Codex Energy Fission Reactor

Fission Reactor

The Fission Reactor burns Uranium Fuel Rods and turns their heat into Hot Coolant. It makes no electricity itself: a Heat Exchanger boils feedwater with the Hot Coolant and sends the water back, and the steam drives a Steam Turbine. It is the first large heat source of the mid game and needs the whole fuel cycle behind it.

How it works

1. Fuel rods come in through the Item Input Port. Every Fuel Assembly holds one rod.
2. The neutron flux of the core follows its reactivity: Graphite Moderators raise it, inserted Control Rods and a hot core lower it.
3. The flux burns the fuel and heats the core. Above 100 °C the Coolant Channels turn cooling water into Hot Coolant and carry the heat away.
4. Hot Coolant leaves through the Fluid Output Port to the Heat Exchanger; its cooled water comes back through the Fluid Input Port.
5. Spent rods leave as Depleted Fuel Rods through the Item Output Port.

Building

Shown size: 5 wide, 5 high, 5 deep (adjustable: Width 5–15, Height 5–15, Depth 5–15).

One example of many: within the rules on this page, size and arrangement are up to you; the Build Projector shows the plan in every allowed size.

	Key	Block	Count
	A	Reactor Casing	84
	E	Control Rod	8
	B	Shielded Sight Glass	8
	C	Graphite Moderator	7
	D	Coolant Channel	6
	F	Fuel Assembly	6
	I	Fluid Input Port	1
	J	Fluid Output Port	1
	G	Item Input Port	1
	H	Item Output Port	1
	K	Reactor Instrumentation	1
	0	Fission Reactor Controller	1

Step by step

Each picture adds one layer, from the bottom up; the newest layer is bright. The controller wall faces you on the left.

Step 1: Layer 1

Parts in this step: Reactor Casing (A) ×25

Step 2: Layer 2

Parts in this step: Reactor Casing (A) ×11, Graphite Moderator (C) ×5, Coolant Channel (D) ×2, Fuel Assembly (F) ×2, Shielded Sight Glass (B) ×2, Fission Reactor Controller (0) ×1, Item Input Port (G) ×1, Item Output Port (H) ×1

Step 3: Layer 3

Parts in this step: Reactor Casing (A) ×11, Control Rod (E) ×4, Shielded Sight Glass (B) ×3, Coolant Channel (D) ×2, Fuel Assembly (F) ×2, Fluid Input Port (I) ×1, Fluid Output Port (J) ×1, Graphite Moderator (C) ×1

Step 4: Layer 4

Parts in this step: Reactor Casing (A) ×13, Control Rod (E) ×4, Shielded Sight Glass (B) ×3, Coolant Channel (D) ×2, Fuel Assembly (F) ×2, Graphite Moderator (C) ×1

Step 5: Layer 5

Parts in this step: Reactor Casing (A) ×24, Reactor Instrumentation (K) ×1

Rules

• Size: at least 5 × 5 × 5, at most volt.maxFissionReactorSize (default 15, allowed 5–32) blocks in every direction. Width, height and depth are free.
• Edges and corners: only Reactor Casing.
• Walls, floor and roof: Reactor Casing, Shielded Sight Glass, Inspection Hatches, Reactor Instrumentation, Emergency Shutdown, the ports and the controller.
• Inside: air, Fuel Assemblies, Control Rods, Graphite Moderators and Coolant Channels, in any arrangement.
• Needed: at least one Fuel Assembly, one Control Rod and one Coolant Channel.
• Control rod columns: the rods are driven in from the roof. Every Control Rod must have a Control Rod above it, up to the top interior layer.
• Controller: in a wall face (not on an edge), front facing out, with the inside directly behind it.
• Ports (each works only on its outer face):
• Item Input Port: Uranium Fuel Rods in (nothing else is accepted).
• Item Output Port: Depleted Fuel Rods out.
• Fluid Input Port: cooling water in (water only).
• Fluid Output Port: Hot Coolant out.
• Wall parts: Reactor Instrumentation measures the core and is needed for the automatic SCRAM. An Emergency Shutdown block scrams the reactor while it gets a redstone signal. An Inspection Hatch opens the controller screen from wherever it sits.

Note

Shielding built in Shielded Sight Glass also counts as radiation shielding in the world, like lead. See Radiation.

Reactivity and power

The standard model (when the Advanced Reactor Model is off) works like this:

• Moderation grows with the number of moderator blocks per loaded fuel rod: 0.3 without moderators, full (1.0) at 0.75 moderator blocks per loaded rod or more.
• Control rods: one Control Rod covers 4 loaded assemblies. With fewer rods than that, even full insertion leaves part of the reactivity: the core cannot be shut down completely.
• Temperature: every degree above 20 °C takes 0.00025 off the reactivity. A hotter core runs weaker, so a cooled reactor settles by itself.
• Reactivity = moderation × (1 − insertion × rod coverage) − temperature effect, never below 0.
• Neutron flux follows the reactivity with a lag: every tick it closes 0.05 of the gap.
• Thermal output (HU per tick) = flux × loaded rods × 400.

The control rods move 1 % per tick towards their target, 10 % per tick during a SCRAM. A new reactor starts with all rods fully inserted.

Tip

Power from the rods Without moderators the core reaches at most 30 % flux. Mix moderators in until there are three for every four fuel assemblies, then the rods alone decide the power.

Fuel

• Every loaded rod gives 10,000,000 HU of heat, divided by the server setting volt.fuelConsumptionMultiplier (default 1.0, allowed 0.01–100.0).
• Empty assemblies are refilled from the input slots, but not while the reactor is scrammed or failed, and not while depleted rods still wait for room in the output.
• When the remaining fuel drops by one rod's worth, one rod leaves the core as a Depleted Fuel Rod. When the output slots are full, it waits and no new rod is loaded.
• 5 % of the heat of the burned fuel comes out later as after-heat. A shut-down core therefore keeps warming for a while; keep the cooling running.

Cooling

• Above 100 °C every Coolant Channel turns up to 50 mB of water per tick into Hot Coolant. Each mB carries 10 HU away.
• The channels open with the temperature: at 100 °C they move nothing, 200 °C higher they run at full flow.
• Cooling capacity (HU per tick) = channels × 50 × 10. Plan at least as much as the thermal output you want.
• The water tank and the Hot Coolant tank each hold 16,000 mB, or one second of the channels' full flow if that is more.
• One Heat Exchanger takes up to 100 mB of Hot Coolant per tick. A large reactor needs several.

Important

Close the loop The Hot Coolant tank must be emptied. If it is full or the water runs out, the channels stop, the alarm says "Coolant problem" and the core heats up quickly.

Alarms and escalation

Core temperature / state	Alarm	What happens
below 600 °C	Normal	–
from 600 °C	Warning: high temperature	–
from 900 °C	Overheating	Smoke and flames at the controller; Reset is refused.
channels move less than half of what they should (above 120 °C)	Coolant problem	Steam at the controller. With instrumentation and above 600 °C: automatic SCRAM.
above 1,200 °C	Fuel damage!	Core damage grows every tick, the faster the hotter. Reset is refused.
from 1,800 °C or 100 % damage	Severe failure	Meltdown: see below.

The core never gets hotter than 3,000 °C.

SCRAM and reset

• SCRAM drives all rods in at full speed. It comes from the SCRAM button, from a redstone signal at an Emergency Shutdown block (checked every 4 ticks), automatically, or when the structure breaks while fuel is loaded.
• Automatic SCRAM needs Reactor Instrumentation in a wall. It triggers at the set limit (default 900 °C, adjustable from 300 to 1,200 °C in steps of 50 °C) and when the coolant falls short above 600 °C.
• While scrammed the rod buttons do nothing and no fresh rods are loaded.
• Reset clears the SCRAM. It is refused while the alarm says "Overheating" or "Fuel damage!". After a severe failure it only works once the core is at 100 °C or below; it also clears the core damage. After a reset the rods stay inserted: withdraw them again with -.

Severe failure (meltdown)

At 1,800 °C or 100 % core damage the reactor fails:

• All loaded fuel is destroyed; nothing comes back.
• A meltdown explosion happens at the core centre, stronger with more assemblies. Whether it breaks blocks, hurts players and how strong it is depends on the server's safety settings, see Incidents.
• The site stays radioactive for a while, see Radiation.
• The state line says "Severe failure – let it cool, then reset".

The screen

• Status and Alarm lines, and the Auto-SCRAM line (on, off or "needs instrumentation").
• Bars: core temperature (up to the failure temperature), coolant, Hot Coolant and control rods (inserted).
• Values: core temperature, coolant outlet, neutron flux, reactivity, rod insertion, rod target, thermal output, heat removed, cooling capacity, coolant flow, fuel rods loaded, fuel assemblies, fuel left, core damage, Auto-SCRAM at.
• A flow diagram: fuel → core → Hot Coolant → heat exchanger, with the coolant flow.
• Buttons: SCRAM, Reset, Auto-SCRAM (switch), +/- for the rod target (±10 %), and -/+ for the Auto-SCRAM limit (±50 °C).
• With the Advanced Reactor Model a core view button appears, see Advanced Reactor Model.
• 4 fuel slots and 5 output slots.

Status line

Status	Meaning
Not formed	The structure is not complete (the screen shows the structure problem instead).
No fuel	Formed, but no rod is loaded.
Subcritical	Fuel is loaded, but the flux is (nearly) zero: rods in, or not enough reactivity.
Critical, producing heat	The chain reaction runs.
SCRAM – reset required	Scrammed; press Reset.
Severe failure – let it cool, then reset	The core failed; wait until it is cool enough.

Automation

• Pipes put fuel rods in through the Item Input Port and take Depleted Fuel Rods out through the Item Output Port.
• Pipe water into the Fluid Input Port and take Hot Coolant out of the Fluid Output Port. The returned water of the Heat Exchanger can go straight back in.
• A redstone signal at an Emergency Shutdown block scrams the reactor; a Sensor Module can read the reactor (temperature, coolant temperature, flux, control rods, power output, fuel level, alarm and reactor state) and give a signal.

Error messages

Message	What to do
The controller must sit in a wall, front facing out	Put the controller into a wall face, front outwards, with the inside behind it.
Structure too small (…)	Build at least 5 × 5 × 5.
Structure too large or not closed near …	Close the wall there, or stay within volt.maxFissionReactorSize (default 15, allowed 5–32) blocks.
Wrong block at … (expected: Reactor Casing)	Only Reactor Casing on edges and corners.
Wrong block at … (expected: …)	Only the wall parts and the core parts listed in the rules.
Missing parts: …	Add at least one Fuel Assembly, one Control Rod and one Coolant Channel.
Control rods must form columns up to the top interior layer (near …)	Fill the column above that Control Rod with Control Rods up to the roof.
Port not allowed here: …	Only item and fluid input and output ports work on a reactor.
Second controller at …	Remove the other controller.

Breaking it

• When the structure breaks while fuel is loaded or the flux is above zero, the reactor scrams. The core keeps cooling down slowly, but without cooling.
• Breaking the controller drops the fuel and depleted rods in its slots; the fuel loaded in the core is lost with the controller.

In the world

• While the reactor runs, the control rods slide up out of the core by how far they are withdrawn, and a blue Cherenkov glow fills the inside, the brighter the higher the flux.
• Fuel assemblies, moderators and control rods glow red-hot from about 250 °C to the overheating temperature.
• A running reactor radiates: up to 4 damage per second at its centre at full flux, less further away and behind shielding.

Tip

A safe first reactor Start with the example: it is fully moderated, every fuel assembly lies between control rod columns and its channels carry full power away. Fill the input with rods and the water tank, connect a Heat Exchanger, then withdraw the rods step by step and watch the core temperature. Build Reactor Instrumentation in from the start: the automatic SCRAM saves the fuel when the water runs out.

Warning

Fewer rods, no off switch Every Control Rod only covers 4 assemblies. A core with too few rods keeps running even with all rods in. Build enough rods before you add fuel.