CHEMISTRY PARAMETERSDOE-HDBK-1015/2-93Reactor Water ChemistryCH-03Rev. 0Page 28FuelElementFailureDuring operation of a nuclear reactor facility an equilibrium level of fission products isestablished in the reactor coolant. These fission products are the result of trace impurities offuel material contained in the cladding surfaces as either natural impurities or a result of the fuelfabrication process. The mechanism by which the fission products enter the coolant is normallyby fission recoil. Weld porosity is another potential path for the fuel, but generally qualitycontrol prevents this from occurring. During normal facility operation, these fission productsare minor contributors to the overall radioactivity of the reactor coolant system.If a defect were present or a failure of a fuel element occurred, large amounts of fissionproducts would potentially have a path to the coolant system. If this happened, significantchanges would occur within the reactor coolant chemistry parameters. Because most facilitiesanalyze for gross coolant radioactivity either continuously or periodically, the analysis wouldbe likely to detect all but the most minute failures. When routine gaseous radioactive levels are monitored, an increase in this parameter's valuewould be seen. This is because many of the fission products are gaseous, and these gases aremore mobile than particles of exposed fuel (the exposed fuel generally undergoes a process oferosion that washes the fuel into the coolant stream). The other parameter that may change isthe ion exchange efficiency (where utilized), because many of the fission products released havea lower affinity for the exchange sites on the resin beads than the exchange anion or cation.Accordingly, the ion exchanger would not effectively remove these fission products and effluentradioactivity levels would increase significantly. Fission gases would also pass on through theion exchanger and contribute to effluent activity. In addition, because some of the fission gaseshave relatively short half-lives, the amount of time they are held up in the ion exchanger issufficient for some of these gases to decay to a radioactive solid. These solid particles would contribute to effluent samples that may be concentrated prior toanalysis. Some facilities monitor for specific fission product inventories in the reactor coolantto provide base level information. If a defect or failure were to occur, these levels wouldobviously increase to indicate the failure.ResinOverheatingBecause the potential for elevated temperatures exists during most conditions of facilityoperation, we will summarize the results from the resin in an ion exchanger overheating.Module 4 addresses resin in great detail, and the actual resin breakdown will be included there.Basically the resin of an ion exchanger is an inert polystyrene structure with ion exchange sites"loosely" attached. The basic structure is stable up to fairly high temperatures (approximately300 F), but the active exchange sites are not. There are two types of exchange sites: anion andcation. The anion resin begins to decompose slowly at about 140 F, and the decomposition
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