Criticality Alarms and Nuclear Accident Dosimetry

DOE-STD-1128-98

time period with about 20% in the first half-hour. The excursion

concluded after the boiling off of about 6 L of water and the settling of

some organic matter after it had extracted plutonium from the aqueous

phase. Three workers in the vicinity of the tank during the initial spike

received doses greater than regulatory limits. One worker about 5 to 6 ft

from the tank received 110 rem, another approximately 9 ft away

received about 43 rem, and the final worker about 26 ft away received

about 19 rem.

7.4

CRITICALITY ALARMS AND NUCLEAR ACCIDENT DOSIMETRY

Requirements for criticality alarm systems and nuclear accident dosimetry are presented in

this section. Criticality alarm systems provide rapid warning to individuals in the

immediate accident location and nearby locations to evacuate to a predesignated assembly

location. Specific requirements for the criticality alarm system are found in DOE Order

420.1A (DOE, 2002a) and ANSI/ANS-8.3 (ANSI, 1986a). Key requirements that may be

of interest for the health physics staff are summarized in Section 7.4.1. Paxton (1966) noted

that lives have been saved in past criticality accidents by radiation alarms coupled with

effective evacuation procedures. Nuclear accident dosimetry, discussed in Section 7.4.2,

provides the means of determining the dose to workers in the vicinity of the excursion.

7.4.1

Criticality Alarm System

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 alarm systems,

and installation of such equipment where total risk to personnel will be reduced.

The basic elements and control parameters of programs for nuclear criticality safety

shall satisfy the requirements of the following American Nuclear Society's

ANSI/ANS nuclear criticality safety standards:

ANSI/ANS-8.3-1986, "Criticality Accident Alarm System," however paragraphs

4.1.2, 4.2.1 and 4.2.2 shall be followed as modified in section 4.3.3.c and e of DOE

Order 420.1A.

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