Diapositiva 1

n_TOF(neutron Time-of-flight @ CERN)

Nicola ColonnaIstituto Nazionale Fisica Nucleare, Sez. di Barinicola.colonna@ba.infn.it

Nuclear Data for Science, Technology and Society(Hans Blix, ND 2008)Neutron cross-section measurementswith high accuracyat high resolutionin a wide energy rangefor Nuclear Astrophysicsand for Nuclear Technology1Nicola ColonnaMotivations (15)The n_TOF facility and experimental setups (10)Results (15)Status and perspectives (5)Outline2Isolde CERN, July 14th, 2010 N. Colonna INFN Bari

2Nicola ColonnaAstrophysics

Nuclear Astrophysics(stellar nucleosynthesis)Nuclear energy(fission products &Structural material)Advanced nuclear reactors(actinides)n_TOF in the Chart of Nuclides3Isolde CERN, July 14th, 2010 N. Colonna INFN Bari

3Neutron studies for Nuclear Astrophysicsrs

FusionBBNeutron captureFe Mass number Abundance sr4

s-process (slow process):Capture times long relative to decay timeInvolves mostly stable isotopesNn = 108 n/cm3 , kT = 0.3 300 keVr-process (rapid process):Capture times short relative to decay timesProduces unstable isotopes (neutron-rich)Nn = 1020-30 n/cm3

s-process (Red Giants) r-process (Supernovae)Radioactive beam facilitiesThe stellar nucleosynthesis 5Neutron beamsIsolde CERN, July 14th, 2010 N. Colonna INFN Bari5

The s-process nucleosynthesis56Fe 91.72

57Fe 2.2

58Fe 0.28

60Ni 26.223

59Co 10059Fe 44.503 d

60Fe 1.5 106 a

60Co 5.272 a61Co 1.65 h61Ni 1.140

62Ni 3.634

63Ni 100 a

64Ni 0.926

58Co 70.86 d62Cu 9.74 m63Cu 69.17

64Cu 12.7 h

61Fe 6 m

Along the b-stability valleys-process nucleosynthesis proceeds through neutron captures and successive b-decay.The abundance of elements in the Universe depends on thermodinamic conditions (temperture and neutron density) and on the neutron capture cross-sections.s-processcapture rate: ln = NnkTs(n,g) is a key quantity6Neutron cross-sections are needed to:refine models of stellar nucleosynthesis in the Universe;obtain information on the stellar environment and evolutionIsolde CERN, July 14th, 2010 N. Colonna INFN Bari6Nicola Colonna

The neutron capture cross-section

Bao et al. ADNDT 76 (2000)7For three classes of nuclei data are lacking or need substantial improvements:1. Nuclei with low cross-section, in particular neutron magic nuclei (s-process bottleneck)N=5086Kr, 87Rb, 88Sr, 90ZrN=82138Ba, 139La, 140Ce2.Isotopes unavailable in large amount, such as rare or expensive isotopes: 186,187Os, 180W, etc3.Radioactive branching isotopes (stellar thermometers):79Se, 85Kr, 151Sm, 163Ho, 204Tl, 205PbHuge amount of data collected on many isotopes, mostly stable. Main features of s-process now well understood.However, cross-section uncertainties in some cases remain high, in particular if compared with progresses in:observations of abundances (i.e. in meteorite grains)models of stellar evolutionIsolde CERN, July 14th, 2010 N. Colonna INFN Bari7Nicola ColonnaNeutron studies for energy applications

8The energy problem9Recently, renewed interest in nuclear energy due to:continously increasing energy demand;growing concern over production of greenhouse gases and related climate changes

More than 80 % of the energy consumed in the world comes from fossil fuels

Isolde CERN, July 14th, 2010 N. Colonna INFN Bari

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CO2 and climate changes10,Report of the Intergovernmental Panel on Climate Changes (IPCC), 2007www.ipcc-wg1.unibe.ch/publications/wg1-ar4/wg1-ar4.html

Isolde CERN, July 14th, 2010 N. Colonna INFN Bari

Nicola Colonna10

The emission of CO211

To satisfy the world energy demand (in particular from developing countries), minimizing the impact on the climate, it is necessary a mix of energy sources which includes nuclear energy (Intergov. Panel on Climatic Change, IPCC-ONU, Valencia, 17 Nov. 2007).Isolde CERN, July 14th, 2010 N. Colonna INFN Bari11Nicola Colonna

Main problems of current nuclear reactors1297%238UFuel (LWR)94%238USpent fuel1% 235U1% Pu and Minor Actinides4% Fission products3% 235U96%potentialfuelCurrent reactors use only few percent of U resources.Availability of U resources may become a problem in the medium term (100 y).Closed cycle (recycling) would make U resources sufficient for thousands of years !!Existing reactors have low burn-up efficiency and produce large amount of radioactive waste.Isolde CERN, July 14th, 2010 N. Colonna INFN Bari12Nicola ColonnaFigura Nucleosintesi (frecce che si muovono)

Foto FIC

239Pu: 125 Kg/yr237Np: 16 Kg/yr

241Am:11.6 Kg/yr 243Am: 4.8 Kg/yr244, 245Cm 1.5 Kg/yrLLFPLLFP 76.2 Kg/yr13The nuclear waste problemQuantities refer to yearly production in 1 GWe LW reactorIsolde CERN, July 14th, 2010 N. Colonna INFN Bari

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,The actinides problem14Main problem in the nuclear waste are the transuranic actinides: Pu and MA (Np, Am, Cm,...)1.5% in mass but give the biggest contribution to radiotoxicity and heat after 100 yproblem persists for more than 105 ysome isotopes are fissionable (proliferation and criticality concern).At present, only solution to the high radiotoxicity nuclear waste is geological repositoriesIsolde CERN, July 14th, 2010 N. Colonna INFN BariNicola Colonna14Geological repositories

15With current reactors, it would be necessary to find a new geological repository like Yucca Mountain every 20 years.Isolde CERN, July 14th, 2010 N. Colonna INFN Bari

15Nicola Colonna

Figura Nucleosintesi (frecce che si muovono)

Foto FIC

LLFPLLFPThe Th/U fuel cycle16232Th(n,g)233Th 233Pa 233Ub-, t1/2=22 mb-, t1/2=27 dIsolde CERN, July 14th, 2010 N. Colonna INFN Bari16Nicola Colonna

RecyclingNew generation reactorsThe revolutionary idea of Generation IV reactors is the recycling of the spent fuel (including minor actinides).17Other advantages of Generation IV (fast breeder) reactors:improved safety, proliferation-resistence, lower costs and construction timehydrogen production (to substitute fossile fuels in transport)Other options now being considered:Accelerator Driven Systems (nuclear waste incineration)Use of the Th/U fuel cycle (currently being devoloped in India for energy production)Isolde CERN, July 14th, 2010 N. Colonna INFN Bari

Once throughThe development of Gen IV (fast breader) reactors requires accurate neutron data to minimize design uncertainty and optimize safety parameters.17Nicola Colonna

Data needs for nuclear energy18Topic: Fission-2009-2.3.2: Improved nuclear data for advanced reactor systems. The combination of advanced simulation systems and more precise nuclear data will allow optimising the use of and need for experimental and demonstration facilities in the design and deployment of new reactors. A concerted effort including new nuclear data measurements, dedicated benchmarks (i.e. integral experiments) and improved evaluation and modelling is needed in order to achieve the required accuracies. The project shall aim to obtain high precision nuclear data for the major actinides present in advanced reactor fuels, to reduce uncertainties in new isotopes in closed cycles with waste minimisation and to better assess the uncertainties and correlations in their evaluation.FP VII EURATOMThe overall list of requirements is rather long:capture cross sections of 235,238U, 237Np, 238-242Pu, 241,242m,243Am, 244Cmfission cross sections of 234U, 237Np, 238,240-242Pu, 241,242m,243Am, 242-246CmData on a large number of isotopes are needed for design of advanced systems and for improving safety of current reactors.Nuclear fuel (U/Pu and Th/U cycles)Th, U, Pu, Np, Am, Cm (n,f), (n,) Long-lived Fission Products99Tc, 103Rh, 135Xe, 135Cs, 149Sm (n,)Structural and cooling materialFe, Cr, Ni, Zr, Pb, Na, ...allNEA/WPEC-26 (ISBN 978-92-64-99053-1)Isolde CERN, July 14th, 2010 N. Colonna INFN Bari18Energy RangeCurrent Accuracy (%)Target Accuracy (%)U238inel0.5 6.1 MeV10 202 3capt2.04 24.8 keV3 91.5 2Pu241fiss454. eV 1.35 MeV8 202 5Pu239capt2.04 498 keV7 154 7Pu240fiss0.498 1.35 MeV61 3Pu242fiss0.498 2.23 MeV19 213 5Pu238fiss0.183 1.35 MeV173 5Am242mfiss67.4 keV 1.35 MeV173 4Am241fiss2.23 6.07 MeV92Am243fiss0.498 6.07 MeV123Cm244fiss0.498 1.35 MeV505Cm245Fiss67.4 183 keV477Fe56Inel0.498 2.23 MeV16 253 6Na23inel0.498 1.35 MeV284 10Pb206inel1.35 2.23 MeV143Pb207Inel0.498 1.35 MeV113Si28inel1.35 6.07 MeV14 503 6capt6.07 19.6 MeV536Target Accuracies for Gen IV Fast ReactorsNecessary to reduce uncertaintied to ~3-7 % for most Pu isotopes and Minor Actinides, in the energy range from a few keV to several MeV.Source: Aliberti, Palmiotti, Salvatores, NEMEA-4 workshop, Prague 200719Nicola Colonna

The n_TOF facility at CERN20n_TOF is a spallation neutron source based on 20 GeV/c protons from the CERN PS on a Pb target (~360 neutrons per proton).Experimental area at 200 m.Isolde CERN, July 14th, 2010 N. Colonna INFN Bari

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21Nicola ColonnaTechnical details 22

pn

80x80x80 cm3 Pb target surrounded by 5 cm water for moderation (isolethargic flux) and cooling200 mt time-of-flight tunnelseveral iron and concrete walls for shielding (from n, g, m, etc)sweeping magnet for charged particle deflection2 collimatorsIsolde CERN, July 14th, 2010 N. Colonna INFN Bari

22Nicola ColonnaThe n_TOF facility23

n_TOF is at present one of the most important facilities for neutron time-of-flight in the world (other TOF facilities are GELINA and LANSCE).

Other features of the neutron beam:high resolution in energy (DE/E = 10-4) ..study resonanceslarge energy range (25 meV