Appendix C - Causal Factor Analysis Examples

EXAMPLE 1

Contaminated water leaked from a pump (wrapped in plastic) after the pump was removed from a hot cell.

Investigation using Mini-MORT revealed:

A safe-work permit was obtained and properly signed off but did not contain adequate

precautions against possible water involvement in the task

The safe-work permit included a list of hazards but omitted liquid potential

A Safety Analysis Report (SAR) identified this particular hazard, but this information was

not used in preparing the safe-work permit checklist.

This occurrence was an off-normal release of radionuclides. Using Mini-MORT as a guide, "controls less

than adequate" was identified. The problem was leakage of contaminated water. The direct cause was not

draining the pump before removing it from the hot cell. Following down the Mini-MORT chart,

Performance Error, Job Assignment Less Than Adequate (LTA) was found. The operator had not been

instructed or trained on this hazard, and the safe work permit did not include this precaution (Cause Code

2A, Defective or Inadequate Procedure - lacks something essential to successfully perform activity).

Continuing on the Mini-MORT chart, Technical Information, Communication, and Knowledge were

found. Asking questions about these factors revealed that the root cause was the safe-work permit form.

The checklist on the form was developed without reviewing the hazard identified on the SAR (Cause Code

6B, Management, Work Organization/Planning Deficiency). Also on the Mini-MORT chart under

performance error, training is listed. Investigation of this factor revealed that a contributing cause was

that neither the health physics technician nor the operator recognized the hazard (Cause Code 5A,

Training Deficiency, No Training Provided).

Note that water in the pump was a condition. Some may feel that this condition was the direct cause of

this occurrence, but water in a pump given as a cause of water leaking from a pump is too simplistic; there

is a need to know why a pump containing water was removed from a hot cell. In addition, operator error

should be listed as a cause only if the operator had been trained and reasonably could have been expected

to recognize the hazard. Also note that full MORT analysis was not used for this off-normal occurrence;

the Mini-MORT chart led to asking the few, right questions with a low level of effort required to perform

the root cause analysis.

EXAMPLE 2

With the reactor at full power, the outer shim cylinder would not move when attempting to adjust power.

While there was no immediate safety concern, the reactor was shut down. Since this was a physical barrier

that did not perform its function, we use barrier analysis to ask why. Investigation revealed a broken

connection in the wire that activates a solenoid to release the cylinder brake. The Barrier Analysis

Checklist asks: Were there unwanted energies present? Vibration was determined to be the cause of the

broken solder connection. Using other questions in the Barrier Analysis Checklist or by merely asking the

next logical questions, we discover that vibration had not been considered in the design. Inspections had

been conducted during the last shutdown. The installation had been according to design specifications and

verified by quality assurance.

This was classified as an unusual occurrence involving performance degradation of Class A equipment.

The direct cause was Cause Code 1A, Equipment/Material Problem - defective or failed part; lacking

something to perform its intended function. The joint was soldered adequately but lacked support. The

root cause was Cause Code 4B, Design Problem - something essential was not included.

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