Effect of Prompt Neutron Lifetime on Nuclear Safety

Effect of Prompt Neutron Lifetime on Nuclear Safety

The prompt neutron lifetime belongs to key neutron-physical characteristics of reactor core. Its value depends especially on the type of the moderator and on the energy of the neutrons causing fission. Its importance for nuclear reactor safety is well known for a long time.

The longer prompt neutron lifetimes can substantially improve kinetic response of reactor (the longer prompt neutron lifetime gives simply slower power increase). For example under RIA conditions (Reactivity-Initiated Accidents) reactors should withstand a jump-like insertion of relatively large (~1 $ or even more) positive reactivity and the PNL (prompt neutron lifetime) plays here the key role. Therefore the PNL should be verified in a reload safety evaluation process.

In some cases (especially in some fast reactors) reactor cores or can be modified in order to increase the PNL and in order to improve nuclear safety.

See also: Improving Nuclear Safety of Fast Reactors by Slowing Down Fission Chain Reaction

Prompt Neutron Lifetime - Reactor Types
Dependencies of asymptotic time period on the reactivity required for different reactor types with different prompt neutron lifetimes. Source: http://www.hindawi.com/journals/ijne/2014/373726/

Interactive chart – Infinite Multiplying System Without Source and Delayed Neutrons

Press the “clear and run” button and try to stabilize the power at 90%.

Look at the reactivity insertion you need to insert in order to stabilize the system (of the order to tenth of pcm).

Do you think that such a system is controlable?

Nuclear and Reactor Physics:
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  7. Robert Reed Burn, Introduction to Nuclear Reactor Operation, 1988.
  8. U.S. Department of Energy, Nuclear Physics and Reactor Theory. DOE Fundamentals Handbook, Volume 1 and 2. January 1993.

Advanced Reactor Physics:

  1. K. O. Ott, W. A. Bezella, Introductory Nuclear Reactor Statics, American Nuclear Society, Revised edition (1989), 1989, ISBN: 0-894-48033-2.
  2. K. O. Ott, R. J. Neuhold, Introductory Nuclear Reactor Dynamics, American Nuclear Society, 1985, ISBN: 0-894-48029-4.
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  4. E. E. Lewis, W. F. Miller, Computational Methods of Neutron Transport, American Nuclear Society, 1993, ISBN: 0-894-48452-4.

See previous:

Example – Point Kinetics

See above:

Prompt Neutrons

See next:

Energy Spectrum