ML18129A390
| ML18129A390 | |
| Person / Time | |
|---|---|
| Issue date: | 05/09/2018 |
| From: | Office of Nuclear Material Safety and Safeguards |
| To: | |
| Faraz Y | |
| Shared Package | |
| ML18129A389 | List: |
| References | |
| Download: ML18129A390 (5) | |
Text
Information Contained Within Does Not Contain Export Controlled Information Reviewing Official: ECI Reviewer #154 Date: 04/03/18 NRC Question: What was the basis for using a smaller circular contaminated source area of 531 m2 within the 676 m2 room?
Centrus Response: Centrus staff performed the initial dose calculation assuming an area of 531 m2, which does not consider the entire area of the room. Centrus has revised the analyses which takes into consideration the entire area of the room (using the rectangular geometry). While the resulting DCGLW changed, the Centrus still intends to use 5,000 dpm/100 cm2 as the release criteria for the Final Status Survey contamination levels since it is more restrictive and consistent with ALARA practices.
Below provides a revised screen shot of the RESRAD-BUILD parameters used for this dose calculation.
10 CFR 1045 review and Export Controlled Information review completed by DC #4771 / ECI #154 on 04/03/2018 Page l 1
Below is a revised screen shot of the resulting calculation from RESRAD-BUILD.
The RESRAD-BUILD results indicate nearly 100 percent of the projected dose is due to the uranium isotopes and the highest dose occurs in the first year. Since a concentration of uranium isotopes equal to 5,000 dpm/100 cm2 will cause a projected dose of 3.19 mrem, this ratio can be used to calculate the concentration that will cause a projected dose of 25 mrem (DCGLW). Accordingly, the DCGLW is calculated using the Time 0 Dose (effectively the 1st years dose) in the following manner:
5,000 100
= 25 = 39,185 100 3.19 The resulting calculation establishes the DCGLW as 39,200 dpm/100 cm2 (rounded). While this value will meet the criteria from 10 CFR 20.1402 for unrestricted release, Chapter 4.0 of the Lead Cascade License Application Table 4.6-1 (cited below for reference) requires total contamination levels to be less than 5,000 dpm/100 cm2 prior to releasing for unrestricted use. Therefore, the Licensee intends to use 5,000 dpm/100 cm2 as the release criteria for the Final Status Survey contamination levels since it is more restrictive and consistent with ALARA practices.
10 CFR 1045 review and Export Controlled Information review completed by DC #4771 / ECI #154 on 04/03/2018 Page l 2
NRC Question: What was the basis for using the U-238 values from Table 5.7, Illustrative Example of Indoor Area Dose Factors, from NUREG-1575, Multi-Agency Radiation Survey and Site Investigation Manual (MARSSIM), Revision 1, for deriving the area factor provided in the submittal?
Centrus Response: The calculation provided in the Decommissioning Plan was intended to be a generic analysis. Centrus staff also performed a site-specific Indoor Area Dose Factor calculation. Below provides the revised information.
NUREG-1505 A Nonparametric Statistical Methodology for the Design and Analysis of Final Status Decommissioning Surveys was consulted to determine the method for determining the Area Factor (AF). Using NUREG-1505 guidance, RESRAD-BUILD was used to estimate a AF for 5,000 dpm/100 cm2 of natural uranium. The following values were plotted in Microsoft Excel. The graphical representation is shown below in Table XIV.a-1:
10 CFR 1045 review and Export Controlled Information review completed by DC #4771 / ECI #154 on 04/03/2018 Page l 3
Table XIV.a-1 Plot of Calculated Area Factors The resulting equation was then used to extrapolate the AF for the area with elevated activity.
AF = 36.098 x Area of Elevated Activity-1.001 The area of elevated activity for the two Class 1 survey units located in the X-3001 building is 9.316 m2. Therefore:
AF = 36.098 x 9.316-1.001 = 3.866 This yields a DCGLEMC of:
DCGLEMC = 39,200 dpm/100 cm2 x 3.866 = 151,555 dpm/100 cm2 To ensure that no additional sampling points were required, the Scan Minimum Detectable Concentration (MDC) (see Table XIV.c-1 of this Decommissioning Plan) was determined for the selected scanning technique and compared to the DCGLEMC. The Scan MDCactual for the scanning technique using a Floor Monitor is 1,786 dpm/100 cm2 beta and 1,594 dpm/100 cm2 alpha. Since Scan MDCactual < DCGLEMC, no additional sampling points are necessary for the elevated activity area survey.
Using the estimated size of the Class I area located in Train 2 Utility Bay at the Lead Cascade (roughly 9 m2), the calculations for determining the DCGLEMC are shown assuming a triangular grid spacing (L), 9 data points, and a DCGLW of 39,200 dpm/100 cm2.
10 CFR 1045 review and Export Controlled Information review completed by DC #4771 / ECI #154 on 04/03/2018 Page l 4
9
= = 1.075 0.866 9 AF = 36.098 x 1.075-1.001 = 33.577
= 39,200 33.577 = 1,316,218 100 Summary: This recalculated DCGLW of 39,200 dpm/100 cm2 (rounded) supersedes the DCGLW of 50,000 dpm/100 cm2 previously provided within Revision 1 of the Decommissioning Plan provided by ACO 18-0001 on January 5, 2018.
10 CFR 1045 review and Export Controlled Information review completed by DC #4771 / ECI #154 on 04/03/2018 Page l 5