Fixed and Personnel Nuclear Accident Dosimeters

DOE-STD-1128-98

Guide of Good Practices for Occupational Radiological Protection in Plutonium Facilities

Oyan (1987) showed that radiation doses estimated from induced body activity can

vary by a factor of about 2 due to neutron energy spectrum or orientation effects and

by as much as 30% due to probe position. Doses based on indium foil activity can

vary by a factor of about 9 due to neutron energy spectrum effects, a factor of 3

depending on foil orientation relative to the incident field, and a factor of about 2 due

to probe window setting. Swaja and Oyan (1987) recommended that those count rates

above background during quick-sort techniques should be initially interpreted only as

an indication that the person has been exposed.

7.4.2.2 Fixed and Personnel Nuclear Accident Dosimeters

A comprehensive nuclear criticality dosimetry system should consist of stationary

(fixed-location, area) dosimeters, neutron and gamma dosimeters worn by personnel

(i.e., PNADs), and specialized laboratory equipment to evaluate the dosimeters.

Fixed nuclear accident dosimeter units should be capable of determining neutron

doses in the range of 10 rad to 10,000 rad with an accuracy of 25%. They should

also be capable of providing the approximate neutron spectrum to permit the

conversion of rad to rem. The gamma-measuring component of the dosimeter should

be capable of measuring doses in the range of 10 rem to 10,000 rem in the presence of

neutrons with an accuracy of about 20%. The number of fixed dosimeter units

needed and their placement will depend on the nature of the operation, structural

design of the facility, and accessibility of areas to personnel. Generally, dosimeters

should be placed such that there is as little intervening shielding and as few

obstructions as possible (ANSI, 1969b). The number and placement of dosimeters

should be periodically reverified to reflect changes in building design and operations.

Ease of dosimeter recovery after a criticality event should be considered in their

placement, including the possible need for remote retrieval.

10 CFR 835.1304 requires that PNADs be worn by all individuals who enter a

controlled area with specified quantities of fissile material. The PNADs should be

capable of determining gamma dose from 10 rad to 1000 rad with an accuracy of

20% and neutron dose from 1 rad to 1000 rad with an accuracy of 30% without

dependence upon fixed-unit data.

ANSI N13.3 (ANSI, 1969b) provides general criteria for nuclear accident dosimeters

that are reviewed below. Dosimeters, both fixed and personnel, should be protected

against radioactive contamination to avoid false measurements. Periodic inventory

methods should be established and audits made to ensure that the dosimeters are not

removed or relocated without appropriate approvals. Techniques for estimating the

effect of body orientation at the time of the exposure should also be developed.

7-14