ML19312D278

Order to Show Cause Directing Licensee to Submit Detailed Design Proposal for Site Dewatering Sys to Preclude Occurrence of Liquefaction in Event of Earthquake & Make Sys Operational

ML19312D278
Person / Time
Site:	La Crosse File:Dairyland Power Cooperative icon.png
Issue date:	02/25/1980
From:	Harold Denton Office of Nuclear Reactor Regulation
To:	DAIRYLAND POWER COOPERATIVE
Shared Package
ML19312D276	List: ML19312D275 ML19312D278
References
NUDOCS 8003240108
Download: ML19312D278 (10)

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UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMISSION In the Matter of DAIRYLAND' POWER COOPERATIVE (La Crosse Boiling Water Reactor)-

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Docket No. 50-409

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ORDER TO SHOW CAUSE 4

I.

Dairyland Power Cooperative (DPC or licensee), La Crosse, Wisconsin, is.the holder of Provisional Operating License No. DPR-45, issued on August 28,1973, which authorizes the operation of the la Crosse Boiling Water Reactor (LACBWR),. located in Vernon County, Wisconsin.

LACBWR i s

. a direct-cycle, variable-flow forced circulation-boiling water. reactor,

.which is. designed to operata at a rated power nit in excess of 165

. rnega' watts thennal..

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, II.

In June 1978 the NRC staff initiated a review of the geology and seismology of the LACBWR site in connection with the Systematic Evaluation Program-(SEP). The SEP is 'a program under which the safety margins for eleven of the older operating plants are being reassessed. A brief review of the information on the LACBWR docket raised some questions regarding the stability of the underlying soils during earthquakes.

The NRC contracted.he U. S. Army Engineer Naterways Experiment Station (WES) to perform an analysis of the potential for liquefaction of the soils under conditions of seismic ~ stress.

WES made appropriately conservative assumptions to analyze the then existing soils data. Since the SSE has yet to be established under the SEP, the WES analysis treated the seismic acceleration parametrically.

The WES analysis concluded in December 1978 that the soils below the LACBWR site could strain badly for an earthquake producing a ground surface level peak acceleration of 0.12g1/, and excessive strains and liquefaction would occur for ground surface level peak accelerations of 0.2g or greater.

-1/ DPC has. designated this value as the SSE in their October 9, 1974 Full Term License Application.

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g 1The'NRC staff's assessment of the WES analysis. indicated that the then available soils data'wasiinadequate to accurately estimate the Lliquefaction resistance,-principally because it was based on questionable Standard Penetration Tests (SPT)-and remolded soil samples, rather than

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, undisturbed sarp?as. IIn! addition, the staff' concluded that the assumptions Eregarding seismicity.at the site lwere conservative.. For these reasons they concluded at the time that continued _ operatio" 3 the LACBWR plant for a reasonable. length-of time would ~not present a hazard to the health and safety of the public., However,Lto attain a long term resolution of the liquefaction issueithe staff concluded that a thorough investigation should be undertaken, including an effort to obtain soil samples that more accurately represented the, true soil l characteristics.

In January and February 1979, we met with the licensee -in Bethesda,

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- Maryland, to express the staff's concerns. The licensee agreed to initiiate

-al soils properties investigation program, subject to NRC approval.

The program 11ncluded ' additional test borings at the site to obtain undisturbed samples, SPT, laboratory testing of' samples (cyclic triaxial tests), and

. variousianalyses techniques to determine the resistance of the soils to

liquefaction. -The proposed program was received in March and was approved, with some ' modifications, by; NRC on April -30,1979.

The. preliminary results from the soils properties investigation program were provided to the NRC11n late August 1979, and the final report

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~ entitled " Liquefaction Poten* C c La Crosse _ Boiling Wat / Reactor _ (LACBWR)

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.l 4 Site' Near Genoa, lVernon ' County, Wisconsin," dated September 28,1979, l

.~was-presented to_ the NRC staff in a meeting with DPC on October 17, s

1979. c.This; report concluded."that; a threshold liquefaction resistance lesel<for the LACBWR site corresponds to.an SSE producing an acceleration between 0.18g and 0.20g ~at the. ground: surface." However, based on a

' review of -the soils data ' presented in 'this' report, the NRC staff has concluded that-if. sustained strong ground motion with peak accelerations c off.12g or higher occurs:(normally associated with a magnitude 5 or greater earthquake within 10 km of the site) liquefaction can occur at the LACBWR' site.down to a depth of 40 feet. Below.08g, the staff has concluded that there is-little potential for liquefaction. These conclusions are based on our. comparison of this site with non-nuclear sites where liquefaction has occurred and on'the use of laboratory strength data.

The September 28, 1979 report submitted by DPC used results of undrainei cyclic triaxial tests and dynamic stresses. computed using the computer co'de SHAKE to assess the -liquef action potential at the _ site.

LThe;NRC staff;and its consultant, WES, believe that -the soil strength curves determined in the laboratory and used.in this analysis are not

-a'dequately conservative;for the following_ reasons. Our experience -is 1that loose cohesion'ess' material densifies when sampled, and'this

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densification,may be.as. great ~ as 2Lto 3 lo/cu ft. Data provided in the l

DPC report' indicatss that the specimens -further densified.an additional

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[2 to 3 lb/cu ft.from the frozen' condition to the thawed.'ind consolidated condition in the lab ~ oratory. - This indicates a totalfincrease in density

. that could:be'as great as'4 to 6 lb/cu ftnfrom the in situ condition, and

.we est mate 1t at ~t e pro ab ble. total increase in; density is 3 to'4 lb/cu ft.-

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l LThisrisid' substantial change in density considering that the minimum

? density reported was approximately 97 lb/cu ft and the maximum density capproximately 11.4 lb/cu ft.. This' increase in density has not -been f taken-into account in the results presented in the September 28 report..

I' :is the NRC staff's conclusion that-correction for this increase in t

density would substantially reduce the DPC. reported factors of safety

> against -liquefaction.-

In addition, if the SPT N values presented in this report are-

' corrected to;an overburden pressure of 1 ton /sq ft and then compared

.with' the empirical correlations between'N values. and the liquefaction occurrence at-Niigata, Japan,; liquefaction can occur in foundation soils

below the' water table down to a depth of about 35 ft. Low factors of-safety are indicated ~ from 35 ft down to a depth of about 40 ft.

Therefore, based on our judgment concerning the density and

.. strength data,- on the analysis submitted-by DPC,.and on comparisons

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of the SPT data-with liquefaction and.SPT correlations, we have 4

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Leoncluded that the soils at-the LACBWR site' below the water table down

.to a<aepthlof 'approximately 40 ft:could oe subject tofliquefaction if

.theilicensee designated ' safe shutdown earthquake with a peak acceleration.

'of.0.12g occurs..The staff has not yet established' the SSE value but

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expects.to do-so by the spring of.1980: consistent with the setting of suchia value for other SEP ' plants.

Based on our-consideration of the data suomitted by DPC, we have'

' concluded,thatta potentially hazardous condition ray exist at the LACBWR site with Lrespect to continued operation off the plant for an~ extended period of -tine.

For.this reason, the NRC ' staff has made an estimate of -the proDaoility

' of exceecing a range -of peak accelerations at tne LACBWR site in orcer to make an estimate ofl the ~hazara associatec with-the liquefaction potential.

In doing iso, we utilizeo all' readily 'available estimates of earthquake proDability tnat included the site region. These were estimates taken

.from Milne and Davenport-(1969), Algermissen and Perkins (1976), the Appliao Technology. Council (1978), the Haven Site Preliminary Safety

. Analysis Report.(1978),.und-preliminary results from the Systematic -

Evaluation-Program -(SEP) probabilistic. study of the LACBWR ~ site.

Based'onLour review'of,the prooabilistic stucies listed aoove, tne return period for.12g would be Rat least 1,000 years. This~ peak' accelerations (.129) is equivalent to IntensityL VII when-utilizing the-relationsnip of Trifunac ano Bracy (1975)~. TneLreturn perioc.

1.for.08 would'be-at.least 400: years.' Tnese values' are based upon 9

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(the. minimum return period calculated in the above studies. While these

values'sh' uld not be interpreted as

absolute minfrums, the actual. return o

period.could be an order of magnitude larger.

' Based on these estimates of return periods, we have concluded that the general level of seismic hazaro at the LACBWR site is sufficiently low..that operation of the plant for the' next twelve months would not

endanger;the health and' safety of the public.

LIn our meeting of November 2,1979, OPC committed to consider

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various options to mo'dify the site soils to preclude the occurrence ofDliquefaction in the event an: earthquake with a peak acceleration m

of 0.12g' occurs. ' Byfletter dated November 29, 1979, OPC submitted-La concept'ual design of a dewatering system for the LACBWR site to-preclude liquefaction. Our preliminary review of the proposed dewatering system indicates that' it is a feasible solution to the liquefaction issue at LACBWR..However, since the final design has not yet-been. developed.nor submitted to the NRC, we are unable to determine conclusively that the. proposed system will preclude liquefaction for earthquakes with peak accelerations.-of 0.12g or less.

In addition, we 'are unable to-conclude at this time that installation of such a

. system would not: create.the potential for a related but somewhat Ldifferent concern 'at -the site, e.g., settlement or the creation of cavities 1 that might? effect safety-related structures.

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III..

LForithe reasons set lforth in Section II above, and pursuant to. the

- Atomic' Energy Act' of 1954,- as amended,' and the Commission's regulations lin110 CFR Parts'2 and 50, IT IS-HEREBY:0RDERED THAT the licensee show cause, in the manner hereinaf ter provided, wh'y the licensee should not:

1. -as soon as_ possible,' but no later than May 27, 1980, submit a' detailed design proposal for a site-dewatering system to

. preclude.the occurrence of liquef action in the event:of an earthquake with peak ground surface accelerations of 0.12g or.less.. The proposal shall, as a minimum, contain:

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Detailed engineering drawings and a system description.

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The results of any testing _ and analyses needed to establish the efficacy of such a system, c.

Proposed Technical Specifications pertaining to the availability and surveillance ofz such a system.

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Information that demonstrates that no adverse effects on existing structures,-systems and components important to safety will result from the installation and operation off the proposed system.

2.1 uas soon as possible after NRC approval of the dewatering system-

identified above. but no later than February 25, 1981, make such

. system operational..or place the LACBWR in a safe-cold shutdown condition.

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"IV.

s For further. details ~regarding-this action, persons should see the staff's letter dated October 30, 1979, to the licensee and enclosures-1 and 2 thereto,

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la Dames and Moore Report dated September 28,'1979 " Liquefaction Potential 3

at La Crosse Boiling Water Reactor (LACBWR) Site, Near Genoa, Vernon County, Wisconsin,"!a~nd theilicensee's letter to NRC dated November'29,1979. These-documents: a'nd other ' pertinent information relative to this issue are available for public: inspection at the Commission's Public Document Room,-1717 H Street, N. Tl., Washington, D. C. and at the La Crosse Publ.ic Library,_800 Main Street, La Crosse, Wisconsin 54601.

V.

The licensee.may file a written answer to this Order under oath or affirmation within twenty-five (25) days of the date of this Order. Upon f ailure of the licensee to file an answer within the time specified, the Director of Nuclear Reactor Regulation will, without further notice, issue an Order' suspending License No. _DPR-45.

The licensee or any other person whose-. interest = may be affected by this Order may request a hearing within twenty-five-(25)' days of the date of the Order.

Any request for a hearing shallLbe addressed 'to the Director, Office of Nuclear Reactor Regulation,

' U._ S. Nuclear-Regulatory Commission, Washington, D. C.

20555. :If a hearing 4

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is requested by a person whose interest may be affected by this'0rder, the Comission will' issue _an, order designating the time and place of any such hearing.'.In the event a hearing is requested, the issues to be considered at such hearing shallLbe:

(1)L Whether tk licensee should submit a detailed design proposal for' a. site dewatering system; and:

(2) Whether the licensee should make operational such a dewatering

- system-as _soon' as possible after NRC approval of the system, but no later than February 25,1981, _ or. place the LACBWR in a

- safe cold shutdown condition. -

FOR-THE NUCLEAR REGULATORY COMMISSION Harold R. Denton,- Director Office of Nuclear Reactor Regulation-Dated at 'Bethesda, Maryland

- this 25th day 'of February,1980.

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