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Next: Conclusion Up: Coupled model theory and Previous: Test case results Contents Index

A little design study

In order to illustrate the usefulness of the implemented model we present a little design study in this chapter.

This very simple example consists of an investigation of the impact of the riser height, $H_{\mbox{\protect\scriptsize riser}}$ [m], on the total circulation mass flow rate, m_i [kg/s] and on the flow quality at the exit of the core, $\mbox{$<\!{x}\!>$}_e$ [--]. The investigation is carried out for three power levels; two with a separator and one (high power level) without a separator installed.

The two quantities, m_i and $\mbox{$<\!{x}\!>$}_e$ , selected for the investigation are of major importance from a safety point of view. In order to ensure stability of the boiling channel ([54], [55]) the mass flow rate has to exceed a certain minimum mass flow rate, m_i,s [kg/s], ie stability requirements demand that

m_i > m_i,s

(16.1)

Furthermore, the core exit quality, $\mbox{$<\!{x}\!>$}_e$ , is closely related to the boiling transition phenomenon which was mentioned briefly in section 11.2. Even though a correlation for the occurrence of boiling transition is to be applied locally over the full length of the rod bundle the requirement can in most cases be stated as

$\begin{displaymath} \mbox{$<\!{x}\!>$}_e < \mbox{$<\!{x}\!>$}_{\mbox{\protect\scriptsize crit}} \end{displaymath}$

(16.2)

where $\mbox{$<\!{x}\!>$}_{\mbox{\protect\scriptsize crit}}$ [--] is the flow quality at which the boiling transition is predicted to occur.

In all the calculations we have used the test case described in chapter 14 and changed the appropriate input values as required. The result of the investigation is shown in Figures 16.1 and 16.2.

For completeness we also show in Figures 16.3 and 16.4 the power distributions and center line fuel temperature for three of the "designs". As we can see a higher power output with a short riser implies a strong flux depression in the upper part of the core which imply that the peak moves even further downwards and becomes considerably higher^16.1. The high power peak result in an increased center line fuel temperature as we can see in Figure 16.4.

$\begin{figure} % latex2html id marker 45899\rule{\textwidth}{0.2mm} \rule{0cm}... ...er level, $P_{\mbox{\protect\scriptsize th,tot}} = 2700$\ MW ($+$).}\end{figure}$

$\begin{figure} % latex2html id marker 45950\rule{\textwidth}{0.2mm} \rule{0cm}... ...er level, $P_{\mbox{\protect\scriptsize th,tot}} = 2700$\ MW ($+$).}\end{figure}$

$\begin{figure} % latex2html id marker 46010\rule{\textwidth}{0.2mm} \rule{0cm}... ...ox{\protect\scriptsize th,tot}} = 2700 {\mbox{ MW}}$, $-$separator.}\end{figure}$

$\begin{figure} % latex2html id marker 46087\rule{\textwidth}{0.2mm} \rule{0cm}... ...ox{\protect\scriptsize th,tot}} = 2700 {\mbox{ MW}}$, $-$separator.}\end{figure}$

Next: Conclusion Up: Coupled model theory and Previous: Test case results Contents Index

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