Information Notice No. 89-24: Nuclear Criticality Safety
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR MATERIAL SAFETY AND SAFEGUARDS
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
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.
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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.
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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
Technical Contacts: Gerald Troup, Region II
George Bidinger, NMSS
Attachment: List of Recently Issued NRC Information Notices
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
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
89-19 Health Physics Network 2/23/89 All holders of OLs
or CPs for nuclear
power reactors, and
the following 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