Industry is not interested in these technical details; it is concerned with the bottom line. RAMI is the acronym for four important criteria: reliability, availability, main­tainability, and inspectability. The Electric Power Research Institute puts it in even more basic terms: economics, public acceptance, and regulatory simplicity. It is of course too soon to know how these will turn out; but designers of fusion power plants as well as fusion technology researchers are well aware of these criteria, which are always kept in mind. The fusion core is only a part of a whole power plant, a cartoon of which is shown in Fig. 9.34. The remote handling system is essen­tial for maintainability and inspectability. The heating, current drive, and fueling systems affect reliability. The complicated fuel cycle system has to be completely

safe in regard to tritium release. The balance of plant, the equipment that generates and transmits the electricity, is a larger part of the power plant than the power core, though it is shown deceptively as a small addition in Fig. 9.34. These are the steam turbines that drive the electric generators and the transformers and capacitors that condition the output for delivery to the transmission lines. All power stations that convert heat into electricity have this equipment, whether the fuel be coal, oil, gas, or uranium. Hydroelectric plants do not need steam; water drives the generators. Wind and solar plants produce electricity directly. Fusion plants can use the same generators and transmission lines that already exist in fossil or nuclear plants; only the power core has to be replaced. However, tokamaks are so complicated and include such temperature extremes that they will require a higher portion of the capital cost than other power cores.

Availability is an important aspect of a fusion reactor that is hard to assess. How often will leaks occur, and how long will it take to do the re-welding? How often do blankets have to be replaced, and how long will the shutdowns be?

Re-circulating power

Fig. 9.34 Main parts of a fusion power plant [37]

How often will disruptions occur, and how long will it take to reassemble the machine? What percentage of the time will the machine be running during a year? During a shutdown, where will the power come from? Will we need a backup tokamak or new transmission lines from other power plants? Educated guesses are made by those who design fusion power plants based on available knowledge.