Reliability Design Features

DOE-HDBK-6004-99

Channel 2 Green

Channel 3 Yellow

Channel 4 Blue

Non-safety class: Black

Reliability Design Features

To meet the expected stringent reliability requirements and to keep partial power system failures from

having a cascading failure effect, the system should be designed with the following features.

1. The design assumes that three sets of lines (circuits) should connect the facility to the switchyard

(grid); two for fusion facility operation and one for main (power) generator output. To maximize

the separation of pulsed (tokamak) and plant loads, it is assumed that one set of circuits will

supply the tokamak loads while the second will supply the plant loads during fusion facility

operation. In the event of loss of one circuit, the fusion facility load would be shed (plasma

shutdown) and the remaining set of circuits would supply the plant loads. During the fusion

power generation (if designed), the third set of circuits will be used.

2. Since each safety bus has double supply paths, any single failure can be limited to a single bus.

This provides redundant backup capability with a high degree of independence.

3. Each type of power is subdivided into two, three, or four segments with limited cross ties to

provide redundancy without excessive cross-links.

4. The distribution system should have automatic fast transfer logic systems which sense the loss of

supply to a bus, determine what alternative supplies are available, and carry out switching to

connect the affected bus to a viable power supply.

5. Physical separation of redundant buses will be provided for protection against common causes

of failure (e.g. fires, or in-plant flooding).

6. Four 125 VDC buses are proposed to provide four independent channels of safety-class system

instrumentation to permit the use of single failure resistant, 2 out of 3, 2 out of 4, or 3 out of 4

channel voting logic on Fusion Facility Protection Systems.

7. The use of two emergency (standby) generators for Safety Train A and B is proposed, each with

the sufficient capability of providing power for the emergency loads needed to safely shut down

the fusion facility.

8. Suitable test capability will be required to allow periodic testing of all safety-class systems and

automatic transfer systems as well as periodic operation of all circuit breakers and disconnects

without adversely affecting system operation or compromising safety. Depending on the

reliability requirements, such testing may have to be on-line.