First-generation nuclear reactors, developed in the 1950s and 1960s, marked the beginning of the civil nuclear industry. Among these reactors, natural uranium graphite gas (UNGG) is a distinct technology that was mainly used in France. This article aims to present the history and characteristics of UNGG reactor technology, addressing an audience that is knowledgeable but unfamiliar with this particular subject.
History of UNGG reactors
UNGG reactor technology has its origins in the 1940s, when France launched its nuclear program for military and energy purposes. The first UNGG reactors were built in the 1950s and 1960s, with the commissioning of the G1 reactor at Marcoule in 1956, followed by the G2 and G3 reactors in 1959 and 1960 respectively.
UNGG reactors were designed in particular to produce plutonium for nuclear weapons. In all, nine UNGG reactors were built in France, some of which were used to power the national grid. However, France gradually abandoned UNGG technology in favor of pressurized water reactors (PWRs) from the 1970s onwards. The last UNGG reactor in operation, Bugey 1, was shut down in 1994.
Characteristics of UNGG reactors
Like the UK’s Magnox reactors, UNGG reactors use natural uranium as fuel, which means they do not require enriched uranium. This has enabled France to develop an independent nuclear industry without recourse to uranium enrichment, a technology that was then mainly held by the USA. This is made possible by the use of graphite rather than water as a moderator. The former absorbs neutrons less than the latter. The coolant is pure CO2, to prevent graphite oxidation.
The legacy of UNGG reactors
Despite their decline, UNGG reactors played an important role in the development of the French nuclear industry, and contributed to the acquisition of technical skills and knowledge in the field of nuclear energy. Today, France is one of the world’s largest producers of nuclear energy, with almost 70% of its electricity coming from nuclear power plants, mainly pressurized water reactors.
In addition, the experience acquired with UNGG reactors has also enabled France to develop research and development programs in the field of advanced reactors, such as fast neutron reactors and molten salt reactors.
The challenge of dismantling UNGG reactors
One problem for reactors using graphite as a moderator is the enormous volume of the block. Radioactively contaminated, it poses specific dismantling challenges. Several companies are working to meet this challenge, notably with the help of robotics. These include Graphitech and the European INNO4GRAPH project.
Conclusion
First-generation UNGG nuclear reactors played a key role in the early development of the French nuclear industry. Although they were abandoned because of their drawbacks in terms of safety, energy efficiency and nuclear proliferation, they provided France with a solid foundation on which to become a world leader in nuclear power. The lessons learned from the UNGG reactor experience continue to influence the research and development of advanced, safer nuclear technologies to meet the energy and environmental challenges of the 21st century.