ML20148G550

Responds to to Rc Deyoung Re Review of Site & Its Relationship to New Madrid Fault.Repts That Aslp Concluded Favorably on All Aspects of Plant Constr Permit Appl W/Copy of from Drs Nieto & Cording

ML20148G550
Person / Time
Site:	Callaway
Issue date:	11/03/1978
From:	Parr O Office of Nuclear Reactor Regulation
To:	Drey L AFFILIATION NOT ASSIGNED
References
NUDOCS 7811130107
Download: ML20148G550 (9)

Text

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% UNITED S T ATES y s* f' ; NUCLEAR REGULATORY COMMISSION

.J ) j WASHINCTON, D. C. 20555 O2SQ,f s.- ...

NOV 0 31978 Docket Nos. STN 50-483 and STN 50-486 Mrs. Leo Drey 515 West Point Ave. ,

University City, Missouri 63130 I

Dear Mrs. Drey:

Your letter, dated October 18, 1978, to Mr. R. C. DeYoung has been referred to me for a reply. In your letter, you (1) request certain documents relating to our review cf the site for the Callaway Plant, Units 1 and 2, (2) discuss the review of the Callaway site performed by our consultants, Drs. E. J. Cording and A. Nieto, and (3) refer to a recent radio program wherein the closeness of the New Madrid fault to the Callaway plant site was discussed. Our responses to your .

requests and to the comments made in your letter are presented in the following paragraphs.

In your letter, you refer to a letter, dated February 11, 1974, fron Mr. R. C. DeYoung to Mr. Nicholas Petrick, Executive Director of SNUPPS and requested a copy of the SNUPPS answer to that letter. The SNUPPS -

utilities in a letter dated October 29, 1973, requested the staff to review information regarding the characteristics of the four proposed SNUPPS sites, including the site for the Callaway plant. It was o understood that the review by the staff would enable the SNUPPS utilities to improve the quality of their Preliminary Safety Analysis Reports (PSAR) and thereby conserve staff manpower in the review effort. The February ll,1974 letter provided the staff's comments on the information supplied by the SNUPPS utilities. The SNUPPS utilities did not provide documentation which specifically addressed those comments but did consider the comments during the preparation of the PSAR's.

Our construction permit review of the four SNUPPS applications, including the Callaway application, was performed on the basis of the information provided in the SNUPPS PSAR's and the amendments thereto. As a result of our review of the Callaway PSAR and its amendments, we were able to conclude that the seismic design bases for the La11away plant are appropriately conservative for the earthquake potential at the Callaway ,

site. This conclusion considered the proximity of the New Madrid fault zone (Mississippi Embayment seismic zone) conservatively estimating

' that this zone comes no closer than 155 miles southwest of the site.

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1 Mrs. Drey fl0V 0 31978 The conclusions resulting from our review of the Callaway site are documented in the staff's Safety Evaluation Report (SER) for Callaway.

Copies of the Callaway PSAR, the staff's SER for Callaway, and Supplement No. I to the SER are available for public inspection at the V. S.

Nuclear Regulatory Commission's Public Document Room,1717 H Street, N. W. , Washington, D. C. 20555; at the Fulton City Library, 209 Market Street, Fulton, Missouri 65251; and at the Olin Library of Washington University, Skinker and Lindell Boulevards, St. Louis, Missouri 63130.

We are enclosing a copy of the October 2,1975 letter from Drs. Nieto and Cording as you requested. As indicated in that letter, Drs. Nieto and Cording concluded that while it is unlikely that large open cavities are present below the Callaway site which could cause subsidence or settlement, additional borings would be required to ascertain that no large cavities are present.

Subsequently in the Callaway Public Hearings on December 10, 1975, Dr. Cording stated that, based on additional information obtained from geologists with the Missouri Geological Survey, he concluded that the Callaway site was adequate without additional borings. Furthermore, both Drs. Nieto and Cording stated that they agreed with the staff's conclusion presented in Supplement No. 1 to the Callaway SER, that the potential for the existence of large cavities beneath the Callaway site was very remote and, therefore, does not constitute a hazard. As a result of the staff's and NRC consultants' evaluation, as discussed above, no additional borings were required.

In its Initial Decision, dated April 8,1976, the Atomic Safety and Licensing Board concluded favorably on all aspects of the Callaway plant construction permit application. Specifically with regard to postulated large cavities beneath the Callaway site, the Board found that the potential for subsidence at the site was remote and did not constitute a safety hazard. As a result of the Board's Initial Decision, we subsequently granted the construction permits for the Callaway plant.

We believe that the above information is responsive to your request.

Sincerely, b% hb Olan D. Parr, Chief Light Water Reactors Branch Nc. 3 Division of Project Management

' E ncl osure:

Letter, dated 10/2/75 from Drs. E. J. Cording and A. Nieto

'., ,. , . ALEERTO in L TO Elm /d:D o. ^ E D ! h ^,

000 technical Censultant Geotechoical ::'sul ant il3b Natural History , , 100? Pr/ fi.-

Urbana, il 61801 Champa ic,n , IL 618'O Phone: 217-333-1068 Phone: 217-333-6933 CISG 2 October 1975 1

i U. S. Nuclear Regulatory Cornission ATIN: Mr. Richard C. T'ullen Division of Technical Review I Wash ington , D.C. 20555

- REF: P0 DR 76-0296, Callaway Units 1 and 2

Dear Sir:

We have summarized in this joint letter repart the infer ;; tion re;uested in the referenced purchase order. We were requested to evalu?te "tha patential for subsidence or collapse et the plant site due to the possibili:/ of cavities below a depth of senral hundecd feet beneath the site." Specifically we were l asked to provide assistance to:

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) "(1) determine the r:axirum size void that could edst oithin the uppcr several hundred feet cnd rcmin undetected by the exploratory techniques at the site,.and (2) determine whether or not such a r:axirm ' cavit:. ceuld c.use surface subsidence or collapse under both static condi ticns and conditions imposed by the safe shutdown carthquale "

Our in'.estigation has been directed to.;ard evalue u.n ci ti.o potential for cavities br. low the base of the Callaway formation (belew a depth of approximately 150 ft).

1. Boring Information Twenty borings extended through the overlying Callaway For.:atien. Of these, six extended over 100 ft below the base of the Callauay Fr" ration.

Four of these six borinns (P-70, P-69, P-148, and P-/4) have been drilled to approxima tely 250 f t l'elow the base of the Callaway fonn ti n. P. 8 is 200

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.- U..S. lluclear Regulatory Commission 2 October 1975 I Page -Two-i ft from P-70, as is P-148 from P-74. A line connecting the first tuo l

boreholes is about 400 f t away from a line connecting the last two.

The spacing of the boreholes is large enough that there is little restriction on the position or maximum size of a cavity that might exist below the Callaway Formation. Thus the boring information does not directly

, indicate the absence of large caverns (approxinately 100 to 150 f t wide) at l the site. In order to conclude that large caverns are absent, several assumptions must be made regarding the geologic conditions under which caverns might form. We agree with the applicant that it is unlikely that large caverns exist in the Cotter-Jefferson City Formation. However, varying interpretations of the geologic information can be made, and we feel that arguments can be l

l advanced for the presence of open cavities below the Callaway Forntion at the site.

2. Airphoto Information Assuming cavities are present there is no evidence from airphotos of the plant site that the features have propagated to the surface and formed sinks. Any sinks that may have formed in the past have existed long enough to be filled and or er ded so that triey are no . longer discernable. Thus it is probable thc rge open cavities are either not present or if present ha'ic been st kce a pericd of time isngcr than !".c time requ: red to 'i!'

or erode the sinks at the surface.

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U. 5. I!uclear Regulatory Comission 2 October 1975 Page -Three-

3. Cotter-Jefferson Citv Forma tion Core recovered below the base of the Callaway reveals the presence of at least two paleokarst features in the Cotter-Jefferson City. These features have estimated diameters of 250 and 150 feet and thicknesses of about 100-150 fc>t. The fill in the features is St. Peter sa'ndstone with 30-50 f t of paleo-karst rubble lining the lower portion. Several of these features are exposed 1

in the bluffs along the Missicur River. The applicant indicates that no open cavities greater than a few inches were observed during drilling in the

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Cotter-Jef ferson City at the site or in the plant area.

Core recoveries and RQD were high. Although no open solutico features were observed in the Cotter-Jefferson City at the plant site, it should be noted that the exploration and exposures of the Cotter-Jefferson City have been linited. Solution features are known to exist in the Cotter-Jefferson City within less than 80 miles' of the site. '

4. Gasconade Formation The Gasconade Formation appears to have a greater tendency to develop open solution cavities than the Cotter-Jefferson City. At the site, the Gasconade Formation is located below the Cotter-Jef ferson City at a depth of 700 f t. It is possible that solution cavities have developed in the Gasconado due to deep ground water flow of undersaturated water.

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'5. Size and Depth of Cavities That Could Cause Surface ."ns : ents The range of cavern widths that are of concern at the site is estimated to be 100 to 150 ft. Most existing caverns have spans less D

U. S. Nuclear Regulatory Comission 2 October 1975 Page -Four-l ,

than 150 ft. It is estimated that the span of the cavern would have to be greater than 100 f t for a cavern collapse to proceed up through rassive-bedded Callaway Limestone.

The depth to the roof of caverns that might cause subsidence or sinks aL the ground surface is estimated to be 400 f t, assuming that the largest cavity beneath the site would have a height of 100 f t and that progressive collapse of the cavity would result in 25% bulking of the debris. It is therefore considered that any solution cavities that might exist in the Gascona, ,

formation, will not result in subsidence at the ground surface.

l Propagation of cavities toward the surface could result from:

1. increase in cavity span by solutioning

2. removal of bouyant forces in cavern (lowering of ground water table);

seepage in roof

3. solutioning along roof joints ,

4. seismic activity

5. time-dependent sagging and slabbing of walls and roof.

The additional load placed on deep cavities by the structures at the Callaway site will not significantly change the stability of the caverns. ,

Conclusion l 6.

l It is unlikely that open cavities are present belou the Caiiauiy l

,. Formation that will cause subsidence or settlement at the ground surface.

Houever, taking a pessimistic view of the geologic evidence, the presence of large caverns in the Cetter-Jef ferson City can be postulated.  !

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U 3. Nuclear Regulatory Comission 2 October 1975 Page -Five-There are few deep borings in the vicinity of the reactor vessels, and the spacing of deep borings is such that there is only a small probability that one of the borings would have intersectcJ a cavern of 100 to 150 f t.

Solution zones connected to the caverns coul,d also be missed by the deep borings. In order to determine that no large caverns, that could cause subsidence at the surface, exist below critical structures, borings spaced on I the order of 100 f t apart and extending to a depth of 450 f t would be required. In the vicinity of each containment vessel, approxiccately 6 to 8 additional borings would be required, in a pattern extending out 40 f t beyond the perimeter of the reactor.

We have considered the possibility of installing a monitoring system to provide early warning of a potential collapse .or surface settlement. It is our conclusion that the effort required in installing a r.onitoring system is equivalent to that required, for direct exploration. We therefore recom end the boring alternative. Appendix A summarizes our conclusions regarding an instrumentation system.

This report is intended as a summary or our investigation, ue will be happy to p avide more detail on the various aspects of this problem.

Sincerely yours, .,

J ) .? / '

AN/MC4/M. $$$!% /

Edward J. Corping b//N[GyQ Alberto S. Nieto EJC/jrm l

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Appendix A:  !!onitoring i

It is our conclusion that surface bench marks do not provide adequate warning becau~.0, by the time surface novements are occurring, the possibility of imminent collapse is likely. For very large mined areas, a wave of syrface subsidence precedes collapse, so that warning can be obtained at the ground surface. For sinks where the depth is great with respect to the diameter, the sink will rapidly reach the ground surface once surface movements are

. observed. Deep anchors in and below the Callaway would provide earlier warning because they would be nearer the source of movement and would be more precise and interpretable at an earlier date. Rod-type extensometers 150- f t deep would be required. Extensometers of such length have been installed on several projects to monitor displacements with a precision of 0.01 in, or better. The techr.iques of installing and using such extensometers are well established.

If the stoping process were very rapid -- then even extensometers would not be adequate. A case has been observed where a 200 ft x 200 ft room and pillar mined area broke vertically 350 ft to the surface through Mississippian shales and limestones in a period of less than i day (probably less than ar hour). The collapse was thought to have been ' triggered by the overloading of the pillars. One pillar failed resulting in overloading and failure of the others. Collapse to the surface was rapid because the roof had a factor of safety considerably less than one once the pillars were gone.

The liiass failed witii very lii.tle bulking. Ai. icosi. 50.5 of the volun:e ui the 15 ft high cavern developed in the sink at the surface.

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For the case of a solutiori cavern that has been stable for a long period, the progression of the cave to the surface should proceed over a longer period, by sag and slabbing of individual beds. Thus conitoring could

be carried out with deep extensometerr, located over the cas.;/. Existing caves show evidence of progressive siahbing. Pronressive failures can also be observed mines and tunnels. In one abr ed railroad tunnel, in Pennsylvanian 'es and sandstones the rool ,obed upward 30 ft above the c rown, form #

ft-wide chimney,and stabilized against a thicker sandstone layer.

Extensometers would provide warning for caverns that are below the

. boring depth. (However, as explained earlier, we feel that borings to 450 f t will provide adequate depth exploration for potential caves). Extensometers with multiple anchors would provide some warning for caves away from the borehole which could influence structure. However the evidence is that the sink would proceed almost vertically until it encountered the shallow soils. The exten-someters would record very little movement if a cavern adjacent to the extensoneters was propagating vertically to the surface. Thus it is con-cluded that the extensometers would not provide inforret ion n addition to that obtainable from borings.

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