Chemical Energy

DOE-STD-6003-96

of structures and volatilization of activation products. Because the decay heat is distributed

throughout the entire structure, the overall power density is relatively low.

B.3.4 Chemical Energy

Large quantities of chemical energy can potentially be liberated by reaction of certain

fusion materials with air or water under off-normal or accident conditions. Potential fusion

materials include the following:

PFCs--W, Be, C, Cu, Nb

Structural Materials--stainless steel, ferritic steel, vanadium alloys

Coolants--water, Li, LiPb, NaK, Na, Ga, He

Most of the reactions between the PFCs and structural materials with water are exother-

mic (some are endothermic). Alkali liquid metals (Li, NaK, and Na) produce exothermic reac-

tions with air, water, and concrete. In the event of an assumed in-vessel reaction, the heat gen-

erated by the reaction can cause the surrounding structures to heat up and volatilize activation

products. Steam reactions can generate flammable or explosive concentrations of hydrogen.

The magnitude of the chemical energy problem is a strong function of the materials that are

used in the machine, the amount of material available for interaction, and the ability of the

design to prevent the chemical interaction and to mitigate the consequences should it occur.

In addition to these chemical hazards, the production of explosive levels of ozone from

external radiation in cryogenic systems such as the cryostat needs to be considered.

B.3.5 Coolant Internal Energy

Pressurized coolants will be used in some of the components of fusion machines. Water

is a common coolant for PFCs. Liquid nitrogen and liquid helium are used in cryopumps and the

cryoplant. Liquid helium is also used to cool the superconducting magnets. The energy released

during a sudden loss of coolant for all of these coolants needs to be considered in the design

because of the high pressures that could be developed as a result of the spill. The case of an in-

vessel loss of coolant water is a particular concern because the blowdown of water will produce

steam that could react with the hot PFCs and generate hydrogen, as discussed previously.

Many design options are available to deal with the pressurization potential of these coolants

including having expansion volumes available to collect the gas and making the component

(e.g., cryostat, vacuum vessel, and building) robust enough to handle the peak coolant pressure

during the event.

B.4 Potential Generic Accident Scenarios

Past conceptual design studies on fusion power plants and recent safety analyses per-

formed for current machines have identified a number of generic accident scenarios that need to

be considered in determining the potential for the energy sources mentioned earlier to mobilize

the radioactive and/or toxic materials available in a fusion machine. This section contains a brief

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