Our confidence in nuclear reactors

Following the three major nuclear accidents in the Three Mile Island Nuclear Power Plant in USA in 1979, the Chernobyl Nuclear Power Plant, now in Ukraine, in 1986, and lately the Fukushima Daiichi Nuclear Power Plant in Japan in 2011, interest has shifted from generation-II nuclear power reactors to much safer generation-III reactors. Generation-I reactors were built as prototypes during the early development of nuclear reactors and are no longer in operation. Most of the nuclear power reactors now in operation are generation-II reactors. They are likely to be retired in phases.

The generation-III power reactors are being developed by major reactor manufacturers in the USA, Europe, Russia, Japan, China, South Korea, and Canada. The common features of the reactors include simple, standardised, and compact designs to reduce capital costs and construction period, higher fuel burn-up and thermal efficiency, higher availability and longer core life, and more importantly, passive and active safety systems. Advanced light water reactors include, among others, advanced boiling water reactors (ABWR) and advanced pressurised water reactors (APWR).

Many countries have showed renewed interest in nuclear power because of global warming and climate changes resulting from the combustion of fossil fuels and high costs of renewable energy. Germany, which announced to phase out nuclear power after the Fukushima accident, is rethinking to introduce nuclear power again. Many scientists and engineers believe that it may not be possible to cope with global warming without nuclear power. Nuclear power reactors emit no greenhouse gases and the generation-III reactors are much safer than the generation-II reactors as they incorporate passive safety systems to make them inherently safe.

ABWRs were originally developed by General Electric of USA in collaboration with Toshiba and Hitachi. Some versions are equipped with core catchers and filtered vents for release of hydrogen gas from the reactor. Four ABWRs were in operation in Japan in 2011 and several more are under construction in Taiwan and the USA. Japan suspended the operation and construction of ABWRs and other reactors under public pressure after the Fukushima accident.

AP-1000 is an APWR developed by Westinghouse of USA. It is a two-loop PWR evolved from a smaller version, AP-600, and certified by US Nuclear Regulatory Commission. Its simple and compact design resulted in cost savings with improved safety features. It has a core cooling system with passive residual heat removal by natural convection and in-vessel retention of core damage with water cooling around it. No safety-related pumps or ventilation systems are used. AP-1000 reactors are also being built in China.

European pressurised water reactor (EPR) has been developed by Areva (former Framatome) in France. It is a standard model producing 1750 MWe gross and 1630 MWe net power. It is designed to use mixed-oxide fuel. The plant availability is expected to be 92% with a service life of 60 years. The reactor has double containment with a core catcher under the reactor pressure vessel. The reactor building is designed to withstand the crash of an aircraft. EPRs are under construction in Finland, France, and China.

Russia is now marketing mainly two APWRs: VVER-1000 and VVER-1200. VVER-1000 reactors are available in different versions. Russia and Ukraine have several VVER-1000 reactors in operation. The VVER-1200 reactor is developed from VVER-1000 reactor and has a standardised model with four coolant loops and 3200 MWt power. It has enhanced safety with some passive safety features.

While generation-III nuclear reactors are under construction in several countries, generation-IV reactors are already on the drawing board. An international task force known as Generation-IV International Forum (GIF), formed in 2001, has selected six nuclear reactor technologies which may be deployed around 2030. The selected reactor systems include gas-cooled fast reactors, lead-cooled fast reactors, molten salt reactors, sodium cooled fast reactors, super-critical water-cooled reactors, and very high-temperature gas reactors.

Two of these are thermal reactors while others are based on fast or epithermal neutrons. Four rectors are designated for hydrogen production. Hydrogen is a clean fuel that produces water as waste after combustion. All the reactors are credited to have better safety, economy, reliability, and sustainability compared to their predecessors. Other advantages include better nuclear waste management through production of wastes with shorter half-lives, possibility of conversion of long-lived actinides from nuclear wastes of current reactors into short-lived fission products, and more energy yield from the same amount of nuclear fuel.

Most of the reactors employ a closed fuel cycle to minimise the volume of high level wastes. Only one reactor is cooled by water, two by helium, and the others by lead-bismuth, sodium, or fluoride salts. The latter three are operated at low pressure with significant advantage in terms of reactor safety. The temperatures range from 510°C to 1000°C while present day light water reactors operate at around 330°C. The high temperatures permit operation at higher efficiencies and production of hydrogen through thermo-chemical reactions.

There are few other types of generation-IV reactors being developed by other countries. Until prototypes of such reactors are operated successfully, safely, and reliably, the generation-III reactors will continue to dominate the nuclear market. It is believed that the advanced nuclear reactors will earn the confidence of the people around the world as clean, safe, and reliable sources of power, and many countries who decided to phase out nuclear power plants will reconsider their decisions.