1. More on Fission Products
 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. (poisoning).
Important for research.
-decay favors high energy  17 MeV compared to 6 MeV for .
Only 7 MeV from -decay appears as heat. Why?
Nuclear and Radiation Physics, BAU, First Semester, (Saed Dababneh).

2. Poisoning
Nuclear and Radiation Physics, BAU, First Semester, (Saed Dababneh).

3. Poisoning
Nuclear and Radiation Physics, BAU, First Semester, (Saed Dababneh).

4. Poisoning Not anticipated! Reactor shut down! 135Xe 106 b Time scale:
Hours and days.
135Xe
106 b
149Sm
105 b
Nuclear and Radiation Physics, BAU, First Semester, (Saed Dababneh).

5. Poisoning
HW 48
Negative reactivity due to poison buildup. It is proportional to the amount of poison.
Nuclear and Radiation Physics, BAU, First Semester, (Saed Dababneh).

6. Assume no spacial dependence.
Poisoning
small
Initial conditions?
Clean Core Startup.
Shutdown (later).
Assume no spacial dependence.
Nuclear and Radiation Physics, BAU, First Semester, (Saed Dababneh).

7. Poisoning The solution is and
Nuclear and Radiation Physics, BAU, First Semester, (Saed Dababneh).

8. Poisoning Now, we know Xe(t)
Nuclear and Radiation Physics, BAU, First Semester, (Saed Dababneh).

9. Poisoning
Shutdown. After the reactor has been operating for a “long” time.
Nuclear and Radiation Physics, BAU, First Semester, (Saed Dababneh).

10. Poisoning The solution is > 0 ?
Height of the peak depends on I() and Xe(), i.e. depends on .
Nuclear and Radiation Physics, BAU, First Semester, (Saed Dababneh).

11. Poisoning
Shutdown  Xe   negative   move control rods out  try to add positive reactivity  need to have enough reserve  costly to do that.
If, the available excess reactivity can compensate for less than 30 minutes of poison buildup, can’t startup again after ~30 minutes of shutdown, because you can’t achieve criticality. Need to wait some 40 hours (in this case) for Xe to decay down.
Nuclear and Radiation Physics, BAU, First Semester, (Saed Dababneh).

12. Poisoning
Nuclear and Radiation Physics, BAU, First Semester, (Saed Dababneh).

13. Poisoning
Strategies
If you plan to shut down for “short maintenance”, think about stepback.
Examine different scenarios using this code from
You will get more experience after you finish the computational physics course.
Nuclear and Radiation Physics, BAU, First Semester, (Saed Dababneh).

14. Poisoning Xe Oscillations
(r,t) (spacial dependence)  flux  locally  Xe burnup    (reactivity)   flux further   control rods globally in  flux  elsewhere  Xe burnup     ….. Xe oscillation but limited by opposite effect due to increase (decrease) of I in the high (low) flux region.
In large reactors (compared to neutron diffusion length) local flux, power and temperature could reach unacceptable values for certain materials  safety issues.
Think of one sensor and one control rod  feel average flux  apparently OK  more sensors and control rods to locate and deal with local changes.
Nuclear and Radiation Physics, BAU, First Semester, (Saed Dababneh).

15. Poisoning Permanent Poisons
149Sm has sizeable but lower cross section than 135Xe.
It does not decay.
Start from fresh fuel:
Thus:
Nuclear and Radiation Physics, BAU, First Semester, (Saed Dababneh).

16. Radioactive Fission Products
Read section 13.7 in Krane.
Look at sections 13.8 and 13.9
Nuclear and Radiation Physics, BAU, First Semester, (Saed Dababneh).

17. Radioactive Fission Products
per watt of original operating power.
T = time of operation.
Nuclear and Radiation Physics, BAU, First Semester, (Saed Dababneh).

18. Radioactive Fission Products
Nuclear and Radiation Physics, BAU, First Semester, (Saed Dababneh).