7.4.1 Improvement of the Fission in Nuclear Power Plants

On the basis of their history and technical condition, nuclear power plants are clas­sified into four groups. The first-generation (Generation I) nuclear power plants were developed in the 1950s—1960s in the Soviet Union, the United States, Great Britain, and France. Most of them have been dismantled now; only a few of these reactors are still operating. They do not fulfill today’s safety, technical, and envi­ronmental requirements.

The second-generation (Generation II) nuclear power plants were the improved version of the first-generation plants; they are more safe, economical, and reliable. Most of the power plants in operation today belong to this type. PWRs are the most widespread; they provide about 65% of the total production of nuclear power plants today. The very important difference between first-generation reactors and the PWRs is that in PWR reactors, the total primary circuit (namely, all the con­taminated parts of the reactor) is placed in containment, which is a high-volume, pressure-proof, hermetically sealed building. This creates a new safety barrier in case of an accident.

The third-generation (Generation III) nuclear power plants are improvements over the second-generation plants. For this reason, they are called “evolution nuclear power plants.” The number of evolution power plants is relatively low, there are some third — generation nuclear power plants, for example, in Japan, at this time, but they are being planned and constructed all over the world. Their typical features are as follows:

• They will be built using standard plans, so they can be up and running in a relatively short time (a few years); the operation time, however, is longer.

• Their structure is simpler and more robust than the previous reactors.

• They are safer because of the application of passive protection techniques.

• Their environmental impact is very low.

• The fuel is burned up better, so the fuel cycle is more economical and produces less waste.

The fourth-generation nuclear power plants are called “innovative plants” because they apply new technical solutions and have new safety requirements. The most important trends are as follows:

• In addition to 235U, 238U, and 232Th will be utilized for energy production.

• Besides electric energy production, hydrogen will be produced by the electrolysis of water. This in itself should have a significant positive environmental impact because right now, hydrogen is produced from natural gas, which also produces carbon dioxide, increasing the greenhouse effect.

• To decrease the quantity of high-level nuclear waste produced, the facilities for the trans­mutation of the long-life radioactive isotopes (see Section 7.3.2) will be included in the nuclear reactor itself.

• The possibility of the production of the nuclear weapons from the spent fuel elements will be significantly reduced.

These aims may be achieved by different reactor types, such as thermal reactors, including the very-high-temperature reactor, the supercritical-water-cooled reactor, and the molten salt reactor; fast reactors, including the gas-cooled fast reactor; and molten metal (sodium, lead, lead—bismuth)-cooled reactors.