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The ongoing effort to convert the world’s research reactors
The Ghana Research Reactor-1, located in Accra, Ghana, was converted from HEU fuel to LEU in 2017. Photo: Argonne National Laboratory
In late 2018, Nigeria’s sole operating nuclear research reactor, NIRR-1, switched to a safer uranium fuel. Coming just 18 months on the heels of a celebrated conversion in Ghana, the NIRR-1 reboot passed without much fanfare. However, the switch marked an important global milestone: NIRR-1 was the last of Africa’s 11 operating research reactors to run on high-enriched uranium fuel.
The 40-year effort to make research reactors safer and more secure by replacing HEU fuel with low-enriched uranium is marked by a succession of quiet but immeasurably significant milestones like these. Before Africa, a team of engineers from many organizations, including the U.S. Department of Energy’s Argonne National Laboratory, concluded its conversion work in South America and Australia. Worldwide, 71 reactors in nearly 40 countries have undergone conversions to LEU, defined as less than 20 percent uranium-235. Another 31 research reactors have been permanently shut down.
Matthias Vanderhaegen, Alix Le Belguet
Nuclear Science and Engineering | Volume 176 | Number 2 | February 2014 | Pages 115-137
Technical Paper | dx.doi.org/10.13182/NSE12-99
Articles are hosted by Taylor and Francis Online.
Sodium boiling phenomena in nuclear reactors have been reviewed in the context of the renewed interest in sodium-cooled fast reactors. This paper presents all properties that influence sodium boiling behavior, including thermodynamic and transport properties, as well as the typical composition of reactor-grade sodium, the surface wetting, radiative heat transfer properties, and noncondensable behavior. Starting from these properties, the tendency for high superheat is explained, together with the reasons that the problem of superheat can be neglected for reactor systems. The peculiar boiling behavior of sodium in assemblies is explained on the basis of the temperature profile. This leads us to conclude that a typical slug flow pattern prevails for sodium boiling. The boiling heat transfer for pool film boiling is also given, deducing that the critical heat flux phenomena for sodium boiling in reactor systems is mainly related to dryout and not to the departure from nucleate boiling. The correlations that exist for the minimum film-boiling temperature are discussed in light of their applicability to liquid sodium. Although there are already a large amount of data, gaps in the current understanding of sodium are highlighted.
