Chernobyl

Description

Chernobyl is a nuclear power plant management environment where agents operate reactors through crisis scenarios inspired by four real historical disasters: Chernobyl (1986), Three Mile Island (1979), Fukushima Daiichi (2011), and Windscale (1957). The simulation couples point kinetics neutronics, thermal-hydraulics, xenon-135 dynamics, fuel integrity, containment physics, and Wigner energy models to create realistic reactor behavior.

Note: This is a synthetic environment which was majority AI-generated; we recommend testing it thoroughly before any use in an RL pipeline.

Capabilities

• Diagnosing reactor emergencies from instrument readings (some of which may be malfunctioning or misleading)
• Managing control rods, pumps, valves, and safety systems under crisis conditions
• Reasoning about reactor physics including reactivity feedback, xenon poisoning, and decay heat
• Trading off competing safety objectives (e.g., venting containment releases radiation but prevents hydrogen explosion)
• Multi-step sequential decision-making under uncertainty

Compute Requirements

Agents interact with the environment through environment-specific tools only. No sandbox or filesystem access is provided.

License

MIT

Tasks

There are 40 training tasks across 4 scenarios (each with 10 random seeds):

• chernobyl_normal_ops (RBMK) -- Steady 3200 MWt operation with random perturbations (pump trips, load changes). Maintain power safely.
• tmi_porv_stuck (PWR) -- Post-scram. PORV stuck open but indicator shows closed. Diagnose the stuck valve and close the block valve to stop the LOCA.
• fukushima_blackout (BWR) -- Post-tsunami station blackout on a generic BWR-4. All AC power lost, batteries draining, RCIC running on steam. Manage diminishing resources.
• windscale_anneal (Windscale Pile) -- Ninth Wigner energy anneal with graphite temperature rising unexpectedly and thermocouple blind spots.

There are 110 test tasks across all 11 scenarios (each with 10 random seeds). The additional test-only scenarios include:

• chernobyl_xenon_pit (RBMK, hard) -- Power collapsed to 30 MWt with xenon building and most rods withdrawn.
• chernobyl_test_start (RBMK, expert) -- Turbine test beginning at 200 MWt with ORM=6 and ECCS disabled.
• tmi_loss_of_coolant (PWR, hard) -- Mid-event LOCA with operators having throttled HPI and core starting to uncover.
• tmi_recovery (PWR, expert) -- Core 40% uncovered, cladding at 1100 C, hydrogen generating. Prevent complete meltdown.
• fukushima_rcic_failure (BWR, expert) -- RCIC failed, batteries at 10%, must depressurize and establish low-pressure injection.
• fukushima_hydrogen (BWR, expert) -- Core damage underway, H2 at 8% in containment, must vent while minimizing radiation release.
• windscale_fire (Windscale, expert) -- Fire detected in pile, must choose between air (fans flames) or water (hydrogen/steam explosion risk).

Reward Structure

This is a dense, verifiable reward environment. Rewards are calculated after each action based on five weighted safety components:

Additional penalties apply for exceeding cladding temperature limits and worsening fuel damage. Terminal conditions (core meltdown, hydrogen detonation, catastrophic release, successful stabilization) provide additional terminal rewards from -1.0 to +1.0.

We do not use LLM graders for this task.

Data

No external data files are required. All scenario parameters and physics constants are defined in the source code based on publicly available reactor design parameters and nuclear engineering references (NUREG reports, IAEA safety series, INSAG-7 Chernobyl report).

Tools

Agents have 10 environment-specific tools:

Time Horizon

Chernobyl scenarios range from 150 to 300 maximum steps, with timesteps from 15 seconds to 10 minutes depending on scenario urgency. Each time-advancing tool call advances the simulation by one timestep.

Environment Difficulty

Scenarios are rated at three difficulty levels:

• Normal: Routine operation with perturbations (chernobyl_normal_ops)
• Hard: Active crisis requiring correct diagnosis and intervention (tmi_porv_stuck, fukushima_blackout, chernobyl_xenon_pit, windscale_anneal, tmi_loss_of_coolant)
• Expert: Severe accident management with cascading failures and no-win tradeoffs (chernobyl_test_start, tmi_recovery, fukushima_rcic_failure, fukushima_hydrogen, windscale_fire)

Other Environment Requirements

There are no further environment requirements. The environment works out of the box with the OpenReward endpoint without any secrets or external API keys.

Safety

Agents in the simulation operate a simulated nuclear reactor and must make safety-critical decisions under uncertainty. The environment models historically accurate instrument failures (e.g., TMI PORV indicator showing "CLOSED" when stuck open) to test whether agents can reason about unreliable information.

The environment does not present direct real-world safety risks, as all physics are simulated. However, the environment teaches reactor operation skills that, in an extreme case, could be misapplied. The physics models are simplified approximations (point kinetics, 1D thermal-hydraulics) and would not be sufficient for actual reactor operation.

Citations

@dataset{GRChernobyl,
  author    = {General Reasoning Inc. Team},
  title     = {Chernobyl},
  year      = {2026},
  publisher = {OpenReward},
  url       = {https://openreward.ai/GeneralReasoning/Chernobyl}
}