On March 20, 1996, at the Hanford Plutonium Finishing Plant, a process operator placed two containers of plutonium less than 10 inches from a third container of plutonium located inside a furnace, thus creating a criticality prevention specification infraction. A process shift manager observed the location of the containers and notified the criticality safety representative, who confirmed the infraction. A recovery plan was written and approved and the two containers external to the furnace were moved farther than 10 inches from furnace. Double contingency was maintained during this event because there was neither a sufficient quantity of plutonium or any moderator present to cause a criticality; however, operators placed fissile material in a configuration that removed a third barrier. (ORPS Report RL--WHC-PFP-1996-0015)
Operators removed two plutonium containers from two furnaces inside a glovebox. They were using the furnaces to stabilize the plutonium. They placed the containers on either side of one furnace to cool and placed a new container of plutonium inside the furnace, leaving less then the required 10 inches of separation between containers.
Investigators determined that the size of the containers used for stabilization had been changed and these were larger than those previously used, which decreased the space available inside the glovebox. They also determined that the operators considered the furnace part of the process equipment and not a factor in spacing requirements.
The facility manager initiated the following corrective actions.
Directed maintenance to change glovebox posting to state that a furnace loaded with a container of plutonium must have more than 10 inches of spacing from other containers of plutonium. Directed operations to change the procedure for plutonium stabilization to limit the number of containers used for plutonium stabilization to no more than two because of the limited space available in the glovebox and the difficulty in maintaining more than 10 inches between containers. OEAF engineers reviewed Weekly Summaries and found that nuclear criticality safety issues were discussed in thirteen 1995 articles (Weekly Summaries 95-03, 95-08, 95-10, 95-14, 95-17, 95-22, 95-25, 95-33, 95-36, 95-40, 95-42, 95-44, and 95-52) and one 1996 article (96-06). Weekly Summary 95-40 discusses criticality spacing and Weekly Summary 94-42 discusses inadequate compliance with criticality safety limits and criticality safety non-compliances at eight DOE facilities.
This event illustrates that procedures involving criticality safety should be followed with rigor and formality. DOE 5480.24, Nuclear Criticality Safety, establishes nuclear criticality safety program requirements at DOE facilities.
It states that geometry control is a priority in maintaining criticality safety and that spacing between equipment is an important part of geometry control. Managers responsible for nuclear criticality safety at DOE facilities should review doe 5480.24 to ensure that requirements are properly addressed in their documents.
KEYWORDS: criticality, procedure, plutonium finishing
FUNCTIONAL AREAS: nuclear/criticality safety