2 H2Oradiation2H2O2radiation2H2O22H2OradiationEFFECTS OF RADIATION DOE-HDBK-1015/2-93Reactor Water ChemistryON WATER CHEMISTRY (SYNTHESIS)CH-03Rev. 0Page 6Another way of viewing the effect of hydrogen on reactor coolant is through its effect on theequilibrium of the reaction.(3-12)By LeChatelier's principle, the addition of excess hydrogen forces the equilibrium to the left,which requires that O be consumed. If the dissolved hydrogen concentration is sufficiently2large, only a very small amount of oxygen will be present at equilibrium. Normally, therefore,reactor coolant contains excess dissolved hydrogen, and there is no significant netdecomposition of water by radiation.Reactor coolant makeup water usually contains a small amount of air, which is composedprimarily of nitrogen and oxygen in a volume ratio of 4:1 (80 percent nitrogen, 20 percentoxygen). These gases undergo radiation-induced reactions. The reactions are the same as thosethat occur in certain accident situations and are included in the following discussion.In addition to the small amount of air normally dissolved in makeup water, there is a smallpossibility that air may be accidentally injected directly into the reactor coolant system.Whenever air enters the reactor coolant system, and the reactor is operating, the most immediatereaction involves oxygen from the air and hydrogen, which is normally present in the coolant.(3-13)That is, the addition of O disturbs the above equilibrium and causes the equilibrium to shift to2the right, consuming both H and O . The concentration of hydrogen normally maintained in22reactor coolant is such that small amounts of oxygen will be rapidly consumed before any excessoxygen can cause severe corrosion problems to occur.Reaction (3-13) also consumes oxygen added to the reactor coolant as a natural consequenceof air dissolved in makeup water. Other than initial fill of the reactor coolant system, thesituations that require the largest amounts of makeup water are feed and bleed operations tocorrect an abnormal chemistry parameter or cooldown after some period of reactor operation.In this case, gamma radiation from the decay of fission products in the reactor core continuesto induce the H - O reaction for some period after shutdown. During initial fill and long22shutdown periods, chemicals other than hydrogen (e.g. hydrazine) may be added to reactorcoolant to remove any dissolved oxygen.
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