ML20248B163
| ML20248B163 | |
| Person / Time | |
|---|---|
| Issue date: | 07/12/1989 |
| From: | Advisory Committee on Reactor Safeguards |
| To: | Advisory Committee on Reactor Safeguards |
| Shared Package | |
| ML20245F415 | List: |
| References | |
| REF-GTECI-A-40, REF-GTECI-A-46, REF-GTECI-SC, RTR-NUREG-CP-0054, RTR-NUREG-CP-54, RTR-NUREG-CR-1161, RTR-NUREG-CR-5347, TASK-A-40, TASK-A-46, TASK-OR ACRS-2654, NUDOCS 8908090141 | |
| Download: ML20248B163 (6) | |
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O DATE ISSUED: July 12, 1989
SUMMARY
/ MINUTES OF THE ACRS SUBCOMMITTEE ON EXTREME EXTERNAL PHENOMENA JUNE 22, 1989 BETHESDA, MARYLAND l'
The ACRS Subconsnittee on Extreme External Phenomena met on June 22, 1989 at Bethesda, Maryland, to review and discuss draft resolution package l
for USI A-40. The. meeting was requested by the NRC and C. P. Siess.
1 Notice of the meeting was published in the Federal Register on June 12, 1989. The schedule of items covered in the meeting and a list of handouts are kept with the office copy. There were no written or oral statements received or presented from members of the public at the meeting.
E. G. Igne was Cognizant ACRS staff member for the meeting.
Principal Attendees ACRS C. P. Siess, Chairmar C. Wylie, Member J. D. Stevenson, ACRS Cortsultant NRC S. K. Shaukat N. Chokshi l:I@i lR"* 2 w ovo? m s'?
l PNV;y Others H. Eckert, NUS hSol c m m C"L3 '? ** M Q.
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Minutes / Extreme External Phenon na 2 Mtg. June 22, 1989 Highlights:
1.
K. Shaukat, RES, in response to a question stated that he has been Task Manager of USI A-40 since 1982. A-40 originated in 1977 with the following' objectives:-
Investigate selected areas of seismic design sequence and quantify margins, if any, in the design process, and modify criteria in the SRP, if changes are found to be justified.
The contractor, LLNL, completed the study and published its' report NUREG/CR-1161 in May 1980. The report summarized all technical studies, developed conclusions and made specific recommendations for SRP changes.
In the 1981-82 time frame, the NRR staff completed review of NUREG/CR-1161 and developed staff position for each recommendation.
In addition, the staff review of LLNL re: commendations resulted in addition-al technical work toncerning 1) development of power spectral density as a secondary check for use of single time history 2) developed proposed SRP changes to reflect current staff practice and 3) developed date on integrity of above-ground steel tanks (LANL contract resulting in a q
report, NUREG/CR 4776) and developed review guidelines.
Two workshops were held because of !4RC staff disagreement with LLNL and other concerns on soil-structure interaction. The first was held in June 1986, sponsored by NRC/BNL, focused on A-40 proposed SRP changes and provided expert consensus on current knowledge of soil-structure l
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.Mtg. June 22.-1989 interaction which resulted in report NUREG/CP-0054. The second workshop was, held in December 1987, and sponsored by EPRI/NRC/TPC, to considered results of the Lotung experiment in Taiwan on actual. recorded earthquakes on scale model and a staff proposal to incorporate results in A-40 by soliciting comments on specific questions during public comments. The proposed resolution was issued for public comments'on June 1988 and comments were received from six organization by.0ctober 1988.
(Note that the.ACRS during this period preferred not to comment on USI A-40 until public comments were received and resolved.)
NRC/BNL and a select panel of five expert consultants addressed the public comments and made recommendations to revise the SRP sections.
The results are summarized in NUREG/CR-5347. The NRC staff then developed final revisions to the SRP section3. The revisions of SRP Sections are 3.7.1, 3.7.2, 3.7.3 which relates to ground motion for design of structures and 2.5.2 on ground motion specifications.
It was stated that all SRP changes are forward fit only.
Lf rge abon ground tar.ks were identified es a potential concern reieting to tank well buckling. Actions on tanks are included in USI A-40.
A survey by the NRC staff of tank design confirms that many above-ground tanks of newer plants are structurally adequate. Request for inforntien was issued on June 1989, to all others (4 licensees) susceptible to tank wall buckling.
Summary of major reconnendations for SRP 3.7.1 through 3.7.3 are as follows:
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- Minutes /Extrtme External Phtnomena 4 Mtg. June 22, 1989 Changes in the specification of ground motion for design of structures.
L Significant changes for soil-structure interaction analysis.
Specific criteria for combination of high-frequency model response.
Rev_ision of damping valves based on stress levels.
Some highlights of changes to SRP Section 2.5.2 are as follows:
Revised to reflect current staff review practice.
Preferred hierarchy of ground motion specifications.
o Site-specific spectra using records suitable for site conditions, o
Site-specific spectra using scaled.' veds, o
Multiple parameter characterization (such as NUREG/CR 0098 spectra),and o
Reg. Guide 1.60 spectra scaled to peak ground accel-eration.
2.
N. Chokshi, RES, briefly described the analysis of above-ground tanks (SRP 3.7.3), soil-structure interaction (SRP-3.7.2) and power spectral density (SRP 3.7.1).
With respect to above-ground tanks, he stated that USI A-46 PRA studies showed tanks to be a dominant risk contributor, i.e., Maine Yankee seismic margin study showed dominant vulnerability of RWST. The use of
Minutes / Extreme External Phenomena 5 Mtg. June 22, 1989 the old analysis procedure based on rigid walls results in the underestirnation of design forces - by as much as a factor of 2 to'2.5.
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There were diverse and conflicting industry connents on soil-structure L
interaction questions. Consensus oa the need for limit on ground motion l
reduction varied among the expert consultants. The NRC staff adopted 40% with provision for case-by-case review when reduction is greater than 40%. Guidance for clarification for soil material properties are provided in the revised SRP 3.7.2.
Reg. Guide 1.60. spectra are still the design basis regarding power spectral censity (SRF 3.7.1).
NRC philosophy on this matter is as follows: A requirement is to assure that there is no deficiency of power over any frequency range. Therefore a time history based on minimum PSD requirement should produce a response spectrum which lies close to, but generally below, the Reg. Guide 1.60 spectrum. Actual time history used in design will have to satisfy both Reg. Guide 1.60 j
enveloping requirements and PSD requirement.
3.
J. G. St2venson, ACRS consultant, in his review of USI A-40, mentioned concerns in the seismic design areas which he believed need 1
fur'ther evaluation and consideration by the NRC staff. Liis concerns are documented in his letter to C. P. Siess, dated June 21, 1989 (Attached),
4.
In his closing statement, the Chairmen complimented the staff for the excellent work and presentation on this matter.
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Minutes / Extreme External ~ Phenomena 6 Mtg. June 22, 1989 '
A'ction:
The sub' committee and NRC will present a report on this matter to the full ACRS at the June meeting. An ACRS letter is planned..
NOTE:
lA transcript of the meeting is available at the NRC Public Document Room, Gelman Bldg., 2120 "L" St. NW., Washington, D.C. Telephone (202) 634-3383 or can be purchased.from Heritage Reporting Corporation, 1220 L Street, NW.,
Washington, D.C. 2000S, Telephone (202) 628-4888.
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