The transmutation of the fission product Tc-99 was studied by neutron
irradiation in the High Flux Reactor at Petten. Six metallic rods of p
ure Tc, distributed over three capsules, were irradiated during eight
reactor cycles to a total neutron fluence of about 2 x 10(26) m(-2). M
etallographic examinations showed that no changes in the microstructur
e were visible after the irradiation. Electron probe microanalysis (EP
MA) of the radial distribution of Ru, the product of the transmutation
process, showed an increase from about 6% in the centre to 12-18% nea
r the rim of the pellets. This effect is due to resonance-shielding of
epithermal neutrons in the rim region. Mass spectrometric analysis of
the pellet-average Ru concentration showed that the extent of transmu
tation is about 6-7%. (C) 1998 Elsevier Science B.V.