A- General presentation
The Basic Nuclear Installation n°101, located at CEA Saclay Centre, comprises the experimental 14-MW thermal power ORPHEE reactor and the experimental buildings used by the teams of the the Léon Brillouin Laboratory (LLB).
The ORPHEE reactor was built between 1976 and 1980 as a, national-based, sister facility of the High Flux Reactor (RHF) of the Laue Langevin Institute (ILL) in Grenoble. The decision to build the reactor steemed from the continuous expansion of European and international neutronic research in the 70s.
The design and construction of the ORPHEE reactor were managed by CEA and Technicatome (presently AREVA TA). ORPHEE design directly benefited from the safety, construction and operation feedback of previous generation reactors like RHF and was contemporary to the development of the PWR equipment program in France.
The reactor first went critical on December 19th 1980. The designers' projections purposely resulted into a moderate investment cost - moderate operation cost facility, ensuring both reliable operation and good safety record. The reactor has been operated circa 5300 days between start up and the end of the year 2008.
The reactor safety case was reassessed twice since 1980 (second reassessment file submitted to the French regulatory body on March 31st 2009). Due to its original design, the reactor is submitted to very limited ageing mechanisms (all of them manageable) and the initial reactor safety features remain in good adequation with up-to-date safety practices.
Since 2006, the start up of the neighbouring SOLEIL synchrotron on the Plateau of Saclay and the massive undergoing R&D development plan of the Plateau of Saclay have constituted the basis of a top-level 21st century integrated complex for the exploration of matter and physical science south of Paris.
B- Reactor technical characteristics
ORPHEE is a « pool » type reactor.
The 14-MWth compact, light-water moderated, core provides up to 3.1014 n/cm2/s thermal flux in the surrounding heavy water reflector tank.
Core life cycle duration is 100 EFPD. Core flow velocity is 7.5 m/s. The core and the heavy water tank are immerged in a pool filled with demineralised light water. This ensures radiological shielding and facilitates handling from above the pool.
The reactor hosts 9 horizontal channels (steeming from the heavy water tank and feeding 20 neutron beams) and 9 vertical channels (steeming mostly from the heavy water tank, and comprising 4 pneumatic channels for activation analysis and 5 irradiation pits for radio-isotope and other industrial productions).
The heavy water tank is equipped with three local moderators: two cold sources (liquid hydrogen at 20K) and one hot source (graphite at 1400 K). These provide neutrons of respectively lower and higher energy. On this basis, experimental users can benefit from 8 thermal neutron beams, 8 ultra-cold neutron beams, 4 hot neutron beams.
ORPHEE neutrons are supplied to 26 experimental areas (including 19 areas with cold neutrons). The experimental areas are located around the reactor, either in the reactor building or along the neutron guides of the guides hall.
One experimental area with specific radiological shielding has been designed for industrial neutronography (mostly used by the aeronautical or space industry, and in particular the European Ariane launchers).
C- Reactor safety
The safety design of the reactor is based upon the defense-in-depth principle in order to ensure permanent control of the three main safety functions: reactivity control, residual heat removal and containment of radioactive material.
The design includes the following elements:
•- Permanent reactor monitoring by a safety system using 3 completely independent channels. If necessary, 2 channels out of 3 will automatically trigger the reactor emergency shutdown (fast control rod drop by gravity).
•- Once the reactor has been stopped, the residual power is removable by purely passive natural convection between the core and the reactor pool.
•- The core and the core cooling circuit are located in the reactor building made of reinforced concrete. The lower section of the building is surrounded by an outer tank which purpose is to collect leaks which may occur to each pipe that exit the building.
Three impervious, resistant and stand alone barriers are placed between dangerous products and the environment. These barriers are: the reactor fuel cladding, the reactor main cooling circuit plus the reactor pool, and the reactor building.
During normal operation, the reactor building is maintained at lower pressure than outside. The reactor building has also been designed to sustain any accident which could occur to the reactor.
The supervision of the impact of the installation onto the environment is included in the Saclay Centre environmental monitoring program.
D- Operation teams
The ORPHEE reactor is operated by the Nuclear Energy Division of CEA (CEA/DEN), acting on behalf of the Physical Science Division of CEA (CEA/DSM), for the benefit of the experimental users of the Léon Brillouin Laboratory and of their French, European or non-European scientific visitors.
ORPHEE + LLB operations are performed as a joint CEA and CNRS undertaking and submitted to a joint annual review by the Physical Science Division of CEA and CNRS.
ORPHEE operation is performed by a 60 people team, about half of which work on a shift basis. This facility benefits from the support of the radiological protection teams and security teams of CEA Saclay Centre.
More generally, the facility is located inside an integrated nuclear research Centre which was an historic cradle of French reactor technology and nowadays hosts up-to-date theoretical and support teams in the fields of core operation, chemistry, nuclear materials and mechanics.
E- 2008 review
The year 2008 was characterized by 189 days of operation, corresponding to a 95% avaibility factor. Specific ten-yearly operations were carried out, notably replacement of most of the reactor batteries and inspection of most of the pressurized equipments.
The 2008 summer outage enabled the replacement of the 4F horizontal channel inside the heavy water tank. This operation, which took place in the framework of the management of irradiated components, was a first of kind since reactor start up and followed a preparatory operation during the year 2006 summer outage.
The irradiated 4F thimble was extracted, then immediately split into sections. The new thimble was put in place and has given satisfaction to experimental users since the restart of September 2008. The 4F operation also demonstrated the technical capability to perform the further replacements of irradiated horizontal channels which are scheduled from 2011 on.
As regards further heavy maintenance and upgrading activities : the contract to manufacture the replacement cold sources of the reactor (to be put into operation before 2011) and the contract to re-manufacture the electronic processing devices of the radiation protection system (to be put into into operation at summer 2009 and then summer 2010) were concluded.
The other main issue of the year 2008 was the preparation and the completion of the work on the 2nd safety reassessment of the reactor.
To this aim, a major non-destructive inspection program was carried out all along the year 2008 (eg. inspection of the natural convection check valves upstream of the core).
In parallel, substantial safety study work was carried out in association with, and with notable support of, the CEA specialists from the Nuclear Energy Division technical departments of the Saclay Centre.
The resulting work underwent CEA internal review and control at the end of the year 2008 and beginning of the year 2009. Results of these actions confirmed the very satisfactory technical and safety condition of the reactor after 28 years of operation.