KAVOSH1.0

An advanced computational software for 3D thermo-neutronic analysis of PWR cores & multi-parameter loading pattern optimization

INTRODUCTION

KAVOSH, meaning exploration, is an advanced computational software planned for 3D thermo-neutronic analysis of PWR cores plus multi-parameter optimization of core loading pattern. It is indeed a combination of two main programs, ALVAND 1.0 and OPTICORE 1.0, both finalized by the I. R. Iran’s Advanced Nuclear Computing Center (ANCC), for core analysis and loading pattern optimization, respectively. The software consists of a variety of solvers for treating hexagonal and rectangular shaped reactors. Forward (direct) and backward (adjoint) diffusion equations are solved via a number of nodal and finite element subroutines empowered with accelerating approaches as well as parallel processing techniques to speed-up the calculations and to reduce the computational cost.

The entire system has been verified using various benchmarks and reference data found in published reports, as well as, comparisons made mainly against PARCS outputs. Excellent agreements found in almost all cases which bring a meaningful trust for the users. Yet, V&V is still going on for more certitude.

KAVOSH 1.0 is currently (Sep. 2022) under finalization and a graphical user interface is supposed to be developed for, making its application as simple as possible. It is supposed to be released in late 2023 by ANCC. Future developments mainly contains enabling dynamic features as well as plug-ins to a number of external TH codes (like RELAP) to realize accident analysis and improved time-dependent core TH evaluations.

METHODOLOGY

KAVOSH 1.0 benefits from the following well-proved numerical approaches to deal with the two-group forward and adjoint diffusion equations:

• Nodal Expansion Method;

• Coarse Mesh Finite Difference Method; and,

• Finite Element Method.

In addition, the heat conduction equation is solved via the simple but efficient single phase multi-channel approach which preserves needed speed along with sufficient accuracy for a wide range of real core thermal-hydraulic performances.

Also, optimizing the core loading pattern is currently provided by the Simulated Annealing Algorithm with objective functions encapsulating several sorts of parameters of interest e.g. neutronic, thermal-hydraulic, economic and safety ones limited by certain user-defined constraints. More optimization algorithms are under investigations at this time for future releases.

FEATURES

Followings are the major capabilities of KAVOSH 1.0:

• BOC to EOC estimation of effective multiplication factor, critical Boron concentration, burn up, peaking factors, poison (¹³⁵Xe & ¹⁴⁹Sm) densities, reactivity coefficients, axial power off-set, prompt and delayed neutron life-time, fuel and moderator temperatures, control rod worth, etc.

• Ability to plan start-up procedure and power maneuvers throughout cycles by regulating control rods.

• Multi-cycle (up to 99) core analysis and reload options.

• Empowered with accelerating approaches as well as parallel processing techniques to speed-up the process and to minimize the computational cost.

• Multi-parameter core optimization regarding pattern constraints and limitations.

• Multi-cycle pattern optimization and equilibrium cycle search option.

• Supporting PMAXS data library, and,

• User-friendly interface and graphical output display.

APPLICATIONS

KAVOSH 1.0 is especially developed for two main purposes:

• PWR core design and analysis, and,

• PWR core loading pattern optimization.

The software covers a wide range of needs for students, researchers and engineers in design and analysis of PWR cores. Core definition can be simply carried out and significant core parameters can be obtained without much difficulties normally associated with old computational codes. KAVOSH 1.0 also empowers the user to set and/or optimize successive cycles according to its constraints.

KAVOSH 1.0 benefits from a single-phase multi-channel thermal-hydraulic analyzer coupled with diffusion solver to realize estimation of core thermo-neutronic parameters including temperatures of fuel and moderator from BOC to EOC. Estimation of ¹³⁵Xe and ¹⁴⁹Sm densities, critical Boron concentration of the core, core burn up, peaking factors, reactivity coefficients, axial power off-set, prompt and delayed neutron life-time, differential and integral worth of control groups   as well as effective multiplication factor, all across the cycle are also capabilities of KAVOSH 1.0.

As the time always matters in design and analysis of industrial plants or even in purely academic interests, the code has been empowered with accelerating approaches as well as parallel processing techniques to speed-up the calculations and to reduce the computational cost. Moreover, PMAXS data structure – which is a standard data library for PARCS – is also supported by KAVOSH 1.0 to make a wide range of applications feasible, BOC to EOC fuel burn-up effects included.

An interesting feature proposed for KAVOSH 1.0 is the ability to analyze successive (up to 99) cycles by reloading once, twice or more burnt-up assemblies of previous cycles onto the next ones. Fuel burn-ups and inventories are automatically preserved for the next working cycle, making the assessment of a multi-cycle service plan remarkably easy.

Furthermore, the software equips the user to plan its start-up procedure and power maneuvers across the cycle through regulating several groups of control rods at arbitrary time steps. It would be interesting to know that these capabilities are not exclusive to a single cycle, and in fact, hands are open to assess up to 99 independent candidate cores by only one click-to-run, after defining the cycles entirely.

Another key option distinguishing KAVOSH 1.0 from the majority of similar tools is a core pattern optimizer embedded within. The search engine (which currently works upon the Simulated Annealing algorithm) enables the user to arrange an initial rough pattern followed by setting, limiting and prioritizing custom search parameters (e.g., cycle length, assembly’s discharge burn-up, costs etc.) as well as constraints on locations, numbers, enrichments or burn-up of fuel assemblies. Based on the given input, the engine runs through the search space by evaluating cores with randomly shuffled assemblies and finally suggests the best found pattern fulfilling the user demand. This of course, is not limited to only one cycle again, and upon request, the code moves on to next cycles until the equilibrium cycle is revealed. This means that KAVOSH 1.0 can propose a complete non-perturbed working plan using just a number of control parameters.

The last but not the least, would be display tools planned for the software to bring a rather suitable show of parameters for the user. This surely makes the software admissible for the engineers as they frequently need to compare and contrast evaluated data with minimum effort but maximum efficiency.