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Posted by Energetic
The Dungeness nuclear power plant are built on the largest area of open shingle in Europe, measuring 12 km by 6 km, which has been deposited by the sea and built up over thousands of years. The entire area is moving slowly north and east as the sea moves the shingle from one side of the ness to the other. It is surrounded by a nature reserve Site of Special Scientific Interest (SSSI). A fleet of lorries is used to continuously maintain shingle sea defences for the plant as coastal erosion would otherwise move shingle away at an estimated rate of 6 m per year. Around 30,000 cubic metres of shingle are moved each year. It seems that deposition on the north shore of the ness does not keep pace with demand. In all 90,000 cubic metres are moved each year along parts of the coast between Pett Level and Hythe. This is necessary for the safety of the entire area including the power stations. Approximately 100 million litres of cooling water are extracted and returned to the sea each hour, after being heated 12° Celsius (22 °F).
The relationship of the power stations with the ness in time is important. Geological history places the beginning of the promontory, some 3000 years ago, as shingle deposits offshore from Pett Level. From there the evidence suggests that the ness enlarged and migrated up Channel to its present position.Importantly the ness and the coastline between Pett Level and Hythe are volatile. In recorded history Walland Marsh to the west of the power stations has been flooded. In the space of sixty years severe inundation occurred bringing the sea inland to Appledore and the original mouth of the River Rother from north of the ness at Romney to the south at Rye Harbour. The site is a few metres above Mean Sea Level and would be isolated in the event of flooding of the magnitude that submerged big areas of East Anglia and the Netherlands in 1953. Conjecture says that the ‘hurricane’ of 1987 did not bring the sea to the stations because there was a low tide at the time. With global warming, more frequent and powerful storms and their associated waves and surges are possible and might increase the instability of the ness.
Dungeness A is a legacy Magnox power station, that was connected to the National Grid in 1965 and has reached the end of its life. It possessed two Nuclear reactors producing 219 MW of electricity each, with a total capacity of 438 MW. The construction was undertaken by a consortium known as The Nuclear Power Group ('TNPG'). The reactors were supplied by TNPG and the turbines by C. A. Parsons & Co.
On 31 December 2006 the A Station ceased power generation. It is anticipated that defuelling will be completed by 2009, the turbine hall demolished in 2010 to be replaced by an intermediate level waste store in 2014. The waste store and reactor building will then be placed on a care and maintenance basis until 2103, with final site clearance and closure by 2111. Decommissioning is estimated to cost £1.2 billion. An alternative proposal has been made to accelerate cleanup for completion by 2030.
Dungeness B is an advanced gas-cooled reactor (AGR) power station consisting of two 615 MW reactors, which began operations in 1983 and 1985 respectively. Dungeness B was the first commercial scale AGR power station to be constructed, the design being based on the much smaller Windscale AGR prototype; the WAGR. The £89 million contract was awarded in August 1965 to Atomic Power Construction ('APC'), a consortium backed by Crompton Parkinson, Fairey Engineering, International Combustion and Richardsons Westgarth. The completion date was set as 1970.
During construction, many problems were encountered in scaling up the WAGR design. Problems with the construction of the pressure vessel liner had distorted it such that the boilers, which were to fit in an annular space between the reactor and the pressure vessel, could not be installed, and the liner had to be partially dismantled and re-built. Although the cost of this work was relatively minor at about £200,000, the cost of financing for an extra 18 unproductive months a power station costing around £100 million of which some 60 per cent was already on the ground, was massive. Serious problems with the design of the boilers, which had to withstand the pounding of hot carbon dioxide (CO2), pressurised to 600psi and pumped around the reactor coolant circuit by massive gas circulators, were also discovered, and the casings, hangers and tube supports all had to be redesigned. The cost of these modifications, and financing during the delays, caused severe financial pressures to the consortium and its backers, and in 1969 APC collapsed into administration.
The CEGB took over project management, issued light penalties in order not to cripple Fairey and International Combustion, and appointed British Nuclear Design and Construction (BNDC) as main contractor. In 1971, problems with corrosion of mild steel components in the first generation Magnox reactors gave the designers cause for concern. The Dungeness B restraint couplings - mechanical linkages that held the graphite core in place whilst allowing it to expand and contract in response to temperature changes - were made of mild steel and could be subject to the same corrosion. A decision was made to replace them with components made from a new material. In 1972, problems with the use of galvanised wire that was used to attach thermocouples to stainless steel boiler tubes were discovered. During heat treatment of the tubes at temperatures up to 1,050oC, the galvanising zinc diffused into the tubes and made them brittle. The cost had by then risen to £170 million. By 1975, the CEGB was reporting that the power station would not be completed until 1977 and that its cost had risen to £280 million. By 1979 the cost had risen further to £410 million. Reactor 1 first generated power on 3 April 1983, some 13 years behind schedule and at a cost of £685 million, four times the initial estimate in inflation adjusted terms.
Like the "A" station, its turbines were built by C.A. Parsons & Company and it has two 600 MWe turbo-alternator sets, producing a maximum output of 1200 MWe, though net output is 1090 MWe after the effects of house load, and downrating the reactor output due to corrosion and vibration concerns.
In March 2009 Unit B21 was brought down for maintenance; serious problems were found and the reactor was shut down for almost 18 months. On 24 November 2009 a small fire in the boiler annexe of Unit B22 caused the second reactor to also be shut down. Subsequently Unit B22 has been intermittently offlined for periods of up to several months. Unit B21 was restarted in August 2010. Shutdowns continued into 2011.
The station's accounting closure date is 2018, 35 years after first power generation. Life-extension options may be considered prior to this date.
On 15 April 2009 Dungeness was included in a list of 11 potential sites for new nuclear power stations, at the request of EDF Energy, which owns and operates Dungeness B. The government did not include Dungeness C in its draft National Policy Statement published on 9 November 2009, citing environmental reasons and concerns about coastal erosion and associated flood risk. The site was ruled out by Secretary of State for Energy and Climate Change Chris Huhne in October 2010 with the former government's list of eleven potential sites reduced to eight.
From 1961 to 1984, Dungeness power station also housed the mercury arc valves of the static inverter plant converting AC into DC for transmission on HVDC Cross-Channel, the high-voltage direct current power cable carrying electric power across the English Channel to France. In 1983, a more powerful new inverter at Sellindge replaced this facility.