CSAS6: Control Module for Enhanced Criticality Safety Analysis with KENO-VI

L. M. Petrie, K. B. Bekar, D. F. Hollenbach,1 S. Goluoglu1

The Criticality Safety Analysis Sequence with KENO-VI (CSAS6) provides reliable and efficient means of performing keff calculations for systems that are routinely encountered in engineering practice. In the multigroup calculation mode, CSAS6 uses XSProc to process the cross sections for temperature corrections and problem-dependent resonance self-shielding and calculates the keff of three-dimensional (3-D) system models. If the continuous energy calculation mode is selected no resonance processing is needed and the continuous energy cross sections are used directly in KENO-VI, with temperature corrections provided as the cross sections are loaded. The geometric modeling capabilities available in KENO-VI coupled with the automated cross-section processing within the control sequences allow complex, 3-D systems to be easily analyzed.

1Formerly with Oak Ridge National Laboratory

ACKNOWLEDGMENTS

The CSAS6 Criticality Safety Analysis Sequence is based on the CSAS control module, and the KENO‑VI functional module, described in their respective chapters. G. E. Whitesides is acknowledged for his contributions through early versions of KENO. Appreciation is expressed to C. V. Parks and S. M. Bowman for their guidance in developing CSAS6.

Introduction

Criticality Safety Analysis Sequence with KENO-VI (CSAS6) provides reliable and efficient means of performing keff calculations for systems that are routinely encountered in engineering practice, especially in the calculation of keff of three-dimensional (3-D) system models. CSAS6 implements XSProc to process material input and provide a temperature and resonance-corrected cross-section library based on the physical characteristics of the problem being analyzed. If a continuous energy cross-section library is specified, no resonance processing is needed and the continuous energy cross sections are used directly in KENO-VI, with temperature corrections provided as the cross sections are loaded.

Sequence Capabilities

CSAS6 is designed to prepare a resonance-corrected cross-section library for subsequent use in KENO‑VI. In order to minimize human error, the SCALE data handling is automated as much as possible. CSAS6 and many other SCALE sequences apply a standardized procedure to provide appropriate number densities and cross sections for the calculation. XSProc is responsible for reading the standard composition data and other engineering-type specifications, including volume fraction or percent theoretical density, temperature, and isotopic distribution as well as the unit cell data. XSProc then generates number densities and related information, prepares geometry data for resonance self-shielding and flux-weighting cell calculations, if needed, and (if needed) provides problem-dependent multigroup cross-section processing. CSAS6 invokes a KENO-VI Data Processor to read and check the KENO-VI data. When the data checking has been completed, the control sequence executes XSProc to prepare a resonance-corrected microscopic cross-section library in the AMPX working library format if a multigroup library has been selected.

For each unit cell specified as being cell-weighted, XSProc performs the necessary calculations and produces a cell-weighted microscopic cross-section library. KENO-VI may be executed to calculate the keff or neutron multiplication factor using the cross-section library that was prepared by the control sequence.

Multigroup CSAS6 limitations

The CSAS6 control module was developed to use simple input data and prepare problem-dependent cross sections for use in calculating the effective neutron multiplication factor of a 3-D system using KENO-VI and possibly XSDRNPM. An attempt was made to make the system as general as possible within the constraints of the standardized methods chosen to be used in SCALE. Standardized methods of data input were adopted to allow easy data entry and for quality assurance purposes. Some of the limitations of the CSAS6 sequence are a result of using preprocessed multigroup cross sections. Inherent limitations in CSAS6 are as follows:

1. Two-dimensional (2-D) effects such as fuel rods in assemblies where some positions are filled with control rod guide tubes, burnable poison rods and/or fuel rods of different enrichments. The cross sections are processed as if the rods are in an infinite lattice of rods. If the user inputs a Dancoff factor for the cell (such as one computed by MCDancoff), XSProc can produce an infinite lattice cell, which reproduces that Dancoff. This can mitigate some two dimensional lattice effects.

It is strongly recommended that the user perform CSAS6 calculations of benchmark experiments similar to the problem of interest to demonstrate the validity of the cross-section data and processing for that type of problem.

Continuous energy CSAS6 limitations

When continuous energy KENO calculations are desired, none of the resonance processing modules are applicable or needed. Moreover, the MG limitations noted in the previous section are eliminated. The continuous energy cross sections are directly used in KENO. An existing multigroup input file can easily be converted to a continuous energy input file by simply specifying the continuous energy library. In this case, all cell data is ignored. However, the following limitations exist:

1. If CELLMIX is defined in the cell data, the problem will not run in the continuous energy mode. CELLMIX implies new mixture cross sections are generated using XSDRNPM-calculated cell fluxes and therefore is not applicable in the continuous energy mode.

2. Only VACUUM, MIRROR, PERIODIC, and WHITE boundary conditions are allowed. Other albedos, e.g., WATER, CARBON, POLY, etc. are for multigroup only.

3. Problems with DOUBLEHET cell data are not allowed as they inherently utilize CELLMIX feature.

Input Data Guide

The input data for CSAS6 are composed of two broad categories of data. The first is XSProc, including Standard Composition Specification Data and Unit Cell Geometry Specification. This first category specifies the cross-section library and defines the composition of each mixture and optionally the unit cell geometry that may be used to process the cross sections. The second category of data, the KENO-VI input data, is used to specify the geometric and boundary conditions that represent the physical 3-D configuration of the problem. Both data blocks are necessary for CSAS6.

All data are entered in free form, allowing alphanumeric data, floating-point data, and integer data to be entered in an unstructured manner. Up to 252 columns of data entry per line are allowed. Data can usually start or end in any column with a few exceptions. As an example, the word END beginning in column 1 and followed by two blank spaces or a new line will end the problem and any data following will be ignored. Each data entry must be followed by one or more blanks to terminate the data entry. For numeric data, either a comma or a blank can be used to terminate each data entry. Integers may be entered for floating values. For example, 10 will be interpreted as 10.0. Imbedded blanks are not allowed within a data entry unless an E precedes a single blank as in an unsigned exponent in a floating-point number. For example, 1.0E 4 would be correctly interpreted as 1.0 × 104.

The word “END” is a special data item. An “END” may have a name or label associated with it. The name or label associated with an “END” is separated from the “END” by a single blank and is a maximum of 12 characters long. At least two blanks or a new line MUST follow every labeled and unlabeled “END.” It is the user’s responsibility to ensure compliance with this restriction. Failure to observe this restriction can result in the use of incorrect or incomplete data without the benefit of warning or error messages.

Multiple entries of the same data value can be achieved by specifying the number of times the data value is to be entered, followed by either R, *, or $, followed by the data value to be repeated. Imbedded blanks are not allowed between the number of repeats and the repeat flag. For example, 5R12, 5*12, 5$12, or 5R 12, etc., will enter five successive 12s in the input data. Multiple zeros can be specified as nZ where n is the number of zeroes to be entered.

The purpose of this section is to define the input data in discrete subsections relating to a particular type of data. Tables of the input data are included in each subsection, and the entries are described in more detail in the appropriate sections.

Resonance-corrected cross sections are generated using the appropriate boundary conditions for the unit cell description (i.e., void for the outer surface of a single unit, white for the outer surface of an infinite array of cylinders, spheres, or planes). As many unit cells as needed may be specified in a problem. A unit cell is cell‑weighted by using the keyword CELLMIX= followed by a unique user specified mixture number in the unit cell data.

To check the input data without actually processing the cross sections, the words “PARM=CHECK” or “PARM=CHK” should be entered, as shown below.

=CSAS6 PARM=CHK

or

#CSAS6 PARM=CHK

This will cause the input data for CSAS6 to be checked and appropriate error messages to be printed. If plots are specified in the data, they will be printed. This feature allows the user to debug and verify the input data while using a minimum amount of computer time.

XSProc data

The XSProc reads the standard composition specification data and the unit cell geometry specifications. It then produces the mixing table and unit cell information necessary for processing the cross sections if needed. The XSProc section of this manual provides a detailed description of the input data and processing options.

KENO-VI data

Table 62 contains the outline for the KENO-VI input. The KENO-VI input is divided into 13 data blocks. A brief outline of commonly used data blocks is shown in Table 62. Note that parameter data must precede all other KENO data blocks. Information on all KENO-VI input is provided in the KENO chapter of this document and will not be repeated here.