District heating plants supplying hot water and steam are widely used in countries with cold winters such as Denmark, Finland, Sweden and Russia. Large cities require 600-1200 MWt, smaller communities perhaps 10-50 MWt (IAEA-TECDOC-1056, 1998). The heat is produced by extracting steam from low-pressure turbines (for base load) and/or high-pressure turbines (for peak heat demand) and then distributed in insulated pipelines. These are on the order of 10 km, the shortest being a few kilometers, the longest built is in excess of 20 km.

The majority of nuclear applications for district heating have been reactors operating in co-generation with electricity producing mode. Such plants have been operated in Bulgaria (Kozloduy), Germany (Greifswald), Hungary (Paks), Russia (Bilibino, Belojarsk, Balakovo, Kalinin, Kola, Kursk, and Sankt Petersburg), Slovakia (Bohunice), Switzerland (Beznau) and Ukraine (Rovno, South Ukraine).

With regard to dedicated heating reactors, there have been demonstration plants constructed and tested in Canada (SLOWPOKE) and also China (NHR-5). There has also been a research reactor operating in Russia (Obninsk) for more than 20 years.

The plants include barriers to prevent any release of radioactivity into the grid network. A leak tight intermediate loop is added which operates at a pressure greater than that of the steam pressure taken from the turbine cycle. The loops are also subject to continuous monitoring. In about 500 reactor-years of operating heat supplying reactors, no radioactive contamination of the network has been reported.

While much experience exists with co-generation, small — and medium-sized reactors may be more appropriate for district and process heating and also desalination applications. These have been reviewed in IAEA-TECDOC-881 (1996).

Some of the newer concepts of reactors for district heating are shown in Table 14.3 and summarised below.