What is the UFTR effective delayed neutron fraction at Beginning of Life (BOL)?

What is the UFTR effective delayed neutron fraction at Beginning of Life (BOL)?

• A. 741
• B. 739
• C. 750
• D. 730

Answer: (A)

The question tests your understanding of the effective delayed neutron fraction and how it’s expressed for a reactor at Beginning of Life. For UFTR, the value at BOL is about 7.41×10^-3, or 741 pcm (per cent mille). This means roughly 0.741% of the neutrons produced by fission are delayed neutrons from precursors. Why 741 is the best choice: at BOL the fuel is fresh and the mixture of fissile isotopes and precursors yields the largest delayed-neutron contribution for that cycle. The fraction is typically given in pcm, so 741 pcm directly corresponds to 7.41×10^-3. The other nearby numbers represent slightly lower or higher fractions (e.g., 7.39×10^-3, 7.50×10^-3, 7.30×10^-3) but the established UFTR BOL value used in practice is 7.41×10^-3, hence 741 pcm. In practice, β_eff is a key parameter in reactor kinetics because it sets how quickly the reactor responds to reactivity changes and how controllable it is; it’s the portion of neutrons that come from delayed precursors rather than immediate fission neutrons. At BOL, this value sits at its typical UFTR standard, making 741 pcm the correct figure.

The question tests your understanding of the effective delayed neutron fraction and how it’s expressed for a reactor at Beginning of Life. For UFTR, the value at BOL is about 7.41×10^-3, or 741 pcm (per cent mille). This means roughly 0.741% of the neutrons produced by fission are delayed neutrons from precursors.

Why 741 is the best choice: at BOL the fuel is fresh and the mixture of fissile isotopes and precursors yields the largest delayed-neutron contribution for that cycle. The fraction is typically given in pcm, so 741 pcm directly corresponds to 7.41×10^-3. The other nearby numbers represent slightly lower or higher fractions (e.g., 7.39×10^-3, 7.50×10^-3, 7.30×10^-3) but the established UFTR BOL value used in practice is 7.41×10^-3, hence 741 pcm.

In practice, β_eff is a key parameter in reactor kinetics because it sets how quickly the reactor responds to reactivity changes and how controllable it is; it’s the portion of neutrons that come from delayed precursors rather than immediate fission neutrons. At BOL, this value sits at its typical UFTR standard, making 741 pcm the correct figure.