Criticality Alarms and Nuclear Accident Dosimetry

DOE-STD-1128-98

Guide of Good Practices for Occupational Radiological Protection in Plutonium Facilities

per liter; however, in this situation apparently the solution was drawn from a sump

through a temporary line that was being used for cleanup. The excursion had an initial

pulse of about 1016 fissions. Following this spike, the tank was supercritical for 37.5

hours with the power level steadily decreasing (Stratton, 1967). The total yield of the

accident was about 8.2 x 1017 fissions distributed over a 37-hour 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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