Power Plant Engineering

(Ron) #1

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:


  1. Mining of the uranium ore.

  2. Milling and refining of the ore to produce uranium concentrates, U 3 O 8.

  3. Processing to produce of uranium hexafluoride, UF 6 , from the uranium concen-trates. This
    provides feed for isotopic (U^235 ) enrichment.

  4. Isotopic enrichment of uranium hexafluoride to reach reactor enrichment require-ments. This
    is done invariably now by the gaseous diffusion process.

  5. 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.

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