Phoenix's Fission
A fission addon for GregTech modern, designed around peak configurability.
⬇ Download on Modrinth
A fission addon for GregTech Modern focused on cool, adaptable features and heavy configurability. It can be used standalone, but it’s primarily designed for pack developers who want to reshape reactor behavior, balance, and progression for their own packs.
There are 3 main reactor multiblocks:
Pressurized Fission Reactor
Uses Fission Coolers, Fission Moderators, and a Driver Fuel Rod to produce EU and waste.
Cooling is provided by all installed coolers (total HU/t).
Coolant consumption behavior is configurable:
Additive: every cooler adds to the coolant draw, or
Primary-only: only the “primary” (highest-tier / most dominant) cooler determines coolant use.
High Performance Breeder Reactor
Uses Fission Coolers, Fission Moderators, Blanket Rods (targets), and a Driver Fuel Rod to produce stronger fuels for future breeder cycles, plus some power.
Blanket processing supports fluid or item inputs/outputs (GT material IDs or Forge registry IDs).
Blanket usage behavior can be made configurable as well (additive blankets vs primary-only), matching the coolant model style.
Molten Salt Reactor
Uses MSR Liners and Fission Coolers to process molten salts.
Designed to process heavier fissile materials and slowly process them into safer more useful products.
Will accumulate Xenon Poisoning over time that you will need to extract from fluid hatches.
Has a different heat model focused around flow, not heat.
Custom UIs.
All 4 base machine classes have a custom UI for your viewing pleasure!
Base fission reactor and breeder reactor ui.
There are even graphs to see your safety at a glance!
And a math page!
Molten Salt Reactor UI.
Heat exchanger UI.
KubeJS Content Support
New Coolers, Moderators, Fuel Rods, and Blanket Rods can all be defined in KubeJS.
Key points:
Coolers now use pure Forge fluid registry IDs for coolant (example:
gtceu:distilled_water).Coolers may optionally define an output “hot” coolant (example: distilled water → steam).
- If the reactor can’t output the hot variant, it can optionally void the output (pack-configurable behavior), so the reactor can still run without requiring an output hatch in every build.
Usage behavior (coolant / fuel / blanket) can be driven by config toggles (additive vs primary-only).
Below is an example of each type.
StartupEvents.registry("block", event => {
// 1. CUSTOM FISSION COOLER
event.create('aether_flow_cooler', 'phoenix_fission:fission_cooler')
.displayName('Aether-Flow Cooler')
.tier(3) // Determines explosion scaling and tier-matching logic
.coolerTemperature(1025) // Active heat dissipation capacity (HU/t)
.coolantUsagePerTick(10) // Millibuckets of coolant fluid consumed per operation tick
.requiredCoolantMaterialId('phoenixcore:frost') // Input fluid registry ID
.outputCoolantFluidId('phoenixcore:warm_frost') // Output heated fluid registry ID
.tintColor(0xFF7DE7FF) // Does nothing but nessecary, leave default
.texture('kubejs:block/fission/aether_flow_cooler') // Note: Requires a matching block and active block texture (active is appended to the end)
.maskTexture('phoenix_fission:block/fission/cooler_mask'); // Optional mask texture layer
// 2. CUSTOM FISSION FUEL ROD
event.create('high_density_driver_rod', 'phoenix_fission:fission_fuel_rod')
.displayName('High-Density Driver Rod')
.tier(3) // Controls internal multi-block priority and explosion tiers
.baseHeatProduction(50) // Core HU/t heat produced before moderator modifiers
.durationTicks(1200) // Lifetime in ticks before burning another cycle of fuel
.amountPerCycle(1) // Quantity of fuel items consumed per cycle completion
.neutronBias(1) // Interacts with nearby Breeder/Blanket rod output instability weights
.fuelKey('gtceu:uranium_235_nugget') // Input item ID (Supports tags or specific registry IDs)
.outputKey('gtceu:depleted_uranium_235_nugget') // Output waste item ID
.texture('kubejs:block/fission/high_density_driver_rod'); // Note: Requires a matching block and active block texture (active is appended to the end)
// 3. CUSTOM FISSION MODERATOR
event.create('niobium_modified_silicon_carbide_moderator', 'phoenix_fission:fission_moderator')
.displayName('Nb-SiC Moderator')
.tier(4) // Primary moderator selection hierarchy weight
.euBoost(15) // Scaling factor for increasing EU generation output
.fuelDiscount(5) // Efficiency discount: Extends fuel rod duration ticks between cycles
.texture('kubejs:block/fission/niobium_sic_moderator');
// 4. CUSTOM BREEDER / BLANKET ROD
event.create('uranium_blanket_rod', 'phoenix_fission:fission_blanket_rod')
.displayName('U-238 Blanket Rod')
.tier(2) // Priority logic tier matching
.durationTicks(2400) // Total tick lifetime per transformation cycle
.amountPerCycle(1) // Item consumption rate per cycle completion
.inputKey('gtceu:uranium_238_nugget') // Target breedable material registry entry
// Dynamic Outputs: .addOutput(RegistryKey, Weight, Instability)
.addOutput('gtceu:plutonium_nugget', 70, 1)
.addOutput('gtceu:plutonium_241_nugget', 20, 3)
.addOutput('gtceu:plutonium_238_nugget', 10, 4) // High instability means higher output if neutronBias matches
.texture('kubejs:block/fission/uranium_blanket_rod');
// 5. CUSTOM MOLTEN SALT REACTOR (MSR) LINER
event.create('advanced_msr_liner', 'phoenix_fission:msr_core_liner')
.displayName('Advanced MSR Core Liner')
.tier(3)
.fluidFlowRate(40) // Max mB/t fluid flow processing rate through the liner
.heatPerMb(15.5) // Thermal energy generation constant per millibucket processed
.inputFluidId('gtceu:enriched_naquadah_salt') // Molten salt fuel blend input
.outputFluidId('gtceu:depleted_naquadah_salt')
.texture('phoenix_fission:block/fission/liner_base'); // Also needs an active texture
});
- Ships as PhoenixFission-0.1.0-slim.jar — drop this file into the mods folder
- Download size: 46.6 MB
- Download link checked 6 Aug 2026 — working
These come from our own check of the pack file, not from the source page.