Home > NRC Library > Document Collections > General Communications > Information Notices > 1993 > IN 93-77
UNITED STATES 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 CYCLE FACILITIES Addressees All nuclear fuel cycle licensees. Purpose 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.) 9309290006. IN 93-77 October 4, 1993 Page 2 of 4 (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. Discussion 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. . IN 93-77 October 4, 1993 Page 3 of 4 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 hopper. 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 following: 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. . IN 93-77 October 4, 1993 Page 4 of 4 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 and Safeguards Office of Nuclear Material Safety and Safeguards Technical contact: Marc Klasky, NMSS (301) 504-2504 Attachments: 1. List of Recently Issued NMSS Information Notices 2. List of Recently Issued NRC Information Notices .
Page Last Reviewed/Updated Thursday, March 29, 2012