DISCUSSION Session 10 : HTR: Fission Product Behaviour

International Conference on Nuclear Fuel Performance

R. HANCOCK Berkeley Nuclear Laboratories

Failed particle fraction is one of the properties monitored for fuel compacts (which I assume is obtained from a statistical sample using destructive techniques). However, in Paper 15 no reference is made to defective particle fraction. Have you any plans to include a test for this parameter?

In para 11 (i) you refer to 100% non-destructive tests being desirable for particle integrity in fuel compacts. Have you any plans for adopting such tests if they were available?

T.J. HEAL

As Mr. Hancock assumes, the failed particle fraction for fuel compacts is obtained statistically using destructive techniques. In reply to his query on defective particle fraction, similar destructive tests have been carried out to determine this parameter. The procedure is as follows: A sample of coated particles is heated in an oxidising atmosphere to remove the outer carbon layer, then thermally cycled 6 times from ambient temperature to 900°C. This treatment opens up any cracks or other defects in the silicon carbide layer and exposes the inner carbon layers and kernel to further oxidation, usually resulting in complete disruption of a defective particle. Following the thermal cycling the particles are acid leached and the uranium content of the leach liquor determined to give a measure of the number of defective particles. The values obtained on the above test indicate an integrity of the silicon carbide layer lying between 1 x 10"3 and 1 x 10""4.