A new dawn for nuclear
Nuclear power is becoming increasingly safe and attractive, writes Eric Russell. Here he outlines the advances in the technology and its likely future
The intense arguments against nuclear power seem to be calming. Even New Zealand, the world’s most ardent anti-nuclear country, is starting to admit that it may be needed at some point. Perhaps people are realising that the usual objections are a decade out of date.
Environmental awareness, corporate responsibility and shareholder pressure were largely undiscussed topics ten years ago. Today they dominate business life, and have been taken on board by the nuclear industry, where developments in materials, experience, technology and safety have changed the substance of nuclear power out of all recognition.
Professor Richard Clegg, Director of the Dalton Nuclear Institute at Manchester University, says: “It is now time for nuclear power to shake off its old image and demonstrate its credentials as being safe, affordable and clean.”
The institute aims to become a world leader for nuclear teaching and research and is the largest of its kind in the UK. But a report in early March from the Government’s independent watchdog on sustainable development, the Sustainable Development Commission, said building new nuclear plants is not the answer to tackling climate change or securing Britain’s energy supply. Chairman of the Commission, Jonathon Porritt (who writes for Environment Business this month, page 14) says: “There’s little point in denying that nuclear power has benefits but, in our view, these are outweighed by serious disadvantages.”
The latest reactor designs are very safety-aware, and a key feature is their relative simplicity. That means lower construction costs, faster build time and – crucially – greater safety and reliability.
Typical of the new order is the Westinghouse AP1000 1,000MW Pressurised Water Reactor (PWR). It features 50% fewer valves, 83% less piping, 87% less control cable, 35% fewer pumps and 50% less seismic building volume than a similarly sized conventional plant. It uses a modular technique for construction, which allows several construction activities to proceed in parallel. This technique reduces plant construction time down to 36 months from first concrete to fuel loading.
Westinghouse says the AP1000 is the safest, most advanced, yet proven, nuclear power plant currently available in the world. It is based on standard Westinghouse PWR technology that has achieved more than 2,500 reactor years of successful operation.
A new design from GE Energy also uses fewer active mechanical systems, with their associated pumps and valves, and relies on more reliable passive systems that utilise natural forces, including natural circulation and gravity. This includes the company’s Economic Simplified Boiling Water Reactor (ESBWR). GE Energy says the 1,500MW ESBWR is a third-generation reactor design because of its new design simplicity and passive safety features. It evolved from GE’s 1,350MW Advanced Boiling Water Reactor (ABWR), which the NRC certified for US construction in 1997.
The ABWR is a design that has already been proven with more than 18 reactor years of operating data from plants completed in Japan.
The ESBWR is considered to be an evolutionary design because, while it incorporates much of the ABWR’s key and proven design features, it also incorporates new technology advances. It claims to be the only reactor that fully relies on natural circulation for routine running.
Areva NP, previously known as Framatome, says its European Pressurised Water Reactor (EPR) features innovations to prevent core meltdown. It is building the first reactor in Finland and the 1,600MW plant is scheduled to start commercial operation in 2009. A key feature is that the possibility of human error is reduced. It also offers exceptional resistance to external hazards such as aircraft crashes and earthquakes.
There is also a greater degree of redundancy. To provide emergency cooling of the reactor core, for example, there are four independent sub-systems, each capable of performing the entire safety function on its own. They are located in separate parts of the plant so the risk of simultaneous failure due to internal or external events is avoided.
In addition, a leak-tight containment around the reactor would prevent radioactivity from spreading outside, even during extremely severe accidents involving core meltdown. Areva NP also emphasises safety with its SWR 1000, an advanced boiling water reactor. Again, the new safety concept of this medium-capacity model emphasises passive safety features based on gravity and natural convection.
By increasing the volume of water in the reactor pressure vessel, the reactor core remains well covered with water during depressurisation. This, and the low core-power density, provides protection for up to three days in the event of an accident before human intervention is needed. Emergency condensers serve to remove heat from the reactor if there is a drop in reactor pressure vessel water level. They come into action automatically without any need for electric power or switching operations.
At the smaller end of the scale, the Pebble Bed Modular Reactor (PBMR) also claims a high level of safety and efficiency. As the reactor gets hotter, the rate of neutron capture by the U-238 increases, reducing the number of neutrons available to cause fission. This places a natural limit on the power produced by the reactor. The reactor is cooled by an inert, fireproof gas, so it cannot suffer a steam explosion as a light-water reactor can. In addition, the reactor vessel is designed so that, without mechanical aids, it loses more heat than the reactor can generate in its idle state.
Instead of water, PBMR uses pyrolytic graphite as the neutron moderator, and an inert or semi-inert gas such as helium, nitrogen or carbon dioxide as the coolant. The gas circulates through the spaces between the fuel pebbles to carry heat away from the reactor at a higher temperature than conventional light-water reactors. This drives a turbine directly and with greater thermal efficiency due to the higher temperature. The design eliminates the usual steam management system although a heat exchanger may be installed to isolate the generating plant from the reactor.
A pebble-bed reactor can have all of its supporting machinery fail, and the reactor will not melt, explode or spew hazardous wastes. It simply goes up to a designed idling temperature, and stays there. The machinery can be repaired or the fuel can be removed.
The technology has been under development in South Africa since 1993. The PBMR project entails the building of a demonstration reactor project near Cape Town and a pilot fuel plant near Pretoria. The current schedule is to start construction in 2007 and for the demonstration plant to be completed by 2010. The first commercial modules are planned for 2013.
PBMR (Pty) has recently signed a memorandum of understanding with the Chinese developers of pebble bed technology, Chinergy Co, whose pebble bed concept is based on a 10MW research reactor that was started up in Beijing in December 2000. The 10MW prototype, the HTR-10, is a conventional helium-cooled, helium-turbine design.
The first 200MW production plant is planned for 2007. There are firm plans for 30 such plants by 2020 generating 6GW. By 2050, China plans to generate as much as 300GW.
But, within a generation, this could all be history. The EURATOM/UKAEA Fusion Association predicts that nuclear fusion will take over from fission and a prototype station could be supplying the national grid in 30 years’ time.
Fusion is based on fusing light nuclei such as hydrogen isotopes to release energy in a process similar to that which powers the sun. The energy is released when gas from a combination of isotopes of hydrogen, deuterium and tritium is heated to 100MÚC (about 17,000 times hotter than the surface of the sun) and confined for at least one second in a magnetic field.
International co-operation is strong with the focus on the International Tokamak Experimental Reactor (ITER) currently being built in France. A Tokamak is a machine that produces a toroidal magnetic field for confining a plasma. ITER will be the first fusion device designed to achieve sustained burn, at which point the reactor becomes self-heating.
Fusion has very good inherent safety qualities: there are no chain reactions and no production of radioactive actinides; the worst possible accident scenario is containable; any releases could not approach levels requiring site evacuation; the radiotoxicity of fusion waste materials decays rapidly; and there are no climate-changing or atmosphere-polluting emissions.
In the meantime, advances in materials and control systems mean today’s reactors are far more able to contain the forces of fission than before and there is no reasonable bar to a global nuclear future.
Visit www.framatome-anp.com, www.eps.manchester.ac.uk/dalton, www.fusion.org.uk, www.gepower.com, www.pbmr.com, www.sd-commission.org.uk or www.westinghouse-nuclear.com
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