Activation Measurement of the Neutron Spectra of the BARS-5, IGRIK, and YAGUAR Reactors

Abstract

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

N-spline reconstruction of neutron spectra on the basis of activation measurements

“…It is evident that the group integrals with one another to within the limits of error. Evidently, the fluence and average energy of the spectra reconstructed in the present work are in good agreement with [15]. The largest reconstruction errors are observed that energy interval 0.1-1 MeV.…”

“…The approach described above was used to reconstruct the spectra in the channels of the BARS-5, IGRIK, and YaGUAR reactors and on the surface of the IGRIK reactor using previous activation measurements (see [12] for the initial data). The activation reaction cross-sections were taken from the GSSD, IRDF-90, ENDF-B/VI, and ADL-3 libraries.…”

“…In this connection, the following system was solved instead of system (11): (2), and the spectrum from [15] (3) in a BARS-5 channel. (2), and the spectrum from [15] (3) in a channel (a) and lateral window (b) of the IGRIK reactor and the channel of a YaGUAR reactor (c).…”

“…The errors of these functionals and of the group integrals F k were found using numerical experiments by the method of statistical tests [12]. The reconstructed spectra F k and their errors are presented in Tables 1 and 2.…”

“…We shall write this relation in a more accurate form using the ϕ i (E) spectrum of the ith detector as follows: (10) Introducing the function S i (E) ≡ ϕ i (E)/ϕ(E), we rewrite relation (10) as follows: (11) The correction functions S i (E) which take account of the distorting effects of the construction of the detectors were first introduced in [12]. Calculating the spectra ϕ i M (E) and ϕ M (E) by the Monte Carlo method taking account of the construction of the reactor facility in the measurements as accurately as possible, we shall assume that…”