Principles of Water Treatment
DISSOLVED GASES, SUSPENDED SOLIDS, AND pH CONTROL
Reaction (4-24) produces an alcohol form of the resin, which has no exchange
capability, and trimethylamine (TMA), N(CH ) . TMA is a weak base, similar to
ammonia, that reacts with water as follows.
If large amounts of TMA are released to the coolant, the pH may increase noticeably.
For example, 1 ppm of TMA in reactor coolant that uses lithium resin will cause a
noticeable increase in pH. TMA may also interfere with the analysis for chloride ions
(which is routinely performed on reactor coolant) by giving a false indication of high
chloride concentration. Another significant property of TMA is its intense odor of dead
fish. Although the presence of such an odor from reactor coolant is not definitive for
TMA, it may give an indication of resin overheating.
The methyl alcohol (CH OH) produced by Reaction (4-25) is not expected to have a
harmful effect on the reactor coolant system. The other product of this reaction
[R - CH N(CH ) ] is an amine with exchange capabilities considerably less than the
original form of the resin. Thus, both reactions lead to partial (or complete) loss of
exchange capability. If the temperature is sufficiently high, or if a lower temperature
(greater than 180 F) is sustained for a long enough period, the resin will be unfit for use.
Cation exchange resin begins to undergo thermal decomposition at temperatures above
about 250 F by the following reaction.
This reaction destroys all exchange capacity of the cation resin and also produces an
acid. The Reactions (4-24) through (4-26) are the initial reactions when resin is
overheated. If the temperature becomes very high (greater than about 450 F), the
polymeric base structure of the resin will decompose, forming a complex mixture of
organic tars and oils.
The preceding discussion concerned the decomposition of resins in their original forms.
It should be noted that if overheating occurs after the resin has been in operation for
some time, part of the resin will be in a different form due to the exchange process. As
a result, some of the previously-removed impurities will be released to the coolant if
decomposition occurs. For example, the chloride form of the anion resin will form
CH Cl by the reaction corresponding to Reaction (4-25).