Burnup is commonly expressed as megawatt days thermal per metric ton of initial heavy metal. The nuclear fuel cycle for typical light-water reactors is illustrated in Figure A1 . Reprocessing of spent commercial-reactor nuclear fuel is not permitted in the United States. The front end of the nuclear fuel cycle commonly is separated into the following steps. A deposit of uranium, discovered by geophysical techniques, is evaluated and sampled to determine the amounts of uranium materials that are extractable at specified costs from the deposit.
Uranium reserves are the amounts of ore that are estimated to be recoverable at stated costs.
Uranium ore normally is mined by openpit and underground methods similar to those used for mining other metals. In situ leach mining methods also are used to mine uranium in the United States. In this technology, uranium is leached from the in-place ore through an array of regularly spaced wells and is then recovered from the leach solution at a surface plant. Some uranium deposits developed in other countries are of higher grade and are also larger than deposits mined in the United States. Mined uranium ores normally are processed by grinding the ore materials to a uniform particle size and then treating the ore to extract the uranium by chemical leaching.