FROM MICRO TO MINI

The water in SLOWPOKE I (prototype) and II (commercial model) circulates by natural convection, not by pumps; its temperature does not exceed 80 DEG C. There is no steam, and no moving parts except the single central control rod that switches it on or off.

Such low temperatures are unsuited for generating electric power, but they are very useful for district heating, and Canada's Chalk River Nuclear Laboratories are now assessing the technical and economic feasibility of SLOWPOKE III, which is to produce heat in the range of 2 to 20 MW. If feasible in both respects, SLOWPOKE III, designed by John Hilborn and Ian Glen, will be built in 1982-3.

Using nuclear reactors for district heating is not a new idea. A 65 MW reactor supplied heat to Agesta, a suburb of Stockholm with a population of 40,000, from 1963 to 1973. It was abandoned because of high operating costs just before the 1973 oil embargo. Since then, the economics have changed drastically, and a consortium of four Swedish and Finnish companies has worked out a design of a 200 MW reactor called SECURE (Safe and Environmentally Clean Urban Reactor), which again produces only heat, allowing it to be operated at low temperatures and pressures, and relying on physical laws for its inherent safety; no engineered safety measures need be added.

For the Swedes, nuclear heat is competitive with all fossil fuels; for the Canadians, it is competitive with imported oil and electric heating, but more expensive than domestic oil or natural gas. Sooner or later, of course, it will be competitive with all of these as the price of oil and gas relentlessly rises.

France is strongly considering the 100 MW "Thermos" reactor to heat 30,000 homes in Grenoble. If the project is approved this summer, it could be in place in 1985. Thermos, too, is a pool-type reactor, so called because it is immersed in a pool of water at normal pressure and low temperature, not pressurized and steam-producing. This is the basis of inherent safety, i.e., safety without engineered redundancies.

The Soviets have been running a 5 MW heating reactor in Dimitrovgrad for more than a year; four 60 MW reactors supply both heat and power to a remote mining town, and two large units are now under construction in Gorki and Novovoronezh. The Soviet designs are pressurized, and therefore not inherently safe. They too, are based on a philosophy of simplicity, but of a different kind: Things never go wrong in a planned economy; and if they do, you just ship in a few thousand new serfs of the Soviet state.

[Sources: SECURE: Nuclear District Heating, booklet by ASEA-ATOM, Box 53, S-721 Vasteras, Sweden, and a number of papers presented at the Symposium on Reactor Installations for Heat Supply, Moscow, Jan. 1980 (kindly made available by ASEA-ATOM).]