Test devices in Jules Horowitz Reactor dedicated to the material studies in support to the current and future Nuclear Power Plants

Transcription

1 Test devices in Jules Horowitz Reactor dedicated to the material studies in support to the current and future Nuclear Power Plants C. Colin 1, J. Pierre 1, C. Blandin 1, C. Gonnier 1, M. Auclair 2, F. Rozenblum 2 1 DEN / DER / SRJH, CEA, Centre de Cadarache, Saint Paul lez Durance, FRANCE 2 DEN / DRSN / SIREN, CEA, Centre de Saclay, Gif sur Yvette, FRANCE * Corresponding Author, christian.colin@cea.fr Before their uses in industrial nuclear power plants (NPP), materials and fuel have to follow a long qualification process with different stages of screening, selection, qualification, optimization, processing, lifetime assessment and safety tests. These studies are most of the time associated with a complex multi-physical modelling of the materials behaviors. It requires well controlled and instrumented irradiation experiments in material testing reactors (MTR). Considering the long term needs of this kind of experiments and the ageing of the present MTRs in Europe, it was decided to construct a new high performance MTR. The Jules Horowitz Reactor (JHR), a tank pool MTR under construction at CEA Cadarache centre with a maximum thermal power designed at 100MW, will meet these issues, in support of the current NPP (Gen.II, Gen.III), as well as investigations related to future reactor systems. The aim of this presentation is to describe the main test devices under development at CEA and dedicated to the material irradiations in JHR reactor. In-core and in reflector devices will be presented, corresponding to large ranges of temperature and neutrons flux for the irradiation conditions. A special attention focuses on the improvement of the thermal stability and gradients of the interest zones in samples despite strong γ heating and on an improvement of the instrumentation devoted to the experiments. Some specific devices in support of LWR type reactors will be described such as equipments designed to the qualification of reactor pressure vessel RPV steels, to the study of the stress corrosion cracking assisted by irradiation phenomena (IASCC), or to the studies of creep-swelling of structural materials. KEYWORDS: MTR, Jules Horowitz Reactor, irradiation, materials, behaviors Introduction A good knowledge of the phenomena controlling the nuclear materials behaviors is required to justify their selections, optimizations and their uses in nuclear power plants (NPP). It is necessary to develop a good predictive material modelling, associated with a large experimental database at different scales and recovering closest as possible range of reactors conditions. But at the end of the process, this approach must be supplemented and validated by an experiment, of course well controlled, in a nuclear reactor environment like in material testing reactors (MTR). The experimental irradiations in MTRs have to be continued to justify safety or to increase lifetime of the current NPP as well as to develop the future reactor systems [1]. On the other hand, it should be noted that the existing MTRs in Europe are or will be more than 50 years old in the next decade and so, they will be probably shut down in few years. Thus for example, because of its ageing, OSIRIS is planned to be shut down in less than ten years [2]. The JHR facility Within this framework, it has been decided to launch the construction of the Jules Horowitz Reactor, implemented in CEA Cadarache. The JHR characteristics have already been exposed elsewhere [3 to 8], but the main points are resumed below. The Jules Horowitz Reactor (JHR) is a tank pool MTR with a maximum thermal power designed at 100MW. Its design allows a large experimental capability (around 20 experiments at the same time) inside the reactor core, close to the fuel with high fast neutron flux and outside the reactor core, in the reflector with higher thermal neutron flux : it is

2 possible to perform irradiations in the core which will provide high damage rates (up to 15 dpa/year) in materials samples, while also carrying out in the reflector zone irradiations on fuel rods on displacement systems with precise positioning for example. The primary circuit which cools the fuel elements in the core will be lightly pressurized (12 bars). The reflector blocks, made of Beryllium, will be cooled by a forced water circulation connected to the reactor pool. The JHR is also designed to produce medical radio elements. Several equipments will be implemented in the reactor building and be used in support to the experimental programs: Hot cells in the nuclear auxiliary building will allow the preparation and examination of devices before and after irradiation. It will be possible to proceed to the first simple post irradiation examinations (PIE) of the irradiated samples. These on-site PIE programs will be of course completed by destructive examinations programs in dedicated hot cell laboratories, like LECI for materials in CEA Saclay or LECA-STAR for fuel in CEA Cadarache or any other foreigner hot lab. Non destructive examination systems (spectrometry γ, X tomography, neutron imaging system) are foreseen in the pools and in the hot cells. Specific laboratories will also be set up in the installation for various uses: a fission product lab, a chemistry lab and a dosimetry lab. In the reactor building, the reactor pool is surrounded by several cubicles to receive instrumentation and control systems of each irradiation devices, linked by a system of fluid pipes and cables. The figure 1 presents the whole of the system. Hot cells (non destructive examinations) Reactor block Storage pools Reactor pool with examination benches Experimental cubicles and analysis laboratories Core (Φ 60cm / h 60 cm) and Be reflector Figure 1 - Views of the main systems in the JHR facility and view of the reactor core. Neutron performances The core of the reactor can house up to 10 experimental devices distributed on three rings: 7 in small locations of 37 mm diameter and 3 in larger locations of 91 mm diameter. The reflector can also receive devices with 20 fixed positions, mainly of 100mm diameter but there will be one location of 200mm diameter. On figure 1, we can also see 6 water channels distributed around the reflector, where displacement systems will receive specific devices, a priori dedicated for fuel irradiations. Many calculations were performed to estimate neutron flux levels, by TRIPOLI 4.7 associated with JEFF-3.1 nuclear data library and considering a start-up fuel configuration (U 3 Si 2 fuel and 70MW of core thermal power).in this configuration, the highest fast flux in the core is n.cm -2.s -1 (E > 1MeV). This allows reaching damage rates about 9dpa/year on the first ring. The corresponding γ heating is 12W.g -1 in stainless steel. Of course, on the third ring, flux levels are lower: n.cm -2.s -1 (E > 1MeV) and 9W.g -1. In the reflector, the fast flux level is in the range from up to n.cm -2.s -1 (E > 1MeV) and γ heating from 1.5 up to 0.2 W.g -1 according to the distance to the reactor tank. The figure 2 underlines the evolution of the neutron spectra in the JHR core up to its reflector.

3 Position 103 Position 101 Position C313 SFR core reference 1/Lethargy E E E E E E+01 E [MeV] Figure 2 Different neutron spectra met in JHR. Experimental devices: material irradiations Technological irradiations carried out in MTRs are in support of the current NPP, as well as of investigations related to future reactor systems. Because of the planned transition between the Gen II-III and Gen IV nuclear power reactors and considering the roadmap for the JHR deployment, CEA chose to mainly first develop new irradiation devices in support of LWR type reactors. Of course, the high technical skills of OSIRIS staff and its evident know-how is important for the setting-up and the design of the experimental capacity of the JHR. The two operating teams are working closely for the design of the new irradiation devices. This paper will expose the materials irradiation devices, which are at this moment under development at CEA. Other available papers present the JHR devices dedicated to the nuclear fuel irradiations, [9] for example. JHR offers a wide range of experimental capacities in terms of neutron flux, neutron spectrum and hosting capacity in the rooms surrounding the reactor pool. More specifically, the JHR objective of experimentation dedicated to GEN IV reactor types led to design JHR core to reach high fast neutron flux while keeping a water technology (easy to operate). This makes that JHR offers experimental capacities which are unusual in other MTR. MICA The MICA device (Material Irradiation Capsule) has the same performances than the current CHOUCA test device widely used in OSIRIS reactor, i.e. irradiation of various geometries of samples in static NaK (up to 450 C) or gas (up to 1000 C). The se test devices are mainly foreseen for in core irradiations were fast flux can reach up to 9dpa a year (at 70 MW). Since adaptation studies where necessary to fit to JHR and few years were available before the manufacturing of first batch of MICA, additional studies have been launched in two main directions: - the specificities of JHR, in terms of test devices outline dimensions, lead to an advanced integrated head of device. The main defined constraints are the handling procedure and the co-activity in the reactor pool during the few days of refueling (inter cycles). The nowadays design embeds the gas circuits control components (valves, pressure sensors, connection) and the current electrical connections (instrumentation and electrical heating). These numerous modifications, compared to former CHOUCA device, lead to manufacture a prototype of a MICA head, tested in 2013: easiness of changing sensors, plugging/unplugging actions, tests with remote manipulator arms, and tightness of circuits - the multipurpose carrier that MICA represents leads to keep most of widely former concepts that made CHOUCA devices successful but improve their thermal behavior in order to meet the requirements, particularly in temperature precision and gradients mastering. The previous technological solutions chosen for the CHOUCA electrical elements have been reassessed to make the additional electrical heating more predictable in terms of modelling. Moreover, a special effort will be done in the determination of reactor γ heating with qualification measurement during the start-up phase of JHR.

4 CALIPSO The CALIPSO device (in-core Advanced Loop for Irradiation in Potassium SOdium) meets the original need of a low temperature axial gradient (a maximum of 8 C ) all along the sample holding, i n liquid metal coolant (NaK), up to 450 C for a first step of development, and up to 600 C in a second phase. The locations of such devices are the same than MICA devices. The design is based on an embedded thermo hydraulic loop, including a heater, an electromagnetic pump and an heat exchanger. The setting of each parameter (power of heater, flow of the pump and efficiency of exchanger) leads to a full control of the thermal conditions inside the test device and in particular in the sample location. The most difficult component turns out to be the pump, mostly because of dimensional and density of integration. Different technical solutions have been tested at the late 2011, and the final prototype should is now under qualification step in a specific platform, named SOPRANO. The layout of such a liquid metal coolant loop has been done in the past, particularly for fast reactor samples irradiations. Nevertheless, theses former devices had an external loop very restrictive for both handling and safety point of view. Because safety rules became more rigorous and handling in JHR more time-consuming, CALIPSO with its embedded coolant loop represent a real innovative test device. OCCITANE Design Figure 3 CALIPSO pump Prototype Figure 4 Thermal calculation in OCCITANE device at 0.6W/g.

5 In the field of pressure vessel steels of NPPs, irradiations are carried out to justify the safety of this 2 nd containment barrier and to improve its lifetime. CEA is designing a hosting system named OCCITANE (Out-of-Core Capsule for Irradiation Testing of Ageing by Neutrons), which will allows irradiations in an inert gas at least from 230 to 300 C. It will be implemented in the JHR reflector a nd reach damage rate about 100mdpa/year (E > 1MeV). OCCITANE will be able to carry out irradiation programs in JHR in the same conditions than the IRMA test device in OSIRIS (CEA Saclay). It will be possible to irradiate samples up to CT25mm size. The associated instrumentation will include at least thermocouples and dosimeters as close as possible to the samples. OCCITANE is based on IRMA device of OSIRIS. The design studies consist mainly in decreasing thermal gradient in the sample area (figure 4) and in integrating the capsule to the JHR environment. A first design has been proposed to accommodate the higher γ heating levels in the JHR reflector, compared to the OSIRIS one. The proposed design mainly allows decreasing thermal gradients in the zones of interest of the samples. Thermal calculations, using COMSOL FEM codes, have been performed to assess the thermal performances in a real samples holder. For example, the figure 4 shows the temperature in a specific sample holder, hosting 70 CT12.5mm samples: the temperatures, close to 300 C, are in the range of ±6 C around the average temperature specified by an OSIRIS customer. Moreover, regarding the implementation of the capsule to the JHR environment, the possibilities of common components with other devices and the safety options analysis, CEA estimates that the feasibility of the OCCITANE device is reached. Finally the Figure 5 summarizes the current development status of the device. CEA is now expecting for customer requirements before launching the next phase, the preliminary and detailed design studies. Figure 5 Development schedule of OCCITANE.

6 CLOE Due to ageing of the NPPs, stainless steel core components undergo increasing radiation doses, which enhance their susceptibility to local corrosion phenomena, known as irradiation-assisted stress corrosion cracking (IASCC) [10]. Cold laboratories can study and model SCC phenomena; but to really be representative of LWR environments, these studies need integral tests to take into account irradiation effects (radiation dose and flux) in MTRs. To answer to these industrial needs and in collaboration with DAE teams (India), CEA has just begun the design of a LWR corrosion loop CLOE (Corrosion LOop Experiment), which will be located in the JHR reflector close to the tank. Its design will integrate the operational experience accumulated by the existing corrosion loops in cold laboratories at CEA and of course by the existing MTRs. A special attention will relate to the instrumentation associated with this device and will be based on the conclusions of the European program MTR+I3 [11].The design of such a loop can be divided in 3 parts on Figure 6 [12]: - The circuits which will be located in one of the cubicles surrounding the JHR pool. These circuits will be used to monitor and to adjust the thermo-hydraulic conditions and the water chemistry. Usually, these circuits are designed and manufactured for a long period of a few tens of years. The design takes into account a large domain of operating conditions and has to be as adaptable as possible. - The main structures of the device which will be under irradiation (pressure tube and thermal insulator in which will be loaded the experimental samples). These tubes are thermal and pressure barriers between the water circuit used for the material samples environment (high temperature, pressurized water) and the external cooling of the test device (external cooling at low pressure, low temperature). The upper part of these structures consists in a head which will fit with the upper end of the sample holder. The typical operating time is few years up to about ten years. The design is done in order to host various types of experiments (i.e. various types of sample holders). - The sample holder which will be loaded in the pressure tubes. The upper part of the holder consists in a plug which fit with the head of the test device. The sample holder is dedicated to one type of experiment (for example: numerous samples under irradiation under controlled conditions but with very limited instrumentation and post irradiation characterizations, or one or few samples heavily instrumented for on-line analysis of the phenomena). Figure 6 Architecture of the Corrosion Loop Experiment loop (CLOE loop)

7 In order to make easier the technological development, the first location of the loop will be in the reflector, close to the reactor tank. The fast flux is still rather high in spite of the in reflector location. It can reach about n/cm².s (100 MW; Φ > 100keV). This value does not allow to accelerate the damages compared to the kinetic in a power plant and it is therefore important to design the sample holder in order to be able to load irradiated samples which could have been pre-irradiated in another reactor or in JHR but in a high fast neutron flux location (within the core), and then transferred within the water loop. Note that the future integration within the core, could make possible to accelerate the damage kinetic by a factor 2 to 8 compared to the power plant kinetic. But this configuration requires preliminary studies about possible limitations due to γ heating, about safety, about core neutron physics and operation. As already said, the design of the loop is done for a rather long period of time and in order to preserve a large operating domain, the design parameters of this loop are chosen to be representative of LWR primary coolant: - maximum operating pressure at 190 bar; - sample temperature up to 360 C; - loop design allowing operation under BWR or PWR (including VVER) conditions; - accurate control and adjustment of the water chemistry (hydrogen and oxygen content, additives,..); - the constitutive material of the loop will be Stainless Steel; - flow-rate will be adapted in order to get an accurate control of the chemistry but preliminary calculations showed that the design criterion for the flow-rate will be the temperature homogeneity in the test device (first estimation: flow-rate greater than 1kg / s ). The main components of the loop will be located in a cubicle in the reactor building. Indeed, the schematic diagram of the loop is given in Figure 7. Note that the connection to a shielded autoclave located within the cubicle is taken into account in order to perform comparative experiments under flux and out-of-flux. The rig will be composed of a double pressure tube for experimental reasons (thermal insulation) and for safety reasons (double barrier between the high pressure hot temperature water and the core tank or core equipments. The instrumentation of the loop will include usual thermal-hydraulic measurements but also an accurate control of the chemistry parameters. Figure 7 Schematic diagram of the CLOE loop

8 The design of the sample holder dedicated to the understanding of IASCC phenomena is a challenge which perfectly meets the objective of a heavily instrumented sample holder. It includes the system that applies on-line controlled stresses on samples and instrumentation able to get information about crack initiation and crack propagation. This kind of instrumentation is usually based on low voltage techniques such as the local electric potential drop measurement. These techniques are very challenging because of low current and voltage in an ionizing environment, and of the necessary tight penetrations through the wall of the tests device containing high pressure and high temperature water. The design has to be as flexible as possible to integrate the present knowledge in this domain and to adapt the sample holder to any relevant instrumentation development. About Gen IV Right now, CEA anticipates the fourth generation research program; a first analysis of the SFR or GFR irradiation needs for materials and fuels has been performed. Accordingly, some feasibility studies have begun in order to prepare future irradiations in JHR. As example, CEA studies the feasibility of a transmutation capsules, of an in-core high temperature device with a large capacity, of metal liquid loops, Conclusion The Jules Horowitz Reactor, even if it follows in the continuity of OSIRIS Reactor, has been designed with improved nuclear performances as well as handling constraints. Therefore all test devices, and in particular those foreseen in material irradiation, take into account the peculiarities of the JHR. Moreover, the constant improvements of modelling induce the associated qualification experiments to more accuracy and representing appropriately the modelling conditions. Thus, intense efforts of development are on progress on test devices design to match to requirements and provide around experimental samples accurate, mastered and reproducible physical and chemical conditions. References [1] D. Iracane, and al., Jules Horowitz Reactor: a high performance material testing reactor, Comptes Rendus Physique, vol. 9, pp , [2] F. Rozemblum, and al., Irradiation rigs in material testing reactor from OSIRIS to JHR, in Fontevraud 7. Avignon, France: SFEN, September [3] M. Boyard, and al., The Jules Horowitz Reactor core and cooling system design. Gaithersburg: IGORR 10, September [4] J. Dupuy, and al., Jules Horowitz Reactor: general layout, main design options resulting from safety options, technical performances and operating constraints. Gaithersburg: IGORR 10, September [5] C. Pascal, and al., Jules Horowitz Reactor: experimental capabilities. Gaithersburg: IGORR 10, September [6] G. Bignan, and al., The Jules Horowitz Reactor: a new european MTR open to international collaboration, description and status. Knoxville, IGORR 13, September [7] D. Parrat and al., Non-destructive examination benches and analysis laboratories in support to the experimental irradiation process in the JHR Knoxville IGORR 13, Sept [8] P. Roux, and al., The MADISON experimental hosting system in the future Jules Horowitz Reactor. Knoxville - TN - USA: IGORR 13, September [9] T. Dousson and al., Experimental devices in JHR dedicated to the fuel studies in support to the actual and future nuclear power plant. Prague: IGORR 14, March [10] M. Postler and al., The influence of corrosion potential on stress corrosion cracking of stainless steels in PWR primary coolant environment, in Electrochemistry in LWR:, Eds. R. Bosch and al.,, EFCP no. 49, 2007, pp [11] J. Dekeyser, et al., Integrated infrastructure initiatives for material testing reactor innovations, Nuclear Engineering and Design, vol. 241, no. 9, pp , 2011 [12] V. Kain, et al., Irradiation assisted stress corrosion cracking: current status and future directions in the framework of the Jules Horowitz material test reactor, under submission