N(CH3)3
H2O
NH(CH3)3
OH
Reactor Water Chemistry
DOE-HDBK-1015/2-93
CHEMISTRY PARAMETERS
Rev. 0
CH-03
Page 29
becomes rapid above 180 F. The cation resin is stable up to about 250 F. Because these
temperatures are well below normal reactor coolant temperatures, the temperature of the
coolant must be lowered before it passes through the ion exchange resin.
The decomposition of resin 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
3
3
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 form 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 other product of resin breakdown, [R - CH N(CH ) ], is an amine with exchange
2
3
2
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 (but greater than 180 F) is sustained for a long enough period, the resin
will be unfit for use. 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.
A number of changes are probable if overheating of resin occurs. Reactor coolant Cl levels
-
would probably increase as a result of thermal breakdown and subsequent release. Ion
exchanger effectiveness would be greatly reduced for similar reasons. Radioactivity levels of
the reactor coolant would increase because of the release of impurities collected and later
released from the resin. pH would likely decrease because of the release of H ions from the
+
resin complex and may cause acidic conditions in the reactor coolant if the temperature is
sufficient (>250 F). Because certain types of resin decompose at lower temperatures, pH may
increase as a result of the release of TMA and be accompanied by a dead fish odor. Because
of the consequences of overheated resin, stringent temperature limitations are necessary. If
overheating occurs, the ion exchanger should be taken out of service immediately and the cause
rectified. The resin must be replaced prior to placing the ion exchanger back in service after
overheating.
