Nuclear Data for Reactor Physics: Cross Sections and Level Densities in in the Actinide Region. J.N. Wilson Institut de Physique Nucléaire, Orsay

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1 Nuclear Data for Reactor Physics: Cross Sections and Level Densities in in the Actinide Region J.N. Wilson Institut de Physique Nucléaire, Orsay

2 Talk Plan Talk Plan The importance of innovative nuclear reactors The need of cross section data for reactor simulations The difficulty of certain measurements and why there is a need to rely on theory/extrapolations How level density measurements can improve cross section calculations Norway and the Thorium fuel cycle

3 Current Nuclear Reactors Current Nuclear Reactors Increase in capacity likely because: World population growth (energy demand) Concerns about CO 2 emissions Economic growth (developing nations) Depletion of reserves of oil, gas (coal) No current economically viable alternative

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5 Cross section data Cross section data Reactor simulations require X-section data over large range of nuclei and a huge range in energy Measurements are often partial and/or have large uncertainties Creation of evaluated data libraries, e.g. ENDF, JENDL, JEFF

6 Nucleosynthesis in a Reactor Core Nucleosynthesis in a Reactor Core Reactor flux φ ~ n/cm 2 /s Supernova φ ~ n/cm 2 /s Reaction data available T 1/2 > 1 hour T 1/2 < 1 hour

7 Nucleosynthesis in reactors Nucleosynthesis in reactors α emitter β emitter α 242 Cm 243 Cm 244 Cm (m) 241 Am 242 Am 243 Am 245 Cm 244 Am 246 Cm 247 Cm 238 Pu 239 Pu 240 Pu 241 Pu 242 Pu 243 Pu α 237 Np 238 Np 239 Np 232 U 233 U 234 U 235 U 236 U 237 U 238 U 239 U α 231 Pa 233 Pa β Th α 230 Th 231 Th 232 Th 233 Th α (n, γ) (n, 2n) 7

8 Reactor Criticality Reactor Criticality Multiplication factor, k eff k = Σ ν i N i σ f φ Σ N i σ c φ + Σ N i (σ f + σ c ) φ We need the sensitivity of multiplication factor, k, to nuclear data Improved accuracy of nuclear data can help reduce safety margins of innovative generation IV designs Cost of data measurements << Cost of generation IV reactor prototype construction

9 Reaction rates in the Core: Long Time Scales Reaction rates in the Core: Long Time Scales What is the composition of the spent nuclear fuel? How much fissile material can be recovered in fuel reprocessing? How will this limited amount of fuel constrain scenarios of the growth of nuclear power? How big will the geological repository need to be to dissipate the decay heat of the spent fuel?

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11 Reaction rates in the Core: Short time scales Reaction rates in the Core: Short time scales PhD Thesis: N. Capellan

12 Dependence of Cross sections on Temperature Dependence of Cross sections on Temperature Doppler Broadening of the resonances can be calculated Neutronics Thermalhydraulics

13 Nuclei where measurements are difficult Nuclei where measurements are difficult Target activity > 10 9 Bq/mg 163 d 242 Cm 243 Cm 244 Cm 245 Cm 246 Cm 247 Cm 88 y α (m) 241 Am 242 Am 243 Am 244 Am 69 y α 238 Pu 237 Np 239 Pu 238 Np 240 Pu 241 Pu 239 Np 242 Pu 243 Pu 26 h 232 U 233 U 234 U 235 U 236 U 237 U 238 U 239 U α 229 Th 231 Pa 230 Th 233 Pa 231 Th 232 Th 233 Th 6.8 d 5.0 h (n, γ) β - α α 26 h 22 m (n, 2n) 13

14 Target activities Target activities Nuclide Target Activity (bq/mg) 232 Th Am 1.01e Am 1.83e Pa 1.11e+12 (ntof facility limited to 800 bq activity maximum for ~100 mg of target material!)

15 Nuclei at equilibrium Nuclei at equilibrium T 1/2 << Fuel Irradiation Time ~ 3-5 years Uranium/ Plutonium Cycle Thorium/ Uranium Cycle + n β- β- 238 U 239 U* 239 Np 239 Pu 23m 2.4d Fertile Fissile + n β- β Th Th* Pa U 22m 27d + n 234 U At equilibrium: N Th σ Th φ = λn Pa Fertile Rate of production of 234 U: dn U4 /dt = N Pa σ Pa φ dn U4 /dt = N Th σ Pa σ Th φ 2 λ

16 It is tempting to conclude: The importance of a given nucleus ~ Mass present in the core Which for nuclei at equilibrium: ~ 1/λ ~ T 1/2 PWR Reactor core inventory at BOC and EOC t=0 t=3 y 238 U U U Np,Am, Cm Pu FP 0 946

17 Important short-lived nuclei Important short-lived nuclei 69 y (n, 2n) 232 U 233 U (n, γ) 135 Xe 136 Xe 1.9 y α 228 Th (n, γ) α 3.6 d 224 Ra α 56 s α 220 Rn 0.15 s α 216 Po 11 h 212 Pb 7.0 m β 212 Bi 45 s β α 212 Po 208 Pb 208 Pb γ MeV 0+

18 Limitations of Nuclear Data Limitations of Nuclear Data For certain nuclei, x-section data are: Sparse (limited energy range) Large uncertainties (> 20%) Evaluated data bases rely heavily on theory and extrapolations 233 Pa For some nuclei there is no experimental data available: Evaluated data bases rely entirely on theory 233 Th

19 233 Pa Capture Experiment Results 233 Pa Capture Experiment Results S. Boyer et al. Nucl.Phys. A775, 175 (2006)

20 Hauser-Fessbach Formalism Hauser-Fessbach Formalism a b Differential cross section depends on transmission coefficients,γ and level densities of the residual nuclei, ρ

21 Level Densities Theory and Experiment Level Densities Theory and Experiment - Level density changes due to collectivity, deformation etc. - Large effects can occur over a small number of nucleons

22 Level Density Measurements Level Density Measurements Oslo method Extrapolation Spectroscopy of low lying states Resonance spacings at the neutron binding energy

23 Norway, Nuclear Power and Thorium Norway, Nuclear Power and Thorium Baseload from hydro power (110 TWh in 2004 out of 120 TWh total) Occasional electricity imports from Europe (coal) European Energy Exchange Spot Electricity prices

24 I: Introduction; The EPR 3rd generation PWR 1600 MWe, 241 assemblies Cycle length months Burnable Gd 2 O 3 poison for longer burn-up MOX compatible Flexible fuel loading Availability of 92 % of service life Technical service life of 60 years Olkiluoto, Finland (2010?) 24

25 Dependent Thorium Cycle Possibilities Dependent Thorium Cycle Possibilities Norway has the world s 3rd largest reserves of Thorium If Norway built a commerical power reactor could Thorium be used? What is the simplest way to incoporate Thorium into the fuel cycle? - Remove 238 U waste precursor and replace with Th - Multi-recycle the Uranium vector (Masters Thesis: Sunniva Rose)

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29 Inventories and Economics Inventories and Economics Tons Unat SWU Over a 60 year life-time the reactor will need: UOX: ~ tons of Uranium, ~17 M SWU Th/UOX 90% enriched: ~ tons of Uranium, ~13.8 M SWU Th/UOX 20% enriched: ~ tons of Uranium, ~13.0 M SWU 29

30 Reduction in MA waste Less decay heat Use of local natural resource (Norway) High U-233 fissile content in the spent fuel Multircycling desirable Spent fuel U2/3/4/5/6/8 is proliferation resistant Higher (initial) fuel cost Spent Uranium must be handled remotedly Possible proliferation concerns (HEU) Pa-233 reactivity effects on safety Breeding not possible 30

31 The Thorium fuel-cycle Extra fissile (U5/Pu) needed Dependent of the U-cycle Mining of Uranium still necessary U5+Th2 Pa3 U3 U-233 fissions and contributes to total energy production CR always less than 1 Regenerates its own fissile (U-233) from the Thorium CR bigger than 1 No extra fissile needed No mining of Uranium necessary 31

32 Neutron capture measurements Neutron capture measurements Cascade of M gammas The neutron capture process If the detector had THIS property Efficiency of detecting a Cascade of M gammas (if efficiency is low) then efficiency of detecting the cascade is proportional to cascade total cascade energy, which is constant

33 Actual detector response It is possible to find weighting functions, W(E i ) which give the detector the desired response