Reactor Operations · Calibrated to DOE-HDBK-1019
Watch iodine-135 decay into xenon-135, burn out under flux, and spike after a trip — the fission-product poison every operator has to out-wait. Set a power history and read the reactivity, the peak, and the dead time.
Each row holds the reactor at that power for that many hours, in order. The simulation runs the schedule, then coasts a further 80 h so any post-shutdown peak is visible.
If xenon's negative reactivity climbs past this margin, the reactor can't be made critical — that window is the xenon dead time (precluded startup), shaded red on the chart.
Thermal power alone does not set the flux — power density does. Two plants at 1000 and 3000 MWth with the same power density run at essentially the same flux and the same xenon concentration. That is why core volume is asked for.
Xe worth pins the reactivity scale to your core; it does not affect the benchmark ratio. Defaults reproduce the NRC reference curves.
Iodine-135 is fed by fission and only decays (it's a weak absorber, so its burnup is dropped). Xenon-135 is fed a little directly by fission and mostly by that iodine decay, then leaves two ways: it decays, and at power it burns out by absorbing a neutron (the σa·φ term). Trip the reactor and the burnout term vanishes instantly, but iodine keeps decaying into xenon for hours — so xenon overshoots to a peak near 8 hours before its own decay finally wins.
| λI — iodine-135 decay | T½ = 6.57 h | 2.930 × 10⁻⁵ s⁻¹ |
| λXe — xenon-135 decay | T½ = 9.10 h | 2.116 × 10⁻⁵ s⁻¹ |
| γI — cumulative I-135 yield | 6.282 % ± 0.088 | 0.062819 |
| γXe — direct Xe-135 yield | 0.2566 % (cum. Xe − cum. I) | 0.002566 |
| σaXe — Xe-135 absorption | 2.6 million barns | 2.6 × 10⁻¹⁸ cm² |
Fission yields from ENDF/B-VIII.1 (U-235 thermal, 0.0253 eV, MF=8 MT=459 cumulative); the direct ¹³⁵Xe term is the difference of the cumulative Xe and I yields. Decay constants and σa from DOE-HDBK-1019/2-93 and the U.S. NRC Reactor Physics Review (HRTD, §2.1), cross-checked against Lamarsh & Baratta, Introduction to Nuclear Engineering. Benchmark curves digitised from NRC Figs 2.1-12 and 2.1-14. The reactivity scale is calibrated so equilibrium ¹³⁵Xe at 100% power equals the reference −2800 pcm; the same model then reproduces the post-trip peak and the equilibrium-versus-power curve without further tuning — see the validation table below.
Every figure below is recomputed live from the constants and flux currently set in the panel above — nothing here is hard-coded. Move the flux slider and the errors move with it. The model is calibrated at one point (equilibrium ¹³⁵Xe at 100% power); everything else is an output.
| Benchmark | Source | Reference | This model | Error |
|---|---|---|---|---|
| Equilibrium ¹³⁵Xe @ 100% | NRC HRTD §2.1, Xenon slide | −2800 pcm | – | anchor |
| Equilibrium ¹³⁵Xe @ 80% (÷ 100%) | NRC Fig 2.1-14, pre-trip | 0.9566 | – | – |
| Equilibrium ¹³⁵Xe @ 50% (÷ 100%) | NRC Fig 2.1-14, pre-trip | 0.8117 | – | – |
| Post-trip peak ÷ equilibrium calibration-free — independent of the anchor, of Σf, and of the yields |
NRC Fig 2.1-14, trip from 100% | 1.7329 | – | – |
The shape of this model is governed by a single dimensionless group, Θ = σaφ / λXe — the ratio of xenon burnout rate to xenon decay rate. Θ is what has been benchmarked, not φ on its own: published σa values span 2.6–3.5 × 10⁶ b, so only the product σaφ is pinned down by the reference curves. Current Θ = –, benchmark Θ = 3.19.
Part of the NeutronRise reactor operations cluster: Point Kinetics Simulator · Decay Heat Calculator