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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: Wed, 14-10-1998
ERF description: Prior to the event the plant was operating stable at 100% power, generator output was 647MWe. All operating parameters were stable and inside the normal operating range. All safety and other significant components were operable; all Protection and Control systems were in function. In progress was a surveillance test according to procedure SMI-4.050, Surveillance Actuation Logic Test SSPS Train B. According to this procedure Reactor Bypass Trip Breaker B was closed. After the simulated signal for Pressurizer High Pressure Trip, Reactor Trip Breaker B opened as it was expected. According to the procedure the breaker was closed again. A few minutes later, the operator noticed indication on the MCB, that the Reactor Trip Breaker B is opened again. As the Reactor Bypass Trip Breaker B was still closed there was no automatic reactor trip. The test was stopped. The breaker was closed manually, and Main Control Room crew decided to perform retest of the breaker. The simulation of the reactor trip signal was performed once more, but the breaker did not open.Further analysis discovered damage to the Undervoltage Card (UV Card) of the Reactor Trip Breaker train B. After precise checking of the UV Card it was found out that the output transistor, which controls current through the undervoltage coil was damaged. A short circuit between the base and collector was found, while the emitter was disconnected. Short-circuited transistor caused the resistor, which is connected to the emitter side of the transistor to burn up, so undervoltage coil stay energized, which caused malfunction of the Reactor Trip Breaker. After the UV card was replaced the test was successfully repeated

.JUSTIFICATION OF RATING
Section IV-3.2.1.3(b) Events without a real initiator (New Draft Manual). Assuming that the defect had led to an initiator this would be the reactor trip. Safety functions Within Operational Limits and Conditions. Level 0.
ERF rating date: 13-10-1998
ERF contact person: Mr. M.F. Levstek
ERF address: Vojkova 59, 1113 LJUBLJANA, Slovenia
ERF affiliation: Slovenian Nuclear Safety Administration

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