Syntax of input file

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Next: Syntax for cross section Up: Input description Previous: Command line arguments Contents Index

Syntax of input file

The majority of input parameters are specified using an input-file, ie a file read by the program in which the input parameters are listed following a closely specified syntax. An input file gives the most user-friendly and flexible input interface since the user may create or edit the file by aid of any text editor.

If only a few numbers serve as input a list of the numbers separated by spaces and line feeds is sufficient, but as the number of input parameter increases the input file becomes more and more unreadable and prone to errors. This is remedied completely by allowing comment statements in the input file. The syntax of the input file is governed by the rules

The input parameters must follow the order to be specified later (see Figure 3.5).
Individual number must not be broken; by a newline etc.
Numbers are specified using standard typography, ie 100.0, 10, 1.9873E-01 or 2.34948326e+02.
Numbers are separated by one or more of the characters: space, tab or newline.
All numbers are at first read as doubles and later converted to the appropriate type, eg. the integer type (ie an integer may be written as 100.0).
Comment statements are issued by the characters "//" also used by C-compilers. When the parser meets "//" the characters from "//" to the end of the line are discarded.

The input parameters in the input file are the following

.

General model parameters.

The number of neutron energy groups to be used in the neutronics calculation [--].
Released energy by fission of one ²³⁵U nucleus [J].
Total thermal power generated by one fuel assembly [W].

.

Geometry of the reactor.

Z-coordinate for the bottom of the core plate [cm].
Z-coordinate for the bottom of the core [cm].
Z-coordinate for the top of the core [cm].
Z-coordinate for the top of the reactor [cm].
Cross-sectional area with fuel for one fuel assembly [ $\mbox{cm}^2$ ].

.

Specification of the requested computational grid.

Requested steplength in the bottom reflector and core plate [cm].
Requested steplength in the core [cm].
Requested steplength in the top reflector [cm].
Number of transition points [--].

.

Specifications in regard to cross section tables.

Number of fuel temperatures in the fuel cross section table [--].
Number of void fractions in the fuel cross section table [--].
Fuel temperatures used for the fuel cross section table [ ${}^\circ\mbox{C}$ ].
Void fractions (true fractions) used for the fuel cross section table [--].
Number of void fractions (true fractions) in the top reflector table [--].
Void fractions (true fractions) used for the table of cross sections for the top reflector [--].
Density of liquid assumed in the cross section tables, $\rho_f^*$ [kg/ ${\mbox{m}}^3$ ].
Density of vapor assumed in the cross section tables, $\rho_g^*$ [kg/ ${\mbox{m}}^3$ ].

.

Convergence criteria for the eigensolutions.

Convergence criterion for the iterations with the power method. If the value is 0 we use a default value (10^-2).
Convergence criterion for the fractional iteration method iterations.

>
Do not perform iterations with the fractional iteration method--simply return the solution obtained with the power method.
>
Use default value (10^-7).

.

Number of reductions of the grid steplengths by a factor 2 before the calculations are carried out. This is useful for numerical experiments.

In order to illustrate the order of the input parameters and to show how the comment statement is used an example of an input file is given in Figure 3.5.

$\begin{figure} % latex2html id marker 12850\rule{\textwidth}{0.2mm} \begin{... ...lof}{figure}{{\sl Figure~\thefigure}\hspace{1em}Input file example.}\end{figure}$

It should be noted that we deliberately have given a low priority to an input file error check because such a check would demand a considerable amount of programming effort. Furthermore, this project has its weight put more on the modeling that on the programming. As a result, the program for instance calculates an erroneous computational grid if we choose a coarse grid and a large number of transition points. Thus the user should write the input files with care.

Finally, if the user chooses to obtain an accurate solution with the fractional iteration method using the solution calculated by the power method with a convergence criterion other that 10^-3 a note of caution is appropriate. To illustrate the problem we have depicted a sequence of iterates typical for the power method for a real power reactor (GE (8 x 8) BWR-assemblies) in Figure 3.6.

$\begin{figure} % latex2html id marker 13433\rule{\textwidth}{0.2mm} \rule{0cm}... ...sequence of iterates for the power method for a real power reactor.}\end{figure}$

If the convergence criterion for the power method, $\epsilon_{\mbox{\protect\scriptsize PM}}$ , is chosen too large we cannot be sure that the criterion on the eigenvalue estimate $\kappa = \lambda^{(k)}$ satisfies

$\begin{displaymath} \min\limits_{i} \vert \lambda_i - \kappa \vert = \vert\lambda_0 - \kappa\vert \end{displaymath}$

(3.1)

This implies that we do not necessarily get the fundamental eigensolution. This is, however, easily discovered by negative elements in the flux solution. Furthermore, the simple forward elimination - backward substitution is only guaranteed to work when $\kappa < \lambda_0$ (see p.

) but in Figure 3.6 it is seen that we probably are in trouble if we choose a too large $\epsilon_{{\mbox{\protect\scriptsize PM}}}$ .

In practice, however, we have observed no problems for $\epsilon_{{\mbox{\protect\scriptsize PM}}}$ .

Next: Syntax for cross section Up: Input description Previous: Command line arguments Contents Index

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