Chain Reaction Multiplication Criticality Conditions

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Chain ReactionMultiplicationCriticality
Conditions
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Overview

• Chain Reaction
• Conversion and Breeding
• Doubling Time
• Neutron Cycle in a Thermal Reactor
• Multiplication Factor k
• Simplified Fuel Cycle
• Fuel at Discharge

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Chain Reaction
n
?
ß
?
?
?
ß
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Uranium Fuel
  238U 4.5 109 yr 235U 0.7 109 yr 234U 247000 yr Application
Unat 99.27 0.72 0.006 CANDU (D2O)
UE 98-95 2-5 0.006 LWR (H2O)
DU (UD) 99.8 0.2 0.006 Fast Reactor (FR, FBR) Armour for tanks Armour-piercing
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Conversion or Breeding
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Conversion
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Conversion
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Neutron Cycle in Reactor
Leakage
E
N2
2 MeV
N1
Fast fission
Slowing down
n n/fission
Energy
Resonance abs.
? 2.5
Non-fuel abs.
Non-fissile abs.
1 eV
Fission
200 MeV/fission
Leakage
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Fast Fission
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Simple Criticality Calculations
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Fuel Cycle (Thermal)
Fissile Materials
Fuel Factory
Thermal Reactor
Actinides (MA)
Fiss. Pr. (FP)
DU
Spent Fuel
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Fuel Cycle (Fast)
Spent Fuel
Fuel Factory
Fast Reactor
FPMA
Spent Fuel
DU
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Neutron Economy
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Breeding Factor
B neutrons captured in fertile
1 neutron absorbed in fuel
? neutrons produced
Non-fuel capture and losses CL
1 neutron to maintain chain reaction
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? Factor
? ?
Isotope (100) Thermal (0.025eV) Fast (gt0.5 MeV)
235U 2.07 2.35
233U 2.29 2.40
239Pu 2.15 2.90
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Fission Neutrons
239Pu
235U
233U
E 1
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Conversion Factor
If B lt 1 it is called conversion factor,
C. Number of 239Pu created per 1 neutron absorbed
Reactor System Initial Fuel Conversion Cycle Conversion Ration
BWR 235U (2-4) 238U ? 239Pu 0.6
PWR 235U (2-4) 238U ? 239Pu 0.6
PHWR (CANDU) Unat 238U ? 239Pu 0.8
HTGR 235U (5) 232Th ? 233U 0.8
LMFBR 239Pu (10-20) 238U ? 239Pu 1.0 1.6
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Neutron Cycle in Reactor
Leakage
E
N2
2 MeV
N1
Fast fission
Slowing down
n n/fission
Energy
Resonance abs.
? 2.5
Non-fuel abs.
Non-fissile abs.
1 eV
Fission
200 MeV/fission
Leakage
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Chain Reaction in Unat?
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Doubling Time
Td for a breeder reactor is the amount of time
required for the original fissile loading to
double
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Doubling Time for FR
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Multiplication Factor
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Chain Reaction by Fast N.
235U
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Time to Fission 1 kg 235U
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Energy Comparison
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Distribution of FP Mass
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Long-Lived Radio Isotopes
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Half-Lives of L.L. Isotopes
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The END