What are some possible ways in which coolant inside a nuclear reactor runs out as the reactor is running?

Oakport

Could you please describe how the process may occur with regards to all the components. Thanks.



Bolindale

There are pressurized water reactors (commercial and naval) and boiling water reactors (commercial). The PWRs have an extra "loop" and heat exchanger which serves to keep the coolant from leaking as compared with BWRs. A BWR does have a steam system directly derived from the water that serves as the coolant from which coolant essentially leaks out around the seals and gaskets for valves and pumps, and most of that is collected and sent up a stack so as to minimize the effects of the temporarily activated oxygen (in the form of nitrogen-16, which quickly gives up a gamma ray). Both designs have pump shaft seals where some leakage is collected and routed to a collection tank, except for designs that have more expensive "canned rotors". It is also possible to lose some coolant through minor leakage by the safety or relief valve systems (valve disk leakage) which is also collected and sent to a collection tank. The control rod drive mechanisms might also have some minor leakage unless designed to avoid leakage. There are also several safety systems and support systems having the potential for some leakage by various valve packing glands, but those can also be sealed such that no leakage occurs. Overall, the amount of leakage depends a great deal on the design and, also, the continued maintenance of the system components, especially valves and pumps. Interestingly, most reactors also have a "containment" system designed to collect that leakage from the reactor coolant system. Ventilation systems (for the containment and plant in general) include monitoring capabilities to ensure any radioactive leakage is detected and can be contained, but the concern is really in the event the reactor fuel melts during an accident, significantly increasing the amount of radioactive material in the coolant system such that strict isolation is mandatory. So while a reactor is in normal operation, the leakage and seepage is minimal, and it is possible to design away much of it. Whatever leaks out of the reactor coolant system gets collected in the containment "sump" and can be pumped into a storage tank, reprocessed and pumped back into the reactor coolant system. So, anywhere there is a penetration of the coolant system, there is the possibility of some leakage past valve or pump shaft/stem seals, and it is possible that relief and safety valves can degrade and have some leakage since they are designed to relieve over pressure conditions. Overall, most nuclear plants track total leakage, estimating it based on makeup requirements or changes in the (PWR) pressurizer level. Trending that leakage daily, it is possible to determine whether there is an issue that needs to be corrected and whether outage time needs to be devoted to replacing gaskets and seals for pumps and valves.



Tubac

What kind of reactor are we talking about? There are quite a few different ones, you know. Anyways; the primary coolant is usually water, pure and simple. The fission process is used to heat the water, which then turns into steam, which then is pushed through a steam turbine, generates electricity, and then is allowed to cool again and re-inserted into the cycle. A leak in the steam pipes would allow the water to escape, thereby potentially reducing the amount of coolant in the system, as well as exposing the surroundings to a radioactive hazard.