ML20024H391
| ML20024H391 | |
| Person / Time | |
|---|---|
| Site: | Oyster Creek |
| Issue date: | 04/23/1991 |
| From: | Dromerick A Office of Nuclear Reactor Regulation |
| To: | J. J. Barton GENERAL PUBLIC UTILITIES CORP. |
| References | |
| TAC-79166, NUDOCS 9106030240 | |
| Download: ML20024H391 (4) | |
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4.
In GE Report Index No. 9-3, Tables 3-3 and 3-4 indicate the large concen-trated loads considered in the analysis; however, these loads are uniformly distributed along the circumference of the pie slice finite element model at various elevations. Since the stresses in the corroded regions of the drywell are close to the allowables, what effect would a more refined treatment of these loads have on the stress evaluation? This question should be addressed for all drywell regions (i.e., cylinder, knuckle, upper sphere, middle sphere, lower sphere, and sondbed).
It should consider stresses directly under the load (if corrosion in this area is present), as well as the effect on the stress distribution at further distances from t!.c load.
5.
In GE Report Index No. 9-3, Section 3.2.3 it is indicated that the seismic loads are imposed on the pie slice model by applying forces at four elevations of the model and matching stresses at selected elevations with those from the axisym metric model.
How sensitive are the calculations to the location and number of elevations chosen to match the stresses?
How well do the stresses compare at other elevations in the drywell?
6.
In order to examine your analysis more closely, the staff is requesting you to provide the ANSYS input file for both the axismmetric and pie slice models.
It would be convenient if this information is provided on a high density 51/4 in. floppy disc for an IBM PC.
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Dear Mr. Hall:
Enclosed for your review and action is a copy of Modification Ib. 4 to the Preliminary Revised Final Remedial Action Plan (PRFPAP) for the Durango, Colorado, uranium mill site. The purpose of this Modification is to rcquest approval for a supplenental standards application involving an excavation protocol for thorium-230 contamination. The enclosure supersedes the previous documentation on thorium-230 excavation transmitted on Novaber 16, 1990, as part of tle PRPRAP for tlw Durango site.
Should you have any questions, please contact S. Harp of nry staff at PTS 845-5640.
Sincerely, Mark L. Matthews Project Manager Uranium Mill Tailings Renedial Action Project Office Enclosure cc w/o enclosure:
M. Abrams, UMTRA 9106030300 910515
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% e MODIFICATION NO. 4 DURANGO, COLORADO PRELIMINARY REVISED FINAL REMEDIAL ACTION PLAN CHANGE NO 1 REV. B, 5/14/91 A.
==
Description:==
The purpose of this change is to establish an excavation protocol for thorium-230 (Th-230) contamination in the absence of excess radium-226 (Ra-226) at the Durango, Colorado, mill tailings site. As required in 40 CFR 192.21(f), Th-230 will be excavated to levels that are as low as is reasonably achievable (ALARA). ALARA conditions at the Durango site will be met by imposing the following supplemental standard:
Excavate Th-230 to a 1,000 year ingrowth corrected Ra-226 concentration of 5 pCi/g above background (14 pCi/g Th-230 with no residual Ra-226 today) in the first 6 inch soil layer and 15 pCi/g above background (42 pCi/g Th-230 with no residual Ra-226 today) in any subsequent 6 inch layer.
The change also allows for the use of a mass correction factor to eliminate measurement bias.
The Department of Energy's commitment to comply with Environmental Protection Agency (EPA) standards for groundwater remains unchanged.
B.
Resultina chanaes to the RAP:
Page C-2 of UMTRA-DOE /AL 050503.0000, June 1986, " Remedial Action Plan and Site Design for Stabilization of the Inactive Uranium Mill Tailings Site at Durango, Colorado." Add the following paragraphs before the last paragraph of Section C.1, " Introduction":
"If other residual radionuclides other than Ra-226 and its decay products are present in sufficient quantity and concentration to pose a significant radiation hazard, supplemental standards shall be applied (40 CFR 192.21(f)).
Remedial actions, in addition to satisfying the control and cleanup standards, shall reduce other residual radioactivity to levels that are as low as reasonably achievable (40 CFR 192.22(b)).
Supplemental standards may be applied when Th-230 contamination is present in the absence of excess Ra-226.
The need for excavation of this material will be determined by comparing the Th-230 concentration to a guideline equivalent to the Ra-226 standard.
This guideline is based upon the residual Ra-226, corrected for decay, and the Ra-226 ingrowth from Th-230."
Page C-7, add the following paragraphs to the end of Section C.3.4,
" Final Radiological Verification Survey for Land":
220H.
i "For areas in which a significant fraction of the material being sampled is rock or gravel, the nine-plug composite 30x30 foot grid may be collected by using a shovel to take bulk samples, separating the fines from the rock using a #4-mesh screen and determining the weight of the fines and rock fractions.
The fines shall then be counted for Ra-226 following the standard RAC-015 specifications and quality controls. The resulting Ra-226 and Th-230 concentrations will be corrected to a final, reportable bulk concentration by dividing the activity measured in the fine fraction by the mass of the entire sample (rocks plus fines).
Larger areas with uniform composition will be corrected by the average of the measured fractions.
In areas where elevated Th-230 is present, excavation first should be to prescribed Ra-226 standards, then verified in accordance with standard procedures, as discussed above. At the time that the radium analysis sample is collected in each grid, a duplicate, 200-gram saniple of the well-mixed material shall be analyzed for Th-230 concentration.
Grid-by-grid results for thorium analyses shall be compared to a Th-230 guideline which is equivalent to the Ra-226 standard. This guideline is based on the residual Ra-226, corrected for decay, and the Ra-226 ingrowth from Th-230."
C.
Overall Impact to Desian and Completed Remedial Action This change simplifies construction and avoids environmental harm which would be unreasonably high relative to the long-term benefits.
The change results in low-level contaminated material remaining in the fines at depth in some areas of the former raffinate ponds area. The material is in a location where construction of structures is not likely and any future excavation will mix the contamination with clean materials and dilute the concentration. As part of the Uranium Mill Tailings Groundwater Restoration Project, DOE will re-evaluate groundwater conditions at the Durango site and take any action which may be required to ensure compliance with applicable standards.
D.
Compliance of Revised Desian with EPA Standards The revised design complies with Supplemental Standards defined under 40 CFR 192.22(a) as " coming as close to meeting the otherwise applicable standard as is reasonable under the circumstances" and 40 CFR 192.22(b) as " reducing other residual radioactivity to levels that are as low as is reasonably achievable".
The mass averaging technique is required because soil, as defined by the EPA standards in 40 CFR 192.11 includes "all unconsolidated materials... including... gravels and small rocks".
It has been demonstrated that the activity encountered on the UMTRA Project is associated with the fine particles and that the larger particles (small rocks and cobbles) are not contaminated. The typical soil analysis 220H ___ __- _________-____-____ - _ -_