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«Association EURATOM / IPP.CR I N S T I T U T E O F P L A S M A P H Y S I C S, v.v. i. ACADEMY OF SCIENCES OF THE CZECH REPUBLIC ANNUAL REPORT ...»

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Task : UT7_IFMIF_IPPCR_NPI Field: Vessel/In-Vessel Collaborative staff: V. Burjan, M. Götz, M. Honusek, V. Kroha, J. Novák and E. Šimečková In collaboration with: U. Fischer and S.P. Simakov, Association EURATOM-FZK, Karlsruhe, Germany The neutron cross-section data of reactions at incident energies En 20 MeV are needed to improve the accuracy of neutronic calculations incorporated with various advanced nuclearenergy technologies. There are almost no experimental cross-sections data on Ni for neutron energies 20 MeV and only limited data exist for neutron energies 20 MeV [1]. In the following sections the quasi-monoenergetic p-7Li neutron source, the activation experiment on CrNi foils and the method of data evaluation are described. The resulting radioactive isotopes were studied by means of gamma spectroscopy methods. The preliminary analysis of measured activities was carried out by comparison of measured and predicted reaction rates.

In the analysis, the neutron cross sections for different neutron reactions on Ni nucleus were taken from EAF 2007 library [1].

The target station of quasi-monoenergetic neutron source based on 7Li(p,n) reaction is described elsewhere [2] together with preliminary results of present work. The proton beam from isochronous cyclotron U-120M strikes 1E15 the 7Li foil at four energies between 20 and Neutron spectra at different proton 37 MeV. The carbon backing of the cooled energies Neutron flux (n/sr/MeV/C)

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Part III - TECHNOLOGY and 37.5 MeV (neutron spectra peaking at 19.0, 24.3 26.6 and 35.6 MeV, respectively – see Fig. 1). The stacks of irradiated foils (NiCr and Au) were activated at two distances (46 and 86 mm) from the source target to test the effect of the flux-density gradient in the vicinity of neutron source. The Au foil was used as a "reference monitor" [3].

The time profile of the neutron source strength during the irradiation was monitored by the proton beam current, recorded by a calibrated current-to-frequency converter on PC. The typical beam current was about 3 µA. The irradiation was carried separately with Li+C and C targets to investigate the contribution of neutrons from carbon stopper. The density of neutron flux at foil positions was approximately evaluated using the data of Ref. 3.

Irradiated samples were investigated by means of gamma-spectroscopy method. Two calibrated HPGe detectors of 23 and 50 % efficiency and FWHM of 1.8 keV at 1.3 MeV were used. Reaction products were identified on the basis of T1/2, γ-ray energies and intensities. Cooling times of gamma measurement ranged from minutes to approx. 100 day.

(Each foil was measured at approx. 5 cooling times).

Up to 14 isotopes (see Tab. 1) were determined 2,0 from measured activities. Experimental cross sections (derived from observed reaction rates) 1,8

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Fig3. C/E ratio for the reaction Ni58(n,pα+)Mn54 As an example, the C/E ratios for the reaction Ni58(n,pα+)Mn54 (Eth=6.424 MeV) are given in Fig. 1. As the preliminary conclusion, an upgrade of EAF-2007 library is needed [4,5].

This work was performed within the partial support of EFDA Technology Program and of the Ministry of Trade and Industry of CR.

References:

[1] R. A. Forrest, J. Kopecky, M. Pillon, K. Seidel, S. P. Simakov, P. Bém, M. Honusek and E. Šimečková, UKAEA Report, UKAEA FUS 526, 2005 [2] P. Bém, V. Burjan, U. Fischer, M. Götz, M. Honusek, V. Kroha, J. Novák, S.P.Simakov, E. Šimečková, Neutron activation experiments on chromium and tantalum in the NPI p-7Li quasi-monoenergetic neutron field, Proc. on the Int. Conf. on Nuclear Data for Science and Technology 2007, Nice, April 2007, in print [3] Y.Uwamino et al., NIM A389 (1997) 463.

[4] E. Šimečková, P. Bém, V. Burjan, U. Fischer, M. Götz, M. Honusek, V. Kroha, J. Novák and S.P.Simakov, Activation experiment on Cr in the NPI p-D2O white-spectrum neutron field, EUR 23235EN, pp. 35-39, http://www.irmm.jrc.be/html/publications/technical_reports/index.htm, [5] M. Honusek, E. Šimečková, P. Bém, V. Burjan, U. Fischer, M. Götz, V. Kroha, J. Novák and S.P.Simakov, Benchmark tests of activation cross sections for Cr and Ni using the quasimonoenergetic neutrons below 35 MeV, ibid, pp. 39-43

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Task : UT7-WELD-IPPCR-IAM Field: Vessel/In-Vessel Collaborative staff: L.Vlček, PhD.

The manufacturing process of the Vacuum Vessel requires a lot of the welding operations.

The weld joints are very long and contain a lot of welding passes. The local global approach is a new methodology for prediction of distortion of the large structure during welding assembly process. Each welding operations and weld joints generate residual distortions.

The final distortion has to comply with the very strict manufacturing tolerances and requirements for final size and shape of the construction parts.

The numerical computation of distortion by using local/global approach can be described by

four following stages:

1. Typical welding joints on the structure are chosen and simulated by numerical analysis of local models. Total elastic-plastic deformations are computed as the results of local model computations

2. The global model which represents the whole welding structure is created





3. Only plastic deformations obtained on local models are transferred onto the global model as the load of global model

4. The structural elastic analysis of the global model including each welding joints is computed. The results of this part are distortion during and on the end of assembly process Local models are usually computed by so-called transient method. This well known method describes the real moving heat source very sharply, but generally the solution is very time consuming. Now, improvement of local model solution is proposed and the whole idea is based on so-called macroelements or macro bead deposition (MBD). Due to the fact mention above the several experimental mock-ups have been done and also these experiments were numerically analyzed. These mock-ups represent one of the main types of welding joints using in real welding assembly process. The aim of this work is to compare between classical transient method and new method of macroelements.

Numerical method of welding solution by macroelements or macro bead deposit (MBD) consists of the same steps as in the case of classical or transient method. It covers thermal calculation followed by mechanical analyses. The main difference of MBD is in temperature analyses. In the case of transient analyses the heat flux into the material is defined by mathematical model of heat source, which is depended on location of its space coordinates and time. To the contrary MBD inserts the whole fictive temperature, which is needed for welding one bead, into the material volume representing the whole bead. Next, inserted heat is distributed by heat conductivity between melting metal and base material in user defined time steps. Number of time steps depends on welding velocity and the length of bead.

Finally, time step (or steps) has to be chosen in order to melt through the real thickness of material. The MBD does not require very fine mesh in melt area and that is why the computational time is reduced in comparison with classical transient method. The MBD has been used in order to verify the process of “right” fictive temperature input in to the bead volume. In parallel different time steps and numbers of macroelements have been tested.

As results from performed analyses very good agreement was observed between experiments and numerical calculations. Moreover, the new MBD method is very promising and power tool for numerical analyses of large welded structures, which consider many beads. The total fictive temperature is defined on the base of temperature measurement by thermocouples and melting zone size. On the base of performed mock-ups and their numerical analyses it can be said, that MBD method reduces computer time very significantly, while numerical outputs has the same quality as in the case of classical transient method. MBD method should be used for numerical simulations of complicated structures.

References:

[1] Diviš V., Slováček M., Evaluation of welding distortion of VV poloidal segment, stage 1: Validation of method, experiments, October 2004, IAM Brno 3616/04 [2] Collective of authors, Material characteristic of AISI 316 LN steel, Material database in electronic form [3] Labanti M., Martignani G., Minoccari G.L., Ricci A., High temperature tensile tests on AISI 316 LN cast and forged stainless steel, ENEA report, IMAP-14011-R-001, Bologna, Italy, 2002

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Task: UT 2007 PFW_IPPCR_NRI Field: Vessel /In Vessel, Area: Blanket, Materials Collaborative staff: Vl. Masařík, T Klabík, J. Hájek The main objective is commissioning and operation of a dedicated workplace for handling and manipulations with beryllium coated Primary First Wall (PFW) mock-up specimens.

This workplace needs to be operated to fulfill requirements for safe handling beryllium to minimize health hazard of the involved personnel. This workplace will be used for preparation and realization of the thermal fatigue tests under the framework of the EFDA technology programmes (EFDA tasks TW3-TVB-INPILE, TW4-TVB-TFTEST2 and TW6TVM-TFTEST).

The Beryllium laboratory for handling and manipulations with Be coated PFW mock-up specimens needs to be commissioning and operating in accordance with the requirements of the health and safety authorities.

In the last period the following activities have been performed:

• Establishing of the certified Beryllium workplace approved by the state health and safety authorities; for this reason necessary documentation has been prepared, including the elaboration of the Safety Report, Limits and Conditions of the Laboratory Safe Operation, the Emergency Plan, the Personnel Monitoring Plan, etc.

• Application of the Quality Assurance and Quality Control system at operation of the Be workplace. These include the elaboration of the Working Procedures, personnel training, personnel entrance/exit checking, utilization of personnel protection tools, etc.

Fig 1. Laboratory for handling and manipulation with beryllium coated specimens

• Installation and testing of the beryllium workplace air-conditioning system, including setting of underpressure in the room, HEPA filters performance, checking, replacing and monitoring.

Part III - TECHNOLOGY

• Necessary adaptation of the PFW mock-up specimens to be used for testing by drilling, grinding, polishing.

• Assembly of the preliminary PFW dummy specimens for qualification test.

• Realization of the qualification test consisting of thermal cycling of dummy specimens.

• Dismantling of the PFW dummy specimens from the test rig after completion of the qualification test.

References:

[1] Technical documentation for beryllium workplace: air-conditioning, cooling, and electrical system, 2007 [2] Working Manual for Beryllium Workplace, NRI Internal Report (in Czech), 2006

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Task: IPP-CR_UT7_SURF_IPM1 Field: Tritium Breeding and Materials, Area: Materials Development Collaborative staff: Jiří Buršík, Jiří Čermák, P. Král, P. Roupcová The motivation of this study was investigation behaviour of the Cr2O3 coating prepared by plasma spraying and its interface with the EUROFER substrate in the dependence on the conditions of heat treatments. Possible effect of tritium penetration was modelled by comparison of effect of surrounding atmospheres by annealing. The detailed structure investigations were focused on stability of both the EUROFER substrate and the Cr2O3 coating during the annealing in range 550-750 °C in argon and hydrogen. No gradients of chemical composition of metallic elements were found in the substrate near the coating by means of EDX analyses.The concentration curves of the main elements at interface Cr203 layer/EUROFER measured by WDS show redistribution of manganese only. For samples annealed in argon, diffusion coefficients of manganese were calculated. The results showed that negative influence of the hydrogen as the surrounding atmosphere by the annealing at 750°C/100h occured. It can be important drawback for an application of the Cr2O3 coating due to expected tritium penetration.

EUROFER steel is taken as possible structural materials in the programme of European Breeding Blanket Programme for the DEMO design. Its properties were already described, e.g., in [1]. Further research has been focused on corrosion and optimising tritium recovery cycle. Coatings which would form barriers protecting EUROFER from a direct lithium lead contact were taken into account [2]. The problem is still open because increase of the steel temperature in contact with the lithium lead increases the tritium penetration towards Hecoolant.

Research on Al based permeation barriers from the side of lithium lead exhibited some problems with applications of these coatings [2,3]. Therefore other kinds of barriers can be important. Cr2O3 can be taken into account as good candidate from the point of view of reduced-activation characteristics of the irradiated EUROFER structures. Another point of view is operation of removing of the coating layer from the supporting steel structures at dismounting of the blanket.

The motivation of this study was investigation behaviour of the Cr2O3 coating prepared by plasma spraying and its interface with the EUROFER substrate in the dependence on the conditions of heat treatments. Possible effect of tritium penetration was modelled by comparison of effect of surrounding atmospheres - argon and hydrogen – by the annealing.

The material used for preparation of the substrate is the European reference steel EUROFER 97 produced by Böhler Edelstahl company. Its chemical composition is given in table 1. The surfaces of the samples were ground by mechanical grinding. Before the plasma spraying the surface was cleaned once more by standard industrial procedure using sand jet. Subsequently thermally sprayed Cr2O3 coating was deposited by Ar+H2 gas stabilized plasma torch.

The structure of the original state of the ingot was characterized in details by x-ray diffraction (XRD), Mössbauer spectroscopy, optical and electron microscopy. The specimens

Part III - TECHNOLOGY



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