432 POWER PLANT ENGINEERING
Besides thermal pollution, which it shares with almost all types of power plants, nuclear power’s
effects on the environment stem mainly from
(1) the nuclear fuel cycle,
(2) low-level dose radiations from nuclear-power plant effluents, and (3) low and high-level dose
radiations from wastes.
13.17.1 The Fuel Cycle
Most nuclear power plants in operation or under construction in the world today are using, and
will continue to use for the near future, ordinary (light) water cooled and moderated reactors: the Pres-
surized Water Reactor (PWR) and the Boiling Water Reactor (BWR). A small number use the heavy
water cooled and moderated reactor (PHWR). The expectations are that the fast-breeder reactor power
plant and perhaps an improved version of the gas-cooled reactor power plant will come on line in
increasing numbers in the twenty-first century. Almost all-current water reactors use slightly enriched
uranium dioxide, UO 2 , fuel. The fuel has to go through a cycle that includes prereactor preparation,
called the front end, in-reactor use, and post reactor management, called the back end.
Front end Back end
Spend fuel storage
Fuel reprocessing
High-level
waste
Plutonium
Uranium
Exploration-mining Fedral repository
Miling
Processing
Enriching
Fuel fabrication
Front end Back end
Spend fuel storage
High-level
waste
Exploration-mining Fedral repository
Miling
Processing
Enriching
Fuel fabrication
(a)(b)
Fig. 13.4. A typical nuclear fuel cycle (a) with reprocessing and (b) without reprocessing.
The different process are briefly explained below:
- Mining of the uranium ore.
- Milling and refining of the ore to produce uranium concentrates, U 3 O 8.
- Processing to produce of uranium hexafluoride, UF 6 , from the uranium concen-trates. This
provides feed for isotopic (U^235 ) enrichment. - Isotopic enrichment of uranium hexafluoride to reach reactor enrichment require-ments. This
is done invariably now by the gaseous diffusion process. - Fabrication of the reactor fuel elements. This includes conversion of uranium hexafluoride to
uranium dioxide UO 2 , pelletizing, encapsulating in rods, and assembling the fuel rods into
subassemblies.