Hazards Assessment - doe-std-1136-20040191

DOE-STD-1136-2004

Guide of Good Practices for Occupatio nal Radiation Protection in Uranium Facilities

9.2.1 Hazards Assessment

The emergency management hazards assessment for a facility that stores or processes uranium or

its compounds should follow the basic assessment process outlined in the Hazards Assessment EMG (DOE

1992d). Unique properties and characteristics of uranium and its compounds should be considered at certain

steps in the hazards assessment process.

9.2.1.1 Description of Facility and Operations

The properties of the hazardous material do not significantly affect the manner in which this step of

the hazards assessment is performed.

9.2.1.2 Identifying and Screening the Hazards

The objective of this step is to identify hazards that are significant enough to warrant consideration

in a facility's emergency management program. It is recommended that screening thresholds (or quantities)

be selected for each hazardous material. This screening threshold value is then compared to the inventories

of the material at risk of being released from a single event. If a particular inventory of material is less than

the screening threshold value, the consequences of its release are presumed to be minimal. The potential

release of that inventory need not be analyzed further.

Several possible sources of screening threshold values are suggested by the EMG; the primary

source is the Threshold Planning Quantities (TPQs) published in U.S. Environmental Protection Agency

(EPA) regulations, 40 CFR 355, Appendix A. Neither uranium nor any of its compounds are listed in 40

CFR 355, Appendix A. A second recommended source of screening threshold values is the 40 CFR 302.4

List of Hazardous Substances and Reportable Quantities (RQs) (EPA 1995). Uranyl acetate and uranyl

nitrate are listed there, both with RQs of 100 pounds. Appendix B to 40 CFR 302.4 gives RQs for

radionuclides and specifies 0.1 Ci as the RQ for 234U, 235U and 238U.

Lacking any widely accepted screening value (such as a TPQ or RQ), it is appropriate to establish

facility and site-specific screening thresholds based on the properties of the material. A screening threshold

can be determined by modeling a unit release of the material to the atmosphere at ground level and

determining the consequences at some reference distance under conservative dispersion conditions. The

screening threshold value is typically a quantity that, if released, would produce consequences on the order

of one-tenth the threshold for protective action at the facility boundary.

Facility- and site-specific screening quantities for most materials are based on one hazardous

property of the material that dominates all other considerations. However, for uranium and its compounds,

three very different hazardous aspects need to be considered. When establishing a screening threshold, the

chemical toxicity of the element or compound and its radiological toxicity need to be compared. The

property for which the smallest release leads to an exposure or dose criterion being exceeded should serve

as the basis for the screening value. In general, for natural or low-enriched uranium, chemical toxicity will

be the dominant concern for soluble materials while radiological toxicity (radiation dose) will be limiting

for insoluble materials. For enrichment above a few percent (as 235U), the limiting concern may be either

chemical or radiological, depending on the chemical form, solubility, and particle size of the material. For

highly enriched material, radiological toxicity will nearly always be limiting.

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