Hazard Categorization Reduction via Nature of the Process Argument Chelise Van De Graaff J. Todd Taylor Chad Pope, PhD, PE Idaho National Laboratory EFCOG Safety Analysis Workshop 2012 May 9, 2012

Two Methods of Reasoning Inductive Reasoning – Takes events and makes generalizations – An inductive argument can demonstrate only that the conclusion is probably true. Deductive Reasoning – Arrives at a specific conclusion based on generalizations – Provides complete proof of the conclusion, as long as the premises used are true. 2

A Deductive Reasoning Exercise This Presentation documents the results of a CSE and Hazard Categorization (HAD) performed for an Inspection Object (not a facility) that has: – not yet received Department of Energy approval. INL has worked toward the end, knowing and fulfilling the initial requirements 3

Hazard Categorization (HC) Methodology DOE-STD-1027 – Hazard Category 1, 2, and 3 facilities DOE-EM-STD – Less than Hazard Category 3, or Radiological, facilities Preliminary categorization primarily determined based on expected threshold quantities of radioactive material – HC2 Radionuclide Threshold: 1.18E+08 g of U-235 – HC3 Radionuclide Threshold: 1.9E+06 g of U-235 Consider the criticality lists for U-233, U-235 and Pu-239 – HC2 :(U-233, 500 g), (U-235, 700 g), (Pu-239, 450 g) Final Categorization may be different than the Initial Categorization based on 3 possible Reduction Methodologies 4

HC Reduction Methodologies 1.Reduce inventory of radionuclides to below threshold value(s) 2.Segmentation of a facility 3.Nature of the Process or the “Unmitigated Release” Argument Source: 5

HC Reduction via Nature of the Process “…the facility may still be shown to be Hazard Category 3 (or less than Hazard Category 3) if it was initially categorized as a Hazard Category 2 facility solely based upon the potential for criticality through an analysis that demonstrates nature of process precludes criticality, provided that no operational criticality safety controls or limits are needed. “In demonstrating that the nature of process precludes criticality, the analysis should demonstrate that a potential for criticality does not exist for a given material configuration, based on actual quantity, form, shape, and collocation with moderators and reflectors.” -DOE-STD-1027 Supplemental Guidance 6

HC Reduction Criteria via Nature of the Process 1.Does not present a criticality for a given material configuration, based on actual quantity, form, shape, and collocation with moderators and reflectors 2.Criticality is precluded through the use of only “high-level controls” – DOE-STD-1027 Supplemental Guidance 7

Inspection Object Five clad plates (10x10x2 cm) Approximate volume is 1000 cm 3 Uranium metal (nominally 100%) Enrichment no greater than 20% U-235 Total U-235 mass not greater than 3.82 kg* Arranged in multiple configurations Close proximity – Reflectors – Moderators – Both * The HC3 U-235 gram threshold quantity is1.9E+06 g 8

IO in Different Configurations 9

Inspection Object Activities Serve as a standard for experimentation aimed at establishing techniques for detection of fissionable materials Experiments performed at various INL facility (i.e. IO is portable), including nuclear, non-nuclear, and radiological facilities. Close proximity to dense materials acting as reflectors Close proximity to lighter materials acting as reflectors Subject to photons generated by linear accelerators at various energy levels Source: Idaho National Laboratory StandOff Experiment Range Source: 10

Inspection Object Possible Collocation Dense Reflectors – Lead – Concrete – Steel – Natural uranium – Depleted uranium Lighter Reflectors – Polyethylene – Light water – Heavy water – Graphite – Beryllium 11

Criticality Safety Evaluation Preliminary models determine the most reactive configurations featuring different reflectors and moderators Materials considered: Most reactive materials: – Moderator: Polyethylene – Reflecting: Graphite and Beryllium  Concrete  Heavy Water  Depleted U  Graphite  Light Water  Lead  Natural U  Polyethylene  Stainless Steel  Beryllium 12

Effectively Infinite Reflectors for Moderated and Unmoderated Inspection Object The most reactive Inspection Object configuration features interstitial polyethylene-moderation (between 2.5 and 3.0 cm) and effectively infinite, 6-sided, contiguous beryllium-reflection. 13

Results from Criticality Safety Evaluation The Bottom Line: All effectively infinite, contiguously reflected Inspection Object models are subcritical. 14

“High Level” Controls 1.A method of tracking and controlling radioactive material inventory in the facility where the Inspection Object is removed from a fully DOT- compliant shipping container shall be implemented such that the sum of the ratios as described in DOE ‑ STD ‑ 1027 ‑ 92 does not exceed one (1). 2.No other fissionable material may be present within the facility containing the Inspection Object. 15

HC Reduction Criteria via Nature of the Process 1.Does not present a criticality for a given material configuration, based on actual quantity, form, shape, and collocation with moderators and reflectors – IO cannot achieve criticality through material configuration – IO cannot achieve criticality through processes or activities 2.Criticality is precluded through the use of only “high-level controls.” – IO is protected via tracking/controlling and isolation methods. 16

The Happy Conclusion Upon Department of Energy approval of the high-level controls, The Inspection Object meets the criteria for the Nature of the Process argument to reduce the Hazard Categorization from Hazard Category 2 to less than Hazard Category 3 (i.e. Radiological) 17

Thank You 18

Additional Slides for Answering Questions “Unmitigated” Release External Neutron and Gamma Sources More results from the CSE 19

“For the purposes of hazard categorization, “unmitigated” is meant to consider material quantity, form, location, dispersibility, and interaction with available energy sources, but not to consider safety features that could prevent or mitigate a release.” –NSTP , DOE-STD-1027 “An evaluation of the nature of process should consider whether planned activities, operational upsets, and derivative design basis abnormal environments could alter the characteristics of the facility, packaging, or fissile material such that controls are needed to address the potential for criticality. For example, controls may not be needed to address criticality hazards in normal environments because material is in a solid form and environment that renders it geometrically safe, and because normal processes would not alter that form. However, nature of process must also consider whether derivative design basis accident environments would alter the physical form or environment of the material such that criticality controls are required.” -Section of DOE-STD-1027 Supplemental Guidance “Unmitigated” Release Source: 20

Interest if neutrons originating from an external source Six-factor formula: Factors related to specific properties related to material composition, physical size, cross sections, or other nuclear properties, and neutron diffusion lengths, i.e. physical properties of the system. No factor is altered by fissions originating from an external source Neutron life cycle basis definition: Does NOT mean that neutrons need to be present for k eff to exist External Neutron and Gamma Sources: Understanding k eff 21

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