Geriatric constipation
By John Busby   
21 May 2009

British Energy (BE) has issued a report “Managing spent fuel at Sizewell B” which was prepared for issue at a public exhibition to “explain the options that British Energy are considering for managing spent fuel at Sizewell B nuclear power station from 2015 onwards”. John Busby touches on some of the unresolved issues.

It appears that the existing spent fuel pond in which used fuel is stored will reach its capacity by 2015. The station was commissioned in 1995 and is expected to remain operational until 2035 after 40 years of generation. The pool was sized in accordance with a packing density specified by the builders, Westinghouse, but at the exhibition held on 6 May 2009, BE’s staff explained that the density allowed was halved by the UK inspectors, in effect halving the life of the pond.

BE is consulting the public on whether to build a second pool and also whether subsequently spent fuel should be transferred to dry casks or to a ventilated vault. See [1] The option to send the spent fuel elements in special rail containers to Sellafield for processing, has not been taken and since its inception in 1995 all the spent fuel has remained in the pool.

The solution in the US, where processing has until recently been disallowed, is to progressively transfer the spent fuel elements into dry casks, which are stored vertically in open “cemeteries” or horizontally in “mausoleums” pending an ultimate transfer to an underground repository. See “Rip van Winkel wakes” [2]

The required residence time of the spent fuel is variously specified, but is normally around 5 years. As the original fuel elements have been in the pool for 12 years, in the 5 years intervening before its fills there seems no reason why the space problem could not be relieved by initiating an immediate transfer to dry casks or to a ventilated vault and thereby no need for a second pool would arise.

In “Geriatric incontinence,” [3] the occurrence of leaks in spent fuel ponds was highlighted. Boric acid is added to water in a spent fuel pool to increase storage densities by absorbing neutrons to obviate the risk of a chain reaction. However, this absorption releases tritium, which can penetrate the stainless steel pond liner. The liner is subject to irradiation and corrosion and there have been many leaks of radioactive substances including tritium into groundwater.

In “Geriatric design assessment" [4] it was recommended that for the new build reactors, claimed to operate for 60 years, that a reserve pond be kept empty in the event that the first pond leaked.

So it may be that BE has taken this advice and will install a second pond for its security or that the present pond has already leaked. Otherwise the immediate recourse to dry casks would suffice to enable the reactor to continue beyond 2015.

[1] British Energy (BE)  Report: "Managing spent fuel at Sizewell B”

[2]  "Rip van Winkel wakes." 

[3] “Geriatric incontinence. ”   

[4]   “Geriatric design assessment.”

[5]   “Geriatric emaciation.”