Paluel (France)

Map of Paluel

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4* 1300 MW PWR constructed by Framatome. operation started 1984-86.

Facilities in Paluel

plantreactor typconstruction startoperation startshut down

Serious safety deficiencies, including a 40-day cover-up by plant staff of errors in a reactor control software program, led French nuclear regulatory agency DSIN to rate at Level 2 on the INES an incident discovered last month at Electricite de France (EDF) Paluel-1.
The 1.345 MW PWR was operated for up to 13 hours February 9-10 at neutron flux distribution levels in excess of authorized operating technical specification limits. Safety margins relative to control rod ejection or jamming were not exceeded, but DSIN said an inspection conducted March 13 had revealed that the plant staff was "weak" in neutronics knowledge and had difficulty coordinating with EDF´s specialized corporate neutronics department.
The violation of operating limits, repeated calculation errors, failure of checks, and "deliberate" concealing of information, constitute safety culture problems, considerably aggravated by the absence of corrective measures.
The right values were finally entered into the control diagram on February 13 during a monthly update, but the tests staff continued to conceal the earlier problems from plant management until March 4, when an operator realized that the neutron flux distribution limits had been exceeded for several hours.

NW, 3.4.1997


Poor management of a periodic low power test of the emergency FW system led to a subcooling accident (test at low power in preparation of startup). To test the SG EFW system operators isolated the regular FW system, sending a large quantity of cold water from EFW to the SGs. Asecondary system valve had failed to close completely, leading to a large discharge at the SG outlet and in turn to too-rapid cooldown of RCS. It needed 1 hour and 15 min. to stop the overcooling by manually closing the blocked open valve. Operators had not taken notice of the indicator for this valve in the control room, which showed the valve beeing open.


Longitudinal cracks in 3 reactor vessel head penetrations found during inspections (first time such cracks found at EdF's 1300 MW PWRs).


Piping on the emergency diesel cooling water system was found to be seriously corroded . The roof penetration was found to have lost its leaktightness, allowing rainwater accumulation on the roof where the piping is located. Same had been observed at Paluel-1 in July. Verification at other sites revealed that a dozen diesels were affected, including all 8 at the Paluel site.


During annual inspection it was discovered that the coat paint of containment sump walls was peeling off.The same was detected at unit-4. Further checks showed that the peeling had affected a significant number of units in the 1300MW series.


Operator error led to overfilling of a concrete tank and cracking of the concrete.


Serious installation problem was discovered in the 1300 -MW series: filters on reactor building sump, connected to the safety injection and containment spray systems were incorrectly installed in all 17 1300 MW PWRs. the fault would have reduced the efficiency of the filter system. the improper installation has left a space between the filter screens and the walls of the reactor building sumps, creating a situation in which debris entrained with coolant flowing into the sumps could have hampred operation of the reinjection system or perhaps even damaged the pumps. Tanguy said this problem is much more serious than the containment filters [ see Penley-1], because it represents degradation of a system that is an integral part of the reactor's safety protection scheme. same problem found in 17 of the 34 900-MW PWRs.


Unit was operating at low power, when one of the PRZ relief valves opened, although pressure in RCS was normal -> electrical control panel replaced.


Spourious closure of a valve on SG outlet due to rupture of a pipe supplying the valve with compressed air. -> led to cooldown of the RCS and actuation of safety injection


Storm led to damage to the stack atop the unit's reactor building: movement of the stack's lowest section caused the whole stack to lean by a few degrees. The top part of Paluel-2 stack was rightened and is being held in place by 3 cables. A similar storm had blown a stack at unit-1.


extremely strong gusts of wind blew off the top part of the auxiliary building stack. reactor was stopped . the top of the stack about 20 m high fell onto the buildings roof, carving a hole of a few sq. meters


Wear was detected in the walls of 2 large-bend SG tubes.


Circumferential cracks found on 6 of 5.400 SG tubes during inspection, 6 healthy tubes had ben plugged by mistake in 1988, and 6 damaged left without plugs.


An isolation valve on a SG closed fully (instead of partially) during periodic testing.Tthe plant was operating at full power -> pressure buildup in the SG, opening of safety valves and automatic actuation of safety injection.


During outage it was detected that 21 sound SG tubes had been plugged during last outage instead of 21 defective ones. one of the faulty tubes had a circumferential crack.


Defective software controlling I&C system, false signals were sent to the control room.


Defective software controlling I&C system., False signals were sent to the control room.