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Nuclear Fission

Nuclear Fission. Segrè. Distribution of fission energy. a b c. Lost … !. How much is recoverable? What about capture gammas? (produced by  -1 neutrons ) Why c < ( a+b ) ?. Nuclear Reactors, BAU, 1 st Semester, 2007-2008 (Saed Dababneh). Nuclear Fission.

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Nuclear Fission

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  1. Nuclear Fission Segrè Distribution of fission energy a b c Lost … ! • How much is recoverable? • What about capture gammas? (produced by -1 neutrons) • Why c < (a+b) ? Nuclear Reactors, BAU, 1st Semester, 2007-2008 (Saed Dababneh).

  2. Nuclear Fission •  and  emissions from radioactive fission products carry part of the fission energy, even after shut down. • On approaching end of the chain, the decay energy decreases and half-life increases. Long-lived isotopes constitute the main hazard. • Can interfere with fission process in the fuel. Example?(poisoning). • Important for research. • -decay favors high energy  ~20 MeV compared to ~6 MeV for . • Only ~8 MeV from -decay appears as heat. Why? Nuclear Reactors, BAU, 1st Semester, 2007-2008 (Saed Dababneh).

  3. Nuclear Fission • Thermal neutron fission of 235U forms compound nucleus that splits up in more than 40 different ways, yielding over 80 primary fission fragments (products). 23592U + 10n ► 9037Rb + 14455Cs + 210n 23592U + 10n ► 8735Br + 14657La + 310n 23592U + 10n ► 7230Zn + 16062Sm + 410n • The fission yield is defined as the proportion (percentage) of the total nuclear fissions that form products of a given mass number. Revisit thermal and look for fast. Nuclear Reactors, BAU, 1st Semester, 2007-2008 (Saed Dababneh). 3

  4. Nuclear Fission f - (n,) A-1, Z j A, Z i A, Z-1 k - (n,) A+1, Z A, Z+1 dNi/dt = Formation Rate - Destruction rate - Decay Rate Ni saturates and is higher with higher neutron flux, larger “fission yield” and longer half-live. ! Nuclear Reactors, BAU, 1st Semester, 2007-2008 (Saed Dababneh). 4

  5. Nuclear Fission HW 7 Investigate the activity, decay and gamma energies of fission products as a function of time. Comment on consequences (e.g. rod cooling). • Shutdown HW 8 Investigate both and giving full description for the buildup and decay of fission fragment i. Nuclear Reactors, BAU, 1st Semester, 2007-2008 (Saed Dababneh). 5

  6. Nuclear Fission per watt of original operating power. T = time of operation. Fission product activity after reactor shutdown? Nuclear Reactors, BAU, 1st Semester, 2007-2008 (Saed Dababneh). 6

  7. Nuclear Fission • The fission gamma radiation • Prompt within 0.1 s and with average energy of 0.9 MeV. •  delayed gammas. • Investigate how prompt • gammas interact with • water, uranium and lead. HW 9 Nuclear Reactors, BAU, 1st Semester, 2007-2008 (Saed Dababneh). 7

  8. Nuclear Fission HW 10 The experimental spectrum of prompt neutrons is fitted by the above equation. Calculate the mean and the most probable neutron energies. Nuclear Reactors, BAU, 1st Semester, 2007-2008 (Saed Dababneh).

  9. Nuclear Fission • Recoverable energy release  200 MeV per 235U fission. • Fission rate = 2.7x1021P fissions per day. P in MW. • Burnup rate: 1.05 P g/day. P in MW. • Capture-to-fission ratio: • Consumption rate: 1.05(1+) P g/day. • 1000 MW reactor. • 3.1x1019 fissions per second, or 0.012 gram of 235U per second. • Two neutrinos are expected immediately from the decay of the two fission products, what is the minimum flux of neutrinos expected at 1 km from the reactor. Work it out, NOW! Nuclear Reactors, BAU, 1st Semester, 2007-2008 (Saed Dababneh). 4.8x1012 m-2s-1

  10. Nuclear Fission • 3.1x1010 fissions per second per W. • In thermal reactor, majority of fissions occur in thermal energy region,  and  are maximum. • Total fission rate in a thermal reactor of volume V • Thermal reactor power (quick calculation) Nuclear Reactors, BAU, 1st Semester, 2007-2008 (Saed Dababneh). 10

  11. Nuclear Fission It is necessary to evaluate the potential hazards associated with an accidental release of fission products into the environment. It is required to determine a proper cooling time of the spent fuel (before it becomes ready for reprocessing) that depends on the decay times of fission products. It is necessary to estimate the rate at which the heat is released as a result of radioactive decay of the fission products after the shut down of a reactor. The poisoning is needed to be calculated (the parasitic capture of neutrons by fission products that accumulate during the reactor operation). Some technicalities, so far! Nuclear Reactors, BAU, 1st Semester, 2007-2008 (Saed Dababneh). 11

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