General Safety Basis Concepts

DOE-STD-1120-2005/Vol. 1

2.0 GENERAL SAFETY BASIS CONCEPTS

2.1

Hazard Categorization

DOE-STD-1027-92 describes an initial and final hazard categorization process that is necessary

to determine applicability of 10 CFR 830, Subpart B requirements. The initial hazard

categorization is based strictly on the total radionuclide inventory as compared with Threshold

Quantities of DOE-STD-1027-92, Hazard Categorization and Accident Analysis Techniques for

Compliance with DOE Order 5480.23, Nuclear Safety Analysis Reports, as well as consideration

of criticality mass limits for fissile materials (i.e., per the asterisk to Table A.1 of the standard).

It is recognized that many retired facilities subject to decommissioning, as well as environmental

restoration projects, may not have adequate records or process knowledge available to predict

material inventory with 100% certainty. Various characterization methods may be employed

such as employee interviews, intrusive sampling, and non-destructive assay (NDA) techniques of

soil, surface and groundwater, and contaminated equipment and structures. These methods are

appropriate for hazard categorization provided they are sufficiently bounding. For example,

NDA techniques should fully account for instrument error.

Some facilities may not exceed Hazard Category 2 threshold quantities, but may contain fissile

materials in quantities greater than the theoretical mass limits for criticality specified in

Attachment 1 of DOE-STD-1027-92. These facilities are considered Hazard Category 2, unless

facility segmentation or the nature of the facility process precludes the potential for a criticality.

"Segmentation" as considered for purposes of determining criticality potential, means that it is

not physically possible to gather into one place the fissile material needed to achieve criticality.

The "Nature of the process" means there are no events that could conceivably lead to the

formation of a critical mass of fissile material, and no criticality controls are needed on any

parameter of the process to prevent a criticality accident.

A Nuclear Safety Technical Position, NSTP-2002-2 (Methodology for Final Hazard

Categorization of Nuclear Facilities from Category 3 to Radiological) describes an acceptable

methodology for a final hazard categorization of a Hazard Category 3 (HC3) nuclear facility.

The HC3 threshold values may be revised based on the physical and chemical form and available

dispersive energy sources, if the credible release fractions can be shown to be significantly

different than the values used in the Environmental Protection Agency (EPA) Technical

Background Document. A facility or activity may be downgraded below HC3 if inventory is

below threshold quantities as modified by these factors (i.e., physical/chemical form of material

and available energy sources).

The base information associated with a hazard categorization should provide adequate

information to: (1) identify the bounding radionuclide inventories at a facility; (2) substantiate

any assumptions used in calculating inventories; and (3) provide a defensible basis to support

hazard analysis associated with final hazard categorization. For facilities that have an initial or

final categorization above HC3, the basis and assumptions should be described within the DSA

as required by 10 CFR 830, Subpart B. Final hazard categorizations that result in a

determination of "below Hazard Category 3" based on a hazard analysis will require DOE

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