Thermal-Hydraulic study on Passive Core Makeup system via OECD-ATLAS project

  • Waleed Al Naqbi

    Student thesis: Master's Thesis


    The goal of the present work is to investigate the mitigation effect of the Core Makeup System (CMS) in nuclear power plants during severe accidents. The CMS is an enhanced version of the conventional Emergency Core Cooling System (ECCS) that utilizes a pipe connection between the SIT and the Primary loop in order to provide high pressure, boron containing cold water into the RCS across all operating pressures. Additionally, RELAP-5/MOD3.3 code Validation and Verification (V&V) was carried out as second major objective of this study by examining certain thermal hydraulic phenomena such as direct contact condensation and thermal stratification. Two items were considered, where the first item (B2.1) investigated the performance of the Hybrid Safety Injection Tank (H-SIT) during a Station Black-Out (SBO) event. The second item (B2.2) simulated a Small Break Loss Of Coolant Accident (SBLOCA) with the Passive Emergency Core Cooling System (PECCS). At the beginning, blind pre-test simulations were performed on both items using the initial conditions and design documents provided by the Operating Agency (OA). Afterwards, experimental data for item B2.1 were received and utilized in improving the accuracy of the original results during the pre-test calculations. A number of parameters such as Environmental Heat Loss (EHL), Nodalization, and Friction factors were examined/utilized in order to reduce the discrepancy between the simulation and experimental results. The results showed that EHL was the biggest contributor in the effort of eliminating the discrepancy between experimental values and the post-test results. For instance, the mismatch in sequence of events timings was decreased by 2-3 folds after adopting EHL within RELAP-5 simulation of item B2.1. Due to certain modifications on the experimental setup, determined by the OA, the investigation of thermal hydraulic phenomena could not be performed and it is recommended for future work.
    Date of AwardDec 2018
    Original languageAmerican English


    • ATLAS Facility; Severe Accidents; Passive Safety System; Core Makeup System.

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