DECIADDING OF CONSOLIDATED EDISON POWER REACTOR FUEL BY SULFEX AND DAREX PROCESSES:CYCLIC DISSOLUTION EXPERIMENTS

摘要

Simulated Consolidated Edison reactor fuel pins (95°5% ThO2-U3O8 pellets encased in 304L stainless steel) were dissolved one-by-one according to the Sulfex and Darex flowsheets in Ni-o-nel and titanium vessels, respectively, 25 pins by each process. With boiling 5 M HNO3—2 M HC1 (Darex), dissolution of the cladding was complete in each cycle with uranium losses of 0.1-0.14$. Dissolution of the ThO2-U3O8 core pellets (which were about 80% of theoretical density) in boiling 13 M HNO3—0.04 M NaF—0.0 M Al(N0-,)o was also complete in each case. No problems arose from passivation of stainless steel or cross-contamination of solutions. Two modifications of the Sulfex process were tested:(l) decladding with 200% excess of 6 M H2S04, and (2) initiating the reaction with 6 M H2SO4. and diluting to k M sulfate shortly thereafter. Uranium losses to the decladding solution were generally between 0.2 and 0.5$ irrespective of the technique, but were as high as 0.9% in the presence of a ThO2-U3O8 heel. The uranium losses were directly related to the amount of heel present. In most cases the fuel pins were passive to boiling 6 M H2SO4 and reaction was initiated by contacting the pin with a piece of iron. Core dissolution was less efficient than in the Darex tests, presumably because of sulfate contamination. Under the flowsheet conditions only 98-99$ of the core was dissolved in each cycle.