ML20217G816
| ML20217G816 | |
| Person / Time | |
|---|---|
| Issue date: | 03/02/1997 |
| From: | Brummett E NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| To: | |
| References | |
| NUDOCS 9804290215 | |
| Download: ML20217G816 (4) | |
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Waste Management '97 Tucson, Arizona, March 2-6, 1997 i
REGULATORY APPROACH TO S0IL CLEANUP VERIFICATION AT l
DECOMMISSIONING URANIUM MILL SITES Dr. Elaine S. Brummett l
Division of Waste Management Office of Nuclear Material Safety and Safeguards l
U.S. Nuclear Regulatory Commission ABSTRACT l
l The U.S. Nuclear Regulatory Commission (NRC), Division of Waste Management, has recently delineated policy and developed staff guidance regarding uranium j
l mill site decommissioning activities.
These activities are primarily related to soil cleanup and verification, because usually mill buildings are buried in
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l the tailings pile.
The policy calls for streamlining the confirmatory survey l
process by putting more emphasis on inspection of licensee performance.
To l
support this approach, staff guidance was developed in the form of a detailed l
generic decommissioning inspection plan. Where possible, the inspection i
program staff is involved at the beginning of decommissioning activities, so l
that deficiencies can be identified and corrected early.
Use of the decommissioning inspection plan provides a means to gain confidence in the licensee's performance and to document the evaluation that performance.
l The licensee's performance is also considered during review of decommissioning plans by the licensing program staff. When evaluating proposed new methods, or new approaches to site-specific problems, staff must ensure that compliance with the regulations can be demonstrated by the licensee.
Staff considers data and policy developed in the U.S. Department of Energy program for l
abandoned mill sites to assist with some of these evaluations.
Implementation l
of both aspects of this regulatory approach to decommissioning allows staff to l
reduce their confirmatory survey effort and allows licensees to comply with applicable standards in a cost-efficient manner.
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INTRODUCTION l
l The U.S. Nuclear Regulatory Commission (NRC), Division of Waste Management, has recently delineated policy and developed staff guidance regarding uranium mill site decommissioning activities.
These activities are primarily related to soil cleanup and verification, because usually mill buildings are buried in l
I the tailings pile. The policy calls for streamlining the confirmatory survey L
process by putting more emphasis on licensee performance.
To support this approach, staff guidance was developed in the form of a detailed generic decommissioning inspection plan. Where possible, the inspection program staff is involved at the beginning of decommissioning activities, so that deficiencies can be identified and corrected early. Use of the decommissioning inspection plan to guide observations of licensee 7
implementation of procedures and data review, provides a means to gain confidence in the licensee's performance and to document the evaluation that performance, v
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i The licensee's performance is also considered during review of decommissioning plans by the licensing program staff. When evaluating proposed new methods, j
or new approaches to site-specific problems, staff must ensure that compliance with the regulations can be demonstrated by the licensee.
The objective of both aspects of this regulatory approach is to allow staff to reduce their confirmatory survey effort because of confidence gained in the licensee's decommissioning procedures, quality assurance program, and performance of the final survey.
POLICY AND STAFF GUIDANCE l
Recent efforts by staff regarding uranium mill site decommissioning (primarily soil cleanup) include definition of a policy on streamlining the confirmatory survey process.
Because of the large areas (up to 900 acres) remediated at mill sites due. contamination with windblown tailings, staff duplication of 5 l
to 10 percent of the cleanup verification measurements (gamma surveys and soil sample analysis primarily for Ra-226) would result in excessive costs.
This l
policy provides for detailed inspections, during the early phases where l
possible, of decommissioning activities.
The inspections, which include close scrutiny of procedures and quality assurance programs, will ensure acceptable implementation of soil cleanup procedures and provide the main basis for determining the scope of the confirmatory survey.
This emphasis on early, detailed inspection allows staff to detect and licensees to correct deficiencies.
By making appropriate' changes early, licensees can save time and money on the decommissioning effort.
Staff can j
also target problem areas, or problem sites on subsequent inspections so that confidence can be gained in the licensee's performance.
To support this policy, staff has developed a Generic Decommissioning Inspection Plan, which provides for consistent, in-depth review of l
decommissioning activities. Areas of inspection include:
sarvey procedures and instrumentation, analytical procedures for soil samples, quality assurance procedures, data reduction and managcnent, and the survey results.
The generic plan was modified to reflect individual mill site conditions and utilized at four sites in 1996.
This resulted in identification of several areas that required follow-up efforts by the licensees.
EVALUATION OF NEW METHODS Staff review of decommissioning plans has involved evaluation of proposed new methods.
For example, one licensee proposed soil cleanup and verification procedures that included an improved gamma scanning system. The system employs a detector mounted on a backpack or vehicle.
The digitized count rate data are recorded every two seconds by transmission to survey equipment utilizing a Global Position System.
The data are then downloaded to a computer and contours of gamma readings are plotted on a site grid map.
The cleanup verification procedure also included a conservative gamma guideline and a limited soil sampling program. This procedure was approved by staff for verification of radium (Ra-226) cleanup in large areas of windblown tailings because of the improved detection of elevated gamma levels for subsequent removal.
Because the licensee was allowed to do less soil sampling, and gamma 2
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Staff has also given tentative approval to a proposal to till soil contaminated by windblown tailings in order to meet the Ra-226 cleanup standard. The constraints set by the staff include:
fairly flat terrain, uniform low-level surface contamination, and a test plot with extensive surface and subsurface samples to demonstrate that compliance can be achieved.
This method costs less than excavation, transportation, and compaction of the material on the tailings pile and provides comparable protection of the health and environment as the traditional remediation method.
EVALUATION OF SITE-SPECIFIC PROBLEMS One problem that has been evaluated by staff is that of determining if the elevated soil Ra-226 is due to the milling process, or due to naturally occurring (in situ) material.
This situation occurs on a few sites because of near surface outcroppings of radioactive mineralized deposits.
Several mill i
sites even have open pit uranium mines on their property.
One approach used l
by DOE for similar sites in their program, has been the use of Ra-226/U-238 ratios; the ratio being much higher for mill tailings than for ore.
- However, l
in some regions an oxidizing roll front has created areas where the uranium was mobilized away from the radium centuries ago, so application of one ratio t
would not reflect every area on the site.
Therefore, other approaches must be considered. One proposal by a licensee that will be evaluated by staff, is the use of sulphate as a surrogate for tailings in areas of naturally deposited radium.
l Another problem concerr.s the cleanup of large amounts of overburden soil l
stockpiled near open pit uranium mines on mill sites. The Ra-226 content of this soil exceeds surface background, but did result from the milling process.
The obvious solution is to place the material on top of the tailings pile to assist in radon attenuation, but this creates a problem with the Ra-226 content of the tailings pile ccver. The h.RC regulation (10 CFR Part 40 Appendix A, criterion 6) states that "Near surface cover materials (i.e.,
within the top three meters) may not include waste or rock that contains elevated levels of radium;..."
Covers thicker than 3.0 meters (9 feet) were considered likely before the radon flux limit was finalized.
However, under current standards, tailings disposal cell covers are often less than 2.0 meters (6 feet) thick.
Therefore, to assist licensees with disposal of these large piles of overburden, staff determined that a cover thickness of 0.61 meters (2.0 feet) would be adequate to consider as "near surface" cover materials.
To substantiate that the radon contribution from this material does not cause a significant increase in the cover radon flux, staff requires that such cover material be characterized for Ra-226 content and that the average value be incorporated in the radon flux model used to estimate the long-term radon flux from the cell. This reinterpretation of "near surface" cover materials meets the intent of the regulation and assists the licensees with site cleanup.
A third problem was the determination of the cleanup limit for Th-230 below a raffinate pond.
Because thorium is more soluble in the acidic solution than the radium, it had migrated farther into the soil.
Excavation had removed soil Ra-226 to nearly background levels, but Th-230 was elevated.
NRC uranium mill regulations do not address radionuclides other than Ra-226 and following NRC guidance on disposal of thorium and uranium would have required expensive 3
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remediation for an area that is next to the disposal cell.
Staff, therefore, considered application of the DOE Uranium Mill Tailings Remedial Action Project policy on Th-230 cleanup, because the pond area is part of the parcel that will be deeded to the ' federal government for perpetual maintenance when the current license is terminated.
The DOE policy allows use of the calculated 1000-year Ra-226 value resulting from the decay of residual Th-230 and Ra-226, as the limit for soil cleanup. Thus the licensee was asked to meet a limit of 14.3 pCi/g (536 mBq), instead of the 5 pCi/g (185 mBq) NRC thorium guideline for surface soils.
Modeling of potential long-term doses was required to support this approach. Use of this alternate Th-230 cleanup limit allowed the licensee to avoid extensive excavation and disposal of material and still provide adequate protection to the public and the environment.
SUMMARY
NRC staff has recently delineated policy and developed staff guidance regarding uranium mill site decommissioning activities.
The policy calls for streamlining the confirmatory survey process by putting more emphasis on inspection of licensee perfornance. As a result, inspection program staff is placing emphasis on early involvement in decommissioning activities, so that deficiencies can De identified and corrected early.
The staff guidance l
l provides for detailed inspections that can provide confidence in the l
licensee's performance.
Staff then limits confirmatory surveys to those sites l
where close scrutiny of soil cleanup and verification has not been possible, l
or where significant problems associated with decommissioning are likely.
Sufficient information is gained so that staff can make the determination, for license termination, that applicable cleanup standards have been met.
To assist with this emphasis on licensee performance, the licensing program staff evaluates proposed new methods and new approaches to site-specific problems related to decommissioning considering the licensee's ability to demonstrate compliance with the regulations.
Implementation of both aspects of this regclatory approach allow staff to reduce their confirmatory survey effort and allows licensees to comply with applicable standards in a cost-efficient manner.
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