A Comparison of Different Neutron Spectroscopy Systems at het Reactor Facility VENUS

The reactor VENUS is a zero-power research reactor mainly devoted to studies on light water fuels among which MOX fuel with high PU content. Around the reactor locally high neutron rates were measured and the ratio of the neutron-to-gamma dose rate can be as high as 3. A first spectrometric measurement was done with the IPSN multisphere spectrometer at three lcations around the reactor. The used two different measuring techniques to cover the spectrum form 0.01 tot 20 MeV. Proton recoil techniques were used for energies above 100 keV, while the multisphere technique was used for the lower energies down to the thermal part of the spectrum. Secondly, a measurement with the Fraunhofer Institut ROSPEC spectrometer was done at het same points. This device consists of four spherical proportional counters. Three of them are filled with hydrogen at different pressures, while the fourth is bigger and is filled with a mixture of argon and methane. Thes spheres are mounted on a rotatin platform and in toatl the neutron spectrum can be measured from 50 keV to 4.5 MeV. A third spectral measurement was done with the Bubble Interactive Neutron Spectrometer (BINS). Here the bubble detector principle is used to meausre the neutrons. By changing the temperature and the detecro liquid, a sieries of different neutron thresholds are attained so that deconvolution of the neutron spectrum is possible. During all these measurements in subsequent years the loading of the reactor core was similar so that the spectrum is possible. During all these measurements in subsequent years the loading of the reactor core was similar so that the spectrum should be comparable. These measurements are compared with a numerical simulation of the neutron field near the reactor and the working fields around it. This numerical simulation of the neutron spectra was performed at het SCK•CEN with the use of the TRIPOLI-3 code. Dosimetric measurements were also done with a Harwell N9 and Studsvik 2202D neutron monitor, and with three types of personal neutron dosemeters: an albedo type, a track etch detector and a bubble detector.