TSTF-427
See TS-3.0.9
DISCUSSION:
This TSTF would add a new LCO Applicability rule, LCO 3.0.9, to address barriers which cannot perform their related support function for Technical Specification systems. LCO 3.0.9 allows barriers to be not able to perform their related support function for up to 30 days before declaring the supported system inoperable.
Many systems require barriers in order to perform their function. For example, there are barriers to protect systems from the effects of internal flooding, such as floor plugs and retaining walls, and barriers are used to prevent steam impingement in case of a high energy line break. Barriers are used to protect systems against missiles, either internally generated or generated by external events.
If a barrier cannot perform its related support function due to some type of failure or due to intentional removal to facilitate plant operation, the supported system may be inoperable under the definition of OPERABILITY. However, the magnitude of plant risk associated with the barrier which cannot perform its related support function does not warrant declaring the supported system inoperable provided at least one train of the system is OPERABLE and the supporting barriers are capable of performing their related support functions.
This TSTF is especially useful when a HELB barrier is defeated (i.e., a door) and the safety system trains inside the room are declared inoperable. However, a separate room with an intact HELB barrier (a door) would contain an operable train for that safety system. In this case, the protected safety system train would remain operable for 30 days.