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Today Issues with nuclear power too cheap to meter, but……

Today Issues with nuclear power too cheap to meter, but……. All power point images are only for the exclusive use of Phys3070/Envs3070 Spring term 2014. Outline. What is fission? Uranium/Radioactivity Reactors/neutron budgets/fuel Problems- financing/costs ionizing radiation

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Today Issues with nuclear power too cheap to meter, but……

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  1. TodayIssues with nuclear powertoo cheap to meter, but…… All power point images are only for the exclusive use of Phys3070/Envs3070 Spring term 2014

  2. Outline • What is fission? • Uranium/Radioactivity • Reactors/neutron budgets/fuel • Problems- financing/costs ionizing radiation waste disposal weapons proliferation • Fusion XX see the text Costs---

  3. Problem #1--Costs/financing A different $$ profile than coal or gas plants.

  4. Ionizing radiation hazards Sensed by an external Geiger counter.

  5. Radioactivity • Fission fragments and transuranics decay by a variety of ways, with characteristic ‘half lives’ • Amount in one half-life= ½ amount now • Amount in two half lives=1/4 initial amount • Amount in three half-lives= 1/8 initial amount. • Radioactivity follows same rule Decay/sec after one half life=1/2 initial decays/sec • In general- falls off as (1/2) #half lives

  6. Exam 2 1 Nov. 2005 How long must you wait for a sample of radioactive material to decay to less than 10% of its initial activity if its half life is 12 minutes? One half life=12 minutes--0.50 Two half lives=24 minutes—0.25 Three half lives=36 minutes—0.125 Four half lives = 48 minutes—0.0625 (choice B “half to one hour”)

  7. Ionizing radiationa,b,g • Changes atoms, chemistry • Disrupts molecules • Kills cells • Confuses cells  cancer

  8. Problem #3—Radioactive Waste • Fission products, including famous 131I, 137Cs, 90Sr, wide range of elements and half lives. • Transuranics, from neutron capture on 238U, including plutonium • Stored on site, in water or casks • Open cycle- to be buried in their rods

  9. What to do with SNF? • Short term storage in water for several years dry casks, outside the plant • Bury it – eg. Yucca Mountain NV • Sort/transmute (re-processing) fission the plutonium fission the other transuranics bury the fission products

  10. 1Year

  11. SNF stored in water

  12. What is in Spent Nuclear Fuel?

  13. Transmutation Use nuclear reactions in the reactor to consume elements heavier than uranium (transuranics) faster than the reactor breeds them. Their fission gives energy. Needs a different class of reactor—’fast spectrum’. Leaving nearly only fission products to bury.

  14. Problem #4-- Proliferation • The hardest part of getting a nuclear bomb is the material • “Front End”- obtain 235U (HEU=at least 80%) by exactly the same methods used to make Low Enriched Uranium (LEU), typically 3-4%. • “Back End”- obtain 239Pu from Spent Nuclear Fuel by chemical reprocessing

  15. Enriched uranium and plutonium-- Every one of the 400+ nuclear power reactors on the globe is fissioning235U uranium and making plutonium, enough for several bombs per hour.

  16. Front End • In a centrifuge farm, re-arrange the pipes to produce 50 kg of HEU instead of the expected larger amount of LEU. • Convert the UF6 gas to metal • Machine two hemispheres • Collide the hemispheres in a gun barrel—works for sure. Hiroshima. • Not very radioactive

  17. Back end • Obtain Spent Nuclear Fuel, after the shortest possible exposure • Reprocess– via chemistry to separate plutonium • Machine a hollow sphere • Implode, with very precise technology. Nagasaki. • Each step involves strong radioactivity • Needs to be tested, and failure is likely.

  18. Nuclear fusion • 21H1 + 21H132He1 +10n1 31H2 + 11H0 • Using 21H1=Deuterium (D), 0.015% of all the hydrogen in the oceans. • Each reaction3.65 MeV • (each fission200 MeV) • (carbon atom combustion3 eV)

  19. But….. • Two positives repel, and can come near enough to react only at high temperatures and pressures. “Thermonuclear” • Plasma– confined only by magnetic fields. • ITER=International Thermonuclear Experimental Reactor

  20. ITER • International Thermonuclear Experimental Reactor • D+D at 150 million deg C • 10 billion euros and counting • Maybe to operate in 2025 • Sustain 500 MW for 1000 sec

  21. Points +: no CO2, lots of deuterium, no fission waste, no runaway -: How to couple energy to the grid? Not heat. Keeping the reaction going- 24/7 Cost Activation- the neutrons hit the walls.

  22. 1.(30 points) A proposed High Temperature Gas Cooled nuclear fission reactor would operate at a temperature of 800 deg C. This facility will be built by the sea, with cooling at 10 deg C. A. (5) What is the best possible efficiency of this plant? eCarnot = 1 – Tcold/Thot, with Tcold = 273+10 = 283 deg K and Thot=273+800 = 1073 deg K. So eCarnot = 1-283/1073 = 1 – 0.264 = 0.736 = 74% B.(10) In fact, this power source will perform at an average of 75% of that best efficiency. If the owners wish to sell 1 GWe, how much thermal power must be provided? Actual efficiency = 0.75*eCarnot = 0.552. For 1 GWe you need 1 GWe/0.552 =1.81 GWt or thermal gigaWatts

  23. C.(5) How much thermal energy is generated in one day by this facility? Energy = power *time = 1.81*109 Joule/sec*24 hours * 3600 sec/hour = 1.56*1014 Joules D.(10) Each nuclear fission releases 1.8*108 eV. How many 235U nuclei were fissioned during that day to make that much heat? Number of fissions (per day) = 1.56*1014Joule/ 1.8*108eV/fission * 1.60*10-19 Joule/eV = 5.42*1025 fissions in one day. {Not asked, but the weight of this many 235U atoms is 235 (amu per U) *5.42*1025 (U)*1.67*10-27 (kg/amu) = 21.3 kg.}

  24. 2. (10) The radioactive isotope 131I is particularly dangerous. The fission of 235U results in the formation of this isotope 3.6% of the time. If a nuclear power plant fissions 23 kg of 235U per day, how much 131I will be produced per day? The iodine is lighter than the uranium, so you make (131/235)*0.036*23 kg = 0.462 kg per day of this nasty stuff. That is why we seal in the radioactive fission products.

  25. 3. (5) The half life of 131I is 8.04 days. How long need we wait after the fission reactions end for the 131I made in the last day to decrease to 1/32 of its hazard? To fall to 1/32 requires 1/2 * 1/2*1/2*1/2*1/2, or 5 halflives. The time is then 8.04*5 = 40.2 days.

  26. 4. (10) You replace your current wind power system with on that goes twice as high to reach winds that are (on average) faster by a factor of 1.3. But that is expensive, so you decrease the radius of the blades to half of the current value. By what factor should you expect the average power output to change? The power goes as v3, so the increase is by 1.33 = 2.197. But halving the radius cuts the area by a factor of 0.25, so the expected power changes by a factor of 0.25*2.197 = 0.55. Not a good plan.

  27. 5. (10) For six hours a wind of 12 m/sec blows through a wind generator with blades 5 m long. The efficiency of the generator is 40% of the best possible. Since you do not need the energy just then, you pump water up a 20 meter hill to be used in a hydro plant on a calm day. How much water is moved? Consider the pumping etc. to be fully efficient. The power in a wind of speed v through a turbine system of area A is P=1/2*density*area*v3. The density of air at sea level is 1.22 kg/m3. The area of this case is p*52 = 78.54 m2. Plugging in— Power = 1/2 * 1.22*78.54 * 123 = 82,787 Watts, in the wind. Of this power, we can only get 0.40 (of the best efficiency)*0.59 (the best) *82,787 W = 19,538 Watts. During the blow of six hours, this gives 19,538 Joules/sec * 6 hours*3600 sec/hour = 4.22*108 Joules. This energy is used to create gravitational potential energy by moving mass m of water up h=20 meters on earth (g=9.8 m/sec2). PE = mgh, m=4.22*108 Joules/(9.8 m/sec2 * 20 meters) = 2.15*106 MKS units, since we have been orthodox, so these are kg. That is 2150 metric tonnes of water you lifted.

  28. 6. (5) But wait—why is that best possible energy not removing ALL of the energy in the wind? Explain to a novice. Because if you removed all the kinetic energy from the wind, it would not be moving and just pile up at the blades. This can’t be, so the best power extraction from the wind that is possible (called the Betz factor) is 59%. Real wind systems get less than this best, much as was the case with Carnot and real thermal efficiencies.

  29. (15) If I invest $5billion to build a nuclear power plant that will • operate for and be paid off in 40 years, how much per year will • my ‘mortgage’ payments be to pay the initial capital cost at an • annualized interest at a rate of 5%? If I produce 1010 kW-hr of • electrical power each year, how much must I charge my • customers per kW-hr to service my debt? • (10) A nuclear power plant operates at 80% of the best • thermal efficiency (Carnot) of 31%. Transmission losses are • 10% before the power gets to the customers. How much • fission heat power must the plant generate to give 60,000 • customers each 5 kW? How much heat power must be extracted from the plant by its cooling facilities? HW #9

  30. A typical fission reaction for uranium is • 1on1 +23592U 14313153I78 +AZ XX N +3 10n1, • where I is the element iodine. • (5) What are the atomic weight A, the atomic • number Z and the neutron number N for the • element XX in the specific fission reaction • above, one of the many possible? • (10) If we fission I kg of 235U completely in one year, • at a plant efficiency of 30%, how many electrical GWe can we sell?

  31. (10) What is the greatest single reason • to enhance US nuclear electricity, and why? • (10) What is the greatest single reason • NOT to continue to rely on nuclear power for the US, and why?

  32. (10) Why is the Arctic such an important source • of feedback to accelerate global climate change?

  33. Friday www.arctic.noaa.gov/reportcard www.arctic.noaa.gov/future = Future of Arctic Climate and Global Impacts Essay on sea ice (Petrovich et al.) Warm Arctic-Cold Continents www.arctic.noaa.gov/essay_serreze.html www.nsidc.org Gaze in awe at the images

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