Low-order multiphysics coupling techniques for nuclear reactor applications

Walker, Erik; Collins, Benjamin; Gehin, Jess C

doi:10.1016/j.anucene.2019.04.022

Cited by 10 publications

(11 citation statements)

References 15 publications

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“…In [36], Herman considered diffusion-level coupling between a CMFD-accelerated Monte Carlo transport code and a thermal hydraulics code. In [110,111], Walker explored diffusion-level coupling of deterministic transport; he referred to this approach as "Low-Order Coupling". In Walker's work, nuclear data in the CMFD diffusion equation were updated through either Picard-based or JFNK-based iteration with a thermal hydraulics solver.…”

Section: Multiphysics Iterative Methodsmentioning

confidence: 99%

“…The essence of this idea has been proposed in various forms under several different pseudonyms in a number of recent publications. (The approach is captured by both the CMFD-Coupling and JFNKbased methods described in [110,111]. In [91], the Nonlinear Fully Coupled Diffusion Acceleration (NFCDA) method is equivalent to what we refer to as X-CMFD.…”

Section: Multiphysics Iterative Methodsmentioning

confidence: 99%

“…We contrast this with the outer iteration, e.g., evaluation of X-CMFD Steps 1 -4. Next, we present two inner iteration schemes based on previous work by Walker and Shen [91,93,110,111]. This will show the limitations of X-CMFD, namely, its tendency to overburden the thermal hydraulics solver and nuclear data update library as compared to M-CMFD and R-CMFD.…”

Section: X-cmfd Step 4 : Diffusion -Thermal Hydraulics Solvementioning

confidence: 96%

“…In this subsection, we describe two inner iteration approaches for X-CMFD, namely, the "Eigenvalue Level" scheme based on work by Walker [110,111], and the "Nonlinear Power Iteration" scheme based on work by Shen [91,93]. Up to this point, we have exclusively used the outer iteration index n. Now that we are describing inner iterations, we must introduce new notation.…”

Section: Inner Iterationmentioning

confidence: 99%

“…(4.24)-(4.26) is to iterate between thermal hydraulics solves, nuclear data updates, and diffusion eigenvalue solves. This procedure was used by Walker in [110,111]. We call Walker's method "Eigenvalue Level" (EL) inner iteration:…”

Section: Eigenvalue Level (El)mentioning

confidence: 99%

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The NILO-CMFD Method for Iteratively Solving Coupled Neutron Transport–Thermal Hydraulics Problems

Adamowicz

Manera

Larsen

2022

Nuclear Science and Engineering

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The interactions between neutron radiation and matter are nonlinear. Specifically, certain neutron nuclear reactions (e.g., fission events) generate heat, which modifies the temperature and density of the surrounding material, which in turn modify the neutron interaction probabilities (through the macroscopic cross sections). This nonlinear process is referred to as neutron transport with thermal hydraulics feedback.Linear transport problems (without feedback) are accurately described by the Neutron Transport Equation (NTE). Discretized forms of the NTE are routinely solved using iterative transport acceleration schemes, for example, the standard Coarse Mesh Finite Difference (CMFD) method. CMFD and related acceleration schemes for linear transport problems are reliable and well-understood. However, when these same iterative methods are applied to nonlinear (i.e. multiphysics) problems, significant performance and stability issues often occur.In this thesis, we propose modifications to the CMFD procedure, so that it can more robustly and efficiently solve loosely-coupled neutron transport -thermal hydraulics multiphysics problems. We refer to the new method as Nonlinearly Implicit Low-Order CMFD (NILO-CMFD). In this method, the transport-corrected diffusion equationa foundational component of the CMFD method -is modifed to include approximate thermal hydraulics and nuclear data update physics.To begin, we provide a general derivation of the 3-D NILO-CMFD method. Then, to initially analyze and test the method, we develop an approximate 1-D multiphysics model of a 3-D nuclear reactor fuel pin. The 1-D model consists of: (i) a 1-D neutron transport equation describing neutron transport, (ii) a 1-D advection-diffusion equation describing fluid temperature variation, (iii) a fuel temperature that depends on the 1-D fission heat source, and (iv) model equations that define the neutron cross sections and related nuclear data in terms of the fluid and fuel temperatures. The implementation of this model in a 1-D test code shows that the NILO-CMFD method overcomes the instabilities that occur in the standard Relaxed-CMFD (R-CMFD) method.x To test the new NILO-CMFD method on realistic 3-D problems, we implemented an incomplete version of the method, NILO-A, in the 3-D neutron transport code MPACT. For multiphysics problems, MPACT is loosely coupled to the 3-D COBRA-TF (CTF) code, which performs subchannel thermal hydraulics calculations. In every 3-D problem that we ran, NILO-CMFD successfully reduced the number of outer iterations to the low number required by CMFD for single-physics calculations. Unfortunately, due to lack of time, we could not implement the full NILO-CMFD method, which would have significantly reduced the wall clock time of the simulations. Consequently, some of our 3-D simulations required more wall clock time to converge than R-CMFD.Nonetheless, our results show that the NILO-CMFD method is a legitimate generalization of single-physics CMFD to multiphysics problems. The number of outer iterations requi...

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Section: Multiphysics Iterative Methodsmentioning

confidence: 99%

Section: Multiphysics Iterative Methodsmentioning

confidence: 99%

Section: X-cmfd Step 4 : Diffusion -Thermal Hydraulics Solvementioning

confidence: 96%

Section: Inner Iterationmentioning

confidence: 99%

Section: Eigenvalue Level (El)mentioning

confidence: 99%

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