Pretreatment of neutralized cladding removal waste sludge: Results of the second design basis experiment
For several years, the Pacific Northwest Laboratory (PNL) has been investigating methods to pretreat Hanford neutralized cladding removal waste (NCRW) sludge. In the past, Zircaloy-clad metallic U fuel was chemically decladded using the Zirflex process; NCRW sludge was formed when the decladding solution was neutralized for storage in carbon-steel tanks. This sludge, which is currently stored in Tanks 103-AW and 105-AW on the Hanford Site, primarily consists of insoluble Zr hydroxides and/or oxides and NaF. Significant quantities of Al, La, U, as well as other insoluble minor constituents are present in the sludge, along with sodium and potassium nitrates, nitrites, and hydroxides in the interstitial liquid. The sludge contains about 2,000 nCi of transuranic (TRU) material per gram of dry sludge, and mixed fission products. Therefore, the sludge must be handled as high-level waste (HLW). The NCRW sludge must be pretreated before treatment (e.g., vitrification) and disposal, so that the overall cost of disposal can be minimized. The NCRW pretreatment flowsheet was designed to achieve the following objectives: (a) to separate Am and Pu from the major sludge constituents (Na, Zr). (b) to separate Am and Pu from U. (c) to concentrate Am and Pu in a small volume for immobilization in borosilicate glass, based on Hanford Waste Vitrification Plant (HWVP). The flowsheet involves: (1) sludge washing, (2) sludge dissolution, (3) extraction of U with tributyl phosphate (TBP), and (4) extraction of TRUs with octyl(phenyl)-N,N-diisobutlycarbamoylmethyl-phosphine oxide (CMPO). As presented in the flowsheet, the NCRW sludge is first washed with 0.I M NaOH to remove interstitial liquid and soluble salts from the sludge including sodium and potassium fluorides, carbonates, hydroxides, nitrates, and nitrites. The washed sludge is then subjected to two dissolution steps to achieve near complete dissolution of Zr.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- AC06-76RL01830
- OSTI ID:
- 10154658
- Report Number(s):
- PNL-9747; ON: DE94012775; TRN: 94:005761
- Resource Relation:
- Other Information: PBD: May 1994
- Country of Publication:
- United States
- Language:
- English
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