAL POSITION CSB 6-3 DETEPfilNATION OF BYPASS LEAKAGE PATHS IN DUAL CONTAltNENT PLANTS A.
BAC KGROUND The purpose of this branch position is to provide guidance in the deternination of that portion of the primary containment leakage that will not be collectec and processed by the secondary containnent. Bypass leakage is defined as that leakage from the primary contain-nent which can circumvent the secondary containnent boundary and escape directly to the environment, i.e., bypasses the leakage collection and filtration systems of the secondary c on ta i nnen t.
This leakage conponent nust te considered in the radinlogical analysis of a loss-of-coolant accident.
The secondary containment consists of a structure which corpletely encloses the primary containment and can be maintained at a pre sure lower than atmospheric so that primary con-tainment leakage can be collected or processea before release to the environment. The secondary containment may include an enclosure building which forms an annular ve lume around the primary contairw.ent, the auxiliery building where it conpletely <.ncloses the prinary montainment, and other regions of the plant that are provided with leakage collec-tion and filtration systens. Depressurization systens are provided as part of the seconda, y containment to decrease or naintain the secondary containrent volume at a negative pressure.
All prinary conteinment leakage may not be coll t ?d because (1) direct primary containment leakage can occur while the secondary containment is being depressurized and (2) primary containment leakage can bypass the secondary containnent through containment penetrations and seals which do not terminate in the secondary containment.
Direct leakage from the secondary containment to the environment can occur whenever an out-wird positive dif ferential pressure exists across the secondary containment boundary. The secondary containment can experience a positive pressure transient following a postulated loss-of-coolant accident in the primary containnent as a result of thermal loading and infiltration from the environment and the primary containment that will occur until the depressurization systems become effective. An outward positite differential on the second-ary containment wall can also be created by wind loads. In this regard, a " positive" pres-sure is defined as any pressure greater than -0.25 in. w.g. (water gauge), to account for
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wind loads and the uncertainty in the pressure neasurements. Wher,ever the pressure in the secondary containment volume exceeds -0.25 in, w.g., the leakage-prevention fe _ tion,f the secondary containment is assumed to be negated. Since leakage fron the secondary contain-e ment during positive pressure periods cannot be determined, the conservative assumption is made that, all primary containment leakage is released directly to the environnent during thest time periods. Therefore, it becones necessary to determine the tire periods during which these threshold conditions exist.
The existence and duration of periods of positive pressure within the secondary containnent should be based on analyses of the secondary containment pressure response to pcstulated loss-of-coolant accidents within the prinary containment and the effectiveness of the depressurization systens.
The evaluation of bypass leakage involves both the identification of bypass leakage pduis and the determination of leakage rates. Potential bypass leakage paths are forned uy pene-trations which pass through both the primary and secondary containment boundaries. Pene-trations that pass through both the primary and secondary containment may include a number of barriers to leakage (e.g., isolation valves, seals, gaskets, and welded joints). While each of these barriers aid in the reduction of leakage, they da not necessarily eliminate leakage. Therefore, in identifying potential leakage paths, each of these penetrations should be considered, together with the capability to test them for leakage in a manner similar to the containment leakage tests required by Appendix J to 10 CFR Part 50.
B.
ERANCH TECHNICAL POSI" _
1.
A secondary contairment structure should completely enclose the primary containment structure, with the exception of those parts of the primary containment that are imbedded in the soil, suc' as the base r,at of the containment structure. For partial dual containment concepts, leak rates less than the design leak rate of the pr containment should not be used in the calculation of the radiological consequeo_es of a loss-of-coolant accident, unless the magnitude of unprocessed leakage can be adequately demonstrated. Quantitative credit for leakage collection in a partial-dual contain-ment will be reviewed on a case-by-case basis.
2.
Direct leakage from the primary containment to the environment, equivalent to the design leak rate of the primary containment, should be assumed to occur following a postulated loss-of-coolant accident whenever the secondary containment volume is at a " positive" pressure; i.e., a pressure greater than -0.25 in, w.g.
Positive pressure periods should 6.2.3-9 g
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5e determined by a pressure response analysis of the secondary containrent volume that includes thernal loads from the primary containment and infiltration. ikage.
3.
The secondary containment depressurization and filtration systems should be designed in accordance with Regulatory e.ide 1.52, " Design, Testing, and Maintenance Criteria for Atmosphere Cleanup Systen Air Filtration and Adsorption Units of Light-Water Cooled fiuclear Power Plants." Preoperational and periodic inservice inspection and test pro-grams should be proposed for these systems and should include means for determining the secondary containment infiltration rate, and the capability of the systens to draw lonn the secondary containment to the prescribed negative pressure in a prescribed time.
4.
For secondary containments with design leakage rates greater than 100 volume percent per day, an exfiltration analysis should be provided.
5.
The following leakage barriers in paths which do not terminate within the secondary containment should be considered potential bypass leakage paths around the leakage collection and filtration systems of the secondary containment:
a.
Isolation valves in piping which penetrates both the primary and secondary contain-rent barriers.
O b.
Seals and ;,askets on penetrations which pass through both the prirary and secondary containnent barriers.
c.
Welded joints on penetrations (e.g., guard pipes) which pass through both the prinary and secondary containment barriers.
6.
The total leakage rate for all potential bypass leakage paths, as identified in item 5 above, should be determined in a realistic ranner, considering equipment design lini-tations and test sensitivities. This value should be used in calculating the offsite radiological consequences of postulated loss-of-coolant accidents and in setting technical specification limits with nargin for bypass leakage.
7.
Provisions should be made to permit preoperational and periodic leakage rate testing in a nanner similar to tae Type B or C tests of Appendix J to 10 CFR Part 50 for each bypass leakage path listed in iten 5 atove. An acceptable alternative for local leakage rate testing for welded joints would be to conduct a soap bubble test of the welds con-currently with the integrated (Type A) leakage test of the prinary containmert required by Appendix J.
Any detectable leakage determined in this nanner would require repair of the joint.
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8.
If air or water sealing systems or leakage control systems are propnsed to proca" or eliminate le3kage through valves, these systens should be designed, to ihr extent practical, using the guidelines for leakage control systens given in Regulatory Guide 1.96 (Ref. 3).
O.
If a closed system is proposed as a leakage boundary to preclude bypass leakage, then the systen should:
Either (1) not directly comunicate with the containment atmosphere, or (2) not a.
directly connunicate with the environt ent, following a loss-of-coolant accident.
b.
f>e designed in accordance with Quality Group B standards, as definnd by Regulatory Guide 1.26.
(Systens designed to Quality Group C or D standards that qualify as closed systems to preclude bypass leakage will be considered on a case-by-case basis.)
c.
Meet seismic Category I design requirenents.
d.
Be designed to at least the primary containment pressure and terperature design conditions, e.
Be designed for protection against pipe whip, missiles, and jet forces in a nanner similar to that for engineered safety features, f.
Be tested for leakage, unless it can te shown that during normal plant operations the system integrity is maintained.
C.
REFERENCES 1.
10 CFR Part 50, Appendix J, " Primary Reactor Containment Leakage Testing for Water-Cooled Power Reactors."
2.
Regulatory Guide 1.26, " Quality Group Classifications and Standards for Water, Steam,
and Radioactive-Waste-Containing Components of Nuclear Power Plants," Revision 1.
3.
Regulatory Guide 1.96, " Design of Main Steam Isolation Valve Leakage Contrcl Systens for Boiling Water Reautor Nuclear Power Plants."
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