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 problemdependent 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 (k eff). 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. ORNL’s 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. 

ML053060039
 IN 2005-31

 Page 2 of 3

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 problemdependent. 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. ORNL’s 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. 
 IN 2005-31

 Page 3 of 3

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.
Attachment 1

IN 2005-31

Page 1 of 3

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.
IN 2005-31

Page 2 of 3

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 CFR 40.13(c)(5).

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.
IN 2005-31

Page 3 of 3

Date GC No. Subject Addressees

4/7/05 IN-05-10 Changes to 10 CFR Part 71

Packages

All 10 CFR Part 71 licensees and

certificate holders.

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.