Question #2 of Assignment 9 involved an electrical generationsystem including a generator with an efficiency of 98%, atransmission line with a 94% efficiency, and finally a light bulbwith a 12% conversion efficiency. Suppose that instead of coal, theprimary energy for the same system is provided by wind turbinesthat have a 45% efficiency, or solar cells with a 23%efficiency.
a) Does the full energy conversion sequence using these renewablesources make significantly more efficient use of the primary energyavailable? Explain why or why not. [2 Marks]. b) For the fossilfuels, a consequence of low efficiency is that to provide a givenamount of energy to customers much more energy, in the form of rawresources, has to be extracted from the ground. For example, todeliver 1000 MJ of electrical energy using coal requires an inputof roughly 3000 MJ of primary energy in the form of coal. What is apractical consequence of lower efficiency for renewable resourceslike wind and solar? In other words, how might 1000 MJ ofelectrical energy be delivered to customers using wind or solarfacilities? Explain. [2 Marks]
3. The Fukushima nuclear reactor accident caused theenvironmental release of significant amounts of radioactive caesium(Cs) isotopes. Specifically, caesium-134 and caesium- 137, whichhave half-lives of, respectively, two years and 30 years. Thesurvey of soil radioactivity conducted in June 2011 revealed soilsurface Cs-134 activity of about 500,000 Bq/m2 in the town of Okuma(roughly 10 km from the stricken power plant) and Cs-137 activityof roughly the same level. Disregarding any other changes orcleanup efforts, what would you expect the radioactivity due tothese caesium iso- topes to be in Okuma today compared to theiroriginal levels? (Semi-quantitative or qualitative statements aresufficient.) Explain. [2 Marks]
4. Your friend is terribly afraid of radiation, so naturally herwealthy and mischievous younger brother offers her a choice for herbirthday: a day-long walking tour of Okuma (during which she maywear a mask), where the residual radiation dose (from the 2011accident) averages roughly 4 micro-Sieverts (or 0.004 mSv) per hourabove normal background, OR dinner in far-from-Fukushima Tokyowhere fresh fish caught off the coast of Fukushima prefecture andrice grown near Okuma will be served. In the absence of any otherinformation which option would you advise your friend to choose,and why? (There is no secret third option...)
