Nuclear Explosions

Nuclear Explosions

This page explains what a nuclear explosion actually does, from the flash to the last bit of soot in the sky.

Sizes

Source	Crater radius	Blast zone	Fallout zone	Radiation at ground zero
Little Man (bomb, Nuclear Missile, MIRV warhead)	72	144	288	40 RAD/s
Fat Man (bomb, ICBM)	160, down to bedrock	320	640	80 RAD/s
Mark 6 (missile only)	224, down to bedrock	448	896	120 RAD/s
Reactor meltdown	28	56	112	140 RAD/s

All radii are in blocks. The blast zone is always twice the crater radius, the fallout zone four times. Little Man and Fat Man radii can be changed in the config, Mark 6 is always 1.4 × Fat Man.

What happens, in order

1. The flash

The flash arrives first, before anything else. Everyone who is looking at it gets flash blinded. Anyone with a free line of sight also gets Flash Burns, an effect that hurts every now and then and slows you down. A wall between you and the fireball protects you from the burns.

2. The fireball

Everything inside the fireball is vaporized. Players and mobs there just die.

3. The crater

Everything inside the crater radius is removed. The crater floor turns into Trinitite. Fat Man and Mark 6 go all the way down to bedrock in the middle (you can turn that off in the config). By default even obsidian and other very blast resistant blocks are vaporized near the center.

4. The shockwave

The shockwave moves outward at 3.5 blocks per tick (70 blocks per second). In the blast zone:

• Trees snap and turn into Charred Logs
• Buildings partly collapse
• The ground burns into Scorched Earth
• Some broken blocks get thrown outward as debris and land somewhere else as rubble
• Players and mobs take damage and get knocked away

5. Fallout zone

Further out, plants wither, grass dies and a layer of Radioactive Fallout settles on everything. This is where most of the long-term radiation comes from.

6. Mushroom cloud and aftermath

• The mushroom cloud stays visible for about 5 minutes
• Black rain starts about 75 seconds after the blast and lasts until about 10 minutes after. It's radioactive if you stand in it under open sky.
• The sky stays brown and smoky and soot hangs in the air. It starts clearing after 20 minutes and is gone after 40.
• A fallout cloud drifts away with the wind and drops radiation on the chunks below it for about 10 minutes.

All of this only happens inside the fallout zone. Walk out of it and the weather is normal again.

Radiation is covered in detail on Radiation and Fallout.

Bunkers

You can survive a nuclear blast in a proper bunker. Any block with a blast resistance of 600 or more stops the shockwave. That includes:

• Reinforced Concrete (and its stairs, slabs, walls)
• Concrete Tiles
• Armored Glass
• Bunker Door
• Obsidian

Lead bricks are great against radiation but don't stop the shockwave. A good bunker uses concrete for the walls and lead on the inside.

How it works:

• If there is such a block between you and the explosion within 10 blocks, the shockwave mostly passes you. You take a fraction of the damage, don't get thrown around and don't catch fire.
• Blocks behind a bunker wall (seen from the explosion) stay standing.
• Anything under a bunker roof doesn't get hit by the shockwave.
• Inside the crater radius nothing helps. That gets vaporized.

For radiation afterwards you want lead, water or concrete around you. See Radiation and Fallout.

Performance

Explosions this big would normally freeze a server. Atomcraft spreads the work over many ticks with a fixed time budget (12 ms per tick by default, shared by all running explosions). The server keeps running smoothly while the crater forms.

Chunks that aren't loaded during the explosion aren't skipped. They get devastated later, as soon as someone loads them. This is saved, so it even works after a restart. Ground zero stays loaded for 5 minutes after the blast.

Shaders

The mushroom cloud, flash, shockwave and sky use their own shaders. With Iris or Oculus active, the mod detects the shader pack and switches to fallback rendering where needed.