Certified nuclear and industrial engineering technical services

System codes and their respective nodalizations are fundamental tools for thermohydraulic safety analyses. The verification and validation of both are essential processes prior to their application in any major engineering study.

ENSO offers independent quality assurance assessment to support plant operation, design basis accident (DBA) analysis, and licensing calculations based on two different methodologies: the Advanced Qualification Process (AQP) and SCUP (SCaling UP). Both methodologies have been developed and tested by our staff at UPC under the auspices and recognition of the Nuclear Safety Council (CSN).

The analysis of DBAs and DECs is a key element in the design and licensing of any nuclear system. These analyses require in-depth knowledge of the behavior of the system in highly dynamic sequences, as well as a thorough understanding of local phenomena. The ENSO team has a solid track record in simulating these scenarios, acquired through its participation in international programs for the simulation of integral experiments and separate effects.

Understanding the phenomenology of these scenarios is crucial to ensuring the validity of analyses for commercial nuclear systems. The ENSO team's experience in this area includes:

• Participation in experimental programmes at comprehensive test facilities. ENSO members have developed or used models to simulate experiments at the following facilities: PKL (AREVA), LSTF (JAEA), ATLAS (KAERI), LOFT, BETHSY and LOBI.
• Simulation of DBA and BDBA scenarios for complete nodal analyses of nuclear power plants. In this area, work has been carried out for the following power plants: Ascó 1&2 (PWR), Vandellós 2 (PWR), Laguna Verde (BWR), Ringhals (BWR), TMI (PWR), Zion (PWR).
• Best estimate plus uncertainty analysis.
• Review of Emergency Operating Procedures.

The regulatory change in 1989 regarding the requirements for Emergency Core Cooling Systems (ECCS), which allowed the use of best estimate codes for licensing accident analysis, requires an assessment of the uncertainty in the calculation results. This evaluation must include initial and boundary conditions, as well as the characteristics of the codes themselves, such as numerical approximations, empirical correlations, and other factors.

Today, uncertainty assessment methods (BEPU), especially the statistical approach that propagates uncertainty from input parameters to results to generate tolerance intervals, are used worldwide by engineers to estimate the uncertainties of code calculations.

The Fukushima Daichii accident highlighted the critical importance of accident management strategies for core damage sequences. In this context, the design, review, and evaluation of Severe Accident Management Guidelines (SAMG) is crucial, and the training of operators under realistic conditions is essential.

ENSO offers an independent evaluation of SAMG using severe accident system codes, as well as the design and implementation of customized Severe Accident scenarios for operator support and training.

The increase in demand for precision has driven the use of coupled codes in the area of deterministic safety analysis. In this context, ENSO offers technical support for the coupling of user-provided TH/NK codes and for the integration of computer codes, including subchannel, containment, fission product chemistry, CFD, fuel, and structural mechanics codes within RELAP5.

Computational tools require formalized procedures for their development, verification and validation (V&V), as well as for their debugging. New reactor designs may require the development of existing computational tools, adding specific system components, such as helical coil heat exchangers, or incorporating new system fluids, such as molten salts. After making significant modifications to the codes, it is essential to ensure the quality of the software through a V&V process. Code validation is performed by evaluating its results against relevant experimental data representing the main phenomena expected. This evaluation can be performed qualitatively, by analyzing the parametric and temporal evolution of the variables, and quantitatively, using uncertainty assessment methods that consider the uncertainties associated with the models and correlations of the computational codes.

Currently, code development and software engineering are essential for maintaining and updating existing tools, as well as for creating new engineering capabilities. The main objectives include:

• Add functionalities such as graphical software and uncertainty assessment tools.
• Introduce recently developed correlations and numerical techniques in order to test them and eventually incorporate them permanently or as an alternative option.
• Adapt existing codes to specific reactor design features, such as multiple channels (Atucha Nuclear Power Plant) and horizontal reactors (CANDU), and Generation IV reactor designs, which incorporate new fluids and their respective heat transfer correlations.
• Develop coupling interfaces to perform more detailed calculations.

ENSO has extensive experience in software engineering solutions. Its team members have worked on projects including the implementation of new fluids, alternative correlations, and the derivation and incorporation of new flow regime maps.

Every year, ENSO, in collaboration with the UPC and Incheon National University, conducts practical training focused on best estimation codes, held in person in Barcelona. This initiative is aimed at knowledge transfer and the promotion of best practices in the modelling of nuclear power plants with system codes. Organisations such as KINS, KHNP, Chosun University, Incheon University, Ulsan University, SENTECH, KyungHee University (Korea), NNL, Rolls Royce (United Kingdom), Skoda, UJV (Czech Republic), NCBJ (Poland), UPM (Spain), Tractebel (Belgium), LEI (Lithuania), PSI (Switzerland), Paks II (Hungary), ENEC (United Arab Emirates), ES Group (Ukraine), and McMaster University (Canada).

Technical support and customized training are designed to meet the specific needs of each client. ENSO offers technical support and training both in person and through online meetings, adapting to our clients' preferences.

Our methodology combines weekly online meetings for technical discussions and practical sessions, complemented by scheduled tasks to be carried out independently by both parties. ENSO members have teaching experience thanks to their role as assistant professors at the Polytechnic University of Catalonia – BarcelonaTech, a public institution dedicated to higher education and research, specializing in the fields of engineering and science.

Specialized courses for companies cover a wide range of topics. These include:

• Use of codes for beginner users. Introduction to modelling with system codes, choosing from RELAP, TRACE, MARS, SPACE, ASYST.
• Advanced modelling: simulation of steady-state and accident conditions in nuclear power plants. Codes: RELAP, TRACE, MARS, SPACE, ASYST.
• Advanced modelling: simulation of separate effect tests (SET). Codes: RELAP, TRACE, MARS, SPACE, ASYST.
• Advanced modelling: simulation of integral effect tests (IET). Codes: RELAP, TRACE, MARS, SPACE, ASYST
• Advanced modelling: simulation of iPWR-type SMRs. Codes: RELAP, TRACE, MARS, SPACE, ASYST.
• Use of codes for simulation of systems with alternative fluids (liquid metals, molten salts). Codes: RELAP, TRACE, ASYST.
• Advanced modelling: simulation and analysis of Severe Accidents. SCDAP code.
• Code development. Introduction to code development to learn how to add your own models, components, etc. Codes: RELAP, MARS
• Uncertainty analysis and BEPU methodologies. Codes: RELAP (with or without IUA2), MARS, ASYST
• Development of effective sections with cell-based neutron codes. Codes: DRAGON, SCALE, HELIOS
• Neutron kinetics for coupled thermohydraulic and neutron code calculations. Codes: RELAP, TRACE, NESTLE, PARCS, 3DKIN

These courses are designed to provide practical and efficient learning, supporting companies in developing key skills in the sector.