How water treatment in thermal power stations?

Answer 1

Water treatment for nuclear power stations is a complicated and specialist subject.

They usually put corrosion inhibitors into the water. These differ from ones in coal and oil fired plants in that they must stand up to the radiation in the core, must not be converted into unacceptably radioactive products themselves or absorb so many neutrons that it would slow the nuclear reaction, and that is it is generally impossible to pull apart the primary loop in a nuclear reactor except for major maintenance or when the reactor is decommissioned. Because of this volatile corrosion inhibitors like amines and amine alcohols are generally preferred to ones like sodium hydroxide.

This is for two main reasons. Firstly sodium becomes radioactive when exposed to neutrons. Secondly it is a solid and if it crystallizes out or evaporates it can cause solid deposits which can plug the cooling system, which could cause a Loss of Coolant Accident (LoCA).

As for treatment of the water after it has reached its end of useful life, generally techniques like ion exchange and evaporation are used when water is significantly contaminated. These usually occur after the waste water has sat for a long time in a tank or pond so that the short lived, more dangerous radioisotopes have had a chance to decay to manageable levels. The solid waste from evaporation is then treated as a radioactive waste, and classified and disposed of according to its level of radioactivity.