ML23037A864
| ML23037A864 | |
| Person / Time | |
|---|---|
| Site: | 99902091 |
| Issue date: | 02/03/2023 |
| From: | Amy Snyder Reactor Decommissioning Branch |
| To: | Fox D APTIM Federal Services |
| References | |
| Download: ML23037A864 (1) | |
Text
1 NRC Request for Additional Information Final Status Survey Plan (FSSP) Surface Ship Support Barge (SSSB) Dismantlement and Disposal, Revision 2, dated January 20, 2023, prepared by APTIM Federal Services, LLC (APTIM). As per previously established agreements with NAVSEA, the NRC has reviewed the FSSP consistent with NRC regulations and guidance and APTIMs commitments in the DWP dated May 29, 2022.
Q1) Request: Clarify the criteria for the FSSP given in Table 2-2, Screening Limits - Surface Contamination with regards to how the fraction of removable activity will be determined.
Discussion: In Table 2-2 of the FSSP, the limits are given for the screening criteria from NUREG-1757, Vol 1., Rev. 2, Consolidated Decommissioning Guidance: Decommissioning Process for Materials Licensees, Table B.1.,Acceptable License Termination Screening Values of Common Radionuclides for Building-Surface Contamination. However, the fraction of removal activity present on surfaces must be addressed when applying surface screening criteria. Specifically, NUREG-1757, Vol 2., Revision 2, Consolidated Decommissioning Guidance: Characterization, Survey, and Determination of Radiological Criteria Consolidated Decommissioning Guidance: Characterization, Survey, and Determination of Radiological Criteria - Final Report, Appendix H, Criteria for Conducting Screening Dose Modeling Evaluations, Table H.1, Acceptable License Termination Screening Values of Common Radionuclides for Building-Surface Contamination, (which is essentially the same table as referenced in Volume 1) states, in part, that unless the fraction of removable activity is determined, then the surface screening criteria should be decreased by a factor of 10 as discussed below.
Note, for cases when the fraction of removable contamination is undetermined or higher than 0.1, licensees may assume, that 100 percent of surface contamination is removable, and therefore the screening values should be decreased by a factor of 10 (see footnote a to Table H.1).
This would seem to be the intended case for the hard-to-detect radiological contaminants of potential concern (RCOPCs) for which smears only are currently planned to be analyzed and no plans for direct measurement are mentioned. NRC staffs concern for this is with respect to the direct beta/gamma measurements that are discussed in the FSSP.
Based on the NUREG and past approaches taken by licensees, one possible path forward that may be taken would be to determine the fraction of removable activity via direct measurement/smears and radiochemical analysis of a sample of the media of concern (e.g.,
both a smear and a sample of media are taken, and the fraction of removable activity can be determined by simply taking the ratio of the smearable activity to the sum of smearable and radiochemical analytical results of the sample). You should note that this may need to be done multiple times to account for each hard-to-detect RCOPC and should ideally be determined at what is believed to be the most contaminated area of a structure to ensure adequate activity is present and minimize uncertainty. For easy-to-detect RCOPCs, a direct measurement can be taken before and after washing the area. The difference in the two measurements is the removable activity portion of the before measurement. Alternatively, a licensee could consider all surface contamination as removable, drop the screening values by a factor of ten, and only take direct measurements to show compliance with the surface criteria (hard-to-detect RCOPCs would still have to be considered through criteria modification/surrogate measurement).
2 Path Forward: Respond to this RAI and either use the RAI response as a supplement to the FSSP or revise the FSSP appropriately to address this issue.
Q2) Request: Provide clarification of ALARA considerations for the containment structure and soil and paved areas consistent with NUREG-1757, Vol 2, Revision 2, Appendix N, ALARA Analyses.
Discussion: In the APTIM, Decommissioning Work Plan, SSSB Dismantlement and Disposal, Rev. 2, (DWP) (ML22151A118) Section 4.4, Unrestricted Release Using Screening Criteria, 4.5, Unrestricted Release Using Screening Criteria for Surface Soil Residual Radioactivity, and 11.1, Release Criteria, APTIM states that it believes the screening criteria are ALARA and that it has an additional ALARA goal of being able to demonstrate that the Final Status Survey (FSS) results are not statistically different from the baseline survey results. While the NRC staff initially felt that this was sufficient because NUREG-1757, Vol 2, Revision 2, Appendix N demonstrates that disposal of soil to meet the decommissioning criteria is considered ALARA, this same logic doesnt apply to building structures. In addition, staff are unclear as to what commitment is being made with respect to the ALARA goal. If elevations greater than the baseline survey exist but still meet the unrestricted release criteria of 10 CFR 20.1402, Radiological criteria for unrestricted use, what is APTIM planning to do to demonstrate compliance with its ALARA goal? Clarification is needed to demonstrate compliance with 10 CFR 20.1402 which has a dose criterion as well as ALARA criterion.
One possible path forward for a licensee would be to evaluate washing the containment structure as shown in NUREG-1757, Vol 2, Appendix N. In the past, some licensees have clearly stated whether they plan to use the Sign Test to evaluate their structures (containment structure) while not subtracting background if no baseline survey was performed. With respect to the ALARA goal, you could clarify that you will evaluate any elevations above baseline to determine if it is ALARA to perform additional remediation (e.g., it likely isnt ALARA for additional remediation of soil as per NUREG-1757, Vol 2, Appendix N, Section N.3.5, Examples of Calculations, Example 3, Removing Surface Soil).
Path Forward: Clarify the ALARA strategy for both soil and structures. Respond to RAI and either use the RAI response as a supplement to the FSSP or revise the FSSP with respect to ALARA. Without this clarification in the FSSP, it appears to NRC staff that APTIM has committed to cleanup to background or baseline conditions.
Q3) Request: Explain how insignificant contributors are accounted for consistent with the difference in RCPOCs listed in Table 2-1, SSSB Radionuclides of Potential Concern, of the FSSP (dated January 20, 2023) and those listed in Table 1 (Radiological Constituents of Potential Concern) of the SSSB Final Status Survey Summary (Attachment 7, Final Status Survey Summary, of the DWP (ML22151A118), dated May 29, 2022).
Discussion: While the NRC staff believe that this is explained to an extent (i.e., the Cs-137 contribution is insignificant with respect to the total activity and dose anticipated and will be accounted for by considering all gross gamma/beta measurements as being related to Co-60 which has a more restrictive screening value than Cs-137), it would be useful for it to be clearly stated as such in the FSSP as a means of accounting for insignificant contributors as discussed in Section 3.3 of NUREG-1757, Vol 2, Revision 2. Related statements should also be made to explain the potential dose contribution of other insignificant radionuclides because Table 1 of the SSSB FSS Summary show that there is a small amount of inventory (activity) not
3 considered in the list of RCOPCs. The NRC staff do not believe that the soil Derived Concentration Guideline Levels (DCGLs) omitting Cs-137 in the FSSP can be explained in the same manner and may be most easily addressed by simply reporting Cs-137 in the FSS data (no additional cost for analysis is likely).
Path Forward: Respond to this RAI and either use the RAI response as a supplement to the FSSP or revise the FSSP as appropriate for this issue. In the FSSP and future Final Status Survey Reports (FSSRs), APTIM should discuss insignificant RPOPCs and how their dose contribution is considered in demonstrating compliance with 10 CFR 20.1402 and in a manner consistent with NUREG-1757, Vol 2, Revision 2, Section 3.3, Insignificant Radionuclides and Exposure Pathways.
Q4) Request: Clarify that adequate Quality Assurance (QA) will be performed during the FSS to verify that radiological contaminants other than the RCOPCs are not present at significant levels and that the ratio of detected RCOPCs is consistent with characterization data.
Discussion: Verification that the characterization data continue to be consistent with expected field conditions is needed for demonstrating compliance with 10 CFR 20.1402 and to ensure compliance with 10 CFR 20.1501, Surveys and Monitoring, General. Some licensees have demonstrated this as a Quality Control (QC) step with respect to the most contaminated materials found on site after completion of the site preparation for FSS. Other licensees have demonstrated this from samples of waste generated during the later steps of decommissioning (e.g., HEPA filters removed from the containment structure, floor sweepings, etc.).
Section 5 of the FSSP currently does not address how APTIM will be verifying the RCOPCs and relative ratios with respect to potential dose calculations and insignificant contributors and with respect to verifying or establishing surrogate ratios for hard-to-detect RCOPCs.
Path Forward: Respond to this RAI and either use the RAI response as a supplement to the FSSP or revise the FSSP as appropriate to explain how APTIM will demonstrate that characterization data continue to be consistent with expected field conditions.
Q5) Request: Explain how the hard-to-detect radionuclides were/will be scaled into the criteria applied to Co-60 direct beta/gamma measurements.
Discussion: APTIM committed to account for hard-to-detect radionuclides by using scaling factors on measurements of easy-to-detect radionuclides (page 11-7 of the DWP) for unrestricted release of materials. This is generally considered performance of surrogate measurements and typically involves consideration of the ratios of the RCOPCs and the criteria applicable to them (see Multi-Agency Radiation Survey and Site Investigation Manual (MARSSIM) (NUREG-1575), Section 4.3.2). The NRC staff believe this issue is also applicable to direct beta/gamma measurements that will be performed during the FSS and may have already been considered as APTIM committed to using a rounded down criteria for Co-60 data comparisons for beta measurements. In addition, this is likely not an issue for soil samples because they are planned to be analyzed for all RCOPCs (including Cs-137?). Appropriate consideration of the hard-to-detect RCOPCs will ensure compliance with 10 CFR 20.1402 and 10 CFR 20.1501.
Path Forward: Respond to this RAI and either use the RAI response as a supplement to the FSSP or DWP or modify the FSSP/DWP as appropriate. When the NRC staff reviews future
4 FSS reports, it expects discussion regarding surrogate measurements for the hard-to-detect RCOPCs consistent with its DWP/FSSP. In this case, since APTIM DWP, Rev 2, indicates that more detail will be in its FSSP, APTIM can choose to update the DWP or its FSSP.
Q6) Request: Verify that the survey efficiency used in determining the scan Minimum Detectable Concentration (MDC) in the FSSP is not set to unity as is stated in the DWP.
Discussion: On page 6-17 of NUREG-1507, Rev. 1, an explanation is offered on why the scan MDC equations for the surveyor with vigilance paradigm do not apply for surveys without surveyor vigilance where the data is post-processed. It states: That is, the statistical paradigm changes for projects where the surveyors do not listen to the audio output and pause to investigate potential anomalies (second-stage scanning). Rather, anomalies must be identified based on evaluations of the processed data. The FSSP does not appear to have carried the surveyor efficiency of unity forward from the DWP but rather kept to the MARSSIM recommendation of 0.5. Staff note that the DWP and FSSP appear to be inconsistent with how the scan MDC is being evaluated with respect to the survey efficiency parameter.
Path Forward: Because APTIM states it plans to consider a 2-stage surveying methodology consistent with MARSSIM in its DWP/FSSP, it should utilize a surveyor efficiency consistent with that method when determining the scan MDC. Respond to this RAI and either use the RAI response as a supplement to the DWP/FSSP or revise the DWP/FSSP to explain the survey efficiency and how it will be used. The DWP and FSSP should be consistent.
Q7) Request: Provide additional detail in the FSSP as to how APTIM will evaluate data against the stated criteria in the DWP/FSSP and demonstrate compliance with 10 CFR 20.1402. APTIM currently mentions the Wilcoxon Rank Sum Test and the Sign Test and MARSSIM. However, applicable details in MARSSIM are omitted (sum-of-fractions, consideration of elevations exceeding the criteria, consideration of multiple media, etc.).
Discussion: APTIM should include in its data analysis section of the FSSP how it will evaluate each media with regards to all RCOPCs (e.g., sum-of-fractions, surrogate measurements, etc.).
In addition, it should also include how APTIM plans to address summing the potential dose from multiple media (structures and soil/pavement), whether it anticipates performing background subtraction or eat the background in field instrument beta measurements, how APTIM will address elevations above the criteria if identified, etc. Because there is more than one media present, many NRC licensees have chosen to establish operational DCGLs that are a fraction of the 25 mrem DCGLs to ensure the eventual total will not exceed the 25 mrem criteria when considering all media. These operational DCGLs only guide the remediation efforts (if needed) of each media but are not utilized when demonstrating compliance with the 25 mrem dose criteria and summing potential dose across all media.
Path Forward: Respond to this RAI and either use the RAI response as a supplement to the FSSP or revise the FSSP to explain how all RCOPCs are considered in demonstrating compliance, how elevations greater than the release criteria may be addressed, and how APTIM will demonstrate compliance if more than one media exists in a survey unit (structures +
soil/pavement). It is assumed that APTIM will generally follow MARSSIM guidance with regards to addressing multiple RCPOCs and elevations, however more detail should be in the DWP or the FSSP so that when the NRC staff evaluates the FSSRs there is no ambiquity as to the licensees process to demonstrate compliance.
5 Q8) Request: Explain how APTIM plans to provide isolation and control of FSS survey units inside the restricted area until the site is released by NAVSEA after APTIM has completed its FSS and is waiting for approval. Clarify how much of each survey unit will be scanned and the analyses performed for soil/sediment samples.
Discussion: While the scanning requirements discussed in the FSSP (Table 3-3) and in the latest revision of the DWP are consistent with MARSSIM, the DWP (Attachment 7, Section 2.4.1) appears to also call for a 100% coverage of the SSSB D&D area when performing a gamma walkover scan. APTIM should resolve the inconsistency. Given the nature of the cutting activities performed, movement of materials, and the relative ease of performing a walk over gamma scan over such a small site, the NRC staff believe it would be reasonable to perform a gamma walkover scan of the entire SSSB D&D area consistent with the DWP. The NRC understands that beta scans may be more in line with the guidance in MARSSIM.
In Sections 3.5 and related sections of the FSSP, APTIM discusses gridding the survey units.
Clarify if APTIM means to establish a grid over Class 2 and 3 survey units, or should this be Class 1 and 2 survey units? Class 3 survey locations are typically random and located by GPS coordinates based on a random number generator.
Clarify if APTIM anticipates calling all storm water drains/catch basins one survey unit. It may be more practical to consider 2 separate survey units for each such area since APTIM states there are 2 storm water drain fields of concern. Does APTIM plan to do any prep for the drain systems (e.g., hydrolasing)? Most commonly, NRC licensees hydrolase any remaining drain systems and collect sediment as it is flushed out. They then analyze collected sediment and take direct measurements of accessible points. This may not be practical if the system is much larger than needed for just the SSSB site (NRC staff are unable to clearly see the storm drain system in Appendix B of the FSSP).
NRC staff believe APTIM implies soil/sediment sample analysis incorporating radiochemical analysis for all RCOPCs. However, the NRC did not find an explicit commitment in the FSSP.
APTIM should commit in the FSSP to incorporating radiochemical analysis for all RCOPCs in soil/sediment sample analysis.
Path Forward: Respond to this RAI and either use the RAI response as a supplement to the FSSP or revise the FSSP to explain the issues discussed above.