In October, during periodic functional testing of the control and safety rods at France’s Phébus experimental reactor, the reactor’s protection system was fully de-activated, instead of being partially de-activated as required by the test procedures.

The facility, located at the Cadarache nuclear centre, is operated by the Institut de Protection et de Sûreté Nucléaire (IPSN).

The tests, which are carried out periodically, involve the raising and lowering of each of the six control rods in succession while the reactor is shutdown. During the testing the remaining five rods are left in the fully inserted position to ensure that the reactor is in a safe state. In order to perform the test, part of the reactor protection system must be de-activated which allows the selected rod to be moved unimpeded. During the test on 2 October, the whole protection system had been mistakenly de-activated. In the event, the operator was monitoring the core directly on the control panel as required by the test procedures.

The tests were carried out on the Friday, after which the operator went home for the weekend and did not notify his manager of the error until returning to work on the Monday, 5 October.

The incident was rated an INES 2 level because of the failure of the operator to follow reporting procedures and the uncertainty of consequences had a second control rod been unexpectedly raised at the time.

The Phébus FP (fission products) programme is at present the principle international research project studying the potential consequences of a severe accident in a PWR. The tests simulate an accident resulting in a fuel meltdown. The programme, with a budget of some FF 1 billion, includes a series of six experiments. The first two were successfully completed in 1993 and 1996. The remaining four will be completed by 2004.