Information Notice 2005-31, Potential Non-Conservative Error in Preparing Problem-Dependant Cross Sections for the Keno V. a or KENO-VI Criticality Code
| ML053060039 | |
| Person / Time | |
|---|---|
| Issue date: | 11/17/2005 |
| From: | Michael Case, Pierson R NRC/NMSS/FCSS, NRC/NRR/ADRO/DIRS |
| To: | |
| Lawrence Berg, NMSS, 301-415-6215 | |
| References | |
| IN-05-031 | |
| Download: ML053060039 (7) | |
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
OFFICE OF NUCLEAR MATERIAL SAFETY AND SAFEGUARDS
WASHINGTON, D.C. 20555
November 17, 2005
NRC INFORMATION NOTICE 2005-31:
POTENTIAL NON-CONSERVATIVE ERROR IN
PREPARING PROBLEM-DEPENDENT CROSS
SECTIONS FOR USE WITH THE KENO V.A OR
KENO-VI CRITICALITY CODE
ADDRESSEES
All licensees using the KENO V.a or KENO-VI criticality code module in Version 5 of the
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 associated with preparation of problem- dependent cross-sections for use with either the KENO V.a or KENO-VI 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 and KENO-VI are Monte Carlo particle-tracking codes that solve the neutron
transport equation in arbitrary three-dimensional geometric configurations and give an estimate
of effective neutron multiplication (keff). KENO V.a and KENO-VI are part of the SCALE
software package.
An ORNL staff member identified a programming error in a rarely used lattice cell cross-section
processing option known as asymmetric slab cell (ASYMSLABCELL) in SCALE 5. In test cases
with materials test reactor (MTR) plate fuel, this error resulted in non-conservative calculated
keff values, which ranged from 4 percent lower (for high-enriched uranium) to 15 percent lower
(for low-enriched uranium) calculated keff values. ORNLs review of the discrepancy determined
that the observed difference in keff was attributed to errors in the calculation of dimensions for
slab cells in cross-section processing. These errors cause an inaccurate Dancoff factor
calculation. Note that the Dancoff factor is a calculated adjustment factor, applied in the
resonance self-shielding of cross-sections, to account for geometrical effects (e.g., lattices).
Accurate Dancoff factors are required to calculate keff in multigroup codes such as KENO.
ORNL provided diagnostic guidance on its website for SCALE users to determine the impact of
the programming error on calculated keff results:
http://www-rsicc.ornl.gov/rsic-cgi-bin/enote.pl?nb=scale5&action=view&page=84 ORNL also provided preventive guidance, for SCALE users, to determine whether cases are
subject to the error and how to modify the associated input files to avoid the error. Because the
programming error, as discussed below, is associated with a code option that is seldom used, ORNL plans to incorporate the fix in the next version of SCALE 5 expected in March 2006.
NRC is continuing to evaluate the extent of the error. If relevant new information is obtained, NRC will provide the information in a future communication.
DISCUSSION
Programming errors in the SCALE 5 LATTICECELL geometry option can cause erroneously
calculated Dancoff factors to be propagated into a non-conservative KENO keff calculation when
the ASYMSLABCELL input option is selected using the new SCALE 5 input format (keywords
"READ COMP"). If a SCALE 5 control sequence is executed using input files developed with
the SCALE 4 format, the input file will not properly convert to a SCALE 5 input format, and a
fatal error will result before any calculations are performed.
The impact of an erroneous Dancoff factor calculation on a calculated keff value is problem- dependent. Analyses performed at ORNL indicate that the error in keff can be potentially
significant if the ASYMSLABCELL option is used. The impact of the error on keff is relatively
minor for cases where the symmetric slab cell (SYMMSLABCELL) option is used (results of test
cases were slightly conservative). Plate-type fuel is one use for the slab cell option in SCALE.
Lower-enriched systems will tend to demonstrate larger errors because of the greater
importance of the Dancoff factor in these cases. ORNL used an infinite system of 20 percent
enriched MTR fuel as a sample test. ORNLs results showed that the erroneous Dancoff factor
could lower keff by as much as 4 percent for higher-enriched uranium and by as much as 15 percent from the predicted value for lower-enriched uranium.
ORNL has recommended that input files using the LATTICECELL geometry option, in
conjunction with either the ASYMSLABCELL or SYMMSLABCELL keywords and the SCALE 5 input format, be replaced with an equivalent MULTIREGION geometry specification and a
SLAB input option. Tests at ORNL have confirmed that the MULTIREGION specification with
the SLAB option will produce the correct prediction of keff.
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/
Michael J. Case, Director
Robert C. Pierson, Director
Division of Inspection & Regional Support
Division of Fuel Cycle Safety
Office of Nuclear Reactor Regulation
and Safeguards
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/
Michael J. Case, Director
Robert C. Pierson, Director
Division of Inspection & Regional Support
Division of Fuel Cycle Safety
Office of Nuclear Reactor Regulation
and Safeguards
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 #: ML053060039 OFC
FCSS/TSG
Tech ED
IMNS
FCSS/TSG
NAME
LBerg
Ekraus: by fax
AMcIntosh
MGalloway
JWermiel
DATE
11/ 02 /05
11/ 02 /05
11/ 03 /05
11/ 07 /05
11/ 09 /05 OFC
FCSS
NAME
CRoque-Cruz
MJRoss-Lee
MJCase
RPierson
DATE
11/ 09/05
11/ 14 /05
11/ 15 /05
11/ 17 /05
Attachment 1 Recently Issued NMSS Generic Communications
Date
GC No.
Subject
Addressees
2/11/05 BL-05-01
Material Control and Accounting at
Reactors and Wet Spent Fuel
Storage Facilities
All holders of operating licenses for
nuclear power reactors, decommissioning
nuclear power
reactor sites storing spent fuel in a pool, and wet spent fuel storage sites.
11/08/05 RIS-05-27 NRC Timeliness Goals,
Prioritization of Incoming License
Applications and Voluntary
Submittal of Schedule for Future
Actions for NRC Review
All 10 CFR Parts 71 and 72 licensees
and certificate holders.
10/28/05 RIS-05-22
Requirements for the Physical
Protection During Transportation of
Special Nuclear Material of
Moderate and Low Strategic
Significance: 10 CFR Part 72 vs.
Regulatory Guide 5.59 (1983)
All holders of licenses for the possession
of special nuclear material (SNM) that
ship Category II and III quantities of this
material.
9/27/05 RIS-04-17, Rev. 1 Revised Decay-in-Storage
Provisions for the Storage of
Radioactive Waste Containing
Byproduct Material
All licensees regulated under 10 CFR
Parts 30, 32, 33, 35, 39, and 50.
8/25/05 RIS-05-18
Guidance for Establishing and
Maintaining a Safety Conscious
Work Environment
All licensees, applicants for licenses, holders of certificates of compliance, and
their contractors subject to NRC authority
8/10/05 RIS-05-16
Issuance of NRC Management
Directive 8.17, Licensee
Complaints Against NRC
Employees
All licensees and certificate holders.
8/3/05 RIS-05-15
Reporting Requirements for
Damaged Industrial Radiographic
Equipment
All material licensees possessing
industrial radiographic equipment, regulated under 10 CFR Part 34.
7/13/05 RIS-05-13
NRC Incident Response and the
National Response Plan
All licensees and certificate holders.
7/11/05 RIS-05-12
Transportation of Radioactive
Material Quantities of Concern
NRC Threat Advisory and
Protective Measures System
Licensees authorized to possess
radioactive material that equals or
exceeds the threshold values in the
Additional Security Measures (ASM) for
transportation of Radioactive Material
Quantities of Concern (RAMQC) under
their 10 CFR Part 30, 32, 50, 70, and 71 licenses and Agreement State licensees
similarly authorized to possess such
material in such quantities under their
Agreement State licenses. Date
GC No.
Subject
Addressees
7/11/05 RIS-05-11
Requirements for Power Reactor
Licensees in Possession of
Devices Subject to the General
License Requirements of 10 CFR
31.5
All holders of operating licenses for
nuclear power reactors and generally
licensed device
vendors.
6/10/05 RIS-05-10
Performance-Based Approach for
Associated Equipment in 10 CFR
34.20
All industrial radiography licensees and
manufacturers and distributors of
industrial radiography equipment.
4/18/05 RIS-05-06
Reporting Requirements for
Gauges Damaged at Temporary
Job Sites
All material licensees possessing
portable gauges, regulated under 10 CFR
Part 30.
4/14/05 RIS-05-04
Guidance 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.
2/28/05 RIS-05-03
10 CFR Part 40 Exemptions for
Uranium Contained in Aircraft
Counterweights - Storage and
Repair
All persons possessing aircraft
counterweights containing uranium under
the exemption in
10/31/05 IN-05-28
Inadequate Test Procedure Fails
to Detect Inoperable Criticality
Accident Alarm Horns
All licensees authorized to possess a
critical mass of special nuclear material.
10/07/05 IN-05-27 Low Dose-Rate Manual
Brachytheraphy Equipment
Related Medical Events
All medical licensees.
7/29/05 IN-05-22
Inadequate Criticality Safety
Analysis of Ventilation Systems at
Fuel Cycle Facilities
All licensees authorized to possess a
critical mass of special nuclear material.
6/23/05 IN-05-17
Manual Brachytherapy Source
Jamming
All medical licensees authorized to
possess a Mick applicator.
5/17/05 IN-05-13 Potential 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)
5/17/05 IN-05-12
Excessively Large Criticality Safety
Limits Fail to Provide Double
Contingency at Fuel Cycle Facility
All licensees authorized to possess a
critical mass of special nuclear material.
4/7/05 IN-05-10
Changes to 10 CFR Part 71
Packages
All 10 CFR Part 71 licensees and
certificate holders. Date
GC No.
Subject
Addressees
4/1/05 IN-05-07
Results 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.
3/10/05 IN-05-05
Improving Material Control and
Accountability Interface with
Criticality Safety Activities at Fuel
Cycle Facilities
All licensees authorized to possess a
critical mass of special nuclear material.
Note: NRC generic communications may be found on the NRC public website at
http://www.nrc.gov, under Electronic Reading Room/Document Collections.