Criticality alarm systems may consist of one to several detectors per unit. In multi-
detector units (e.g., three detectors), at least two detectors shall be at the alarm level
before initiating the alarm; in redundant systems, failure of any single channel shall
be into the trip state (ANSI, 1986a).
Nuclear Accident Dosimetry
In accordance with DOE Order 420.1A, the nuclear criticality safety program shall
be evaluated and documented and shall include:
Assessment of the need for criticality accident detection devices and installation of
such equipment where total risk to personnel will be reduced.
Nuclear accident dosimetry is required when the fissionable material mass exceeds
the ANSI/ANS-8.3 limits discussed in Section 7.4.1 and the probability of
criticality is greater than 10-6 per year.
Requirements for nuclear accident dosimetry programs at DOE facilities are found
in 10 CFR 835.1304 (DOE, 1998a). A nuclear accident dosimetry program shall
include the following:
-- A method to conduct initial screening of personnel involved in a nuclear
accident to determine whether significant exposures to radiation occurred;
-- methods and equipment for analysis of biological materials;
-- a system of fixed nuclear accident dosimeter units (sometimes referred to as
area dosimeters); and
-- personnel nuclear accident dosimeters (PNADs) worn by all individuals who
enter locations with specified quantities of fissile material.
Additional desirable features of a nuclear accident dosimetry program include:
-- Facilities to evaluate fixed dosimeters and/or PNADs;
-- a method to determine the approximate neutron spectrum;
-- a method to determine the activity of 24Na in blood and 32P in hair; and
-- a method to correct dosimeter results for actual spectrum (if known).