SCONE Guide

❮ ConfigurationTallies ❯

SCONE Verification Notice

SCONE is a research-oriented code with a smaller user base than MCNP, OpenMC, or SERPENT. Our examples are intended as educational guidance. For authoritative syntax, physics options, and nuclear data requirements, consult the official documentation.

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Neutron Sources in SCONE

Eigenvalue fission source convergence and fixed-source mode

In k-eigenvalue mode (type eigenPhysicsPackage;), SCONE iterates the fission source internally — no MCNP-style SDEF point source; control convergence with pop, inactive, and active. Fixed-source problems use type fixedSourcePhysicsPackage; and a source block (Shielding Examples).

Source Fundamentals

For eigenvalue calculations, source treatment is driven by pop, active, and inactive plus fission-source convergence behavior.

Eigenvalue header matches tutorial_config_testlib lines 5–15 (same text as in run_all.ps1 when embedded in the full file). Incomplete by itself — no geometry or nuclearData.

tutorial_config_testlib (lines 5–15)
type eigenPhysicsPackage;
pop      10000;
active   50;
inactive 20;
XSdata   ce;
dataType ce;

collisionOperator { neutronCE { type neutronCEstd; } }
transportOperator { type transportOperatorDT; }

inactiveTally {}
caalh/ReactorMCBrowse filesscone-examples/verify/tutorial_config_testlib

Verify harness (testLib + run_all.ps1)

In k-eigenvalue mode, SCONE converges a fission source internally — there is no separate point-source block like fixed-source problems. Convergence is controlled with pop, inactive, and active (see Basics).

Fixed-source point source (verified excerpt)

From tutorial_shielding_slab lines 15–20 — use with the full shielding deck in verify, not as a standalone eigen input.

tutorial_shielding_slab (lines 15–20)
source {
  type pointSource;
  r (2.5 0.0 0.0);
  particle neutron;
  E 1.0;
}
caalh/ReactorMCBrowse filesscone-examples/verify/tutorial_shielding_slab

Verify harness (testLib + run_all.ps1)

Advanced Source Definitions

In practice, you monitor spatial behavior with mapped fission tallies and axial/radial diagnostics before trusting active-cycle statistics.

Eigenvalue source-convergence workflow (checklist)

  1. Start with conservative inactive cycles (often 150–300 for large cores).
  2. Track cycle-wise k and 2D fission-rate maps.
  3. Increase inactive if the source shape still drifts into active cycles.
  4. Compare design variants only after convergence behavior is comparable.

Example: map the fission response during active cycles (same pattern as Tallies):

inactiveTally + activeTally excerpt from tutorial_examples_hub_testlib lines 17–31 — embed in a full eigen deck; the full hub file is in run_all.ps1.

tutorial_examples_hub_testlib (lines 17–31)
inactiveTally {}

activeTally {
  fissionRate {
    type collisionClerk;
    response (fission);
    fission { type macroResponse; MT -6; }
    map {
      type multiMap;
      maps (xax yax);
      xax { type spaceMap; axis x; grid lin; N 64; min -0.63; max 0.63; }
      yax { type spaceMap; axis y; grid lin; N 64; min -0.63; max 0.63; }
    }
  }
}
caalh/ReactorMCBrowse filesscone-examples/verify/tutorial_examples_hub_testlib

Verify harness (testLib + run_all.ps1)

Best practices (eigenvalue)

  • Start with enough inactive cycles that cycle-wise k and fission maps stabilize before active tallies.
  • Use mapped fission tallies (see Tallies) to visually confirm the source shape.
  • Increase pop and/or active to reduce statistical noise once convergence is believable.
  • For fixed-source runs, place the source block in a physically meaningful cell and verify with a low-cycles test.

Related Topics

❮ ConfigurationTallies ❯