Nuclear Physics III
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Created by:
peterandthegoose on May 5, 2011
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16 terms
Terms | Definitions |
|---|---|
 ~ 1ms | Lifetime of neutron |
| Leak from reactor, absorbed, cause further fissions. | Neutron fates |
| ~20,000 km s^-1 | Initial speed of neutron |
| ~2 km s^-1 | Speed of moderated neutron |
| ΦΣ_a | Absorption rate |
| vΦΣ_f | Production rate |
| dn/dt | Rate of increase in neutron number density |
| ∇⋅J | Rate of flow of neutrons away from the location |
| dn/dt = vΦΣ_f - ΦΣ_a - ∇⋅J | Balance equation |
| Neutrons tend to perform a net drift from regions of high flux to regions of low flux at a rate proportional to the flux gradient. | Assumption of diffusion approximation |
| J = -D∇Φ | Diffusion approximation (equation) |
| dn/dt = vΦΣ_f - ΦΣ_a + D∇^2Φ | The Diffusion Equation |
| size of reactor (the larger, the less significant is leakage relative to other neutron fates); amount of parasitic absorption (in structure and coolant); amount of fuel (to cause further fissions) | Criticality depends on... |
| Maximum at centre, zero at edges; a cosine axially (zero at the ends, maximum in the middle); a Bessel function radially (zero at the outer radius, maximum in the middle) | Flux distribution when critical in cylindrical reactor |
| Cosine | Linear heat flux variation in axial coolant channels |
| Ability to remove the heat generated without exceeding safe coolant or structure temperatures | Limiting factor of absolute reactor power |
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