Considerable experience has been gained with lead-bismuth eutectic cooled reactors in the Russian Federation. This has been largely in connection with the development and operation of submarine propulsion reactors (IAEA-TECDOC-1289, 2002). Studies have been carried out by the Russian Federation Institute of Physics and Power Engineering (IPPE) and EDO Gidropress. Lead-bismuth offers some potential advantages, compared with lead, as a coolant and also some disadvantages; these are discussed below.

Lead-bismuth systems are being considered within the GIF Generation IV initiative. Several design concepts have been studied by the Russians. SVBR-75 is designed to produce 75 MWe and to operate for 10 years without refuelling. A smaller transportable combined heat and power version, ANGSTREM, has also been studied, generating 6 MWe. There is also a 25 MWe version being investigated by the Russians.

12.6.3.1 LFR (Gen IV). The main characteristics of the GIF reference design for lead cooled systems in general were discussed above.

12.6.3.2 BRUS-150. An integral type lead-bismuth reactor, generating 150 MWe, is being considered in the BRUS-150 project. All the lead-bismuth is contained in the reactor vessel, which contains the core, pumps and steam generators. This reactor is designed for the burning of weapons grade plutonium and the transmutation of minor actinides. In the present design of this (and other lead cooled) reactors, there is no intermediate circuit between the primary coolant and the water/steam secondary side. This is a concern in the event of steam generator leakage, which might result in Pb or Pb — Bi/water/steam interactions.

Pb-Bi and Pb share a number of similarities in terms of their thermal-hydraulic properties and also some advantages compared with sodium. For example, they have high boiling temperatures and relative chemical inertness compared with sodium. Pb-Bi has some advantages over Pb as a coolant in that it has a lower melting point (123.5°C) compared with Pb (327°C). A disadvantage in the use of Pb-Bi coolant is the formation of the volatile alpha emitter, polonium (210Po) produced from bismuth (and to some extent from Pb). Therefore, leakage poses a hazard to the operators and to the environment in the event of a cover gas release. Careful chemistry control of the primary circuit is also required to avoid the formation of lead oxide and other impurities.

It is concluded in IAEA-TECDOC-1289 (2002) that there are problems in applying much of the experience and data gained from the Pb — Bi cooled submarine studies to commercial-sized lead cooled power plants. This is because of the much greater annual load factor required, the higher temperature of the lead primary circuit, and additional corrosion phenomena at the commercial plant scale. Thus, there is considerable R&D required to extrapolate from the lead -bismuth submarine experience to the civil commercial nuclear plant situation.

12.2. MOLTEN SALT REACTORS

Molten salt reactor (MSR) technology has been available since the 1960s. It was developed at Oak Ridge National Laboratory (ORNL) and the MSR Experiment (MSRE) which operated for nearly 3 years during the late 1960s (IEA/OECD (NEA)/IAEA, 2002). Examples are listed in Figure 12.6.