EFFECTS OF RADIATION
Reactor Water Chemistry
ON WATER CHEMISTRY (SYNTHESIS)
Another way of viewing the effect of hydrogen on reactor coolant is through its effect on the
equilibrium of the reaction.
By LeChatelier's principle, the addition of excess hydrogen forces the equilibrium to the left,
which requires that O be consumed. If the dissolved hydrogen concentration is sufficiently
large, only a very small amount of oxygen will be present at equilibrium. Normally, therefore,
reactor coolant contains excess dissolved hydrogen, and there is no significant net
decomposition of water by radiation.
Reactor coolant makeup water usually contains a small amount of air, which is composed
primarily of nitrogen and oxygen in a volume ratio of 4:1 (80 percent nitrogen, 20 percent
oxygen). These gases undergo radiation-induced reactions. The reactions are the same as those
that occur in certain accident situations and are included in the following discussion.
In addition to the small amount of air normally dissolved in makeup water, there is a small
possibility that air may be accidentally injected directly into the reactor coolant system.
Whenever air enters the reactor coolant system, and the reactor is operating, the most immediate
reaction involves oxygen from the air and hydrogen, which is normally present in the coolant.
That is, the addition of O disturbs the above equilibrium and causes the equilibrium to shift to
the right, consuming both H and O . The concentration of hydrogen normally maintained in
reactor coolant is such that small amounts of oxygen will be rapidly consumed before any excess
oxygen can cause severe corrosion problems to occur.
Reaction (3-13) also consumes oxygen added to the reactor coolant as a natural consequence
of air dissolved in makeup water. Other than initial fill of the reactor coolant system, the
situations that require the largest amounts of makeup water are feed and bleed operations to
correct an abnormal chemistry parameter or cooldown after some period of reactor operation.
In this case, gamma radiation from the decay of fission products in the reactor core continues
to induce the H - O reaction for some period after shutdown. During initial fill and long
shutdown periods, chemicals other than hydrogen (e.g. hydrazine) may be added to reactor
coolant to remove any dissolved oxygen.