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Chcmic~tl dccontuminution tcchnolo~ ~7 For BWRs, the most effective passlvatlon process for decontaminated surfaces would seem to be continuous zinc injection (45). In fact, zinc is most effective on fresh or decontaminated surfaces, and a decontamination represents a desirable starting point for zinc injection. For PNRs, operation at elevated pH is the most cost-effective method of reducing radiation buildup. Preferably, elevated pH should be adopted for the fuel cycle before the decontamination so that the inventory of radioactive corrosion products in the core is reduced, thereby minimizing the source of cobalt-60 for subsequent redepositfon out of core. 6. WASTE MANAGF~ENT 6.1 Introduction After use, chemical solutions from the decontamination process become radioactive and are processed through ion-exchange resins to remove the radioactive material and other unwanted ionic species. The processed liquid is then either transferred to normal plant water systems or further processed as plant liquid effluent. The spent resins become radioactive waste that must be stabilized, transported and disposed according to Nuclear Regulatory Commission regulations 10CFR61 and applicable revisions (46,47). Additional criteria are also imposed by the three licensed commercial disposal sites. Compliance to regulations has been demonstrated for CAN-DECON, LOMI, NS-1 and AP/CITROX processes. The presence of chelating components in the waste products is significant, in that the Baruwell, South Carolina waste disposal site requires a stabilization step for chelate concentrations exceeding 0.1Z and places a maximum 8Z (by weight) on chelate content in a given shipment. A review of decontamination waste management was conducted by EPRI in 1985 describing early utility experience in dealing with this type of waste stream (48). 6.2 Minimizing waste volume generation Chemical decontamination of nuclear power plant systems using dilute chemical processes has replaced earlier processes that used high concentration chemicals not only to overcome concerns about system corrosion but also reduce the volume of wastes generated. However, even with current chemical reagents operating at 0.1% concentrations, disposal of the resultant wastes can represent up to 30% of the cost of a decontamination campaign. Options for optimizing existing decontamination processes have been successfully introduced which reduce the volume of waste generated significantly. Reagent chemistry was adjusted and a new ion exchange material was introduced without loss of process decontamination efficiency (I_II). Similar improvements have been realized for both CAN-DECON and CITROX when the new ion exchange material is adopted. These processes, because of their inherent regenerative mode, result in smaller waste resin volumes. 6.3 Low-formate LOMI reagents The basic LOMI decontamination reagent consists of 1 mole of vanadous formate (V 2+) ion, 6 moles of picolinic acid, and up to 10 moles of formic acid for each mole of ferric (Fe ~+) ion to be dissolved. The quantities of vanadous picolinate and picolinic acid ~e in stoichiometric proportions required to react with the calculated quantity of Fe ~- that will be removed; however, formic acid is present in large excess due to the vanadous manufacturing process. Vanadous formate is manufactured using electrolytic reduction of vanadium pentoxide (V205) in the presence of excess formic acid. High concentrations of formic acid are required during the manufacturing process to act as a charge carrier during the+) electrolytic reduction and to prevent t~ precipitation o~hydrnted vanadic (V ion as the vanadium is reduced from vanadyl (V "T) to vanadous (V'T). Once all the vanadium is In the 2+ oxidation state, the excess formic acid is no longer required and can be removed before the LOM1 reagent is shipped to the user. The LONI solution suppller ~itially believed that the excess formic acid was necessary to maintain the stability of V 6 in solution. However, this excess formic acid then required additional ion-exchange resins at the end of the decontamination process which resulted in larger waste volumes. The additional ion-exchange resin was required for two reasons:
Page 1 and 2: Prt~res.~ io .'~uclear Energy. Vol.
Page 3 and 4: Chemical decontamination technology
Page 5 and 6: ,4. O~¢I~NTAMiNATION Oi I Mfql SYS
Page 7 and 8: Chemical de¢ontaminamm technology
Page 17 and 18: 1.000E-06 1.000E-O7 1.000E-08 Chemi
Page 19 and 20: Types of corrosion testing of decon
Page 21: Chemical decontamination technology
Page 29 and 30: Chemical dccontamim~tion technology
Page 35 and 36: Chcmic~l decontamination technology
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