Advantages/Disadvantages of Borated Water in Coolant 2

[joedevo]

I am doing research to determine some of the advantages or disadvantages of using borated water in reactor coolant. In a typical fission reactor application, borated water is used to control the fission reaction as well as limit neutron radiation exposure. I am trying to determine if the rigors of maintaining boron in coolant is worth using it as an aid in limiting radiation exposure without the need to control a fission reaction. Does anyone know some of the advantages and disadvantages of using borated water for coolant? Thank you for your time.

 

[gmax137]

joedevo - boron is added to the reactor coolant in pressurized water reactors (PWRs) to compensate for the reactivity of the fresh fuel. Boron absorbs neutrons and thus can be used to control the reactivity of the core.

As the fuel "burns" the reactivity decreases and the plant operators will slowly dilute the boron concentration. The initial concentration may be around 1100 ppm and 18 months later when it is time to refuel, the concentration will be close to zero. The boron is not used to reduce radiation exposure. The safety systems that actuate during certain accidents will inject borated water to shut the reactor down (independently from the control rods which are also inserted for shutdown).

Boron concnetration can also be adjusted to keep the coolant temperature at the desired value during load changes (changes in the power demanded by the grid).

The disadvantages of using boron are mostly related to the effects of leaks, since leaks will result in accumulation of boric acid, which is corrosive.

Boiling water reactors (BWRs) do not use boron for routine reactivity control.

If you want more info try googleing "chemical shim" - a generic term for reactivity control using dissolved chemicals.

 

[JohnBreen]

.........and much of the PWR reactor head replacement work that is now in progress is due to the boric acid leaking onto the heads and causing damage. Better design can (will) solve most of the leak problems but boron is here to stay.