ML24040A185
| ML24040A185 | |
| Person / Time | |
|---|---|
| Site: | 07000925 |
| Issue date: | 02/09/2024 |
| From: | Lux J Environmental Properties Management |
| To: | James Smith Office of Nuclear Material Safety and Safeguards, Document Control Desk |
| References | |
| Download: ML24040A185 (1) | |
Text
Page 1 of 4 February 9, 2024 Mr. James Smith U.S. Nuclear Regulatory Commission 11555 Rockville Pike Rockville, MD 20852-2738 Re: Docket No. 07000925; License No. SNM-928 Cimarron Environmental Response Trust Response to NRC Concerns Regarding Responses to RAIs Related to Health Physics
Dear Recipients:
In a letter dated October 2, 2023, the U. S. Nuclear Regulatory Commission (NRC) issued requests for additional information (RAIs) resulting from the NRCs technical review of Facility Decommissioning Plan - Rev 3 (the DP). Solely as Trustee for the Cimarron Environmental Response Trust (CERT), Environmental Properties Management LLC (EPM) submitted responses to those RAIs in a letter dated December 8, 2023.
Subsequent communications with the NRC identified a need for clarification or additional information (addressed herein as concerns) related to those responses. This letter provides that information.
NRC Concern: The formula provided in the Radiation Protection Plan (RPP) for calculating the minimum detectable activity (MDA) is identified as equivalent to Equation 3.11 in NUREG-1507, but it isnt. Where the formula in NUREG-1507 uses the term Ts+b, the licensee uses Ts.
EPM Response: In discussing terms in Equation 3.11, NUREG-1507 states that Ts+b and Tb are the sample and background counting times, respectively. As shown in the Note following section 7.5.2.c of the RPP, Rev. 5, Ts is the sample counting time, which is the same count time as Ts+b in NUREG-1507. We eliminated the term +b in the RPP to minimize the potential for a technician to add the background count time to the sample count time for this term.
When reviewing Section 7.5.2 of the RPP to respond to this comment, we recognized a typographical error in the numbering of the Notes following Section 7.5.2 of the RPP. The first two notes are both numbered 1. The numbering of notes will be corrected to sequentially number each note.
NRC Concern: The formula provided in the RPP for calculating the alpha scan minimum detectable concentration (MDC) is identified as being extracted from NUREG-1575, Volume 2 Equation 6.14. NUREG-1575 is a draft document; each page states, DO NOT CITE OR QUOTE. Is there another document that can be referenced as the origin for this formula?
February 9, 2024 Response to NRC Concerns Regarding Responses to RAIs Related to Health Physics Page 2 of 4 EPM Response: In a letter dated August 21, 2021, the NRC issued a request for supplemental information (RSI) following the acceptance review of Facility Decommissioning Plan - Rev 2.
To expedite the review process, on November 10, 2021, EPM informally submitted a draft version of Facility Decommissioning Plan - Rev 3 (the DP), requesting a pre-application audit.
That submittal included attached responses to the NRCs RSIs. The attachments pointed to sections of the DP (including the RPP which was Appendix M to the DP) that were believed to provide the requested information. Because this was an informal submittal, it was not uploaded to the NRCs Agencywide Document Access and Management System (ADAMS).
In Attachment 3 to the November 2021 document, we explained that scanning will only be used to identify the location of the maximum total surface contamination. A static measurement is then recorded at these area(s) of highest contamination, followed by collection of a smear to be counted in an on-site instrument. This technique (i.e., scanning to identify areas of elevated concentration, followed by static counts and smears in those areas) is used to demonstrate compliance with license limits for releasing materials and equipment for unrestricted use. Only the static measurements and smear counts are considered technically sufficient to document compliance. Counts from scanning are not documented, and do not provide data used to release material or equipment for unrestricted use.
Consequently, the scan MDA is only marginally related to release surveys because data from the scan does not form the basis for a determination of compliance with release limits. However, to address the NRCs RFI, the guidance provided in the draft revision to NUREG-1575 Volume 2 was referenced in the RPP.
The equation for the determination of beta scan MDA correctly referenced NUREG-1507, but not the equation for alpha scan MDA. The RPP will be revised to include the equation for alpha scan MDA in NUREG-1507 and to correctly refer to Equation 6.10 in NUREG-1507, Rev. 1.
Notably, the only difference from the alpha scan MDC used in NUREG-1507 is with respect to total efficiency. The term used in NUREG-1575 Volume 2, as adopted in the RPP, is 4 detector efficiency. NUREG-1507 determines total efficiency by multiplying the instrument efficiency by the surface efficiency. RPP, Rev. 5 will replace the equation in NUREG-1575 with the equation in NIREG-1507 and reference NUREG-1507 Equation 6.10 instead of NUREG-1575 Volume 2 Equation 6.14.
NRC Concern: The formula provided in the RPP for calculating the beta scan MDC is identified as being extracted from NUREG-1507, Revision 2, Section 6.2.4.
EPM Response: The RPP references NUREG-1507, Section 6.2.4,; however, it doesnt reference Revision 2. We believe no revision to the RPP is needed.
February 9, 2024 Response to NRC Concerns Regarding Responses to RAIs Related to Health Physics Page 3 of 4 NRC Concern: Reviewing the example calculation for the beta MDC scan, the surface efficiency is identified as 0.5. NUREG-1507 describes the use of a surface efficiency of 0.5 only for those radionuclides with a maximum beta emission of greater than 0.4 MeV. Th-231 and Th-234, two beta emitting radionuclides identified by the licensee as present on site, have maximum beta energies significantly less than 0.4 MeV. What is the technical basis for using a surface efficiency value of 0.5?
EPM Response: As indicated in our response to NRCs August 2021 request for clarifications related to the RPP (EPM Letter of November 2021), the surface efficiency factor for beta emitters we will use at the site is 0.3, not 0.5. A calculation was performed to determine the appropriate surface efficiency factor (EPM036-CALC-001, Documentation of Calculations to Support Response to NRC-October 2021.). This information was incorporated into Rev. 5 of the RPP.
Note 1 on Page 7-6 of the RPP states that the value for surface efficiency to determine the scan MDC for beta is 0.3. The example calculation on Page 7-8 of the RPP incorrectly shows a value of 0.5 for the surface efficiency. The example calculation will be revised to replace the surface efficiency value of 0.5 with 0.3.
NRC Concern: The licensee states that some instruments used for release surveys have minimum detection limits that are less than 10% of the limit for unrestricted release, while others have minimum detection limits that are less than 50% of the limits for unrestricted release. Please provide additional detail on which instruments will fall into which category. Demonstrate through calculations that that each instrument is capable of meeting that criteria, and the measures the licensee will take to make sure the right instruments are used for the right surveys.
EPM Response: Table 7-1 of the RPP identifies the Ludlum Model 2360, equipped with detector Model 43-93, as the instrument that will used for unrestricted release surveys. This instrument is used to obtain direct surface contamination measurements during release surveys. The Ludlum Model 3030E is used to count smears collected to determine the quantity of removable contamination present on a surface. Typical MDAs for these instruments are:
Model 2360/43 This instrument is used to measure direct surface contamination; the release criterion for direct surface contamination for both alpha and beta is 15,000 dpm/100 cm2 (maximum) and 5,000 dpm/100 cm2 (average). For this instrument, the alpha MDA is <100 dpm/100 cm2; the beta MDA is <650 dpm/100 cm2. The alpha MDA is less than 10% of the average surface contamination limit and the beta MDA is above 10% of this limit, but far below 50% of the limit.
Model 3030E - This instrument is used to measure removable contamination. The release criterion for removable surface contamination for both alpha and beta is 1,000 dpm/100 cm2. For
February 9, 2024 Response to NRC Concerns Regarding Responses to RAIs Related to Health Physics Page 4 of 4 this counter, the alpha MDA is <8 dpm/100 cm2; the beta MDA is 120-140 dpm/100 cm2. The alpha MDA is less than 10% of the limit and the beta MDA is slightly above 10% of the limit, but far below 50% of the limit.
Section 15.3.3 of the DP, Shipping Package Surveys, discusses using instruments that have minimum detection limits that are less than 10% of the unrestricted release limits specified in Section 15.1. This value will be corrected to 50% of the unrestricted release limits to be consistent with DP Sections 15.3.4, Release Surveys and 15.3.5, Routine Surveys.
Exposure rates are measured using a Ludlum Model 19, which is capable of measuring exposure rates <5 µR/hr. Discussions with the instrument manufacturer indicate that the lower detection limit for the Model 19 is approximately 1 µR/hr. The exposure rate limit for unrestricted release is 5 µR/hr above background (at 1 meter). The background exposure rate is rarely if ever less than 5 µR/hr, so the effective exposure rate limit will be greater than 10 µR/hr. The Ludlum Model 19 has an MDA that is far below 50% of that limit.
Should the NRC desire additional clarification or information, EPM will be pleased to respond as soon as practical.
Sincerely, Jeff Lux Project Manager cc: (electronic copies only)
Stephanie Anderson and Linda Gersey, NRC Region IV Rachel Miller, Paul Davis, Keisha Cornelius, Pam Dizikes, David Cates, and Jon Reid, DEQ NRC Public Document Room vcpsubmittals@deq.ok.gov