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Add k-infinity estimator for IndependentOperator #4053

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72be529
Add k-infinity estimator for IndependentOperator
EdenRochmanSharabi Aug 6, 2026
3449f4e
Refactor k-infinity estimator per review suggestions
EdenRochmanSharabi Sep 16, 2026
3bcb558
Merge upstream develop, resolve nuclide.h conflict
EdenRochmanSharabi Sep 16, 2026
3649e66
some mechanical fixes
GuySten Sep 16, 2026
3006080
Address review: volume fix, precondition, C++ refactor, docstrings
EdenRochmanSharabi Sep 17, 2026
bac36b6
some more fixes
GuySten Sep 17, 2026
b83ba27
fix the test
GuySten Sep 17, 2026
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15 changes: 15 additions & 0 deletions docs/source/usersguide/depletion.rst
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Expand Up @@ -270,6 +270,21 @@ transport-depletion calculation and follow the same steps from there.
the depletion chain with at least one reaction, that reaction will not be
simulated.

When the microscopic cross section data includes both 'fission' and
'nu-fission' cross sections and no explicit ``keff`` value is provided,
:class:`~openmc.deplete.IndependentOperator` automatically estimates the
infinite multiplication factor at each depletion step::

op = openmc.deplete.IndependentOperator(materials, fluxes, micros)

The estimate is computed as the ratio of the neutron production rate to the
neutron loss rate based on the one-group reaction rates and is reported as the
eigenvalue in the depletion results, which can be retrieved with
:meth:`~openmc.deplete.Results.get_keff`. Consistent with the definition of
the multiplication factor used elsewhere in OpenMC, neutrons produced in
(n,xn) reactions are not counted as production; instead, each (n,xn) reaction
reduces the loss term by :math:`x - 1`.

.. _micros:

Loading and Generating Microscopic Cross Sections
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14 changes: 14 additions & 0 deletions include/openmc/nuclide.h
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Expand Up @@ -84,6 +84,20 @@ class Nuclide {
double collapse_rate(int MT, double temperature, span<const double> energy,
span<const double> flux) const;

//! \brief Calculate flux-averaged nu-fission cross section
//
//! Computes the one-group nu(E)*sigma_f(E) collapsed against a multigroup
//! flux, using the same integration scheme as collapse_rate but reading
//! the pre-tabulated nu-fission cross section (XS_NU_FISSION), which sums
//! over all partial fission reactions.
//!
//! \param[in] temperature Temperature in [K]
//! \param[in] energy Energy group boundaries in [eV]
//! \param[in] flux Flux in each energy group (not normalized per eV)
//! \return Flux-averaged nu-fission cross section, or 0.0 if not fissionable
double collapse_nu_fission_rate(double temperature, span<const double> energy,
span<const double> flux) const;

//! Return a ParticleType object representing this nuclide
ParticleType particle_type() const { return {Z_, A_, metastable_}; }

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172 changes: 86 additions & 86 deletions openmc/deplete/chain.py
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Expand Up @@ -27,94 +27,94 @@
import openmc.data


# tuple of (possible MT values, secondaries)
ReactionInfo = namedtuple('ReactionInfo', ('mts', 'secondaries'))
# tuple of (possible MT values, secondaries, neutrons emitted in exit channel)
ReactionInfo = namedtuple('ReactionInfo', ('mts', 'secondaries', 'neutrons_out'))

REACTIONS = {
'(n,2nd)': ReactionInfo({11}, ('H2',)),
'(n,2n)': ReactionInfo(set(chain([16], range(875, 892))), ()),
'(n,3n)': ReactionInfo({17}, ()),
'(n,na)': ReactionInfo({22}, ('He4',)),
'(n,n3a)': ReactionInfo({23}, ('He4', 'He4', 'He4')),
'(n,2na)': ReactionInfo({24}, ('He4',)),
'(n,3na)': ReactionInfo({25}, ('He4',)),
'(n,np)': ReactionInfo({28}, ('H1',)),
'(n,n2a)': ReactionInfo({29}, ('He4', 'He4')),
'(n,2n2a)': ReactionInfo({30}, ('He4', 'He4')),
'(n,nd)': ReactionInfo({32}, ('H2',)),
'(n,nt)': ReactionInfo({33}, ('H3',)),
'(n,n3He)': ReactionInfo({34}, ('He3',)),
'(n,nd2a)': ReactionInfo({35}, ('H2', 'He4', 'He4')),
'(n,nt2a)': ReactionInfo({36}, ('H3', 'He4', 'He4')),
'(n,4n)': ReactionInfo({37}, ()),
'(n,2np)': ReactionInfo({41}, ('H1',)),
'(n,3np)': ReactionInfo({42}, ('H1',)),
'(n,n2p)': ReactionInfo({44}, ('H1', 'H1')),
'(n,npa)': ReactionInfo({45}, ('H1', 'He4')),
'(n,gamma)': ReactionInfo({102}, ()),
'(n,p)': ReactionInfo(set(chain([103], range(600, 650))), ('H1',)),
'(n,d)': ReactionInfo(set(chain([104], range(650, 700))), ('H2',)),
'(n,t)': ReactionInfo(set(chain([105], range(700, 750))), ('H3',)),
'(n,3He)': ReactionInfo(set(chain([106], range(750, 800))), ('He3',)),
'(n,a)': ReactionInfo(set(chain([107], range(800, 850))), ('He4',)),
'(n,2a)': ReactionInfo({108}, ('He4', 'He4')),
'(n,3a)': ReactionInfo({109}, ('He4', 'He4', 'He4')),
'(n,2p)': ReactionInfo({111}, ('H1', 'H1')),
'(n,pa)': ReactionInfo({112}, ('H1', 'He4')),
'(n,t2a)': ReactionInfo({113}, ('H3', 'He4', 'He4')),
'(n,d2a)': ReactionInfo({114}, ('H2', 'He4', 'He4')),
'(n,pd)': ReactionInfo({115}, ('H1', 'H2')),
'(n,pt)': ReactionInfo({116}, ('H1', 'H3')),
'(n,da)': ReactionInfo({117}, ('H2', 'He4')),
'(n,5n)': ReactionInfo({152}, ()),
'(n,6n)': ReactionInfo({153}, ()),
'(n,2nt)': ReactionInfo({154}, ('H3',)),
'(n,ta)': ReactionInfo({155}, ('H3', 'He4')),
'(n,4np)': ReactionInfo({156}, ('H1',)),
'(n,3nd)': ReactionInfo({157}, ('H2',)),
'(n,nda)': ReactionInfo({158}, ('H2', 'He4')),
'(n,2npa)': ReactionInfo({159}, ('H1', 'He4')),
'(n,7n)': ReactionInfo({160}, ()),
'(n,8n)': ReactionInfo({161}, ()),
'(n,5np)': ReactionInfo({162}, ('H1',)),
'(n,6np)': ReactionInfo({163}, ('H1',)),
'(n,7np)': ReactionInfo({164}, ('H1',)),
'(n,4na)': ReactionInfo({165}, ('He4',)),
'(n,5na)': ReactionInfo({166}, ('He4',)),
'(n,6na)': ReactionInfo({167}, ('He4',)),
'(n,7na)': ReactionInfo({168}, ('He4',)),
'(n,4nd)': ReactionInfo({169}, ('H2',)),
'(n,5nd)': ReactionInfo({170}, ('H2',)),
'(n,6nd)': ReactionInfo({171}, ('H2',)),
'(n,3nt)': ReactionInfo({172}, ('H3',)),
'(n,4nt)': ReactionInfo({173}, ('H3',)),
'(n,5nt)': ReactionInfo({174}, ('H3',)),
'(n,6nt)': ReactionInfo({175}, ('H3',)),
'(n,2n3He)': ReactionInfo({176}, ('He3',)),
'(n,3n3He)': ReactionInfo({177}, ('He3',)),
'(n,4n3He)': ReactionInfo({178}, ('He3',)),
'(n,3n2p)': ReactionInfo({179}, ('H1', 'H1')),
'(n,3n2a)': ReactionInfo({180}, ('He4', 'He4')),
'(n,3npa)': ReactionInfo({181}, ('H1', 'He4')),
'(n,dt)': ReactionInfo({182}, ('H2', 'H3')),
'(n,npd)': ReactionInfo({183}, ('H1', 'H2')),
'(n,npt)': ReactionInfo({184}, ('H1', 'H3')),
'(n,ndt)': ReactionInfo({185}, ('H2', 'H3')),
'(n,np3He)': ReactionInfo({186}, ('H1', 'He3')),
'(n,nd3He)': ReactionInfo({187}, ('H2', 'He3')),
'(n,nt3He)': ReactionInfo({188}, ('H3', 'He3')),
'(n,nta)': ReactionInfo({189}, ('H3', 'He4')),
'(n,2n2p)': ReactionInfo({190}, ('H1', 'H1')),
'(n,p3He)': ReactionInfo({191}, ('H1', 'He3')),
'(n,d3He)': ReactionInfo({192}, ('H2', 'He3')),
'(n,3Hea)': ReactionInfo({193}, ('He3', 'He4')),
'(n,4n2p)': ReactionInfo({194}, ('H1', 'H1')),
'(n,4n2a)': ReactionInfo({195}, ('He4', 'He4')),
'(n,4npa)': ReactionInfo({196}, ('H1', 'He4')),
'(n,3p)': ReactionInfo({197}, ('H1', 'H1', 'H1')),
'(n,n3p)': ReactionInfo({198}, ('H1', 'H1', 'H1')),
'(n,3n2pa)': ReactionInfo({199}, ('H1', 'H1', 'He4')),
'(n,5n2p)': ReactionInfo({200}, ('H1', 'H1')),
'(n,2nd)': ReactionInfo({11}, ('H2',), 2),
'(n,2n)': ReactionInfo(set(chain([16], range(875, 892))), (), 2),
'(n,3n)': ReactionInfo({17}, (), 3),
'(n,na)': ReactionInfo({22}, ('He4',), 1),
'(n,n3a)': ReactionInfo({23}, ('He4', 'He4', 'He4'), 1),
'(n,2na)': ReactionInfo({24}, ('He4',), 2),
'(n,3na)': ReactionInfo({25}, ('He4',), 3),
'(n,np)': ReactionInfo({28}, ('H1',), 1),
'(n,n2a)': ReactionInfo({29}, ('He4', 'He4'), 1),
'(n,2n2a)': ReactionInfo({30}, ('He4', 'He4'), 2),
'(n,nd)': ReactionInfo({32}, ('H2',), 1),
'(n,nt)': ReactionInfo({33}, ('H3',), 1),
'(n,n3He)': ReactionInfo({34}, ('He3',), 1),
'(n,nd2a)': ReactionInfo({35}, ('H2', 'He4', 'He4'), 1),
'(n,nt2a)': ReactionInfo({36}, ('H3', 'He4', 'He4'), 1),
'(n,4n)': ReactionInfo({37}, (), 4),
'(n,2np)': ReactionInfo({41}, ('H1',), 2),
'(n,3np)': ReactionInfo({42}, ('H1',), 3),
'(n,n2p)': ReactionInfo({44}, ('H1', 'H1'), 1),
'(n,npa)': ReactionInfo({45}, ('H1', 'He4'), 1),
'(n,gamma)': ReactionInfo({102}, (), 0),
'(n,p)': ReactionInfo(set(chain([103], range(600, 650))), ('H1',), 0),
'(n,d)': ReactionInfo(set(chain([104], range(650, 700))), ('H2',), 0),
'(n,t)': ReactionInfo(set(chain([105], range(700, 750))), ('H3',), 0),
'(n,3He)': ReactionInfo(set(chain([106], range(750, 800))), ('He3',), 0),
'(n,a)': ReactionInfo(set(chain([107], range(800, 850))), ('He4',), 0),
'(n,2a)': ReactionInfo({108}, ('He4', 'He4'), 0),
'(n,3a)': ReactionInfo({109}, ('He4', 'He4', 'He4'), 0),
'(n,2p)': ReactionInfo({111}, ('H1', 'H1'), 0),
'(n,pa)': ReactionInfo({112}, ('H1', 'He4'), 0),
'(n,t2a)': ReactionInfo({113}, ('H3', 'He4', 'He4'), 0),
'(n,d2a)': ReactionInfo({114}, ('H2', 'He4', 'He4'), 0),
'(n,pd)': ReactionInfo({115}, ('H1', 'H2'), 0),
'(n,pt)': ReactionInfo({116}, ('H1', 'H3'), 0),
'(n,da)': ReactionInfo({117}, ('H2', 'He4'), 0),
'(n,5n)': ReactionInfo({152}, (), 5),
'(n,6n)': ReactionInfo({153}, (), 6),
'(n,2nt)': ReactionInfo({154}, ('H3',), 2),
'(n,ta)': ReactionInfo({155}, ('H3', 'He4'), 0),
'(n,4np)': ReactionInfo({156}, ('H1',), 4),
'(n,3nd)': ReactionInfo({157}, ('H2',), 3),
'(n,nda)': ReactionInfo({158}, ('H2', 'He4'), 1),
'(n,2npa)': ReactionInfo({159}, ('H1', 'He4'), 2),
'(n,7n)': ReactionInfo({160}, (), 7),
'(n,8n)': ReactionInfo({161}, (), 8),
'(n,5np)': ReactionInfo({162}, ('H1',), 5),
'(n,6np)': ReactionInfo({163}, ('H1',), 6),
'(n,7np)': ReactionInfo({164}, ('H1',), 7),
'(n,4na)': ReactionInfo({165}, ('He4',), 4),
'(n,5na)': ReactionInfo({166}, ('He4',), 5),
'(n,6na)': ReactionInfo({167}, ('He4',), 6),
'(n,7na)': ReactionInfo({168}, ('He4',), 7),
'(n,4nd)': ReactionInfo({169}, ('H2',), 4),
'(n,5nd)': ReactionInfo({170}, ('H2',), 5),
'(n,6nd)': ReactionInfo({171}, ('H2',), 6),
'(n,3nt)': ReactionInfo({172}, ('H3',), 3),
'(n,4nt)': ReactionInfo({173}, ('H3',), 4),
'(n,5nt)': ReactionInfo({174}, ('H3',), 5),
'(n,6nt)': ReactionInfo({175}, ('H3',), 6),
'(n,2n3He)': ReactionInfo({176}, ('He3',), 2),
'(n,3n3He)': ReactionInfo({177}, ('He3',), 3),
'(n,4n3He)': ReactionInfo({178}, ('He3',), 4),
'(n,3n2p)': ReactionInfo({179}, ('H1', 'H1'), 3),
'(n,3n2a)': ReactionInfo({180}, ('He4', 'He4'), 3),
'(n,3npa)': ReactionInfo({181}, ('H1', 'He4'), 3),
'(n,dt)': ReactionInfo({182}, ('H2', 'H3'), 0),
'(n,npd)': ReactionInfo({183}, ('H1', 'H2'), 1),
'(n,npt)': ReactionInfo({184}, ('H1', 'H3'), 1),
'(n,ndt)': ReactionInfo({185}, ('H2', 'H3'), 1),
'(n,np3He)': ReactionInfo({186}, ('H1', 'He3'), 1),
'(n,nd3He)': ReactionInfo({187}, ('H2', 'He3'), 1),
'(n,nt3He)': ReactionInfo({188}, ('H3', 'He3'), 1),
'(n,nta)': ReactionInfo({189}, ('H3', 'He4'), 1),
'(n,2n2p)': ReactionInfo({190}, ('H1', 'H1'), 2),
'(n,p3He)': ReactionInfo({191}, ('H1', 'He3'), 0),
'(n,d3He)': ReactionInfo({192}, ('H2', 'He3'), 0),
'(n,3Hea)': ReactionInfo({193}, ('He3', 'He4'), 0),
'(n,4n2p)': ReactionInfo({194}, ('H1', 'H1'), 4),
'(n,4n2a)': ReactionInfo({195}, ('He4', 'He4'), 4),
'(n,4npa)': ReactionInfo({196}, ('H1', 'He4'), 4),
'(n,3p)': ReactionInfo({197}, ('H1', 'H1', 'H1'), 0),
'(n,n3p)': ReactionInfo({198}, ('H1', 'H1', 'H1'), 1),
'(n,3n2pa)': ReactionInfo({199}, ('H1', 'H1', 'He4'), 3),
'(n,5n2p)': ReactionInfo({200}, ('H1', 'H1'), 5),
}

__all__ = ["Chain", "REACTIONS"]
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