Decay Heat Removal

Techniques for eliminating decay heat from a reactor core can be grouped into two common groups. One group involves techniques that circulate fluid via the reactor core in a closed loop, by using some kind of heat exchanger to transfer heat out of the system. The other group involves techniques that operate in an open system, drawing in cool fluid from some source and releasing warmer fluid to some storage region or the atmosphere.

In most of the reactors, decay heat is generally eliminated by similar techniques used to eliminate heat produced by fission throughout the reactor operation. Additionally, most reactors are designed such that natural circulation among the core and either its common heat exchanger or an emergency heat exchanger can eliminate decay heat. These are illustrations of the first group of techniques for decay heat elimination.

When a reactor design is such that the decay heat elimination is needed for core safety, though accidents are possible which will make the closed loop heat transfer techniques unavailable, then an emergency cooling system of some kind will be involved in the reactor design. Usually, emergency cooling systems consist of some dependable source of water which is injected into the core at an associatively low temperature. This water is heated by the decay heat of the core and exits the reactor through some path where it will either be stored in some structure or discharged to the atmosphere. Use of this kind of system is almost forever less desirable than the use of the closed loop systems.

Students must research systems, limits, and protective features appropriate to their own particular facilities.