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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: Mon, 06-06-1994
ERF description: On 14 May 1994 unit 1 of Kozloduy NPP was shut down and put to cold subritical condition for repair works on the air valve of the first main coolant pump. The shut down was planned due to a small leak from the valve.
On 15 May 1994, while the isolated first circulation loop was drained and while decreasing the pressure in the primary circuit, deterioration of the natural circulation and of the reactor core cooling were observed. After manual actuation of one high pressure injection pump the natural circulation was restored.
The most probable reason for the disturbances of the natural circulation was the formation of a gas bubble in the primary circuit, which expanded during the depressurization and thus provoked disturbance in the natural circulation.
After computer analyses of the thermal-hydraulic behaviour of the reactor core it was proved, that during the short-time increase of the fuel temperature, no overheating of the fuel claddings occurred. The radio-chemical analyses also confirmed that the degradation of the cooling did not affect the integrity of the fuel elements.
Event rating:
The event was rated at level "1" on the INES scale in accordance with the defence-in-depth criteria (items III-3.1 "Events during reactor shutdown" and III-3.1.1 "Degradation of reactor core cooling"' page 34 of the INES User's Manual).
ERF rating date: 03-06-1994
ERF contact person: Mr. T. Gantchev
ERF address: 69 Shipcyenski Prokhod, Bulgaria
ERF affiliation: Inspect. for Safe Use of Atomic Energy, Committee on the Use of Atomic Energy, for Peaceful Purposes

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