Reactor Water Chemistry
EFFECTS OF RADIATION
ON WATER CHEMISTRY (SYNTHESIS)
After essentially all of the oxygen has been consumed by reaction with hydrogen, the nitrogen
contained in air will remain. For small air additions, some hydrogen will also remain; thus, the
reactor coolant will contain both dissolved hydrogen and dissolved nitrogen. These two gases
do not react in an unirradiated solution at low temperature and pressure. When exposed to
radiation, however, the gases do react by the following reaction.
Again, this is an equilibrium reaction, and radiation induces the reaction in both directions.
Ammonia (NH ) produced by this reaction combines with water to form ammonium hydroxide
Under the operating conditions of reactor coolant, Reaction (3-14) is far from complete. In
most cases, less than about 10 percent of the nitrogen will be converted to ammonia. If no
additional base were added to reactor coolant, Reaction (3-14) would be sufficient to cause the
coolant to be mildly basic, pH 9. In the presence of added base, however, the reaction has only
a very slight and negligible effect on pH.
If the base NH were used to control reactor coolant pH, the reverse of Reaction (3-14) would
be more important. The reverse step of this reaction requires that some of the ammonia added
to the coolant decompose into N and H . Because operating conditions favor this step of the
equilibrium, rather than formation of NH , it would be expected that most of the ammonia added
would decompose. However, the rate of the ammonia decomposition reaction is slow, and the
pH of reactor coolant can be maintained in the required range. It should also be noted that the
decomposition of NH would produce hydrogen gas in significant concentrations in reactor
coolant (sufficient to satisfy normal H requirements).
In the event that a large quantity of air is injected into the reactor coolant system, the inventory
of dissolved hydrogen would be rapidly depleted by Reaction (3-13). If the amount of air
injected is sufficiently large, there could be oxygen remaining in the coolant after depletion of
the hydrogen. In this case, another reaction is available to the oxygen and nitrogen in the air.
Nitric acid (HNO ) produced by this reaction will neutralize any base contained in the coolant,
and if sufficient acid is produced, the coolant will acquire an acidic pH.