ML19326A035
| ML19326A035 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 10/21/1976 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19326A033 | List: |
| References | |
| CSB-6-4, NUDOCS 8001310609 | |
| Download: ML19326A035 (5) | |
Text
,
-s ENCLOSURE 2
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Branch Technical Position CSB 6-4 CONTAINMENT PURGING DURING NORMAI, PLANT OPERATICNS A.
BACKGROUND This branch technical position pertains to system lines which can provide an open path frem the contain=ent to the environs during nor=al plant operation; e.g., the purge and vent lines of the centainment purge system.
It supple =ents the position taken in Standard Review Plan 6.2.4.
While the centain=ent purge syste= provides plant operatienal flexibility, its design =ust consider the i=portance of =inimizing the release of centain=ent at=osphere to the environs following a postulated less-of-coolant accident.
Therefore, plant designs cust not rely en its use on a rcutine basis.
The need for purging has not always been anticipated in the design of plants, and therefore, design criteria for the centain=ent purge syctes have not been fully developed. The purgine experience at operating plant's varies considerably from plant to plant.
Sc=e plants do not purge during reactor operation, so=e purge intermittently for short periods and some purge centinuously.
The contain=ent purge system has been used in a variety of ways, for exa=ple, to alleviate certain operational probic=s, such as excess air leakage into the contain=ent from pneumatic controllers, for reducing the airborne activity within the centain=ent to facilitate personnel access during reactor power operation, and for centrolling
- the contain=ent pressure, te=perature and relative hu=1dity. However, the purge and vent lines provide an open path from the contain=ent to the envircus. Should a LOCA occur during contain=ent purging when the reactor is at power, the calculated accident doses should be within 10 CFR 100 guideline values.
The si:ing of the purge and vent lines in =ost plants has been based on the need to control the contain=ent at=osphere during refueling ope rations. This need has resulted in very large lines penetrating
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the contain=.c (about 42 inches in dia=eter).
Since these lines are
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'...e ca.y ones provided that will per=it some degree of control over the containment at=osphere to facilitate personnel access, sece plants have used them for containment purging during nor=al plant operation. Under such conditions, calculated accident doses could be significant. Therefore the use of these large contain=ent purge and vent lines should be restricted to cold shutdcun conditions and refueling operatione.
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- 7 i! una of the pur3 end vent lines should be based on the i
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- - pr ' u 4 ;.:1._:i ng acceptable calculated offsite radiological conse-6 ques:ce - =.C ssuring that emergency core cooling (ECCS) ef fectiveness is not degraded ty a reduction in the contain=ent backprassure.
Purge system dcsigns that are acceptable for use on a non-routine basis during nor=al plant cperation can be achieved by providing additional purge and vent lines. The si:e of these lines should be limited such that in the event of a less-of-coolant accident, assuming the purge and
.vm. th are open and subsequently close, the radiological conse-quences calculated in accordance with Reculatory Guide 1.3 and 1.4 would not exceed the 10 CFR 100 guideline values.
Also, the maxi =um time for valve closure should act exceed five seconds to assure that
.the. purge and vent valves would be closed before the onset of fuel i
-.failura.;.following a LOCA.
The size of the purge.and vent lines should be about eight inches in diameter for FWR plants. This line size =ay be overly conservative
... fres.a.:rrc'f.ci 31 cal viewpoint for the Mark III BWR plants and the HIGR pl:n :r-Sr.
use of contain=ent and/or core design features. Therefore,
. -..largar 2 :..a sizes may be justified. Ecwever, for any proposed line si:e, the applicant =ust de=enstrate that the radiological consequences following a loss-of-coolant accident would be within 10 CFR 100 guidelines values.
In susmary, the acceptability of a specific line size is a functica of the site meteorology, contain=ent design, sad radiological source term for the reactor type; e.g., SWR, PRR or HTGR.
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B.
BPANCH TECHNICAL POSITION The s? stem used to purge the contain=ent for the reactor operational modes ol power operation, 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:
The perfor=ance and reliability of the purge system isolstica a.
valves should be consistent with the operability assurance program outlined in :-E3 Branch Technical Position ME3-2, Pu=p and Valve Operability Assurance Progra=.
(Also see Standard Review Plan 3.9.3.)
The design basis for the valves and actuators should include the buildup of contain=ent pressure for the LCCA break spectru=, and the purge line and vent line flows as a function of ci=e up to cnd during valve closure.
b.
The number of purge and vent lines that may be used should be 11=ited to one purge line and one vent line, The size of the purge and vent lines should not exceed about c.
eight inches in dia:eter unless d,etailed justification for larger line sizes is provided.
d.
The contain=ent isolation provisiens for the purge systes lines should =eet the standards appropriate to engineered safety features; i.e., quality, redundancy, testability and other appropriate criteria.
Instrumentation and control syste=s provided to isolate the purge e.
system lines should be independent and actuated by diverse par==eters; e.g., contain=ent pressure, safety injection actuation, and contain=ent 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 ti=es, including instru=entation delays, should not exceed five seconds.
Provisions should be made to ensure that isolation valve closure g.
will not be prevented by debris which could potentially beccce entrained in the escaping air and stea=.
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The purge systes should not be relied on for temperature and 2.
humidity control within the contain=ent.
Provisions should be made to minimire the need for purging of the 3.
contain=ent by providing containment accosphere cleanup syste=s within the containment.
Provisions should be made for testing the availability of the 4.
isolation fuhetion and the leakage rc.cc of the isolatica valves, ind1vidually, during reactor operation.
The following analyses should be perfor=ed to justify the containment 5.
purge system design:
An analysis cf the radiological censequences of a 1 css-of-coolant a.
The analysis should be done for a spectrum of break accident.
sizes, and the instru.entation and setpoints that will actuate
~he the vent cnd purge valves closed should be identified.
source term used in the radiological calculatien.; should be based on a calculation under the ter:s of Appendix K to deter =ine the extent of fuel failure and the cencomitant release of fission h
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. products.. and the fission product activity in t e pr mar A pre-existing lodine spike should be considered in coolant.
The volu=e of conta1==ent determining pri=ary coolant activity.
in which fission products are mixed should be justified, and the fission products from the above sources should be assu=ed to be released through the open purge valves during the maximu= interval The radiological consequences should required for valve closure.
i be within 10 C?R 100 guideline values.
' An analysis which de=enstrates the acceptability of the provisions
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b.
e.g.,
made to protect structures and safety-related equipment; fans, filters and ductwork, located beycnd the purge system isolation valves against loss of function from the envirenzent created by the escaping air and stess, An analysis of the reduction in the containment pressure resulting c.
- from the partial loss of contain=ent atmosphere during the accident for ECCS backpressure determination.
m The allowable leak rates of the purge and vent isolation valves d.
should be specified for the spectn::2 of design basis pressures and flows against which the valves must close,
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