Department

Nuclear Engineering TechnologyCourse Code

NUC K117Professor

AbelChapter

13This

**preview**shows half of the first page. to view the full**3 pages of the document.**I. Neutron Life Cycle!

1. !

•The above physical factors are encompassed into the keﬀ ‘Six Factor

Formula’ as simple ratios.!

•By multiplying the ratios together, we get a unitless value of keﬀ that reﬂects a

multiplication factor for change in neutron population from one generation to

the next!

2. All values below: All factors over 1 is a contributor !

3. Fast Fission Factor ( ) !

• !

•About 2% of U235 ﬁssions caused by fast neutrons!

•Therefore, for a 2% reactor a typical value is: ≈ 1.02!

•Commonly a breeder reactor!

•Not really needed

4. Fast Non-Leakage ( Lf )!

• !

•Fast neutrons begins slowing down through collisions with moderator!

•Some fast neutrons leak out of the core and are ‘lost’ to the ﬁssion process!

•Lf is expressed in terms of fast neutrons that DO NOT leak out of the core!

•Typically value: Lf ≈ .97!

5. Resonance Escape Probability ( )!

• !

•As fast neutrons begin slowing down, they are subject to ‘resonance capture’

by the fuel!

•These neutrons do not cause ﬁssion, and therefore ‘escape’ the ﬁssion

process!

•Typical value ≈ .87!

6. Thermal Non-Leakage ( LTH )!

• !

•Some thermal neutrons also leak out of the core and are not available to

cause ﬁssion!

kef f =ϵLfρLth fη

ϵ

ϵ=Number of fast Neutrons produced by All Fission

Number of fast Neutrons produced by Ther m al Fission

ϵ

Lf=Number of Fast Neutrons that do NOT L eak

Number of Fast Neutrons produced by All Fission}

ρ

ρ=Number of Neutrons that Reach T her m al Energy

Number of Fast Neutrons that Start to Slow Down

ρ

LTH =Number of Neutrons that Reach T her m al Energy

Number of Fast Neutrons that Start to Slow Down

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