Natural-Circulation Loop Model: BWRX-300-Representative SMR

Overview

The BWRX-300 is the small modular reactor under construction at OPG's Darlington New Nuclear site. It has no recirculation pumps. Coolant flow comes entirely from natural circulation: dense water in the downcomer pushes against the lighter steam-water mixture rising through the core and a tall chimney. This project models that balance to show how core flow responds to reactor power.

What I'm building

• A 1-D loop model covering the downcomer, lower plenum, core, chimney and steam separators
• An energy balance that includes feedwater mixing, which sets the core inlet subcooling
• Two void-fraction models (homogeneous equilibrium and drift-flux) compared side by side
• A momentum-balance solver that finds the flow rate at each power level
• IAPWS water and steam properties via CoolProp

How I'm checking it

• Verification against an analytical single-phase solution
• Energy and mass balance closure, a nodal convergence study and an independent hand calculation
• Benchmarking against published data: the IAEA's nominal core flow figure and large-diameter chimney tests run at BWRX-300 conditions
• Sensitivity studies on loss coefficients, feedwater temperature, chimney height and axial power shape

Deliverables

• A formal calculation report (JW-TH-001) with numbered inputs, assumptions and references, revision control and independent verification
• A public GitHub repository with automated tests and one script that regenerates every figure

Tools

Progress

1. Scope, public design inputs and report structure
2. Single-phase model and analytical verification
3. Two-phase model (HEM and drift-flux)
4. Calibration, benchmarking and sensitivity studies
5. Calc report issued (Rev 0) and repository published

Educational project based on publicly available information. Not affiliated with GE Vernova Hitachi Nuclear Energy or Ontario Power Generation.