N(CH3)3H2ONH(CH3)3OHReactor Water ChemistryDOE-HDBK-1015/2-93CHEMISTRY PARAMETERSRev. 0CH-03Page 29becomes rapid above 180 F. The cation resin is stable up to about 250 F. Because thesetemperatures are well below normal reactor coolant temperatures, the temperature of thecoolant 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 exchangecapability, and trimethylamine (TMA), N(CH ) . TMA is a weak base, similar to ammonia, that33reacts with water as follows.If large amounts of TMA are released to the coolant, the pH may increase noticeably. Forexample, 1 ppm of TMA in reactor coolant that uses lithium form resin will cause a noticeableincrease in pH. TMA may also interfere with the analysis for chloride ions (which is routinelyperformed 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 presenceof such an odor from reactor coolant is not definitive for TMA, it may give an indication ofresin overheating.The other product of resin breakdown, [R - CH N(CH ) ], is an amine with exchange232capabilities considerably less than the original form of the resin. Thus, both reactions lead topartial (or complete) loss of exchange capability. If the temperature is sufficiently high, or ifa lower temperature (but greater than 180 F) is sustained for a long enough period, the resinwill be unfit for use. If the temperature becomes very high (greater than about 450 F), thepolymeric base structure of the resin will decompose, forming a complex mixture of organic tarsand oils.The preceding discussion concerned the decomposition of resins in their original forms. Itshould 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 ofthe 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. Ionexchanger effectiveness would be greatly reduced for similar reasons. Radioactivity levels ofthe reactor coolant would increase because of the release of impurities collected and laterreleased 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 issufficient (>250 F). Because certain types of resin decompose at lower temperatures, pH mayincrease as a result of the release of TMA and be accompanied by a dead fish odor. Becauseof the consequences of overheated resin, stringent temperature limitations are necessary. Ifoverheating occurs, the ion exchanger should be taken out of service immediately and the causerectified. The resin must be replaced prior to placing the ion exchanger back in service afteroverheating.
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