1 / REACTOR BASICS
Different materials. Different jobs.
Start with the core: choose a component to see what it does.
RBMK–1000 / CORE SECTIONS · Schematic
Original conceptual cutaway. A few representative channels; geometry and rod positions are not to scale.
Why steam can change the chain reaction
Water cools the fuel and absorbs some neutrons. Graphite supplies most of the moderation. If water becomes less dense as steam forms, absorption can fall while the graphite remains. In the accident configuration this could increase reactivity. Fuel temperature also gives feedback; the net response depends on the state and spatial distribution. The exhibit draws this relationship without solving reactor physics.
INSAG-7 §2.2 ↗2 / CONTROL ROOM EXPLORER
Read the system. One panel at a time.
Select an instrument or panel. Each opens its function and the limits of what it can tell you.
БЛОК 4 / UNIT CONTROL ROOMR · PANEL ARRANGEMENT
PROCESS INSTRUMENTS
S · POINTERS WITHOUT MEASUREMENT SCALE● channels● groups
Fuel → heat → water / steam → turbine → electrical supply
PROTECTION & CONTROL
INSPECTION ONLY
Controls open explanations.
D · Documented AZ-5 was a shutdown demand. The precise reason for pressing it was not established in Annex I of INSAG-7.
Reasoned visual reconstruction of functional groups, not a surveyed replica. All dial pointers, channel colours and lamps are schematic.
3 / PROCESS COMPUTING
Measured. Recorded. Calculated.
Three different kinds of knowledge — and three different limits. Select a stage to inspect it.
СКАЛА / SKALAR · Reconstructed
V–3M / PROCESS INFORMATION
Data is not omniscience.
S · MODERN TEACHING INTERFACE / NOT HISTORICAL SOFTWARE
01:22:30 — what did the operators actually know?
Annex I describes a magnetic-tape state recording at 01:22:30, then calculations performed after the accident at Smolensk with PRIZMA-ANALOG. The calculated operating reactivity margin must not be mistaken for an instrument reading seen by the crew at that time. ORM is a reactivity-equivalent quantity, not a simple head count of inserted rods.
INSAG-7 Annex I §1-4.5 · printed pp.64–65 ↗4 / GUIDED HISTORICAL RECONSTRUCTION
The night of 25–26 April.
Eleven captioned chapters. Automatic playback uses reading time; historical intervals are not reproduced in real time.
Start begins at chapter 1. Manual navigation pauses playback. Switching stations or hiding the page pauses it too.
04 / REACTOR STATES · Schematic
—
Schematic visual states. No continuous historic telemetry, no calculated power curve.
All chapters · select a historical event
Read the complete chronology & source notes
25.04.1986 · An electrical test in a nuclear plant
D · DocumentedBefore a maintenance shutdown, a turbine rundown test was planned. It concerned the interval between a loss of electrical supply and emergency diesel power becoming available. A grid-related delay prolonged operation at reduced power.
The calendar compresses many hours into one chapter. It is not a real-time replay.
INSAG-7 §3, Annex I Table I-I; NEA chapter I ↗26.04 · ~00:28 · An unintended power reduction
D · DocumentedDuring a change of power-control mode the thermal power fell to about 30 MW, according to the operating-log chronology. The causes and reactor response cannot be captured by a single “operator error” label.
The source distinguishes thermal power from neutron-power indication. The exhibit shows thermal power only.
INSAG-7 Annex I Table I-I, printed p.53; §1-4.4 ↗26.04 · ~01:03 · Low power, changing neutron balance
D · DocumentedPower was raised and stabilized at about 200 MW(th). Xenon absorption, the spatial power distribution and the rod configuration mattered. Low power alone is not a complete explanation of the accident.
The patterned core is a schematic, not a calculated xenon or neutron-flux distribution.
INSAG-7 §§2–3; Annex I Table I-I, printed p.54 ↗26.04 · 01:22:30 · A recording is not yet a calculation
R · ReconstructedSKALA recorded a reactor-state snapshot on magnetic tape. The operating reactivity margin for that state was calculated after the accident using PRIZMA-ANALOG. It was not a live result available to the control-room team at 01:22:30.
The timestamp is documented; the inferred margin belongs to post-accident reconstruction. No retrospective value is drawn onto an operator instrument.
INSAG-7 Annex I §1-4.5, printed pp.64–65 ↗26.04 · 01:23:04 · The turbine rundown begins
D · DocumentedClosure of the turbine-generator No. 8 stop valves marks the test start. Changes in pump delivery, steam formation and reactivity must be considered together. The diagram shows their relationship, not a numerical prediction.
This is a documented anchor event. A large power surge before AZ-5 is not asserted here.
INSAG-7 Annex I §§1-4.3.3, 1-4.6.2 ↗26.04 · 01:23:40 · AZ-5: a shutdown demand
D · DocumentedThe emergency-shutdown signal was recorded and rod insertion began. The exact reason for the button press was not established by the commission in Annex I. The intended safety function and its adverse initial effect must be distinguished.
DREG: 01:23:40; teletape: 01:23:39. The moving rods are a schematic, not a recovered position trace.
INSAG-7 Annex I Table I-I, printed p.55; §1-4.6.3 ↗26.04 · seconds after AZ-5 / Sekunden nach AZ-5 · A dangerous initial response
R · ReconstructedPost-accident analyses identify how graphite displacers could initially add reactivity in the lower core. In this configuration, steam feedback and the spatial power distribution amplified the danger. The precise evolution is reconstructed, not fully recorded.
The shaded core is symbolic. No peak power or second-by-second physical simulation is claimed.
INSAG-7 §4; Annex I §1-4.6.3; Annex II §II-4 ↗26.04 · 01:23:43–49 · Signals of rapid failure
D · DocumentedThe report chronology lists overpower and short-period protection signals, then pressure and measurement-system failure signals. The surviving instruments do not provide a complete trustworthy trace of the final power excursion.
The event window comes from the report; the fading diagram is a museum convention for loss of reliable observability.
INSAG-7 Annex I Table I-I, printed p.55 ↗26.04 · ~01:24 · Destruction and release
D · DocumentedThe reactor was destroyed. Explosions, fires and radioactive release turned an engineering failure into a human catastrophe. The exact mechanics of the final destructive events retain uncertainties. The display stops at a restrained diagram.
Approximate chronology, not an exact explosion timestamp. There is no valid operating-power readout after destruction.
INSAG-7 Annex I Table I-I; NEA chapter I ↗1986 → · The consequences were human
D · DocumentedWorkers and emergency responders suffered fatal injuries and radiation illness. Evacuation, displacement and contamination changed many lives. UNSCEAR separately evaluates acute effects, thyroid cancer and long-term evidence; no single counter can represent the suffering.
This station covers the accident mechanism. The linked health assessments have their own dates, populations and uncertainties.
UNSCEAR, Chornobyl assessments ↗1992 · INSAG-7 · A system-level explanation
D · DocumentedThe revised assessment put reactor design, deficient safety information, operating decisions and organizational safety culture into a broader picture. Explaining the accident solely as operator misconduct misses essential causes.
Continue to Technical findings for the design issues, source limitations and later changes.
INSAG-7 §§4–5 ↗5 / TECHNICAL FINDINGS
A failure across several layers.
Reactor physics, protection design, operating decisions and safety culture must be examined together.
Reactivity feedback
The positive void effect could reinforce a power increase in the accident configuration. The core was large, and spatial effects mattered.
INSAG-7 §2.2 ↗A protection-system design flaw
Initial rod insertion could add local reactivity. A command intended to shut down the reactor was not reliably protective in the relevant state.
INSAG-7 §§2.2, 4 ↗Information and operating conditions
Operating constraints and decisions mattered, but the hazards were not adequately communicated. A calculated margin was poorly integrated into real-time protection.
INSAG-7 §§2.3–3 ↗Revising the narrative
INSAG-7 revised the emphasis of the 1986 assessment. Technical design, regulation and organizational safety culture were essential to understanding the accident.
INSAG-7 §§4–5 ↗What changed after 1986?
Subsequent measures addressed control-rod design, shutdown performance, reactivity characteristics and operating restrictions. This exhibit concerns the 1986 Unit 4 configuration; it does not describe all later RBMK variants or evaluate current plants.
INSAG-7 §2.2 · Annex II §II-5 ↗The people affected are part of this history. Technical explanation cannot measure the loss experienced by workers, responders, families and displaced communities.