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

2. 2  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. Example? (poisoning). Can interfere with fission process in the fuel. Example? (poisoning). Important for research.  -decay favors high energy  ~ 20 MeV compared to ~6 MeV for . Why? Only ~8 MeV from  -decay appears as heat. Why? Nuclear Fission

3. 3 Nuclear Reactors, BAU, 1 st Semester, 2007-2008 (Saed Dababneh). Thermal neutron fission of 235 U forms compound nucleus that splits up in more than 40 different ways, yielding over 80 primary fission fragments (products). 235 92 U + 1 0 n ► 90 37 Rb + 144 55 Cs + 2 1 0 n 235 92 U + 1 0 n ► 87 35 Br + 146 57 La + 3 1 0 n 235 92 U + 1 0 n ► 72 30 Zn + 160 62 Sm + 4 1 0 n 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.

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

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

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

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 Investigate how prompt gammas interact with water, uranium and lead. 7Nuclear Reactors, BAU, 1 st Semester, 2007-2008 (Saed Dababneh). HW 9

8. Nuclear Reactors, BAU, 1st Semester, 2007-2008 (Saed Dababneh). 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.

9. 9Nuclear Reactors, BAU, 1 st Semester, 2007-2008 (Saed Dababneh). Recoverable energy release  200 MeV per 235 U fission. Fission rate = 2.7x10 21 P fissions per day. P in MW. Burnup rate Burnup rate : 1.05 P g/day. P in MW. Capture-to-fission ratio: Consumption rate Consumption rate : 1.05(1+  ) P g/day. 1000 MW reactor. 3.1x10 19 fissions per second, or 0.012 gram of 235 U 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. 4.8x10 12 m -2 s -1 Nuclear Fission Work it out, NOW!

10. 10Nuclear Reactors, BAU, 1 st Semester, 2007-2008 (Saed Dababneh). Nuclear Fission 3.1x10 10 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)

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). 11Nuclear Reactors, BAU, 1 st Semester, 2007-2008 (Saed Dababneh).