A FULL REFERENCE APOLLO3® DETERMINISTIC SCHEME FOR THE JHR MATERIAL TESTING REACTOR

JHR is a new material testing reactor under construction at CEA Cadarache. Its high flux core contains 37 fuel assemblies loaded along concentric rings into alveolus of an aluminum matrix. For the operation of the reactor, twenty-seven of these fuel assemblies hovnst hafnium rods in their center while the other ones but also the beryllium radial reflector can accommodate experimental devices. In order to accurately predict its operating core characteristics but also its irradiation performance, a recently developed scheme based on the APOLLO3® platform is being developed which uses the sub-group method for spatial self-shielding, the 2D method of characteristics and the 3D unstructured conform MINARET Sn transport solver. A 2D model of JHR has been built and optimized for calculating, at the lattice step, the self-shielded and condensed cross sections thanks to the sub-group method and the method of characteristics. Results are benchmarked against a TRIPOLI-4® stochastic reference calculation. A more refined spatial mesh gives better results on fission rates and reactivity compared to the ones of the former APOLLO2 scheme. The classical 2-step calculations use the hypothesis of infinite lattice configuration, which is reasonable for the assemblies close to the center but not for peripheral ones. Hence, a new approach is being set up taking into account the surrounding of each assembly. The newly 3-step scheme uses the Sn solver MINARET and gives better results than the traditional 2-step scheme. This approach will be applied to a 3D modelling of the heterogeneous JHR core configurations incorporating experimental devices and enabling burn up calculations.

SENSITIVITY ANALYSIS OF STAINLESS STEEL REFLECTOR FOR VR-1 TRAINING REACTOR

Pressurized water reactors are typically surrounded in the radial direction by neutron reflectors made from stainless steel and water. These reflectors decrease neutron leakage and provide protection of pressure vessel from fast neutrons damaging its integrity. Such a radial reflector influences multiplication factor of the core and distribution of neutron flux and fission power inside the core. All these effects can be analyzed by full-core simulations using macroscopic constants. Methodology for generation of the macroscopic constants for non-fuel regions will be tested for new stainless steel reflectors at the VR-1 reactor. Rods from SS 304l material will be used for construction of radial reflectors for the VR-1 reactor. They will be design to generate sufficient measurable response in selected core characteristics. The study is focused on core power distribution and reactivity worth of absorbing rods in a VR-1 reactor core. The core typically consists of about 20 IRT-4M fuel assemblies and seven absorbing rods UR-70. Replacing water surrounding the core by several reflector assemblies containing stainless steel will influence leakage and distribution of neutrons inside the core. The current analysis deals with local effects and employs the sensitivity study to discover the nature of reflectors’ impact on the reactor core. These effects were studied even for several past VR-1 reactor core configurations. All calculations were carried out in Serpent2 Monte-Carlo code with various evaluated libraries: ENDF/B-VII.1, ENDF/B-VIII.0, and JEFF-3.3 data.

Validation of Pin Power Calculations Using DYN3D on MIDICORE Benchmark

Three-dimensional code DYN3D is widely used for the calculation of steady states and transients in light water reactors with hexagonal fuel assemblies like VVER. The capability of pin-by-pin power calculation is implemented in the code through an intranodal power reconstruction approach. The calculations of pin power distribution using DYN3D were performed for AER MIDICORE benchmark for the validation of given extension and developed cross-section library. MIDICORE VVER-1000 core periphery power distribution benchmark was proposed on the 20th Symposium of AER. It is a 2D calculation benchmark based on the VVER-1000 core cold state geometry taking into account the geometry of explicit radial reflector. The main issue of MIDICORE benchmark is to provide the reference solution for the validation of pin-by-pin power distribution at the VVER-1000 core periphery calculated by few-group diffusion codes. Various 3D neutron kinetics nodal solvers HEXNEM1, HEXNEM2 and HEXNEM3 are used in DYN3D for neutron flux distribution calculation. The AER MIDICORE benchmark was solved using all solvers implemented in DYN3D with regard to the three most representative fuel assemblies. Considered fuel assemblies are placed both in the inner part and in the peripheral part of the core, and contain the pin with integrated gadolinium burnable absorber. This paper provides results of comparing the effective multiplication factor, assembly-wise power distribution and pin-by-pin power distribution calculated by DYN3D with benchmark data.

Development of Cross-Section Library for DYN3D Code

At present, SSTC NRS uses the HELIOS code for generation of few-group cross-section libraries for WWER core calculations. There is an urgent issue of selecting the appropriate approach to implement the cross-section library into the DYN3D code. The paper overviews the application of approaches used by SSTC NRS, such as a multidimensional table and polynomial dependences. The capabilities and possible extension of each approach are described with inherent advantages and disadvantages. In addition, the model development and cross-section preparation for the WWER-1000 radial reflector taking into account discontinuity factors are discussed. Brief results of calculations with the use of different approaches are presented.