Design for Reliability

DOE-STD-6002-96

Normal operation, anticipated operational occurrences, and off-normal conditions created

by PIEs shall be classified for fusion facilities into two categories: (a) normal operation and

anticipated operational occurrences; and (b) off-normal conditions that may be expected with

lower but still credible probability. A bounding subset of these conditions shall be identified in

the safety analysis.

4.4 Design for Reliability

Unavailability limits for items that perform public safety functions shall be specified to

ensure the reliability needed to meet evaluation guidelines. Similar limits are recommended but

optional for items that perform worker safety functions. The required reliability of items shall be

developed in accordance with the importance of their safety function in protecting the workers,

the public, and the environment.

4.4.1 Redundancy

The principle of redundancy shall be considered as an important design principle for

improving the reliability of items and guarding against common-cause failures. Multiple sets of

equipment that cannot be operated and tested independently do not meet the redundancy prin -

ciple. The degree of redundancy shall reflect the potential for undetected failures that could

degrade reliability.

4.4.2 Diversity

The principle of diversity s hall be considered as a means to enhance reliability and

reduce the potential for common cause failures.

4.4.3 Independence

The principle of independence shall be considered to enhance the reliability of systems, in

particular with respect to common-cause failures. Independence is accomplished in the design

of items by using functional isolation and physical separation (e.g., separation by geometry or

barriers).

4.4.4 Simplicity

The principle of design simplicity shall be considered to enhance the reliability of items.

Less complex items are generally more reliable.

4.4.5 Testability/Surveillance Capability

Items performing public and worker safety functions shall be designed and arranged so

that they can be adequately inspected, tested, and maintained as appropriate before being

placed in service and at suitable and regular intervals thereafter.