Page 266 - Dynamics and Control of Nuclear Reactors

APPENDIX C Basic reactor physics 267

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15
C.3. The neutron flux in a high flux reactor is approximately 10 neutrons/cm -sec.
The microscopic neutron cross section for fission in U-235 for this reactor is
2
3
500 10 24 cm . The density of U-235 target nuclei is 10 24 nuclei/cm .
(a) Calculate the rate at which fission reactions take place in this reactor.
Simplify your answer and indicate the units.
(b) If the energy generated per fission is approximately 200MeV, calculate
3
the total power produced in the reactor per cm . Indicate the units.
1MeV¼1.60 10 13 J.
C.4. Match the following neutron energies (E) with thermal neutrons, fast neutrons,
and neutrons in the resonance energy range.
E: 0.1MeV - 15MeV _________________.
E<1eV _________________.
E: 1eV – 0.1MeV _________________.

C.5. The energy of neutrons in a light water reactor is approximately equal to
0.0253eV. This corresponds to a speed of about 2200m/s for neutrons at
20deg. C.

12 2
(a) If the neutron flux is 2 10 neutrons/(cm -sec) calculate the neutron
density. Indicate the units. 1m¼100cm.
24 2
(b) If the microscopic absorption cross section is σ a ¼694 10 cm for
3
24
U-235 and the density of target nuclei of U-235 is N¼0.048 10 /cm ,
calculate the total reaction rate. Indicate units.
(c) What is the rate at which U-235 nuclei are consumed in this reactor?

References
[1] J.J. Duderstadt, L.J. Hamilton, Nuclear Reactor Analysis, John Wiley, New York, 1976.
[2] J.K. Shultis, R.E. Faw, Fundamentals of Nuclear Science and Engineering, second ed,
CRC Press, Boca Raton, FL, 2007.
[3] A.R. Foster, R.L. Wright, Basic Nuclear Engineering, Allyn and Bacon, Boston, 1983.
[4] J.R. Lamarsh, Introduction to Nuclear Reactor Theory, Addison-Wesley, Reading, MA,
1983.
[5] https://www.nuclear-power.net/glossary/, 2018.