Nuclear Data Activities at the IAEA Nuclear Data Section

Transcription

1 Nuclear Data Activities at the IAEA Nuclear Data Section Stanislav P. Simakov International Atomic Energy Agency Vienna International Centre P.O. Box 100 A-1400 Vienna, Austria ABSTRACT The Nuclear Data Section of IAEA assembles, develops and disseminates nuclear data for basic science and practical applications. This paper gives an overview of the NDS activities aimed at the development and maintenance of general purpose databases, such as collection of experimental and evaluated reaction cross sections data, as well as those for the specific energy and material applications, namely for ion material beam analyses, neutron dosimetry, fission and fusion neutronics. The latest upgrades, developments and existing weaknesses are highlighted. 1 INTRODUCTION Nuclear data have both fundamental and practical importance. They are produced and intensively used in the experimental and theoretical studies of nuclear reactions and structure of excited nuclei. In practical applications, assessed and verified nuclear data are of extreme importance since they are used in the performance and safety analyses of nuclear facilities. The large variety of applications such as fission and fusion energy generation, particle acceleration, use of radiation in medicine, analytical techniques for material properties analysis, management and safeguards of spent fuel and radioactive wastes dictate the needs for variety of basic nuclear data. The Nuclear Data Section of IAEA [1] addresses these issues by compilation and distribution of the relevant experimental and calculated databases as well as by coordinating Member States research activities through Coordinated Research Projects (CRPs). This paper gives an overview of the activities in NDS aimed at the development and support of the class of nuclear data relevant for energy generation and material science. These include assimilation, development and maintenance of general purpose databases such as the collection of experimental reaction cross sections in EXFOR and general purpose evaluated cross sections files ENDF/B, JEFF, JENDL, ROSFOND and many others. Specific applications often require nuclear data for particular energy ranges, target nuclei, reactions or higher accuracy. Among these are FENDL and EAF transport and activation data for fusion and IFMIF neutronics, IRDF selected reactions and cross sections for dosimetry and spectral unfolding, IBANDL data for material analysis employing ion beams. The paper focuses on the efforts undertaken by NDS to keep these databases updated so as to respond to the actual needs

2 GENERAL EXPERIMENTAL AND EVALUTED CROSS SECTION DATA 2.1 Experimental cross section database EXFOR The published experimental nuclear reaction cross sections are compiled in the EXFOR database [2], which is maintained by the International Network of Nuclear Reaction Data Centres under the auspices of the IAEA [3]. It is compulsory for the incident projectiles with mass number up 12 and incident energies up to 1 GeV. Other cross sections for reactions induced by photons, heavier projectiles and at higher energies are voluntary compiled regarding the user interests. The reaction parameters assembled in EXFOR are integral, differential and partial cross sections including angular distributions, secondary particle spectra, polarization data, resonance parameters, fission products, neutron and gamma yields from thick targets, reaction rates etc. Currently the database contains information from more than 19,000 experiments and more than 141,000 numerical datasets. The EXFOR database is continuously under improvement and extension. As an example, it is worthwhile to mention the initiative of the comprehensive collection of neutron energy spectra produced by light ion induced reactions at accelerators and at fission reactors, which were employed to measure spectra averaged cross sections [4]. It was also found that more than 40 original articles reporting results on accelerator driven neutron sources were not yet included in EXFOR. After compilation of detailed information on neutron sources, it will be possible to use hundreds of the experimental energy averaged cross sections already available in EXFOR for validation of the evaluated data. Another recent example of EXFOR extension is the inclusion of the Nuclear Resonance Fluorescence data [5]. This is a gamma scattering reaction (γ,γ') with excitation of strong dipole scissors resonances in the nucleus and consequent prompt γ-ray decays enabling a specific fingerprint of the isotope. It is now experiencing a renaissance as a novel nondestructive method for detecting clandestine materials. The compilation of cross sections and decay modes for nuclear fusion synthesis of new super heavy elements and isotopes evidences the extension of EXFOR towards heavy projectiles and frontier physics. In order to make best use of all collected measured data, NDS maintains a retrieval and visualization system [6]. The numerical data and original reference sources can be searched for and presented in various formats: EXFOR exchange original (X4) or extended (X4+, X4±), tabulated (T4), XML, bibliographical (DOI, BibTeX, XREF, NSR), computational standard or extended (C4, C4+, C5) and special (R33) for particular applications (IBANDL). 2.2 Collection of evaluated cross section data ENDF Evaluated Nuclear Data Files database (ENDF) is a collection of the recommended general purpose evaluated nuclear reaction cross sections, yields, energy and angular distributions of reaction products, resonance and radioactive decay parameters and covariances for individual isotopes and thermal scattering laws for compound materials. The largest ones are produced and maintained in the frames of the national nuclear data projects (China, Europe, Japan, Russia and USA) and include original contributions from NDS. The ENDF collection on the NDS web-site contains the latest updates as well as archived versions. NDS also provides access to more than 20 special libraries for fission, fusion, medical, activation and other applications. Last year the ENDF collection was updated with EAF European Activation File (816 isotopes, neutrons, protons and deuterons up to 60 MeV) [7], JENDL-4.0 Japanese general purpose neutron-induced reaction data library (406 nuclides up to 20 MeV) [8], RUSFOND-2010 Russian evaluated file (619 nuclei and 20 materials) for advanced nuclear reactors [9] and TENDL TALYS-based Evaluated

3 305.3 Nuclear Data Library (targets between 6 Li and 281 Ds for incident neutrons, photons and light ions up to 200 MeV) [10]. All data are stored in the internationally-adopted ENDF-6 format. For convenience of external users NDS provides web-retrieving for data search, down loading, plotting and intercomparison with experimental data from the EXFOR database [6]. For this purpose the data were reprocessed into pointwise format by the PREPRO codes or stored in a groupwise representation. As an example, Fig. 1 displays a plot of all measured as well as JEFF-3.1 evaluated data for the 55 Mn(n,2n) reaction with their specific uncertainties to help the user estimate the data status. It is worthwhile to note that correlation matrices can also be plotted as 2D or 3D plots, when they are available. The interactive mode of graphical presentation on the NDS web-site allows many options for manipulation of the data. Figure 1: ZVView plot of all measured (available in EXFOR) and evaluated (JEFF-3.1) cross sections with uncertainties for 55 Mn(n,2n) reaction. 3 DATABASES FOR MATERIAL ANALYSES, FISSION AND FUSION APPLICATIONS 3.1 Ion Beam Analysis Nuclear Data Library IBANDL The Ion Beam Analysis Nuclear Data Library (IBANDL) [11] contains recommended and evaluated data for Ion Beam Analysis (IBA). The database covers the most important techniques such as proton Elastic Backscattering Spectroscopy (EBS) and Nuclear Reaction Analysis (NRA) by means of (p,α) and (d,p) reactions. This year a new CRP Particle Induced Gamma-ray Emission (PIGE) was launched to extend the scope of IBANDL. All these powerful analytical techniques exploit the interactions of fast (~ MeV) charged particles with matter to determine the composition and structure of the surface regions of solids up to 500 μm depth by measuring the scattered light ions, reaction products or characteristic prompt γ-rays. For successful implementation with sufficient analysis accuracy, all published (and

4 305.4 available in EXFOR) experimental differential cross sections were collected, carefully assessed and evaluated with the help of reaction model calculations. As an example, the assessed double differential cross section for elastic back scattering of protons on aluminium is displayed in Fig. 2. Exact reproduction of the resonance structure in the IBANDL database improves the accuracy of determination of the impurity profile in the material. Figure 2: Proton back elastic scattering cross section (ratio to Rutherford) at angle 150 o for aluminium from IBANDL. 3.2 International Reactor Dosimetry File IRDF The International Reactor Dosimetry File (IRDF-2002) [12] contains a standardised, updated and benchmarked evaluated cross section library of neutron dosimetry reactions accompanied by uncertainty information for use in lifetime management assessments of nuclear power reactors and other applications. It consists of cross section data for 66 neutron activation (and fission) reactions, radiation damage cross sections for 5 materials, total cross sections for 3 cover materials, decay data for reaction product nuclei and other auxiliary data. Pointwise cross section data are given in the ENDF-6 format, while multigroup data are supplied in the SAND-II 640 energy group structure. Recently NDS initiated the updating of IRDF-2002 that will finally result in the inclusion of 29 new reactions and energy extension up to 60 MeV [13]. Such an upgrade will meet the needs for IFMIF and other accelerator-based neutron sources relevant for fusion technology. The new file will be called the International Reactor Dosimetry and Fusion File (IRDFF). The extension of excitation functions and their covariances beyond MeV (where experimental data practically do not exist) will be performed by using the TENDL evaluation. Fig. 3 displays available experimental and evaluated data for the 197 Au(n,2n) reaction. One may note the large spread among experimental (including recently measured at Řež [14]) and evaluated data (including last versions of EAF-2010 and IRDF) above 20 MeV. Obviously the validation of the extended IRDF-2002 library in high energy neutron fields is required.

5 x Au(n,2n) 196 Au(g+m+n) σ, b 10 0 Veeser'77 Bayhurst'75 Rez'10 ENDF/B-VII IEAF-2001 EAF IRDF(Zolotarev) Uwamino'92 Soewarsano' Neutron Energy, MeV Figure 3: Experimental and evaluated data for dosimetry reaction 197 Au(n,2n) 196 Au. 3.3 Fusion Evaluated Nuclear Data Library FENDL Fusion Evaluated Nuclear Data Library FENDL 3.0 [15], currently under preparation, will be substantial extension to FENDL-2.1 toward higher energies to cover advanced fusion systems ITER and IFMIF. It will comprise (i) neutron transport cross sections up to 150 MeV for 180 materials, (ii) neutron, proton and deuteron activation cross sections up to 60 MeV for 816 materials and (iii) covariances of the evaluated cross sections for uncertainty assessment in the facility design studies. The library now contains new evaluations for the stable (Ar, Sc, Zn, Ge, Br, Y, Rh, Ag, Cd, Sb, I, Cs, Ba, La, Ce, Gd, Er, Lu, Hf, Re, Pt) and fissile (U, Th) isotopes and elements since they were found to be used in the major facility components (magnets, mirrors ) or as detectors for neutron diagnostics. Figure 4: Measured and evaluated cross sections for tritium production in 23 Na.

6 305.6 To demonstrate the status of nuclear data for fusion application two examples were selected. Fig. 4 and 5 show the measured and evaluated cross sections for tritium and helium production reactions in sodium and iron by neutrons [16]. As seen, the experimental data above 14 MeV are scarce and the differences between the evaluations are large. After completion of the CRP some of these problems should be resolved. Fe(n,xα) 0.20 ENDF/B-VII TSL,Uppsala σ, b INPE-FZK( 56 Fe) LANSCE IEAF-2001 LA-150 JENDL-HE ( 56 Fe) TENDL Neutron Energy, MeV Figure 5: Measured and evaluated cross sections for helium production in Fe. 3.4 Radiation Damage Libraries To predict the lifetime and safety issues for the components of fission and fusion reactors and accelerators the radiation induced damage and gas accumulation rates in materials are needed. For this NDS assembles the displacement (dpa), hydrogen, helium and tritium production cross sections. These data are presently available in the following databases: IRDF-2002 displacement cross sections for Cr, Fe, Ni, Si and GaAs up to 20 MeV [12], BISERM-2 - neutron displacement cross sections and hydrogen and helium production cross sections for 259 stable nuclei from 27 Al to 209 Bi up to neutron energies 1 GeV [17], DXS - displacement cross sections up to 1 GeV for some structural materials irradiated by neutrons (Cr, Fe, Ni) and protons (Cr, Fe, Ni, Cu and W) [18]. Presently, the dpa-cross sections are traditionally estimated employing the Norgett- Robinson-Torrens (NRT) standard [19] that predict the number of atoms knocked from the lattice nodes without further consideration of the evolution and morphology of recoil cascades. New theoretical studies based on the Molecular Dynamics model (MD) and Binary Approximation (BCA) have demonstrated that during the cascade relaxation stage many initial vacancies and interstitials will recombine and only survived Frankel pairs (FP) or interstitial clusters will form primary defects in materials. The MD and BCA predictions for FP available for selected materials were implemented in the DXS database. Fig. 6 shows the iron dpa-cross sections from this library estimated both with the NRT standard and with inclusion MD/BCA results. The comparative assessment of the survived primary defects in the iron components of IFMIF, fusion power reactor and fast research reactor are presented in Table 1 [20]. It shows the substantial lower number of survived primary defects. Moreover, the intercomparison of the different irradiation environments on the level of survived primary defects instead of the

7 305.7 NRT standard now takes into consideration the difference in neutron and recoil energy spectra in these facilities Damage Cross Section Library (DMX) for Fe 10 6 σ dpa, b protons: NRT MD-BCA neutrons: NRT MD-BCA Neutron or Proton Energy, MeV Figure 6: Displacement cross sections caused by neutrons and protons in Fe. Table 1: Estimation of dpa rates as NRT standard and as primary survived defects (Frankel pairs or interstitial clusters) in iron components in different facilities. Facility IFMIF high flux module Fusion Power Reactor first wall Fast Research Reactor, Petten Thermal Power, MW n-flux, n/cm 2 /s maximal PKA energy, MeV dpa (NRT), 1/fpy dpa (MD: Frankel pairs) dpa (MD: interst. clusters) CONSLUSIONS A few general and special purposes libraries of experimental and evaluated nuclear reaction data compiled and developed by the Nuclear Data Section of IAEA are presented. Their regular intercomparison, updating and maintenance guarantee their general mature status. Nevertheless, as was demonstrated in several examples, to meet the specific requirements for the particular energy or material applications further measurements and evaluations are still needed. ACKNOWLEDGMENTS The author gratefully acknowledges the work of the NDS staff members and external experts who made contribution to the presented results. REFERENCES [1] The Nuclear Data Section of IAEA:

8 305.8 [2] EXFOR experimental cross section database: [3] International Network of Nuclear Reaction Data Centres: [4] S.P. Simakov and F. Käppeler, Summary Report of the Consultants' Meeting on Neutron Sources Spectra for EXFOR, Report INDC(NDS)-0590, IAEA, [5] S.P. Simakov, N. Otuka, V. Semkova, V. Zerkin, "Experimental Data for Nuclear Resonance Fluorescence", 52 nd Annual Meeting of INMM, Palm Desert, July 17-21, CA. [6] V. Zerkin and A. Trkov, Development of IAEA nuclear reaction databases and services, Proc. Int. Conf. Nucl. Data for Sci. and Techn., Nice, France, April 22-27, EDP Sciences, 2008, pp [7] EASY European Activation System: [8] JENDL-4.0: [9] RUSFOND: [10] TENDL-2010: TALYS-based Evaluated Nuclear Data Library, [11] The Ion Beam Analysis Nuclear Data Library: [12] International Reactor Dosimetry File IRDF-2002: [13] R. Capote, K.I. Zolotarev et al., Updating and Extending the IRDF-2002 Dosimetry Library, 14 th Int. Symp. on Reactor Dosimetry, May 22-27, 2011, Bretton Woods, USA. [14] S.P. Simakov, P. Bem et al., Analysis of the dosimetry cross sections measurements up to 35 MeV with a 7 Li(p,xn) quasi-monoenergetic neutron source, J. of Korean Nuclear Society, 59, 2011, pp [15] Fusion Evaluated Nuclear Data Library FENDL 3.0: [16] A. Klix, U. Fischer, S. Simakov, Assessment of the tritium production in the HFTM specimen cells of IFMIF, IEEE Transactions on Plasma Science, 38, 2010, pp [17] Yu.A. Korovin, A.Yu. Stankovsky et al., Nuclear Data Library for Evaluation of radiation effects in materials induced by neutrons of intermediate energy, Report IAEA- NDS-0203, IAEA, 1997 [18] A.Yu. Konobeyev, U. Fischer et al., Displacement cross section files for structural materials irradiated with neutrons and protons, Report IAEA-NDS-214, 2009, IAEA. [19] M.J. Norgett, M.T. Robinson and I.M. Torrens, Nucl. Eng. and Design, 33, 1975, p. 50. [20] S.P. Simakov, A.Yu. Konobeyev et al., Comparative study of survived displacement damage defects in iron irradiated in IFMIF and Fusion Power Reactors, J. Nucl. Mat., 386, 2009, p. 52.