1. Research and Technology, BNFL Sellafield, Seascale, Cumbria, CA20 1PG, U.K.
2. A.A. Bochvar All-Russia Research Institute of Inorganic Materials, VNIINM, PO Box 369, Moscowx, 123060, Russia.
3. Research and Technology, BNFL Springfields, Salwick, Preston, Lancashire, PR4 OXJ, U.K.