Nuclear Design Bureau Implosion — Compression, Casing and Criticality

Nuclear Design Bureau implosion, in game terms, is the compression step: you drive material inward so a sub-critical assembly becomes denser, hotter and finally self-sustaining. The official description is unusually specific about the physics underneath, naming hydrodynamics, neutron transport and thermonuclear fusion, and the store page promises real-time modelling of shockwaves, heat, radiation and chain-reaction behaviour. The practical problem is the same one the criticality lab exists to solve: knowing how close you are before you commit to a layout.

How the Game Models Implosion

The simulation is not a stat check, which is why the developer keeps patching it. It runs detonation physics in real time from the red button, and the roadmap says the detonation viewer is being refined with better shockwaves, damage radius and thermal radiation modelling, destructible buildings and targets, and finer grid resolution for stronger GPUs. That means the fidelity of your compression result is tied to both your design and the current build.

Modelled element	Documented detail
Shockwaves	Simulated in real time during detonation
Heat	Included in the real-time physics model
Radiation	Modelled, and displayed on the operator in the criticality lab
Chain reaction	Explicitly named in the core feature list
Neutron transport	Named in the store pitch and touched by a physics patch
Criticality estimate	Live Monte Carlo k-effective in the criticality lab

• Approach criticality in the lab rather than by intuition, because the k-effective estimate gives you a trend while the wall counter lags.
• Watch the operator, not just the instruments, since exposure accumulates on the character.
• Expect the numbers to move: one physics patch changed how fissile material resists compression and warned that yields would change.
• Keep early devices small, because large designs are compute-heavy and run slowly at minimum specification.

Layering and Casing Findings from Players

The developer publishes the loop and the physics, but not a build recipe, so the practical layering advice comes from player threads and should be treated as reported rather than authoritative. The most detailed thread describes a three-stage device, and the numbers in it come with the usual Early Access caveat.

Player finding	Reported detail
Overall shape	Lay the device out as an ellipse within an ellipse; a long potato-shaped outer ellipse with an egg-shaped second stage inside
Primary placement	Put the primary to one side with space around it rather than centred
Second stage	Fill the largest ellipse you can with D-T ice and give it its own thick casing
Casing thickness	Keep layers below roughly 20 units so x-rays and neutrons are not blocked
Tertiary	Use a large LiD sphere with concentric rings for neutron generation, and keep those rings sub-critical
Neutron activity	A reported peak around 10^28 in the third stage, with anything above roughly 10^26 enough for the reaction to be tritium-positive

• Foam and an outermost duralumin-uranium shell with gold lining recur in the reported working designs.
• Keeping tertiary rings sub-critical until the shockwave arrives is described as the key to stopping them activating early.
• Asymmetry is the most common cause of failure: players report the second stage generating the implosion through x-ray heating, so a lopsided first stage ruins it.
• A reported bug once made a particular fissile material unusable, and the thread's advice was to substitute another; check the patch notes for the current state rather than trusting the workaround.

Checking a Compression Design Before You Detonate

The workflow that the game itself recommends is measure, design, simulate, refine, and the measuring step is the one that saves the most rebuilds. Use the criticality lab first, then simulate, then diagnose. A physics patch also fixed several failure modes that used to look like design errors: hot gas not expanding, single particles slowing or stopping designs, a simulation refusing to restart after one broken run, and fusion yield not showing the percentage of fuel burned.

Two habits keep this loop productive. First, save your designs as you iterate, because the game keeps them in a design files box rather than preserving every experiment automatically. Second, read each patch note before trusting an old design, since compression resistance, neutron leakage and burn speed have all been changed at least once. For the whole loop in order, see the guide page; for the specific directive that asks for a first implosion device, see the rds-1 page.