Opal fuel modifications approved

01 May 2008

Approval has been given to use a modified fuel design in Australia's Opal research reactor, altered to prevent dislodgement of nuclear fuel plates.


Cerenkov radiation (at Opal) 
Opal at full power. The blue glow is
Cerenkov radiation caused by
faster-than-light particles travelling
through cooling water (Image: Ansto)
The 20 MWt Open Pool Australian Light-water (Opal) reactor began commissioning in 2006, reaching full power during November that year. It is owned and operated by the Australian Nuclear Science and Technology Organisation (Ansto) and was supplied by Invap of Argentina.


On 24 July, however, it was noticed during refuelling that three of the reactor core's 16 nuclear fuel assemblies each had one of their 21 fuel plates partially dislodged. This appeared to have been caused by the motion of coolant water, which flows from the bottom to the top of the tank in which the core sits and causes a certain amount of vibration.


Ansto's response was to shut down the reactor in order to analyse the problem. The organisation decided that a revised fuel assembly design was needed because the existing fuel was subject to "inadequate design and fuel manufacture techniques." Ansto said the roll-swaging process used for the faulted fuel was to blame.


The new fuel plate design incorporates what Ansto describes as 'stoppers' which limit longitudinal movement within the fuel assemblies. These 'defence in depth' features, which Ansto said prevent significant movement, take the form of two 4 mm plates of aluminium fixed by two screws to a side-frame of the fuel assembly and are held in position by the screws and the assembly handling pin.


This design was approved today by the Australian Radiation Protection and Nuclear Safety Agency (Arpansa), and Ansto is now free to restart Opal when ready.


Ansto said in a submission to Arpansa that it would improve video surveillance of fuel assemblies with in-core video inspection before and after fuel changes. Ansto will also inspect fuel destined for Opal at the point of manufacture and perform pull tests on the plates in a test sample of each batch of new nuclear fuel.


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