plutonium

2.2 Components of a nuclear power station

• The fuel. The elements that undergo the fission are generally uranium (U) or plutonium (Pu).
• The control rods. A nuclear fission reaction at criticality can be maintained by controlling the critical mass (as you heard about in Week 1).
• The moderator.
• The coolant.

Thermal neutrons have a far higher cross section (probability) of fissioning the fissile nuclei uranium-235, plutonium-239, and plutonium-241, and a relatively lower probability of neutron capture by uranium-238 (U-238) compared to the faster neutrons that originally result from fission, allowing use of low-enriched …

This makes it difficult to use water as a coolant for a fast reactor because the water tends to slow (moderate) the fast neutrons into thermal neutrons (though concepts for reduced moderation water reactors exist).

Proponents of this nuclear technology argue that it can eliminate large stockpiles of nuclear waste and generate huge amounts of low-carbon electricity. But as the battle over a major fast-breeder reactor in the UK intensifies, skeptics warn that fast-breeders are neither safe nor cost-effective.

The “fertile” material is not fissionable, but it can be converted into fissionable material by exposure to radiation in a reactor. Fast reactors can thus be used to breed more fissile material than they consume or to burn nuclear waste or for a combination of these two tasks.

(Unlike water moderated reactors, sodium-cooled fast breeders can explode due to an accidental nuclear criticality.) Fueling a fast breeder reactor with plutonium would require routine operation of a reprocessing plant that could handle large amounts of spent fuel with high plutonium concentrations.

Burning this weapons-grade plutonium in a reactor will pollute it with non-fissile isotopes. Completely altered, it becomes useless for making bombs. There are long-term prospects for reducing or stabilising the quantity of plutonium – or inventory – built up by reactors currently in operation.

Another is that, to extract the plutonium, the fuel must be reprocessed, creating radioactive waste and potentially high radiation exposures. For these reasons, in the U.S., President Carter halted such spent fuel reprocessing, making the use of breeder reactors problematic.

There are four countries in the world that currently have operating fast breeder nuclear reactors: China, Japan, India and Russia. That total is down from nine countries, including the U.S., that had operating breeder reactors, some since the 1950s, according to World Nuclear Association (WNA).

A breeder reactor creates 30% more fuel than it consumes. After an initial introduction of enriched uranium, the reactor only needs infrequent addition of stable uranium, which is then converted into the fuel. It can generate much more energy than traditional coal power plants.

Breeder reactor, nuclear reactor that produces more fissionable material than it consumes to generate energy. This special type of reactor is designed to extend the nuclear fuel supply for electric power generation.

A fast-breeder nuclear reactor produces more fuel than it consumes, while generating energy. Conventional reactors use uranium as fuel and produce some plutonium. Breeders produce much more plutonium, which can be separated and reused as fuel.

Fast breeder reactors The plutonium-239 is then bombarded with high-speed neutrons. When a plutonium nucleus absorbs one such free neutron, it splits into two fission fragments. This fissioning releases heat as well as neutrons, which in turn split other plutonium nuclei, freeing still more neutrons.

Uranium-235

A major advantage of the BWR is that the overall thermal efficiency is greater than that of a pressurized water reactor because there is no separate steam generator or heat exchanger. Controlling the reactor is a little easier than in a PWR because it is accomplished by controlling the flow of water through the core.

One of the major concerns of electricity production with nuclear energy has to do with safety. As with BWRs, the most severe operating condition affecting a PWR is the loss of coolant accident (LOCA).

The steam in a pressurized water reactor is produced in a secondary system while the steam in boiling water reactor is produced directly in the reactor core. The pressure of a pressurized boiling reactor varies from the primary system to the output steam while the pressure of a boiling water reactor remains constant.

The molten-salt reactor, a less developed technology, is considered as potentially having the greatest inherent safety of the six models. The very-high-temperature reactor designs operate at much higher temperatures.

SMRs are a slimmed-down version of conventional fission reactors. Although they produce far less power, their smaller size and use of off-the-shelf components help reduce costs. These reactors are designed to be safer than traditional water-cooled reactors, using coolants such as liquid sodium or molten salts instead.

Light water is used as the primary coolant in a PWR. Water enters through the bottom of the reactor’s core at about 548 K (275 °C; 527 °F) and is heated as it flows upwards through the reactor core to a temperature of about 588 K (315 °C; 599 °F).

[1] One major advantage of this reactor is that it is easy to operate because less power is being produced as the heat increases. [3] In addition, the core of the reactor contains less fissile material, decreasing the chances of additional fission events to occur, making the reactor safer and more controllable.

BWR