Cladding hulls

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. 

A basket can be used to introduce the fuel element pieces into the nitrate melt and withdraw the cladding hulls following the disaggregation of the fuel material. 

High-Level Solid Waste Treatment. Cladding hulls and dissolver solids are generated as wastes from reprocessing LWR fuels. The alpha activity associated with these head-end wastes is normally low, but as a precautionary measure the WTF provides an area where these wastes may be given an extended tertiary HNO3/KF/ HC1 leach. Experimental studies with mixed-oxide reactor fuels (10,11,12) suggest that actinide losses can be held to 0.01 or less if fluoride and chloride are present in the leachant. 

Fuel cladding hulls will also contain uranium, plutonium, and other transuranic radio-... 

When a solid residue such as cladding hulls remain, design of a continuous dissolver is much more complicated. Provision must be made for washing dissolver solution from the residue and for discharging the residue without escape of off-gases. A number of possible design concepts for continuous dissolvers have been tested by Oak Ridge National Laboratory [G15, 012]. 

Solid high-level wastes are the cladding hulls of spent fuel elements from the chop-leach... 

HLW arising in solid form, mainly cladding hulls, has activity concentrations more than two orders of magnitude lower than liquid HLW. It presents somewhat different technical problems, which wiU be discussed briefly in this chapter. 

Cladding hulls. Cladding hulls as collected from the chop-leach head end are radioactive due to activation products in the zircaloy and to fission products and actinides from (U,Pu)02 adsorbed at the inside of the hulls. The principal activation products are Co, Sb/ Te, and Ni. Their total activity is on the order of 10 /rCi/g zircaloy after 6 years and about 100 times lower after 100 yrars. The fission-product activity after 6 years is of the same order of magnitude and is dominated by Cs, Sr, and tritium. The residual (U,Pu)02 after leaching is estimated to be of the order of 0.1 percent of the charge. 

The chopped pieces are transferred to the dissolver unit, where the oxide fuel is leached by boiling in 6 —11 M HNO3 (the cladding hulls do not dissolve) in thick stainless steel... 

In a modern PUREX plant, the fuel pins are first cut into pieces that are 3-5 cm long. The fuel is then dissolved in 6-11 M nitric acid, while the cladding hulls do not dissolve. Sometimes <0.05 M AIF3 is added to the nitric acid to improve dissolution of, e.g., zirconium by complex formation. The solution is then diluted to 3-4 M and nitrite is added to assure that plutonium is present as Pu(IV) and uranium as U(VI). Plutonium and uranium are then selectively extracted into TBP in aliphatic kerosene. Fission products and trivalent actinides remain in the aqueous phase. The extract is scrubbed with nitric acid to remove all contaminants except traces of ruthenium, neptunium, and zirconium. 

Residual quantities of minor actinides and fission products that are removed from the purification parts of the cycle are usually reduced in volume and then combined in the aqueous raffinate HLW stream. The cladding hulls are managed as high-level solid waste by packaging them in drums and storing the drums in a dry disposal site. 

The metal waste is formed by distilling-off residual salts and alloying the cladding hulls with some additional zirconium to form an alloy with nominally 85 wt% steel and 15% zirconium. Both of these HLW forms have been extensively characterized for the proposed geologic repository. 

Intermediate Level and Long-lived waste present a mean activity of over one million Bq.g and are characterized by a significant presence of long lived radionuclides. For AREVA La Hague concerns, it is mostly composed of metal structures (cladding, hulls and end caps). It also comes from residues (waste from effluent treatment, equipment, etc.) originating from the operation and maintenance of nuclear facilities. 

LL-ILW Metal structures (cladding, hulls and end caps) Compacted raw waste CSD-C I I 2E8... 

---