Benchmark analysis of a multiple steam generator tube rupture nuclear accident scenario using Apros code

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master_Alblouwy_Fares_2025.pdf (4.48 MB)

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School of Engineering | Master's thesis
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Date

2025-11-17

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Major/Subject

Energy Conversion Processes

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Degree programme

Master's Programme in Advanced Energy Solutions
Kehittyneiden energiaratkaisujen maisteriohjelma
Magisterprogrammet i avancerade energilösningar

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en

Pages

67

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Abstract

Accurately modelling complex transients in a nuclear power plant requires analytical and design tools that are sufficiently reliable to ensure both reactor safety and regulatory confidence. This thesis presents a benchmark study of the Apros thermal-hydraulic code through the simulation of a Multiple Steam Generator Tube Rupture (MSGTR) transient under the framework of the International Standard Problem No. 52, based on the PKL III J5.1 Run 2 experiment. The study was carried out in two phases. In the blind phase, the Apros model of the test facility was fully revised and developed, and a complete analysis of the transient was performed while the experimental data remained undisclosed. In the open phase, the model was further refined, and a second set of analyses was performed using the disclosed experimental data and additional clarifications, followed by a structured sensitivity analysis. The results show that Apros is able to reproduce the main characteristics of the MSGTR transient with good qualitative agreement and generally reasonable quantitative accuracy for key parameters such as system pressure, core temperature response, mass inventories, and the timing of safety system actuations. The study identifies several modelling parameters that strongly influence the results, including the discharge coefficient and the main steam relief valve pressure setpoint. The work also highlights the influence of user modelling choices and experimental uncertainties in benchmark analyses. Overall, the thesis concludes that Apros can produce credible best-estimate simulations of such events when the key parameters, initial conditions and modelling assumptions are well justified. It also emphasizes the value of international validation activities, such as the International Standard Problem activity, in supporting nuclear safety.

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Supervisor

Holmberg, Henrik

Thesis advisor

Karppinen, Ismo

Keywords

nuclear safety, Apros, international standard problem, MSGTR, OECD/NEA, PKL

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https://urn.fi/URN:NBN:fi:aalto-202512159149

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[dipl] Insinööritieteiden korkeakoulu / ENG