Page 27 - Thermal Hydraulics Aspects of Liquid Metal Cooled Nuclear Reactors

2 Thermal Hydraulics Aspects of Liquid Metal Cooled Nuclear Reactors

coolants for such fast reactors. Mostly, liquid sodium has been applied, for its great
heat transport and neutronic characteristics. However, sodium also has its drawbacks,
especially stemming from its chemical reactivity with air and water. Other liquid
metals, such as lead or lead-bismuth eutectic, do not react violently with air and water
and are also considered for that reason.

1.2 Liquid metal reactor design

Nuclear reactor design is highly multidisciplinary. In each reactor, disciplines like fuel
and material science, reactor physics, thermal hydraulics, and structural mechanics
interact. This makes nuclear engineering one of the most demanding professions.
There may be only a few people who have a thorough understanding covering all these
disciplines. Most engineers specialize in one or two of the disciplines allowing them to
obtain a deep understanding. Designing a reactor and performing safety assessments
of reactors therefore remain a team effort and strongly depend on the interaction
between people and the integration by the few engineers having a basic understanding
of all involved disciplines. This book puts the focus on the specialized topic of liquid-
metal thermal hydraulics for advanced (fast) nuclear reactors, a discipline that is
essential for liquid-metal fast reactor design and the subsequent safety assessment
of the design and the reactor as built.

1.3 Short history of liquid metal reactors

For an elaborate overview on the liquid-metal fast reactor designs constructed and
operated all over the world, excellent textbooks are available. In IAEA (2012,
2013), such overviews can be found. More recently, Pioro (2016) provided an over-
view of the most recent developments not only focusing on liquid-metal fast reactors
but also covering a wider range of advanced nuclear reactor designs.
Fig. 1.1 sketches the history of liquid-metal fast reactors worldwide. Even before
the EBR-I, which was the sodium-potassium-cooled first nuclear reactor to produce
electricity, there was the experimental mercury-cooled Clementine reactor in the
United States. As can be seen in the figure, after EBR-I, the United States and the rest
of the world mostly switched to the use of pure sodium. The United States operated
sodium-cooled experimental and prototype reactors until the early 1990s. Today, the
United States still has a limited active program on liquid-metal-cooled reactors but has
no such reactor in operation.
In Europe, the development of liquid-metal-cooled reactors started in the early
1960s resulting in experimental reactors being constructed in France, the United
Kingdom, Italy, and Germany. In France, after successfully operating the experimen-
tal Rapsodie reactor, the prototype reactor Ph enix was constructed and operated,
followed by the construction and operation of the commercial Superph enix power
plant. The Ph enix reactor successfully provided electricity to the grid. The reactor
was taken from the grid in 2009, after which for 1 year several important safety tests
were performed providing unique data to future liquid-metal fast reactor designers and