A THERP/ATHEANA Analysis of the Latent Operator Error in Leaving EFW Valves Closed in the TMI-2 Accident

Table 1

Operational levels based on pre-accidental factors.

Operational level 1
Plant is operating under adequate operational and safety standards.
Preaccidental factor = 1 (skilled operator)
Preaccidental factor = 1 (novice)
Operational level 2
Plant requires few operational reviews without which safety will be jeopardized in the long run.
Preaccidental factor = 1 (skilled operator)
Preaccidental factor = 2 (novice)
Operational level 3
Plant requires operational reviews without which safety will be jeopardized in the medium run.
Preaccidental factor = 2 (skilled operators)
Preaccidental factor = 4 (novice)
Operational level 4
Plant requires shutdown to allow operational safety review.
Preaccidental factor = 5 (skilled operators)
Preaccidental factor = 10 (novice)
Operational level 5
Plant requires partial design basis backfitting. Safety is jeopardized.
HEP = 0.25 (skilled operator)
HEP = 0.50 (novice)
Operational level 6
Plant requires total design backfitting. Safety is greatly jeopardized.
HEP = 0.50 (skilled operator)
HEP = 1.00 (novice)
Operational level 7
Plant must be shutdown
HEP = 1.00 (skilled operator or novice)