During the early years of nuclear energy R&D in Europe, between 1960 and 1980, the main experimental projects involving Th fuels were related to the HTRs (DRAGON OECD international project in the UK, ATR and THTR reactors in Germany) and also to an irradiation of Th-MOX fuel in the Lingen BWR in Germany. These projects can be seen as scientific successes, but they were not pursued on a commercial basis because of the priority given in Europe to the development of LWRs (except in the UK, where low-temperature gas-cooled reactors were developed), with UO2 as reference fuel, and, for countries having selected the reprocessing cycle strategy, the recycling of the recovered Pu as MOX fuel.

Afterward, several studies were undertaken to examine worldwide interest in Th. In 1997, M. Lung wrote a report entitled “A present review of the thorium fuel cycle” [1] at the request of the European Commission. Then, in the 4th EURATOM Framework Programme, a review of the benefits of the Th cycle as a waste management option was carried out [2].

As a result of these studies, it was recognized that this option presented major advantages in term of actinides management through the “burning” of excess Pu in a non-U matrix (Th oxide), at least for those countries in Europe that considered Pu as a waste and not a source of energy for future utilization in fast reactors. These assessments opened the door to several European irradiation experiments during the 5th EURATOM Framework Programme using Th-MOX, namely in the KWO PWR in Obrigheim (Germany), in the HFR MTR in the Netherland (operated by NRG), and in the BR2 MTR in Mol (SCK^CEN) (“THORIUM CYCLE [3]” and “OMICO

[4] ” projects). These efforts were pursued and completed within the 6th EURATOM Framework Programme, with the demonstration at laboratory scale that this fuel would behave in a comparable way as current MOX fuel (see Sect. 18.3). In the 6th EURATOM Framework Programme, the fuels irradiated in the programs THORIUM CYCLE and OMICO were further investigated (postirradiation examination, radiochemical analysis, and leaching tests) in the “LWR-DEPUTY” project [5] and a strategy study on the “Impact of Partitioning, Transmutation and Waste Reduction Technologies on the Final Nuclear Waste Disposal” (“RED-IMPACT”) was performed [6].

In parallel, efforts at the European level started in early 2000 and are still under way concerning the development of the MSR, using a Th-233U cycle in liquid Th fluoride fuel. Between the 5th and the 7th EURATOM Framework Programmes, several projects (MOST, ALISIA, EVOL) were funded (see Sect. 18.4).

Within the European nuclear research community, a Technology Platform named SNETP (Sustainable Nuclear Energy Technology Platform: www. snetp. eu) gathers most of the stakeholders involved in reactor research. SNETP issued a “Strategic Research Agenda” in May 2009 (revised in 2013 following the Fukushima accident) with an Annex (in January 2011) devoted to Th. In the annex, Th systems are noted as having significant long-term potentialities but also significant challenges before reaching industrial implementation. The two aspects (Pu management, molten salts) mentioned in this chapter were specifically recognized in the Th Annex to the Strategic Research Agenda.