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Background

Didcot ‘A’ is a 2000MW(e) coal burning power station that has been operating since 1970. At full working capacity, it consumes approximately 5 million tonnes of coal per year. As a result of this burning, ash is produced at a maximum rate of 3420 tonnes/day which equates to a maximum of 1.25 million tonnes per year. 20% of this is furnace bottom ash (FBA). The remaining 80% is pulverised fuel ash (PFA) which is removed mechanically or electrostatically from the gas stream. PFA is therefore produced at a rate of up to 1 million tonnes per year. Approximately 99.9% of the PFA is collected. The remaining 0.1% (up to 1000 tonnes per year) is discharged into the atmosphere, along with up to 15 million tonnes/year of carbon dioxide.
DidcotPS_5333

 

From 1970 to 1984, Didcot ash was disposed of in landfill at Sutton Courtenay, to where it was transported by road under a concession granted by the County Councils. This had to cease as a result of pressure to make more landfill available for London waste. However the embargo on disposal by road, a condition of the planning consent granted in 1964 for the construction and operation of the power station, led to the power station operators to seek to dispose of the surplus ash in gravel pits via a pipeline. Radley was a convenient choice for them, being only 8km from the power station with no intervening obstacles. Conditional planning permission was granted to the power station operators, the CEGB, on 17 February 1982 (ref: SUT/RAD/5948) to dispose of ash in the area designated as comprising lakes A thru N. (see map) Under the terms of this consent, Didcot were required to restore the land to agriculture and to the original topography. They also needed approval for specific proposals through each phase of the operation. In 2005, the current Power Station Operators, RWE Npower, submitted such a proposal seeking approval to fill lakes E and F. When it became clear that they were seeking significant variations, some imposed on them by new environmental and waste disposal regulations, which did not exist in 1982, and that there was significant public opposition to the filling of these remaining lakes, the application for approval was put into abeyance. However in January 2006, they submitted a brand new planning application to fill only Lake E (Thrupp Lake). Despite being granted full planning permission in early 2007, RWE npower eventually gave up the idea and, in December 2008, announced that they would give Thrupp Lake to the community.

 

In addition, facilities for the stockpiling up to half a million tonnes of ash were supposed to have been constructed at the power station site. This was to enable meeting fluctuating demands for PFA for use as a construction material. Unfortunately this bund (if it ever existed) was lost when Didcot ‘B’ was constructed and has not been replaced. Didcot operators therefore have no proper means of stockpiling ash at the Power Station. This limits their ability to recycle the ash and requires on-demand pumping to Radley even perhaps when conditions there are less than suitable. It is worth noting that, in 1982, when submitting their original application, the Power Station operators considered this stockpile to be essential to the ash disposal operation.

Since dry ash is required for some applications, approximately 5000 tonnes of dry ash are also stored in silos on the site.

The process of disposal involves pumping a 30% PFA/water slurry via a specially constructed 440mm pipeline into the lakes at Radley. The ash is allowed to settle while the water is drained off through a gravel filter and series of weirs into the Thames. Cenospheres are collected by filter meshes at each weir, harvested and removed from the site by road.

When filling is complete and the ash has stabilised, the area is covered with a sandy overburden (50-85mm) for restoration to woodland or a thicker (254mm) overburden plus 153mm of topsoil for restoration to “agricultural land”. Throughout this time, the land is securely fenced off with no public access allowed. This is because the filled lakes are a hazard to the unwary; the surface may appear solid and safe, especially as moss starts to appear, when in fact it may conceal dangerous quicksand. As a result, the lakes are securely fenced off and remain so for decades.

The status of the Radley lakes and gravel pits in 2005 was:

  • Lakes A-D have been filled and partially restored to woodland. They however remain fenced off and there is no public access.
  • Lakes H & I have been recently filled, and are fenced off.
  • Lakes G, J & P are in process of being filled, and are fenced off.
  • Lakes E, F, M & N are unfilled and there is limited public access..
  • Lakes K & L are not (fully) excavated and may remain in their present state.
  • Lake P, although outside the area covered by the original consent, is currently being filled as part of the lake G/J operations. Planning consent was given for this in 2003.

Table of estimated lake capacities (from 1982 Planning Application Brief)

Lake

(see map)

Capacity

(cubic metres)

A
784,000
B
333,000
C
293,000
D (silt lagoon)
not given
E
436,000
F
68,000
G,J,N,P
666,000
H, I
278,500

The total capacity of the lakes listed above is therefore in the region of 3 million cubic metres (sufficient for around 4.5 million tonnes of ash). The capacity of lakes E and F is around 500,000 cubic metres, sufficient for about three quarters of a million tonnes of ash, if the lakes are filled to the depth (2.1m) proposed in 1982. Increasing the depth to 4 metres virtually doubles their capacity to a million cubic metres, equivalent to about 1.5 million tonnes. This would have represented the largest single lake filling operation to date.

 

Didcot ‘A’ Power Station is an “opt-out” power station under Article 3 of the European Large Combustion Plant Directice. This means that, in 2004, the power station operators elected to be exempt from the emissions limits imposed by the directive, and undertook not to operate for more than 20,000 hours in the period 1 January 2008 to 31 December 2015, after which time the station must cease operating.

This means that Didcot ‘A’ Power Station is committed to closure before 1 January 2016.

 

Other Links and Sources of Information

Permanent link to this article: http://www.radleyvillage.org.uk/ourvillage/didcot-fuel-ash-disposal/background/