Fixed and Personnel Nuclear Accident Dosimeters

DOE-STD-1128-98

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.

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