A new approach is proposed and investigated for reconstructing the neutron spectra of reactors from activation measurements: the parameterization of the neutron spectrum is changed and the spectrum is represented in the form of a B spline. A Monte Carlo method is proposed for taking account of the distortions of the neutron spectrum by the measuring design of the detectors. The results of the activation measurements show that the approach developed can be used to reconstruct the neutron spectra of BARS-5, IGRIK, and YAGUAR reactors.The determination of neutron spectra ϕ(E) from activation measurements reduces to solving a system of integral equations of the form [1,2] (1)where Q i is the number of reactions on one nucleus of the main isotope of the ith indicator, measured with absolute rms error ∆Q i (1σ); E is the energy of the neutron; i is the number of the indicator; σ i (E) is the activation cross section of the ith indicator; N is the number of indicators used to measure the neutron field. Relation (1) is approximate, since it lacks the distortion which the measurement design of the activation detectors introduces into the neutron field. A more accurate relation is (2) where ϕ i (E) is the spectrum in the ith detector. The spectra ϕ i (E) are unknown and depend on the activation measurement scheme used.For further analysis, it is convenient to write system of equations (2) in the form (3) where S i (E) = ϕ i (E)/ϕ(E) are correction functions which take account of the distorting effect of the measurement construction. Calculating the spectra ϕ i M (E), ϕ M (E) by the Monte Carlo method, taking account, to the maximum extent possible, of the design of the reactor setup and the measurement scheme, and assuming the average-group values of the functions S i (E) to be Q ES E E d E i N i i i = = ∞ ∫ σ ϕ ( ) ( ) ( ) , ,..., , 0 1 Q E E d E i N i i i = = ∞ ∫ σ ϕ ( ) ( ) , ,..., , 0 1 Q E E d E i N i i = = ∞ ∫ σ ϕ ( ) ( ) , ,..., , 0 1
3HeDf'LiD thermal-to-fusion (E=14 MeV) neutron converters have been developed at the IWW-2M reactor to simulate the irradiation of structural materials in a fusion reactor. These converters increase the highest energy part of the neutron spectrum (E > 14 MeV) by =10lo n/ (cm2*s) in the reactor's test channel (=6-cm dim.), corresponding to a 14-MeV neutron fluence of =2*1016 dcm' per 500-hour reactor cycle. However, the high energy release (up to 1-2 kW/gr) in the converters from the 6Li(n,T)a and 3He(n,T)p exothermal reactions created there can be a critical problem in conducting experiments of this kind.
An approach is proposed for validating the nuclear and radiation safety of a container for spent fuel assemblies from reactors at the Beloyarskaya nuclear power plant. To validate the radiation safety, the characteristics of fuel assemblies and their classification according to the average fuel burnup in the casing, and the intensities of n and γ radiation in the casing are analyzed. Nuclear safety is validated on the basis of the concept of a "model" casing. This model makes it possible to obtain an upper estimate of the effective coefficient of neutron multiplication for all real casings with fuel assemblies. Calculations are used to determine the minimum necessary thickness of the vessel, bottom, and cover for 17-and 35-place casings. It is shown that no special neutron protection is needed. The container design to be developed meets the IAEA and OPBZ-83 safety standards.The holding ponds of the AMB reactors at the Beloyarskaya nuclear plant currently contain about 3000 spent fuel assemblies packed in 35-place casings and about 2000 assemblies packed in 17-place casings. A casing consists of 17 tubes, made of No. 3 steel, or 35 tubes made of 12Kh18N10T corrosion-resistant steel. A 13.5 m long fuel assembly (see Fig. 1) is placed in each approximately 14 m long tube. The relative arrangement of the tubes is fixed, using steel tube separator plates. The long holding period of the casings τ~ 15-40 yr in water is of concern because there are grounds for believing that the tubes in 17-place casings developed leaks and some fuel assemblies contain damage and on interacting with water can lose their shape and form a nuclear-dangerous configuration.The concept of switching to dry storage has been adopted at Rosatom and the concern Rosénergoatom. According to this concept, the spent fuel is held in storage ponds after which it must be either reprocessed at the Industrial Association Mayak or stored for a long period of time (τ > 50 yr) and then reprocessed at the Krasnoyarsk Mining and Chemical conglomerate. The fuel sent to the conglomerate contains fuel from the AMB reactors at the Beloyarskaya nuclear power plant. The Russian Federal Science Center -All-Russia Research Institute of Technical Physics has been tasked with developing a container for shipping and dry long-term storage of spent fuel from these reactors.The validation of nuclear and radiation safety is the first stage in the development of a container. It is at this stage that the thickness of the vessel walls is determined, the need for and the material of neutron shielding is determined, and the need for using neutron-absorbing components in the construction of the casing to meet nuclear safety requirements is determined. These data determine the mass/size, thermophysical, and strength characteristics and cost of the container. This article examines approaches to validating the nuclear and radiation safety for the example of a container for 17-place casings with spent fuel assemblies and presents the most important results of the calculation of the dos...
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