problem with setting the inlet temperature in a helium cooled reactor

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András Keresztú...
problem with setting the inlet temperature in a helium cooled reactor

Dear ATHLET developers,

We would like to simulate an SBO transient on the ALLEGRO helium gas-cooled fast reactor. The ATHLET model contains only the active core. The boundary conditions (inlet mass flow, pressure and temperature) are given as a function of time.

According to the following graphs, the flow rate can be set perfectly, but there is a small difference between the given inlet pressure and the actual pressure. The difference is very large regarding the inlet temperature, which largely influences the results of the simulation.

We believe that there is a mistake in the input, but we couldn’t find it.

Could you take a look at it and send us some information about how can we modify the input to set the inlet temperature according to the given function?


Dear András,

Thank you for your comment.

As far as I can see from your input deck, you specified an open system with two boundary conditions, inlet and outlet, both defined as fill/leak.

The general difficulty of such a configuration is that you are not able to exactly control the system pressure. Thus, it is recommended to use one massflow boundary condition (i.e. fill/leak) and one pressure boundary condition (time-dependent volume). This recommendation basically holds for every CFD-like code.

For example: you could define the upper bc as time-dependent volume with a given pressure. Depending on pressure losses inside your system, a certain pressure distribution will establish. The lower bc (fill) could then consider the pressure inside the injecting CV (the CV where the fill injects to) for the calculation of the enthalpy. (Currently, you use an independently of your system defined "inlet pressure" T.PIN, which finally results in the temperature deviations.)

Of course, the pressure inside the injecting CV may vary depending on the considered transient. In order to "adjust" the pressure, you could try to adequately control the pressure of the time-dependent volume via GCSM by considering the deviation of the pressure in the injecting CV.

Please let me know if you need further assistance.

Best regards,

Philipp Schoeffel