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[en] An analytical approximation of the Doppler broadening function ψ(ξ,x) is proposed. This approximation is based on the solution of the differential equation for ψ(ξ,x) using the methods of Frobenius and parameters variation. The analytical form derived for ψ(ξ,x) in terms of elementary functions is very simple and precise. It can be useful for applications related to the treatment of nuclear resonances, mainly for calculations of multigroup parameters and resonances self-protection factors, the latter being used to correct microscopic cross section measurements by the activation technique. (author)
[en] In the present paper a new analytical solution for the point kinetics equation system with temperature feedback is presented. This solution is based on the expansion of the neutron density in terms of the generation time of prompt neutrons (Nahla, 2009) and presents the advantage of being explicit in time and having a simple functional form in comparison with other existing formulations in supercritical transients. (orig.)
[en] The purpose of this paper is to present a proposal for a procedure to be adopted by the Brazilian Nuclear Energy Commission (CNEN) to evaluate the safety of fuel rods being used in nuclear power reactors in operation in the country. It should also guide the licensing process of new fuel rods designs clearly delimiting safety criteria related to its thermo-mechanical behavior. This activity is under technical collaboration of multidisciplinary design INSC BR3.01/09-BR/RA/01 Project signed between Brazil and the European Union (EU). This paper presents a first step towards establishing a CNEN standard on specific safety requirements to be met by designs of fuel elements of NPP reactors (PWR) that are operating in Brazil. (author)
[en] The risk informed decision making - RIDM is a modern approach to apply an integrated decision-making process that combines the insights from the deterministic approach and the probabilistic analysis with further requirements, where applicable (legal, regulatory, cost-benefit, etc) to aid the decision-making process. It can help regulatory bodies make decisions about safety issues (including plant licensing) in nuclear facilities and in organizing their activities so that their resources are more efficiently used and there is a reduction in the unnecessary burden on the licensees without compromising safety. This work intends to show Brazilian efforts to improve Probabilistic Safety Assessment - PSA regulations and licensing process toward establishing a well structured RIDM process discussing the steps, lessons learned and the difficulties. (author)
[en] An analytical approximation of the interference term χ(x,ξ) is proposed. The approximation is based on the differential equation to χ(x,ξ) using the Frobenius method and the parameter variation. The analytical expression of the χ(x,ξ) obtained in terms of the elementary functions is very simple and precise. In this work one applies the approximations to the Doppler broadening functions and to the interference term in determining the neutron cross sections. Results were validated for the resonances of the U238 isotope for different energies and temperature ranges. (author)
[en] The activation technique allows either absolute or relative very precise neutron intensity measurements. This technique requires the knowledge of the Doppler broadening function to determine resonance self-shielding factors. In the present work a new formulation is proposed for the self-shielding factors where the Doppler broadening function is calculated using the Frobenius's method and compared to the values obtained from the four-pole Pade method. This calculation method is shown to be effective from the point of view of accuracy. (author)
[en] The analytical solution of point kinetics equations with a group of delayed neutrons is useful in predicting the variation of neutron density during the start-up of a nuclear reactor. In the practical case of an increase of nuclear reactor power resulting from the linear insertion of reactivity, the exact analytical solution cannot be obtained. Approximate solutions have been obtained in previous articles, based on considerations that need to be verifiable in practice. In the present article, an alternative analytic solution is presented for point kinetics equations in which the only approximation consists of disregarding the term of the second derivative for neutron density in relation to time. The results proved satisfactory when applied to practical situations in the start-up of a nuclear reactor through the control rods withdraw.
[en] It has been a consensus in the Academy that, for a nation to grow and develop in economic terms, an adequate supply of power should be available to provide its industrial sector as well as the needs of its people. Brazil did in the past make the decision to use the power generated from a nuclear source in its power generation matrix. The country today has two nuclear power plants in operation, Angra I and Angra II, with a third plant currently under construction, Angra III. The Angra I facility is nearly 40 years old and, should this country not manage to extend its lease of life, it should be decommissioned and taken apart, as provisioned for in prevailing legislation. In order to face the decommissioning costs of a nuclear power generation facility a sizeable amount of financial resources should be available to implement the decommissioning plan the operator is required to submit to the regulatory body. As the expected operating life of a nuclear power plant is of 40 years, some extensions were added to it to see the facilities go through successive and different governments and economic plans. This work studies some of the economic and financial aspects that go into the decommissioning of the Angra I power plant, pursuant to the IAEA documents published on the subject, covering different scenarios for yearly interest and the manner of the deposits, such as those of an uniform series of deposits and those of a growing and finite arithmetic progression. (author)
[en] Highlights: • One of the Beth–Placzek approximation were relaxed. • An additional term in the form of an integral is obtained. • A new mathematical formulation for the Doppler broadening function is proposed. - Abstract: In all nuclear reactors some neutrons can be absorbed in the resonance region and, in the design of these reactors, an accurate treatment of the resonant absorptions is essential. Apart from that, the resonant absorption varies with fuel temperature due to the Doppler broadening of the resonances. The thermal agitation movement in the reactor core is adequately represented in the microscopic cross-section of the neutron-core interaction through the Doppler broadening function. This function is calculated numerically in modern systems for the calculation of macro-group constants, necessary to determine the power distribution of a nuclear reactor. It can also be applied to the calculation of self-shielding factors to correct the measurements of the microscopic cross-sections through the activation technique and used for the approximate calculations of the resonance integrals in heterogeneous fuel cells. In these types of application we can point at the need to develop precise analytical approximations for the Doppler broadening function to be used in the calculation codes that calculate the values of this function. However, the Doppler broadening function is based on a series of approximations proposed by Beth–Plackzec. In this work a relaxation of these approximations is proposed, generating an additional term in the form of an integral. Analytical solutions of this additional term are discussed. The results obtained show that the new term is important for high temperatures.