Words to the Wise...

Error in B4C Default Density

The concept of the Material Information Processor and the Standard Composition Library in SCALE has been to provide users with an easy way to specify common materials in their problems (e.g., water, stainless steel, B4C, UO2) using nominal densities and natural distributions of individual isotopes in multi- isotope nuclides (e.g., boron and uranium). Users can modify the default densities or isotopic distributions as needed through specific input parameters. The Material Information Processor then calculates the atomic number densities of each isotope based on the input data. The user can specify the density and/or atomic densities for a material by one of four methods:

• accept the default density,
• adjust the default density by a density multiplier,
• specify the density using the "DEN=" parameter, or
• specify the atomic density for each isotope as calculated by the user.

The default densities in the SCALE Standard Composition Library are the default for nominal conditions, based on published data and standards that are widely used in the technical community (e.g., the CRC Handbook or industry standards). In the same manner, the default relative weight fractions of individual isotopes in a multi-isotope nuclide (e.g., 10B and 11B in boron) correspond to the natural distribution of these isotopes from the same literature references.

It is an error for the user to accept the default density in the case of enriched material, especially for elements with low atomic masses and isotopes that are large neutron absorbers (e.g., boron and lithium). A user modeling any highly enriched material should have as-built or other data from the vendor documenting the density of the material that could be input directly in SCALE using the "DEN=" parameter.

Unfortunately, this topic is not discussed adequately in the appropriate sections of the SCALE manual. The SCALE manual will be updated to explain that the code treats the default mass density as fixed regardless of enrichment, exactly as it treats a user-specified mass density. The implications of a fixed default density change will be discussed for materials such as enriched B4C, boron, or lithium. Likewise, the CSASIN input processor for SCALE criticality safety analyses issues no warning to this effect. The CSASIN input processor will be updated in SCALE-4.4 to issue a warning if the user specifies a change in the default isotopic distribution of boron or lithium and also uses the default density. The warning will state that the default density is only consistent with the default natural isotopic distribution of that element.

When the same resonance nuclide occurs in more than one zone of the cell in the standard composition specification of a SCALE problem, the Dancoff factor is unable to account for the repetition. This limitation leads to under predicting the self-shielding for this nuclide, as the resonance overlap between the two zones is not considered. For further discussion of the Dancoff factor see Sect. M7.5.2.3 of the SCALE manual, and for more on resonance overlap effects, see Sect. M7.A.7.

A user problem recently led to the identification of two undocumented limitations in QADS and QAD- CGGP. If more than 20 elements or mixture numbers greater than 40 are specified in QADS, erroneous results can be produced. This limitation exists in the point kernel module QAD-CGGP, upon which QADS is based. QADS uses MIPLIB to calculate the number densities of individual nuclides. QADS then sums the nuclide number densities by element for input to QAD-CGGP.

In SCALE-4.3 no error message was generated for this condition. Depending on the number of materials specified, the case would either run and give inaccurate results or fail with a memory-related error message. It is recommended that previous QADS cases be checked to ensure valid results. With SCALE 4.4, an error message is generated and execution terminates. Ordinarily this limitation is minor, since shielding cases typically have either single- or few-material sources and a limited number of shield materials with 3 to 4 nuclides per material. Note that the limitations are for a total of 20 elements, not for 20 materials per mixture. Spent fuel obviously has many more than 20 elements, but typically only the fresh fuel material is specified.

When a problem includes reflection, the total volumes calculated by KENO V.a do not include the effects of that reflection. If one face is reflected, the total volumes are a factor of 2 too small, if two adjacent faces are reflected, the volumes are too small by a factor of 4, and if three faces meeting in a corner are reflected, the volumes are too small by a factor of 8. If opposing faces are reflected, then the system is infinite, and the volumes are also infinite. This discrepancy in the calculated volumes results in the masses calculated by KENO V.a being too small by the same factor as the volumes, and the fission densities and fluxes being too high by the same factor.

Many times it is desirable to generate a source in multiple group structures. In review work, it allows the reviewer to compare directly with an alternative group structure. In point kernel applications or using point-wise energy Monte Carlo techniques, the group structure of the source is arbitrary and a flexible group structure option is very useful. Some confusion has arisen regarding the generation of source spectra in multiple group structures, since the primary SCALE source-term module SAS2H only uses the group structure of the shielding cross-section library.

Currently in SCALE-4.3, users have the option in either a stand-alone ORIGEN-S or ORIGEN-ARP case of specifying built-in group structures or a completely arbitrary group structure for both neutrons and gamma rays. In the PC-based ORIGEN-ARP input processor, users can specify the option "OTHER" for the neutron- and gamma-group structures and then specify their own group structures. This ORIGEN-ARP case can be a complete LWR fuel assembly source characterization (i.e., input the initial fresh fuel loadings, burnup and cooling history) or a decay-only case using a previously generated assembly source term read from unit 71 (ft71f001). In either case, ORIGEN-ARP is simple to use to set the ORIGEN-S option of specifying source terms in an arbitrary energy group structure.

A very useful technique would be to use ORIGEN- ARP to set up a case designed to read the source from unit 71, decay it a series of cooling times, and generate the output source in the desired group structure. The ORIGEN-S input stream generated by ORIGEN-ARP can then be used to perform these transformations on any SAS2H output cases. This ORIGEN-S input can be stacked immediately after the SAS2H input, and the results are automatically translated into the new group structure.

Error in CSASIN Default Wt % Values

For example, cases P4267B and P4267D from NUREG/CR-6102 contain 2550 ppm soluble boron. If CSASIN is used as described in the previous paragraph, the calculated k-eff values are 1.7% and 1.3% lower, respectively, which is nonconservative.

SCALE Minor Modifications

The following minor corrections and updates will be included in the RSICC release of SCALE-4.4. Unless otherwise noted, these modifications resulted in insignificant changes in overall results or allowed cases to run that previously failed. Other minor modifications from version 4.3 to 4.4 have been listed in previous issues of the SCALE Newsletter.

MARSLIB: (1) Updated to change the value of epsilon used to check for round-off errors in the geometry and, thereby, reduce the number of such errors. This modification eliminated the errors previously experienced with several of the SCALE Shielding V&V problems. (2) Variables IR in subroutine AZIP and IRET in subroutine UNIS are now initialized to 0 before they are used as arguments to function IREAD. In AZIP and in UNIS a 'CALL EXIT' was changed to a 'STOP'. In subroutine ALBERT, the nH was removed from two formats and replaced with quotes. (MRRs 98-025 and 98- 040)

MORSE: Updated the limit on number of tracking errors, the unit number for surface detector results, and increased dimensions on surface detector arrays. (MRR 98-014)

KENO-VI: (1) Updated to correctly number error messages, replace the word PICTURE with the word PLOT throughout the program, and print plot symbol data only for character plots. (2) Updated subroutine TRACK to correctly sum fluxes. The fluxes didn't sum properly for units that were crossed by an array boundary. (3) Enhanced to allow HOLEs to be used without explicitly defining a geometry region where the HOLE was to be inserted. The code automatically adds to the unit containing the HOLE, the equations that define the boundary of the unit contained within the HOLE, properly rotated and translated as specified on the HOLE record. (4) Fixed problem writing restart file on Sun workstation. (5) Modified the subroutine GEOMIN to correct an infinite loop problem. A pointer to the array that contained the unit boundary x, y, and z position was improperly specified. The pointer LBOXGM has been respecified. (6) Corrected a problem where a particle's inability to cross an array boundary due to round-off problems caused an infinite loop. (MRRs 98-019, 98-030, 98-045, 98-052, 98-033, 98-035)

KENO V.a: Updated subroutine RDPLOT to correct the format used to print the error message for incomplete input data. (MRR 98-022)

QADS/QAD-CGGP: (1) Updated to make the combinatorial geometry input data have the same format as the combinatorial portion of the MARS geometry input which is used in other SCALE modules. Old input files will no longer run. (2) Updated to add error checks for limits on number of compositions and elements and to fix the code to handle upper- or lower-case input. (MRRs 98-003, 98-004, 98-037, 98-038, 98-049, 98-050, and 98- 051)

SUBLIB / UNIXLIB: (1) Updated to remove year 2000 problems. These changes basically changed the year format for the QA verification table to 4 digits. Additionally, the date format was changed to use a 3-character month abbreviation so that the date would be unambiguous. A new line was added to the QA verification table printout to identify the machine on which the program was run. (2) Updated to remove an artificial limit of 8-character-length filenames for non-standard files in subroutine OPNFIL. (3) Modified subroutines LISTQA and VERGET for consistency of the length of the string containing the executable name, the creation date, and the directory path to the executable. The directory path was increased to 256 characters. (4) Updated subroutine FINDQA to place underscores in place of the blanks in the date to simplify the automatic updating of the QA verification table. (5) Replaced the CHARACTER*8 type of variable CAT with a variable length CHARACTER type in subroutine NOTE. This corrected a problem in WAX on the Sun workstation. (6) Added comments to subroutine OPENDA indicating how to replace the Fortran 90 specific INQUIRE statement with a Fortran 77 compatible statement. (MRRs 97-039, 98-016, 98- 020, 98-024, 98-042)

ORIGEN: (1) Updated cross-section edit of binary libraries to add option to change cross-section values to quantities derived from total flux (as in ORIGEN- S) instead of thermal flux. (2) Corrected calculation of printed average power. (3) Added error message if number of time steps is less than 4 for reactor startup case. (4) Updated to correct the loop index for re-normalizing the R8 array. (MRRs 98-011 and 98-013)

SAS2H: (1) Updated to fix a problem where the reload feature failed to reload correctly for the final cycle type. (2) Modified subroutine SZNSEG so that it would not cause the ORIGEN library creation to fail by not recognizing the cross-section library specified. The problem was an uninitialized variable ERSET. The change was to initialize the variable as "FALSE" before calling subroutine GETLIB. A change was also made so that the library name was passed to GETLIB instead of only the first 4 characters. (MRRs 98-031 and 98-046)

OSBICO / OSBIRE: Updated for compatibility with lastest version of ORIGEN-S. (MRRs 98-017 and 98-018)

ARP: Updated for optional interpolation on moderator density and made more general to handle user-created basic cross-section libraries. ARP now runs under SCALE driver on PCs and workstations. (MRRs 98-005 and 98-034)

ARPLIB: This is a new utility program that creates binary ORIGEN libraries for ARP. It extracts libraries at the desired burnups from large multi- burnup library files generated by SAS2H. (MRR 98- 026)

PRISM: This is a new utility program for ARP that can read a single SAS2H or other type of input file and generate multiple copies by replacing generic symbols with the specified values. (MRR 98-029)

XSECLIST: This is a new utility program for ARP which prints lists of absorption and fission cross sections vs burnup for nuclides from ORIGEN-S multi-burnup binary libraries. (MRR 98-027)

SAS1: Scratch unit N16 was not opened when SCALE driver returned to SAS1 after cross-section processing and prior to XSDRNPM shielding calculation. This problem caused SAS1 to fail on the PC. The OPEN statement was moved to the beginning of main program so it would always be opened. (MRR 98-023)

SAS3: Variable IR in subroutine OAKTRE is now initialized to 0 before it is used as an argument to function AREAD. Subroutine RINPUP was updated to initialize the variables JMK and IML in COMMON JOMK because they are used when SAS3 calls MARSLIB routines and they were not being defined prior to the calls to JOMIN. (MRR 98-043)

SAS4: Subroutine MORINP was updated to add common JOMK and to initialize the variables JMK and IML in common JOMK because they are used when SAS4 calls MARSLIB routines and they were not being defined prior to the calls to JOMIN. (MRR 98-044)

XSDRNPM: The special activity file and balance table file were not written correctly, and the correct file structure is not what was documented. Subroutine SETUP was changed such that it would not read or write dummy records after the files were opened. These read/writes were the only way to open the files before Fortran 77, but when the code was converted to Fortran 77 and OPEN statements were added to explicitly open the files, the extra statements were not removed. (MRR 98-047)

MALOCS: Corrected error in weighting a coupled master library using a neutron-spectrum from a neutron library combined with an explicitly specified gamma-ray spectrum. Also introduced several options for truncating upscattering terms. Changes were made to properly weight the delayed and prompt values of nu. (MRR 98-012)

AJAX: Corrected a portability problem in subroutine ANN caused by the array D being typed real by default, and then printing variables from it using an integer format. (MRR 98-039)

PERFUME: Improved the selection of new moments when a moment is found to be invalid and converted coding to a more standard Fortran 90. (MRR 98-010)

RADE: Corrected an error in subroutine MCHEK that caused RADE to fail on a Sun workstation. A constant was passed as an argument to subroutine MCHEK to be used for dimensioning, but MCHEK later used the same variable for other purposes. The argument was renamed and used in the dimension statement. (MRR 98-008)

H7MAP: For 1-D problems, if the number of nodes is large enough that the output exceeds one page in length, only part of the output is displayed. The output from the first page is repeated, and the rest of the output is never printed. Correcting this problem involved simply moving one statement from within a DO loop to a point before the DO loop. (MRR 98-048)

Standard Composition Library: (1) The default density of B4C was corrected from 2.54 to 2.52 g/cc. This error was introduced in SCALE-4.3. For an LWR fuel problem with B4C pins between fuel assemblies, the calculated keff value increased less than 0.2%. (2) Updated to reference the nuclides used for zirconium hydride which have been added to ENDF/B-V libraries and to add four new standard composition names related to zirconium hydride. (3) The densities for SS304 nuclides were made identical to the standard versions of the same nuclides. (DRRs 98-009 and 98-018)

238-group and 44-group ENDF/B-V libraries: Updated to remove resonance parameters from specially weighted stainless steel nuclides because they were being doubly applied. Also, zirconium and hydrogen cross sections for zirconium hydride were added to both libraries. (DRR 98-015)

44-group library: Re-collapsed the 238-group library using the updated MALOCS that correctly weights the prompt and delayed values of nu by the fission rate. (DRR 98-008)

ORIGEN-S master photon library: The library was updated to correct the photon yield data for Ra-222 and Th-226, and the photon yields for gammas accompanying (alpha,n) and spontaneous fission reactions were updated to reflect small changes that occurred during the last decay data update. (DRR 98-001)

KENO-VI sample problems: Sample problem 22 has been altered in the KENO-VI input file. The geometry data were changed to take advantage of the simplified method of adding HOLEs. (DRR 98-020)

QADS and QAD-CGGP sample problems: Updated to change the geometry input format to agree with the changes made to QADS and QAD- CGGP. (DRR 98-003)

SAS4 sample problems: Added a ninth sample problem to SAS4 to illustrate the new enhanced surface detector option. (DRR 98-013)

COUPLE sample problem: Updated to change the inner radii in the 3$$ array to zero for consistency with the NITAWL-II input requirements. (DRR 98-007)

PERFUME sample problem: The special cross- section data file required for the PERFUME sample problem has been added to SCALE on the workstation, and the sample problem input data have been updated to use it. This problem has not been included in SCALE since SCALE was moved from the mainframe to the workstation several years ago. (DRR 98-006)

HEATING sample problems: The input file for the second HEATING sample problem was modified to first compile and run a simple Fortran program to convert an ASCII node connector file to binary format for use by HEATING. This modification improves installation portability on different Unix workstation platforms. (DRR 98-014)