Nuclear Fission UCSD UCSD 2 Lecture 14 1 Nuclear Fission UCSD UCSD . Barium and Krypton represent just one of many potential outcomes 3 4 Lecture 14 2 Nuclear Fission UCSD UCSD 5 6 Lecture 14 3 Nuclear Fission UCSD UCSD 4 protons: mass = 4.029 2 neutrinos, photons (light) 4He nucleus: mass = 4.0015 26 MeV of energy THIS FUSION IS THE SOURCE OF THE SUN’S ENERGY, 7 (and of energy in thermonuclear hydrogen bombs) 8 Lecture 14 4 Nuclear Fission UCSD UCSD Question Nuclear energy in nuclear reactors comes from: A. Uranium 238 B. Uranium 235 C. Plutonium 239 D. Hydrogen E. Both B and C 9 10 Lecture 14 5 Nuclear Fission UCSD UCSD 11 12 Lecture 14 6 Nuclear Fission UCSD UCSD Plutonium bomb is a little harder; need high Little boy:Hiroshima explosives to squeeze Pu close. But critical mass is only 10 kg. In fact with better design and neutron reflecting materials critical masses can be made much smaller (e.g. about 15 kg for 235U and less than 5 kg 239Pu) Fat boy: Nagasaki (Pu) 13 14 Lecture 14 7 Nuclear Fission UCSD UCSD 15 16 Lecture 14 8 Nuclear Fission UCSD UCSD 17 18 Lecture 14 9 Nuclear Fission UCSD UCSD • 1.2GW BWR • 46000 fuel rods (170 tons) • 71 atmospheres pressure • 2.8% enriched U-235 • Emergency core cooling system if control rods fail (adds boron to not shown are water); back-up water system the control rods that absorb neutrons and thereby keep the process from running away 19 20 Lecture 14 10 Nuclear Fission UCSD UCSD 21 22 Lecture 14 11 Nuclear Fission UCSD UCSD A Z X N 12 €6 C6 14 6C8 235 92U143 238U € 92 146 239 € 94 Pu145 € 23 € 24 € Lecture 14 12 Nuclear Fission UCSD UCSD 25 26 Lecture 14 13 Nuclear Fission UCSD UCSD 27 28 Lecture 14 14 Nuclear Fission UCSD UCSD 29 30 Lecture 14 15 Nuclear Fission UCSD UCSD 31 32 Lecture 14 16 Nuclear Fission UCSD UCSD 33 34 Lecture 14 17 Nuclear Fission UCSD UCSD • Iron (Fe) is at the peak • On the heavy side of iron, fission delivers energy • On the lighter side of iron, fusion delivers energy • This is why normal stars stop fusion after iron • Huge energy step to be gained in going from hydrogen (H) to helium-4 via fusion 35 Lecture 14 18 Nuclear Fission UCSD UCSD 37 38 Lecture 14 19 Nuclear Fission UCSD UCSD 39 40 Lecture 14 20 Nuclear Fission UCSD UCSD 41 42 Lecture 14 21 .