Information Notice 2005-13, Potential Non-Conservative Error in Modeling Geometric Regions in the Keno-V. a Criticality Code
ML051180228 | |
Person / Time | |
---|---|
Issue date: | 05/17/2005 |
From: | Hiland P, Pierson R NRC/NMSS/FCSS, NRC/NRR/DIPM/IROB |
To: | |
References | |
IN-05-013 | |
Download: ML051180228 (4) | |
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
OFFICE OF NUCLEAR MATERIAL SAFETY AND SAFEGUARDS
WASHINGTON, D.C. 20555 May 17, 2005 NRC INFORMATION NOTICE 2005-13: POTENTIAL NON-CONSERVATIVE ERROR IN
MODELING GEOMETRIC REGIONS IN THE
KENO-V.A CRITICALITY CODE
ADDRESSEES
All licensees using the Keno-V.a criticality code module in Standardized Computer Analyses for
Licensing Evaluation (SCALE) software developed by Oak Ridge National Laboratory (ORNL).
PURPOSE
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to inform
recipients of a potential non-conservative error in modeling geometric regions in the Keno-V.a
criticality code. It is expected that recipients will review the information for applicability to their
facilities and consider actions, as appropriate, to avoid non-conservative results. However, suggestions contained in this IN are not new NRC requirements; therefore, no specific action
nor written response is required.
DESCRIPTION OF CIRCUMSTANCES
Keno-V.a is a Monte Carlo particle tracking code that solves the neutron transport equation in
arbitrary three-dimensional geometric configurations. Keno-V.a is part of the SCALE software
package.
An ORNL staff member identified a problem while performing a criticality safety benchmark
evaluation in which some cases produced 1 to 1.5 percent lower k-effective (k-eff) values. This
statistically significant difference was brought to the attention of the Keno-V.a code manager at
ORNL. ORNLs review of the discrepancy determined that the observed difference in k-eff was
attributed to round-off error.
ORNL provided diagnostic guidance on its website for SCALE users to determine the impacts of
round-off errors on calculated k-eff results:
http://www-rsicc.ornl.gov/rsic-cgi-bin/enote.pl?nb=scale5&action=view&page=56 ORNL also provided preventive guidance, for SCALE users, to avoid modeling geometric
configurations that were potentially sensitive to numerical round-off errors. Subsequently, ORNL
issued a Keno-V.a patch to fix the numerical round-off error in SCALE Version 5. ORNL did not
issue a patch for earlier versions of SCALE. NRC informally notified fuel cycle licensees of the
existence of the Keno-V.a error.
NRC is continuing to evaluate the extent of the error and the adequacy of the patch. If relevant
new information is obtained, NRC will provide the information in a future communication.
DISCUSSION
Modeling geometric configurations using Keno-V.a is accomplished by defining regions
composed of simple geometric shapes. Holes are one type of geometric region that could be
used to construct complex geometric configurations. Holes may contain bodies or arrays
having any geometric shape. The numerical round-off error only occurs when using the hole
option to define geometric regions and the body in the hole is a cylinder or hemi-cylinder. A
similar round-off error was previously identified and corrected for holes containing other
geometric shapes.
The reported condition arises when the end face of a hole, whose outer boundary is a cylinder
or a hemi-cylinder, shares a common flat boundary with another hole, region, or unit. Neutrons
crossing the common boundary are incorrectly tracked when the numerical round-off error
causes the code to misinterpret which region the neutron is entering. If the tracking failure
results in missing absorber material, calculated k-eff values could be overestimated. If the
tracking failure results in missing fuel, calculated k-eff values could be underestimated.
ORNL has recommended that geometric configurations that were modeled using
cylindrical/hemi-cylindrical holes be checked for shared boundaries. If shared boundaries exist, ORNL recommends inserting a small gap, larger than potential round-off error [at least 1.0 x 10-5 cm (3.9 x 10-6 in.)], between the boundaries. ORNL has also issued the following patch, for
SCALE Version 5, that can be downloaded from the SCALE website:
http://www.ornl.gov/sci/scale/download kenova.htm . This patch is intended to prevent tracking
errors in geometric configurations having boundaries. If the patch is installed, the modified
Keno-V.a code should be verified by re-running validation cases to ensure the code is working
correctly.
CONTACT
This IN requires no specific action nor written response. If you have any questions about the
information in this notice, please contact the technical contact listed below.
/RA/ /RA/
Patrick L. Hiland, Chief Robert C. Pierson, Director
Reactor Operations Branch Division of Fuel Cycle Safety
Division of Inspection Program Management and Safeguards
Office of Nuclear Reactor Regulation Office of Nuclear Material Safety
and Safeguards
Technical Contact:
Lawrence Berg, NMSS
301-415-6215 E-mail: ljb2@nrc.gov
Attachment: List of Recently Issued NMSS Generic Communications
Note: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under Electronic Reading Room/Document Collections.
CONTACT
This IN requires no specific action nor written response. If you have any questions about the
information in this notice, please contact the technical contact listed below.
/RA/ /RA/
Patrick L. Hiland, Chief Robert C. Pierson, Director
Reactor Operations Branch Division of Fuel Cycle Safety
Division of Inspection Program Management and Safeguards
Office of Nuclear Reactor Regulation Office of Nuclear Material Safety
and Safeguards
Technical Contact:
Lawrence Berg, NMSS
301-415-6215 E-mail: ljb2@nrc.gov
Attachment: List of Recently Issued NMSS Generic Communications
Note: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under Electronic Reading Room/Document Collections.
ADAMS ACCESSION #: ML051180228 OFC FCSS/TSG Tech ED FCSS/TSG FCSS/TSG
NAME LBerg:dw* Ekraus: by fax* RCesaro* MGalloway*
DATE 04/28/05 05/02/05 04/28/05 04/28/05 OFC NRR NRR NRR FCSS
NAME JWermiel CRoque-Cruz PHiland RPierson
DATE 05/10/05 05/13/05 05/13/05 05/ 17 /05
Attachment
IN 2005 -13 Recently Issued NMSS Generic Communications
Date GC No. Subject
Addressees
04/18/05 RIS-05-06 Reporting Requirements for All material licensees possessing
Gauges Damaged at portable gauges, regulated under
Temporary Job Sites 10 CFR Part 30.
04/14/05 RIS-05-04 Guidance on the Protection All holders of operating licenses
of Unattended Openings or construction permits for nuclear
that Intersect a Security power reactors, research and test
Boundary or Area reactors, decommissioning
reactors with fuel on site, Category 1 fuel cycle facilities, critical mass facilities, uranium
conversion facility, independent
spent fuel storage installations, gaseous diffusion plants, and
certain other material licensees.
02/28/05 RIS-05-003 10 CFR Part 40 All persons possessing aircraft
Exemptions for Uranium counterweights containing
Contained in Aircraft uranium under the exemption in
Counterweights - Storage 10 CFR 40.13(c)(5).
and Repair
05/17/05 IN-05-013 Potential Non-conservative All licensees using the Keno-V.a
Error in Modeling criticality code module in
Geometric Regions in the Standardized Computer Analyses
Keno-v.a Criticality Code for Licensing Evaluation (SCALE)
software developed by Oak Ridge
National Laboratory (ORNL)
05/17/05 IN-05-012 Excessively Large All licensees authorized to
Criticality Safety Limits Fail possess a critical mass of special
to Provide Double nuclear material.
Contingency at Fuel Cycle
Facility
04/07/05 IN-05-010 Changes to 10 CFR Part 71 All 10 CFR Part 71 licensees and
Packages certificate holders.
IN-05-007 Results of HEMYC All holders of operating licenses
04/01/05 Electrical Raceway Fire for nuclear power reactors, except
Barrier System Full Scale those who have permanently
Fire Testing ceased operations and have
certified that fuel has been
permanently removed from the
reactor vessel, and fuel facilities
licensees.
03/10/05 IN-05-005 Improving Material Control All licensees authorized to
and Accountability Interface possess a critical mass of special
with Criticality Safety nuclear material.
Activities at Fuel Cycle
Facilities
Note: NRC generic communications may be found on the NRC public website, http://www.nrc.gov, under Electronic Reading Room/Document Collections.