Nuclear Decay Heat Curves: U238_fast
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 (%) |
|---|---|---|---|---|---|
| U238_fast | 1 | 0.07 | Fast fission of U-238; slightly higher initial fraction than U-235 due to different fission product yield distribution; per ANS 5.1-2014 Table for U-238 fast fission | ANS_5.1_2014 | 6 |
| U238_fast | 10 | 0.0571 | 10 s after shutdown; U-238 fast fission product decay; slightly higher early decay than U-235 | ANS_5.1_2014 | 6 |
| U238_fast | 100 | 0.0413 | 100 s; Way-Wigner correction for U-238 fast fission; comparable to U-235 values but with different isotope distribution | ANS_5.1_2014 | 5 |
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