ML20137Y992
| ML20137Y992 | |
| Person / Time | |
|---|---|
| Issue date: | 04/15/1997 |
| From: | Gillen D NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| To: | Rael G ENERGY, DEPT. OF |
| References | |
| REF-WM-61 NUDOCS 9704230306 | |
| Download: ML20137Y992 (5) | |
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April 15, 1997 Mr. George Rael, Acting Director U.S. Department of Energy Albuquerque Operations Office ERD /UMTRA
'P.O. Box 5400 Albuquerque, NM 87185-5400
SUBJECT:
REVIEW OF THE COMPLETION REPORT OF FEBRUARY 1997 (PAGE CHANGES) AND THE RESPONSES TO NRC COMMENTS ON THE COMPLETION REPORT OF MAY 1996 FOR THE GUNNISON, COLORADO, URANIUM MILL TAILINGS REMEDIAL ACTION PROJECT SITE
Dear Mr. Rael:
By letter of January 21, 1997, the U.S. Department of Energy (DOE) provided responses to the U.S. Nuclear Regulatory Commission staff's concerns of November 6, 1996, related to its review of the Gunnison Final Completion Report (CR) of May 1996.
The DOE responses were followed shortly thereafter by its February 6,1997, transmittal of the revised Final Completion Report.
This letter provides the results of the NRC staff's review of the completion report documentation.
Based on its evaluation of the two DOE documents, the NRC staff has identified areas where additional information is needed (see Enclosure).
Of the 13 CR comments identified in its November 6,1996. letter to DOE, three remain unresolved.
Furthermore, two additional concerns (Comments 14 and 15) have been identified based upon new data contained in the expanded February 1997 CR. Although the staff considers Comment 5, which relates to DOE's thorium cleanup efforts, to be resolved the NRC staff suggests that, in future cleanup efforts, DOE fully consider possible health risks due to remaining thorium as expressed by the NRC in its July 5,1994, letter concurring with the thorium protocol.
See Enclosure Comment 5 for additional discussion on this matter.
If you have any questions regarding this subject, please contact the NRC Project Manager Harold E. Lefevre, at (301) 415-6678.
Sincerely,
$Ill0l"k blD eN, sistant Chief Uranium Recovery Branch Division of Waste Management
.t Office of Nuclear Material Safety mph and Safeguards
Enclosure:
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l U.S. NUCLEAR REGULATORY COMMISSION STAFF REVIEW OF U.S. OEPARTMENT OF ENERGY RESPONSES TO NRC COMMENTS ON THE GUNNIS0N COMPLETION REPORT OF MAY 1996 AND ON THE GUNNISON COMPLETION REPORT (PAGE CHANGES) 0F FEBRUARY 1997 Comments 1 4 The NRC staff considers Comments 1 through 4 to be resolved.
Comment 5 DISCUSSION:
In its November 6. 1996, comment discussion, the NRC staff noted that 38 verification grids contain residual Ra-226 and Th-230 that will result in the 1000-year Ra-226 level at. or just below, the subsurface standard and stated that this remediation of thorium did not appear to meet the as low as reasonably achievable (ALARA) objective.
In its response to the NRC comment.
DOE replied that the UMTRA Project thorium protocol indicated that meeting the 1000-year Ra-226 standard is ALARA.
However. DOE should refer to the NRC letter that concurred with the thorium protocol (July 5.1994).
NRC staff stated that "Because the generic thorium protocol does not consider the volume of Th-230 contamination.... implementation of the protocol should include a site-specific analysis of the health risk, and should emphasize reducing the Th-230 to ALARA levels.
In addition, when elevated levels of Th-230 are to remain below the water table, DOE should consider the likelihood that the material could be excavated in the future and take measures to control access to the material." The NRC staff is concerned that DOE considers the 1000-year Ra-226 standard as a stopping point in cleanup instead of the limit for individual isolated grids.
It ap] ears that DOE has not given enough consideration to possible future lealth risks due to the remaining material.
COMMENT: The NRC staff considers Comment 5 to be resolved.
However, in the future. DOE's thorium cleanup efforts should consider the NRC concerns as expressed in the above discussion.
Comment 6 The NRC staff considers Comment 6 to be resolved.
Comment 7 The NRC staff considers Comment 7 to be resolved.
Comment 8 OISCUSSION:
DOE provided the requested uranium data and cleanup protocol in the revised CR.
There is also a brief discussion of the uranium cleanup on l
revised page 5 of Appendix J. but no rationale concerning the procedure is given and no conclusion is stated on whether the data met a standard, or if a health risk remains.
Also, the data tables report ug/g, not the usual pCi/g.
and the brief protocol mentions pH measurements as an option, but it is not Enclosure 1
l
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2 clear that any such measurements were done.
In addition, the ma) of pit i
locathrt' and the data are designated by N & E coordinates, not Jy grid block j
urt staff is not sure the area of test pit 16 was adequately sampled.
1 t~, ntNT :
Provide the grid numbers associated with test pit 16.
In addition.
provide discussion of the protocol and data at the end of Appendix J to l
include the size of the area excavated to 3 feet below the tailings interface, the rationale for the uranium protocol. and the conclusions to be drawn from the data.
Comment #9 Comment 9a DISCUSSION:
The DOE response said that the CR will be modified to indicate that for 41 grids, select fill was not placed over elevated Th-230 due to art administrative error.
Contrary to the above. the revised CR (Appendix K.
page 6) does not say why select-fill was not placed.
COMMENT:
Indicate on page 6 of Appendix K why the select-fill was not placed.
Comment 9b DISCUSSION:
DOE justified only modeling the radon flux for a slab-on-grade house, with no excavation. by saying that is what 3robably will be built.
However. DOE did provide the estimated dose from T1-230 inhalation for workers in a utility trench, but neglected to include the gamma dose information.
COMMENT:
Since an all pathways dose limit is mentioned on page 6 of Appendix K. revise the CR by indicating the total potential dose for the worker scenario.
Comments 9c and 9d The NRC staff considers Comments 9c and 9d to be resolved.
Comment 10 The NRC staff considers Comment 10 to be reselved.
Comment 11 DISCUSSION: The NRC staff clarified in discussions with DOE. subsequent to transmittal of the NRC's CR comments of Nov. 6.1996, that DOE should justify that the grid (s) with the highest dose potential (considering source term and backfill depth) had been modeled.
DOE re-evaluated the highest health risk i
grid, and identified grid D-04-21 as producing enough radon (maximum level in year 1000) to lead to a potential residential dose of 1600 mrem /yr (Appendix K page 9), based on the modeled radon flux.
The staff used the parameter values indicated in the new Exhibit K.1. and using an assumed depth of contamination Enclosure
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4 of one foot, arrived at a radon flux value similar to the DOE value. However.
when cobbly soil parameter values are taken from the CR radon flux model (calculation 643-01-03) for the disposal cell, the flux value is slightly higher.
Staff also notes that the diffusion coefficient for the select fill and topsoil is less conservative than the value used for the radon barrier.
Diffusion coefficient measurements or the clay content of these materials were 1
not provided to substantiate the low value used in the model.
COMMENT:
Provide information related to the general thickness of the Th-230 contaminated material and clarify the depth of fill material over grid D 22.
If the fill is about 100 cm (3.3 feet), this grid could produce a higher radon flux than D-04-21.
DOE should also justify why the site-specific cobbly soil parameter values from calculation 643-01-03 were not used and why a low (non-conservative) diffusion coefficient was used for the select fill and topsoil layers in the radon flux modeling.
Alternatively. DOE should revise the maximum and average dose estimates using the site specific parameter z
values.
Comment 12 The NRC staff considers Comment 12 to be resolved.
l Comment 13 f
The NRC staff considers Comment 13 to be resolved.
Comment 14*
DISCUSSION: Appendix K. Exhibit K.1. Sheet B-16 contains confusing data on test pit 3.
It has data for 11 grids (should be 12), and some grids have up to four lines of data (C-12-3) indicating different depths to the thorium.
COMMENT:
Indicate if Sheet B-16 is complete (if not complete, revise the sheet accordingly), and indicate which depth values were used in the flux modeling.
Comment 15*
DISCUSSION: Appendix E of the CR indicates that depth checks were not performed for Type C and Type D riprap, because depth checks were not required for these ripra) types.
However, similar to Types A and B. the specifications required that t1e depth and placement of riprap be verified.
For Ty)es A and B. DOE verified the thickness by performing numerous depth checks; t1ese results were re)orted in the CR and are acceptable for those rock types.
For i
Types C and D.10 wever. DOE did not provide any verification of the depth of rock placement.
COMMENT:
DOE should provide further information in the CR to indicate how the depths and thicknesses of Types C and D riprap were verified. To resolve this issue (assuming depth checks were not performed). DOE could indicate that: (1)
Enclosure L
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careful quality control of the finished elevations of the subgrade, filter layer, and riprap was accomplished by surveys; and (2) the volume of each type of material placed indicates that adequate thicknesses were achieved: and (3) visual inspections by 0A/0C inspectors of the finished riprap layers showed that the required thicknesses were achieved.
New comment based on new data contained in the CR of February 1997 1
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i Enclosure 4