Why do nuclear reactors use coolants

Their use has been mainly restricted to fast reactors. Collier, J. DOI: Nuclear Power Technology , Volume 1, Ed. Marshall Clarendon Press. Login: Guest. View in A-Z Index. The general features that make a particular gas or liquid attractive as a reactor coolant are as follows: Chemically compatible and noncorrosive to circuit materials; Cheap and readily-available in pure state; Good nuclear properties and stable under radiation; Well-defined phase state and high boiling point; High rates of heat transfer; High specific heat and ease of pumping.

Table 1. If there is an issue with the diesels, you have a battery backup. And the batteries usually last long enough for you to get the diesels going. How much time is there before a meltdown? It depends on the plant. It depends on whether it's a boiling-water reactor or a pressurized-water reactor. Basically, [in both] you have the benefit of natural forces such as convection. There is a coolant loop no matter what, so you end up to some degree cooling the core because the heated water rises and colder water gets pulled in.

But that's not as effective as a pump bringing in cool water. Just to speak very broadly, you have many hours to restore power to the system to get normal cooling going. It's really not possible to get more specific than "many hours.

What's the worst-case scenario? The event we are looking to avoid is damaging the core. Once you start damaging the core, you are then releasing radioactive material into the coolant and thereby increasing the chances that something travels outside the reactor.

The reactor that was not cooling properly in Japan, the Fukushima Daiichi No. How are these different from pressurized-water reactors in terms of cooling? Particularly useful to boiling-water reactors is a system that is steam driven. It does not require an outside power source. Steam generated by the heat of a cooling down reactor has enough force to run a turbine, which then runs a pump that provides coolant to the core.

That sort of system is supposed to withstand an earthquake, and that can run for an extended period. It's a self-limiting condition. That system does use batteries for the controls, but it can also be operated manually.

So even in the face of a complete station blackout—you don't have any power at all—there are methods for using the steam-driven pump to continue to keep cooling going.

Are there other coolants besides water? Water would be it, essentially. The reserve tanks at a reactor contain the same grade of water in terms of purity and chemical composition that are normally used in the core. It is possible, if you have a situation where you have exhausted that source of coolant to introduce, quote—unquote, regular water. That will do the job of cooling.

Why do nuclear power plants need electricity to be cooled? Nuclear reactors are net positive in terms of supporting the grid. After a few minutes, the reactor achieves passive shut-down.

An even more effective coolant and moderator is heavy water, or deuterium liquid D 2 O , because its absorption cross section is three orders of magnitude smaller than that of hydrogen. When it comes to fast breeder reactors, molten sodium is the coolant of choice because it causes negligible moderation.

The sodium becomes intensely radioactive from contact with the fuel, but it stays contained within the reactor and has a short half-life of approximately 15 hours. However, liquid sodium has significant disadvantages as well: it ignites spontaneous upon contact with the air, and reacts violently with water. Besides burning, sodium exposed to the air produces aerosols that are highly toxic and can cause equipment damage to the surfaces onto which they are deposited.

An alternative to liquid metal is molten salt. This coolant can run at high temperatures for better thermodynamic efficiency, but remains at a low vapor pressure, which reduces the effects of mechanical stress and increases the intrinsic safety of the reactor. Since heat transfer by molten salt is so efficient, reactors can be designed with smaller cores and less complicated piping systems.

Structurally, the biggest difference is that the fuel — a mixture of sodium, zirconium and uranium fluorides — can be dissolved into the coolant itself, a set-up that eliminates the need for fuel fabrication and the disadvantages of having variable isotopic ratios within the fuel rods. Other nuclear reactor currents include liquid lead, gases such as helium and carbon dioxide, and organic compounds. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only.