Potential System Safety Functions

DOE-HDBK-6004-99

Fusion Facilities which require safety-class electrical systems should be supplied by two independent

off-site sources and one on-site source of electric power to ensure the supply of electric power to

each train of safety-class equipment

The electrical power system equipment that provides the power supply to safety-class systems and

components to perform fusion facility safety functions are classified as safety-class. Other electrical

systems should be non-safety-class (NSC). The safety-class electrical power system should be fed

from the safety bus.

The safety-class electrical equipment defined by the facility safety analysis should be designed in

accordance with the accepted design Standards given in this section. Where alternative methods are

used, justification should be provided in the facility authorization basis.

Equipment that is used for both safety and non-safety functions should be classified as part of the

safety systems. Isolation devices used to effect a safety system boundary should be classified as part

of the safety system.

No credible failure on the non-safety side of an isolation device should prevent any portion of a safety

system from meeting its minimum performance requirements during and following any design basis

accident requiring that safety function. A failure in an isolation device should be evaluated in the

same manner as a failure of other equipment in a safety system.

Potential System Safety Functions

The potential safety functions for the back-up electrical systems are:

1. Normal Operation and Maintenance - Normal and backup power should be on-line or available

to supply safety functions. Specific potential safety functions are:

a) Provide for ability to survive or recover from off-normal events.

b) Monitor normal/back-up power

c) Monitor status of active components which must function during Design Basis Accidents

(DBA).

d) Monitor equipment required to isolate in the event of on-site or off-site system faults.

2. Design Basis Accidents - The safety analysis should specify design basis accidents and related

safety functions. The electrical power systems design provide power needed to enable the safety

functions. The following are potential design basis accidents for back-up electrical power

systems:

a) Internal Initiators:

1) Missile or pipe whip resulting from sudden failure of high energy systems. This accident

has potential for causing release of radioactive material and simultaneously disrupting

multiple electrical equipment.