Nuclear Criticality Safety - doe-std-1136-20040169

DOE-STD-1136-2004

Guide of Good Practices for Occupational Radiation Protection in Uranium Facilities

7.0 NUCLEAR CRITICALITY SAFETY

This chapter emphasizes present-day criticality concerns from the standpoint of what nuclear

criticality safety and radiological control personnel in a uranium facility need to know for the DOE mission

to be accomplished in a safe and cost-effective manner. It provides an overview of the administrative and

technical elements of current nuclear criticality safety programs. It does not provide a definitive discourse

on nuclear criticality safety principles or repeat existing guidance. For radiological control personnel who

require a greater understanding of nuclear criticality safety, the listed references provide a source of

detailed requirements and information.

Health physicists and other radiation protection personnel have the technical responsibility to

understand nuclear principles and the impact of these principles, in the form of the radiological conditions

that exist in DOE facilities as the result of the processing, handling, and storage of radioactive and/or fissile

materials. Radiation protection personnel provide an additional knowledgeable resource to help recognize

workplace situations that might lead to the violation of a nuclear criticality control parameter that could

contribute to an inadvertent nuclear criticality event. There have been occasions in which radiation

protection personnel have observed and stopped unsafe actions by facility personnel that, if allowed to

continue, might have resulted in a nuclear criticality accident. Radiation protection personnel must also be

aware of the potential impacts of their actions that would be viewed as routine for normal radiation

protection practice, but which could result in the violation of a nuclear criticality safety control parameter.

Finally, radiation protection personnel are the focus of emergency response actions should an inadvertent

nuclear criticality occur. These actions include use of emergency instrumentation, accident dosimetry,

radiological dose assessment, and recovery.

This section reviews 1) nuclear criticality safety regulations and standards, including TSARS,

applicable to DOE facilities, 2) criticality control factors, 3) past criticality accidents and associated

lessons learned, 4) roles, responsibilities, and authorities of radiological control staff with regard to nuclear

criticality safety, and 5) the content of an acceptable nuclear criticality safety program.

7.1 REGULATIONS AND STANDARDS

Nuclear criticality safety program requirements for DOE facilities are presented in DOE O 420.1A,

Facility Safety (DOE 2002). There are two objectives for nuclear criticality safety in the Order: 1) nuclear

criticality safety is comprehensively addressed and receives an objective review, with all identifiable risks

reduced to acceptably low levels and management authorization of the operation documented, and 2) the

public, workers, property, both government and private, the environment, and essential operations are

protected from the effects of a criticality accident.

The following standards of the American Nuclear Society provide recommendations for criticality

operations, alarms, storage of fissionable materials, programs, training and documentation:

a. ANSI/ANS-8.1, Nuclear Criticality Safety in Operations with Fissionable Materials Outside

Reactors (ANSI 1983b). This standard provides the basic criteria and limits for operations with

fissionable materials outside reactors except for critical experiments. It also provides requirements

for establishing the validity and the areas of applicability for any calculational method used in

assessing nuclear criticality safety.

b. ANSI/ANS-8.3, Criticality Accident Alarm System. This standard provides the performance

criteria for the location, selection, design, operation, and testing of nuclear criticality detection

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