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Event Report Forms (ERFs) are filed to the IAEA. Sometimes there are multiple event reports, updating the rating, the event description. Here you only see the latest event report

ERF send date: Thu, 01-12-1994
ERF description: This PWR type has two different systems for the insertion of control rods. The first one is the usual fast hydraulic scram system, the second is a slower back up system, based on electrical motor operated screws. Further, there is an option called "partial scram" when only a limited number of the control rods are inserted with the fast hydraulic scram system.
At this event at 92% power. erroneously insertion of all the control rods by the screw system was initated. Correctly the speed of the main circulation pumps was automatically decreased to minimum. However, erroneously the expected partial scram was not automatically actuated. The reactor operator observed the consequences of these two equipment failures and manually initiated the partial scram after 1 min and 50 secs.
If the unintentional insertion of the control rods by the screw system had not been counteracted by the operator, fuel damage (pellet clad interaction, PCI) could have occurred due to high local power and/or high neutron flux increase rate.
Planned corrective action: upgrading of the electronic system for initating scrams.
Justification of level 1: Anomaly beyond the authorized operating regime.
ERF rating date: 01-11-1994
ERF contact person: MR. F. REISCH
ERF address: Sweden
ERF affiliation: SWEDISH NUCLEAR POWER INSPECTORATE (SKI)

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