Nuclear Decay Heat Curves: U235_thermal
Decay heat power fraction vs time after shutdown for nuclear reactor design and spent fuel management. Covers U-235 thermal fission, U-238 fast fission, Pu-239 thermal fission, standard PWR (45 GWd/tHM), standard BWR (45 GWd/tHM), and MOX fuel per ANSI/ANS-5.1-2014. Time range: 1 second to 10 years. Includes dominant isotope contributors and 2-sigma uncertainty.
| fuel type | time after shutdown s | decay heat fraction of operating power (dimensionless) | notes | standard | uncertainty pct 2sigma (%) |
|---|---|---|---|---|---|
| U235_thermal | 1 | 0.0667 | Immediately after shutdown; fission products from thermal U-235 fission; value per fission event normalized; infinite irradiation approximation; 2-sigma uncertainty per ANS 5.1-2014 Annex B | ANS_5.1_2014 | 5 |
| U235_thermal | 10 | 0.0544 | 10 seconds after shutdown; rapid initial decay of short-lived fission products (Kr-88 t1/2=2.84h not yet significant; I-135 t1/2=6.6h; Xe-138 t1/2=14.1min beginning to decay) | ANS_5.1_2014 | 5 |
| U235_thermal | 100 | 0.0394 | 100 seconds; beta decay of short-lived FP chains dominates; Ba-140/La-140 chain building up; Way-Wigner approximation: 0.066*(t^-0.2) gives ~0.042 at 100s for infinite irradiation | ANS_5.1_2014 | 4 |
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