Addressing Daughter Products as Part of a Facility’s Inventory

1. Addressing Daughter Products as Part of a Facility’s Inventory Nathan Cathey EFCOG Safety Analysis Work Shop Santa Fe, New Mexico May 6, 2012 Information Release – PNNL-SA-87527

2. Addressing Daughter Products as Part of a Facility’s Inventory • Why consider in-growth of daughter products? • Some daughter products have higher DOE-STD-1027 Threshold Quantities (TQ) or ICRP-71 dose conversions factors than their parents • This can impact • Hazard Categorization - comparison to TQ • Comparison to facility’s limits placed on inventory to maintain dose consequences within analyzed values • Describe an approach to address potential impacts from daughter products as part of a facility’s radioactive material inventory. • The isotopes of concern are identified, • The method of evaluating the decay chains, and • Factors comparing the daughter products to their parents are presented

3. Overview – Types of Material at PNNL Facilities

4. Overview – Types of Material at PNNL Facilities (cont.) • PNNL has several radiological facilities and one Hazard Category 2 facility • PNNL uses a wide variety of materials in performing various research activities. • Isotopes run the gamut • Medical • Spent fuel • National Security • Waste stream treatment studies

5. Overview – Types of Material at PNNL Facilities (cont.) • Thousands of sealed sources and samples of radioactive materials are in use at PNNL • Some radioactive materials are kept for decades • Inventory of isotopes within in given source or sample will change over time which could potentially impact comparison of material to • Hazard Category threshold quantities (HC-3 TQs) • Radioactive material inventory limits

6. Method of Evaluation • Initial effort performed in 2005 • Purpose was to determine impact on HC-3 TQs • Work expanded to look at impact on Inventory Tracking at PNNL Hazard Category 2 facility in 2012 • Overview of Method • Determine isotopes of interest • Evaluated selected isotopes for various time periods (from weeks to up to 100 years) • Determine impact on HC-3 TQs • Determine impact on inventory tracking

7. Evaluation of Potential HC-3 TQ Impact • Initial work • 816 isotopes • First five daughters • Estimated parent and daughters’ activities for time at maximum activity or 100 years • Compared to HC-3 TQs then extended to HC-2 TQs • Excel Spreadsheet used to perform screening analysis

8. Evaluation of Potential HC-3 TQ Impact (cont.) • Screening narrowed consideration to 42 isotopes for evaluation • Some decay schemes can be complicated and require analysis via computer code.

9. Evaluation of Potential HC-3 TQ Impact (cont.) 226 Ra decay Radiological Health Handbook, US Department of Health, Education, and Welfare, January 1970

10. Evaluation of Potential HC-3 TQ Impact (cont.) • Three primary methods were used to determine the activity of the parent and daughters at different decay times • Determine decay with ORIGEN-S code (within the SCALE software package) (ORNL) • Determine activity based on derived equations (isotopes with one or two daughters) • Zr-88, Pm-144, Eu-147, Gd-146, Lu-174m, and Pt-188 • Combined approach for longer decay chains that were not in ORIGEN-S, • Pa-230, Cm-240, and Cf-248 • Determine and evaluate first daughter product in ORIGIN-S • Calculate parent and first daughter analytically

11. Evaluation of Potential HC-3 TQ Impact (cont.) • Decay Times (Years) Examined based on Isotope Type • Light Element 0.05, 0.1, 0.2, 0.3, 0.5, 1, 3, 10, 30, 100 • Actinide 0.05, 0.1, 0.3, 0.5, 1, 3, 5, 10, 30, 100 • All analysis started with 1 Ci of parent

12. Sum of Fraction for HC-3 TQs • For isotopes with one or two daughters or that the parent is in ORIGIN-S • Parent activity divided by HC-3 TQ • Daughter activity divided by HC-3 TQ • Summed for each time point • For isotopes with longer decay chains not in ORIGIN-S • Determine adjusted HC-3 TQ for first daughter • Sum of Fraction for decay chain • Parent activity divided by HC-3 TQ • First daughter activity divided by adjusted HC-3 TQ

13. Sum of Fraction for HC-3 TQs (cont.) • New HC-3 TQ was reciprocal of the maximum Sum of Fractions • Some reached their maximum in the first 2-3 weeks • Others continued to grow through 100 years. • HC-3 TQ unaffected for 28 of the 40 isotopes evaluated. • Fourteen isotopes that would impact HC-3 TQs • Ac-227, Gd-146, In-114m, Pa-231, Pt-188, Pu-241, Ra-223, Ra-225, Ra-226, Th-234, U-232, U-233, U-234, and Zr-88. • Established administrative thresholds in PNNLs Radioactive Material Tracking (RMT) system to account for daughter product in-growth

14. Results of HC-3 TQs

15. Impact on Inventory tracking at 325 Building • PNNL operates one Hazard Category 2 facility: 325 Building – Radiochemical Processing Laboratory (RPL) • Dose Consequences and TSR Inventory Limit based on “Equivalent Curies” • Pu-239 Equivalent (Pu-239E) for particulates • H-3 Equivalent (H-3E) for gases • Approach similar to that of HC-3 TQ • Evaluated same 40 isotopes based on earlier work • Tracked particulates and gas (e.g., Rn-222) separately. • Pu-239E and H-3E conversion factors based on : • ICRP-71 dose conversion factors • Considered inhalation, groundshine, and submersion • Conversion factors are divisors

16. Equivalent Dose For Each Decay Chain • For isotopes with one or two daughters or the parent is in ORIGIN-S • Parent divided by Dose Conversion Factor (DCF) • Daughter activity divided by DCF • Summed for each time point • For isotopes with longer decay chains not in ORIGIN-S • Determine adjusted DCF for first daughter • Parent divided by DCF • Daughter activity divided by adjusted DCF • Summed for each time point

17. Equivalent Dose For Each Decay Chain (cont.) • Impact on H-3 E • Maximum Quantity from daughter ingrowth is approximately 2 CiH-3 E • Five orders of magnitude less than they RPL TSR limit for H-3 E • Not analyzed further • Fifteen nuclides have adjusted Pu-239 E conversion factors greater than the parents alone. • Values for Gd-146 and Pt-188 not calculated since these isotopes are not presently at PNNL.

18. Results of Equivalent Dose Evaluations

19. Impacts of Equivalent Dose Evaluations • How does this impact the RPL inventory in RMT? • Using the adjusted Pu-239E CF would • Increase the Pu-239E by < 10 % (includes “double counting” any parent –daughter inventory entries) • Increase the Pu-239E by ~ 6 % (accounting for top parent –daughter inventory entries) • Options considered addressing the in-growth of daughters • Have user enter daughter product activity at specified times • Revised RMT to periodically calculate parent and daughter activities • Revise RMT to use adjusted DCF to report Pu-239E inventory • Monitor impact through periodic assessments

20. Recommendations for Equivalent Dose Impacts • Recommend that DCFs in RMT not be changed at this time • Monitor impact through periodic assessments • Basis of Recommendation; • Quantities of applicable isotopes are generally small • Doesn’t introduce new requirements on users or complicated routines in RMT • Current inventory is ~ 18% of TSR LCO limit • TSR LCO OPERATING LIMT is 10% less than that analyzed in DSA • RPL Control Range is 10% less than the TSR LCO OPERATING LIMIT

21. Summary • Hazard Category 3 Threshold Quantities • Fourteen nuclides have adjusted HC-3 TQs greater than the parents alone: • Ac-227, Gd-146, In-114m, Pa-231, Pt-188, Pu-241, Ra-223, Ra-225, Ra-226, Th-234, U-232, U-233, U-234, and Zr-88. • Results have been integrated into PNNLs Radioactive Material Tracking system • Radioactive Material Inventory • Fifteen nuclides have adjusted Pu-239E conversion factors greater than the parents alone: • Ac-227, Bk-249, Cf-253, Gd-146, In-114m, Pa-231, Pt-188, Pu-241, Ra-223, Ra-225, Ra-226, Th-234, U-232, U-233,, and Zr-88 • Impact will be monitored through periodic assessment