OWEN
Open Workspace for Engineered Neutronics
The nuclear reactor modeling toolkit for VS Code & Cursor — syntax highlighting, a visual lattice builder, geometry preview, deep input validation, and workflow automation for MCNP, OpenMC, Serpent, and SCONE.
A BelvoirDynamics product · part of ReactorMC
OWEN brings first-class editor support for the four major Monte Carlo neutron-transport
codes to VS Code and Cursor. Write decks faster with smart snippets, catch mistakes before
you run with language-aware validation, build lattices visually, and launch solvers without
leaving your editor.
Features
| Feature |
Description |
| Syntax highlighting |
TextMate grammars for MCNP (.i, .mcnp, .inp), Serpent (.serp), and SCONE (.scone). OpenMC is detected from Python files that import openmc. |
| Snippets |
Ready-to-edit decks: PWR pin cell, 17×17 PWR assembly, criticality array, and shielding slab for MCNP; full OpenMC pin/assembly Python scripts; SCONE fuel pin, 5×5 assembly, and shielding tutorials. |
| Lattice Builder |
A visual grid editor that generates MCNP / OpenMC / Serpent lattice code from a few clicks. |
| 3D geometry preview |
Three.js webview rendering of MCNP cz cylinders, with graceful empty-states for other codes. |
| Deep validation |
Language-aware diagnostics with codes — ZAID format, density/fraction sign conventions, mt/S(α,β) hydrogen checks, macrobody parameter counts (MCNP); IndependentSource/RectangularPrism API checks (OpenMC); cuboid vs rect, trcl, CLI omp (Serpent); aceNeutronDatabase, temperature-suffix matching, pinUniverse radii/fills (SCONE). |
| Workflow automation |
One-command simulation runner that launches the right solver in a dedicated terminal. |
| Parametric sweep |
JSON-described parameter sweeps with per-run input mutation, output capture, k-eff parsing, and a manifest + TSV summary. |
| Material insertion (NRDP) |
Insert reactor materials from the Nuclear Reactor Data Project database — bundled snapshot with optional live refresh from reactormc.net, language-aware output. |
| Community Library |
Browse and insert community-approved models (opt-in via owen.community.enabled; you supply your own Supabase backend). |
| Tutorials |
Deep-links into the reactormc.net learning material via OWEN: Open Tutorial. |
Install
From the Marketplace (once published):
- Open the Extensions view (
Ctrl+Shift+X / Cmd+Shift+X).
- Search for OWEN and click Install — or install
belvoirdynamics.owen-neutronics.
From Open VSX (Cursor, VSCodium, etc.): install belvoirdynamics/owen-neutronics.
From a VSIX (available now via GitHub Releases):
code --install-extension owen-neutronics-0.1.0.vsix
# Cursor:
cursor --install-extension owen-neutronics-0.1.0.vsix
Or in the editor: Extensions view → ... menu → Install from VSIX….
Commands
Open the Command Palette (Ctrl+Shift+P / Cmd+Shift+P) and type OWEN:
| Command |
Description |
OWEN: Open Lattice Builder |
Visual lattice grid editor |
OWEN: Validate Input File |
Deep MCNP / OpenMC / Serpent / SCONE checks |
OWEN: Run Simulation |
Launch the appropriate solver in a dedicated terminal |
OWEN: Run Parameter Sweep |
Generate and run a JSON-described sweep |
OWEN: Open 3D Geometry Preview |
Three.js webview (MCNP cylinders) |
OWEN: Open Tutorial |
Jump to a reactormc.net tutorial page |
OWEN: Insert Material from Database |
NRDP material picker, language-aware |
OWEN: Search Reactor Library |
Community Library browser (disabled by default) |
Configuration
All settings live under the OWEN section (Ctrl+, → search "owen"):
| Key |
Default |
Notes |
owen.mcnp.executable |
mcnp6 |
Path to the MCNP executable |
owen.serpent.executable |
sss2 |
Path to the Serpent executable |
owen.openmc.executable |
openmc |
Non-Python OpenMC entry point only |
owen.openmc.pythonExecutable |
python |
Interpreter for OpenMC model scripts |
owen.scone.executable |
scone |
On Windows, SCONE typically requires WSL |
owen.simulation.workingDirectory |
"" |
Empty = the input file's directory |
owen.nrdp.live |
true |
Live-fetch NRDP snapshots when online |
owen.nrdp.endpoint |
https://reactormc.net/data |
Base URL for live NRDP JSON |
owen.community.enabled |
false |
Enable the Community Library browser |
owen.supabase.url |
"" |
Supabase project URL (you supply this) |
owen.supabase.anonKey |
"" |
Supabase anon/public key (you supply this) |
The Community Library is off by default and ships with no credentials. To use it,
point owen.supabase.url / owen.supabase.anonKey at your own Supabase project.
Requirements
OWEN is an editor toolkit — it does not bundle the Monte Carlo solvers. To run simulations,
install and point the settings above at your own builds of:
- MCNP (Los Alamos National Laboratory — export-controlled, requires a license)
- OpenMC (open source; run via the Python interpreter you configure)
- Serpent (VTT — requires a license)
- SCONE (University of Cambridge — open source; on Windows it typically runs under WSL)
Syntax highlighting, snippets, validation, the lattice builder, and geometry preview all work
without any solver installed.
Supported languages
| Language |
Highlighting |
Snippets |
Validation |
Runner |
| MCNP |
Yes |
Yes |
Yes (deep) |
mcnp6 inp=… |
| OpenMC (Python) |
Via Python ext |
Yes |
Yes (deep) |
python <file> |
| Serpent |
Yes |
Yes |
Yes (deep) |
sss2 <file> |
| SCONE |
Yes |
Yes |
Yes (deep) |
scone <file> (WSL on Windows) |
- ReactorMC — tutorials, the community library, and the NRDP material data that powers OWEN.
- GROVES — the companion desktop editor for the same input languages.
License
MIT © 2026 BelvoirDynamics.
