ML22031A177
| ML22031A177 | |
| Person / Time | |
|---|---|
| Site: | 07000925 |
| Issue date: | 01/31/2022 |
| From: | James Smith NRC/NMSS/DDUWP/URMDB |
| To: | Lux J Environmental Properties Management |
| James Smith, 301-415-6103 | |
| Shared Package | |
| ML22031A162 | List: |
| References | |
| Download: ML22031A177 (5) | |
Text
REQUEST FOR CLARIFICATIONS
RADIATION PROTECTION PLAN
Soil
The licensee addresses its previous commitments 1 for surveying subsurface soil brought to the surface during installation of injection and extraction trenche s, monitoring wells, trenches for piping and utilities, etc., in Section 12.5 of the Radiation Pr otection Plan (RPP). The licensee stated that these soils have been previously released from lice nse controls. However, this statement is not accurate. The three subareas remaining under NRC license SNM-928 (the license), F, G, and N, have had various surveys performed withi n them for the purpose of demonstrating that they could be released from radiological con trols and removed from the license. These surveys are described, in part, in the licensee s May 3, 2021, letter.2 However, there has been no regulatory action to release these subareas f rom the license and they are therefore not released from license controls as stated by the licensee.
For the purpose of surveying areas of disturbed soils (not incl uding the 1206 Drainage sediment and spoils), the licensee divided soil depths into three groups : less than one foot below the ground surface, from one foot to one meter below the ground sur face, and one meter or more below the ground surface. As the NRC staff understands the pro posed method for surveying disturbed soil, the licensee will perform a gamma scan of soil before and after excavation of these three soil depths. The licensee proposed using an action level of two times background to determine if soil samples need to be obtained from excavated soil and sent offsite for laboratory analysis. The results for the laboratory analyses w ould then be compared to the requirements in License Condition 27.c. of the license to deter mine if the soil can be released for unrestricted use. The NRC staff notes that 2 times backgr ound is not an objective measure and cant be used for comparison against decommissioning criter ia.
Clarification requested:
Provide the rationale for dividing the soil into the three spec ified depths.
Provide a methodology for confirming that subsurface soil broug ht to the surface (not including the 1206 Drainage sediment and spoils) will not result in soils exceeding soil release criteria in any land area.
Internal Exposure Determination
The licensee discusses the use of a dispersibility factor (D) l ess than 10. However, this is not substantiated in NUREG-1400. The factors discussed by the lice nsee (resin being moist, large particles, a closed processing system) are already captured by the release fraction R and the confinement factor C.
1 Agencywide Documents Access and Management System (ADAMS) Accession No. ML19154A597 2 ADAMS Accession No. ML21123A290 3 ADAMS Accession No. ML13051A671 The licensee also states:
In considering an appropriate dispersion factor for particles t hat do not tend to become airborne, Figure 2.6 of NUREG-1400 was reviewed. This figure p rovides an example where quantitative dispersion factors are determined directly t hrough air sampling.
Although quantitative values cannot be determined at this time, NUREG-1400 supports use of dispersions factors less than 1.
The NRC staff reviewed Figure 2.6 of NUREG-1400 and cant corro borate the licensees interpretation. Figure 2.6 is related to Section 2.2.2.2 of NU REG-1400 discussing quantitative airflow studies. Figure 2.6 is related to the dispersion of ae rosols from the source of a release:
The D in Figure 2.6 is referred to as the dispersion factor. This is not the same as the dispersibility factor discussed in Section 1.2.3 of NUREG-140 0 for determining potential intakes.
Clarification requested:
Provide a justification for the use of a dispersibility factor (D) less than 10 that is consistent with Section 1.2.3 of NUREG-1400 for determining potential intakes.
The licensee was requested to address the requirements of 10 CF R 20.1204(g) for their expected mixture of radionuclides. 10 CFR 20.1204(g) states:
(g) When a mixture of radionuclides in air exists, licensees ma y disregard certain radionuclides in the mixture if
(1) The licensee uses the total activity of the mixture in demo nstrating compliance with the dose limits in § 20.1201 and in complying with the monitori ng requirements in
§ 20.1502(b), and
(2) The concentration of any radionuclide disregarded is less t han 10 percent of its DAC, and
(3) The sum of these percentages for all of the radionuclides d isregarded in the mixture does not exceed 30 percent.
The licensee evaluated 10 CFR 20.1204(g)(2) and (3) but did not address 10 CFR 20.1204(g)(1).
Clarification requested:
The requirements that specify when a licensee may disregard cer tain radionuclides in a mixture when determining internal exposure are found in 10 CFR 20.1204( g). NRC guidance on 10 CFR 20.1204(g) can be found in NUREG-1736. 4 NUREG-1736 presents several examples of calculations using mixtures of radionuclides.
The following questions and answers on the NRC website may also be helpful in addressing mixtures of radionuclides and when certain radionuclides may be disregarded when assessing internal dose:
Q121: http://www.nrc.gov/about-nrc/radiation/protects-you/hppos/qa121.html
Q403: http://www.nrc.gov/about-nrc/radiation/protects-you/hppos/qa403.html
Q453: http://www.nrc.gov/about-nrc/radiation/protects-you/hppos/qa453.html
In particular, question Q403 addresses disregarding the contrib ution of a radionuclide for recording and reporting purposes if it is less than 10% of the committed effective dose equivalent.
The licensees proposed method of assessing mixtures of radionu clides does not meet the requirement of 10 CFR 20.1204(g)(1) and is not consistent with the guidance provided above for this regulation. Specifically, the licensees proposed methodo logy does not account for the activity of those radionuclides it disregarded based on the der ived air concentration analysis.
Either provide the NRC staff with a proposed method of assessin g mixtures of radionuclides that meets the requirement of 10 CFR 20.1204(g)(1) and is consistent with the guidance provided above for this regulation or provide justification for an alter nate methodology. An alternate methodology that does not meet the requirement of 10 CFR 20.120 4(g)(1) will require an exemption to this regulation.
Radiation Protection Instrumentation
Scan MDC
The licensee provided an example scan MDC calculation for beta contamination. However, the scan MDC for alpha contamination uses a different equation. Th e licensee should provide an example of a calculated scan MDC for alpha contamination as pre viously requested.
The NRC staff notes that there appears to be an extra subscript for the surface efficiency in its equation for scan MDC:
4 ADAMS Accession No. ML013330179 This appears to have been addressed in the RPP (Note 3 in Secti on 7.5 of the RPP). However, in Note 1, the licensee provides the following equation for min imum detectable activity (MDA),
where PA is the probe area as defined above:
The PA/100 term appears to be incorrectly divided in the denomi nator.
In Section 7.5.1, Contamination Survey Instrument Counting Effi ciency, of the RPP, the licensee states:
The RSO may provide alternative methods for determining calibra tion efficiency, which could include use of the counting efficiency provided on the in strument calibration certificate. Alternative methods shall be documented with the instrument records.
Please provide the NRC staff with an example of such an alterna tive method. The NRC staff can accept alternative methods to those given in guidance docum ents, but not without details sufficient for the NRC staff to understand those alternative me thods.
Also, please clarify the use of calibration efficiency and c ounting efficiency as used above.
Clarification requested:
- Provide an example of a calculated scan MDC for the alpha cont amination expected at the Cimarron site as previously requested.
- Confirm the PA/100 term in the MDA equation above.
- Clarify the use of calibration efficiency and counting eff iciency as used above.
- Provide the NRC staff with the details of any alternative meth ods that the licensee wants to use for determining counting efficiency, scan MDC, etc.
Surface efficiencies
The licensee provided a novel approach to assigning beta surfac e efficiencies to its radionuclide mixture. This novel approach derived an overall surface efficie ncy for the radionuclide mixture based on an average beta energy of that mixture.
The NRC staff cant corroborate this novel approach as it doesn t address the physics behind the derivation of the surface efficiency. The surface efficien cy is derived for individual particles, not for mixtures. For example, a radionuclide with a high ener gy beta particle emission, such as Pa-234m (Emax=2.28 MeV), has no bearing on a radionuclide with a low energy beta particle emission, such as Th-234 (E max=0.19 MeV).
Clarification requested:
The licensee should provide a calculation of counting efficienc ies that utilizes an accepted methodology for incorporating surface efficiencies. If the lic ensee wants to use an alternative approach to determine counting efficiency, it should provide su fficient information for the NRC staff to evaluate the approach. This information could include, for example, a comparison of the alternative approach with the accepted methodology and any empi rical data developed by the licensee.