BIAS - A measure of the systematic disagreement between the results calculated by a method and
experimental data. The uncertainty in the bias is a measure of both the precision of the
calculations and the accuracy of the experimental data.
CALCULATIONAL METHOD - The mathematical equations, approximations, assumptions,
associated numerical parameters (e.g., neutron cross sections), and calculational procedures that
yield the calculated results.
CONTINGENCY - A possible but unlikely change in a condition/control important to the
nuclear criticality safety of a fissionable material operation that would, if it occurred, reduce the
number of barriers (either administrative or physical) that are intended to prevent an accidental
CRITICALITY SAFETY EVALUATION (CSE) - A documented process that establishes the
technical basis for nuclear criticality safety and provides subcritical operating values.
CREDIBLE - Offering reasonable grounds for being believed on the basis of commonly
acceptable engineering judgment. Assigning a numerical probability that defines credible is not
required when demonstrating compliance with the double contingency principle.
DESIGN FEATURES - Passive or active features that are necessary to prevent or reduce the
probability of a criticality accident.
DOUBLE-CONTINGENCY PRINCIPLE [Per DOE 5480.24 7a(2)(a)*] - Process designs
shall incorporate sufficient factors of safety to require at least two unlikely, independent, and
concurrent changes in process conditions before a criticality accident is possible. Protection shall
be provided by either:
The control of two independent process parameters (which is the preferred approach, if
A system of multiple (at least two) controls on a single parameter.
In all cases, no (credible) single failure shall result in the potential for a criticality accident.
*NOTE: DOE 5480.24 has been replaced by DOE O 420.1, Section 4.3.
PROCESS PARAMETER - A physical property whose value affects the nuclear reactivity of a
system. Parameters include the mass, density, and isotopic enrichment of fissionable material; the
and neutron absorption characteristics of the fissionable material mixture and other system