Information Notice No. 89-24: Nuclear Criticality Safety

                                  UNITED STATES
                          NUCLEAR REGULATORY COMMISSION
                             WASHINGTON, D.C.  20555

                                  March 6, 1989

Information Notice No. 89-24:  NUCLEAR CRITICALITY SAFETY


All fuel cycle licensees and other licensees possessing more than critical 
mass quantities of special nuclear material.


This information notice is being provided to alert addressees to potential 
problems resulting from inadequate administration and application of the 
double contingency principle in establishing nuclear criticality safety limits 
and controls.  It is expected that licensees will review the information for 
applicability to their facilities and consider actions, as appropriate, to 
avoid similar problems.  However, suggestions contained in this information 
notice do not constitute U.S. Nuclear Regulatory Commission (NRC) 
requirements; therefore, no specific action or written response is required.

Description of Circumstances:

The double contingency principle, as used in ANSI/ANS-8.1-1983*, states that 
"Process designs should, in general, incorporate sufficient factors of safety 
to require at least two unlikely, independent, and concurrent changes in 
process conditions before a criticality accident is possible."  Proper 
application of the double contingency principle provides assurance that no 
single error or loss of a control will lead to the possibility of a 
criticality accident.  

In March 1988, an NRC licensee was authorized to operate a new pilot plant 
operation involving highly enriched uranium solution.  Provisions were made 
to remove liquid scrap in 2.5 liter bottles from the operations area (Area 1).  
Because of increased quantities of scrap solution and lack of temporary 
storage, an alternate liquid-handling process was established.  The alternate 
method allowed both dilute and concentrated scrap solution to be stored in 
11-liter bottles in the same area.  After an analysis of a single sample, the 
11-liter bottles of dilute scrap solution were to be transferred to an 
adjacent area (Area 2) and emptied into mass-limited 55-gallon drums. 

*American National Standard For Nuclear Criticality Safety in Operations With 
Fissionable Materials Outside Reactors, ANSI/ANS-8.1-1983.

.                                                            IN 89-24
                                                            March 6, 1989
                                                            Page 2 of 3

During an inspection in July 1988, NRC personnel recognized that an operator 
could inadvertently transfer an unsafe quantity of scrap solution into a drum 
by either selecting the wrong bottle of solution or as a result of an 
erroneous sample analysis.  Such an unsafe transfer could have been effected 
with only one unlikely, independent, and concurrent change in process 
conditions (viz., selecting the wrong bottle, recording the wrong analysis or 
using the wrong sample analysis, etc.) and hence, the double contingency 
principle was not satisfactorily implemented.  Because this method of handling 
11-liter bottles was somewhat similar to the handling method contributing to 
the Wood River Junction accident in 1964, the NRC inspectors expressed 
concern.  The licensee immediately ceased all scrap handling and subsequently 
shut down the entire process area to review the safety limits and controls.

Further review disclosed that the nuclear criticality safety analyst who had 
analyzed the process before startup was not familiar with the alternate scrap-
solution-handling procedure.  Administrators within the licensee's safety 
group had approved the change because a safe mass limit had been imposed on 
each drum in Area 2.  The licensee claimed that the alternate method of 
solution-handling, permitted by procedure, had not been used because the 
material control and ac-counting restrictions made the method inefficient. 

NRC personnel also noted that Area 2 contained several open 55-gallon drums.  
Area 2 was used to remove solids from Raschig ring filled drums which were 
used in Area 3 (scrap recovery).  Raschig ring filled drums and drums of 
chemicals were taken from Area 2 into Area 3.  Because a 55-gallon drum was 
involved in the Oak Ridge Y-12 accident, NRC personnel expressed concern with 
the lack of controls on open drums.  The licensee immediately shut down Areas 
2 and 3 so that the nuclear criticality safety limits and controls could be 


These events highlight the need for continuing vigilance in providing a sound
nuclear safety program.  Some of the licensee's actions taken after the inspec-
tion are discussed here.  Licensees are encouraged to review these actions and 
their own vigilance in assuring nuclear criticality safety.  

A team led by a safety director from another of the licensee's nuclear facili-
ties conducted an immediate audit of the three areas.  The team consisted of 
safety and production personnel.  The audit team confirmed NRC's findings and 
identified other safety items.

All nuclear criticality safety analyses were reviewed to ensure proper appli-
cation of the double contingency principle.  Documentation of analyses has 
been revised to provide explicit consideration of the double contingency 

The nuclear criticality safety analysis group now reviews all changes to 
nuclear criticality limits and controls.  The administrative group can no 
longer approve seemingly simple changes such as authorizing new mass limits 
for work stations, based on established safe mass limits. 

.                                                            IN 89-24 
                                                            March 6, 1989
                                                            Page 3 of 3

Production personnel were not involved in establishing nuclear safety limits 
and were not familiar with the above-mentioned nuclear criticality accidents.  
The safety training program has been revised to include selected accident 

All involved personnel, including production operators, have reviewed all 
procedures.  Before startup of Areas 1, 2, and 3, procedures were revised to 
include nuclear safety limits and controls.  Procedures in other plant areas 
will be revised to include safety limits.

Liquid scrap from Area 1 is now collected in favorable geometry containers.  
After analysis, the solution is transferred to a favorable geometry quaran-
tine tank for a second analysis.  Then the solution is transferred to uniquely 
identified favorable geometry containers, for transfer to the drums in Area 2.  

Most 55-gallon drums in Area 2 have been eliminated by engineering redesign.  
Barriers and other controls are in place to prevent unauthorized transfer of 
drums into Area 3.  Engineering studies are underway to eliminate or reduce 
the use of all unfavorable geometry containers in Area 3.

No specific action or written response is required by this information notice.  
If you have questions about this matter, please contact the technical contacts 
listed below or the Regional Administrator of the appropriate regional office.

                                   Richard E. Cunningham, Director
                                   Division of Industrial and
                                     Medical Nuclear Safety
                                   Office of Nuclear Material Safety
                                     and Safeguards

Technical Contacts:  Gerald Troup, Region II
                     (404) 331-5566

                     George Bidinger, NMSS
                     (301) 492-0683

Attachment:  List of Recently Issued NRC Information Notices
.                                                            Attachment 
                                                            IN 89-24
                                                            March 6, 1989
                                                            Page 1 of 1

                             LIST OF RECENTLY ISSUED
                             NRC INFORMATION NOTICES
Information                                  Date of 
Notice No._____Subject_______________________Issuance_______Issued to________

89-23          Environmental Qualification   3/3/89         All holders of OLs
               of Litton-Veam CIR Series                    or CPs for nuclear
               Electrical Connectors                        power reactors.

89-22          Questionable Certification    3/3/89         All holders of OLs
               of Fasteners                                 or CPs for nuclear
                                                            power reactors.

89-21          Changes in Performance        2/27/89        All holders of OLs
               Characteristics of Molded-                   or CPs for nuclear
               Case Circuit Breakers                        power reactors.

88-73,         Direction-Dependent Leak      2/27/89        All holders of OLs
Supplement 1   Characteristics of Contain-                  or CPs for nuclear
               ment Purge Valves                            power reactors.

89-20          Weld Failures in a Pump       2/24/89        All holders of OLs
               of Byron-Jackson Design                      or CPs for nuclear
                                                            power reactors.

89-19          Health Physics Network        2/23/89        All holders of OLs
                                                            or CPs for nuclear
                                                            power reactors, and
                                                            the following fuel
                                                            Nuclear Fuel 
                                                            Services of Erwin, 
                                                            General Atomic, UNC
                                                            Montville, B&W LRC
                                                            Lynchburg, and B&W

89-18          Criminal Prosecution of       2/22/89        All holders of OLs
               Wrongdoing Committed by                      or CPs for nuclear
               Suppliers of Nuclear                         power reactors.
               Products or Services

89-17          Contamination and Degra-      2/22/89        All holders of OLs
               dation of Safety-Related                     or CPs for nuclear
               Battery Cells                                power reactors.

OL = Operating License
CP = Construction Permit 

Page Last Reviewed/Updated Friday, May 22, 2015