Some fission yields forSome fission yields for235U (n,f), 239Pu (n,f), 238U (n,f) 235U (n,f), 239Pu (n,f), 238U (n,f) reactions in ΣΣ neutron spectrumreactions in ΣΣ neutron spectrum

Dr. Cristina GarleaNational 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 - CB4 screen; 3 - Vertical plug; 4 - Horizontal plug; 5 - Cavity in graphite

Details of ΣΣ–ITN system

1 - Uranium converter

2 - CB4 screen

3 - Channels for instrumentation

ΣΣ–ITN system

Maneuvering cell

Comparison between neutron spectrum calculatedby ANISN code and that determined by SAND II

Characteristics: - conversion factor: 0.731- average energy of spectrum: 0.791 MeV- flux (2 MW) E ≥ 10 keV: 3.385 x 1013 n/m2s E > 1 MeV: 8.1 x 1012 n/m2s

Comparison between measured and calculated ΣΣ spectrum

Characterization in the intermediate energy range

± 15% E < 0.1 keV multiple foil methods

± 5% 0.1 keV ≤ E ≤ 2 MeV spectrometry and calculation

± 5% E > 2 MeV multiple foil methods

Method

• Neutron flux measuring in the place of detector exposure by absolutely calibrated fission chambers (FC – 235U)

• Exposure of fissionable detectors- irradiation in the central position of ΣΣ-ITN system- fluence > 1014 n/cm2 (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 408 152Eu calibration point standard source- 5 cm source – crystal distance- SAMPO software package

Characteristics of fissionable detectors

Detector identification

MaterialDetector mass (g)

Isotope mass (g)

Main isotope (%)

Impurities

D2011 238U + 400 ppm 235U 0.534239 0.5342390 ~100.00 238U 400 ppm 235U

D209 Al 10% 239Pu 0.087823 0.0087230 99.95 239Pu 0.05% 240Pu

D204 Al 20% 235U 0.087843 0.0175686 98.00 235U 2.00% 238U

D205 Al 10% 235U 0.087164 0.0087164 98.00 235U 2.00% 238U

D208 Al 5% 239Pu 0.084411 0.0042206 99.95 239Pu 0.05% 241Pu

Note: Mass of alloys are certified by Reactor Experiments USAwith uncertainty of ± 1%.

Results

Fission products

Measured yields

Recommended ENDFB/IVRatio

ΣΣ-ITN / ENDFB/IVΣΣ-ITN CFRMF

95Zr 6.71 ± 3.2% 6.43 ± 2.1% 6.39 ± 1.0% 6.37 1.05

103Ru 3.17 ± 3.2% 3.25 ± 4.2% 3.25 ± 1.5% 3.28 0.97

140Ba 6.13 ± 3.1% 6.04 ± 1.8% 6.07 ± 1.3% 6.04 1.01

131I 3.46 ± 5.6% 3.32 ± 4.5% 3.16 ± 1.29% 3.25 1.06

Fission yields in ΣΣ spectrum for 235U(n,f)

Fission products

Measured yields

Recommended ENDFB/IVRatio

ΣΣ-ITN / ENDFB/IVΣΣ-ITN CFRMF

95Zr 5.11 ± 4.2% 4.64 ± 2.5% 4.74 ± 1.5% 4.73 1.08103Ru 7.18 ± 4.0% 6.66 ± 4.1% 6.94 ± 2.0% 6.73 1.07140Ba 5.73 ± 3.8% 5.14 ± 2.3% 5.37 ± 1.0% 5.24 1.09

131I – 4.10 ± 4.6% 4.02 ± 2.0% 4.10 –

Fission yields in ΣΣ spectrum for 239Pu(n,f)

Fission products

Measured yields

Recommended ENDFB/IVRatio

ΣΣ-ITN / ENDFB/IVΣΣ-ITN CFRMF

95Zr 5.29 ± 4.1% 5.13 ± 2.0% 5.19 ± 2.5% 5.29 1.00103Ru 5.79 ± 3.7% 6.36 ± 2.4% 6.32 ± 4.3% 6.32 0.92140Ba 6.06 5.96 ± 1.5% 5.98 ± 3.8% 6.04 1.00

131I 3.41 ± 5.4% 3.20 ± 1.6% 3.24 ± 4.7% 3.24 1.05

Fission yields in ΣΣ spectrum for 238U(n,f)

Uncertainties

• In neutron flux- fissionable deposit mass 1.6%- statistics 1.0%- monitoring 0.8%

• In activation rate- fitting and background 0.62 – 4.7% subtraction- absolute efficiency 1.8 – 2% calibration of Ge(Li) crystal- statistics 1 – 3.8%