htgr-desalination

Python simulation of a scaled High-Temperature Gas-Cooled Reactor (HTGR) coupled to a hybrid Multi-Effect Distillation (MED) desalination complex.

Based on the Imperial College London HTGR / HR group design project (2026) , a 300 MWth scaled HTTR reactor supplying zero-emission freshwater to 80,000 people while offsetting 267,000 tonnes of CO₂ per year.

The original model was built in MATLAB/Simulink with Python (CoolProp) for real-gas helium properties. This repository ports the core physics into a clean Python package.

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Physics Modules

Module	Description
kinetics.py	6-group delayed-neutron point kinetics ODEs
thermal_core.py	3-node lumped thermal model (fuel/moderator/coolant)
power_cycles.py	Helium Brayton + Steam Rankine combined cycle
desalination.py	MED freshwater production, CO₂ offset, economics

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Reactor Architecture

HTTR Core (300 MWth, 950°C He outlet)
    │
    ├── Helium Brayton Cycle (primary)
    │       Compressor → Reactor → Gas Turbine → HRSG
    │
    └── Steam Rankine Cycle (secondary)
            HRSG → Steam Turbine → MED Desalination Plant
                                         │
                                    12,000 m³/day freshwater
                                    ~80,000 people served

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Installation

git clone https://github.com/defnalk/htgr-desalination.git
cd htgr-desalination
pip install -r requirements.txt

Quick Start

from htgr import PointKinetics, ThermalCore, MEDDesalination

# Simulate a reactivity transient
pk = PointKinetics(Q_nominal=300e6)
t, P, Q = pk.simulate(t_end=400, rho_step=0.001, step_time=100)

# Check thermal core response
tc = ThermalCore()
print(f"He outlet at nominal: {tc.helium_outlet_temperature(300e6):.1f} K")

# Desalination performance
med = MEDDesalination(GOR=11.1)
print(f"Daily production:  {med.daily_production():,.0f} m³/day")
print(f"Population served: {med.population_served():,} people")
print(f"CO₂ avoided:       {med.co2_saved_annual()['total_t_yr']:,} t/yr")

Run the Full Simulation

python examples/full_simulation.py

Produces a 4-panel figure:

Panels:

• A — Point kinetics power transient (reactivity pulse)
• B — Core temperature response (fuel / moderator / coolant)
• C — 3D freshwater production surface (GOR × availability)
• D — Annual CO₂ emissions offset breakdown

Running Tests

python -m pytest tests/ -v

21 tests, all passing.

Key Design Parameters (from group report)

Parameter	Value
Reactor thermal power	300 MWth
Helium flow rate	105 kg/s
Core outlet temperature	950 °C
Combined cycle electrical output	30–50 MWe
MED GOR	11.1
Daily freshwater production	~11,400 m³/day
Population served	~80,000
Annual CO₂ offset	267,000 t/yr
30-year CO₂ saving	~8 million t
Project IRR	27%
CAPEX payback	4.3 years

Physics Background

Point Kinetics

The reactor neutron population is governed by 7 coupled ODEs — one for normalised power P(t) and six for delayed-neutron precursor groups Cᵢ(t):

dP/dt  = [(ρ(t) − β) / Λ] P + Σ λᵢ Cᵢ
dCᵢ/dt = (βᵢ / Λ) P − λᵢ Cᵢ

For subcritical-prompt insertions (ρ < β), a reactivity pulse produces a characteristic power spike followed by return to equilibrium — exactly as validated in the group report against HTTR literature data.

Thermal Core

Three lumped nodes (fuel Tf, moderator Tm, coolant Tc) with energy balance ODEs and negative temperature feedback coefficients (Doppler + moderator), ensuring inherent passive safety.

Why Combined Cycles?

The Helium Brayton cycle extracts work from 950 °C exhaust; the Steam Rankine bottoming cycle captures residual heat at 673 °C, providing the precise steam quality (70 °C, 0.31 bar) required for Multi-Effect Distillation. Combined Carnot efficiency: 72% vs 24.5% for Brayton alone.

References

• IAEA Nuclear Desalination programme
• HTTR design documentation (Japan Atomic Energy Agency)
• Smith, Van Ness & Abbott — Chemical Engineering Thermodynamics
• El-Dessouky & Ettouney — Fundamentals of Salt Water Desalination