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Documentation
The computer code DRAGON[1,2,3,4] results from an effort made at École Polytechnique de Montréal to rationalize and unify into a single code the different models and algorithms used to solve the neutron transport equation. One of the main concerns of the DRAGON development team was to ensure that the structure of the code was such that the development and implementation of new calculation techniques would be facilitated. DRAGON is therefore a lattice cell code which is divided into many calculation modules linked together using the GAN generalized driver[5,6]. These modules exchange information only via well defined data structures.
The two main components of the code DRAGON are its multigroup flux solver and its one group collision probability (CP) tracking modules. The CP modules all perform the same task but using different levels of approximation.
The JPM tracking option uses the interface current technique at the level of each homogeneous zones associated with a geometry (J± method).[7] Such calculations can be performed through the use of the JPMT: module.[8,9,10,11,12] In this case one can either built the complete collision probabilities matrix or generate a response matrix both of which can be processed by the general multigroup solver. This last method permit a non iterative calculation of the one group neutron flux carried out using sparse matrix algebra.
The SYBIL tracking option emulates the main flux calculation option available in the APOLLO-1 code,[13,14] and includes a new version of the EURYDICE-2 code which performs reactor assembly calculations in both rectangular and hexagonal geometries using the interface current method. SYBIL is slightly more accurate than JPM due to the fact that it performs a complete calculation of the collision probabilities on the whole or a large part of the domain therefore avoiding for a large number of interfaces the angular flux approximation. The option is activated when the SYBILT: module is called.
The EXCELL tracking option is used to generate the collision probability matrices for the cases having cluster, two dimensional or three dimensional mixed rectangular and cylindrical geometries.[15,16] A cyclic tracking option is also available for treating specular boundary conditions in two dimensional rectangular geometry.[17,18,19,20] EXCELL calculations are performed using the EXCELT: module.
After the collision probability or response matrices associated with a given cell have been generated, the multigroup solution module can be activated. This module uses the power iteration method and requires a number of iteration types.[21] The thermal iterations are carried out by DRAGON so as to rebalance the flux distribution only in cases where neutron undergo upscattering. The power iterations are performed by DRAGON to solve the fixed source or eigenvalue problem in the cases where a multiplicative medium is analyzed. The effective multiplication factor (keff) is obtained during the power iterations. A search for the critical buckling may be superimposed upon the power iterations so as to force the multiplication factor to take on a fixed value.[22]
DRAGON can access directly microscopic cross-section libraries defined according to the following standard formats: MATXS,[23,24,25] WIMS-D4[26,27,28], WIMS-AECL[29] and APOLLO.[13] It has the capability of exchanging macroscopic cross-section libraries with a code such as TRANSX-CTR or TRANSX-2 by the use of GOXS and ISOTXS format files.[23,30] The macroscopic cross section can also be read in DRAGON via the input data stream.