ML20198C848
| ML20198C848 | |
| Person / Time | |
|---|---|
| Issue date: | 10/17/1985 |
| From: | Knapp M NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| To: | Higginbotham L NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| References | |
| REF-WM-58 NUDOCS 8511120198 | |
| Download: ML20198C848 (5) | |
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SUBJECT:
REVIEW 0F DOE RESPONSE PERTINENT TO SEISM 0 TECTONIC CHARACTERIZATION AS A CONCURRENCE CONDITION IN THE SHIPROCK RAP. In response to TAR-85840, we have reviewed the DOE response pertinent to seismotectonic characterization as a concurrence condition in the Shiprock RAP. Along with other conditions, NRC's conditional concurrence in the Shiprock RAP (letter from L. Higginbotham to J. Themelis, 6/6/85) provided that, prior to complete concurrence, DOE address the deficiencies identified in the seismotectonic hazard characterization for Shiprock. The present DOE response does not satisfy this concurrence condition, but describes how DOE proposes to do so. We consider that the information submitted for review has been superseded by the September, 1985 Seismic Hazard Assessments chapter of DOE's UMTRAP Design Manual, which will govern the scope of DOE investigations at Shiprock as well as other sites. Therefore, the attached review comments pertain to the aforementioned version of the Seismic Hazard Assessment chapter, transmitted to NRC by DOE at the September 27th DOE-NRC Group II (Geotechnical Stability) meeting. WMGT reviews of the DOE responses to the groundwater contamination and erosion protection concurrence conditions have been addressed in previous memos. This review was prepared oy Jose' Valde's and Michael Blackford. Malcolm R. Knapp, Chief, WMGT Division of Waste Management
Enclosure:
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N 1 Attachment Comments Section 1.0, Page 1, Paragraphs 1 and 2 It is stated that geologic studies provide an initial set of earthquake design parameters that includes an on-site peak horizontal ground acceleration value. It should be stated clearly where this acceleration is considered to occur, - 1.e., at the site, at the surface or at some depth below the site. It should also be stated whether or not the effect of local geologic conditions, which, according to paragraph 2, constitute part of further engineering analyses, are included in the determination of this acceleration. Section 2.0, Page 2, Bullet 4 It is :tated parenthetically in the description of the macro-seismicity characteristics of a capable fault that earthquakes of magnitude 3.5 or greater constitute such seismicity. This assumption gives undue weight to the size of earthquakes at the expense of other parameters, such as rate of activity or persistency,_that help to describe macro-seismicity. The NRC staff considers macor-seismicity to be a level of seismicity that implies significant, sustained, and coherent tectonic activity representative of major deformational moverent movement within the earth's crust. Thresholds tc define this level of seismicity are neither stated nor implied in 10 CFR 100, Appendix A. The parenthetical magnitude value in item b of this bullet should be removed in order to eliminate any misinterpretation of the significance of this artificial threshold. Section 3.0, Page 4, Bullet 1 It is stated tht the pertinent data to be acquired and interpreted to define seismotectonic hazards at a site "...will include existing maps which delineate capable faults and bedrock faults of any age..." As " capable fault" and " bedrock fault" are not mutually exclusive terms, the meaning and intent of this statement could be made clearer by replacing " capable faults and bedrock faults" with the term " faults."
1 T 2 Section 3.0, Page 4, Bullet 3. It is stated that a 200 kilometer radius was selected as the radius for investigations of seismicity so that any seismic event which could have caused detectable on-site ground motion will be included in the compiled record. Since seismic events more distant than 200 kilometers from the site can cause detectable on-site ground motion, it is suggested that this statement be clarified by including some minimum threshold ground motion for events beyond 200 kilometers so as to limit the compilation to earthquakes that can significantly affect the site. It is also stated in this bullet-item that "all earthquake data files, epicentral listings from state-maintained seismic nets, and available microseismic data will be obtained and evaluated." The term " state-maintained" is unclear, or at least limiting, in the consideration of available seismic data. A more general phrase (such as: "To the extent practicable, all federal and state, as well as privately or commercially available earthquake data bases ... ) could be used to describe those data bases expected to be obtained and evaluated. Also, care should be taken in using the term " microseismic" so that there will be no confusion as to whether the user is referring to microearthquakes or microseisms. Section 3.0, Page 4, Bullet 4. It is stated that the seismic records for provinces within 200 km of the site will be analyzed "and the maximum recorded earthquake for each province will be identified." We would like to emphasize that it it the maximum recorded earthquake not associated with a known tectonic structure that is of concern in determining the largest floating earthquake for a given province. It is also stated in this bullet-item that: "For outlying provinces, the credible earthquake will also be identified." The meaning of the term " credible earthquake" needs to be stated. Section 3.0, Page 4, Bullet 5. It is stated that, in plotting all photogeologic lineaments or geomorphic features indicative of an active seismic setting, " specific attention will be paid to active fault or bedrock fault traces indentified by previous investigators." As " active fault" (which has various meanings) and " bedrock fault" are not mutually exclusive terms, the intent and meaning of this
T 3 statement could be made clearer by replacing " active fault or bedrock fault traces" with simply " fault traces." Section 3, Page 4, Bullet 6. 'In this and other parts of the document the term " floating earthquake" is used rather ambiguously and inconsistently. In referring to the maximum floating earthquake within a given arovince, it would be advisable to use the term " largest floating earthquace." The term " controlling floating earthquake" (as used in section 3, page 5, bullet 7) should be consistently and explicitly used in referring to that floating earthquake which, from amongst all the largest ^; floating earthquakes for different provinces, yields the largest on-site peak horizontal ground acceleration. Explicit use of these terms, rather than merely " floating earthquake," would help clarify ambiguities in meaning. Section 3.0, Page 4, Bullet 6 It is stated, with regard to determining "the magnitude of the [ largest] floating earthquake within each province," that its magnitude "will not be less 4 than the largest recorded event not associated with a known structure." NRC l suggested at the September 27th Group II meeting that the word " recorded" be dropped from the term " largest recorded event." We would like to further elaborate on our rationale for suggesting this change. Specifying the use of " recorded" earthquakes would exclude from consideration any paleoseismological data that may indicate prehistoric seismic activity, of inferrable intensity, not associated with an established tectonic structure. Obermeir and others (1985), for example, have found that. late Quaternary sand blows in the area of Charleston, South Carolina, indicate at least two prehistoric earthquakes with shaking severities comparable to the recorded 1886 event. To the extent that they may be available or reasonably ~ obtainable, paleoseismological data may thus permit the extension of the existing seismic record and allow for a more accurate determination of the magnitude of the largest floating earthquake in a given province. Section 3, Page 5, Bullet 7. The term " design acceleration" is used in the last sentence of this bullet-item ~without prior' definition'in the text, though it is later referred to (section 3.0, page 6, bullet 10) as "the largest on-site acceleration." Notwithstanding the latter, it.is implied in this bullet-item that the " design acceleration" is
1 4 4 equivalent to that associated with the controlling floating earthquake. This implication arises from the statements that: "All fault systems which could produce accelerations in excess of the [ controlling] floating earthquake value a will be.further analyzed. Any faults _which appear capable of producing the
- design acceleration will be subject to the actions discussed...."
It is NRC's recommendation that the term " design acceleration" be restricted to the; actual acceleration value for which the pile is to be designed. This value + should reflect the largest peak horizontal acceleration at the site associated with either the controlling floating earthquake or a capable fault, as well as any amplification effects associated with subsurTace materials. Section 3.0, Page 5, Bullet 8. ItLisstatedinregardtofaultstudiesthat ... reconnaissance will be performed for~the critical faults identified as being potentially capable of producing the design acceleration." NRC's views on the. usage of the term " design acceleration" are detailed in the comments on section 3.0, page 7, bullet 7. NCR also recommends that the term " critical faults" be eliminated ' from this and other statements in the text. Though it is apparent, within the 7 context of the document, that the term refers to faults that may cause accelerations at.the site equal to or greater than that produced by the controlling floating earthquake, confusion or misuse may arise if the term is used out of context. 4 REFERENCE CITED Obermeier, S.F., G.S. Gregory, R.E. Weems, R.L. Gelinas and M. Rubin, 1985, " Geologic Evidence for Recurrent Moderate to Large Earthquakes Near Charleston, South Carolina," Science, vol. 227, p. 408-411. 4 l.- l I + ,v., ~r- _. -, - - -}}