Neutron-induced fission cross section of 240;242Pu Paula Salvador-Castineira~ Supervisors: Dr. Franz-Josef Hambsch Dr. Carme Pretel Doctoral dissertation PhD in Nuclear Engineering and Ionizing Radiation Barcelona, September 2014 Curs acadèmic: Acta de qualificació de tesi doctoral Nom i cognoms Programa de doctorat Unitat estructural responsable del programa Resolució del Tribunal Reunit el Tribunal designat a l'efecte, el doctorand / la doctoranda exposa el tema de la seva tesi doctoral titulada __________________________________________________________________________________________ _________________________________________________________________________________________. Acabada la lectura i després de donar resposta a les qüestions formulades pels membres titulars del tribunal, aquest atorga la qualificació: NO APTE APROVAT NOTABLE EXCEL·LENT (Nom, cognoms i signatura) (Nom, cognoms i signatura) President/a Secretari/ària (Nom, cognoms i signatura) (Nom, cognoms i signatura) (Nom, cognoms i signatura) Vocal Vocal Vocal ______________________, _______ d'/de __________________ de _______________ El resultat de l’escrutini dels vots emesos pels membres titulars del tribunal, efectuat per l’Escola de Doctorat, a instància de la Comissió de Doctorat de la UPC, atorga la MENCIÓ CUM LAUDE: SÍ NO (Nom, cognoms i signatura) (Nom, cognoms i signatura) President de la Comissió Permanent de l’Escola de Doctorat Secretària de la Comissió Permanent de l’Escola de Doctorat Barcelona, _______ d'/de ____________________ de _________ Universitat Politecnica` de Catalunya Institut de Tecniques` Energetiques` Neutron-induced fission cross section of 240;242Pu Author: Paula Salvador-Castineira~ Supervisors: Dr. Franz-Josef Hambsch Dr. Carme Pretel Barcelona, Setembre 2014 Programa de Doctorat: Enginyeria Nuclear i de les Radiacions Ionitzants Tesi presentada per obtenir el t´ıtol de Doctora per la Universitat Politecnica` de Catalunya Abstract Nuclear data needs for the newest generation (Gen-IV) of nuclear power plants focus, mainly, on several neutron-induced fission cross section in the fast neutron energy re- gion. Following the directions of the Nuclear Energy Agency (NEA) [1] and within the Accurate Nuclear Data for nuclear Energy Sustainability (ANDES) collabora- tion [2], the neutron-induced fission cross section of 240;242Pu needs to be determined with improved accuracy of 1-3% and of 5%, respectively. At the Institute for Refer- ence Materials and Measurements (JRC-IRMM) a measurement of this cross section relative to three different fission cross section standards (235U, 238U and 237Np) was performed using a Twin Frisch-Grid Ionization Chamber. The neutrons were produced at the 7 MV Van de Graaff accelerator, covering an energy range from 0.3 MeV to 3 MeV. In addition to an extended study on the overall corrections needed to achieve accurate cross section results, the spontaneous fission half-life for 240;242Pu has been determined, too. Keywords: neutron-induced fission cross section, 240Pu, 242Pu, 237Np, 238U, spon- taneous fission half-life, Ionization chambers, accelerator. iii Als meus Pares i germans Publication List I. Salvador-Casti~neira,P., Bry´s,T., Eykens, R., Moens, M., Hambsch, F.-J., Ober- stedt, S., Pretel, C., Sibbens, G., Vanleeuw, D., Vidali, M., Highly accurate measurements of the spontaneous fission half-life of 240;242Pu, Physical Review C 88.6 (2013): 064611. II. Vanleeuw, D., Sapundjiev, D., Sibbens, G., Oberstedt, S., Salvador-Casti~neira, P., Physical vapor deposition of metallic lithium, Journal of Radioanalyt- ical and Nuclear Chemistry, DOI: 10.1007/s10967-013-2669-6 (2013). III. Salvador-Casti~neira,P., Bry´s, T., Hambsch, F.-J., Oberstedt, S., Pretel, C., Vidali, M., Neutron-induced fission cross section of 240;242Pu up to En=3 MeV, Nuclear Data Sheets 119, 55-57 (2014). IV. Salvador-Casti~neira,P., Bevilacqua, R., Bry´s,T., Hambsch, F.-J., Oberstedt, S., Pretel, C., Vidali, M., Measurement of the neutron-induced fission cross section of 240;242Pu, Physics Procedia 47, 150-155 (2013). vii Contents Abstract iii Publication List vii Table of Contents ix List of Acronyms xiii List of Figures xv List of Tables xix Introduction 1 1. The future of nuclear energy 3 1.1 Nuclear energy and power plants . 3 1.2 Evolution of nuclear power plants . 5 1.2.1 Fast neutron reactors . 6 1.2.2 Nuclear data needs for the Gen-IV . 8 1.2.3 The importance of 240;242Pu and other actinides . 9 1.3 The ANDES collaboration . 10 1.3.1 Related projects within the ANDES collaboration . 11 2. State-of-the-Art 13 2.1 Experiments ANDES collaboration . 13 2.1.1 240;242Pu(n,f) measurement at the n TOF facility (INFN, ITN) 13 2.1.2 240;242Pu(n,f) measurement at the AIFIRA facility (CNRS) . 15 2.2 The MetroFission experiment . 16 2.3 Previous experiments . 16 2.3.1 240Pu(n,f) . 16 2.3.2 242Pu(n,f) . 17 2.3.3 Common experiments, 240;242Pu(n,f) . 19 2.3.4 Data comparison and discussion . 19 ix x CONTENTS 3. Experimental laboratories 25 3.1 The Van de Graaff accelerator . 25 3.1.1 Neutron production . 26 3.2 Ionization Chamber . 29 3.2.1 Twin Frisch-Grid Ionization Chamber . 29 3.2.2 Gases used, potential applied and pressure . 32 3.3 Experimental setup . 33 3.4 Sample description . 36 3.4.1 Measurement of the 238U sample mass . 38 3.4.2 Measurement of the 235U (#1) sample mass . 39 3.4.3 Vacuum deposition vs electrodeposition . 40 4. Data aquisition and DSP 43 4.1 Data acquisition . 43 4.1.1 Treatment of the signals . 44 4.2 Corrections to the Pulse Height . 47 4.2.1 Grid inefficiency correction . 47 4.2.2 Alpha pile-up rejection . 48 4.2.3 Extrapolation to zero pulse height . 48 5. Improvements and SF half-lives 49 5.1 Measuring high α-active targets . 49 5.2 Efficiency determination . 51 5.2.1 Angular dependence . 52 5.2.2 Improving the signal rise time: P10 vs CH4 . 54 5.2.3 Theoretical calculation of FF losses in the sample . 59 5.2.4 GEANT4 simulations . 59 5.2.5 Results . 59 5.3 Spontaneous fission half-life . 60 5.3.1 Results and comparison with available data . 60 6. Cross section measurements 65 6.1 Cross section formulation . 65 6.2 Corrections to the data . 67 6.2.1 Lost counts due to electronic threshold . 67 6.2.2 Target thickness and anisotropy of FF angular distribution . 68 6.2.3 Influence of the neutron spectrum and the sample spot size and inhomogeneity . 69 6.2.4 Correction due to the excited state of 7Li(p,n)7Be . 71 CONTENTS xi 6.2.5 Correction of the neutron spectrum by thermalized fast neutrons due to the setup . 71 6.3 Evaluations . 75 6.4 Uncertainties . 76 7. Fission cross section results 79 7.1 Results on the fission cross section . 79 7.1.1 Measurements of 240;242Pu(n,f) relative to 237Np(n,f) . 79 7.1.2 Measurements of 240;242Pu(n,f) relative to 238U(n,f) . 80 7.1.3 Measurements of 237Np(n,f) relative to 238U(n,f) . 83 7.1.4 Measurements of 238U(n,f) relative to 235U(n,f) . 84 7.1.5 Measurements of 237Np(n,f) relative to 235U(n,f) . 85 7.1.6 Measurements of 240;242Pu(n,f) relative to 235U(n,f) . 86 7.2 Discussions . 88 7.2.1 238U(n,f) cross section . 88 7.2.2 237Np(n,f) cross section . 88 7.2.3 240Pu(n,f) cross section . 90 7.2.4 242Pu(n,f) cross section . 90 Conclusions 93 Appendix A. Numerical values MCNP 101 Appendix B. Numerical cross section results 105 B.1 Numerical results of the 238U(n,f) . 105 B.2 Numerical results of the 237Np(n,f) . 106 B.3 Numerical results of the 240Pu(n,f) . 107 B.4 Numerical results of the 242Pu(n,f) . 110 Acknowledgements 113 References 115 Paper I 123 Paper II 133 Paper III 143 Paper IV 147 List of Acronyms ABTR Advanced Breeder Test Reactor ANDES Accurate Nuclear Data for nuclear Energy Sustainability CFD Constant Fraction Discriminator DAQ data acquisition system DSP digital signal processing EXFOR Experimental Nuclear Reaction Data Library FF fission fragment FNR Fast Neutron Reactors GIF Generation IV International Forum HPRL High Priority Request List HV high voltage IC ionization chamber IEA International Energy Agency JRC-IRMM Joint Research Center - Institute for Reference Materials and Measurements NEA Nuclear Energy Agency PCI Peripheral Component Interconnect PH pulse height SF spontaneous fission TFA Timing Filter Amplifier TFGIC Twin Frisch-Grid Ionization Chamber xiii xiv LIST OF ACRONYMS VdG Van de Graaff WFD Waveform Digitizers WP Work Package List of Figures 1.1 World electricity production in 1973 and 2011. 4 1.2 Growth in nuclear power capacity and its share of global electricity production. 4 1.3 Example of processes that can lead to the production of 240;242Pu and other minor actinides in the fuel of a nuclear power plant core. 10 2.1 Schematic view of part of the Micromegas assembly. 14 2.2 The Micromegas assembly. 14 2.3 Preliminary results of the n TOF experiment for 242Pu. 14 2.4 Experimental setup of the measurement performed at Bruy`eres-le-Ch^atel relative to the 1H(n,p) reaction. 15 2.5 Summary of the most relevant experiments performed on the neutron- induced fission cross section of 240Pu compared with current evaluations. 22 2.6 Summary of the most relevant experiments performed on the neutron- induced fission cross section of 242Pu compared with current evaluations. 23 3.1 Scheme of the Van de Graaff facility at JRC-IRMM. 26 3.2 Neutron flux spectrum of the 7Li(p,n)7Be reaction and the T(p,n)3He reaction.