The OpenMOC method of characteristics neutral particle transport code

Boyd, William; Shaner, Samuel Christopher; Li, Lulu; Forget, Benoit; Smith, Kord

doi:10.1016/j.anucene.2013.12.012

Cited by 129 publications

(48 citation statements)

References 6 publications

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“…We perform the deterministic transport simulation with OpenMOC, an open-source method of characteristics (MOC) code developed at MIT [213]. We utilize the identical 33-group MC**2 cross-sections.…”

Section: Carlomentioning

confidence: 99%

The “virtual density” theory of neutronics

Reed¹,

Smith

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2018

Annals of Nuclear Energy

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Sustainable nuclear energy will likely require fast reactors to complement the current light water reactor paradigm. In particular, breed-and-burn sodium fast reactors (SFRs) offer a unique combination of fuel cycle and power density features. Unfortunately, large breed-and-burn SFRs are plagued by positive sodium void worth. In order to mitigate this drawback, one must quantify various sources of negative reactivty feedback, among which geometry distortions (bowing and flowering of fuel assemblies) are often dominant. These distortions arise mainly from three distinct physical phenomena: irradiation swelling, thermal swelling, and seismic events.Distortions are notoriously difficult to model, because they break symmetry and periodicity. Currently, no efficient and fully generic method exists for computing neutronic effects of distortions. Computing them directly via diffusion would require construction of exotic hyperfine meshes with continuous re-meshing. Many deterministic transport methods are geometrically flexible but would require tedious, intricate re-meshing or re-tracking to capture distortion effects. Monte Carlo offers the only high-fidelity approach to arbitrary geometry, but resolving minute reactivities and flux shift tallies within large heterogeneous cores requires CPU years per case and is thus prohibitively expensive. Currently, the most widely-used methods consist of various approximations involving weighting the uniform radial swelling reactivity coefficient by the power distribution. These approximations agree fairly well with experimental data for flowering in some cores, but they are not fully generic and cannot be trusted for arbitrary distortions. Boundary perturbation theory, developed in the 1980s, is fully general and mathematically rigorous, but it is inaccurate for coarse mesh diffusion and has apparently never been applied in industry.Our solution is the "virtual density" theory of neutronics, which alters material density (isotropically or anisotropically) instead of explicitly changing geometry. While geometry is discretized, material densities occupy a continuous domain; this allows density changes to obviate the greatest computational challenges of geometry changes. Although primitive forms of this theory exist in Soviet literature, they are only applicable to cases in which entire cores swell uniformly. Thus, we conceive a much more general and pragmatic form of "virtual density" theory to model non-uniform and localized geometry distortions via perturbation theory.In order to efficiently validate "virtual density" perturbation theory, we conceive the "virtual mesh" method for diffusion theory. This new method involves constructing a slightly perturbed "fake" mesh that produces correct first-order reactivity and flux shifts due to anisotropic swelling or expansion of individual mesh cells. First order reactivities computed on a "virtual mesh" agree with continuous energy Monte Carlo to within 1-uncertainty.We validate "virtual density" theory via the "virtual mesh" me...

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Section: Carlomentioning

confidence: 99%

The “virtual density” theory of neutronics

Reed¹,

Smith

Forget

2018

Annals of Nuclear Energy

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“…In OpenMOC, CMFD has been implemented and shown to reduce the number of transport sweeps by nearly a factor of 40 in some cases. [14] The objective of this section, therefore, is to determine SEAM's ability to accelerate fine group 2D transport calculations by implementing it in OpenMOC and comparing its performance to that of CMFD acceleration.…”

Section: D Results Using Openmocmentioning

confidence: 99%

“…This damping factor is largely problem dependent but a reasonable value can be applied across a number of different problems. [14] Partial current Coarse Mesh Finite Difference (pCMFD) is a more recent development which has also been shown to improve stability. This approach adds a second degree of freedom to CMFD by calculating two partial current corrective factors at the boundaries of a coarse mesh instead of forming a single net current corrective factor.…”

Section: Coarse Mesh Finite Difference Diffusion and Coarse Mesh Rebamentioning

confidence: 99%

“…OpenMOC is an open source 2D Method of Characteristics (MOC) transport solver. [14] Instead of solving for the average angular flux across an entire cell all at once, MOC tallies angular fluxes solved across many tracks superimposed upon the problem. One of the primary simplifications in standard MOC is that the source in each cell is spatially flat.…”

Section: A Brief Introduction To Openmocmentioning

confidence: 99%

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The Source Equivalence Acceleration Method

Everson

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2015

Annals of Nuclear Energy

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Fine-group whole-core reactor analysis remains one of the long sought goals of the reactor physics community. Such a detailed analysis is typically too computationally expensive to be realized on anything except the largest of supercomputers. Recondensation using the Discrete Generalized Multigroup (DGM) method, though, offers a relatively cheap alternative to solving the fine group transport problem. DGM, however, suffered from inconsistencies when applied to high-order spatial methods. While an exact spatial recondensation method was developed and provided full spatial consistency with the fine group problem, this approach substantially increased memory requirements for realistic problems. The method described in this paper, called the Source Equivalence Acceleration Method (SEAM), forms a coarse-group problem which preserves the fine-group problem even when using higher order spatial methods. SEAM allows recondensation to converge to the fine-group solution with minimal memory requirements and little additional overhead. This method also provides for consistency when using different spatial methods and angular quadratures between the coarse group and fine group problems. SEAM was implemented in OpenMOC, a 2D MOC code developed at MIT, and its performance tested against Coarse Mesh Finite Difference (CMFD) acceleration on the C5G7 benchmark problem and on a 361 group version of the problem. For extremely expensive transport calculations, SEAM was able to outperform CMFD, resulting in speed-ups of 20-45 relative to the normal power iteration calculation.

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“…Various codes including DRAGON (Marleau et al, 2006), OpenMC (Romano and Forget, 2013), OpenMOC (Boyd et al, 2014), MocDown (Seifried et al, 2014), PyNE (Scopatz et al, 2012) are examples of codes being developed as open source. Active participation of nuclear community in such projects helps in verification & validation and debugging of such codes, and helps these codes to rise to the level of well-established codes.…”

Section: Introductionmentioning

confidence: 99%