Beyond Design Basis Accidents

DOE-HDBK-6004-99

Potential Safety Functions

The cooling system potential safety functions for design basis accidents are:

1. Remove heat from safety-class structures, systems and components.

2. Transfer the combined heat load to a safety-class heat sink.

3. Partially confine radioactivity entrained or deposited in the coolant system, and provide for

suitable releases to environment or transfer to a waste facility.

4. For a large break in the cooling system pressure boundary:

Provide makeup coolant at a sufficient rate that the system' heat removal and rejection

capacity will prevent damage of safety-class structures, systems or components while

allowing only negligible materials reactions with the coolant.

Collect coolant spilled from a large break to prevent damage to safety-class structures,

systems or components.

Beyond Design Basis Accidents

Beyond design basis accidents include internal and external initiators whose frequencies are lower

than the design basis frequency limit specified in the safety analysis. There are no cooling system

safety functions for beyond design basis accidents.

Safety Design Standards and Criteria

Structures, systems and components needed to perform safety functions should be designated safety

class. Components which do not perform safety functions but whose single failure causes loss of a

safety function should also be designated safety class. Included in the safety-class are:

1. Gauges, instrument tubing, sensing lines, stubs and other pressure containing hardware on the

pressure boundary of the safety-class coolant system,

2. Membrane interfaces and isolation devices between safety-class and non-safety-class coolant

systems.

The different designs and operating characteristics of fusion facilities limit the amount of specific

guidance that these criteria can provide. Existing DOE and NRC design requirements and guidance

documents provide helpful general guidance for implementing these criteria at a particular fusion

facility.

For safety-class cooling systems, the following design standards and criteria should apply to the

structures, systems and components.