Lecture13-16

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Unformatted text preview: o  man hit by both atomic bombs in Japan had healthy children u༇  However, some radioisotopes that we may ingest or breath in do harm o  131I o  90Sr o  Rn 36 Example: 14C Da;ng u༇  If we use a 1 milligram sample of Carbon, aRer what ;me will the decay rate be reduced to 10- 5 per second? (The frac;on of 14C is 1.3 X 10- 12 and the life;me is 5730 y.) u༇  N0=10- 6 kg X 1.3 X 10- 12 / 1.66 X 10- 27 kg /12 = 6.5 X 107 u༇  R(t)=N0/τ e- t/τ = 4.05 X 10- 4 e- t/τ u༇  e- t/τ = 10- 5/4.05 X 10- 4 = 0.0247 u༇  t=21210 y u༇  For small samples, we can’t go back too many years. 37 Geiger Counter u༇ Geiger counter detects ionizing radia;on. 38 Fission u༇  Naturally occurring isotope of Uranium 235U will split (approximately) in half if it absorbs a neutron. o  Several neutrons are produced allowing a chain reac;on. o  About 200 MeV of energy is released Fairly easy to do in a reactor. u༇  Fission products neutron rich and radioac;ve. u༇  o  This is the only real problem with reactors o  Not a very big problem??? o  0.001 kg/day of U produces 1 megaWaF 39 Example: Fission Reactors and Atomic Mass Units (u) u༇ 235U+n - > 140Ce+94Zr + 2n + E u༇ 140Ce m=139.9054 u u༇ 94Zr m=93.9063 u༇ 235U m=235.0439 u༇ n m=1.0086 u u༇ How much Energy is released per U atom? 40 Fission Reactor u༇  Fast neutrons from fission are moderated by collisions to slow or thermal n. u༇  Fission produces several neutrons. u༇  Chain reac;on is controlled by rods that absorb thermal neutrons. u༇  Water is heated by the fuel rods. u༇  Heat exchanged to secondary water circuit. u༇  Steam used to turn turbine which turns electric generator. 1/3 of the heat turned to Electric Power 2/3 of the heat dumped in ocean 41 Three Mile Island u༇  Secondary water circuit failed (pumps) o  Turbine shutdown o  Reactor shutdown u༇  Pressure in primary water circuit grows o  Relief valve opens to relieve pressure o  Valve fails to close •  Coolant boils off reactor o  Operators do not understand that coolant is gone Significant damage and mel;ng of fuel rods. u༇  Containment vessel holds everything u༇  Led to many improvements o  Negligible radia;on released •  some people claim this is a lie o  Some worry about hydrogen bubble •  should we vent the gas? 42 Chernobyl 1986 u༇  Bad design, cover- up of flaws, bad training, bad management, dangerous test, lack of care u༇  Meltdown u༇  No real containment vessel. u༇  Steam explosion u༇  Burning graphite u༇  Lots of radioac;ve material spread. u༇  workers sent in with shovels the concrete u༇  thyroid cancer u༇  uninhabitable region? 43 Fukushima Daiichi 44 Hydrogen Explosion 45 Fukushima Dai- ichi...
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