Nuclear Power
Metal reactor decommissioning
Dealing with the coolant is a demanding and hazardous challenge when decommissioning liquid metal cooled reactors. Jason Casper looks at how this may be addressed to complete the timely decommissioning of the UK’s Dounreay reactors.
Lidiar con el refrigerante es un reto arriesgado y difícil cuando se desactivan los reactores refrigerados de metal líquido. Jason Casper observa sobre cómo puede dirigirse para completar el cierre oportuno de los reactores de Dounreay en el Reino Unido.
Bei der Außerbetriebnahme von Flüssigmetallreaktoren ist die Handhabung des Kühlmittels eine schwierige und gefährliche Aufgabe. Jason Casper überlegt, wie sie gelöst werden kann, damit die Außerbetriebnahme der Dounreay- Reaktoren in Großbritannien fristgerecht erfolgt.
L
ast year saw the disposal of 57 tonnes of alkali liquid metal successfully completed at Dounreay, representing the destruction of one of the most hazardous legacies of Britain’s earliest
atomic research. Now, parent body organisation Babcock Dounreay Partnership (responsible, for the decommissioning, demolition and clean-up of the Dounreay nuclear site), working with the Dounreay Site Restoration Limited team, face a further, significant challenge; to tackle the destruction of the hazardous alkali metal remnants inside the reactors vessel, which could not be extracted for disposal in the purpose-built chemical processing plant.
Potential hazards Dealing with the nature of the coolant – commonly sodium or the sodium-potassium alloy NaK – is a major consideration in decommissioning liquid metal cooled reactors. Sodium metal reacts vigorously when exposed to
water, releasing hydrogen and large quantities of heat – thereby providing not only an explosive gas mixture but also a source of ignition. Te products of combustion are also toxic, and can cause severe caustic and thermal burns on coming into contact with skin, as well as being hazardous to ingest or inhale. Methods of destruction or disposal can range from a purpose- built sodium disposal plant to high temperature incineration, among others. Te challenges involved in treating the sodium or NaK in such decommissioning programmes are considerable and will be encountered at various stages. At the defuelling phase, for example, the assembly will be covered by a residual film of sodium that has to be removed before storing the elements in the pond. Every component extracted from the reactor will also be covered by a film of sodium, and can sometimes retain larger amounts of sodium, which is best removed before dismantling the components. Additionally, the metallic
Fig. 1. Inside the sphere, new chemical plant was installed above the reactor as part of the process and to neutralise and destroy batches of liquid metal lifted from its primary circuit.
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