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Modelling of the PACTEL SBL‐50 Transient Using RELAP5 Computer Code

MD.Hasib Uddin Talukder ; Mohammed Fazlur Rahman Bhuyan
Göteborg : Chalmers tekniska högskola, 2012. 97 s. CTH-NT - Chalmers University of Technology, Nuclear Engineering, ISSN 1653-4662; 262, 2012.
[Examensarbete på avancerad nivå]

The main purpose of the current Master of Sciences Thesis was modelling of the PACTEL SBL‐50 transient using RELAP5/MOD 3.3 Patch‐04 system thermal hydraulic computer code all through the process. For assessment of performance or evaluation of safety of the nuclear power plants, different kind of thermal‐hydraulic experiments are needed. However, experiments are not possible, or rather prohibited to be performed with real nuclear power plants. Therefore, it is essential to accomplish the tests under safe circumstances, and obtain the test data in a small scale before implementation in a large‐scale. In small‐scale test facilities, computer system codes (such as RELAP5) can simulate most of the postulated transients. Due to the similarity laws in heat and mass transfer, it is assumed that, if a code is capable of predicting the parameters in a scaled‐down geometry (i.e. in a test facility) then the features of a similar type of transient can also be predicted in a real reactor. Nevertheless, in order to achieve that, extensive validation and verification efforts are needed. In most cases, a large amount of effort is necessary for estimation of the possible conditions of a real transient, both in the analytical and experimental fields. The best example for such a coordinated action is an international benchmark project. Different organizations can participate in the international benchmark projects from various countries, which give good opportunities to the code users to construct their own models and to simulate the same transient by a certain computer code. Uncertainties originating from code performance, model parameters, or even user experiences can be revealed by comparison of the results. It can be seen that a large number of codes, models, model options, users, etc. participating in a benchmark may contribute to underlining a range of factors that are involved in uncertainty evaluation. In a few cases during the last two decades, the PACTEL Facility (Parallel Channel Test Loop), located at Lappeenranta University of Technology (LUT) in Finland, served as a subject for these benchmarks. The PWR PACTEL Benchmark Project was accomplished during a period between 2010 and 2011. The test simulated a small (1.0 mm) break in the cold leg with continuous inventory loss. The project consisted of a “pre‐test” (also known as the “blind calculation”) phase and the “post‐test” (in other words “open calculation”) phase. Together with many participants, Chalmers University of Technology took part, both in the pre‐test and post‐test phases of the benchmark. A simplified single‐tube steam generator (SG) model was applied in the pre‐test phase and it resulted in a reasonably good agreement with the measured data. Still, there was a margin for improvement, particularly in the temperature measured at the longest heat exchanger tubes of the SGs. Deviations in the initial temperatures were suspected to be originating from a specific phenomenon. Assumption of reverse flow in the longest tube was a realistic explanation of the temperature behaviour. Obviously, the single tube model was not able to reproduce this phenomenon by its one‐dimensional nature. However, it was expected that an extension of the model with multiple tubes might confirm or deny existence of this behaviour. In our investigations, we were focusing on proper modelling of reverse flow in the SGs. According to the simulations, the results obtained with the modified multi‐tube SG model showed better agreement with the test results. In particular, the new refined nodalization of the model contributed to a significantly improved temperature variation in the longest tubes of SGs, where flow reversal was experienced.

Nyckelord: RELAP5, PACTEL, benchmark, simulation, thermal‐hydraulics

Publikationen registrerades 2013-06-14. Den ändrades senast 2013-06-17

CPL ID: 178531

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