Today, nuclear energy meets only 11% of the world’s electricity generation from 434 nuclear power plants (NPPs) around the world. Besides electricity generation, nuclear energy has many applications in medicine, industry, and material research. Around 225 research reactors (RRs) are utilized in 50 countries for the research and education, as well as for the production of medical and industrial isotopes purposes. Nuclear energy is also a low-carbon power generation method along with other sustainable energy sources.
The safe and efficient operation of NPPs and RRs is of continued importance for existing and future reactors. Modeling of fuel behavior and studying of high burnup effects on fuel behavior during both normal operation and accident scenarios lead to the enhanced safety of a reactor and more efficient use of the nuclear fuel.
Many reactor modeling and simulation codes have been developed for safe and efficient operation of RRs and NPPs since the operation of the first reactors. Multiple benchmark studies have been conducted to assess the accuracy of the depletion codes used to predict the isotopic composition of the spent fuel. There are mainly two types of reactor modeling and simulation codes: Deterministic and Monte Carlo codes. Deterministic codes are equation-based codes, while Monte Carlo codes are stochastic, probability-based.
In this study, two deterministic codes are investigated and compared: HELIOS-2.1 and SCALE-6.1. HELIOS-2.1 is a two-dimensional transport code for fuel burnup and flux calculation designed by Studsvik Scandpower, Sweden, to perform nuclear fuel analysis. HELIOS is a neutron and gamma transport code capable of analyzing nuclear fuel designs for nuclear power reactors and experimental type research reactors. SCALE-6.1 is a code’s system developed and maintained by Oak Ridge National Laboratory, USA, which is a widely-used simulation tool for nuclear safety analysis worldwide. It became an internationally-recognized and widely-used depletion and decay code in the nuclear industry over the last years.
The main objective of this study was the determination of the isotopic distributions of selected actinides (uranium and plutonium isotopes) at high burnups. Another objective was to compare the HELIOS-2.1 and SCALE-6.1 codes, in order to identify systematic differences and the origins of any discrepancies between these two deterministic codes and to validate the SCALE/TRITON code for the building the specific cross section libraries for use in the Halden boiling heavy water reactor.
The HELIOS-2.1 and SCALE-6.1 codes were compared using pin-cell models for light water reactor (LWR) and heavy water reactor (HWR) cases. The infinite multiplication factor, flux distribution, absorption, fission, production reaction rates, and burn-up dependent concentrations of major fuel isotopes were investigated and compared. The codes have shown better agreement in the case of LWR calculations. The main disagreement between the codes is in the calculation of low energy resonances in the neutron thermalization process (in both the LWR and HWR cases).
It was concluded that more extensive research is required to model the thermalization process in the HWR case. This process needs to be investigated further to determine the root cause. Possible causes could be the neutron group structure, cross-section condensation, treatment of up-scatter, angle dependence of scatter, and spatial homogenization during source iterations.
These findings are described in the article entitled, Comparison of HELIOS-2.1 and SCALE-6.1 codes on pin-cell model, recently published in the journal Annals of Nuclear Energy. This work was conducted by Sabina Maharramova, William Beere, Knut Eitrheim, Ole Reistad and Tord Walderhaug from the University of Oslo and Institute for Energy Technology, Norway.