Chooz (France)

Map of Chooz

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Chooz A: 310 MW PWR shut down since 1991.
Chooz B: 1500 MW PWR ( N4-type constructed by Framatome). First started opeartion in 1996; a second unit is still under construction.
Chooz site is at the Meuse River bordering Belgium.

Facilities in Chooz

plantreactor typconstruction startoperation startshut down

Grid connection of EdF's most powerful and advanced reactor. Chooz 1/2 is a joint venture of EdF and Belgian utilities. Belgium contributed a quarter of the investment needed for the two-unit plant.


Startup of France´s newest PWR at Chooz-B1 has been delayed again by problems with inadequate control rod guide tubes.
But following precritical hot tests in January, in which two of the modified guide tubes failed to meet drop time criteria, EDF has abandoned the new tubes and will now start the reactor with a set of earlier-model guide tubes, which are being fabricated.
When Chooz-B1 was being planned in the 1980s, the first unit was scheduled to begin operation in 1991. But the N4 project was hit with a major delay in early 1991, when EDF ditched the original ambitious digital instrumentation & control system being designed by Cegelec and turned to Sema Group for help in integrating a new, more conventional product line.
Ironically, the "revolutionary" I&C system has performed very well in tests and no-power operation of Chooz-B1 up to now, say both EDF and safety authorities. Ditto the Arabelle turbine newly designed by GEC Alsthcom, and the new main coolant pumps by Jeumont Industrie, which nuclear regulators DSIN have identified as a component to watch on the N4 because of recurrent deviations in flow during tests.
The problem confronting the N4 series now is one that was not anticipated until the Daya Bay PWRs in China experienced control rod drop-time problems beginning one year ago.


Chooz-B1 is the lead unit in new 1500 MW N4 PWR series.
Loading of the 205 fuel elements began in November.

EDF has pledged to replace the Chooz-B1 modified guide tubes with ones of an earlier design considered more dependable.
Its companion, Chooz-B2 is expected to load fuel in about three months, and the two remaining N4 units at Civaux in 1996.
Fuel load marks the transfer of responsibility for nuclear safety at Chooz-B1 from EDF's engineering & construction division to its Nuclear Power Plant Operations group.
The N4, the first PWR of totally French design and the first designed completely to incorporate lessons of the Three Mile Island-2 accident, features several newly designed components including main coolant pumps and steam generators. It is coupled to the world's most powerful nuclear turbine, GEC-Alsthom's 1,450-MW Arabelle, which despite ist performance is four meters shorter than a 1,300-MW PWR turbine and weighs significantly less, and produces 900 MW in ist low- and medium-pressure sections alone.
The N4 also has a revolutionary, fully computerized control room with interactive control terminals, backed up by significant digital instrumentation & control technology throughout the plant.
Analysis of the Daya Bay incidents had shown that the number of open slits in the lower part of the control rod guide tube had caused primary coolant to circulate up through the tubes at too high a pressure, pushing the control rods against their guides and slowing their drop.
Chooz-B1 is EDF's first reactor to use alloy 690 in all zones which were alloy 600 in previous PWR series and suffered stress corrosion cracking, as well as in zones considered to be most sensitive to corrosion.
The new Framatome steam generators, designed to increase performance, feature a more compact tube layout with a triangular pitch rather than the traditional square pitch (there are 5,614 tubes in an N4 steam generator, compared to 5,342 in 1,300-MW unit). Greater compactness leads to a smaller volume of secondary coolant, "unfavorable in case of accident".
The N4 main coolant pumps, designed and manufactured by Jeumont-Industrie, are equipped with a new hydraulic system that allows a greater flow rate. Tests have shown a departure of the pumps from their nominal characteristics "which can lead to an abnormal increase in primary coolant flow in the reactor vesselectrical This could lead to both an increase in control rod drop time and reduction in the margin for fuel assembly mechanical strength.


Plant will start up with a modified version of its new-designed control rod guide tubes, but it is planned to replace them with tubes of an earlier design after one or two operating cycles. DSIN did not allow fuel load before the guide tube problem was solved.


Chooz units feature Framatome's N4 four-loop nuclear steam supply system, the first designed entirely in France and the first reactor integrating all the lessons from TMI-2 accident in 1979 !! The N4- series has a completely computerized control room, a first in nuclear plant design. Two more N4 units are under construction at Civaux, but EDF has abandoned original plans for a second N4 series.

During construction Framatome modified the guide tube design of the 1500 MW N4 reactor, to remedy the vibration problem, which led to deformation of control rods and to incidents where rods stuck. (Dampierre-1, Blayais-4).
Another delay was caused by troubles during the development of computerized I&C for the new PWR. EdF had to change the suppliers in mid-stream adding several years to the schedule.


Leak on a valve of a auxiliary pipe in RCS detected during test. Reactor shutdown: another leak discovered in the joint between the pipe itself and the RCS.