ML19290B964
| ML19290B964 | |
| Person / Time | |
|---|---|
| Issue date: | 08/01/1979 |
| From: | Anderson C, Charemagne Grimes, Teh-Chiun Su NRC COMMISSION (OCM) |
| To: | |
| References | |
| REF-GTECI-A-08, REF-GTECI-A-09, REF-GTECI-A-39, REF-GTECI-CO, REF-GTECI-SY, TASK-A-08, TASK-A-09, TASK-A-39, TASK-A-8, TASK-OR NUDOCS 8001080001 | |
| Download: ML19290B964 (6) | |
Text
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@f-ROUTING AND TRANSMITTAL SUP 8/l/79
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Action File Note and Retum Approval For Clearance Por Conversation As Requested For Correction Prepare Reply Circulate For Your Information See Me Comment investigste Signature Coordination Justify RD4 ARKS At your request, attached is our contribution for the forthcoming NUREG 0510 update related to the BWR Mark I and II Pressure Suppression Containments.
The task Managers for the A-7, A-8 and A-39 programs participated in the preparation of this update.
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DO NoT use this form as a RECORD of approvals, concurrences, d sposa!s, clearances, and simiar act!cns I. Room No.-Bids-FROM:(Name, org. symtof, Agency / Post) b$
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4 BWR Mark I and Mark II Pressure Suppression Containments In the course of performing large scale testing of an advanced design pressure-suppression containment (Mark III), and during in-plant testing of Mark I containments, new suppression pool hydrodynamic laods were identified which had not explicitly been included in the original Mark I or Mark II containment design basis. These additional loads result from dynamic effects of drywell air and steam being rapidly forced into the suppression pool during a postulated LOCA and from suppression pool response to various modes of safety relief valve (SRV) operation generally associated with plant transient operating conditions. Since these new hydrodynamic loads had not been explicitly con-sidered in the original design of the Mark I and Mark Il containments, the NRC staff determined that a detailed reevaluation of these containment system designs was required.
As a result of the need for this reevaluation the affected utilities formed ad hoc Mark I and Mark II Owners' Groups. They developed two-phase programs cnnsisting of a short-term program and a long-term program for resolution of the pocl dynamic concerns for their respective containment designs.
The Owner's Group programs include a number of comprehensive experimental and analytical programs to establish generic pool dynamic loads, load combinations and design criteria.
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-2 The NRC staff has identified and init;ated a number of generic tasks to review and evaluate the results of the Mark I and Mark II Owner's Groups short-term and long-term programs to develop technical positions for use in licensing actions on individual plants utilizing the Mark I and Mark II containment designs. These generic tasks are included in the NRC Program for Resolution of Generic Issues (described in NUREG-0410 as noted above).
Specifically, they are Task A-6, Mark I Short-Term Program; Task A-7, Mark I Long-Term Program; Task A-8, Mark II Containment Program; Task A-39, Determination of Safety Relief Valve (SRV) Pool Dynamic Loads and Temperature Limits for BWR Containments.
The objectives of the Mark I Short-Term Program were:
(1) to examine the containment system of each BWR facility with a Mark I containment design to verify that it would maintain its integrity and functional capability when subjected to the most probable hydrodynamic loads induced by a postulated design basis loss-of-coolant accident; and (2) to verify that licensed Mark I BWR facilities may continue to operate safely, without undue risk to the health and safety of the public, while a methodical, comprehensive Long-Term Program is condacted.
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The NRC determined that, for the Short-Term Program, " maintenance of containment integrity and function" would be adequately assured if a safety factor to failure of at least two were demonstrated to exist for the weakest structural or mechanical component in the Mark I containment system (i.e., if the calculated stresses in all components of the affected containment structure were shown to be less than one-half the stress which would cause the component to lose its structural integrity).
The NRC concluded that the objectives of the Short-Tenn Program had been satisfied and documented the basis for this conclusion in the " Mark I Containment Shnrt-Term Program Safety Evaluation Report," NUREG-0408, dated December 1977.
(Thus Task A-6 was completed in December 1977).
The objectives of the LTP are (1) to establish design basis (conservative) loads that are appropriate for the anticipated life (40 years) of each Mark I BWR facility, and (2) to restore the original intended design safety margins for each Mark I containment system.
The LTP consists of a series of major tasks and subtasks which are designed to provide a detailed basis for hydrodynamic load definition and to provide the methodology and acceptance criteria for the Mark I containment systems structural assessments. The generic aspects of the program are described in a Plant Unique Analysis Applications Guide, which was submitted in February, 1979, and a Load Definition Report, which was submitted by parts in December 1978 and March 1979.
These reports describe the proposed load 1733 335
definition and assessment techniques for the Mark I Long Term Program.
These reports are currently under review by the NRC staff and, upon the completion of this review, the staff will issue a set of acceptance criteria for these ger.aric assessment techniques. Subsequently, each utility will perform a plant-unique analysis using approved load definition and structural analysis techniques to demonstrate conformance with the LTP structural acceptance criteria.
The scheduled completion date for the Mark I LTP, including the issuance of license amendments and the implementation of any plant modifications necessary to satisfy the LTP structural acceptance criteria, is December 1980.
To maintain this schedule, a number of utilities have undertaken plant modifications prior to the completion of their plant-unique analysis.
This action has been considered necessary to minimize the potential for extended plant outages later in the program.
Similarly, modifications to components external to the containment (e.g., support structures) have and are being conducted during normal plant operation.
The objective of the NRC staff's efforts under Generic Task A-8 related to the Mark II Short Term or Lead Plant Program (LPP) was to review and evaluate the pool dynamic loads associated with a postulated large loss-of-coolant accident proposed by the Mark II Owner's Group to determine 1733 336
. their acceptability for use in plant unique analyses.
The Mark II Lead Plant Program was essentially completed in October 1978 with the publication of NUREG 0487, " Mark II Contailment Lead Plant Program Load Evaluation and Acceptance Criteria." The lead Mark 11 plants proposed several exceptions to the NRC staff's acceptance criteria.
The staff has reviewed these proposed exceptions and found most of them acceptable.
These exceptions and their bases will be discussed in a supplement to NUREG 0487.
Issuance of this supplement is scheduled for November 1979.
The function of the Mark II Long Term Program (LTP) is to confirm the loads used in the Lead Plant Program and to support a reduction in selected conservatively prescribed lead plant loads for use in the evaluation of those Mark II plants following the lead plant.s.
The Mark II Long Term Program is currently scheduled for completion in October 1980.
Under Generic Task A-39, the NRC staff will review and evaluate the results of the Mark I and Mark II Owners' Group's experimental and analytical programs to establish and justify the safety relief valve-related pool dynamic loads for BWR Mark I and Mark II containment designs.
The results of Generic Task A-39 will be an integral part of the final acceptability of the Mark I and Mark 11 pressure suppression containment designs.
This generic task related to the Mark I containment and Mark II lead plants is currently scheduled for completion in December 1979; for tasks related to the Mark II Long Term Program the comple-tion date is scheduled for July,1980. These schedules are consistent with the 1733 337
Generic Tasks A-7 and A-8 discussed above. An interim assessment of multiple-consecutive SRV discharges was performed for the operating Mark I facilities to support deferral of the resolution of this issue until the completion of the Mark I Long-Term Program.
This review was completed in December 1978 and deferral was found to be acceptable. A safety evaluation describing the flRC staff's interim assessment was issued in February,1979 in the form of a letter safety evaluation on each affected docket.
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