Fuel and Core

The project CaNel – Calibration of Fuel Performance Codes aims to address challenges in calibrating fuel performance codes, which are critical for predicting thermo-mechanical behavior and ensuring nuclear fuel safety during various reactor operations and incidents. Calibration challenges include handling interlinked models, biased and sparse data, input uncertainties, computational costs, and model inadequacies. Accurate inverse uncertainty quantification (UQ) is essential for establishing plant operation safety limits, preventing fuel cladding breaches, and efficiently managing reactor operation and fuel utilization, all while minimizing waste and costs.

A significant focus of the project is to address a specific challenge in calibration, namely, model inadequacies. Inadequacies occur when models fail to replicate physical reality accurately and can significantly impact safety predictions if not adequately accounted for. Therefore, the project has developed a methodology to address model inadequacy on calibration parameters for subsequent propagation. The developed method is based on Markov Chain Monte Carlo (MCMC) and uses Gaussian Process surrogate modeling for efficiency. In addition, in the project, other machine learning surrogate modeling techniques are developed to address sequential data to improve calibration and UQ techniques, benefiting related nuclear technology projects.

The project's applications focus on calibrating models for cladding oxidation, hydrogen pickup, and gas release, as these factors directly affect fuel safety. It uses both commercial data from Westinghouse and open-source data.

This project is part of WP6- “Advance fuel performance modeling” in the EU-supported APIS project (https://apis-project.eu/), with the aim to deliver a new calibration methodology to the stakeholders.

APIS is short for Accelerated Program for Implementation of secure VVER fuel Supply. The objective of the APIS-program is to create security of supply of nuclear fuel for Russian-designed pressurized water reactors (VVER) operating in the EU and Ukraine by diversification of fuel sources in full compliance with nuclear safety. The project is reinforcing European capabilities for supply of VVER-440 type of nuclear fuel by providing Western fuel designs and fabrication capacities as well as by creating cooperation among participating countries in the fuel licensing. The program is co-funded by the European Union through the Horizon program.

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Gustav Robertson

During the 20th and the beginning of the 21th century, a set of different reactor design have been proposed, studied and constructed all around the world. Historically, the first attempt to categorize the different reactor types is by the neutron flux spectrum, or, in simple words, by the average energy of the neutrons. Fast reactors use neutrons characterized by energies similar to those produced by fission reaction to sustain the fission chain reaction, while thermal reactors make use of neutrons which are in thermal equilibrium with the surrounding media. In order to obtain these energies, there is the need to slow down the fast neutrons and it is necessary a moderating media. Water is one of the best media for this purpose and engineers and physician soon realized that it is also the perfect coolant of a nuclear reactor. Today the vast majority of the nuclear reactor cores uses thermal spectrum and light water coolant.

During the ‘70s and ‘80s most of the attention was focused to create larger and larger nuclear reactors, but after Three Mile Island accident and Chernobyl accident, and even more recently with the Fukushima accident, the attention of designers has been shifted towards small modular reactors (SMR) in order to limit the potential economical and safety risks associated to reactor construction, operation and future reactor decommissioning operations. By contrast, the reactor dimension has negative effects on the fuel cycle performance since the reduced dimension is responsible for a lower neutron economicity, which can be interpreted as the capability of neutrons to cause a fission reaction without being absorbed by different materials or escape through the reactor boundaries. The reduced neutron economicity has direct negative consequences on the volumes of nuclear wastes produced for unit energy output and for what concerns the economic performance of the fuel cycles. For this reason, ad hoc solutions must be studied for these reactors to improve their performance, including but not limited to fuel assembly design, fuel composition, reflector design and control and shutdown system design.

In this project, as part of the ANItA competence center, we aim to propose and apply modern optimization techniques for fuel composition and loading pattern design for two SMRs: AP300 from Westinghouse and BWRX-300 from General Electric Hitachi. Additionally, extensive studies will be performed on the possible operation of AP300 with boron-free cycles and load following operations for both reactors designs.

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Flavio Ferella

Small Modular Reactors (SMRs) have garnered substantial attention in recent years due to their compact size and modular design, allowing for quicker and more cost-effective manufacturing. These reactors, tailored for various end uses, are at different stages of development globally, with some ready for near-term deployment. Many SMR designs are based on established large-scale reactors, primarily Light Water Reactors (LWRs), leveraging operational experience. However, differences in core sizes, composition, and operational modes may impact fuel behavior and operational limits in SMRs. As part of the ANItA competence center, we aim to identify key differences in fuel behavior in near-deployment SMRs. The project will assess these changes through modeling and post-irradiation examination. Additionally, the need for establishing poolside fuel inspection capabilities to support Post Irradiation Examination (PIE) at distributed reactors will be examined to minimize fuel transportation to hot cell laboratories.

Contact

Vikram Rathore