Some fission yields for 235U (n,f), 239Pu (n,f), 238U (n,f) reactions in ΣΣ neutron spectrum Dr. Cristina Garlea National Institute for R&D of Physics and Nuclear Engineering “Horia Hulubei”, Magurele, Romania Dr. Ion Garlea SENDRA – Nuclear Technology Ltd., Bucharest, Romania

ΣΣ–ITN facility in thermal column of VVR-S Magurele reactor 1 - ΣΣ–ITN system; 2 - CB 4 screen; 3 - Vertical plug; 4 - Horizontal plug; 5 - Cavity in graphite

Details of ΣΣ–ITN system 1 - Uranium converter 2 - CB 4 screen 3 - Channels for instrumentation

ΣΣ–ITN system

Maneuvering cell

Comparison between neutron spectrum calculated by ANISN code and that determined by SAND II Characteristics:- conversion factor: average energy of spectrum:0.791 MeV - flux (2 MW) E ≥ 10 keV:3.385 x n/m 2 s E > 1 MeV:8.1 x n/m 2 s

Comparison between measured and calculated ΣΣ spectrum Characterization in the intermediate energy range ± 15%E < 0.1 keVmultiple foil methods ± 5%0.1 keV ≤ E ≤ 2 MeVspectrometry and calculation ± 5%E > 2 MeVmultiple foil methods

Method Neutron flux measuring in the place of detector exposure by absolutely calibrated fission chambers (FC – 235 U) Exposure of fissionable detectors - irradiation in the central position of ΣΣ-ITN system - fluence > n/cm 2 (2 MW reactor power) - packaging in 0.5mm Al Flux monitoring by two monitors fission chambers - in the second vertical channel - in graphite block Fission yields measuring by high resolution  spectrometry - PTB Eu calibration point standard source - 5 cm source – crystal distance - SAMPO software package

Characteristics of fissionable detectors Detector identification Material Detector mass (g) Isotope mass (g) Main isotope (%) Impurities D U ppm 235 U ~ U400 ppm 235 U D209Al 10% 239 Pu Pu0.05% 240 Pu D204Al 20% 235 U U2.00% 238 U D205Al 10% 235 U U2.00% 238 U D208Al 5% 239 Pu Pu0.05% 241 Pu Note: Mass of alloys are certified by Reactor Experiments USA with uncertainty of ± 1%.

Results Fission products Measured yields RecommendedENDFB/IV Ratio ΣΣ-ITN / ENDFB/IV ΣΣ-ITNCFRMF 95 Zr6.71 ± 3.2%6.43 ± 2.1%6.39 ± 1.0% Ru3.17 ± 3.2%3.25 ± 4.2%3.25 ± 1.5% Ba6.13 ± 3.1%6.04 ± 1.8%6.07 ± 1.3% I3.46 ± 5.6%3.32 ± 4.5%3.16 ± 1.29% Fission yields in ΣΣ spectrum for 235 U(n,f)

Fission products Measured yields RecommendedENDFB/IV Ratio ΣΣ-ITN / ENDFB/IV ΣΣ-ITNCFRMF 95 Zr5.11 ± 4.2%4.64 ± 2.5%4.74 ± 1.5% Ru7.18 ± 4.0%6.66 ± 4.1%6.94 ± 2.0% Ba5.73 ± 3.8%5.14 ± 2.3%5.37 ± 1.0% I–4.10 ± 4.6%4.02 ± 2.0%4.10– Fission yields in ΣΣ spectrum for 239 Pu(n,f) Fission products Measured yields RecommendedENDFB/IV Ratio ΣΣ-ITN / ENDFB/IV ΣΣ-ITNCFRMF 95 Zr5.29 ± 4.1%5.13 ± 2.0%5.19 ± 2.5% Ru5.79 ± 3.7%6.36 ± 2.4%6.32 ± 4.3% Ba ± 1.5%5.98 ± 3.8% I3.41 ± 5.4%3.20 ± 1.6%3.24 ± 4.7% Fission yields in ΣΣ spectrum for 238 U(n,f)

Uncertainties In neutron flux - fissionable deposit mass1.6% - statistics1.0% - monitoring0.8% In activation rate - fitting and background0.62 – 4.7% subtraction - absolute efficiency1.8 – 2% calibration of Ge(Li) crystal - statistics1 – 3.8%