Nuclear Accident Dosimetry - doe-std-1136-20040177

DOE-STD-1136-2004

Guide of Good Practices for Occupational Radiation Protection in Uranium Facilities

7.4.2 Nuclear Accident Dosimetry

Nuclear accident dosimetry shall be provided for installations that have sufficient quantity of

fissionable material such that the excessive exposure of individuals to radiation from a nuclear criticality

accident is possible (10 CFR 835.1304(a)).

Requirements for nuclear accident dosimetry programs at DOE facilities are found in 10 CFR 835. A

nuclear accident dosimetry program shall include the following:

a. a method to conduct initial screening of individuals involved in a nuclear accident to determine

whether significant exposures have occurred

b. a system of fixed nuclear accident dosimeter units. Sometimes referred to as area dosimeters,

the dosimeters should be capable of yield ing estimated radiation dose and the approximate

neutron spectrum at their locations

c. personal nuclear accident dosimeters (PNADs)

d. methods and equipment for analysis of biological materials (such as 24Na activity in blood and

P activity in hair)

7.4.2.1 Initial Screening Evaluation

A nuclear accident dosimetry program should provide absorbed dose information within 24 hours after

the incident. A method should be established for immediately obtaining preliminary dose estimates to

distinguish exposed persons from the unexposed and should permit the detection of doses in excess of

approximately 10 rad (see ANSI N13.3 (ANSI 1969)). Discussions on initial screening evaluations to

segregate exposed from unexposed individuals (sometimes referred to as "quick sort techniques") are found

in several references (Moe 1988; Delafield 1988; Petersen and Langham 1966; Hankins 1979; Swaja and

Oyan 1987).

A common initial screening method is to provide all workers in areas requiring nuclear accident

dosimetry with an indium foil in their personnel dosimeter or security badge. During a criticality

excursion, the foil will become activated by neutrons per the 115In (n,gamma) 116mIn reaction and can be

measured with a portable beta-gamma survey instrument or ion chamber. The 116mIn has a 54-minute half-

life and releases a 1-MeV beta (maximum energy) and a 1.3-MeV gamma (80% of the time).

An alternate screening is to measure body activity due to neutron activation of the sodium in the

blood via the 23Na(n, gamma)24Na reaction. Sodium-24 has a 15-hour half- life and releases a 1.4-MeV beta

(maximum energy) and two gammas (1.37 MeV and 2.75 MeV). A beta-gamma survey meter is used to

measure the 24Na activity in the blood by placing the detector probe against the individual's abdomen and

having the individual bend forward to enclose the detector (Moe 1988). Alternatively, the probe can be

positioned under the armpit with the open window facing the chest area. Moe noted this

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