Resin Overheating:
The potential for elevated temperatures exists in during most conditions of facility operation; we will examine in feature the processes which occur if the resin in an ion exchanger is overheated. While the inert polystyrene basic structure of resin is stable up to fairly high temperatures (approximately 300º F), the active exchange sites are not. An anion resin starts to decompose slowly at about 140ºF, and the decomposition becomes rapid above 180º F. The cation resin is stable up to about 250ºF. Because these temperatures are well below normal reactor coolant temperatures, a temperature of the coolant must be lowered before it passes by the ion exchange resin.
The anion resin (hydroxyl form) decomposes through either of two mechanisms with around equal possibility.
R- CH2N (CH3)3+ OH- → R - CH2OH + N (CH3)3 (4-24)
Heat
or
R- CH2N (CH3)3+ OH- → R - CH2 N (CH3)2 + CH3OH (4-25)
heat
The given Reaction (4-24) generates an alcohol form of the resin that has no exchange capability, and trimethylamine (TMA), N (CH3)3. TMA is a weak base, same to ammonia which reacts along with water as follows.
N (CH3)3 + H2O ↔ NH (CH3)3+ + OH-
The pH might increase noticeably if large amounts of TMA are released to the coolant. For instance, 1 ppm of TMA in reactor coolant which uses lithium resin will cause a noticeable increase within pH. TMA might also interfere along with the analysis for chloride ions (that is routinely performed on reactor coolant) through providing a false indication of high chloride concentration. The other significant property of TMA is its intense odor of dead fish. While the presence of such an odor from reactor coolant is not definitive for TMA, it might provide an indication of resin overheating.