ML20023D397
| ML20023D397 | |
| Person / Time | |
|---|---|
| Site: | La Crosse File:Dairyland Power Cooperative icon.png |
| Issue date: | 05/19/1983 |
| From: | Crutchfield D Office of Nuclear Reactor Regulation |
| To: | Linder F DAIRYLAND POWER COOPERATIVE |
| References | |
| 80-445-01-SC, 80-445-1-SC, LSO5-83-05-042, LSO5-83-5-42, NUDOCS 8305200452 | |
| Download: ML20023D397 (3) | |
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May 19,1983 DISTRIBUTION
' Docket NRC PDR Docket No. 50-409 Local PDR LS05-83-05-042 ORB Reading NSIC DCrutchfield Mr. Frank Linder HSmith General !!anager RDudley Dairyland Power Cooperative OELD - CWoodhead 2615 East Avenue South ELJordan La Crosse, Wisconsin 54601 JMTaylor ACRS (10)
Dear Mr. Linder:
SEPB RJackson, GSB
SUBJECT:
LIQUEFACTION POTEHilAL AT THE LA CROSSE KCyr, OELD BOILING WATER REACTOR SITE
Reference:
10 CFR 2.206 - Order to Show Cause dated February 25, 1980 Enclosed with this letter is the Atenic Safety and Licensing Board's
" Initial Decision," (80-445-01 SC) cated April 21,198', relating to the captioned subject. Based on this Decision, Dairyland Power Cooperative is neither required to submit a detailed design proposal for, nor to make operational, a site dewatering system to preclude the occurrence of liquefaction in the event of an earthquake with peak ground surface accelertions of 0.129 or less, as proposed by the staff's Order to Show Cause, dated February 25, 1980.
Sincerely, Original signed by/
Dennis H. Crutchfield, Chief Operating Reactors Branch #5 Division of Licensing
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Enclosure:
As stated MSE cc with enclosure:
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Docket NRC PDR Docket No. 50-409 Local PDR ORB Reading NSIC DCrutchfiela Mr. Frank -Linder HSmith General Manager RDudley
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D61ryland Power Cooperative OELD - C W b *J 2615 East-Avenue South ELJordan La Crosse, Wisconsin S4601 JMTaylor ACRS (10)
Dear Mr. Linder:
SEPB
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SUBJECT:
LIQUEFACTION POTENTIAL M THE LA CROSSE j-BOILING WATER REACTOR SITE F. C [r, oft 3 i
Reference:
10 CFR 2.206 - Order to Show Cause dated February 25, 1980 Enclosed with this letter is the Atomic Safety and Licensing Board's
" Initial Decision," (80-445-01 SC) dated April 21, 1983, relating to the captioned subject. Based on this Decision, Dairyland Power t
Cooperative is neither required to submit a detailed design proposal for, nor to make operational, a site dewatering systen to preclude the occurrence of ligt.efaction in the event of an earthquake with peak l
ground surface accelertions of 0.12g or less, as proposed by the staff's Order to Show Cause,- dated February 25, 1980.
Sincerely, L
I Dennis M. Crutchfield, Chief Operating Reactors Branch 95 l
Division of Licensing 3
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Mr. Frank Linder May 19,1983 cc Fritz Schubert, Esquire Clarence Riederer, Chief Engineer Staff Attorney Wisconsin Public Service Dairyland Power Cooperative Commission 2615 East Avenue South Post Office Box 7854 La Crosse, ' Wisconsin 54601 Madison,. Wisconsin 53707
- 0. S. Heistand. Jr., Esquire Thomas Houvenagle Morgan, Lewis & Bockius Regulatory Engineer 1800 M Street, N. W.
Iowa Commerce Commission Washington, D. C.
20036 Lucas State Office Building Des Moines, Iowa 50319 Mr. John Parkyn La Crosse Boiling Water Reactor John N. Ferman, Ph.D.
Dairyland Power Cooperative Nuclear Engineer P. O. Box 275 Minnesota Pollution Centrol Agency Genoa, Wiscensin 54632 1935 U. County Road B2 Roseville, Minnesota 55113 Mr. George R. Nygaard Coulee Region Energy Coalition 2307 East Avenue La Crosse, Wisconsin 54601 U. S. Nuclear Regulatory Ccmmissicn Resident inspectors Office Rural Route 71, Scx 276 Genca, Wisconsin 54632 Tcwn Chairman Tcer cf Genca Route 1 Genoa, Wisconsin 54632 Chairman, Public Service Commission.
of Wisconsin Hill Farms State Office Building
. Madison, Wisconsin 53702 U. S. Environmental Protection Agency Federal Activities Branch Region V Office ATTN: Regional Radiation Representative 230 South Dearborn Street Chicago, Illinois 60604 James G. Keppler, Regional Administrator Nuclear Regulatory Commission, Region III 799 Roosevelt Road Glen Ellyn,111inois 60137 9
LBP-83-23 SER'!E APR 2 81983 UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMISSION ATOMIC SAFETY AND LICENSING BOARD Before Administrative Judges:
Charles Bechhoefer, Chairman Dr. George C. Anderson Ralph S. Decker
)
ASLB Nos. 78-368-05 OL In the Matter of:
)
80-445-01 SC
)
DAIRYLAND POWER COOPERATIVE
)
Docket Nos. 50-409 FTOL
)
50-409 SC La Crosse Boiling Water Reactor,
)
Operating License and Show Cause)
)
April 21, 1983
)
INITIAL DECISION (Safe Shutdown Earthquake for Liquefaction Purposes)
This conrolidated proceeding involves both (1) the application by Dairyland Power Cooperative (Applicant or DPC) to replace its current Provisional Operating License DPR-45 with a full-term operating license (FTOL) for the La Crosse Boiling Water Reactor (LACBWR), a 50 MWe boiling water re.ctor located on the Mississippi River about 20 miles l
south of La Crosse, Wisconsin, and (2) a show-cause order dated February 25, 1980, which concerned the potential for liquefaction at the LACBWPs site.
The operating license application and the show-cause order were originally considered in separate proceedings, which were consolidated by our Memorandum and Order dated August 19, 1981, LBP-81-31, 14 NRC 375.
The background of this consolidated proceeding i.s set forth in our Memorandum and Order dated August 2,1982, LBP-82-58, 16 NRC (slip op. pp. 1-9), as well as in our Partial O
70D 991
a.
. Initial Decision of February 24, 1981, LBP-81-7, 13 NRC 257, 260-63, and will not be repeated here.
As is reflected in both LBP-81-7 and LBP-82-58, there is only one issue remaining to be decided with respect to the show-cause proceeding:
the size of the safe-shutdown earthquake (SSE) which is to be used in determining whether there is liquefaction potential at the LACBWR site.
(This was the only show-cause issue left undecided when we consolidated the two proceedings.) We treat that issue in this opinion.
For the reasons hereafter set forth, we conclude that the SSE utilized by the Staff in its SER in the show-cause proceeding and by us in our Partial Ini.tial Decision (LBP-81-7) is appropriate for evaluating the liquefaction potential at La Crosse.
I.
Description of the Issue In our Partial Initial Decision in the show-cause proceeding, we determined that liquefaction under pile supported structures was not a problem for an earthquake up to magnitude 5.5 with a peak ground acceleration of 0.12g or less.
For that reason, we held that the dewatering system suggested by the show-cause order need not be installed at that time.
(We did approve the installation of a dedicated safe shutdown system to provide emergency cooling water in the event an earthquake producing ground acceleration of up to 0.12g caused damage to the crib house and underground piping.) LCF-Sl-7, supra, 13 NRC at 279.
. In that decision, however, we stressed that the appropriate SSE for the LACBWR site had never been formally determined and that the findings regarding liquefaction potential were only valid if the SSE were no larger than magnitude 5.0-5.5 with peak ground acceleration at the site no greater than 0.12g.
This was the SSE assumed by the Staff as a basis for issuing the show-cause order.
Earlier in the proceeding, it had come to our attention that the SSE utilized by the Staff for another reactor (Tyrone) less than 100 miles from LACBWR was an intensity MM VII-VIII earthquake analyzed as producing ground acceleration at the Tyrone site of 0.20g.
Because the Staff had not made any final determination of an SSE for the LACBWR site--indeed, prior to the future issuance of its SEP report ar.d its SER l
based thereon, it still will not have done so --we raised as an issue in this proceeding the appropriate size of the SSE and the ground acceleration at the site which it could produce.2 Prior to our Partial Initial Decision, we took evidence as to the i
seismic hazard of earthquakes producing ground acceleration at the LACBWR site greater than 0.12g and the ccr. comitant risk of operating l
1 The Staff's safety review of the FTOL application is based on the results of its Systematic Evaluation Program (SEP), which is still not complete for LACBWR.
2 Prehearing Conference Order, LBP-80-26,12 NRC 367, 376-379 (1980),
affirmed, ALAB-618, 12 NRC 551 (1980), review declined by l
Commission, letter dated April 21, 1981 from the Secretary of the l
Commission to DPC's counsel.
l i
. LACBWR prior to a final determination of the appropriate SSE.
In our Partial Initial Decision, we determined that the risk presented by such operation was no greater, and possibly less, than the risk represented by the temporary operation permitted by the show-cause order pendente lite. We therefore concluded that there was reasonable assurance that continued operation without a dewatering system pending our resolution of the SSE question would not endanger the health and safety of the public. LBP-81-7, supra, 13 NRC at 279.
To resolve the SSE question, the NRC Staff submitted an affidavit of four Staff members on January 28, 1982.3 Neither DPC nor any intervenor took advantage of the opportunity we provided to comment on that affidavit. As a result of certain apparent inconsistencies in the affidavit, the Board posed certain questions related to the affidavit and, in addition, asked other questions concerning the regulatory status of the method of review adopted by the Staff. Memorandum dated July 2, 1982 (unpublished).
The Staff responded to the latter questions in a filing dated July 30, 1982, and it filed additional affidavits on 3
Affidavit of Robert E. Jackson (Branch Chief, Geosciences Branch, l
Div. of Engineering, NRR), Jeffrey K. Kimball (Seismologist /
l Geophysicist, Geosciences Branch, Div. of Engineering, NRR), Leon Reiter (Section Leader, Seismology Section, Geosciences Branch, Division of Engineering, NRR), and William Russell (Branch Chief, Systematic Evaluation Program Branch, riv. of Licensing, NRR)
(hereinafter Staff Aff. I).
August 18, 1982.4 As with the earlier affidavit, neither DPC nor any intervenor availed itself of the opportunity we provided for responding to the additional affidavits and other material provided by the Staff.
We have reviewed the Staff affidavits and, together with the hearing record developed on December 16-17, 1980, we regard the record adequate to determine the appropriate SSE to be utilized to assess the potential for liquefaction at the LACBWR site.
II.
Determination of Safe-shutdown Earthquake for Assessing Liquefaction Potential at LACBWR A.
Legal Standards The Commission's currently applicable standards for determining the geologic and seismic aspects of a site, which must be taken into account in establishing the design basis for a plant, appear in 10 CFR Part 100, Appendix A.
Those regulations were proposed in 1971 and adopted late in 1973 (38 Fed. Reg. 31279, November 13,1973). LACBWR was initially authorized to operate in 1967 and hence was not licensed pursuant to the requirements of Appendix A.
At the time, the Commission (then the AEC) had no specific seismic criteria (comparable to Appendix A) applicable to reactors; conformance with the Uniform Building Code 4
Affidavit of Messrs. Reiter and Kimball (hereinafter Staff Aff. II); affidavit of Mr. Russell (Staff Aff. III).
. was deemed to be sufficient (Levin, Tr. 318). Moreover, the Commission did not make Appendix A applicable to reactors authorized to operate at the time of its issuance (38 Fed. Reg. 31279), nor has it used its backfitting authority (see 10 CFR 9 50.109) to apply it to such reactors.
For those reasons, the requirements of Appendix A need not be applied to this reactor.
C_f. General Electric Co. (Vallecitos Nuclear Center), LBP-82-64, 16 NRC (August 16, 1982) (slip op.,
pp. 187-188); acq., ALAB-720, 17 NRC
, fn.3 (March 23, 1983).
In its safety review of LACBWR, the Staff is using the results obtained from its SEP. As indicated in the material provided us by the Staff on July 30, 1982, and by Staff Aff. III, the overall program (and the proposal to apply it to LACBWR, among others) was initially presented for Commission approval in 1976 (SECY-76-545) and was approved by the Commission on November 15, 1977.
The Commission requested periodic status reports. The SEP methodology for quantifying seismic l
parameters was explained to the Commission during a briefing session on I
l May 6, 1980 (see Tr. 14-23 of that session, which has been provided to t
us by the Staff).
l In addition, the Staff advises that the Commission is aware that the Site Specific Spectra Program documented in NUREG/CR-1582, Vols. 2-5, is a state-of-the-art program to develop a realistic estimate l
of the seismic hazard (reanalysis spectra) for SEP plants (Staff i
. Aff. III, p. 2).5 Although the Commission (as of August 1982) had not yet approved specifically the SEP approach to definition of seismic hazard, it is expected to review formally the application of the SEP seismic methodology to LACBWR this Spring (id. at 4).
Based on this material, we believe that the Staff had an adequate basis to perform its seismic review of LACBWR under the methodology it developed for the SEP (i.e., the Site Specific Spectra Program).
B.
Safe Shutdown Earthquake for Tyrone The Staff has explained the way the Tyrone SSE (characterized by a peak acceleration of 0.20g) was determined and why it is not necessarily incompatible with the SSE producing peak Acceleration of 0.12g which has
~
been used by DPC and the Staff to analyze the liquefaction potential at La Crosse.
As a new reactor, Tyrone was subject to the requirements of Appendix A to 10 CFR Part 100.
In the Tyrone SER (NUREG-75/102, October 1975), the Staff considered the intensity VII-VIII Anna, Ohio earthquake of 1937 as the largest earthquake in the Central Stable Region (in which both Tyrone and La Crosse are located) which could not be reasonably associated with known geologic structure.6 That earthquake was calculated under Appendix A criteria to produce a peak ground 5
Volumes 2 and 3 of NUREG/CR-1582 were entered into evidence as Staff Exhs. 6 and 7 (Tr. 155).
Volumes 4 and 5 were subsequently i
provided by the Staff to the Board and all parties.
6 An intensity VII earthquake is roug ly equivalent to a magnitude 5.0-5.5 earthquake (Reiter, Tr. 167.
. acceleration at the Tyrone site of 0.20g.
Since Tyrone was a SNUPPS (Standardized Nuclear Unit Power Plant System) plant which used 0.20g as its design basis, the Tyrone Applicant chose 0.20g peak acceleration for the standard design of Tyrone.
However, that Applicant had proposed the use of 0.14g for the non-standard portion of the plant. The Staff recommended the use of 0.20g for all safety related features of the plant, for conservatism, and the Applicant apparently did not object.
Staff Aff. I, at 'pp. 2-3, 4.
Furthermore, the Staff, both in the past and currently, recognizes that significant variations exist in historic seismicity within the Central Stable Region.
Based on the low level of seismicity in the vicinity of the Tyrone site, had the Applicant given sufficient supportive bases, the Staff indicated that it might have considered acceptable an intensity lower than MMI VII-VIII, and a peak ground acceleration lower than 0.20g, for the design of the Tyrone plant.
However, the requisite supporting data were never submitted by the t
l Tyrone Applicant.
The Staff reviewed the Tyrone application on the I
basis of the information submitted to it. H.at4-5,9.
In other cases, applicants subject to Appendix A have provided sufficient information to justify selection of a tectonic sub-region or zone within the Central Stable Region and thus the use of an earthquake of lesser intensity than the Anna, Ohio earthquake.
For example, the Staff approved an SSE producing peak ground acceleration of 0.129 for both the Wolf Creek plant located in Kansas and the Black Fox site in I
-g-eastern Oklahome. Staff Aff. I, Attachment 1.
In 1973-74, Dames and Moore completed a similar study for La Crosse in which a smaller sub-region with a maximum random earthquake of intensity VI was proposed.7 Using methods available in 1973, Dames and Moore estimated acceleration of 0.12g at the ground surface.8 Although the 1974 Dames and Moore study was submitted to the Staff in support of Dairyland's full term operating license application, the Staff has never to our knowledge explicitly accepted that study nor approved the SSE it recommends. However, throughout these proceedings, the Staff has consistently maintained that a 5.0-5.5 magnitude or intensity VII earthquake is appropriate for La Crosse and that, using the relationship proposed by Trifunac and Brady, this earthquake produces a peak acceleration of 0.129 at the site.9 We conclude that, because of the particular circumstances which we have outlined, the acceptance at Tyrone of an SSE with 0.20g peak 7
Seismic Evaluation of the La Crosse Boiling Water Reactor, SS-1162, Janua ry 11,1974, p. 5; see also attachment 5 to Staff Aff. I, p.1 of enclosed SER.
8 An intensity VI earthquake occurring at or near the site would result in a peak ground acceleration of 0.06g according to a March 21, 1980 Dames and Moore report " Response to NRC Concerns on Liquefaction Potential at La Crosse Boiling Water Reactor (LACBWR)
Site Near Genoa, Vernon County, Wisconsin" (attachment to Licensee's Answer to Order to Show Cause, dated March 25,1980),at
- p. 5.
9 Show Cause Order; Staff Aff. II, pp. 2-4; SER fol. Tr. 96, pp. 2-3, 5; Staff Aff. I, Attachment 3, p. 17.
. acceleration does not dictate use of a similar SSE for this facility, despite the close proximity to Tyrone.
C.
The SEP Methodology The Systematic Evaluation Program (SEP) is an on-going effort by the Staff to re-evaluate eleven early nuclear plants (including La Crosse) in light of current standards. 'To determine the capability of the soils underlying these plants to withstand shaking caused by earthquakes withcut detrimental effects such as liquefaction, it is first necessary to specify the expected ground motion.
For this purpose, the Staff is using the results of a method developed for the Staff by the TERA Corporation under the technical direction of the Lawrence Livermore National Laboratory.10 This approach, the Uniform Hazard Methodology (UHM), differs from the method prescribed by Appendix A to 10 CFR Part 100 for earthquakes which cannot be reasonably associated with known geologic structure.11 10 Tne SEP investigation also extends to the plant structures and equipment, of course, for which a complete response spectrum is required.
The same SEP methodology is used for that purpose.
Here, however, we confine ourselves to ground motion which can be characterized primarily in terms of peak ground surface acceleration.
11 Testimony in these proceedings has used various nomenclatures for the UHM, including Site Specific Spectra.
(See attachments 2 and 3 to Staff Aff. I for examples.)
In this decision we do not use the Site Specific Spectra terminology since entirely different methods conforming strictly to Appendix A have been used for plants such as Wolf Creek, Black Fox and La Crosse to develop response spectra which are also site specific.
, The UHM incorporates two important features.12 First, unlike Appendix A, the UHM does not assume that the largest earthquake in the tectonic region occurs at or near the site.
Rather it considers earthquakes of all reasonable magnitudes and assumes that they occur randomly in time and space.
Therefore it is necessary to develop a cummulative density distribution function based on historical evidence.
Greeves, Tr. 187. Moreover, a means of considering attenuation over the distance separating the site from the randomly located epicenter is required (Reiter Testimony, ff. Tr. 85, pp. 3-6; Tr.173-174).
One then integrates over the whole of an appropriate zone for some arbitrary period of time--1,000 years for the SEP program.
The ultimate result is response spectra covering the range of frequencies important in evaluating the ability of soils, structures and equipment to withstand shaking.
At very high frequencies, the response spectra become asymptotic to the peak ground surface acceleration.
- Greeves, Tr. 188-191.
The second important feature is that the input parameters for the UHM (as mentioned in the preceding paragraph) have been determined from an extensive and systematic polling of ten or more leading authorities in seismology of the eastern and central United States (Reiter, Tr. 156-165).13 12 See NUREG/CR-1582, Vol. 2 (Staff Exh. 6) for a more detailed l
description of the UHM.
13 See also Attachment 3 to Staff Aff. I (which is also Staff Exh. 4),
(
l pp. 5-6.
l l
o
. The Staff believes that the UHM is potentially superior to deterministic methods since it reflects more accurately the true s'eismicity in which a site is located.14 We agree. The results of the UHM have now been applied to all eleven nuclear plants under review in the SEP.
For La Crosse, the UHM gave a result for peak ground surface acceleration of 0.099.15 However, the Staff concluded that no UHM spectra should be allowed to fall below the mean value for actual historic spectra.
For La Crosse, that raised the peak ground surface acceleration to 0.11g and the Staff has adopted that value for LACBWR.10 D.
The Choice of 1000 Year Spectra t
Although the spectra used in the SEP are labled 1,000 year spectra, the Staff believes that due to conservatisms in the UHM, the actual return times could be as much as 10,000 years.17 A Dames and Moore study using a similar methodology fcund the return time for a 0.129 or greater earthquake to be 10,000 years with a range of 6,000 to 15,000 14 Id. p. 15; Staff Aff. I, p. 6.
15 Staff Aff. I., Attachment 3, Fig.10; Greeves, Tr. 188-189; Reiter Testimony, ff. Tr. 85, p. 3.
10 Staff Aff. I, Attachment 2; Reiter, Tr. 174-175.
I7 Staff Aff. I, Attachment 3, at p. 11-13; Reiter, Tr. 168-169.
. years.18 The difference can be traced to different input parameters, notably the low magnitude cut-off to the density distribution function which Dames and Moore set at 5.0 (vs,. 4.25 for the TERA analysis) on the basis that liquefaction is not known to have cecurred at magnitudes lower than 5.0.
McGuire, Tr. 339; Greeves, Tr. 112-113.
In March 1983 the Nuclear Regulatory Commission published a preliminary policy statement on safety goals for nuclear power plants.
48 Fed. Reg. 10772 (March 14, 1983).19 Therein, the Commission announced, inter alia, the following plant performance design objective:
The likelihood of a nuclear reactor accident that results in a large-scale core-melt should normally be less than one in 10,000 per year of reactor operation.
18 McGuire, Tr. 308, 344; see also Attachment 4 to Staff Aff. I, at
- p. 9.
19 The policy statement is subject to change after a two year evaluation period.
The qualitative goals and quantitative design objectives are not to be used in the licensing process or to be litigated in hearings; conformance with regulatory requirements is to continue to be the exclusive licensing basis for plants.
---Id. at 10775.
Nontheless, where, as here, no particular regulations prescribe the seismic and geological evaluation of the site, we regard it as both useful and consistent with the foregoing use limitations to refer to the performance design objectives in ascertaining the reasonableness of the methodologies used to develop the SSE for this reactor.
Cf. " Proposed Commission Policy Statement on Severe Accidents and ReTated Views on Nuclear Reactor Regulation," where the Commission observed that use of the policy statement on safety goals is to be limited to uses such as
" examining proposed and existing regulatory requirements," 48 Fed.
Reg. 16014, 16015 (April 13, 1983).
t,
. 48 Fed. Reg. at 10775.20 As we have seen, the Staff's probability estimate of an earthquake resulting in peak ground acceleration of 0.11g or higher is at least as low as one in 1,000 per year and could be an order of magnitude lower. Dames and Moore's best estimate that a 0.12g or higher earthquake could occur at La Crosse is one in 10,000 per year.
Hence, the earthquake occurrence probability estimates alone essentially provide a basis for meeting the Commission's design objective as far as liquefaction potential is concerned.
In addition, excedence of these peak ground accelerations (0.119 or 0.12g) does not necessarily lead to itquefaction because of significant factors of safety under pile-supported buildings important to nuclear safety.21 Moreover, there are several additional barriers against large-scale core-melt.
Even should some degree of liquefaction occur, the pilings would continue to offer foundation support. Greeves, Tr. 233. Disruption of the reactor and other safety related buildings would have to be so severe as to render emergency cooling systems 20 In February,1982, the Commission had published for comment a proposed policy statement.
That proposal provided guidance with respect to evaluating large-scale core melts in identical terms with the design objective quoted above.
47 Fed. Reg. 7023, 7026 l
(February 17,1982).
21 A Dames and Moore report entitled " Liquefaction Potential at La Crosse Boiling Water (LACBWR) Site Near Genoa, Vernon County, l
Wisconsin," September 1979, concluded that a " threshold liquefaction resistance level for the LACBWR site corresponds to an SSE producing an acceleration between 0.18g and 0.20g at the ground surface." See Show Cause Order, Part II.
- ineffective (Levin, Tr. 222-223; Greeves/ Levin, Tr. 231-232).22 Although not yet quantified and currently unquantifiable, the failure probability of these additional barriers to core-melt combined with the already low probability of occurrence of earthquakes larger than 0.12g gives the Board ample assurance that core-melt probability due to liquefaction at La Crosse is extremely remote and well below the Commission's preliminary design objective.
E.
Comparison of UHM with Other Methodologies After having selected the SSE for new reactors derived by the essentially deterministic methods of Apperidix A, the Staff has often been asked to estimate the probability that the SSE will be exceeded.
In general, the answer turns out to lie in the range of 10-3 to 10'4 per year, i.e., to be characterized by a return time on the order of 1,000 to 10,000 years.
Reiter, Tr. 168-169. Hence the excedence probability derived by the UHM method is not inconsistent with the excedence probability of an SSE determined pursuant to Appendix A.
As one method of exploring the validity of the Uniform Hazard Methodology, the results using UHM were compared with those derived from deterministic methods for nine of the eleven SEP plants located in the eastern and central United States.
Intensities for the earthquake 22 In addition, the fuel cladding, primary coolant boundary and containment would have to be breached before core inventories could be released.
. assumed to occur at or near the five sites located in the central U.S.
were constant ard somewhat higher (Intensity VII-VIII) the: the Staff nad heretofore taken as conservative for La Crosse (Intensity VII).
The resultant peak ground acceleration for all five sites was the same, 2
viz., 132 cm/sec which translates to 0.135g.23 According to the Staff, this somewhat higher result is overly conservative because it does not reflect the fact that La Crosse lies in an area of low seismicity and low seismic hazard in the Central Stable Region.24 We see no flaw in that judgment. We also agree with the Staff that difference! on the order of 0.01g are not significant and are lost within the scatter of estimation techniques.25 Moreover, we are aware of other factors in addition to those already discussec which would mitigate the effects of liquefaction, should it occur.
Among other things, LACBWR is a very small reactor producing only about four percent of the power of a modern reactor, with correspondingly lower fission product inventories, lower power densities, and consecuently lower fission product release even in case cf severe core damage.
Therefore, even were liquefaction to occur at the LACBWR site, it would present a lower overall risk of adverse impacts than would a larger reactor.
23 to Staff Aff. I, pp. 14-16, and Tables 1 and 2.
24 Id.. at p. 15; Staff Aff. II, p. 3 (response to Question 3).
25 Staff Aff. II, p. 4.
l l
.l 17 -
F.
Conclusions We agree with the Staff's conclusion (Staff Aff. I, p. 9) that, based on the methodologies used in the SEP seismic review, the SSE of 0.12g used to anchor a Regulatory Guide 1.60 design spectra which was used for evaluation of the liquefaction potential for the LAC 8WR site, is an adequate and conservativt description of the size of the SSE for that site.
Our conclusion (as our review) is limited at this time to liquefaction at the LACBWR site and does not extend to other seismic parameters which have not yet been reviewed by us.
Based on all the evidence before us and the factual findings and conclusions reached here and in our previous Partial Initial Decision (LBP-81-7, supra), we conclude that a dewatering system need not be installed at the LACBWR site to preclude liquefaction and any cor. comitant adverse effect on public health and safety.
a
. III.
ORDER Based on the foregoing, it is, this 21st day of April, 1983, hereby ORDERED 1.
That Dairyland Power Cooperative is neither required to submit a detailed design proposal for, nor to make operational, a site dewatering system to preclude the occurrence of liquefaction in the event. of an earthquake with peak ground surface accelertions of 0.12g or less, as proposed by the Order to Show Cause, dated February 25, 1980; 2.
That, in accordance with 10 CFR 99 2.760, 2.762, 2.764,26 2.785, and 2.786, this Initial Decision shall become effective immediately and shall coastitute, with respect to.the matters covered herein, the final action of the Commission thirty (30) days after the date of issuance hereof, subject to any review pursuant to the l
Commission's Rules of Practice.
Exceptions to this Initial Decision may be filed by any party within ten (10) days after service of tnis Initial Decision. A brief in support of the exceptions shall be filed within thirty (30) days thereafter (forty (40) days in the case of the NRC Staff).
Within thirty (30) days of the filing and service of the brief of the appellant 26 The immediate-effectiveness review by the Commission under 10 CFR 5 2.764 is not required for either type of proceeding under consideration here.
-~
,. (forty (40) days in the case of the NRC Staff), any other party may file a brief in support of, or in opposition to, the exceptions.
THE ATOMIC SAFETY AND LICENSING BOARD
$k.- A a 0- n) ).v v'
Charles Bechhoefer, Chairman ADMINISTRATIVE JUDGE
/
CC i
d)r. George C. Anderson l
ADMINISTRATIVE JUDGE O
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Ralph S. Decker ADMINISTRATIVE JUDGE I
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