CORDIS - Resultados de investigaciones de la UE

Codes And Methods Improvements for VVER comprehensive safety assessment

Periodic Reporting for period 1 - CAMIVVER (Codes And Methods Improvements for VVER comprehensive safety assessment)

Período documentado: 2020-09-01 hasta 2022-02-28

The European nuclear fleet is composed of Gen. II and Gen. III reactor types. This fleet is currently going through LTO upgrades and that remains an important concern for the European Community. Several VVER reactor units are planned for construction – or are currently under construction. It is realistic to think that VVER type reactors will keep playing a strategic role for the European energy and economic stability, its de-carbonation strategy, and the Europe safety in general. In this framework, the Euratom Supply Agency (ESA) underlined as a matter of concern the 100% reliance on a single Russian supplier and therefore an issue for all EU countries operating VVER reactors. Dependence on a single supplier constitutes a significant risk and qualifying an alternative supplier could take several years because of licensing and testing requirements.
In order to support the development and the qualification of fuel and more generally to provide the required elements for the safety analysis report (SAR), an important place is reserved to the development, improvement, verification and validation of computer codes and methods used in the VVER safety analysis. The codes and methods continuous update needed for answering the regulatory requirements for reactors LTO is the basis of CAMIVVER project, for the improvement of codes and methods for VVER comprehensive safety assessment in support to other activities carried out concerning VVER fuel development and qualification.
The CAMIVVER project activities have been built to reach four main objectives:
- The improvement of scientific computer codes, models, and methods to be used at an industrial level for the comprehensive safety assessment of Generation II and III reactors.
- The promotion of 3D neutronics-thermalhydraulics coupled calculations to improve the safety assessment by a better representation of the physical phenomena (e.g. accidental transient characterized by strong heterogeneities in power or coolant fields), an important aspect for the LTO upgrade when considering the evolution of margins with respect to safety criteria.
- The promotion of the use of advanced mathematical methods (metamodels, deterministic sampling, etc.) for the assessment of uncertainty propagation within numerical simulations.
- The integration of the VVER context (VVER-1000), slightly different from western PWR but with some common features, to challenge the robustness of codes and methods and their validation strategy.
It is worth noticing that the project is proceeding normally despite the pandemic.
Project coordination is managed by FRAMATOME within Work Package 2. Project coordination through regular Executive Committee meetings has been put in place. So far those meetings are held by web conference means.
With regard to technical works, first activities have consisted in collecting all necessary reference data to be used by project partners. Those essential tasks have been conducted within Work Package 3 led by INRNE and have been achieved since the summer 2021.
In Work Package 4 led by CEA, the activities are dedicated to setting up the framework (first steps) for the industrialization of a computing platform capable of performing lattice neutronic analysis and to generate multi-parameter neutron data libraries based on the new lattice code APOLLO3®, up to now developed mostly as a research computational tool. Two important tasks have been completed in 2021 in relation with the multi-parameter library generator: the definitions of tests cases for the verification phases, and the definition of representative use cases and specification requirements. Work is now progressing with the aim to have a first version of the library generator this year and provide a first optimized numerical scheme for VVER assembly calculations. As well, new capabilities of the TDT-MOC solver of APOLLO3® in three dimensions have been published in a paper, this feature will open the way to the construction of exact 3D model of the axial reflector to evaluate the accuracy of current industrial calculations.
Work Package 5 led by KIT is tightly connected to Work Package 4. The WP consists of three main tasks: (1) the definition of the VVER and PWR reduced size core reference test cases with their corresponding initial and boundary conditions; (2) the evaluation of the test cases with coupled neutronics and closed channel thermal-hydraulics tools (APOLLO3®, SERPENT/SUBCHANFLOW, PARCS/TRACE); (3) the development of a 3D neutronics-thermal-hydraulics reference calculation based on APOLLO3®/CATHARE3 coupling based on the outputs from (1) and (2). The first task has been successfully completed in 2021: the VVER and PWR test cases have been specified with all necessary information: geometries, materials, thermophysical properties, transient scenarios (initial/ boundary conditions), and output parameters to be observed. Test cases consist of so-called ‘minicores’ of 7 fuel assemblies for the VVER case and 32 fuel assemblies for the PWR case. Such small configurations have been chosen to limit necessary calculation resources and times. A first feasibility of APOLLO3®/CATHARE3 coupling has been achieved and tested on the 32 PWR fuel assembly’s case. Information related to those Work Package 4 and Work Package 5 activities has been recently published.
Works performed in Work Package 6 led by FRAMATOME consisted in the development of the VVER-1000 vessel CFD models by each of the five contributing partners to the benchmark exercise, each with his own calculation tool. This task has been completed in 2021. Steady state conditions have been simulated and compared between models and results have been released at the beginning of 2022. The Kozloduy-6 mixing experiment exercise is now progressing.
A comparable progression was achieved in Work Package 7 led by LLC ENERGORISK in the field of system analyses. Each partner has developed his own model and steady-state calculations have been produced in 2021. First transient calculations have been achieved at the very beginning of 2022. A new document has been recently produced about the Kozloduy-6 MCP start-up transient benchmark, showing consistency of results with test data.
Finally activities in Work Package 8 led by UNIPI have allowed to put in place the framework reports and tools for the project communication, dissemination and exploitation activities.
CAMIVVER is based on new generation scientific computer codes presently under continuous development to be used for comprehensive safety assessment and modelisation of all accident events (including severe accidents initiators). CAMIVVER will improve the robustness and qualification level of these codes in the VVER scope.
Reinforcement of the safety features of the Generation II and III nuclear reactors fleet is obtained through the use of improved physical models and the development of 3D multiphysics coupled methods that provide a better evaluation of local heterogeneities (e.g. local reactivity feedbacks impact on the 3D power distribution and therefore on core behaviour during transients), allowing a more comprehensive assessment of the accidental events.
CAMIVVER will provide guidance on 3D multi-physics coupled methods that will be available to the whole nuclear industry.
CAMIVVER will demonstrate to European safety authorities and European VVER operators the capabilities of European codes to provide comprehensive safety assessment.