Information Notice No. 90-63: Management Attention to the Establishment and Maintenance of a Nuclear Criticality Safety Program
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR MATERIAL SAFETY AND SAFEGUARDS
WASHINGTON, D.C. 20555
October 3, 1990
Information Notice No. 90-63: MANAGEMENT ATTENTION TO THE ESTABLISHMENT
AND MAINTENANCE OF A NUCLEAR CRITICALITY
All fuel cycle licensees and other licensees possessing more than critical
mass quantities of special nuclear material.
This information notice is provided to alert addressees to an incident
resulting from inadequate management attention to the establishment and
maintenance of a nuclear criticality safety program. The licensee's
inattention to Information Notice No. 89-24, Nuclear Criticality Safety,
dated March 6, 1989, may have been a contributing factor in the incident.
It is expected that licensees will review this information and the 1989
Information Notice 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:
In March 1990, a licensee's routine sample analysis for a Raschig-ring
filled waste collection tank (a non-favorable geometry vessel) yielded a
concentration of approximately 2 grams of highly enriched uranium per liter
of solution. Contents of the tank are normally transferred to a second
larger tank (a non-favorable geometry vessel without Raschig rings) at a
release limit of 0.01 grams uranium per liter. The analysis of a second
sample confirmed that a major upset had occurred in the waste collection
system. Consequently, the waste processing area was shutdown, and the waste
collection tank was isolated. Corrective actions were taken to recover the
uranium (in excess of 4 kilograms).
The licensee's investigation team concluded that the contents of two
favorable diameter 11-liter cylinders, one or both containing high
concentration solution, had been dumped into a sump used to pump solution to
the waste collection tank. By procedure, operators were allowed to dump low
concentration uranium solutions into the sump after receiving authorization
and key access from supervisors. Findings which supported the team's
conclusion are: (1) the quantity of uranium in the tank, (2) an operator's
statement that two 11-liter cylinders of process
October 3, 1990
Page 2 of 3
solution were poured into the sump, (3) traces of yellow uranium solids in
the sump and filter, and (4) ineffective isolation of the sump caused by
failure to perform maintenance and to conduct access control. The
investigation team also speculated that one or both of the 11-liter
cylinders had been mislabelled based on an operator's statement that
11-liter cylinders were mislabelled in the past and the team's observation
of an 11-liter cylinder of high concentration solution that was improperly
The failure of the licensee's management control systems resulted in an
unsafe transfer of the uranium solution through the sump into the collection
tank. Both the sump and the collection tank had risks of a criticality
event and no controls remained. Even though the administrative control led
to the detection of the high concentration of uranium and precluded its
transfer to the second larger tank, an additional unsafe transfer could have
occurred with only one unlikely, independent, and concurrent change in
process conditions (viz., recording the wrong analysis or using the wrong
sample analysis, etc.). In both the actual incident and the postulated case
of transfer of concentrated solution to the second larger tank, controls to
satisfy the double contingency principle were not implemented.
This event and those events described in the 1989 Information Notice
emphasize the need for continuing vigilance in providing a sound nuclear
safety program. Although the licensee had a copy of the 1989 Information
Notice on file, no action was taken to avoid similar events. Some of the
recommendations made by the licensee's investigation team are listed below.
Licensees are encouraged to review these recommendations, the 1989
Information Notice, and their own programs to ensure nuclear criticality
- Eliminate sumps and install piping to transfer waste solutions,
thereby, eliminating the use of the 11-liter cylinders in this
- Evaluate the procedures and practices for affixing labels to 11-liter
cylinders in all process areas.
- Install in-line detectors and totalizers on all streams to waste
collection tanks containing Raschig rings. Consider automatic shutoff
of the flow when a detected uranium concentration exceeds an acceptable
nuclear criticality control limit.
- Install additional controls on all streams to the collection tank
without Raschig rings. This should include an evaluation of
interlocked valves, as well as valves controlled by in-line detectors
or conductivity meters connected to an alarm system.
October 3, 1990
Page 3 of 3
- Develop training material for, and train, first responders to unusual
- Retrain supervisory personnel on issues important to safety, labor
relations, training, and emergency response.
- Evaluate the existing training program to ensure that personnel are
trained and knowledgeable of assigned tasks in waste processing areas
and of nuclear criticality safety issues, including selected
criticality accident histories.
- Reevaluate all nuclear criticality safety analyses to ensure proper
application of the double contingency principle, with emphasis on
unsafe geometry vessels.
- Reevaluate the audit and inspection programs to ensure that management
control systems are being properly implemented.
- Review operating procedures for accuracy and completeness.
- Retrain personnel with procedural requirements with emphasis on
No specific action or written response is required by this Information
Notice. If you have any questions, please contact the technical contacts
listed below or the Regional Administrator of the appropriate regional
Richard E. Cunningham, Director
Division of Industrial and
Medical Nuclear Safety
Office of Nuclear Material Safety
Technical Contacts: Edward McAlpine, Region II
W. Scott Pennington, NMSS
1. Information Notice No. 89-24,
Nuclear Criticality Safety,
dtd March 6, 1989
2. List of Recently Issued
NMSS Information Notices
3. List of Recently Issued
NRC Information Notices
Page Last Reviewed/Updated Wednesday, March 24, 2021