Fusion Material Transmutation and Activation Analysis Induced by Fast Neutrons

Transcription

1 IEA International Workshop on Fusion Neutronics September 5, Dresden - Germany Fusion Material Transmutation and Activation Analysis Induced by Fast Neutrons a) Vitenea-IEF radiation transport library b) ANITA-IEAF Activation code package D. G. Cepraga ENEA, FIS-MET, Bologna, Italy G. Cambi Bologna University, Physics Dept., Bologna, Italy M. Frisoni Athena s.a.s., Bologna, Italy Presented by Dan Gabriel Cepraga I

2 I Background The Bologna group (ENEA & University) effort for the IFMIF facility project during is related to the setting up, production and application of new computational tools and data libraries for shielding analysis (deterministic approach) and activation calculations to contribute to define and establish shielding design criteria and to assess the radiological protection related to beam-on and beam-off operational phases: production of the new groupwise radiation transport library, Vitenea-IEF, extended over 20 MeV, for deterministic Sn codes; production of the Anita-IEAF activation code package (code and libraries) able to handle the numerous reaction channels for neutron energies over 20 MeV; application of the computational tools for radiation transport, material activation calculations and dose rate evaluation in various IFMIF test facility rooms and cells for beam-on and beam-off operating phases to verify the compliance with the maximum allowable limit.

3 II a) Vitenea-IEF radiation transport library The Vitenea-IEF is a new intermediate energy coupled 256-neutron and 49-gamma-ray multigroup cross-section library, in Ampx format, suitable for Sn radiation transport codes. The library was obtained by processing the LANL evaluated files of ENDF/B-VI release 6 and FZK/INPE files via the Njoy-Smiler- Ampx-Scale code systems. The library contains the following materials/isotopes: H-1,H-2, C, O-16, Al-27,Si-28,Si-29, Si-30, P-31, Ca, Cr-50, Cr-52, Cr-53, Cr- 54, Fe-54, Fe-56, Fe-57, Ni-58, Ni-60, Ni-61, Ni-62, Ni-62, Ni- 64,Cu-63, Cu-65, Nb-93, W-182, W-183, W-184, W-186, Pb-206, Pb-207, Pb-208 from ENDF/B-VI Release 6 and K-39, Li-6, Li-7, V-51 from FZK/INPE Nuclear Data. The inclusion in the library of the ENDF/B-VI materials together with FZK ones makes it possible to handle the most part of materials, as lithium target, steel and concrete, planned to be used in IFMIF design.

4 III The following choices in the Njoy processing (99.50 version) were applied. For neutrons: 256-group energy structure till 150 MeV (standard 175-group Vitamin-J structure until MeV and 81 groups above; constant energy bins of 1 MeV and 2 MeV were used for the energy domains MeV and MeV, respectively); weighting function: thermal + 1/E + flat 4 temperatures: 300K, 600K, 900K, 1500K; 10 values of background cross sections: 1.0E+10, 1000, 300, 100, 30, 10, 3, 1, 0.1, 1.0E-06 For gamma s: 49-group energy structure till 100 MeV (standard 42-group Vitamin-J structure until 50 MeV and 7 groups above; constant energy bins of 5 MeV and 10 MeV were used for the energy domains MeV and MeV, respectively); weighting function: flat over the entire energy range.

5 IV Remarks The production of the library required the development of a new Smiler code, which converts the Njoy output from GENDF to AMPX format, in collaboration with the ORNL group of the Ampx-2000 system, in order to let it manage the not standard ENDF format lumped MT=5 cross section structure contained in the evaluated files for neutron energies over 20 MeV. In order to perform the dose rate calculations by Sn method, a new file, containing the groupwise neutron and gamma fluence to ambient dose equivalent conversion factors, was produced. It was obtained by integrating the neutron and gamma pointwise factors available in literature (ICRP-74 and Ferrari-Pelliccioni evaluation) on the same weighting functions and group structures previously described, converted in Ampx format and included in the Vitamin- IEF library.

6 V ENDF/B-VI release 6 & FZK/INPE Nuclear Data Photons Neutrons RECONR Reconstruct pointwise cross sections RECONR Reconstruct pointwise cross sections BROADR Doppler treatment GAMINR Multigroup photon interactiondataproduction UNRESR Processing of unresolved resonances GROUPR Multigroup neutron data production GENDF 49-group data GENDF 256-group data SMILER-IEF GENDF to AMPX format conversion (Cross sections over 20 MeV treatment - MT=5) RADE-PERFUME-AJAX Check and assembling of Master AMPX library VITENEA-IEF Coupled 256n-49g cross section library Procedure for generating Vitenea-IEF Library

7 VI b) ANITA-IEAF activation code package The new ANITA-IEAF activation code package traces back to the ANITA-2000 code [2]. It is able to manage the many reaction channels that open for neutron energies higher than 20 MeV and up to 150 MeV. It computes the radioactive inventories of materials exposed to neutron irradiation, continuous or stepwise. It provides activity, isotope nuclide density, decay heat, biological hazard, clearance index and decay gamma ray sources, in the 42 standard Vitamin-J energy structure, at shutdown and at different cooling times. The code package is provided with a complete data base that includes neutron activation data library, decay, hazard and clearance data library, and gamma library

8 VII. The new ANITA-IEAF activation code package is based on the Anita code (NEA-1638, RSICC CCC-606). 256-group neutron fluxes from radiation transport calculation ANITA-IEAF neutron activation library Decay and Hazard data library ANITA-IEAF Activation code Unconditional Clearance Level Data Library Decay gamma library Radioactive inventories Activity Contact Dose Clearance index Decay Heat Decay gamma source Biological Hazard

9 VIII New Anita-IEAF activation library It has been derived by the FZK IEAF-2001 activation library. IEAF-2001 contains neutron activation cross sections for 679 nuclides, in Gendf format, not suitable to be used in Anita code, in the 256 neutron energy groups structure. In this library the neutron activation cross sections for each nuclide are identified in the MF=3, MT=5 structure by the recoil nucleus produced. This is due to the fact that for neutron energies greater than 20 MeV many reaction channels open, to which don t correspond well defined MT numbers in the standard ENDF6 format notation. IEAF group data activation library (GENDF format) CONVLIB Production of ANITA-IEAF activation library in EAF groupwise format ANITA-IEAF neutron activation library 679 nuclides, reactions 256 energy groups A fixed reaction table, as required in Anita code, is so created, by associating to every recoil nucleus, characterized by a well known difference in charge Z and mass A, a, not standard, MT number.

10 IX Anita-IEAF Decay, Hazard and Clearance Data Library This library contains the information describing the decay properties of unstable nuclides useful for the calculations performed by ANITA- IEAF. This file has been completely updated. It contains the following data for 1840 nuclides: The decay data have been taken from the Fusion Evaluated Nuclear Decay Data Library FENDL/D-2.0. The Annual Limit of Intake (Bq) by ingestion or inhalation for the public or workers (ALI) quantities are obtained from the ICRP-72. The clearance level data. They are the unconditional clearance levels (Bq/g), based on IAEA-TECDOC-855. Anita-IEAF Gamma Library This data base contains gamma ray spectra emitted by the radioactive nuclei (1390 isotopes) in the Vitamin-J 42-γ energy group structure. The data of the library are based on the FENDL/D-2 evaluated decay data file (gamma radiation spectra).

11 X Application of ANITA-IEAF code package: activation calculation for IFMIF Test Cell steel liner The Sn radiation transport calculation sequence, via the Bonami S - Nitawl II - Xsdrnpm modules of the Scale 4.4a system with the new intermediate energy coupled 256n-49γ multigroup cross-section library Vitenea-IEF was used to define the neutron flux spectra for the activation calculations. A total neutron source (due to the interaction of the primary 40 MeV deuteron beam on the Li target) of 1.1 x s -1 was considered to normalise the calculations. A continuous 5 years irradiation has been applied.

12 XI The IFMIF Test Cell modelled in the calculations contains: a. Lithium target, b. Back plate, c. High Flux Test Module-HFTM, d. Test Cell vacuum room, that encloses the test module and the lithium target, e. Neutron and gamma concrete shielding system. A test cell liner, constructed from stainless steel, is located between the vacuum room and the shielding concrete wall. The thickness of the liner has been chosen to be 20 mm.

13 XII Specific activity and decay heat of the Test Cell steel liner Cooling Activity Decay heat time [Bq/g] [W/g] zero 9.01E E-5 1 s 9.00E E-5 30 m 8.54E E-5 1 h 8.42E E-5 5 h 7.87E E-5 1 d 7.29E E-5 7 d 6.78E E-5 30 d 5.71E E-5 90 d 4.33E E-5 1 y 2.78E E-6 3 y 1.49E E-6 10 y 2.61E E-7 30 y 1.99E E-8 50 y 1.56E E y 1.10E E y 2.02E E-11

14 XIII Isotope specific activity of the Test Cell steel liner at the end of beamon phase (IFMIF plant shut down) Isotope Activity % [Bq/cm 3 ] Fe E E+01 Cr E E+01 Co E E+01 Mn E E+00 Co E E+00 Co 58m1 3.81E E+00 Mn E E+00 V E E+00 Cu E E+00 V E E-01 Al E E-01 Ni E E-01 Fe E E-01 Co 60m1 2.40E E-01 Co E E-01 Mn 52m1 2.13E E-01 Co E E-01 Cu E E-01 Ni E E-01 Fe E E-01 Cr E E-01 Ni E E-01 Mn E E-01 V E E-01 Cu E E-01 Sum 7.10E+09 Rest 3.41E+07 Total 7.13E+09

15 XIV Isotope specific activity of the Test Cell steel liner during beam-off phase (1 year cooling time) Isotope Activity % [Bq/cm 3 ] Fe E E+01 Mn E E+00 Co E E+00 Co E E+00 V E E-01 Co E E-01 Ni E E-01 Sum 2.20E+09 Rest 1.24E+06 Total 2.20E+09

16 XV Impact of the neutrons with energy higher than 20 MeV The following index is considered where: R = A without /A with A with = steel liner activities when all the neutrons taken into account A without = steel liner activities when only the neutrons up to 20 MeV taken into account Ratio R vs. cooling time R Cooling time [y] The steel liner activity results to be underestimated by about 20% up to 3 years from the end of beam-on operations if the higher energy neutrons are not considered.

17 XVI CONCLUSIONS THE ANITA-IEAF IS A CODE PACKAGE ABLE TO PERFORM ACTIVATION CALCULATIONS FOR MATERIALS EXPOSED TO NEUTRONS WITH ENERGIES UP TO 150 MEV. A NEW ANITA-IEAF ACTIVATION LIBRARY HAS BEEN PRODUCED A NEW NEUTRON AND GAMMA TRANSPORT LIBRARY (VITENEA-IEF) HAS BEEN PRODUCED AN APPLICATION OF THE NEW TOOLS AND LIBRARIES TO THE IFMIF TEST CELL STEEL LINER HAS BEEN PERFORMED. IT POINTED OUT THAT THE STEEL LINER SPECIFIC ACTIVITY IS UNDER-ESTIMATED BY ABOUT 20% UP TO FEW YEARS FROM THE END OF BEAM-ON OPERATIONS WHEN THE CONTRIBUTE OF INTERMEDIATE ENERGY NEUTRONS IS NOT TAKEN INTO ACCOUNT.

18 XVII MAIN REFERENCES D.G. Cepraga, G. Cambi, M. Frisoni, G.C. Panini, Anita-2000 Code Package, Isotope Inventories from N irradiation, for Fusion Applications, NEA data Bank Program Libraries, NEA 1638, 22-November U.Fischer, D.Leichtle, A.Konobeyev, Yu. Korovin, U.v.Mollendorf, P.Pereslavtsev, I.Schmuck, Intermediate Energy Activation File 2001 (IEAF-2001), Forschungszentrum Karlsruhe, Technik und Umwelt, Interner Bericht, IRS-Nr.10/01- FUSION-Nr. 179, August 2001; U.Fischer, D.Leichtle, U.v.Mollendorff and I.Schmuck, ZZ-IEAF-2001, Intermediate Energy Activation File, NEA-1656/01. M. Frisoni, D.G. Cepraga, G. Cambi, New computational tools and data libraries for IFMIF shielding calculations, ENEA report FUS-TN-SA-SE-R-034, June 2002.

19 XVIII APPENDIX Difficilis facilis Iucundus acerbus es idem Nec tecum possum vivere Nec sine te

20 XIX To study the irradiation effects on fusion materials some facilities have been proposed to produce accelerator-based neutron sources at sufficient intensity to test samples of candidate materials to be used in future fusion plants. In these facilities there is a considerable amount of neutrons produced with energy above 20 MeV. One of the most important effects of the neutron irradiation is the induced activation of the materials. Nuclear activation data above 20 MeV are still scarce and the existing available activation codes cannot treat the numerous and exotic reaction channels that open at these energies. In the frame of the European Fusion Development Agreement (EFDA), the ENEA-Bologna team was committed to perform shielding calculations of various Test Facility rooms and cells for the International Fusion Materials Irradiation Facility (IFMIF). That assessment required the setting up, production and application of new computational tools and data libraries for shielding analysis and activation calculations to contribute in defining and establishing shielding design criteria related to beam-on and beam-off operational phases. In particular, the presence in IFMIF facility of a considerable amount of neutrons produced at energies above 20 MeV implied the production of the ANITA-IEAF activation code package

21 XX IFMIF TEST CELL GEOMETRICAL CONFIGURATION To perform the neutron transport calculations via the one dimensional discrete ordinates code XSDRNPM ( TRANSACT modular code system) the IFMIF Test Cell geometrical layout was modelled in order to maintain the real equivalent volumes of the various regions of the Test Cell (lithium target, back plate, High Flux Test Module, Test Cell vacuum room, shielding walls etc.). This choice assures that the total volumetric collision densities are preserved in the various zones. The IFMIF Test Cell modelled in the calculations contains:(1)- Lithium target (24 cm*6 cm *3 cm,volume=432 cm 3 ),(2)- Back plate (24.1 cm*6.1 cm *3.1 cm), (3)- High Flux Test Module- HFTM (20 cm*5 cm *5 cm, volume=500 cm 3 ), (4)- Test Cell vacuum room (300 cm* 250 cm * 300 cm) that encloses the test module and the lithium target, (5)- neutron and gamma concrete shielding system A test cell liner, constructed from stainless steel, is located between the vacuum room and the shielding concrete wall. The thickness of the liner has been chosen to be 20 mm. An helium gap as active cooling is provided along the internal surface of the liner, in order to maintain the liner itself at a temperature less than 50 0 C. A concrete shielding, consisting of concrete 80%, plus He 20% for cooling, thickness 100cm, and concrete 100% up to a total thickness of 310 cm, was placed after the test cell vacuum room.

22 XXI Material compositions The neutron and gamma transport calculations were performed by using the new intermediate energy coupled 256-neutron and 49 gamma-ray multigroup cross-section library Vitenea-IEF, in Ampx format. In order to use the materials/isotopes contained in the library the following material compositions were chosen: lithium target: lithium natural isotopic abundance. back plate: stainless steel SS-316 LN-IG High Flux Test Module : Eurofer. liner and thermal shield: stainless steel SS-316 LN-IG biological shield: concrete.

23 XXII SS 316 LN -IG Density = 7.92 g/cm3 C , Al 0.05, Si 0.5, P 0.025, V 0.004, Cr 17.5, Fe , Ni 12.25, Cu 0.3, Nb 0.01, W SS 316 LN IG (for activation calculation) Density = 7.92 g/cm3 C , Al 0.05, Si 0.5, P 0.025, Ti 0.14, V 0.004, Cr 17.5, Mn 1.8, Fe , Co 0.05, Ni 12.25, Cu 0.3, Nb 0.01,Mo 2.5, W Eurofer Density = 6.24g/cm3 C 0.105, O 0.01, Al 0.01, Si 0.05, P 0.005, V 0.2, Cr 9.526, Fe , Ni 0.005, Cu 0.005, Nb W 1.1 Lithium Density = g/cm3 Li Concrete Density = 2.32 g/cm3 H 0.555, O , Na 1.708, Al 4.691, Si , K 1.922, Ca 8.667, Fe 1.238

24 XXIII Neutron Source In order to perform the coupled n-γ transport calculation an angleand group-dependent boundary neutron source was used to take into account that the real neutron source is not isotropic, but peaked in the forward direction In this case, one specifies not a source but a flux condition on the boundary The energetic neutron source distribution, due to the interaction of the primary 40 MeV deuteron beam on Li-target, calculated by Oyama based on the Serber model has been produced in the same 256 group structure of the Vitenea-IEF library. A total neutron source of 1.1E+17 s -1 was used to normalise the calculations.

25 XXIV IFMIF energy source distribution for 40MeV deuteron beam probability P(E) energy (MeV) Figure 1 Neutron energy source distribution for 40 MeV deuteron beam

26 XXV Neutron zone-averaged total flux [n/cm2 s] 1.E+16 1.E+14 1.E+12 1.E+10 1.E+08 1.E+06 1.E+04 Total neutron flux vs. distance from target Standard configuration Frontal wall case 1.E+02 1.E Distance from target [cm] TOTAL ZONE NEUTRON FLUX (n/cm 2 s) Lithium Target Back Plate HFTM Liner 1.27E E E+12

27 XXVI