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Norway’s Halden reactor takes first step toward decommissioning
The government of Norway has granted the transfer of the Halden research reactor from the Institute for Energy Technology (IFE) to the state agency Norwegian Nuclear Decommissioning (NND). The 25-MWt Halden boiling water reactor operated from 1958 to 2018 and was used in the research of nuclear fuel, reactor internals, plant procedures and monitoring, and human factors.
Eric Leclerc, Georges J. Berthoud
Nuclear Technology | Volume 144 | Number 2 | November 2003 | Pages 158-174
Technical Paper | Thermal Hydraulics | doi.org/10.13182/NT03-A3437
Articles are hosted by Taylor and Francis Online.
In hypothetical Severe Accident studies for a PWR, a large amount of molten corium may be poured into water. There is then a risk of Steam Explosion. After the premixing sequence in which the melt is more or less dispersed into water, a fine fragmentation process may start, which can lead to an escalation. Such an event is generally triggered by the destabilization of the vapor film surrounding the hot melt droplets. In this paper, an attempt to describe all the successive processes leading to this fine fragmentation is presented.First, a critical analysis of previous models is performed, allowing us to propose a new sequence of events. As in the previous models, the film destabilization leads to the growth of cold liquid peaks induced by Rayleigh Taylor instability. As these peaks have a smaller density than the drop, they do not penetrate into the hot drop. At the cold liquid-hot liquid contacts, transient heat transfer leads to the explosive boiling of a small amount of coolant. The generated local pressurization deforms the hot melt interface. This can produce fine fragments from the filaments issued from the melt. Some of them may reach the vapor-coolant interface where intense and rapid vaporization occurs. A large bubble then develops, and a new fragmentation sequence may again appear at the bubble collapse. The present model is supported by experimental results.