1. a single uranium-bearing particle = a single particle that contains uranium...
2. engine wear is caused by bearing particles = bearing particles are particles that originate in bearings breaking down. Bearings: A bearing is a device to allow constrained relative motion between two or more parts, typically rotation or linear movement; typical in wheels are "ball bearings", que en Venezuela se suelen traducir como "rolineras." Si las bolitas metálicas interiores de las rolineras se fracturan esas partículas son "bearing particles", que pueden causar desgaste del motor.
Saludos,
Wendy
PS: Check
http://en.wikipedia.org/wiki/Bearing for two meanings of "bearing", and
http://mw4.m-w.com/dictionary/bearing for even more.
The translation workplace 
