Criticality Alarm Systems.

DOE-STD-1128-98

Criticality Alarm Systems. ANSI/ANS 8.3 (ANSI, 1986a) discusses the

performance and design criteria for criticality accident alarm systems.

The criteria include the following:

-- Criticality alarm systems shall be designed to detect immediately the

minimum accident of concern; the minimum accident may be

assumed to deliver the equivalent of an absorbed dose in free air of

20 rad at a distance of 2 meters from the reacting material within 60

seconds.

-- Systems shall be designed so that instrument response and alarm

latching shall occur as a result of radiation transients of 1-

millisecond duration. The alarm signal shall be for evacuation

purposes only and of sufficient volume and coverage to be heard in

all areas that are to be evacuated. Very high audio background noise

in some areas may require that the alarm be supplemented with

visual signals; however, high background noise is a dangerous

situation that should be prevented by design. Instrument response to

radiation shall be calibrated periodically to confirm the continuing

performance of the instrument. The calibration interval may be

determined on the basis of experience but shall be no less frequent

than annually. Tests should be performed at least monthly and the

results of testing should be documented.

The standard does not quantify criteria for reliability or the rejection of

false alarms. Consideration should be given to the avoidance of false

alarms as accomplished by providing reliable single detector channels or

by requiring concurrent response of two or more detectors to initiate the

alarm. (ANSI 1986a).

Fixed Nuclear Accident Dosimeters. All DOE facilities that have

sufficient quantities and kinds of fissile material to potentially constitute

a critical mass, such that the excessive exposure of personnel to radiation

from a nuclear accident is possible, shall provide nuclear accident

dosimetry for those personnel (10 CFR 835.1304). Requirements for

fixed nuclear accident dosimeters are found in DOE Order 420.1A

(DOE, 2003a).

Effluent Monitors. Facilities that deal with unencapsulated plutonium

should have continuously operating effluent monitors to determine

whether or not plutonium is being released to the environment. Effluent

monitor criteria is found in IEC Publications 761-1 and 761-6 (IEC,

1983) and ANSI N42.18 (ANSI, 1974b) and should be performed.

Similar to airborne contamination monitors, effluent monitors should be

tested for air in-leakage at least annually or when seals or "O" rings are

replaced.

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