An educational pressurized-water-reactor simulator in plain HTML/CSS/JavaScript, built around the reactor theory in John R. Lamarsh, Introduction to Nuclear Reactor Theory. No dependencies, no build step.
⚠️ Educational use only. Parameters are representative, lumped, and tuned for teaching — this is not a licensing-grade plant model.
Open the live demo, or run it
locally by double-clicking index.html (or serving the folder with any static
server).
- Control rod slider sets the bank's insertion target (0 % = fully withdrawn, 100 % = fully inserted). Rods drive at 5 %/s, so the actual position (shown in the bars and the schematic) lags the target.
- ▲ OUT / ▼ IN step the target by 1 %.
- SCRAM drops the whole bank in ~2 s. After a SCRAM only RESET restores control.
- RESET returns the plant to its critical, 100 %-power reference state.
- 🔊 / 🔇 toggles the alarm sounds — a slow beep in WARNING, a two-tone klaxon in DANGEROUS, a continuous siren during meltdown (all synthesized with the Web Audio API; no audio files). Browsers block sound until your first click or keypress, after which alarms arm automatically.
| Action | What happens | Why |
|---|---|---|
| Withdraw to ~43 % | Power settles slightly above 100 % | Negative Doppler + moderator feedback compensate the added reactivity |
| Withdraw to ~38 % | Power stabilizes near 160 % — DANGEROUS | Feedback still wins, but margins are gone |
| Withdraw below ~33 % | Coolant passes ~345 °C → boiling crisis (DNB) → fuel runs away → MELTDOWN | Film boiling collapses fuel→coolant heat transfer, and the damage is irreversible |
| Withdraw to 0 % | Prompt-critical excursion; core melts in seconds | Inserted reactivity exceeds β = 650 pcm — the reactor is critical on prompt neutrons alone |
| SCRAM from any pre-melt state | Power collapses to a few % | −9000 pcm bank worth ≫ excess reactivity |
Point-reactor kinetics, six delayed-neutron groups (U-235, Keepin data; β = 0.006502, Λ = 10⁻⁴ s), integrated semi-implicitly at 5 ms substeps:
dn/dt = ((ρ − β)/Λ)·n + Σ λᵢcᵢ
dcᵢ/dt = (βᵢ/Λ)·n − λᵢcᵢ
Reactivity balance (pcm): ρ = ρ_rods + ρ_Doppler + ρ_moderator
- Rod bank integral worth follows the classic S-curve
W(x) = W_tot·(x − sin 2πx / 2π)with W_tot = −9000 pcm; the core is exactly critical with the bank 45 % inserted at reference temperatures. - Doppler: −2.7 pcm/°C of fuel temperature (defect capped at −3000 pcm — it saturates at high fuel temperature).
- Moderator: −8 pcm/°C of coolant temperature.
Six-factor formula, displayed live and kept exactly consistent with ρ:
k_eff = 1/(1 − ρ) = ε · p · f · η · P_f · P_t
f = Σa(fuel) / [Σa(fuel) + Σa(moderator) + Σa(rods)]
with ε = 1.02, p = 0.87, η = 2.06, P_f = P_t = 0.983, Σa(fuel) = 0.100 cm⁻¹, Σa(moderator) = 0.060 cm⁻¹. Moving the rods changes Σa(rods), hence f, hence k — the "absorption coefficient" readouts on the panel.
Thermal-hydraulics — two lumped nodes (3000 MWt nominal):
C_f·dT_f/dt = P − UA·(T_f − T_c) C_f = 3.0×10⁷ J/K
C_c·dT_c/dt = UA·(T_f − T_c) − H·(T_c − T_sg) C_c = 1.65×10⁹ J/K
Hot/cold legs split ±18 °C around T_c at full power; pressure tracks coolant temperature around 155 bar.
DNB / boiling crisis: above 345 °C coolant, the fuel→coolant conductance degrades linearly to 15 % by 352 °C and latches (cladding damage is irreversible until RESET). Meltdown latches when fuel reaches UO₂ melting (2865 °C) — after that, not even a SCRAM helps.
| State | Condition |
|---|---|
| 🟢 SAFE | power ≤ 100.5 %, T_fuel < 1600 °C, T_cool < 335 °C |
| 🟡 WARNING | power > 100.5 % or T_fuel > 1600 °C or T_cool > 335 °C |
| 🔴 DANGEROUS | power > 112 % or T_fuel > 2200 °C or T_cool > 345 °C |
| ☢️ MELTING DOWN!! | T_fuel ≥ 2865 °C (latched — RESET only) |
| File | Responsibility |
|---|---|
index.html |
Page structure + SVG plant schematic |
style.css |
Control-room theme, alarm states, animations |
physics.js |
Pure simulation engine (no DOM) — also loadable in Node |
ui.js |
Renders a state snapshot to the DOM/SVG each frame |
audio.js |
Synthesized warning/danger/meltdown alarm sounds (Web Audio) |
main.js |
Controls wiring + requestAnimationFrame loop |
test/physics.test.js |
Headless sanity tests: node test/physics.test.js |