LFE Database | Nuclear Criticality Safety Program

LFE ID	Facility Type	Description of Event	Criticality Safety Parameters Affected	Immediate Actions Taken	Method of Resolution	Apparent Cause(s)	Root Cause	Lessons Learnt	Type of Operation	Keyword(s)
001	Fuel Cycle Facility	Uranium Accumulation in Casting Furnace	Mass	Material was cleaned out & whole set of Corrective Actions		Incorrect Assumption	Assumptions about uranium accumulations in the casting process did not align with operations in the field	Need to understand process you are assessing - view it in action	Operations	Furnace, accumulation, hidden
002	Storage/ Waste/ Repository	Storage of Materials Above Height of CAAS Analysis Assumptions (On Top of a Cabinet)	CWS/ CAAS	Material immediately relocated		Human Error	Unknown - possibly lack of awareness of CAAS assumptions ?	None given - but presumably lessons for (i) training / briefing, and (ii) investigate whether height restriction is required	Emergency Planning/ Recovery	Storage, CAAS, stacking
003	In Review
004	Fuel Cycle Facility	Samples inputted on the wrong inventory system	Mass	Operations stopped to rectify issue		Human Error	Unknown - but believed to be different parts of the same Inventory sheet	Unknown	Operations	Inventory, software
005	Fuel Cycle Facility	Over pressurisation of domestic water supply resulting in multiple facility leaks	Moderator	Unknown		Human Error	Isolation activities in a different facility knocked onto main facility	Many creative ways that water can leak from systems	Operations	Water, leak, over pressurisation
006	Storage/ Waste/ Repository	Non-conservative assumption about concentration of product solution entering steam condensate isolation unit	Concentration/ Density	Unit taken out of service & will not be operated until issue has been resolved		Incorrect Assumption	Lack of understanding of process	None given - but presume lessons regarding a full understanding of the process	Operations	Response, steam, dissolver
007	Storage/ Waste/ Repository	Erroneous storage of contaminated exhaust pipes without spacing requirement	Mass, Spacing	Erroneous items were removed and compliantly stored in a separate storage area		Human Error	Lack of understanding of requirements	None given - but presume lessons for training	Decommissioning	Spacing, contamination
008	Storage/ Waste/ Repository	Erroneous opening of transport container in a CSI array	Other	None required as operation already completed - discovered during final moves		Human Error	Believed to be the right course of action on shielding grounds	None given	Operations	Transport container, array, shielding
009	Fuel Cycle Facility	Simultaneous loading of drop box with twice the permitted amount of material	Mass	Transferred material back to original location		Human Error	Simultaneous moves by two independent organisations	None given	Operations	Mass, Drop Box, Simultaneous
010	Fuel Cycle Facility	Transfer of erroneous concentrated liquor heel to a downstream process during flushing	Concentration/ Density	Unknown		Equipment Failure	Level indication anomaly didn't reveal the erroneous heel which was subsequently transferred downstream during flushing	None given	Major Maintenance/Facility Modification/Shutdown	Heel, Level Indication, Downstream transfer
011	Fuel Cycle Facility	A portion of the ventilation system associated with a scrubber was found to have exceeded the criticality safety mass limit	Mass	The operation was shutdown and the ventilation system was opened and cleaned out; the extent of condition was evaluated for other scrubber systems in the facility	The inspection and cleanout frequency was increased for this scrubber	Incorrect Assumption	Slow accumulations of material downstream of scrubbers occur at different rates, the ventilation system had not had an extensive cleanout for many years.	The accumulation rates of material should be checked on a regular frequency. The estimated accumulation rate for one location should not be applied to many locations. Ventilation systems will accumulate material over time and need to be evaluated.	Operations	scrubbers, mass accumulations, ventilation system
012	Reactor	A duty holder derived safety limits using random distributions of fuels rods in moderator. Ths came to light after the plant was running.	Other	The plant was shutdown until the dutyholder produced an adequate safety case.	This safety case needed to address (a) the criticality code had not been validated (b) normal operations were assessed using a probabilistic approach.	Human Error	Use of unvalidated criticality safety assessment method.	None given but lessons on use of a validated code and adequate safety cases.	Operations	Unvalidated code, probabilistic
013	Fuel Cycle Facility	During an inspection, when asked about the fissile content of a mobile filtration unit, the plant manager was not certain about the quantity.	Mass	A safety case was created to support a mobile filtration unit.	Although isolated and not in operational use, the organisation did not have a safety case for a mobile filtration unit. As a result of the error a safety case was created.	Human Error	Uncertain Fissile content in mobile filtration unit	None given but lessons on ensuring items on plant have a safety case	Operations	mobile filtration unit, safety case, undertain mass
014	Fuel Cycle Facility	HEPA filter was found to have exceeded mass limits, while still having an acceptable delta pressure	Mass	Operation was shutdown; evaluate similar HEPA filters and replace as needed; Increase monitoring of HEPA filters	Replace the HEPA design with one that did not need mass a control; develop a criteria for using delta-P as a primary control	Incorrect Assumption	The delta-P limit was developed for UO2 powder with known particle size distribution; a new oxidation process produced U3O8 powders with different particle size distribution that did not correlate with the former UO2 delta-p behavior for primary HEPA filters.	Staff should question the basis of a criticality limit on a regular basis. Accumulation locations should be monitored to verify compliance with the limits; new or changed operations should be monitored more frequently.	Operations	HEPA filters, mass accumulations, ventilation system
015	Fuel Cycle Facility	In a laboratory, the transfer of a sample between two units was performed without verifying compliance with the mass limit	Mass	Update of the mass record of the unit	1. Improvement of the ergonomics of the workstation; 2. Addition of a lockout to prevent unverified transfer	Human Error	Misunderstanding of the transfer process (different from the other parts of the facility which are mostly automated) due to the lack of a documented procedure	1. Standardize transfer processes; 2. Establish detailed documentation and training for non-standardized transfers	Operations	transfer, overbatching
016	Research	Inspection trolleys were used for the movement of fissile material, rather than the approved movement trolleys. The inspection trolleys had not been assessed by the criticality safety case and were not specifically designed to provide engineered spacing.	Interaction/Spacing	Use of inspection trolleys was embargoed until fully assessed.	A criticality safety assessment of the inspection trolleys was conducted.	Incorrect Assumption	Unknown - possibly due to pressures to commence operations.	1. The need for auditable documentation of any proposed deviation from operations specified within the safety case; 2. The need for targeted criticality inspections to witness operations; 3. Encouraging a questioning attitude.	Operations	Movement trolleys, engineered spacing
017	Research	Residue bottles were used to hold liquor at a higher concentration than stated in the criticality safety case. Plant personnel thought they were compliant because they considered the bottle to hold "product" rather than "residue". The safety case did not make such a distinction.	Concentration/Density	Advised plant personnel that the bottles in question must not be used to hold liquor at greater than the concentration limit irrespective of whether they consider the content of the bottles to be true “residue” material.	The resolution will be the withdrawal of the concentration control. A review of the safety evaluation has concluded that other existing controls are adequate to ensure safety under normal and credible abnormal conditions.	Incorrect Assumption	Unknown - difficult to know how the difference in understanding of the definition of a “residue bottle” originated.	1. Ensure no unnecessary safety designations; 2. Greater use of diagrams/pictures could have helped understanding; 3. More plant visits/inspections may have identified this sooner.	Test/Trial/Experiment	Residue bottles, concentration