ML20079L055
| ML20079L055 | |
| Person / Time | |
|---|---|
| Site: | Peach Bottom  |
| Issue date: | 10/31/1982 |
| From: | Laudenbach D, Wade W EG&G, INC. |
| To: | NRC |
| Shared Package | |
| ML20079L057 | List: |
| References | |
| NUDOCS 8301180459 | |
| Download: ML20079L055 (4) | |
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ENCLOSURE 2 October 1982 DRAFT TECHNICAL EVALUATION REPORT FOR CONTAINMENT PURGING AND VENTING DURING NORMAL OPERATION OF THE PEACH BOTTOM ATOMIC POWER STATION, UNITS 2 AND 3 (Docket Numbers 50-277 and 50-278)
. By W. O. Wade D. H. Laudenbach EG&G, Inc.
Energy Measurements Group San Ramon Operations s
'1 XA Copy Hos Been Sent to PDR 0
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1.0 INTRODUCTION
A number of significant events have occurred over the past several years which directly relate to the practice of containment purging and/or venting (P/V) during normal plant operations. These events have caused concern by the Nuclear Regulatory Commission (NRC) for potential failurr.s affecting the purge penetrations which could lead to degradation of con-tainment integrity, and, for PWRs, degradation in ECCS performance. By letter dated November 28, 1978, the NRC requested all licensees of .
operating reactors to respond to certain generic concerns about containment P/V operations. The concerns were two fold:
(1) Events had occurred where licensees overrode or by-passed the safety actuation isolation signals to the containment isolation valves. These events were determined to be abnormal occurrences and were so characterized in our report to Congress in January 1979.
(2) Recent licensing reviews have required tests or analyses to show that containment purge and vent valves would shut without degrading containment integrity during the dynamic loads of a design basis loss of coolant accident (DBA-LOCA).
The NRC requested licensee to cease P/V of the containment or limit P/V to an absolute minimum. Licenses who elected to purge or vent the containment were requested to demonstrate that the containment P/V system design met the criteria outlined in the NRC Standard Review Plan (SRP) 6.2.4, Revision 1, and the associated Branch Technical Position (BTP) CSB 6-4, Revision 1.
2.0 EVALUATION The Containment Atmospheric Control System and Containment Atmospheric Dilution System are utilized to control the containment atmosphere during
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normal plant operations and following a loss-of-coolant accident (LOCA).
Portions of these systems used for containment venting are shared. All vent lines discharge to the Standby Gas Treatment System (SGTS).
The licensee responded to the NRC position letter of November 1978 by stating that they would limit purging to 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> per year, and submitted (by letter dated July 31,1979) a Technical Specification change request that limited the use of the purging system to 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> per year during those periods when a LOCA is possible (e.g., when the reactor pressure is greater than 105 psig, with the reactor critical and the mode switch in the startup or run position). i 1
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1 The licensee responded (reference letter dated August 26, 1982) to the NRC's draft SER dated August 14, 1981 and forwarded to the licensee on July 7,1982 by providing the following infomation regarding their analyses of the provisions to protect structures and safety-related equipment located downstream of the purge system isolation valves. ,
Gases being vented from the Peach Bottom primary containment are transported through duct work to the~ SGTS for filtration prior to release. Our architect-engineer (Bechtel) has com-pleted an analysis of the pressure surge that the SGTS duct and filters could be exposed to if a DBA-LOCA were to occur while the large-diameter (18-in.) vent valves.were fully open.
The pressure differential across the filters was detemined to be limiting and was calculated to exceed the differential
- for which the, filters were designed. A later analysis, assuming 400 open valves, has demonstrated that acceptable pressures are encountered. However, filter effectiveness following such an event would be somewhat questionable due to the amount of moisture absorbed on the charcoal filters. We have thus undertaken a probabilistic assessment of the signif-icance of potential damage. This effort has been completed to the point that we can conclude that there will be no increase in risk above WASH-1400 if' duct failure does not occur. Further evaluations are continuing to support the same conclusion even with assumed duct and/or filter failure.
Although the licensee has submitted considerable justification for concluding tnat failure of the Peach Bottom SGTS ducting and filters would not result in an increase in safety risk, it is our opinion that the SGTS should be modified to withstand the pressure differential across the filters imposed by DBA-LOCA with the 18-in. vent valves fully open.
3.0 CONCLUSION
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Subject to the successful implementation of an NRC-approved design modification to provide protection against overpressurization of the SGTS, we conclude that the Peach Bottom purge / vent system design and operating practices are acceptable.
ENCLOSURE 3 l SAFETY EVALUATION REPORT l
PURGE / VENT VALVE ISOLATION DEPENDABILITY CRITERIA (ITEM II.E.4.2.(6 ) 0F NUREG-0737) 1.0 Introduction As a consequence of the accident at TMI-2, implementation of a number of new requirements has been recommended for operating reactors. These new l requirements are described in NUREG-0737, ~ " Clarification of TMI Action 1 Dlan Requirements", November 1980. The staff has requested licensees to l verify that these TMI action plant requirements have been met. This l report provides an evaluation of the response to Action Plan Item II.E.4.2, position 6 by Philadelphia Electric Company (the licensee).
2.0 Review Criteria. -
Position 6 requires that containment purge / vent isolation valves must l either satisfy-the operability cri:eria set forth in Branch Technical !
Position CSB 6-4 of the Staff Interim Position of October 23,1979, or l they must be sealed closed during operating conditionsl . 2, 3, and 4, !
as defined in SRP 6.2.4, item II.fi.f (NUREG-0800). These valves must be verified closed at least every 31 days. )
3.0 Evaluation and Conclusions i In a letter dated August 24,1982 (S. L. Daltroff to J. F. Stolz), Phila-delphia Electric Company (the licensee) indicated that the butterfly l valves used in containment purge / vent isolation will close against design !
basis accident loss-of-coolant accident pressures, if they are limited to 400 open. In accordance with this analysis, de licensee indicated l that the valves have been limited to a maximum of 400 open. Based upon ;
our review of the licensee's position, we concl :de that the operability '
of the Peach Bottom butterfly valve: meet the staff's Interim Position ,
for Containment Purge and Vent Valve Operation by limiting the valves '
to no more than 40 open. Therefore, we conclude that the Peach Bottom Atomic Power Station, Units 2 and 3 conform to II.E.4.2 Position 6. ,
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g Enclosure 4.
.Supolemental Evaluation of 5WR Owners ' Grouc 1
Position on Item II.E.4.2.(7) of NUREG-0737 ' I l
l In NUREG-0737, Item II.E.4.2.(7), we state that containment purge and vent isolation valves must close on high radiation signal . The BWR Owners '
Group performed an assessment to detemine the benefits of providing automatic closure cf the containment purge and vent isolation valves on a con tainment high radiation signal . This assessment was submitted to the !
staff by a letter from Mr. T. J. Dente to Mr. D. G. Eisenhut dated '
June 29,1981. The staff reviewed that submittal and transmitted an evaluation to the owers' . group by a letter from Mr. D. G. Eisenhut to Mr. T. J. Dente dated October 14, 19'81. In that evaluation, the staff concluded that the owners group' rational for not installing a high radiation isolation,, signal on purge and vent isolation valves was not accep tabl e. '
Following a meeting between the staff and the SWR Owners' Group on November 19, 1981, the owners group submitted an additional evaluation by a letter from Mr. T. J. Dente to Mr. D. G. Eisenhut dated June 14, 1982.
In this submittal the owners group provided an evaluation of the radiological consequences of a limiting reactor coolant system break which would not result in an automatic containment isolation in the current design of a typical plant. The owners group concl._uded that the calculated off-site doses from a limiting reactor coolant system break are acceptably small, and should be considered in lieu of ins.tallation of an automatic high radiation isolation signal on purge and vent isolation valves.
The staff has reviewed the evaluation hovided by the owners group. The staff considers it to be optimistic and, furthermore, not consistent with the Commission's defense-in-depth policy on containment ~ isolation. The
, staff's position is that the containment should be isolated, as required by the TMI Action plan Item II.E.4.2.(7), by a high radiation signal.
This eliminates reliance on operator action and on the indirect parameters such as high drywell pressure or low reactor vessel water level, for assuring the closure of purge and vent isolation valves in a timely manner.
Furthermore, the isolation by high radiation signal provides a necessary margin for unknowns inherent in the transiert conditions. This automatic radiation isolation signal to the containment purge and vent isolation valves need not originate from a safety grade radiation monitoring system.
However, some reasonable provisions will be required in the Technical Specifications dealing with equipment operability and testability. This is acceptable because other isolation signals, that are diverse and safety grade, are available to perfom the primary isolation function.
In summary, the staff's position is that the purge and vent isolation valves should be closed as quickly as possible, by diverse signals (including l containment high radiation signal), to avoid the release of radiation from l the containment during accident conditions. We consider that a high radiation isolation signal to the purge' and vent isolation valves will provide the assurance necessary to protect the public against the release of radiation during most accident conditions without relying on the operator for manual actions, or automatic isolation based upon relatively slow responses to releasu of radioactivity. Therefore, the staff concludes that purge and vent isolation valves should be closed as required' by TMI Action Plan Item II.E.4.2.(7). The Safety Evaluation Report transmitted to the owners group by letter dated October 14, 1981 is still applicable to al.1 plants involved.
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Enclosure 5
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. l CONTAINMENT SYSTEMS BRANCH EVALUATION OF BWR OWNERS GROUP POSITION ON ITEM II.E.4.2(7) 0F NUREG-0737 In NUREG-0737, Item II.E.4.2(7), we state that containment purge and vent isolation valves must close.on a high radiation. signal. The BWR Owners Group has performed an assessment to determine the benefits of providing automatic closure of the containment vent and purge' valvis :
on a containment high radiation signal. This assessment, contained in a letter from J. T. Dente to D. G. Eisenhut, dated June 29, 1981, concludes that this automatic closure on a high radiation signal will not appreciably alter the probability for significant releases of radioactivity through these lines. The basis for the BWR Owners Group conclusion relies on the following points:
- 1) Automatic isolation is already achieved through diverse inputs (high drywell pressure and low reactor water level); '
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- 2) The containment vent and purge valves are nonnally closed; t
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- 3) Several diverse methods exist for detection of primary coolant boundary leakage that could indicate to the operator that a Mgh -
radiation condition in the containment may exist; and
- 4) Pipe breaks less than the technical specification limits that are not immediately isolated by the operator result in offsite doses less than 10 CFR Part 100 dose limits.
It is the staff's posi. tion that the above arguments for not having a nigh radiation isolation signal for the large containment vent and purge valves (greater than'3" in diameter) are inadequate. The staff strongly believes that these valves should be isolated on the basis of a direct measurement of the parameter that the containment isolation system is designed to protect the public from, i.e., radiation. This view is based on the potentially greater impact on offsite doses '
relative to releases thru other lines penetrating the containment, since the vent and purge lines provide a direct path from the containment atmosphere to the environs. The staff's view is that having indirect parameters as isolation signals, such as high drywell pressure or low reactor water level, is insufficient for assuring that these valves will close in a timely manner.
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The argument that large containman ,ent and purge valves are normally )
cicsec and, therefore, do not re:.'re a hign raciation isolation signal is insufficient because these valves are normally open during startup and snutdown. Since these are trar.sie.nt conditions , we would expect a higner likelihood of an accident o: curring during these periods than !
during steady state periods. Moreover, since it large containment vent and purge valves toe receiv,is essential for the timely isolation ]
signals under these circumstances, the staff's position is that a i high radiation isolation signal is. needed to accomplish this funct1on. ;
l Reliance on operator action to close the lq,rge containment vent and purge valves is not desirable because of the delays that could occur .
while the opera:pr is handling more pressing matters. .
In response to the argument that leakages less than the technical specification limits produce low offsite doses, the staff feels that the purpose of adding a high radiation isolation signal to the large containment vent and purge valves is to protect against substantial releases of radiation (10 CFR Part 100 dose limits) for accident cor.di tions . The setpoint for the radiation isolation signal should be such that any release exceeding normal conditions, f.e. doses exceeding 10 CFR Part 20 levels at the site boundary, result in automatic containment isolation. - .
I In summary, it is the staff's position that all containment vent and purge valves in lines that are used during startup, normal operation, and shutdown of the plant be provided with a high radiation isolation signal. The range and sensitivity of the radiation monitors used for this purpose shall be sufficient to assure timely closure of the vent i and purge valves under conditions ranging from large offsite doses on the order of 10 CFR Part 100 doses to releases just exceeding normal operatin conditions (offsite doses on the order of less than 10 CFR 20 doses .
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