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Technical Brief

Calculations and Measurements of Pressure Vessel Thermal Neutron Fluxes in the VVER-1000 Mock-Up in the LR-0 Research Reactor

[+] Author and Article Information
Michal Košťál

Research Center Rez Ltd., Department of Neutron Physics, 250 68 Husinec-Rez 130, Czech Republic e-mail: Michal.Kostal@cvrez.cz

Vlastimil Juříček

Research Center Rez Ltd., Department of Neutron Physics, 250 68 Husinec-Rez 130, Czech Republic e-mail: Vlastimil.Juricek@cvrez.cz

Ján Milčák

Research Center Rez Ltd., Department of Neutron Physics, 250 68 Husinec-Rez 130, Czech Republic e-mail: Jan.Milcak@cvrez.cz

Vojtěch Rypar

Research Center Rez Ltd., Department of Neutron Physics, 250 68 Husinec-Rez 130, Czech Republic e-mail: Vojtech.Rypar@cvrez.cz

Antonín Kolros

Czech Metrology Institute, Inspectorate for Ionizing Radiation, 120 00, Radiova 1 Prague 10, Czech Republic e-mail: Akolros@cmi.cz

Manuscript received July 8, 2014; final manuscript received October 23, 2014; published online March 24, 2015. Assoc. Editor: Juan-Luis Francois.

ASME J of Nuclear Rad Sci 1(2), 024509 (Mar 24, 2015) (7 pages) Paper No: NERS-14-1019; doi: 10.1115/1.4029284 History: Received July 08, 2014; Accepted December 03, 2014; Online March 24, 2015

This paper deals with measured as well as calculated parameters of thermal neutron transport in the reactor pressure vessel model, located behind the LR-0 reactor vessel. A VVER-1000 mock-up core placed in the LR-0 reactor is the source of neutrons, whose transport through heavy steel structures surrounding the core (i.e., the side reflector up to the area behind LR-0 vessel), is studied. The change of neutron distribution due to the variable thickness of the steel reactor pressure vessel (RPV) layers was measured and calculated using MCNPX code. The experimental results are compared with calculations performed with CENDL 3.1 and ENDF/B VII using both the thermal scattering law sublibrary with the S(α,β) model and the free gas transport model. When steel thickness increases, the measured reaction rate attenuation coefficients show a considerable decrease in thermal neutron flux, while measured Cd ratios show a faster decrease in the thermal part of the neutron spectra than the epithermal part. The calculation to experiment (C/E) for the Cd ratio shows in most cases better correspondence when the thermal neutron transport is described by means of a free gas transport model than with the thermal scattering law (TSL) model. Significantly better agreement of reaction rates is observed for the epithermal reaction rate attenuation coefficients than for thermal ones. The results are similar for both the free gas and TSL models at these energies.

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References

Košťál, M., Schulc, M., Rypar, V., and Novák, E, 2014, “VVER-1000 Mock Up Physics Experiments Hexagonal Lattices (1.275 cm Pitch) of Low Enriched U(2.0, 3.0, 3.3 wt.% 235U) O2 Fuel Assemblies in Light Water with H3BO3,” International Handbook of Reactor Physics Evaluated Experiments (IRPhE), NEA/NSC/DOC(1), Nuclear Energy Agency, Paris.
Kyncl, J., Rypar, V., and Novák, E., 2008, “VVER Physics Experiments: Hexagonal Lattices (1.275 cm Pitch) of Low Enriched U(3.6, 4.4 wt.% U235) O2 Fuel Assemblies in Light Water with H3BO3,” LEU-COMP-THERM-086, International Handbook of Evaluated Safety Criticality Benchmark Experiments, NEA/NSC/DOC(2006)1, Nuclear Energy Agency, Paris.
Kolros, A., Huml, O., Kříž, M., and Kos, J., 2010, “Equipment for Neutron Measurements at VR-1 Sparrow Training Reactor,” Appl. Radiat. Isotopes, 68(4–5), pp. 570–574. [CrossRef]
Pellowitz, D. B., 2007, “MCNPX User’s Manual, version 2.6.0,” , Los Alamos National Laboratory.
Chadwick, M. B., Obložinský, P., Herman, M., et al. , 2006, “ENDF/B-VII.0: Next Generation Evaluated Nuclear Data Library for Nuclear Science and Technology,” Nucl. Data Sheets, 0090-3752, 107(12), pp. 2931–3060. [CrossRef]
Košťál, M., Cvachovec, F., Rypar, V., and Juříček, V., 2012, “Calculation and Measurement of Neutron Flux in theVVER-1000 Mock-Up on the LR-0 Research Reactor,” Ann. Nucl. Energy, 40(1), pp. 25–34. [CrossRef]
Košťál, M., Milčák, J., Rypar, V., Juříček, V., Novák, E., and Kolros, A., 2013, “The Effect of Biological Shielding on Neutron Transport in the VVER-1000 Mock-Up on the LR-0 Research Reactor,” Ann. Nucl. Energy, 53, pp. 129–134. [CrossRef]
Košťál, M., Cvachovec, F., Ošmera, B., Hansen, W., and Juříček, V., 2010, “Thermal Scatter Treatment of Iron in Transport of Photons and Neutrons,” Ann. Nucl. Energy, 37(10), pp. 1290–1304. [CrossRef]

Figures

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Fig. 1

Scheme of LR-0 mock-up with reactor pressure vessel model dimensions in mm [1]

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Fig. 2

Scheme of the measuring points in reactor pressure vessel model

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Fig. 3

Vertical view of window in Cd clad of LR-0 reactor vessel

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Fig. 4

Cd cover transmission coefficients [5]

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Fig. 5

Influence of PE tube insertion or Cd cover over detector on neutron spectra in point 6

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Fig. 6

Angular distribution of elastically scattered neutrons in ENDF VII and CENDL 3.1 [8]

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Fig. 7

Calculated neutron flux densities in peripheral regions of reactor pressure vessel model

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Fig. 8

Calculated neutron flux densities in inner regions of reactor pressure vessel model

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Fig. 9

Neutron capture rate variations in various positions of air gap in VVER-1000 mock-up

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