Exchange capacity of the cation resin:
The methyl alcohol (CH3OH) produced through Reaction (4-25) is not expected to have a harmful effect on the reactor coolant system. Another product of this reaction [R - CH2N (CH3)2] is an amine along with exchange capabilities considerably less than the real form of the resin. Therefore, both reactions lead to partial (or full) loss of exchange capability. The resin will be unfit for use if the temperature is sufficiently high, or if a lower temperature (greater than 180ºF) is sustained for a long sufficient period.
Cation exchange resin starts to undergo thermal decomposition at temperatures above about 250ºF through the following reaction.
R- SO3H + H2O → R - H + 2 H+ + SO4 = (4-26)
Heat
This reaction destroys all exchange capacity of the cation resin and also generates an acid. The given Reactions (4-24) by (4-26) are the initial reactions while resin is overheated. A polymeric base structure of the resin will decompose, creating a complex combination of organic tars and oils if the temperature becomes extremely high (greater than about 450ºF).
The preceding discussion concerned the decomposition of resins in their real forms. It should be remembered which if overheating occurs after the resin has been in operation for a few time, part of the resin will be in a different form because of the exchange procedure. Conclude, a few of the previously-removed impurities will be released to the coolant if decomposition occurs. For instance, a chloride form of the anion resin will form CH3Cl through the reaction corresponding to Reaction (4-25).
R- CH2N (CH3)3+ Cl- → R - CH2 N (CH3)2 + CH3Cl
heat
The CH3Cl (chloromethane) will be released to the coolant and will decompose within the radiation field of the reactor core, generating Cl- ions. As same, the sodium form of the cation resin will release Na+ ions through the following reactions.
R- SO3H + H2O → R - H + H+ + Na + SO4=
heat