The USR reference 625 MWe design developed by ORNL builds on earlier experience from the laboratory (IEA/OECD (NEA)/IAEA, 2002).

12.7.2 MSR-NC

The MSR-NC 470 MWe reference design has been put forward by the Kurchatov Institute (RRC-KI) in Russia.

12.7.3 FUJI

The FUJI reactor developed by ITHMSO in Japan is a low-pressure vessel loop style reactor with a graphite moderator and a molten salt coolant. It built on the ORNL technology and has an electrical output of 100 MWe. It includes inherent and passive features in that no moderating materials are located near the reactor vessel. Thus the reactor cannot achieve criticality outside of the core in the event of molten salt leakage.

In MSRs such as FUJI, the fuel (uranium and thorium) is dissolved in the molten salt. The salt is 7LiF-BeF2 and it can contain fissile material, 233UF4, and fertile material, 232ThF4. The temperature reactivity coefficient is strongly negative with increasing temperature due to the presence of the graphite moderator and reduction in molten salt density.

The FUJI reactor has other important safety features, decay heat can be passed passively to the environment, on-line fuelling ensuring that reactivity is minimum at all times, the pressure is low and the vessel is designed against high fluence embrittlement. There are no soluble poisons in the molten salt coolant.

Economically, there is good thermodynamic efficiency because of the high core outlet temperature. This also makes the reactor a good candidate for combined heat and power applications compared with present generation water reactors. The reactor has a smaller number of components, reduced containment requirements and is of small size so capital costs are kept down. It has on-line refuelling so refuelling outages are eliminated.

Environmentally, this fuel cycle has some attractions; the presence of thorium implies that a smaller number of higher actinides are produced. Over the operating life of the reactor, the fuel is not removed, so no fission products are removed from the fuel/coolant. It also operates as a near breeder (breeding ratio near unity); thus uranium resource requirements are reduced.

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