ML20210E462
| ML20210E462 | |
| Person / Time | |
|---|---|
| Site: | Big Rock Point File:Consumers Energy icon.png |
| Issue date: | 06/24/1999 |
| From: | Lesinski M CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | NRC OFFICE OF ADMINISTRATION (ADM) |
| References | |
| FRN-64FR14952, RTR-NUREG-1640 64FR14952-00004, NUDOCS 9907280227 | |
| Download: ML20210E462 (3) | |
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US NRC June 24,1999 Chief, Rules and Review Directives Branch U.S. Nuclear Regulatory Commission Office of Administration Mail Stop T-6D59 Washington, D.C. 20555-0001
Subject:
Comments on draft NUREG-1640 " Radiological Assessments for Clearance of Equipment and Materials from Nuchar Facilities," December,1998 Regulatory standards for the clearance of materials with residual contamination are appropriate in order to allow recycle and reuse of these resources at levels which are low relative to natural background and therefore safe for the general public. We support such regulatory action.
It is our belief that contamination limits should be based on doses in the range of from 5 mrem tol0 mrem per year, consistent with the limits for gaseous and liquid effluents under 10CFR50, Appendix 1. The following comments are provided with the recognition that the tabulated
" limits" of Draft NUREG-1640 are per unit dose (1 mrem /y). Ilowever, tbc comments apply equally over the range of proposed values for annual dose.
NUREG-1640 provides excellent documentation of the pathways by which radiation exposure may occur to the average individual of various population groups. The attempt to view such exposures in a probabilistic manner is commended. Ilowever, it is noted that many significant doses are driven by very conservative point estimates of computational parameters rather than probabilistic evaluations: the assignment of an arbitrary driver exposure time of 1,000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br /> per year, while exposed to scrap at 100% of the contamination limit, for all trucking scenarios, is an important example.
Because of several overly conservative assumptions made in the selection ofinput parameters, a number of which are described here, the limiting values of residual surface contamination for Cobalt-60 (steel scrap transport scenario) and cesium isotopes (Cs-134 and Cs-137 in electric arc furnace baghouse dust transport) are factors of from 18 to 42 belmv the current guidance for survey monitoring sensitivity (NUREG-1640 Table 2.3).
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y These restrictions on Cobalt-60 and the cesium isotopes would be extremely costly to the nuclear power industry. The NUREG-1640 values for these radionuclides also are significantly below the clearance levels of the European Commission and the IAEA (NUREG-1640 Tables 2.5 and 2.6), and as such, would create significant import trade restrictions.
NUREG-1640'could be significantly improved by a more careful application of the nuclear
, industry volumes of contaminated scrap which would be affected by this rule. The EPA draft TSD " Radiation Protection Standardsfor Scrap Metal: Preliminary Cost-Benefit Analysis" (June 1977)is referenced as the basis for the NUREG-1640 contaminated steel scrap data.
. However, the EPA reference cases from which the NUREG volumes are taken (TSD Appendix 2
G) include scrap contamination levels above 70,000,000 dpm/100 cm (TSD Table A5-4). Only 2
29% of this scrap exhibits contamination levels ofless than100,000 dpm/100 cm,
2 The draft NUREG-1640 suggests limits of only a few hundred dpm/100 cm for nuclides associated with nuclear power facilities. Consequently, even with significant decontamination effort, it is not appropriate to assume clearance of scrap from the categories above 100,000 2
dpm/100 cm. By including scrap with much higher contamination levels than allowed under the clearance rule, NUREG-1640 calculations artificially skew the limits to overly conservative values.
NUREG-1640 also neglects mixing with clean scrap prior to shipment at the nuclear facility. The EPA' draft TSD data (ratio of Table A5-4 to A4-4) demonstrates that only 16% of nuclear facility steel (other metals also listed) is contaminated, and that the volume under 100,000 j
2 dpm/100 cm is only 4.6% of the clean volume. This results in a dose reduction (or contamination limit increase) equal to a factor of 22 because a lower initial volume is diluted by
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clean scrap. It should be noted that there would be no incentive (and there is no simple mechanism available) to segregate clean scrap from scrap contaminated below the clearance level under a clearance rule: there would be dilution prior to shipment.
Both trucker and downstream public doses are reduced a factor of 22 by use of appropriate 1
volumes. We believe that use ofinappropriately high contaminated scrap volumes, coupled with the neglect of mixing with clean scrap at the nuclear facility, contribute significantly to the exceptionally low limits resulting from the draft NUREG-1640 analysis.
Volumes for all types of scrap (steel, copper, aluminum and concrete) have been overestimated in NUREG-1640 relative to the amounts of contaminated materials available in the range of the proposed contamination limits. Pre-shipment mixing with clean material also has been neglected for each of these materials.
I Post-shipment mixing factors at the recycle facility also require correction. With steel as an j
example, NUREG-1640 Section D.3.2 uses maximum and average annual values from the EPA's drafl TSD,' Appendix G, for maximum and minimum mixing factors, respectively, applied (contrary to EPA data) as a uniform distribution. This results in a chosen value equal to % the maximum since the minimum approaches zero. However, the EPA draft TSD provides actual 1
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- volume distributions as a function of time over the 55-year interval of nuclear power piant decommissioning which is.not a uniform distribution. The actual distribution results in much smaller mi.
- ing factor than the value chosen under the simplified assumption of uniform
' distribution.
We support the use of probabilistic analyses in the derivation oflimits such that the concept of dose to an average individual of the critical population group may be determined. However, 3
individuals performing such analyses must take care to establish appropriate distribution modeh for key parameters rather than making simplifying assumptions which are not justified by available data.
Sensitivity analyses are suggested in order to define the specific parameters which have the greatest effect on dose. Our own analyses indicate that scrap volume assumptions (for both contaminated and clean scrap), mixing factors throughout the process stream (particularly at the l
nuclear facility, since this affects all downstream doses), and exposure time for truckers (rs related to available regional scrap volumes) have the greatest effects on limiting pathway doses.
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'As far as can be determined, none of these critical parameters have been modeled with the actual i
frequency distributions of available data: distributions have either been assumed, or conservative point estimates have been assigned in each case.
In summary, we believe that the chosen dose pathways are appropriate, but corrections are required for the calculational parameters and distribution assumptions discussed above, before contamination limits are finalized. In the areas we have identified concerns, it appears that very conservative assumptions were applied in order to error on the safe side. While this may have been appropriate as a worst case initial iteration, it is now time to replace these conservatisms with real data in order to improve the accuracy of the dose calculations and derived limits.
It is hoped these comments have been explicit enough in describing the errors found in this draft report to allow appropriate corrections to be made. Please contact me at 213-547-8416, or Dr.
Robert English (tel. 231-547-8348, E-Mail raenglish@cmsenergy.com) if additional information is desired.
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l Mark Lesinski, ianager Radiological Protection and Environmental Services