radiation2H2O22H2OradiationReactor Water ChemistryDOE-HDBK-1015/2-93CHEMISTRY PARAMETERSRev. 0CH-03Page 17The use of hydrogen gas at temperatures above 200 F precludes the generation of thecompounds formed by Reactions (3-16) and (3-22). In addition, hydrogen is compatible withthe high flux levels present in the reactor core. Accordingly, advantage may be taken of thereversibility of the radiolytic decomposition of water. The following reaction illustrates thescavenging process utilizing hydrogen.(3-13)As indicated, the reaction is an equilibrium process and will therefore depend on the relativeconcentrations of the reactants and the products. By maintaining an excess of hydrogen (H ),2the reaction is forced to shift to the right and theoretically eliminates any dissolved oxygen thatmay be present. As long as an inventory of H is present in the coolant, dissolved oxygen will2be eliminated or forced to recombine immediately after radiolytic decomposition, thereby beingunavailable for corrosion reactions.A boiling water reactor (BWR) facility is susceptible to corrosion, resulting from dissolvedoxygen, in the same reactions as are present in a pressurized water reactor (PWR). However,because of the design of these facilities the use of chemical additives is prohibited becausecontinuous concentration would occur in the reactor vessel due to boiling. Boiling would resultin a plating out process, and the irradiation of these concentrated additives or impurities wouldcreate an extreme environment of radiation levels as well as adverse corrosion locations.By the very nature of operation of a BWR facility, the buildup of high concentrations ofdissolved oxygen is prevented. Because boiling is occurring in the reactor vessel and the steamgenerated is used in various processes and subsequently condensed, removal of dissolved gasesis a continual process. As stated, boiling is an effective means of removing gases from asolution. If we were to compare the oxygen content of the steam and the water in a BWR, wewould find typical concentrations of 100 ppb to 300 ppb in the water and 10,000 ppb to30,000 ppb in the steam. This concentration process is continuous during operation, and thedissolved oxygen remains in the gaseous state and is subsequently removed in the condensingunits along with other noncondensible gases. As with PWR facilities, BWR facilities minimizethe introduction of dissolved oxygen by pretreating makeup water by some method. The largeoxygen concentrations measured in the steam system result primarily from the radiolysis ofwater according to Reaction (3-12), and as operation is continued, the equilibriumconcentration of 100 ppb to 300 ppb is established. This concentration of oxygen is consistentwith the objective of minimizing corrosion.
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