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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: Tue, 19-11-1991
ERF description: At Bugey during the hydrotest which is conducted every ten years a leak has been detected at one of the sixty-five leaktight Inconel 600 alloy sleeves via which the control rod drive shafts enter the core through the reactor vessel head.
Controls are being undertaken on the other PWR reactors (when shut down). Identical findings have been discovered on Bugey 4 and Fessenheim 1. This event is temporarily classified at level 2. Until it is possible to assess the extent of the problem on French facilities.
On Monday 23 September, while the Bugey 3 was shut down for the ten-yearly and refuelling a leak was detected at a sleeve in the reactor vessel head during the primary circuit hydrotest.
Pressurized water reactor primary circuit hydrotests are carried out every ten years by the operating organization, in accordance with the regulations applicable to such installations. Hydrotests are carried out at a pressure of 207 bars, after removing the fuel assemblies from the reactor core. The normal operating pressure is 155 bars. This test makes it possible to check the leaktightness of the primary circuit and to detect any defects which might give rise to leaks during operation of the installation.
The leak detected, which was of the order of one litre per hour, was at one of the sixty-five leaktight Inconel 600 alloy sleeves via which the control rod drive shafts enter the core through the reactor vessel head.
Investigations carried out when the defect was discovered revealed the presence of a certain number of axial cracks in the sleeve involved. Additional checks and metallurgical examinations are being carried out by the operating organization.
Checks have been begun of all the reactor vessel head penetrations of Bugey 3 and other French reactors. The first checks carried out, as part of this process, on Bugey 4 and Fessenheim 1, which are currently shut down, have revealed the presence of axial cracks of the same nature in a reactor vessel head sleeve in each of them.
These defects in Bugey 3 and 4 and Fessenheim 1 do not endanger the mechanical strength of the penetration affected.
The investigations in hand should make it possible to assess the extent of the problem throughout the French facilities, to organize a systematic in-service monitoring process and to determine the necessary repair operations.
Thus this defect has been classified as level 2 on the severity scale.
BASIS FOR RATING:
DIFFICULTIES IN RATING:
ERF rating date: 01-01-1991
ERF contact person: Mr. J. Breuil
ERF address: 99 rue de Grenelle, F-75700 Paris, France
ERF affiliation: Ministere de l'industrie, Service central de surete des, installations nucleaires

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