| 摘要 |
PURPOSE:To control the density using a heat resistant crystalline cellulose as a density lowering agent for forming multiple micropores in a pellet. CONSTITUTION:Powder of uranium dioxide is admixed with the powder of oxide mixture fuel and ground before it is added with a crystalline cellulose binder, i.e., zinc stearate, having a structure as shown by the formula as a density lowering agent. It is then passed through a granulation process comprising three steps of roughening, grinding, and classification thus forming a green pellet. In the following degreasing process, it is heated at 800 deg.C or above in a mixture gas atmosphere at argon and hydrogen thus removing the crystalline cellulose by thermal decomposition or evaporation. Subsequently, it is sintered at about 1700 deg.C for about 2 hours in similar atmosphere and subjected to degassing in high temperature vacuum of 800 deg.C. Thus formed pellet is ground on the outer periphery thereof to obtain a complete pellet. This method prevents the density lowering agent from melting or decomposing thermally due to heating of plutonium thus making uniform the density of pellet.
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