Release Fractions cont'd

DOE-STD-1027-92

ATTACHMENT 1

volatile/combustible category as defined by NRC, with the addition of sodium to the group.

The release fraction of 0.5 is somewhat higher than is usually estimated for these

compounds, but DOE chose to retain the conservative value. At the same time, DOE also

noted that use of such a release fraction would not be appropriate if a flammable

substance such as phosphorus had been turned into a phosphoric acid solution, the

normal form for research activities. At that point, it would be a material best represented

by the general powder/liquid/solid category described below.

DOE did not consider carbon-14 thresholds to be a major issue on the basis of typical

quantities used. As a result, carbon was grouped as a semi-volatile with the same release

fraction of 1 E-2. The DOE then decided to abandon the use of the unknown form

category as an unnecessary complication. NRC used this value for a number of the

isotope thresholds, largely relating to materials unlikely to be found outside of fission

product mixtures or sources. The use of a curie threshold for fission product mixtures

would capture such material in most DOE applications. Additionally, there was no

compelling reason to believe these materials would react to physical energy stresses

differently from most powders, liquids, or solids.

NRC did not use the nonvolatile in flammable liquid, nonvolatile in non-flammable liquid, or

nonvolatile solid categories in final calculations. DOE concurred with this approach and

dropped these categories because applying average release fractions over an entire

building makes such detailed subdivision of questionable value. DOE believes that the 1

E-3 value is a reasonably conservative approximation because it will be applied to an

entire building without scenario-specific considerations. DOE recognizes that some

accidents, particularly those involving powders and liquids, can produce much higher

values, whereas metal incidents would normally produce slightly smaller release fractions.

However, it is unlikely that any event will affect all material in a building, and high release

phenomena such as ion exchange explosions, powder pressurization, etc., will affect only

a localized fraction of the material. Therefore, the value is believed an adequate average

for hazard categorization purposes.

The final release fraction values for Hazard Category 2 were produced by DOE as listed

below:

Gases

1.0

(such as tritium, krypton, xenon, argon, radon,

chlorine, etc.)

Highly volatile/combustible

0.5

(phosphorus, sulfur, potassium, iodine,

sodium, bromine)

Semi-volatile

1 E-2

(selenium, mercury, cesium, polonium,

tellurium, ruthenium, carbon)

A-8