ML20052D601
| ML20052D601 | |
| Person / Time | |
|---|---|
| Issue date: | 01/26/1982 |
| From: | Advisory Committee on Reactor Safeguards |
| To: | Advisory Committee on Reactor Safeguards |
| References | |
| ACRS-1946, NUDOCS 8205060619 | |
| Download: ML20052D601 (14) | |
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0 ACRS FLUID DYNAMICS SUBC0'1MITTEE MEETING MINUTES
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JANUARY 22, 1982 7
\\ '.3.y v, g The purpose of the meeting was for the Subconmittee to:
(15continueitsreview of the BWR Mark III Containment Modification Program; and (2) discuss the status of the Unresolved Safety Issues for the BWR Mark I and 11 containments.
Notice of the meeting was published in the Federal Register on December 28, 1981.
The meeting convened at 8:30 a.m.
Attendees:
Principal attendees of the meeting included:
ACRS NRC M. Plesset, Chairman J. Kudrick J. Ebersole, Member M. Fields H. Etherington, Member G. Maise W. Mathis, Member A. Sonin I. Catton, Consultant T. Theofanous, Consultant Mississippi Power & Light T. Wu, Consul tant J. McGaugby, Jr.
Z. Zudans, Consultant Y. Chen, ACRS Fellow P. Boehnert, Staff *
- Designated Federal Employee A complete list of attendees is attached to the office copy of these minutes.
Meeting Highlights, Agreements, and Requests:
1.
In opening the meeting, Dr. Plesset said he hoped that the NRC and its consultants would provide best-estimate information rather than overly conserative evaluations for the issues at hand associated with the Mark III review.
NRC responded that they were in agreement on this point.
C..;0I: aL 8205060619 820126 Certif e.] 37 M PDR ACRS 1946 PDR
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Fluid Dynamics Meeting January 22, 1982 l
2.
Mr. M. Fields (NRC) provided a brief overview of the licensing status for the Mark III containment.
He said that NRC would review the draft load acceptance criteria, provide response to specific Subcommittee questions previously sub'mitted to the NRC, and discuss the current status of the pool dynamic load definition review for the Grand Gulf pl ant. NRC has resolved most of the outstanding issues on the Mark III containment review. A draft NUREG on the LOCA related pool dynamic load criteria will be issued in March 1982 with a final WUREG scheduled for issuance in June 1982.
i 3.
Dr. G. Maise (NRC Consultant) detailed the status of the load definition issues identified as unresolved at the last Subcommittee meeting in September 1981.
These issues and their status (in parenthesis) cre:
f (1) pool swell velocity (NRC and GE have agreed on a maximum value of 50 ft/sec. as a function of the height above the pool (Figure 1); (2) bulk impact on structures (a specific pressure pulse has been accepted (Figure 2) subject to certain limitations which will be satisfied in the standard plants; (3) froth impact load (NRC has proposed a triangular pulse function (Figure 3) which results in a higher pressure load than the originally proposed GESSAR criteria (Figure 4).
GE has not yet accepted this NRC proposal); and (4) submerged structure drag load (NRC has accepted the GESSAR specification with limitations - Figure 5).
During the above discussion, Mr. Ebersole asked if the hydraulic control units (HCUs) will be able to function, and assure plant scram, during the froth impact and associated water fall-back. GE replied that the HCU's are designed for the uplift loads, and the fall-back is similar to the containment spray which they are also qualified to withstand.
Drs.
Theofanous and Zudans felt that the mechanism of momentum transfer associated with the froth load impact on the HCU floor is not well understood, and that the scaling of this load from small targets to a large surface area (HUC floor) is suspect (GE used the results of beam target impact studies to determine the HCU froth drag load). Dr. Maise said he will provide additional detailed information to Drs. Theofanous and Zudans on this scaling effort via a letter to the Subcommittee.
o Fluid Dynamics Meeting January 22, 1982 i
4.
Dr. A. Sonin (NRC Consultant) discussed, in response to Subcommittee request, the NRC analysis of the GE 1/3-and 1/9-scale test data and the scaling methodology used by the Staff to argue for a pool well velocity of 60 ft/sec (NRC has now accepted a 50 ft/sec value). Dr. Sonin detailed the problems encounted in properly intrepreting the GE-scaled test data. The 1/3-scale test results give a pool swell velocity of 47 ft/sec when scaled to full scale. NRC chose 50 ft/sec to account for uncertainties in the test data.
Additional Subcomittee discussion brought out the fact that the test data show a range of pool swell velocities between 38 to 47 ft/sec.
NRC has accepted a 50 ft/sec value which is m 20% above the GE best-estimate value (40 ft/sec). NRC stated that they believe they have a sufficient understand-ing of the pool swell phenomenon to assure that the plant's safety functions will net be impariled in the event of a large-break LOCA.
GE, responding to Dr. Theofanous' concern over the scaling of the froth impact load, said the information of interest will be found in Attachment 0 to GESSAR Appendix B, and GE will provide this information.
5.
Mr. Fields responded to Subcommittee questions on:
(1) the calculation of the containment drywell pressure rise for a LB LOCA, and (2) whether the plant will be scrammed before froth impact occurs.
In response to (1),
NRC discussed the details of the drywell pressure rise model, noting that the model has been verified by comparisons with test results from the GE Pressure Suppression Test Facility (model shows a 15% conservatism vs test results).
For question 2, Mr. Fields said the froth impact would occur before the control rods are fully inserted (2 seconds vs 2.5 - 3.5 seconds).
Therefore the HCUs must be able to function during and after froth impact.
6.
The current status of the Mark III review for the Grand Gulf p1 ant was discussed by Mr. Fields.
nighlights of the discussion include:
'The pool dynamics load definitions for Grand Gulf have been agreed to i
by NRC and the Applicant (MP&L).
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Fluid Dynamics Meeting January 22, 1982
' Grand Gulf proposes to use the results of the Kuosheng (Taiwan) SRV tests in lieu of performing its own SRV tests. MP&L has submitted a report arguing this point. NRC's initial position is that MP&L will not have to run the tests but the applicability of the Kuosheng structural response to Grand Gulf is still at issue. Final determination of the need for the tests will be based on NRC evaluation of a March 1982 report from MP&L.
'ihe structural capacity of the HCU floor has been evaluated using the NRC-proposed alternate froth-impact load discussed above.
Preliminary results show that the floor has adequate structural capability.
NRC will, however, review the structural methodology used by MP&L for the plant. MP&L noted that their structural model shows that while the beams supporting the floor grating will ext erf ence some deformation (beyond yield stresses), the HCU floor beams do not see yield stresses. MP&L noted that they have installed blast shields on some of the HCU units for protection against pool dynamic effects.
Mr. Ebersole requested details on the blast shield design and installation.
NRC said they will provide the information in the near future.
7.
Mr. J. Kudrick summarized the status of the Mark II USI review.
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l are three activities / concerns currently associated with this review. These (1) ability of downcomer vent-mounted vacuum breakers to withstand are:
chugging loads, (2) BNL study on the consequences of an SRV line break in the wetwell airspace; and (3) a NRC consultant's recent concern on the chugging load specification.
Concerning item (3) Dr. Benkowski (Prinston University) raised a concern related to the Monte Carlo approach used for picking vent chug times for the chugging source term. Using a different set of start times within the NRC-approved 50 millisecond " window" changt.s the forcing function above 20 Hertz.
The preliminary Staff assessment is that there is minimal impact on the chug load specification and no structural loads are impacted.
NRC will provide a final report on this item in a few months.
i AAW rat m m e n a N utr e
Fluid Dynamics Meeting January 22, 1982 Mr. D. O'Connor (Mark II Owners Group) discussed item (1) above. Recent testing has shown that the vacuum breaker valves r;ounted on the down-
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comer pipes are subject to cyclic condensation loads that may fail valve components.
Four Mark II plants were cited as being affected. These are Shoreham, Susquehanna, Limerick, and VPPSS Unit 2.
Follow-on testing is under consideration to test the valves beyond yield as well as testing of a prototype redesign.
Shoreham and Susquehanna have elected to " cap" the downcomers as a " quick fix" to prevent delay of fuel load.
Other fixes (relocate valves, modify valves) are under consideration for the other af fected plants.
Analyis shows no significant impact on the plant hydro-dynamic loads due to the loss of use of the capped downcomers.
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8.
Dr. Maise discussed the on-going BNL study of the consequences of a struck-open relief valve combined with a rupture of the relief valve discharge line in the wetwell airspace (Figure 6).
The objectives of the study are to:
(1) quantify the containment failure potential for Mark I & II plants given such an event, and (2) estimate the significance of this event relative to overall plant safety. The plants to be examined are Peach Bottom (Mark I), and Limmerick (Mark II)
These plants were chosen because of the safety studies that have been done, WASH-1400 and a PRA study, respectively. Key elements of the study include an analysis of containment response, a study of failure rates and system availability for critical components / systems, and a risk assessment of the accident's impact on overall plant safety. The study should be complete in June 1982.
Preliminary findings include:
'for an accident with 100% bypass to the wetwell, rupture pressure is exceeded in 10 minutes for Mark I and 14 minutes for Mark II.
' containment spray is very effective in mitigating the accident but the spray system availability is probably dominated by operator action re-liability.
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Fluid Dynamics Meeting January 22, 1982 In response to questions from Messrs. Ebersole and Etherington, NRC said GE estimates pipe failure potential to be N10-7/RY and the possibility of a stuck open SRV to be W 10-2/RY.
9.
Mr. J. Kudrick discuss the status of the Mark I Unresolved Safety Issue (USI) long-term program (LTP) fixes.
Recently (December 1981) NRC extended the LTP completion schedules for the Mark I operating plants and tied schedule completion to the plant's respective fuel cutage schedule. The major problems encountered in the LTP include:
(1) complexity of the torus attached piping analyis; (?) alternate approaches taken/ interpretations of LTP requirements, (3) equipment delivery problems, and (4) a general underestimation of tne magnitude of the LTP requirements.
Referring to the latest schedule (Figure 7), Mr. Kudrick said 2/3 of the operating plants will complete major Program modifications in 1982.
All of the modifications will be completed by June-July 1984.
Mr. Ebersole asked NRC if any of the older Mark I plants still provide for steam bypass relief into the drywell instead of the suppression pool.
NRC said they would check on this and respond at a later date.
Mr. Ebersole also asked if adequate measures are being taken to prevent formation of rust in the suppression pool.
10.
During a Subcommittee discussion session Mr. Ebersole, referring to the potential for rust fomation in the suppression pool, urged NRC to investi-gate the potential for particulate contamination of ECCS and other safety system pumps.
Dr. Zudans requested NRC response to a question on the determination of the pressure at a given point in the pool based on individual downconer chug source terms. NRC said they would respond to this question via a letter to the Subcommittee.
Prior to adjournnant, Dr. Plesset requested that the consultants provide a written report to the Subcommittee detailing their thoughts on the material provided at the meeting.
- 11. The meeting was adjourned at 3:15 p.m.
Fluid Dynamics Meeting January 22, 1982 NOTE: Additional Meeting details can be obtained from a transcript of this meeting available in the NRC Public Document Room,1717 H Street, N.W.,
Washington, D.C., or the transcript can be purchased from Alderson Re-porting Company, Inc., 400 Virginia Avenue, S.W., Washington, D.C. 20024,
(
(202) 554-2345.
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