Information Notice No. 93-77: Human Errors That Result in Inadvertent Transfers Of Special Nuclear Material At Fuel Cycle Facilities
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR MATERIAL SAFETY AND SAFEGUARDS
WASHINGTON, D.C. 20555
October 4, 1993
NRC INFORMATION NOTICE 93-77: HUMAN ERRORS THAT RESULT IN INADVERTENT
TRANSFERS OF SPECIAL NUCLEAR MATERIAL AT FUEL
All nuclear fuel cycle licensees.
This information notice is to alert addressees to possible sampling program
deficiencies that may arise at nuclear fuel cycle facilities because of the
human factors component of nuclear criticality sampling programs. 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
new U.S. Nuclear Regulatory Commission requirements; therefore, no specific
action or written response is required.
Description of Circumstances
In August 1992, a licensee notified the NRC that an operator had emptied the
contents of a favorable geometry slab hopper, used to store UO2 powder on an
interim basis, into an unfavorable geometry blender before receiving the
sample analysis for the contents of the slab hopper. The sampling of the UO2
powder in the slab hopper provides one of the controls to ensure that the
moisture content of the powder is below 1 wt(%) H2O. This restriction on the
water content in the UO2 powder is necessary to ensure nuclear criticality
safety in the unfavorable geometry blender.
The licensee conducted an evaluation to determine the cause(s) of the
inadvertent transfer of UO2 powder from the slab hopper to the blender. This
evaluation revealed that the inadvertent transfer occurred as follows:
(1) An operator erroneously assumed that a completed powder release form
lying on a desk common to all slab hoppers was for a slab hopper whose
sample results had not yet been received.
(2) The operator then retrieved a key from the control room and subsequently
released the contents (750 kg of UO2 powder) of the slab hopper into the
unfavorable geometry blender. (This key was supposed to be controlled by
the shift supervisor, as stipulated by procedure.)
October 4, 1993
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(3) The operator informed the supervisor that he had dumped the contents of
the slab hopper into the blender. The shift supervisor subsequently
recorded this information in the shift log. (At this time, the shift
supervisor should have realized that this was an unauthorized transfer
because he had not signed the powder release form for the slab hopper, as
required by procedure.)
The inadvertent transfer was later discovered when the next shift operator
found an unsigned powder release form (lying on the common desk in the
operating room) for the slab hopper whose powder had been released. The
operator did note, from the form, that the laboratory results for the slab
hopper were within the release limits. The operator informed the supervisor,
who subsequently verified that the results were within the prescribed moisture
limits. The supervisor then completed and signed the powder sampling record
form. NRC was informed of the event in accordance with NRC Bulletin 91-01.
The inadvertent transfer of special nuclear material, in the previously
described event, resulted from deficiencies associated with the human factors
component of the licensee's sampling program. In this instance, the sampling
program was deficient in two respects. Using a common desk for all powder
line paper work represented a less than favorable method to store completed
powder release forms. This led to a situation in which an operator could
easily mistake one powder release form for another. To prevent this problem
from reoccurring, the licensee uses a separate desk to house the forms for
each powder line. (This action has made the inadvertent reading of the wrong
powder release form unlikely.) The licensee's sampling program was also
deficient with respect to securing control of the keys, which are used to
release the powder from the slab hoppers to the blender. By not having a
supervisor control the keys, the licensee created a situation where an
operator's single mistake could lead to an inadvertent transfer. The
licensee's corrective action is to require that the supervisor control the
release keys for the slab hoppers. The licensee's corrective actions are
sufficient to ensure that the following two independent and unlikely events
are necessary before a criticality is possible:
1. The operator mistakenly reads the wrong powder release form.
2. The supervisor misreads the form and subsequently gives the operator the
key to release the powder from the slab hopper.
October 4, 1993
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It should be noted, however, that another possible path to a nuclear
criticality could involve a contingency in which an operator is given a common
key by the supervisor. In this scenario, the operator could mistakenly use
the common key to release special nuclear material from the wrong slab hopper.
To preclude this event, the licensee utilizes individual keys for each slab
In addition to the previously described event, there have been other occasions
in which a deficient nuclear criticality sampling program has led to an
inadvertent transfer of special nuclear material. One such case occurred when
a licensee operator analyzed two samples from one tank, but recorded them as
being from another tank. As a result, an inadvertent transfer occurred.
Another type of event occurred, on two separate occasions, in which a licensee
reported the inadvertent transfer of liquid-bearing uranium to an unfavorable
geometry container. These transfers occurred when an operator mistakenly
entered the analyses for a different tank into the computer.
The previously discussed events illustrate the necessity for licensees to
carefully review their nuclear criticality sampling programs. Licensees
should vigilantly review their respective programs to ensure that the double
contingency principle is fulfilled. This principle requires that at least two
independent and unlikely concurrent process changes occur before a criticality
is possible. For nuclear criticality sampling programs, this requires the
1. Assurance that an operator mistake (contingency) at any juncture
cannot lead to an inadvertent transfer. That is, a second contingency is
necessary before a nuclear criticality event is possible.
2. A contingency must be an unlikely event. This may require one of the
following controls: using color-coded forms, segregating forms, using
different keys, requiring multiple individuals to inspect results, etc.
October 4, 1993
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This information notice requires no specific action or written response. If
you have questions about the information in this notice, please contact the
technical contact listed below or the appropriate regional office.
/s/'d by Robert F. Burnett
Robert F. Burnett, Director
Division of Fuel Cycle Safety
Office of Nuclear Material Safety
Technical contact: Marc Klasky, NMSS
1. List of Recently Issued NMSS Information Notices
2. List of Recently Issued NRC Information Notices
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