This standard specifies minimum design, actuation, testing, and maintenance requirements for the containment isolation of fluid systems after a LOCA. These fluid systems penetrate the primary containment of light water reactors and include piping systems (including instrumentation and control) for all fluids entering or leaving the containment. Electrical systems are not included. The provisions for containment isolation impose additional requirements which are not required for the fluid system function. This standard does not consider any isolation requirements that may exist for controlled leakage areas either enclosing the primary containment or contiguous to the primary containment. Also, this standard does not address containment isolation requirements for events other than LOCAS.

This standard presents requirements and conditions that are needed for the isolation of the containment and covers requirements for isolation barriers, their actuation, their operators, and connecting piping between isolation barriers. The standard does not cover penetration assemblies, protection systems, power supplies, and equipment qualification.

The design requirements in this standard consider: the system isolation and actuation function, isolation function testing, leakage rate monitoring and testing, and maintenance. This standard gives general requirements or refers to other standards, codes, and regulations for the following requirements: fire protection; protection against natural phenomena such as earthquake, tornado, or flood; environmental conditions such as normal operation, maintenance, testing, and postulated accidents (including the dynamic effects from missiles, pipe whip, and discharging fluids); and separation criteria.

Purpose. Containment isolation is the closure of isolation provisions in lines penetrating the containment in the event of the loss-of-coolant accident within the containment or any other accident which calls for actuation of the same containment isolation provisions. Containment isolation provisions are, therefore, provided for these accidents. If such accidents occurred, fluid systems penetrating the containment would be isolated except those which are engineered safety feature systems, or systems which are not required to function following a loss-of-coolant accident but, if available, can be used to accomplish a function similar to an engineered safety feature system (examples of such systems are BWR feedwater systems and PWR fluid systems required for reactor coolant pump operation).

Other accidents may require isolation of a specific fluid system or group of systems. The isolation provisions for such accidents are defined as accident isolation, and in many instances the provisions of this standard apply.

The objective of containment isolation shall be to allow the normal or emergency passage of the following through the containment boundary while preserving the integrity of the containment boundary:

(i) Engineered safety feature system fluids, or

(2) Fluids of systems which are not required to function following a loss-of-coolant accident but, if available, can be used to accomplish a function similar to an engineered safety feature system.

Other fluid systems shall be isolated immediately after a postulated loss-of-coolant accident.

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