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Next: A little design study Up: Coupled model theory and Previous: Input for the thermal Contents Index

Test case results

The normalized flux distribution within the reactor is depicted in Figure 15.1. The effective multiplication constant, $k_{\mbox{\protect\scriptsize eff}}$ , (the largest eigenvalue) is given by

$\begin{displaymath} k_{\mbox{\protect\scriptsize eff}} = 1.2272 \end{displaymath}$

(15.1)

which indicates that the reactor is highly super-critical (due to the assumption of no burnable poison). The linear heat generation rate for one fuel rod, $q_{\mbox{\protect\scriptsize rod}}'$ [W/m], is depicted in Figure 15.2.

As we can see both the thermal flux and the linear heat generation profiles show a high bottom peak due to the high steam contents in the upper part of the core.

$\begin{figure} % latex2html id marker 45035\rule{\textwidth}{0.2mm} \rule{0cm}... ...The boundary of the core is indicated by the dotted vertical lines.}\end{figure}$

$\begin{figure} % latex2html id marker 45081\rule{\textwidth}{0.2mm} \rule{0cm}... ... Note that the z-coordinates are given relative to the core bottom.}\end{figure}$

The steady-state total recirculation mass flow rate, m_i [kg/s], obtained is

$\begin{displaymath} m_i = 6300 {\mbox{ kg/s}} \end{displaymath}$

(15.2)

ie a value which is remarkably close to the value given in Table 14.1 but we have to remember that this could be a coincidence since we do not know the sensitivity of the more uncertain input quantities, like the height of the riser and the separator loss coefficient.

The core pressure distribution, p(z) [Pa], is depicted in Figure 15.3. It is easy to identify the pressure losses due to the 5 spacers. We notice that the pressure loss of a spacers increases with the distance from the core bottom due to the increasing flow quality.

$\begin{figure} % latex2html id marker 45103\rule{\textwidth}{0.2mm} \rule{0cm}... ...thefigure}\hspace{1em}The core pressure distribution, $p(z)$\ [Pa].}\end{figure}$

The flow quality, $\mbox{$<\!{x}\!>$}$ [--], and void fraction, $\mbox{$<\!{\alpha}\!>$}$ [--], distributions within the core are illustrated in Figures 15.4 and 15.5 respectively. The liquid temperature in the core, $T_\ell(z)$ [ ${}^\circ\mbox{C}$ ], is illustrated in Figure 15.6.

The flow quality at the exit of the core is about 14.5% which corresponds to values obtained in forced circulation BWRs.

$\begin{figure} % latex2html id marker 45123\rule{\textwidth}{0.2mm} \rule{0cm}... ... distribution within the reactor core, $\mbox{$<\!{x}\!>$}$\ [---].}\end{figure}$

$\begin{figure} % latex2html id marker 45143\rule{\textwidth}{0.2mm} \rule{0cm}... ...ion distribution within the core, $\mbox{$<\!{\alpha}\!>$}$\ [---].}\end{figure}$

$\begin{figure} % latex2html id marker 45163\rule{\textwidth}{0.2mm} \rule{0cm}... ...temperature within the core, $T_\ell$\ [\mbox{${}^\circ\mbox{C}$}].}\end{figure}$

In Table 15.1 we list a number of important results from the hydraulics model, among others the inlet subcooling^15.1 , $h_{\mbox{\protect\scriptsize sub}}$ , and the point of void departure, z_d. As we can see the point of void departure is located very close to the bottom of the core.

$\begin{table} % latex2html id marker 45227\rule{\textwidth}{0.8mm} \refstepcou... ... & 0.9 & 909.4 & 5404.0 & 10.8\\ \hline \end{tabular*}\end{minipage}\end{table}$

In Table 15.2 we list all the pressure changes in the primary coolant system. As we can see the major pressure losses are due to the core and the steam separator. Other noteworthy pressure losses are losses due to the core plate, the lower plenum local loss and the singular pressure change from the riser to the steam separator flow paths.

The author finds reasons to question the pressure drop across the riser to separator contraction since the magnitude of this pressure change is 10 times larger than the pressure change across the core to riser expansion. It is therefore seem appropriate to review the model of the two-phase singular contraction pressure change given in 5.7.

$\begin{table} % latex2html id marker 44945\rule{\textwidth}{0.8mm} \refstepco... ...- & $-7.679$\ & $-7.679$ \\ \hline \end{tabular*} \end{minipage} \end{table}$ ^15.2 ^15.3

The results from the thermal design code are shown in Figures 15.7 and 15.8.

As we can see in Figure 15.8 we are far from a situation of (steady-state) fuel center melt.

$\begin{figure} % latex2html id marker 45295\rule{\textwidth}{0.2mm} \rule{0cm}... ...$). All the temperatures are measured in \mbox{${}^\circ\mbox{C}$}.}\end{figure}$

$\begin{figure} % latex2html id marker 45337\rule{\textwidth}{0.2mm} \rule{0cm}... ...$). All the temperatures are measured in \mbox{${}^\circ\mbox{C}$}.}\end{figure}$

Next: A little design study Up: Coupled model theory and Previous: Input for the thermal Contents Index

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