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, 2005NRC 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 wh
ile 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. ORNL's 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 sensitiv
e 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 check
ed 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, ChiefRobert C. Pierson, Director Reactor Operations BranchDivision of Fuel Cycle Safety
Division of Inspection Program Management and Safeguards
Office of Nuclear Reactor RegulationOffice 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, ChiefRobert C. Pierson, Director Reactor Operations BranchDivision of Fuel Cycle Safety
Division of Inspection Program Management and Safeguards
Office of Nuclear Reactor RegulationOffice 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 #: ML051180228OFCFCSS/TSGTech EDFCSS/TSGFCSS/TSG
NAMELBerg:dw*Ekraus: by fax*RCesaro*MGalloway*
DATE 04/28/05 05/02/0504/28/0504/28/05OFCNRRNRRNRRFCSS
NAMEJWermielCRoque-CruzPHilandRPierson
DATE05/10/0505/13/0505/13/0505/ 17 /05
Attachment
IN 2005 -13 Recently Issued NMSS Generic CommunicationsDateGC No.Subject
Addressees
04/18/05RIS-05-06Reporting Requirements for
Gauges Damaged at
Temporary Job Sites
All material licensees possessing
portable gauges, regulated under
10 CFR Part 30.04/14/05RIS-05-04Guidance on the Protection
of Unattended Openings
that Intersect a Security
Boundary or Area
All holders of operating licenses
or construction permits for nuclear
power reactors, research and test
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.02/28/05RIS-05-00310 CFR Part 40
Exemptions for Uranium
Contained in Aircraft
Counterweights - Storage
and Repair
All persons possessing aircraft
counterweights containing
uranium under the exemption in
10 CFR 40.13(c)(5).05/17/05IN-05-013Potential Non-conservative
Error in Modeling
Geometric Regions in the
Keno-v.a Criticality Code
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)05/17/05IN-05-012Excessively Large
Criticality Safety Limits Fail
to Provide Double
Contingency at Fuel Cycle
Facility All licensees authorized topossess a critical mass of special
nuclear material.04/07/05IN-05-010Changes to 10 CFR Part 71
Packages All 10 CFR Part 71 licensees and
certificate holders.
04/01/05IN-05-007Results of HEMYC
Electrical Raceway Fire
Barrier System Full Scale
Fire Testing
All holders of operating licenses
for nuclear power reactors, except
those who have permanently
ceased operations and have
certified that fuel has been
permanently removed from the
reactor vessel, and fuel facilities
licensees.03/10/05IN-05-005Improving Material Control
and Accountability Interface
with Criticality Safety
Activities at Fuel Cycle
Facilities
All licensees authorized topossess a critical mass of special
nuclear material.
Note: NRC generic communications may be found on the NRC public website, http://www.nrc.gov , under Electronic Reading Room/Document Collections.