Published online by Cambridge University Press: 28 February 2011
Reacted solids from 200°C, 25 MPa tests with spent light water reactor fuel and other component materials of a high-level nuclear waste repository in basalt were analyzed by scanning electron microscopy, X-ray powder diffractometry, transmission electron diffraction, Auger electron spectrome- try, and microautoradiography. The work complements solutions analysis from the same tests conducted in Dickson-type rocking autoclaves for the Basalt Waste Isolation Project. Spent fuel reacted very slowly in fuel/water tests, exhibiting noticeable grain boundary etching and uranium silicate formation only after six months. Particle abrasion in the rocking autoclave produced fuel fines that remained apparently unaltered. In spent fuel tests with basalt or basalt and steel, iron smectite clay formed at the expense of mesostasis phases in the basalt. Low concentrations of β-emitters, probably Cs and Tc released from grain boundaries in the fuel, were incorporated in the clay. Steel corroded very slowly under the low-oxygen conditions of the tests, forming minor amounts of magnetite, hematite and wustite. The sluggishness of spent fuel/water and steel/water reactions is attributed to limited availability of oxygen under the test conditions.