[en] The stochastic neutron flux fluctuations in boiling water reactors represent a significant source of information about thermohydraulic parameters. In this paper, experimental results of in core measurements are described together with the development of a theoretical model. (author)

No abstract available

[en] A comparative study has been made on the mechanical energy released in a core disruptive accident resulting from an unprotected loss of flow accident (LOFA) in a medium sized liquid metal fast breeder reactor with oxide, carbide and metal fuels. The study is conducted by ignoring the passive safety features incorporated in the design so that the accident scenario culminates in an energetic disassembly of the core with large energy release. The paper further provides the salient features of the analysis and presents the results with suitable physical explanations

[en] The effect is studied of fuel particle size on the course of power excursion in a fast reactor fuelled with Th-Pu0₂ kernels by taking into account the Doppler feedback effect as the excursion terminating mechanism. Reactor power, energy release, temperatures of the fissile and fertile parts are studied as a function of time for different reactivity inputs and sizes of the fuel particles. For temperature calculations the finite difference method has been employed to solve the heat conduction equations in spherical geometry. Power calculations have been performed by solving the point kinetics equations using Cohn's method. It has been found that: (a) high thermal conductivity and lower specific heat of thorium metal results in lower peak temperatures of kernel during the excursion: (b) as the fuel burn-up proceeds, larger reactivity additions could also be tolerated; and (c) the numerical approach to solve the heat conduction equations is quite straightforward and can be used conveniently to solve such problems. (author)

[en] The neutron-noise transmission characteristics of non-multiplying media typical to LMFBRs are studied using transport theory and the results are compared with the corresponding results for diffusion theory. In transport theory suitable expressions are derived for the discrete (asymptotic) and continuum (transient) solutions for the frequency-dependent neutron flux. Further, it is examined how the break frequency of the neutron flux ASPD, calculated using transport theory and diffusion theory, changes with distance from the neutron-noise source for materials like graphite, stainless steel and borated concrete. The 1-D, isotropic monoenergetic neutron transport equation for an infinite medium is used. (author)

[en] Hypothetical core disruptive accident (HCDA) energy release, if it occurs during startup of a reactor is shown to be independent of the initial neutron source strength. Furthermore, because of the reactivity feedback in the predisassembly phase the power at the beginning of the disassembly phase is weakly dependent upon initial source strength. Therefore it is concluded that as long as initial neutron source strength satisfies during startup, there is no need for the enhancing of the initial source strength from the HCDA energy release point of view. (U.K.)

[en] Frequency composition of inherent coolant boiling noise in BWRs is analysed using the equations governing the bubble formations and their detachment from the fuel-pin surface and a parametric study is conducted with respect to core cooling-channel parameters such as pressure, coolant flow velocity, cavity size and the contact angle. The results indicate that the frequency composition of inherent boiling noise in BWRs is not white but lies in the frequency range of 15-45 Hz. (author)

[en] An attempt has been made to investigate the space cross-correlation of boiling noise in boiling water reactors by assuming the slip ratio to be unity and power profile to be constant along the core height of the reactor. Two cases have been considered: One, no flow fluctuations (ΔV = O) caused by boiling noise and two, finite flow fluctuations (ΔV is not equal to O) caused by the boiling noise. It has been found that range space cross-correlation of noise sources exists only for ΔV is not equal to O case and not for ΔV = O case. Auto power spectral density of steam content fluctuations, Δα have a break frequency which is directly related with the flow velocity and attenuation coefficient, μ of the cross-correlation of noise sources in BWRs. Normalized root mean square value of Δα is more sensitive to μ in the upper half of the core for μ < 10. For μ>approximately equal to 20, it is more sensitive to μ in the lower half of the core. (author)

[en] The noise that may arise due to boiling of Na in LMFBRs is investigated. The study deals specifically with investigations of the likely frequency range of Na boiling and its dependence on local parameters like coolant flow velocity, cavity size and contact angle. (author)

No abstract available