Waste processing, flowsheet

The work on hi level waste solidification has led to applications of the same materials to other areas of waste management. These include decontamination of defense wastes currently in tank storage at Richland, WA, selective separation of Cs for beneficial uses, and development of a process flowsheet for conversion of Zircaloy fuel cladding hulls to sodium zirconate for use in waste stabilization. Each is briefly described below. 

The Zircaloy Conversion Process (24, 25, 26) is a concept whereby one waste stream, Zircaloy fuel hulls, can be utilized in the stabilization of a second waste stream. The process flowsheet which is conceptual in nature, details the steps required to convert the fuel hulls to sodium zirconate to be used in the solidification of liquid high level waste. 

The CSSX process flowsheet for the decontamination of high-level waste was demonstrated in a 33-stage, 2-cm contactor apparatus at the Savannah River National Laboratory (formerly the Savannah River Technology Center).107 Simulated SRS average waste, simulated Tank 37H/44F composite waste, and actual Tank 37H/44F composite high-level waste were processed in three tests lasting 6,12, and 48 hours, respectively. 

After a few years of storage, the main radioactive heat emitters in HLW are 90Sr and 137Cs. In addition, extremely long-lived actinides—neptunium, plutonium, americium, and curium—should be collected for transmutation in the future. Therefore, different flowsheets can be proposed for waste processing. It is possible to extract each radionuclide in the special extraction (sorption) cycle, for example, uranium and plutonium in the PUREX process, and after that, minor actinides (MAs) by the TRUEX process,4 strontium by the SREX process,5,6 and cesium by sorption7 or extraction.8... 

In 2001, the SRS announced its choice of CSSX as the baseline cesium-removal technology over small-tank precipitation (a small-scale version of the ITP process) and ion exchange with CST for its Salt Waste Processing Facility (SWPF) to go into operation in 2010 [22], An optimized solvent system, model, and flowsheet were developed and demonstrated in 2001 and 2002 [37,49], and a modular concept was developed by ORNL in 2003 [68], Thus, the past decade has seen the emergence and maturation of a powerful new technology based on a macrocyclic cation receptor designed to function in solvent extraction to meet the critical need of the USDOE for a means of cleanly separating Cs from alkaline tank waste. 

At the end of the Level 4, the result is a close-to-optimum process flowsheet together with a consistent material balance. The next levels will have as a goal the solution of the problems related with the optimal use of energetic resources and material utilities, as well as with waste minimization and plantwide process control. 

Process flowsheets. The flowsheets of the chemical processes used for the treatment of Pu/Al targets and the Masurca waste were described recently ( , 23), so that we shall only discuss the major principles here. However, we shall dwell in greater detail on the process flowsheet adopted for treatment of the waste produced by the recycling of Pu02 scrap, which is expected to go on stream in August 1980. 

Treatment of Waste Solutions containing Americium. The process flowsheets developed to treat Masurca waste and the solution from recycling of Pu02 scrap are presented in Figure 6. Treatment of the Masurca whste is complex and requires the following steps. 

Pilot-plant work has been performed for the Savannah River Laboratory and for Battelle s PNL to develop fluidized-bed process flowsheets for solidifying neutralized AEG waste and for acid Purex waste. A Purex waste, partially neutralized and containing 2M Na (type PW-6), will... 

Based on the analysis of the process flowsheet, there are generated several sources of wastes. An attempt will be made to minimize or eliminate the following wastes ... 

The development of the process flowsheet begins with the determination of the type of process to be designed. Successive layers are then added to provide more details, leading to the final flowsheet that consists of all of the necessary process units and their coimections to meet the steady-state design objectives. It is important to note that (i) design is a steady-state concept while control issues are dynamic in nature, and (ii) steps three and five are based solely on economics (maximize profits, minimize waste of raw material and energy, etc.) and not on operational or design considerations. 

There are other process flowsheets for the HDA process. Some of the other alternatives are recycling of diphenyl to eliminate losses of benzene to the waste diphenyl by way of the reverse reaction in reaction 2 combine the stabilizer and product columns into a single column with the benzene product as a side draw stream, rind the use of a membrane system to reduce hydrogen losses in the purge. These alternative designs are not examined in this work, rather, this work considers the control of the benchcase design discussed in the literature by [1,7,19]. 

Process Flowsheets. The second step is to prepare process flowsheets in sufficient detail to indicate the flow of all raw materials, additives, by-products, and waste streams.The flowsheet should identify all points of feed input, and all points at which atmospheric, liquid, and solid wastes are discharged.The engineer or supervisor responsible for each process should verify that the flowsheets identify all sources. Many plants have numerous sources, which must be identified correctly for tracking purposes. 

The IFR waste treatment process flowsheet includes a salt-stripping step in which the TRU-free salt from the salt extractiong step is treated with Li(Cd) to remove all residual uranium and rare earth fission products. Testing of the prototype salt-stripper vessel has begun. 

Figure 3 shows a flowsheet for plutonium processing at Rocky Flats. Impure plutonium metal is sent through a molten salt extraction (MSE) process to remove americium. The purified plutonium metal is sent to the foundry. Plutonium metal that does not meet foundry requirements is processed further, either through an aqueous or electrorefining process. The waste chloride salt from MSE is dissolved then the actinides are precipitated with carbonate and redissolved in 7f1 HN03 and finally, the plutonium is recovered by an anion exchange process. 

The above information was used to develop conceptual flowsheets for the extraction of all of the actinides (U, Np, Pu, Am, and Cm) from high-level liquid waste from PUREX processing using 0.4 M 0fuel using 0.8 M DHDECMP in DEB. In both flowsheets, no oxidation state of Pu is necessary since the III, IV, and VI state extract into the organic phase. 

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