NJOY Input Generator

Validation →

Form-driven NJOY-2016 deck builder with reactor-domain presets. Picks a preset → choose your isotope → tweak temperatures / self-shielding → copy or download a runnable deck. The template engine is deterministic; this page never asks an LLM to write NJOY cards.

mode

pick isotopes below; current preset / stages / sub-modules apply to all

Preset

Parameters

Isotope

Temperatures (K)

Whitespace- or comma-separated. NJOY broadens to each T in BROADR and condenses to multigroup in GROUPR. ACER uses the first T only (single-T per ACE file is the convention) — to get a multi-T ACE set, run separate batch entries with different T grids.

Output stages

PENDF

RECONR + sub-modules

GENDF

GROUPR (multigroup)

DRAGR

draglib (DRAGON)

ACER

single-T fast ACE (OpenMC / MCNP)

ERRORR

MF=33 multigroup covariance

PENDF sub-modules

RECONR

resonance reconstruction · always on

BROADR

Doppler broaden to T list

UNRESR

unresolved RR (deterministic)

PURR

prob tables (Monte Carlo)

HEATR

heating + KERMA + damage

GASPR

gas-production xs

THERMR

free-gas + S(α,β) (MT=221)

Emission order (matches PyNjoy reference): RECONR → BROADR → UNRESR → HEATR → GASPR → PURR → THERMR. UNRESR and PURR are mutually exclusive in practice — PURR for OpenMC/MCNP, UNRESR for DRAGON. PURR/UNRESR auto-pick by mass parity (odd → PURR, even → UNRESR, isomer → PURR).

THERMR — S(α,β) coupling

Couples THERMR with the matching ENDF thermal sublibrary. Picks the correct MAT (mat_inc + optional coherent-elastic mat_coh) and atom count from the PyNjoy SAB dispatch table. Use H₂O for H-1 in water, ZrH for H in zirconium hydride, BeO for Be in beryllia, etc. "Free-gas only" emits the MT=221 free-gas card without an ENDF Sab tape — fine for non-moderator isotopes. Options that don’t pair with the current iso (Fe + H₂O, U + ZrH-Zr, …) are greyed out so the deck can’t hit a silent NJOY rejection mid-stream.

GROUPR extras

MT=3 scattering total

adds an extra `3 /` card per T (full inelastic-scatter sum)

MT=300 resonance xs + matrix

emits `3 300 /` + `6 300 /` — needed for self-shielding diagnostics

MF=16 photon production

adds `16 /` per T — coupled n+γ transport (DONJON / SCALE)

All three are off by default — they extend the deck and aren't needed for most plotting / OpenMC workflows. Turn on for self-shielding work (MT=300), coupled n+γ transport (MF=16), or when downstream tools need the full inelastic sum on MT=3.

Self-shielding range (eV)

DRAGR autolib subgroup table covers this range. Structural isotopes use 4.63 eV – 1.05 MeV; actinides use 4.63 eV – 320 keV.

GROUPR fehi (eV)

Upper energy for the GROUPR flux calculation. Should match the self-shielding upper bound; for SHEM-370 IRENA the structural fehi is 1.05 MeV (Fe-56 / Cr-52 RRR).

Group structure

SHEM-281 (NJOY built-in IGN=24)

NJOY built-in mesh (IGN=24) — boundaries are not emitted in the deck; NJOY uses its hard-coded SHEM CEA 281-group structure.

Batch — sfr_shem281

Fe56 (MAT=2631, structural) — PENDF + GENDF + DRAGR, 5T, 10 dilutions

Pick isos from the grid, then tweak any per-iso overrides in the cards below. PURR / UNRESR auto-pick by mass parity (PyNjoy convention); per-iso preset-bound knobs (ssRange / fehi / dilutions) stay catalog-driven.

warningGROUPR fehi (1.86e+4 eV) and SS upper (1.23e+5 eV) differ by >1 % — for structural-flow isotopes these should match so flux & SS treatments cover the same energy range. · 33 iso(s):

Th230, Pa231, Pa233, U232, U233, U234, U236, U237, …+25

infodropped T = [1200] K — TSL caps at 1000 K. · 3 iso(s):

H1_ZRH, Zr90_ZRH, Be9

infodropped T = [1200, 1600, 2000] K — TSL caps at 1000 K. · 1 iso(s):

C12_GR

Selected (325)

tick cards → bulk-edit T / stages / S(α,β) / PURR-UNRESR

Bundle layout: runner_all.sh (master loop, ENDF_DIR=) · per-iso <HMAT>/runner.sh (cached, FORCE=1 to rebuild) · per-stage .in files · README.txt · convert_to_hdf5.py when ACER is enabled.