Criticality Accident Dosimetry - STD-1128-98master0188

DOE-STD-1128-98

Guide of Good Practices for Occupational Radiological Protection in Plutonium Facilities

boxes or nonuniform distribution of plutonium oxide dust on the surface of gloves, can

produce large variations in the dose rate. Examples of these variations were given

previously.

Extremity doses are typically determined by TLD finger rings, which are usually worn

with the TLD chip facing the radiation source on the palm side of the hand. In glove-box

and in D&D operations, the photon dose is usually significantly higher than any neutron

dose. However, neutron dosimeters are sometimes worn to estimate extremity doses.

Two types of neutron extremity dosimeters have been used: nuclear track dosimeters

worn in special finger rings and specially calibrated TLD-albedo dosimeters worn on the

wrist or forearm. DOE STD-1095-95 (DOE 1995h) is currently applicable to personnel

dosimeters for whole body irradiation. However, it contains guidance for the

development of correction factors for neutron doses that may be applicable for

developing correction factors for neutron extremity dosimeters.

There is some question about the correct quality factor to apply to extremity neutron

dosimeters. Existing quality factors are defined in terms of linear energy transfer (LET),

so a numerical value for quality factor can be readily derived by calculation or

measurement of the neutron energy spectra. However, the relationship between quality

factor and LET was derived from biological experiments on cancer induction, especially

leukemia in blood-forming organs. There are no blood-forming organs in the extremities,

so there is no biological basis for large values of quality factors for extremity exposures.

However, regulatory agencies typically apply quality factors derived for whole-body

exposures to the extremities, thus for compliance purposes qualify factors should be

applied for extremity exposures.

6.3.4

Criticality Accident Dosimetry

A criticality safety program, which includes material control, criticality alarms, and

criticality accident dosimetry, is required as outlined in DOE Order 420.1A (DOE,

2003a). The requirements in 10 CFR 835.1304 require that fixed nuclear accident

dosimeters (NADs) and personnel nuclear accident dosimeters (PNADs) shall be worn by

all individuals entering a controlled area that contains certain quantities of fissile

materials, such as those required in DOE Order 420.1A (DOE, 2003a); which requires

installed criticality alarms. The criticality accident dosimetry system should follow the

provisions of ANSI/ANS 13.3-1988, Dosimetry for Criticality Accidents (ANSI, 1969a);

this standard is currently being revised. Information on criticality accident dosimetry is

also available from the International Atomic Energy Agency (IAEA, 1982).

6-24