The Shaking

Chapter Twenty

"So it's safe for now?"

"Yes. As long as nothing else happens."

"Such as?" Madden was beginning to sound less confident.

"Another strong aftershock damaging the unit still further."

"What more could go wrong?"

"Quite a lot actually. My greatest fear is that some of the graphite moderator blocks comprising the core may collapse. There's a possibility that after decades of being heavily irradiated they can become brittle and fracture; not forgetting they've long exceeded their planned service life. Instances of cracked blocks have been observed in other AGRs; fortunately they were overdesigned and had plenty of redundant strength built-in, the units continued running without any problems. But when these stations were planned this level of seismic activity wasn't anticipated, this area not being a severe earthquake risk zone and nothing on this scale ever happening here before, so there was no reason to build-in extra safety features; nor was there a rationale for developing contingency plans to deal with something which was so inconceivable it could never happen-"

"And if those blocks were to suffer a failure?"

"That would depend on how bad the event was. In the worst case a major collapse would allow the fuel rods to fall into close proximity with each other, and were that to happen the increased nuclear activity would raise their temperature way above the design level. Also bear in mind the fuel may be isolated from the cooling effect of the gas flow"

"What then?"

"The rods might melt together into a white hot, highly energetic molten blob which under the influence of gravity would eat its way through the floor of the containment structure. Eventually it would reach the underlying soil and encounter the groundwater table, which this being a coastal area is quite high. Should that occur a number of things will happen: Firstly if the blob contacts the water, much of the liquid will flash into superheated steam which will expand at a phenomenal rate, and finding no release against the incompressible earth, burst upward at great pressure. In addition the generated heat will be such as to separate the water into its component elements of hydrogen and oxygen, a combustible mixture which is bound to explode. When it does so the resulting pressure wave will seek any weakness to vent itself, and that will be found through the reactor fueling channels. Bear in mind the steam will give the shock wave an added kinetic force so breaching through the channels should pose no problem; it may even take out the entire refuelling level and spent fuel storage tanks above the reactor as well. Once it's done that it will most likely blow the roof off and exhaust into the open air..."

Both Madden and Williams were shocked into rapt attention.

"But unfortunately that's not the end of the matter." Alan continued. If the carbon dioxide gas is lost from the cooling system the graphite blocks as well as the fuel elements are likely to oxidise, catch fire and issue radioactive smoke directly into the atmosphere. One of the reasons the Dungeness spit was chosen as the site for this power station - in addition to a ready access to cooling sea water - was that if anything ever did go that badly wrong the prevailing winds would carry the fallout away to settle into the North Sea.

Unfortunately the weather forecast for the next few days is the winds will blow in a north-northwesterly direction from the continent, which means if such an event were to occur within that time high level radiological contamination would be dispersed over large areas of Kent and London."

"Bloody hell!" Madden exclaimed. "But that is an extremely unlikely worst case scenario, isn't it? It sounds like that old film The China Syndrome! And that was just based on conjecture, wasn't it?"