ML20197F345
| ML20197F345 | |
| Person / Time | |
|---|---|
| Issue date: | 05/02/1986 |
| From: | Knapp M NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| To: | Themelis J ENERGY, DEPT. OF |
| References | |
| REF-WM-58 NUDOCS 8605150535 | |
| Download: ML20197F345 (6) | |
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PS Justus J0 Bunting JT Greeves Mr. John G. Themelis, Project Manager EF Hawkins,- URF0 Uranium Mill Tailings Project Office DM Gillen U.S. Department of Energy
- GN Gnugnoli Albuquerque Operations Office B Jagannath P.O. Box 5400 Albuquerque, New Mexico 87115
Dear Mr. Themelis:
In response to your submittal of Modification Number 2 to the Shiprock, New Mexico Remedial Action Plan, we have reviewed the proposed changes (8-12) which all relate to erosion protection design.
In general, we find that the proposed design changes are acceptable. Upon our receipt of your transmittal of the appropriate signature page, we will execute our concurrence.-
In addition, we have reviewed your related submittal addressing the failure of select rock material to meet specification requirements concerning the ratio of particle thickness to particle length. We conclude that the infomation provided is not sufficient to demonstrate that the Type B and Type B1 rock gradations are acceptable.
Our examination of the riprap test data' indicates that the single test performed to determine the gradation of Type B riprap may not be representative of the rock that will actually be placed. This conclusion is based on the following:
1.
The sample tested contained only 16 individual rocks and had a weight.of only 154 pounds; such a sample is probably too small to be meaningful.
2.
The sample tested contained two rocks which weighed about 25 pounds each and two rocks which weighed.about 17 pounds each. The NRC staff is not aware of the widespread availability of such large rocks in the immediate site area. Additionally, the presence of these four large rocks may have distorted the gradation curve significantly.
The NRC staff recommends that additional gradation testing be performed to conclusively document the rock gradations that.are currently available at the site. Two additional tests should be performed for each representative Type B and Type B1 riprap (total of four tests).
If the representative rock is found once again to be significantly larger than required by the specifications, the.
rock gradation specifications should be modified to allow the placement of this larger, locally available rock. Furthermore, with.use of larger rock,-
i consideration could be given to additional design modifications that might-effect significant reductions in rock quantities. An NRC construction site-8605150535 860502 PDR WASTE WM-58 PDR 7
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visit has been planned for the week of May 5,1986. This would be an ideal time for the tests to be conducted, since NRC staff would be available to verify the representativeness of the rock samples tested. Appropriate DOE and Remedial Action Contractor staff have been contacted and have agreed to perform these tests during the site visit.
On a final note, we have completed our review pertinent to the Shiprock conditional concurrence issue on seismotectonic characterization. After reviewing the submitted supplemental seismic studies, the staff concluded that a 6.2 magnitude earthquake resulting in a peak horizontal acceleration of 0.21g
- ,hould be applied at the Shiprock site rather than the magnitude 5.7 proposed in the studies (see enclosed review).
Following this review conclusion, additional evaluation of dynamic slope stability was obtained from staff of your Technical Assistance Contractor (TAC). Based on a review of this information, the staff concurs with your conclusion that over the long-term, the remediated tailings pile slopes will remain stable even with the revised MCE event.
If you have any questions regarding these issues, please contact myself (FTS 427-4433) or Daniel M. Gillen of my staff (FTS 427-4160).
Sincerely, M
Malcolm R. Knapp, Acting Chief Low-Level and Uranium Recovery Projects Branch Division of Waste Management Office of Nuclear Material Safety and Safeguards
Enclosures:
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DATE. :4/30/86
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Enclosure REVIEW OF " SUPPLEMENTAL SEISMIC STUDIES PERFORMED IN SUPPORT OF THE REMEDIAL ACTION PLAN AT THE SHIPROCK TAILINGS SITE" The conclusion of the DOE document reviewed is that: "It is... recommended that the seismic design parameters employed during pile design not be modified or reevaluated at this time." Whereas the validity of this conclusion ultimately depends on engineering considerations, our review of the geotechnical aspects of the issue leads us to conclude that the proposed maximum credible earthquake of magnitude 5.7 for the Shiprock site is not jus:ified and therefore not acceptable. Our reasons for this conclusion are the following:
- 1) Table 1 of Algermissen et al. (1982) indicates that the maximum magnitude for the Colorado Plateau (Algermissen's source zone no.16) should be 6.1.
Using Algermissen's relationship for magnitude as a function of intensity, M =
1.3 + 0.6I, a magnitude 6.1 would be the equivalent of Modified Mercalli Intensity 8fI = 8.
This is near or slightly above the maximum intensity observedwithi8theColoradoPlateauduringitsbriefhistoricalperiod.
It would not be overly conservative to assume a somewhat higher magnitude value since the period of performance is significantly longer than the historical period.
?) In its assessment of the seismic hazard of two potential sites for the disposal of high-level radioactive waste in the Paradox Basin of the Colorado Plateau, the DOE (1984) identified structures capable of generating earthquakes with magnitudes as high as 6.5.
The presence of such structures within the plateau, and the fact that surface ruptures or other geomorphic manifestations of earthquakes in the 6.0 to 6.5 magnitude range may be muted by a few decades to a few centuries of erosion, gives rise to the possibility that such an earthquake may have occurred despite the lack of any existing structural deformations.
( 3) Preliminary estimates of the MCE by the DOE / TAC for other uranium mill tailings sites in in the vicinity of the Shiprock site are given as Weeks of Sergent, Hauskins & Beckwith, 1986, personal communication)_6.2 (R.
Based on the above infomation, we consider that a value of 6.2 for the magnitude of the maximum credible earthquake for the Shiprock site is. justified and would be reasonable and acceptable.
The peak horizontal acceleration resulting at the site from a 6.2 magnitude earthquake occurring at a distance of 15 km is 0.21 g (using Campbell,1981, 84th percentile values in accordance to criteria in NRC's UMTRAP Standard Review Plan).
Engineering considerations would detemine how the seismic coefficient derived from this number compares with the present 0.13 g design acceleration for the pile.
It should be noted that the DOE document endorses the use of mean maximum acceleration values in rock derived from Schnable and Seed (1973) but does not provide a adequate rationale for the adoption of a mean maximum acceleration value of 0.13 g as f'or the Shiprock site.
Figure 5 of Schnable and Seed (1973) indicates that an earthquake of magnitude 5.7 yields a mean maximum acceleration value in rock of 0.13 g at a distance of approximately 25 kilometers. The DOE document does not justify why this distance was chosen to detemine the acceleration for the site. At 15 kilometers, which is the site-to-source distance recomended by NRC in the UMTRAP SRP for "fluating earthouakes," the mean value for the acceleration from Schnable and Seed would be about 0.21 g.
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In regard to the characterization of geologic structures in the region of the site, we find that, although the investigations undertaken precede the formulation of NRC's UMTRAP SRP and DOE's Technical Approach Document (TAD),
DOE's studies are commensurate with the criteria stipulated in the SRP and are therefore acceptable. We would like to note, however, that the information in the Supplemental Seismic Studies document itself was inadequate to enable us to reach this determination as it lacks supporting documentation on the details and scope of the investigations undertaken. Our findings, therefore, rely on additional information supplied by the DOE / TAC during the course of the review.
This information, now on file in the Document Control Center, consists of the following:
a) Comprehensive NOAA Earthquake Data File for the Colorado Plateau.
b) Province boundary map.
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, c) Notes and discussion of the observations made during aerial reconna.issance, field investigations, and photogeologic interpretations, d) Clarification of the numbered references associated with fault listings.
e) Clarification of the specifications of the Landsat imagery used for photointerpretation (multispectral scanner, band 4).
In regard to item (a) specifically, it should be emphasized that NRC reviewers need to have reasonable assurance that the scope and nature of the investigations undertaken by DOE are adequate to support a particular finding.
Supporting information is particularly important when negative conclusions are presented regarding the presence of capable faults in the region of investigation. To this end, detailed notes of the field observations made (from aerial or ground reconnaissance, photogeologic interpretations, etc.)
with dates, names of the investigators, locations examined, geologic descriptions of formations present, etc., should be compiled. The notes should be written so as to be interpretable by other geologists. Selected field notes r
and other supporting information that DOE considers important and illustrative should accompany the primary document sent to NRC for review. Additional supporting information should be retained and made available to NRC on request.
In the future, NRC reviews of UMTRAP documents could be expedited and facilitated if the types of information deficiencies encountered in this review were remedied.
As a final comment, in regard to item (e), we would like to note that the use of Landsat multispectral scanner (MSS) bands 6 and 7, rather than band 4, is considered preferable for obtaining structural geologic information (Carter, 1976).
It is recommended that DOE use MSS band 6 or 7 imagery in performing geologic characterization at other UMTRAP sites.
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- REFERENCES CITED
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Algennissen, S.T., D.M. Perkins, P.C. Thenhaus S.L. Hanson, and B.L. Bender, 1982, "Probabilistic Estimates of Maximum Acceleration and Velocity of Rock in the Contiguous United States," U.S. Geological Survey Open-File Report 82-1033, Washington, D.C.
Campbell, K.W., 1981, "Near-Source Attenuation of Peak Horizontal Acceleration," Bulletin of the Seismological Society of America, vol. 71,
- p. 2039-2070.
Carter, W.D., 1976, " Structural Geology and Mineral-Resources Inventory of the Andes Mountains, South America," in Williams, R.S., Jr. and W.D. Carter (eds.) "ERTS-1, A New Window on Our Planet," U.S. Geological Survey Professional Paper 929, p. 92-98.
Schabel, P. and H.B. Seed, 1973, " Accelerations in Rocks for Earthquakes in the Western United States," Seismological Society of America Bulletin, vol. 63, p. 501-516.
U.S. Department of Energy, 1984, " Draft Environmental Assessment-Davis Canyon Site, Utah (DOE /RW-0010)," Washington, D.C., p. 6-108.
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