Diagram & zoom
Click any highlighted plant region on the diagram to zoom in and read a technical description with real engineering data. Click empty canvas or press Esc to zoom out. Hover over a region to see a quick tooltip.
The diagram shows the RBMK primary heat transport circuit: from the reactor core through drum separators, turbines, condenser, and back via feedwater pumps — a single-circuit boiling water design unique among power reactors.[1]
Reactor physics
The RBMK (Реактор Большой Мощности Канальный — "High-Power Channel-Type Reactor") uses a graphite moderator with light-water coolant in a channel-type design. Unlike Western BWRs or PWRs, the RBMK separates the moderator (graphite, ~1850 tonnes) from the coolant (light water), creating a fundamentally different neutron economy.[1][2]
Positive void coefficient: When coolant boils, neutron absorption decreases while graphite moderation continues — adding reactivity instead of reducing it. This is the key safety concern unique to RBMK designs and was the principal factor in the 1986 Chernobyl accident.
[3][5]
Control rods
Use the Control Rods slider: 100% = fully withdrawn (higher reactivity / power); 0% = fully inserted (lower reactivity / power). The simulation models differential rod worth using a belly-shaped curve — rods are most effective at mid-insertion, consistent with actual reactor physics.[2]
SCRAM (Safety Control Rod Axe Man) triggers emergency rod insertion. The simulation includes the infamous graphite displacer tip effect: boron carbide absorber rods in the RBMK had graphite followers at their lower ends. During the first ~2 seconds of a SCRAM from fully withdrawn position, these graphite tips displaced water in the lower core, momentarily increasing reactivity before the absorber sections entered — a design flaw that contributed directly to the Chernobyl explosion.[3][4]
Xenon-135 dynamics
The simulation models iodine-xenon transient behaviour. Xenon-135, a fission product and the strongest known neutron absorber (σa ≈ 2.6 × 10⁶ barns), builds up during operation and decays after shutdown. The "xenon pit" following power reduction can trap the reactor at low power for 24–48 hours — the operators at Chernobyl attempted to override this effect with fatal consequences.[3][6]
Iodine-135 → Xenon-135 chain: ¹³⁵Te (β⁻, 19s) → ¹³⁵I (β⁻, 6.6h) → ¹³⁵Xe (β⁻, 9.1h) → ¹³⁵Cs. Equilibrium Xe-135 poisoning at full power is worth approximately −3,000 to −3,500 pcm in an RBMK core.
[6]
Time control
Play/Pause toggles simulation. Speed buttons 1x / 2x / 5x control simulation rate. Keyboard: Space = pause, 1–3 = speed. Time acceleration is useful for observing xenon transients and decay heat evolution.
Training modes
- Free Play — full manual control with no constraints; explore reactor behaviour freely.
- Normal Ops — guided operation with safety limit warnings. Exceeding 110% power or 35% void fraction triggers violations, reflecting actual ORM (Operating Reactivity Margin) limits.[4]
- Safety Training — random transient events (MCP trip, pipe rupture) trigger during operation; respond within 15 seconds by mitigating the event.
- Accident Analysis — opens the debrief panel for post-incident review with timeline markers.
RBMK variants
RBMK-1000 (3200 MWt / 1000 MWe) — deployed at Leningrad, Kursk, Chernobyl, and Smolensk NPPs. 1661 fuel channels, graphite stack mass: 1,850 tonnes. Void coefficient of reactivity: +4.5β (early design, pre-modifications).[1]
RBMK-1500 (4800 MWt / 1500 MWe) — uprated design deployed at Ignalina NPP (Lithuania). Higher void coefficient (+5β) due to increased power density. Both Ignalina units are now permanently shut down (Unit 1: 2004, Unit 2: 2009).[7]
Scenarios & events
- Auto Run — scripted startup → full power → coast-down → shutdown cycle demonstrating normal operational phases.
- Chernobyl — dramatized reconstruction of the April 26, 1986 accident sequence at Unit 4. On-screen timestamps (00:00, 00:28, 01:23:xx) follow the familiar narrative clock; simulation time is compressed (a few tens of seconds) so the phases stay playable. The scenario begins at low thermal power so the xenon/rod-withdrawal beat is visible before the AZ-5 and excursion. It still shows ORM violation, graphite-tip SCRAM effect, and a spike to ~30,000 MWt (~100× nominal).[3][5]
- MCP Trip — simulates failure of the Main Circulation Pumps (8 × 5,500 kW centrifugal pumps in 2 loops). Reduces coolant flow, causing rapid void formation and positive reactivity insertion.[1]
- Pipe Rupture — simulates a Loss of Coolant Accident (LOCA) with depressurisation of the condenser circuit.
Key parameters explained
- Reactivity (pcm) — measure of deviation from criticality. 1 pcm = 10⁻⁵ Δk/k. Positive = supercritical (power rising); negative = subcritical (power falling).[6]
- Void fraction — volume fraction of steam in the coolant. Higher void → less neutron absorption → positive reactivity in RBMK.[2]
- Fuel temperature — models Doppler broadening feedback. Higher fuel temperature increases resonance absorption in U-238, providing negative reactivity feedback (the primary self-limiting mechanism).[6]
- Decay heat — residual heat from fission product decay after shutdown. Initially ~6.6% of operating power, declining with the Todreas-Kazimi approximation: Q(t) ∝ t⁻⁰·².[8]
Keyboard shortcuts
- Space — pause / resume
- 1 2 3 — 1x, 2x, 5x speed
- S — SCRAM
- R — Reset
- A — Auto Run toggle
- Esc — close panels / zoom out
- ? — open this help
Debrief
Click Debrief to review peak values, event timeline, and operator rating for the current session. The rating system reflects operational safety standards: any safety violation or explosion results in "Needs Improvement" or "Critical Failure".
Share
Click Share to copy a URL encoding the current simulation state (rod position, power, temperature, pressure, xenon level, active faults). Anyone opening that link will start with the same parameters.
References & further reading
- RBMK Reactors — Appendix to Nuclear Power Reactors, World Nuclear Association, updated 2023. world-nuclear.org
- A.N. Grigoriev, V.V. Nesterenko, RBMK Channel-Type Reactor: Design & Engineering Fundamentals, Energoatomizdat, Moscow, 1989.
- INSAG-7, The Chernobyl Accident: Updating of INSAG-1, Safety Series No. 75-INSAG-7, IAEA, Vienna, 1992. iaea.org
- G.I. Toshinsky, RBMK Reactor Safety Features and Modifications After Chernobyl, Nuclear Engineering and Design, vol. 195, pp. 45–52, 2000.
- A.V. Karpov, Analysis of the Causes of the Chernobyl NPP Accident (Positive Scram Effect), Nuclear Energy, vol. 81, no. 1, pp. 3–8, 1996.
- J.R. Lamarsh, A.J. Baratta, Introduction to Nuclear Engineering, 4th ed., Pearson, 2017. Chapters 4 (Reactor Kinetics) & 7 (Fission Product Poisoning).
- Ignalina Nuclear Power Plant Decommissioning, Lithuanian Energy Institute / IAEA. iaea.org/topics/decommissioning
- N.E. Todreas, M.S. Kazimi, Nuclear Systems Volume I: Thermal Hydraulic Fundamentals, 2nd ed., CRC Press, 2012. Chapter 2 (Decay Heat).
This simulation is for educational purposes only. All behaviour, physics models, and numerical values are simplified and illustrative — not validated against any real RBMK plant data or licensed safety analysis codes (e.g., RELAP, ATHLET). The Chernobyl scenario is a dramatized reconstruction, not a forensic simulation.