Lawrence Livermore National Laboratory (the plutonium resource recovery, PuRR, program), we studied the effect of silicon on plutonium recovery from some of the production residues. We found that addition of zirconium, which forms very stable compounds with silicon, carbon, nitrogen, etc., tied up the silicon and allowed the plutonium to be extracted.

Magnesium is another element that can interfere with operation of the electrorefiner, because the stability of MgCl₂ is similar to that of uranium and plutonium. Therefore, magnesium will electrotransport along with uranium and plutonium in this system. The presence of magnesium in these “products” should be of little consequence, because the objective in this application is not to make pure uranium or plutonium. If the uranium product is contaminated with magnesium, this should not interfere with disposal of the uranium as a low-level waste, because the magnesium contaminant is not radioactive. It could make the recycling of the recovered uranium as LWR fuel material somewhat more complicated.

7. Is there any objection to inclusion of the Questions and Answers as an Appendix?

   No objection. We would like to revise one response to the questions posed by the Committee on November 3, 1995: the response to Question 13(c). The revised response is as follows:

   (c)Page 32 shows the Zr-Fe binary phase diagram; what are the consequences to this diagram of additional stable (e.g., Cr) and radioactive (e.g., U, Pu) components at the several wt% level? Because Pu is found to partition preferentially into the Zr-rich phase (page 35), what techniques will be used to separately evaluate the long-term corrosion behavior of this phase, rather than the bulk intergrowth of Zr- and Fe-rich phases?

   A preprint¹ of a paper dealing with the effects of the additional metals on the basic Fe-Zr system is attached. We are currently preparing other papers on this topic, but they are not yet available as preprints; they deal with actinides in the metal waste form, as does the attached presentation, which is to be given at the SPECTRUM 96 meeting. In this presentation, it is reported that the actinides seem to follow the zirconium. The corrosion behavior of this phase cannot be evaluated separately from the matrix in which it exists, because the matrix largely determines the corrosion rate. However, the behavior of the actinide-rich phases is being and will be carefully followed during corrosion testing, using all the appropriate tools at our disposal including all the usual metallographic and surface analysis methods as well as special corrosion tests such as applied potential studies and testing at extreme pH. We will provide a pre-publication copy of the paper as soon as internal reviews are complete.

8. What is zeolite's stability with respect to conversion of zeolite A to sodalite at 500°C? (ORNL/TM 12515, Petek, et al.)

   The question of the stability of zeolite A under the conditions that we use or anticipate using is of major interest to us. Determination of the allowable times and temperatures for hot pressing is being addressed along two separate lines of work, which have been assigned highest programmatic priority. Zeolite stability under other conditions (high water contents, for example, or other salt compositions) is also of interest, but much lower on our priority list. In particular, at least some of the ORNL salts contain 5% or more of fluoride, which is known to destroy the zeolite structure.

   We have observed, by X-ray diffraction, that zeolite remains as zeolite in the mineral waste form that had been uniaxially hot-pressed at temperatures in excess of 700°C for 1/2 h at 7,000 psi.