Stichting Laka

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, 11-03-2002
ERF description: On 14.12.2001 during full power operation a small steam leakage inside the containment was observed by plant personnel. From the alarms plant personnel concluded on a steam leakage at a flange in the reactor vessel head spray system. Four minutes in the event the leakage could be terminated by closing an isolation valve in a drain line of the reactor vessel head spray system. The reactor vessel head spray system (which has no safety function) is isolated from the reactor pressure vessel by a check valve and two containment isolation valves which are closed during operation. The leak occurred between the check valve and the inner contain-ment isolation valve. This part of the reactor vessel head spray system is drained via a drain line which is also connected to drains of main steam lines inside containment. The leakage observed was due to the backflow of main steam via the drain line to the leak in the reactor vessel head spray system. There was no significant release of radioactivity into the containment. After thorough analysis the licensee concluded that a hydrogen explosion may have occurred in connection with the leakage. On 18.02.2002 during a load reduction of the reactor the leakage location has been inspected. A significant part of piping between the check valve and the inner containment isolation valve of the reactor vessel head spray system was completely destroyed. Based on the inspection it is assumed that a hydrogen (radiolysis gases) explosion inside the pipe caused the destruction of the piping (100 mm diameter). The plant was brought to cold shutdown for repair and further investigation.
ERF rating date: 20-02-2002
ERF contact person: Dr. Klaus Kotthoff
ERF address: Schwertnergasse 1, 50667 Cologne
ERF affiliation: Gesellschaft fuer Anlagen- und Reaktorsicherheit (GRS) mbH

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