A full array full height core would have taken too much time to build, and due to the ease of handling scaled fuel bricks it would make a scaled model faster to assemble. The new scaled core model had to meet two criteria firstly it had to be easy to manipulate and secondly it had to be easy to monitor. The results of this represent a very onerous worst case scenario – the bricks were on a smooth base with no end face keying to constrain them, The rig was no longer valid as the full scale clearances allowed unrepresentative disengagement.Ī new scale core rig was developed to replace the original 1/8th scale core rig, as the inherent pessimisms were no longer able to represent the proposed cracking scenarios accurately.
BRICK RIGS WIKI CRACKED
Single layer tests to determine the upper bounds of possible displacements with varying percentages of doubly cracked bricks showed that key disengagement occurred much earlier than would be expected in real AGR geometry. As the core rig is tested with increasing fuel brick cracking, the full scale key / keyway clearances cause the displacements observed to become overly pessimistic. The 1/8th scale core rig was not intended to model the effects of doubly cracked bricks. having clearances of the order of 0.13 – 0.19mm, it would not have been practical to observe the displacement effects. Had the 1/8th scale core rig been completely scaled i.e.
rotations and key engagement were not representative. Unfortunately, this meant that other factors i.e. The full scale key /keyway clearances were maintained in order that the maximum displacements observed were equal to those possible in the reactor core. The outcome suggested that the spacer and filler keys could be omitted, as the rigidity of the AGR core is only slightly effected. An assessment of the effect of the primary and secondary keying systems was made using computational models.
The secondary keying system, comprising filler and spacer keys, were omitted. These simplified components represented the primary keying system and allowed it to transmit the loads in a representative manner. The 1/8th scale core rig design simplified the HPB/HNB components by incorporating keys into the bricks: the fuel brick included two integral bearing keys and the interstitial brick included four integral keys. The rig was made up of simplified fuel and interstitial brick components scaled by a factor of 1:8, however, the clearance were maintained at full scale to facilitate displacement measures. The 1/8th scale core rig was developed in stages, firstly as a single scale rig, then a full array, testing channel distortions, and more recently as a core with a limited number of doubly cracked bricks. The whole core experimental rig work was originally based on a 1/8th scales model of a HPB/HNB reactor cores being the lead stations. Whole core modelling is another approach of British Energy’s graphite core safety case strategy to determine the extent of tolerable cracking in the graphite core.
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