Reactor Post-Shutdown Decay Heat Calculator (ANS-5.1)

Determine post-trip thermal power decay fraction P(t)/P_0 from 1 second to 30 days following scram using ANSI/ANS-5.1-2014 standards.

Reactor Core Operating History

Licensed Thermal Power P_0 (MWth):

Operating Time at Power (Days): Fuel cycle burnup duration

Time Since Reactor Scram t_s:

Time Unit:

2-Sigma Regulatory Uncertainty (10 CFR 50 App K):

Dominant Fissile Isotope:

Post-Scram Decay Heat Output

Decay Power Fraction P(t)/P_0:

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Decay Heat Thermal Power:

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Fission Product Component:

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Actinide Component (U-239 / Np-239):

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Coolant Boil-off Rate (at 1 atm):

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Decay Heat at Key Milestones:

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Reactor Post-Trip Decay Heat Physics

When control rods are inserted into a commercial reactor core, prompt fission terminates within milliseconds. However, radioactive decay of accumulated fission product isotopes (beta and gamma emission) and neutron capture actinides ($\text{U-239}$ and $\text{Np-239}$) continues to generate substantial thermal power.

Safety Systems & ECCS Design (10 CFR 50 Appendix K)

At $t = 1\text{ second}$, decay power is approximately $6.5\%$ to $7.0\%$ of full licensed thermal power ($~230\text{ MWth}$ for a $3400\text{ MWth}$ unit). After 1 hour, it remains around $1.4\%$ ($~48\text{ MWth}$), and after 24 hours, around $0.55\%$ ($~19\text{ MWth}$). Emergency Core Cooling Systems (ECCS), auxiliary feedwater, and residual heat removal (RHR) heat exchangers must run continuously to prevent core meltdown.

Reactor Post-Shutdown Decay Heat Calculator (ANS-5.1)

Reactor Core Operating History

Post-Scram Decay Heat Output

Reactor Post-Trip Decay Heat Physics

Safety Systems & ECCS Design (10 CFR 50 Appendix K)

Frequently Asked Questions