Criticality Control Factors - STD-1128-98master0207

DOE-STD-1128-98

Guide of Good Practices for Occupational Radiological Protection in Plutonium Facilities

-- ANSI/ANS-8.15, Nuclear Criticality Control of Special Actinide Elements (ANSI, 1981). This

standard provides the single nuclear criticality control parameter limits for the unique aspects of

the special actinides (e.g., certain neptunium, plutonium, americium, and curium isotopes).

-- ANSI/ANS-8.19, Administrative Practices for Nuclear Criticality Safety (ANSI, 1984). This

standard provides the elements of an acceptable nuclear criticality safety program for

operations outside of reactors.

Additional Standards of interest that are not required by DOE Order 420.1A include:

-- ANSI/ANS-8.20, Nuclear Criticality Safety Training (ANSI, 1991). This standard (referenced

in DOE Order 5480.20A) provides the criteria for the administration of a nuclear criticality

safety training program for personnel who manage, work in or near facilities, or work outside

of reactors, where the potential exists for nuclear criticality accidents.

-- ANSI/ANS-10.3, Documentation of Computer Software (ANSI, 1986b). This standard

presents guidelines for documenting computer codes (i.e., user documentation) for engineering

and scientific applications.

-- ANSI/ANS-10.4, Guidelines for the Verification and Validation of Scientific and Engineering

Computer Programs for the Nuclear Industry (ANSI, 1987a). The objective of this standard is

to identify processes that will enhance the reliability of computer codes used in the nuclear

industry and reduce the risk of incorrect application.

7.2

CRITICALITY CONTROL FACTORS

For a criticality accident to occur, there must be a critical mass of fissionable material. As noted in

ANSI/ANS-8.1 (ANSI, 1983b), the critical mass is a function of the radionuclides in the material as

well as its density, chemical and physical form, shape, and surroundings (i.e., moderators,

reflectors, neutron absorbers). Nuclear criticality safety is achieved through the control over both

the quantity and distribution of fissile materials and other materials capable of sustaining a chain

reaction as well as the control of the quantities, distributions, and nuclear properties of all other

materials with which fissile materials are associated. For new facilities, DOE requires that design

considerations for the establishing controls should be mass, density, geometry, moderation,

reflection, interaction, material types, and nuclear poisons (neutron absorbers). The use of

administrative controls is to be minimized (DOE, 2002a).

Nuclear criticality control factors can be classified as technical (e.g., geometry controls and mass-

limitation controls) or administrative (e.g., operating procedures).

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