Recent developments in the GENESIS code based on the Legendre polynomial expansion of angular flux method

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Recent developments in the GENESIS code based on the Legendre polynomial expansion of angular flux method. This paper describes recent development activities of the GENESIS code, which is a transport code for heterogeneous three-dimensional geometry, focusing on applications to reactor core analysis. For the treatment of anisotropic scattering, the concept of the simplified Pn method is introduced in order to reduce storage of flux moments.
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Nuclear Engineering and Technology
journal homepage: www.elsevier.com/locate/net
Original Article
Recent developments in the GENESIS code based on the Legendre
polynomial expansion of angular ux method
Akio Yamamoto*, Akinori Giho, Tomohiro Endo
Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan
a r t i c l e
i n f o
a b s t r a c t
Article history:
This paper describes recent development activities of the GENESIS code, which is a transport code for
Received 28 May 2017
Received in revised form
26 June 2017
Accepted 27 June 2017
Available online 18 July 2017
heterogeneous three-dimensional geometry, focusing on applications to reactor core analysis. For the
treatment of anisotropic scattering, the concept of the simplied Pn method is introduced in order to
reduce storage of ux moments. The accuracy of the present method is veried through a benchmark
problem. Next, the iteration stability of the GENESIS code for the highly voided condition, which would
appear in a severe accident (e.g., design extension) conditions, is discussed. The efciencies of the coarse
Keywords:
Acceleration
Anisotropic scattering
C5G7 Benchmark Problem
mesh nite difference and generalized coarse mesh rebalance acceleration methods are veried with
various stabilization techniques. Use of the effective diffusion coefcient and the articial grid diffusion
coefcients are found to be effective to stabilize the acceleration calculation in highly voided conditions.
© 2017 Korean Nuclear Society, Published by Elsevier Korea LLC. This is an open access article under the
GENESIS
Simplied Pn
Stability
1. Introduction
and diffusion/low order transport calculations, respectively. In
typical commercial reactors, axial heterogeneity is much smaller
Signicant efforts have been devoted to high delity simulation
than it is in the radial direction, and thus different treatments of
methods of core characteristics. Monte Carlo and deterministic
neutron transport for radial and axial directions are justied and
methods are two important approaches for high delity simula-
can be applied without signicant loss of prediction accuracy. The
tions. As for deterministic methods, spatial, angular, energetic, and
planar MOC has a signicant advantage in computational efciency
temporal resolutions are being continuously increased and three-
because it uses the conventional MOC in two-dimensional (2D)
dimensional (3D) multigroup transport calculations considering
geometry.
explicit 3D heterogeneous geometries of reactor core are becoming
Recently, high delity simulations of core characteristics under
feasible (e.g., [1e11]).
severe core conditions, e.g., loss-of-coolant accident or anticipated
Various approaches can be considered for a 3D multigroup
transient without scram, are being required from the viewpoint of
transport calculation with explicit heterogeneous geometry. A
safety analysis. In these conditions, the highly voided condition
straightforward approach to realize this type of calculation is the
should be considered with signicantly skewed power distribution
direct application of method of characteristics (MOC) in 3D geom-
not only for the radial direction but also for the axial direction.
etry [9e11]. However, this requires large computational resources
Because the planar MOC uses a diffusion or low-order transport
(both memory and computation time), and thus its practical appli-
method to approximately consider the axial leakage, it would incur
cation to large-scale geometry, e.g., a commercial light water reactor
degradation of the prediction accuracy and/or convergent issues in
(LWR), would be limited. Instead, the planar MOC method is suc-
severe core conditions. This issue is discussed in detail by Hursin,
cessfully applied for high-delity core analyses [2e8].
and some improvements for axial coupling among axial planes are
In the planar MOC method, neutron transport calculations for
proposed [8].
radial and axial directions are performed by the conventional MOC
In order to address this issue, the Legendre polynomial Expan-
sion of Angular Flux (LEAF) method is proposed as an extension of
the axially simplied method of characteristics in 3D (ASMOC3D)
method [12e14]. In the LEAF method, axial leakage is explicitly
* Corresponding author.
E-mail address: a-yamamoto@nucl.nagoya-u.ac.jp (A. Yamamoto).
considered
without
approximation.
Thus,
higher
accuracy
is
1738-5733/© 2017 Korean Nuclear Society, Published by Elsevier Korea LLC. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/