Perhaps surprisingly for an industry that prides itself on cutting edge technology, nuclear reactors aren’t very efficient. They rarely operate to capacity, so although they are generally designed and licenced to operate for 40 years their actual generating life is nearer 24-years. Essentially, nuclear power stations work in pretty much the same way as fossil fuel-burning stations, except that a ‘chain reaction’ inside a nuclear reactor makes the heat instead. The reactor uses the fabricated uranium rods as fuel, and the heat is generated by nuclear fi ssion. Neutrons smash into the nucleus of the uranium atoms, which split roughly in half and release energy in the form of heat. Carbon dioxide gas is pumped through the reactor to take the heat away, and the hot gas then heats water to make steam that drives turbines, which in turn drive generators.
The reactor is controlled with ‘control rods’ made of boron, or by including boric acid in the coolant water. Boron acts to slow down the fission process by absorbing neutrons. To generate more power, the presence of boron in the reactor is reduced, allowing more neutrons to crash into uranium atoms. Boric acid is produced mainly from borate minerals by reaction with sulphuric acid in a chemical process similar to milling and
enriching uranium.
British Nuclear Group employs approximately 30,000 people full time, and 30,000 people indirectly, as sub-contractors, to run the 14 nuclear reactors in the UK. Sellafield alone employs around 10,000 full-time staff and 4,000 sub contractors.
The thousands of staff employed to run nuclear facilities are there to refuel the reactor, monitor its performance and, when required, to perform running repairs.
Refuelling is a major operation that occurs on average every 18 months and requires the reactor to be shut down for about 40 days, although some reactors can refuel on the job. Fuel rods have a natural fission life of around four to five years, after which they simply wear out. At this time the core pressure reactor is shut down and allowed to cool, before the 60,000 fuel rods that form the payload are removed. Thousands of fuel rods, which are commonly around 3.5-4m long, are used to form a fuel assembly, which is an open lattice that can be lifted into and out of the reactor core. Between one quarter and a third are removed at any one time and replaced, as the rods wear down at different rates depending on where they sit in the lattice.
During routine operations and refuelling ‘small’ amounts of radioactive isotopes such as hydrogen-3, carbon-14 and plutonium-239 are routinely leaked into the atmosphere in what are known as ‘licenced emissions’ and ‘controlled releases’. These occur for many reasons:
• fuel rods emit radiation into the atmosphere during refuelling, and this is filtered out of the facility through air vents;
• pipes, tanks and valves leak as, in engineering
terms, there is no way to perfectly seal them;
• mechanical failure and human error can also cause leaks;
• as a nuclear plant ages, so does its equipment – and leaks increase;
• some contaminated water is intentionally removed from the reactor vessel to reduce the amount of radioactive and corrosive chemicals that have built up during fission and could damage valves and pipes. The water is filtered and then either recycled back into the cooling system or released into the environment;
• some radioactive fission gases, stripped from the
reactor cooling water, are held in decay tanks for days before being released into the atmosphere through filtered rooftop vents; and
• some gases leak into the power plant buildings
and are released during periodic ‘purges’ and
‘ventings’. These airborne gases contaminate not only the air, but also soil and water.
While the industry has always said that these releases are at levels too insignificant to effect human health, and the regulatory authorities accept they are permissible, CERRIE, a government committee established three years ago to look into the health impact, thought otherwise. (See ‘Licenced Emissions and Controlled Releases’, p51)
The potential hazards were all too clearly exposed when pigeons that had been roosting at the Sellafield reprocessing plant were found to be highly radioactive – 40 times the EU intervention level. The then Ministry of Agriculture warned against handling, slaughtering or eating any pigeon found within 10 miles of the facility.
At some facilities, plutonium is extracted from the spent fuel rods for reprocessing. This involves bathing the rods in a succession of chemical baths, containing at various times boiling nitric acid and caustic soda, among other solvents. These too give off radioactive gases, which the industry claims are captured. As no records are kept, it’s impossible to prove either way.
What is known is that it is a highly dangerous operation. In April 2003, the Paks nuclear reactor in Hungary came within seconds of a nuclear explosion comparable to Chernobyl. About 30 fuel assemblies – one tenth of the reactor core load – did not cool down sufficiently after being chemically cleaned during refuelling. Instead, they boiled the water in the cooling tank dry and finally crumbled like porcelain when operators flooded the tank with water. A massive release of radioactive gas leaked into the reactor room, from which operators fled, and was later blown unfiltered into the atmosphere at full ventilator strength for more than 12 hours.
While human error might have contributed to the Paks ‘incident’, it is more indicative of a malaise that is known to be pervasive in the industry – inattentiveness. In May 2005 it was revealed that thousands of litres of highly radioactive liquid had been leaking unnoticed at the Thorp reprocessing plant in Sellafield for nine months. By that time, 83,000 litres of radioactive coolant – enough to fill an Olympic-sized swimming pool – had already been accidentally spilled, with an estimated cleanup cost of £500 million.
British Nuclear Group, which runs the plant, said workers had failed to respond to indicators that would have warned that there was a leak.
In America in 2001 warning signs were missed that indicated boric acid corrosion had eaten through the reactor wall. Between 35-40 pounds of carbon steel were gone, and the only thing that contained the radioactive, highly-pressurised coolant water inside the vessel was the thin skin of stainless steel cladding. Not designed to endure such pressure, the lining had started to bulge outward. It was only identified when regulators became concerned about the design of the nozzles that delivered boric acid to the reactor. If it had continued to go unnoticed, the results would have been catastrophic.
The industry describes such events as ‘inexplicable’. What they mean is a succession of errors occurred that had not been envisaged. While publicly they reassure that the industry is safe, privately there is grave concern for the future.
When the World Association of Nuclear Operators (WANO) met in Berlin in 2003, ‘carelessness and complacency’ by operators was at the top of the agenda. Both ‘threaten the continued existence of our business,’ Nucleonics Week quoted a Swedish delegate as saying. The then President of the WANO, Hajimu Maeda, diagnosed a ‘terrible malaise’ that threatened the business from within. It starts with loss of motivation, complacency and ‘carelessness in upholding a culture of safety due to severe cost pressures resulting from deregulated electricity markets’. If these problems are not recognized and countered, he warned, ‘a serious accident will destroy the industry’.
To read the full Nuclear Power Dossier click here
This article first appeared in the Ecologist June 2006
