# 7.7. CRAWDAD: Module to Produce CENTRM-Formatted Continuous-Energy Nuclear Data Libraries

*M. L. Williams, D. Wiarda, and S. W. D. Hart*

ACKNOWLEDGMENTS

The authors would like to acknowledge the important contributions to CRAWDAD made by former ORNL staff N. M. Greene and D. F. Hollenbach.

## 7.7.1. Introduction

SCALE uses the code CRAWDAD (Code to Read And Write DAta for Discretized solution) to read nuclear data from the SCALE-6 continuous (CE) library files, and write it to an output file in the particular format needed for the discretized energy solution in CENTRM. Prior to SCALE-6, the CE data used by the CENTRM and PMC modules were distributed directly in the CENTRM library format. However beginning with SCALE-6, the same CE data are used by both CENTRM/PMC and by the CE versions of the KENO and Monaco Monte Carlo codes. CE nuclear data for each nuclide are stored in individual files contained in the SCALE permanent data directory. CRAWDAD reads the files for each material appearing in a problem and combines all data into a single problem-dependent CENTRM library file stored in the temporary directory for execution.

All SCALE-6 calculations that use modules CENTRM and PMC for self-shielding multigroup (MG) cross sections must first execute the CRAWDAD computational module. During execution of SCALE sequences, the XSProc self-shielding module automatically executes CRAWDAD whenever the CENTRM/PMC method is specified. CRAWDAD also can be run in stand-alone mode to process and save a CENTRM-formatted library for subsequent CENTRM/PMC calculations.

PMC allows the energy range of the CE data to be selected, as well as which reactions are placed on the output CENTRM library. The output CENTRM library always contains the following “standard” nuclear data types for all materials: total (1); elastic (2); complete inelastic (4); radiative capture (102); fission (18); total/prompt/delayed nubars (452, 455, 456); and (n,:math:alpha) cross section for 10B and 7Li. In this list, the number shown in parenthesis corresponds to the ENDF/B “mt numbers.”

CE data are obtained for arbitrary energies by linear interpolation of discrete cross sections defined on a pointwise (PW) energy mesh. The PW energy mesh for a given nuclide is sufficiently fine that error introduced by linear interpolation between any two points is less than 0.1%. CRAWDAD also interpolates the CE data to the specific temperatures needed for the problem. The default temperature interpolation method uses square-root of temperature below 1200 Kelvin and a finite difference procedure above this temperature [CRAWDADHCML16].

## 7.7.2. CRAWDAD Input Data

For standalone CRAWDAD execution, the user prepares the FIDO input deck
as described below. However during a SCALE sequence computation, the
XSProc module always executes CRAWDAD for CENTRM/PMC self-shielding
calculations, and defines appropriate CRAWDAD parameter values based on
specified CENTRM and PMC options. This is the recommended mode of
operation. Some XSProc default values for CRAWDAD can be changed using
keywords in the CENTRM DATA block; e.g., see parameters *mtout=* and
*kernel=* in Sect. 7.4.4. Several options available for stand-alone
execution cannot be controlled by keywords in the sequence runs, as
these are set automatically

```
CRAWDAD STANDALONE INPUT
************** DATA BLOCK 1
0$$ LOGICAL UNIT ASSIGNMENTS [4 entries. Default values given in parentheses]
Entry Number Variable Name Description Default Value
1 lcen logical unit number of output CENTRM library (81)
2 n17 logical unit for scratch (17)
3 n18 logical unit for scratch (18)
4 n19 logical unit for reading CE-KENO libraries (88)
1$$ INTEGER PARAMETERS [10 entries ]
1 num_nucs number of PW nuclides to process (1)
2 idtap identifier placed on header of output CENTRM library (66666)
3 iprt print out option (1)
-1 no print out AT ALL
0 hardly any print
1 normal print
2 debug print
4 obsolete feature
5 iterp temperature interpolation method for PW cross sections (0)
0 square-root-T interpolation for T<1200 K and finite difference for T>1200 K
1 square-root-T interpolation for all temperatures
2 finite difference interpolation for all temperatures
6 libth create CENTRM thermal kernel library for bound moderators (1)
0 no
1 yes (output kernel file is named lib_cen_kern)
7–10 N/A extra integer parameters (not used) (0)
1** REAL PARAMETERS [10 entries]
1 teps tolerance on temperature differences (5.0)
( temperatures within +/- "teps" are assumed equal)
2 tole not implemented
3–10 N/A extra real parameters (not used) (0.0)
T terminate data block 1
```

```
************** DATA BLOCK 2
***** Repeat data block(s) 2 and 3, stacked "num_nucs" times to create a new
CENTRM library containing specified temperatures and reaction types
2$$ NUCLIDE INFORMATION [5 entries]
Entry Number Variable Name Description Default Value
1 za zaid for this nuclide in PW XS library
2 lver version number of evaluated nuclear data (e.g, 7 for ENDF/B-VII)
3 mod desired mod number of evaluated nuclear (-1)
-1 => use latest mod
4 inum desired number of temperatures for this nuclide (0)
0 - put all available temperatures on output CENTRM library
n - include data at the "n" temperatures in 4** array
5 mtout MTS to be included on output CENTRM PW library (2)
0 - output PW data for all available MTs
1 - output PW data only for default standard MTs:
1, 2, 4, 102, 18, 452, 455, 456 for all materials; and 107 for 10B and 7Li
2 - output standard MTs, plus inelastic levels and (n,2n)
3 - standard MTs plus those listed in 5$$ array
-3 - out all MTs EXCEPT those listed in 5$$
6 kmod mod number for ENDF thermal scattering law data (-1)
:math:`\geq` 0 – use cross section data with this thermal mod number
-1 – use cross section data with latest thermal mod and kernel (if available)
-2 – do not include bound kernel data (i.e., free-gas scattering will be used in CENTRM)
7 lsrc Source of nuclear data (0 only allowed at present)
0/1/2/3/4 => ENDF/JEF/JENDL/BROND/CENDL
3** ENERGY LIMITS [2 entries]
1 pemin minimum energy for PW data (0.0001 eV)
2 pemax maximum energy for PW data (20 MeV)
T terminate data block 2
```

```
************** DATA BLOCK 3
***** Only enter if inum >0, or mtout= +/- 3 )
4** DESIRED TEMPERATURES for this nuclide [inum entries]
5$$ MT VALUES (if mtout = +/-3) [always end with an "E"]
T terminate data block 3
Optional 72 character title for the CENTRM library
```

## 7.7.3. CRAWDAD Sample Input

Example 7.7.1 shows an example input file for standalone execution of CRAWDAD. The CRAWDAD output for this case is shown in Example 7.7.2. In more typical cases where CRAWDAD is executed automatically by the XSProc module as part of a SCALE sequence calculation, no CRAWDAD input is needed, but similar CRAWDAD output will be printed.

```
=crawdad
0$$ 81 17 18 77 e
1$$ 5 66666 0 0 2 1 e
1** 5.00E+00 e
t
2$$ 8016 7 3 2 2 -1 0
3** 1.00-03 1.30+04 2t
4** 6.00+02 9.00+02 3t
2$$ 13027 7 1 1 2 -1 0
3** 1.00E-03 1.30E+04 2t
4** 6.50E+02 3t
2$$ 92235 7 7 1 2 -1 0
3** 1.00E-03 1.30E+04 2t
4** 9.00E+02 3t
2$$ 92238 7 5 1 2 -1 0
3** 1.00E-03 1.30E+04 2t
4** 9.00E+02 3t
2$$ 1001 7 5 1 2 0 0
3** 1.00E-03 1.30E+04 2t
4** 6.00E+02 3t
end
, move the generated PW CENTRM library to execution directory
=shell
mv ft81f001 $RTNDIR
end shell
' ……………………………………………………………………
```

```
A new centrm library has been written on unit number: 81
The number of input nuclides was: 5
Number of Nuclides on output PW library: 5
Directory containing input PW library files: /scale/scale6.dev/data/cekenolib_7.0
Description of Output CENTRM Library
Entry ZA Data Src Vers No. Mod No. MT-Optn Thermal ID XS temperatures
----- ----- -------- -------- ------- ------- ---------- ---------------
1 8016 endf 7 3 2 0 600.00
900.00
2 13027 endf 7 1 2 0 650.00
3 92235 endf 7 7 2 0 900.00
4 92238 endf 7 5 2 0 900.00
5 1001 endf 7 5 2 7000001 600.00
Nuclides in Problem-Dependent Thermal Kernel Library
Library Identifier: 901
Number of kernels: 1
Maximum Order of Scattering: 6
Maximum Number of Temperatures: 9
Library Directory
Nuclide Identifier Sigfree File
---------- ---------- ------- -------------------------------------------
h(h2o) 7000001 20.48 endf_b/vers7/1-0
===============================================================================
logical 18 (problem dependent centrm thermal kernel library)
dataset name: /usr/tmp/xmw.9890/lib_cen_kernel
volume:
===============================================================================
CRAWDAD has terminated normally
```

References

- CRAWDADHCML16
Shane WD Hart, Cihangir Celik, G. Ivan Maldonado, and Luiz Leal. Creation of problem-dependent Doppler-broadened cross sections in the KENO Monte Carlo code.

*Annals of Nuclear Energy*, 88:49–56, 2016.