Guidance for Special Case Criticality Safety Evaluations

DOE-STD-3007-2007

III. GUIDANCE FOR SPECIAL CASE CRITICALITY SAFETY EVALUATIONS

This portion of the standard concerns itself with special case CSEs. The purpose is to provide guidance

for special types of evaluations often encountered at DOE facilities. For these special case CSEs, the

format and content provided in Section II of this standard is not required, but may be followed. Content

guidance for selected common special case CSEs is provided below. Examples of special case CSEs

include evaluating the need for a CAAS (either installation or removal), application of ANSI/ANS-8.10-

1983 for shielded facilities, CSEs supporting transportation and shipping, and to evaluate as-found

conditions if a facility has been mischaracterized relative to the need for CAAS. This is not meant to be

an exhaustive list of CSE types that could fall outside of the guidance of Section II. The Criticality Safety

Program (CSP) description required by DOE Order 420.1B should clearly define what content and

regulatory guidance applies to the types of CSEs generated under the CSP.

A. NEED FOR CRITICALITY ACCIDENT ALARM SYSTEMS

ANSI/ANS-8.3-1997 requires that the need for a CAAS be evaluated if the inventory of fissionable

materials exceeds specified amounts. The installation of an alarm system implies a nontrivial risk of

criticality. A nontrivial risk of criticality should be considered to exist in facilities whose inventory

exceeds the specified threshold levels in ANSI/ANS-8.3-1997 and where a criticality accident is credible

for a process or processes with fissionable materials in the facility. The purpose of an alarm system is to

reduce risk to personnel. Evaluation of the overall risk should recognize that hazards may result from

false alarms and subsequent sudden interruption of operations and relocation of personnel. Guidance for

emergency plans and procedures are contained in relevant ANSI/ANS-8 Standards.

A CSE should be prepared that documents the evaluation of the need for a CAAS. This CSE should

contain input from appropriate technical disciplines such as NCS, safety basis, operations, emergency

preparedness, and radiation protection. The evaluation of overall risk should take into consideration the

impact of the CAAS itself on the risk to workers and the public. In some facilities, the hazard of

responding to a CAAS alarm, real or inadvertent, may outweigh the benefit of having a facility alarm or

detection system in place. One example of such a facility may be a facility where it is possible to have a

criticality accident in a shielded portion of a facility such that workers outside the immediate area of the

criticality accident will not receive a substantial prompt radiation dose. However, the workers outside the

immediate area of the accident might be put at risk if they responded immediately to an evacuation alarm,