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(1905) Albert Einstein: He comes up with a little formula you may have heard of:
E = mc 2
This equation changes everything.
1 g = 9 x 10 13 J (equivalent to burning 1000 tons of coal!!!)
Binding energy of helium nucleus can be calculated:
Mass  of  2  protons  and  2  neutrons  :
Mass  of  a  helium  nucleus:
4 x 1.67x10
-27 kg
6.644 x 10 -27 kg
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(1905) Albert Einstein: He comes up with a little formula you may have heard of:
E = mc 2
Binding energy of helium nucleus can be calculated:
Mass  difference:   4 x 1.67x10
-27 kg - 6.644 x 10 -27 kg = 3.6 x 10 -29 kg
E bind
=  mc 2    =  (3.6x10
-­‐29   kg)  x  (3x10 8  m/s) 2
=  3.2x10
-­‐12  J  =  20.2  MeV
Binding  Energy
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Fission  is
•   the  breaking  apart  of  a  nucleus
•   what  occurs  during  radioacPve  decay
•   naturally  occurring  and  happens  in  power  plants
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Fusion  is
•   the  combining  of  two  nuclei  to  form  a  heavier  nucleus
•   what  occurs  inside  the  core  of  the  Sun
•   the  magic  bullet  for  solving  human  energy  problems…   or  maybe  not
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•   If Fusion is the process of obtaining energy by adding things together.
•   Then Fission is the process of obtaining energy by Breaking things apart.
•   A fissionable element can spontaneously decay into one or more different (lighter) elements, releasing energy as it decays.
238 U ⇒
234 Th + 4 He + (4.2 MeV)
(92P+146N) (90P+144N)
•   The 238 U reaction is SLOW , taking 4.5 billion years!
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•   Stimulated Fission occurs when the interaction with another particle triggers element breakup.
•   Fission reactors operate on this principle using a stable isotope of Uranium, 235 U . About 0.7% of natural U is 235 U.
235 U + n ⇒
140 Cs + 93 Rb + 3n (+ 200MeV)
(92P+143N) (55P+85N) (37P+56N)
•   This reaction is easier to trigger than P-P fusion because both the neutron and 235 U are neutral.
•   It produces a LOT of energy per reaction, but not as much per mass as 3 He fusion.
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n
235
Did you notice that a byproduct of 235 U fission by neutron collision is MORE neutrons?
Need  something   to  slow  down   reacPon  and     prevent  it  going
“criPcal”
The 235 U chain reaction is self sustaining when natural uranium is enriched to 5% of 235 U.
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235
•   Nuclear generators work by starting a chain reaction in Uranium that is enriched in 235 U.
•   The rate of the chain reaction rate is managed by;
1.
By inserting control rods to block neutrons.
2.
By cooling the reactor core to slow neutrons.
The Down Side:
•   Failure to control the reaction leads to a runaway or meltdown .
(Chernobyl + 3 mile Island)
•   235 U reactors produce toxic materials including both ‘depleted’ rods and the containment vessel.
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•   PWR/BWR:  Regular  water  (coolant),  carbon  control  rods
(moderator)  and  enriched  Uranium  (fuel)
•   PHWR:  Heavy  water  (coolant/moderator)  and  natural
Uranium  (fuel)
•   RBMK:  Regular  water  (coolant),  graphite  moderator,
and  natural  Uranium  (fuel)  –  VERY  unstable
•   LMFBR:  Liquid  metal  (coolant/moderator),  various
natural  fuel  sources  (Uranium,  Thorium)
•   IFR:  Like  an  LMFBR  but  recycles  the  fuel
•   And  many,  many  others….
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•   Oklo  –  Gabon,  Africa
•   Like  HWR  without  the  heavy  water
•   1.7  billion  years  ago,  the  abundance  of  U 235  much
higher  (3.1%,  now  0.7%)
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1)   Nuclear  reactor  zone
2)   Sandstone
3)   Uranium  ore  layer
4)   Granit
5)   Water
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Radioisotope  thermoelectric  generator
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RTGs  used  on  Pioneer  10  &  11,  Voyager  1  &  2,
Galileo,  Ulysses,  Cassini,  New  Horizons,  MSL,
Viking  landers,  Apollo  12-­‐17
Typically  provide  a  few  100  Waks  of  power     for  50-­‐100  years.
Because  RTGs  contain  plutonium  and  other     highly  radioacPve  material,  they  can  be  more     dangerous  to  launch  that  a  fission  reactor
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7%  of  World’s  Power  Plants
16%  of  World’s  Electricity
No  new  Nuclear  Power  Plants  in  the  US   since  the  1970s.
Should  we  build  more  plants?
What  about  coal?   Courtesy  of  Fox  TV
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•   No  such  things  as  hydro-­‐power  or  wind  power   in  space
•   Solar  power  is  possible  but  increasingly   limited  pasts  Mars’  orbit
•   All  past  or  current  missions  going  to  Jupiter   and  beyond  used  a  form  of  power  based  on   radioacPve  decay
•   Juno  mission  will  use  solar  panels:  >10  kW  at
Earth  but  only  480  W  (max)  at  Jupiter
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•   1365  W/m 2  at  the  top  of  the  Earth’s   atmosphere  (about  1000  W/m 2  at  noon
at  equator  at  the  surface)
•   Decreases  with  (distance) 2  :  Flux  *  R 2  is  const.
•   Flux  at  Mars    =  (1365  W/m 2 )*(1.0/1.5) 2
=  607  W/m 2
•   Flux  at  Jupiter    =    55  W/m 2
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•   Flux  at  MarPan  surface    ~  590  W/m 2  (max)
•   Solar  Panels  the  size  of  a  football  field  (ISS)
=  3200  kW  intercepted
•   Solar  Panels  10  m  x  10  m
=  59  kW
•   But  solar  panels  not  100%  efficient,  best  ones
today  30%   è  960  kW  /  18  kW
ISS:  14% è  448  kW  /  8  kW
•   Average  person  uses  250  kW  a  month,  9  kW  day
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