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A comment on Pictures show cracks in Ayrshire nuclear reactor. Parent comment

Re:Pictures show cracks in Ayrshire nuclear reactor by petre on Sunday June 09, 2019 @11:12AM (#20139702)
If the moderator (graphite) crumbles into the channel it could jam it and prevent the control rods from entering the core and stop the nuclear reaction. However there are secondary (Nitrogen injection) and tertiary (Boron beads) modes of shutting down the reactor.

"In October 2014 a new kind of crack in the graphite moderator bricks was found at the Hunterston B reactor. This keyway root crack has been previously theorized but not observed. The existence of this type of crack does not immediately affect the safety of a reactor – however if the number of cracks exceed a threshold the reactor would be decommissioned, as the cracks cannot be repaired."

https://en.m.wikipedia.org/wiki/Advanced_Gas-cooled_Reactor

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Re:Pictures show cracks in Ayrshire nuclear reactor by Reason077 on Sunday June 09, 2019 @11:43AM (#20139901)
> "However there are secondary (Nitrogen injection) and tertiary (Boron beads) modes of shutting down the reactor."

Hunterston B has also been fitted with "super-articulated" control rods that are designed to be insertable even if the graphite channels are destabilised/distorted.

https://www.bbc.co.uk/news/uk-england-somerset-37789654

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Re:Pictures show cracks in Ayrshire nuclear reactor by Reason077 on Sunday June 09, 2019 @11:33AM (#20139848)
> "however if the number of cracks exceed a threshold the reactor would be decommissioned, as the cracks cannot be repaired"

This is the issue currently. The cracking in reactor 3 has progressed more rapidly than modelled, and has exceeded the threshold of 350 cracks. EDF are arguing that the reactor can be safely operated with more cracks, and want the threshold increased to 700.

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