ML19091A082
| ML19091A082 | |
| Person / Time | |
|---|---|
| Site: | 07000925 |
| Issue date: | 04/01/2019 |
| From: | Lux J Environmental Properties Management |
| To: | Davis P, Robert Evans, Kenneth Kalman Document Control Desk, Office of Nuclear Material Safety and Safeguards, NRC Region 4, State of OK, Dept of Environmental Quality (DEQ) |
| References | |
| Download: ML19091A082 (4) | |
Text
9400 Ward Parkway
- Kansas City, MO 64114 Tel: 405-642-5152
- jlux@envpm.com April 1, 2019 Mr. Ken Kalman U.S. Nuclear Regulatory Commission 11555 Rockville Pike Rockville, MD 20852-2738 Mr. Paul Davis Oklahoma Department of Environmental Quality 707 North Robinson Oklahoma City, OK 73101 Mr. Robert Evans U.S. Nuclear Regulatory Commission 1600 East Lamar Blvd; Suite 400 Arlington, TX 76011-4511 Re: Docket No.70-925; License No. SNM-928 Residual Dose Modeling
Dear Sirs:
In a letter dated November 21, 2018, solely as Trustee for the Cimarron Environmental Response Trust (CERT), Environmental Properties Management LLC (EPM) submitted a proposal to the U.S. Nuclear Regulatory Commission (NRC) and the Oklahoma Department of Environmental Quality (DEQ) regarding the scope of work and budget for calendar year 2019. In a letter dated March 20, 2019, the NRC expressed concern with one aspect of the scope of work proposed for Task 2, License Compliance. Scope Item 10 read, Perform probabilistic dose modeling using reasonable exposure scenarios and known uranium enrichment values to evaluate possible area-specific alternative derived concentration goal levels (DCGLs).
The NRCs expressed concern, as presented in the March 20, 2019 letter, was stated as follows:
During our January 24, 2019 teleconference, the NRC staff noted that changes in DCGLs would cause Cimarron to no longer be grandfathered under the Site Decommissioning Management Plan (SDMP). Mr. Lux stated that CERT is evaluating the option of staying under the SDMP or switching to the license termination rule.
The NRC staff cautions that it is important for Cimarron to fully understand the costs as well as the benefits when considering whether to use alternative DCGLs.
At this time, CERT does not propose to perform probabilistic dose modeling in order to propose an alternate DCGL. The CERT wants to make clear its intention to decommission the Cimarron
Mr. Ken Kalman U.S. Nuclear Regulatory Commission April 1, 2019 Page 2 site in accordance with the SDMP (under which it is currently grandfathered) and has no intention to switch to the license termination rule (LTR).
The CERT recognizes that uncertainty associated with aquifer remediation will remain significant until actual concentration decline rates are established during groundwater remediation, and to a certain extent throughout groundwater remediation. However, EPM believes that, as both licensee and as fiduciary, the development of a site-specific, probabilistic dose model is appropriate at this time.
Under the SDMP, once activity concentration limits for soil and groundwater established in the license have been achieved, the site may be released for unrestricted use. For the Cimarron site, the activity concentration of uranium in soil must be less than 30 picocuries per gram (pCi/g),
and the activity concentration of uranium in groundwater must be less than 180 picocuries per liter (pCi/L). The decommissioning criterion for soil was derived from the 1981 Branch Technical Position Disposal or Onsite Storage of Residual Thorium or Uranium (Either as Natural Ores or Without Daughters Present) From Past Operations. The decommissioning criterion for groundwater was based on an annual dose from drinking water, derived from default activity-to-dose ratios for uranium isotopes and an assumed enrichment value for uranium in groundwater. It has been subsequently determined that the enrichment of uranium in groundwater is lower than had been used for that determination.
Under the LTR, a site may be released for unrestricted use if the residual dose to the maximally exposed individual is less than 25 millirem per year (mrem/yr) total effective dose equivalent (TEDE). The licensee is required to determine the residual dose to the maximally exposed individual prior to license termination. If the calculated residual dose is between 25 and 100 mrem/yr, the site can only be released for restricted use. The license termination process will be much longer and more costly due to the requirements which must be satisfied to justify termination of the license with restriction on the future use of the Site.
Under the SDMP, the licensee must demonstrate that the residual dose is less than 25 mrem/yr to obtain quick and economical termination of the license. If the residual dose is between 25 and 100 mrem/yr, the license termination process is just as complicated and costly as under the LTR, even if the activity concentration limits stipulated in the license have been achieved. If the residual dose is greater than 100 mrem/yr, it is unlikely that the license will be terminated, even if the activity concentration limits stipulated in the license have been achieved.
A site-specific dose probabilistic dose model will enable the CERT to determine the dose associated with uranium in soil as well as in groundwater. The use of site-specific inputs and the
Mr. Ken Kalman U.S. Nuclear Regulatory Commission April 1, 2019 Page 3 use of distributions in place of deterministic values for some parameters will provide valuable information to the CERT in considering the groundwater remediation endpoint needed to achieve not only the license criteria, but a residual dose that is less than 25 mrem/yr considering both soil and groundwater.
For example, assume that a site-specific, probabilistic dose model indicates that 25 mrem/yr equates to 300 pCi/L uranium in groundwater and 50 pCi/g in soil. Also assume that the maximum activity concentration of uranium is 30 pCi/g in soil and 180 pCi/L in groundwater.
The residual dose from that soil would be 15 mrem/yr, and the residual dose from that groundwater would be another 15 mrem/yr. The total residual dose may exceed 25 mrem/yr (if that soil and groundwater is co-located). In that instance, the CERT would want to reduce the concentration of uranium in groundwater to less than 180 pCi/L. Having that information in advance would enable the CERT to not only achieve the SDMP criteria, but to plan for a residual dose of less than 25 mrem/yr to expedite license termination.
If after ten years of remediation, the CERT determines that funding is not sufficient to achieve license termination, it may become necessary to propose an alternate decommissioning criterion for groundwater. At that time, it would be important to know if a site-specific, probabilistic dose model would provide sufficient benefit to justify switching from the SDMP to the LTR; that may be the only viable path to license termination.
The CERT has access to only those funds which are available in the Trust accounts. Unlike a licensee who is conducting business, there is no external source of funds which could be tapped to increase the funds available for decommissioning. The decommissioning cost estimate provided in Facility Decommissioning Plan - Rev 1 showed that funding is sufficient to achieve license termination without the inclusion of a 25% contingency cost. With the addition of a 25%
contingency (per NUREG 1757, Consolidated Decommissioning Guidance), the Trust accounts are under-funded.
The CERT will monitor the rate of contaminant concentration decline and periodically revise the decommissioning cost estimate as in-process monitoring data enables revision of the estimated duration of remediation. The benefit of developing a dose model at this time is to enable the CERT to account not only for the rate of decline for uranium concentration, but for residual dose reduction.
To reiterate, the CERT has no intention to switch from the SDMP to the LTR. But the CERT believes that the development of a residual dose model is the responsible and technically defensible way to prepare for the future. The CERT also believes that the development of the
Mr. Ken Kalman U.S. Nuclear Regulatory Commission April 1, 2019 Page 4 dose model when both the CERT and the NRC have available personnel who have a long history with the site and who can ensure that the dose model was developed appropriately.
In submitting revision 1 of the proposed budget for 2019, EPM will re-word the description of the dose model to clarify that rather than evaluate alternative DCGLs, a residual dose model will be prepared to determine the relationship between concentration and dose for both soil and groundwater. This will provide valuable information for the continued evaluation of the adequacy of Trust funding to complete the decommissioning of the Cimarron Site.
Should you have any questions or desire clarification of this response to NRCs concern, please contact me at jlux@envpm.com or 405-642-5152. Thank you.
Sincerely, Jeff Lux, P.E.
Project Manager cc:
Michael Broderick, Oklahoma Department of Environmental Quality NRC Public Document Room (electronic copy only)