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60 C.J. Wooo 6.9 Complications encountered with the cement solidification of spent resins In a recent EPRI seminar, the subject of waste solidification, packaging and burial took center stage in view of field experience from reactor decontamination activities (51-53). The Nuclear Regulatory Commission seminar participants made several key observations that warrant mentioning. Over the past couple of years there have been several incidents where problems have been encountered with cement solidified wastes. These incidents include problems with expansion, disintegration, non-solidlflcatlon, and overly-rapld solidification of cement solidified waste forms. Examples are (I) the cracking and splitting of two liners at Three Mile Island (caused by expansion and disintegration of the cement-solldlfled bead resin waste); (2) expansion of a liner containing cement-solldlfled LOMI decontamination waste on bead resin at Millstone; (3) non-solldlflcatlon of LOMI- decontamination waste (on resin beads) at Fitzpatrick; (4) too-rapid solidification (occurring before the prescribed amount of cement could be added to the mix) st Quad Cities; and (5) excessive foaming (due to detergent "impurities") at Sequoyah. Contributing factors in these cases appear to include the following: Excessive loading (as a fraction of the total volume of the waste form) of bead resin. The presence of decontamination solution chemicals. The presence of ingredients ("impurities") in the waste stream that were not tested in the laboratory development of the waste formulation or recipe. A lack of knowledge by the waste generator/processor of what specific composition is being processed. The potential impact of this situation on the future use of cement for low-level waste stabilization is that NRC may take certain actions in the near future. First, at least for certain troublesome waste streams such as those involving bead resins and decontamination chemicals, waste loadings will have to be significantly reduced. In some cases, the current waste loading approach 70 to 80 percent by volume of the waste; that is, cement comprises only 20 percent by volume of waste form. Thus, there is simply too little cementitiOus material available to bind the waste together and to provide the required structural stability. The approach taken toward qualifying the waste formulation, or recipe, has been essentially empirical and is not one that is primarily based on a precise scientific understanding of the fundamental mechanisms involved. Some margin must be provided to compensate for effects that are not addressed in the laboratory testing where PCP data are generated. A second approach that should help to reduce the llkellhood of encountering problems in producing stable solidified waste forms is to improve the waste handling end characterization. Though some utilities are doing well in that regard, it is clear that in some cases the wastes are being handled in a manner that can lead to solidification problems. Examples include situation where wastes from different waste streams are placed in the same tank and where adequate analyses of the resultant mix of wastes are not obtained prior to processing. A few hundred parts per million of ingredient can have a drastic effect on the set time and ultlmate solidification of a cement waste form. A third approach that should be investigated further involves the chemical or thermal treatment of the waste material, particularly bead resin material, to render it move resistant to interaction with the cementltlous material. An example of such a process is one that is used in Sweden, where certain resins wastes are heated to 150 degrees Celsius for ten to fifteen hours, as a pretreatment before solidification in cement. The volume of organic ion exchange resins is reduced by loss of interstitial and internal water by the heat treatment. Thermal decomposition of the quaternary ammonium groups produces a reduced tendency to swell when wetted. Recent attempts to solldlfy waste resins generated from reactor system decontamination provided an opportunity to study the cementation process more closely (5_~4). The genesis of the problem is believed to be the introduction of weak anion resin Ionac A-365 with a capacity 2.5 times that of anion resins used in the past to remove plcollnlc acid from LOMI streams (I0). A "solidlfled" llner was found to contain serious nonhomogeneltles, sample portions showing large concentrations of resin not set into cement.
Chemical decontamination technology 6! Independent studies by two waste disposal vendors (51,52). and by a utility affected by a "non-solidlfled" liner revealed that plcolinic acid forms a calcium hydrate compound when lime is added to the resin which is to be cemented. When the amount of ptcolinic acid is "excessive" as in the Ionac A-365 anion beads, the hydrate formed interferes with the mixing process (54). Although the mechanism is still being studied, thixotroplc mixtures were produced in the laboratory where picolinic acid was treated with lime. The same studies showed that solidification could be improved by a) reducing the loading of picollnlc acid on the resins, or b) reducing the fraction of anion resins in the liner, c) using sodium hydroxide in whole or in part for pH adjustment or d) dilution of resins with water. The overall impact of all but remedy c) will be to increase the volume of the final waste form and thus impact burial costs. A cost/benefit analysis during the planning stages of decontamination should include remedial strategies for waste dlsposal, Including impact on volume increase in order to achieve solidified liners acceptable for burial. 6.10 Reduction of waste volume - new techniques When cemented for disposal, each cubic foot of resin yields 2 to 3 cubic feet of buriable volume. Thus, burial charges alone could be as high as $180/ft ~ of untreated resins waste..There is a compelling incentive to reduce the volume of waste resins either by loading more activity per unit volume or by converting the resin to volatile products (H20, CO 2) and then treating the small fraction of residue by solidification (50). Ion speclfic,_high capacity "media" were reported to absorb radioactive species with a total dose of 109 fads, a factor of I0 higher than the levels now permitted for organic resins (55). In addition, these "media" can be further volume reduced by heating to 150°F, and their selectivity and capacity can be further tailored to make them more efficient. Work is in progress to develop specific information to handle radioactive wastes using the absorption, ion specific media. Yet another approach is to "wet oxidize" resins using hydrogen peroxide to form CO 2 and H20, plus a smell volume of residue which can be solidified using conventional techniques (3__O0). This effort, underway at EPRI and CEGB (UK) is now being brought to pilot scale for testing in early 1989. Initial tests will include only non-radloactlve resins, to be supplemented with later demonstrations featuring resins which contain radioactive species. Projected volume reductions of 3 to 5 are targeted, a significant improvement over the 2.5 to 3 increase when burlal-ready resins are now the normal disposal options. 7. METHODOLOGY FOR COST-BENEFIT ANALYSES FOR DECONTAMINATION 7.1 Introduction Several methods have been developed for determining if decontamination is cost beneficial or not. They range from analyzing doses received on a Job-by-Job basis to more global approximations of doses saved followlng a decontamination at the beginning of a major outage. There is no simple formula that allows a utility to quickly and easily determine if a decontamination will be cost beneficial for a particular maintenance Job. 7.2 Description of elements used in cost-beneflt analysis Experience suggests that a more complex algorithm will be required, such as that developed by LeSurf (56). Value = Benefit - Cost (I) Benefit = Man-rem Saved + Critical Path Time Saved + (2) Future Residual Benefits ÷ Intangible Benefits Cost = Vendors Charges + Waste Disposal Charges + (3) Utility In-house Costs ÷ Critical Path Time + Rem Expended Each element in these equations can be accurately determined for past decontaminations, or estimated for future work based on past experience. Items included in each element are discussed below, looking first at the elements of cost.
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