 INES 2 |
Spill of High-Enriched Uranium Solution |
In a facility authorized to process high-enriched uranium (HEU), a glovebox enclosure containing bag filters was connected to a transfer line for HEU solution when a new process system was first constructed. The facility operator decided not to use the filter glovebox enclosure when it began processing HEU solution in the new process system but left the enclosure connected to the HEU transfer line. Before the event, a system diagram was updated and mistakenly indicated that a sample valve was a ball valve. The sample valve diverted flow to a sample line without stopping flow to the glovebox. Workers mistakenly believed that the valve isolated the glovebox from the HEU transfer line.
On several occasions before the event, workers reported signs of a yellowish liquid in the glovebox. Supervisors failed to fully investigate the reports because they assumed the yellowish liquid was natural uranium solution which had been used to initially test the new process system. Immediately prior to the event, the facility operator decided to move the unused filter glovebox enclosure to another location. Workers opened the filter housings and observed yellowish liquid which they were instructed to drain so that the enclosure could be moved. After the liquid was drained, workers failed to reseal the system tightly. During the next transfer of HEU solution through the transfer line, approximately 35 liters of HEU solution leaked into the glovebox.
The primary controls to prevent accumulation of a critical mass of HEU solution in the enclosure were drains to divert solution to the floor. Management measures to verify that the drains remained open and free of debris were never applied to the enclosure because the enclosure was considered out of service. During the event, there was debris in the enclosure but the drains were not blocked. When the HEU solution reached the floor, it began spreading and ran under a door. Neither the worker posted at the vessel being drained nor the worker posted at the vessel being filled were close enough to the glovebox to detect the spill. Another worker in the hall outside the room noticed the solution coming under the door and alerted the other workers of the spill. The transfer was complete and the lines were being drained when operations were secured and actions were taken to address the spill.
The primary control to prevent accumulation of a critical mass of HEU solution on the facility floor was a flat floor with no accumulation points. During the investigation of the event, the operator identified a pit under an unused elevator near the door where the spill was identified. The pit provided an accumulation point that compromised the control provided by the floor. The total volume of the transfer was more than enough solution to create a critical mass in the glovebox or the elevator pit if the circumstances had been different. If a criticality accident had occurred in the glovebox or the elevator pit, it is likely that at least one worker would have received an exposure high enough to cause acute health effects or death.
The operator stopped all processing of HEU in the affected processing area. Adequate corrective actions must be implemented and approved by regulatory authorities before processing can be restarted.
Event date: Mon, 06-03-2006
