Environmental Problems, Their Causes, and Sustainability 1

Small amounts ofradioactive gasesUranium fuel input(reactor core)Containment shellEmergency corecooling systemWaste heatElectrical powerControlrodsHeatexchangerHot coolantSteamTurbineGeneratorHot water outputUseful energy25 to 30%CoolantPumpModeratorCoolantpassagePressurevesselShieldingWaterPumpCondenserCool water inputPumpPumpWasteheatWasteWater source heat(river, lake, ocean)Periodic removaland storage ofradioactive wastesand spent fuel assembliesPeriodic removaland storage ofradioactive liquid wastesFigure 17-23 Light-water–moderated and –cooled nuclear power plant with a pressurized water reactor. Someplants use huge cooling towers to transfer some of the waste heat to the atmosphere.fuel, using it in a reactor, safely storing the resultinghighly radioactive wastes for thousands of years, anddealing with the highly radioactive reactor after itsuseful life.Nuclear power plants, each with one or more reactors,are only one part of the nuclear fuel cycle (Figure 17-24,p. 368). Unlike other energy resources, nuclear energyproduces high-level radioactive wastes that give off largeamounts of harmful ionizing radiation for a short timeand small amounts for a long time. Such wastes, consistingmainly of spent fuel rods from commercial nuclearpower plants and assorted wastes from the productionof nuclear weapons, must be stored safely forthousands of years.After approximately 15–60 years of operation, anuclear reactor becomes dangerously contaminatedwith radioactive materials, and many of its parts becomebrittle or corroded and worn out. Unless theplant’s life can be extended by expensive renovation, itmust be decommissioned or retired.Once a nuclear reactor comes to the end of its usefullife it cannot be shut down and abandoned like acoal-burning plant. It contains large quantities of intenselyradioactive materials that must be kept out ofthe environment for many thousands of years.In the closed nuclear fuel cycle (Figure 17-24, dottedlines), the fissionable isotopes uranium-235 and plutonium-239are removed from spent fuel assemblies forreuse as nuclear fuel. Their removal means that the remainingradioactive wastes must be stored safely forabout 10,000 years. Currently, these isotopes are rarelyremoved from spent fuel rods and other nuclearwastes because of high costs and the potential use ofthe removed isotopes in nuclear weapons.http://biology.brookscole.com/miller14367