Criticality Control Factors - doe-std-1128-98

DOE-STD-1128-98

-- 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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