[en] An analysis has been performed for the linear instability modes of unventilated boiling parallel channels and an associated hydraulic loop. This analysis was based on a one-dimensional space dependent model of boiling system dynamics. Experimental verification of the model is shown. The relationship between the classical parallel channel instabilities, channel to channel instabilities, and loop instabilities has been investigated. The theoretical considerations are illustrated with numerical calculations in both time and frequency domains. (author)

[en] It is known that the fission product xenon 135, with a half life of 9.17 hours, has a very large absorption cross section for thermal neutrons. A small fraction of this nuclear species is formed directly in fission, but the major part results from the decay of iodine 135 with a half life of 6.59 hours. In this paper we shall present the 'fundamental' theory of an 'adiabatic' approach which appears to be promising both in cutting down computational time and in giving additional physical insight into the combined spatial-temporal variations. An adiabatic motivation is implicit in early work on reactor kinetics in which the reactor flux is separated into a product of a time dependent function and a function of all the other relevant variables, including the time; if the latter factor is slowly varying in time the approach is 'adiabatic'. (author)

[en] A model for the thermal-hydraulic behaviour of a CANDU fuel channel is presented. A single-phase or a two-phase flow model is transformed into a low order dynamical system of ordinary differential equations. This model is applied to simulation of thermal-hydraulic CANDU fuel channel transients. Some typical results are reported and compared with the predictions of FIREBIRD code. (authors)

[en] The CANDU NPP has two modes of operation: - 'alternative' mode, when the turbine power follows the reactor power; - 'normal' mode, when the reactor power follows the turbine power. The aim of this paper is to present the difficulties to operate the plant in 'normal' mode, and the cause which generate them. At present, the 'normal' mode is not in operation at Cernavoda NPP Unit 1. Some tests have been done to put in service this mode of plant operation but the results have been not satisfactory. Details concerning the testing procedure are presented. (author)

[en] Ever since the collapse of the former Soviet Union reports have circulated with increasing frequency concerning attempts to smuggle materials from that country's civil and military nuclear programs. Such an increase obviously raises a number of concerns (outlined in the author's introduction), chief among which is the possibility that these materials might eventually fall into the hands of proliferant states or terrorist groups. The following issues are presented: significance of materials being smuggled; sources and smuggling routes; potential customers; international efforts to reduce nuclear smuggling; long-term disposition of fissile materials. (author)

[en] Under present circumstances relating to the national nuclear program and strategy, the exploitation activities in two important uranium mining areas in Romania are foreseen to be ceased. This shutdown decision implies a number of technical measures concerning the environmental restoration. Reduction of radioactive contamination of the waters in these zones during both operation period and after the closing period is one of the main components of the environmental rehabilitation strategy. In this paper there are presented the current situation and the program foreseen for ground and surface water treatment at an uranium mining unit situated in the SW side of Romania, a program based on the results of our own research carried out to decrease the content of pollutant radioactive elements. (authors)

[en] In this paper the analytic nodal method is used for the solution of the 2D-neutron diffusion equations both for one and two energy groups. For one energy group calculations, different transverse leakage approximations are presented. A new model, named transverse leakage proportional with flux is proposed. For two energy group calculation only the flat transverse leakage approximations are employed. The models are applied and tested for CANDU 600 reactor case, and accurate static and dynamic results in very short computing times were obtained. Also, a flux reconstruction method is presented. The method starts with the averaged nodal fluxes calculated with nodal analytical method. The flux reconstruction method is specific for CANDU reactors. (authors)

[en] The paper presents a simplified theoretical modelling of the laminar flow for real liquids through the imperfect tightness of technological installation at high pressure (p = 100 bar) and temperature (t = 300 deg C), taking into account the steam-liquid phase exchange. The physical mathematical model allows establishing the formulas to evaluate the mass/volume flow of the fluid losses. Finally, the paper presents the experimental results obtained during some light water tests at Institute for Nuclear Research (INR) Pitesti, Romania that led to the verification and validation of the theoretical model. By using the physical-mathematical model, a method has been developed to detect the steam losses that has been certified at INR Pitesti and has been used in 'Channel closure testing' for Cernavoda NPP U1. (authors)

[en] Experimental data show a variation of the calibration factor with the source distance, for some specific energies, in some kind of monitors. This work presents, as a fist attempt, an explanation of this dependence for the monitor Babyline 81 in the energy range of Cs-137. Different laboratories in U.E. accomplished measurements to determine the importance of the calibration factor variation with the distance for the monitor Babyline 81. The calibration was done for Co-60 and Cs-137 energy range. The values of the calibration factor normalized for a distance of 1.227 meters are presented. The physical cause explaining the dependence of the calibration factor with the distance to the source, for the Babyline monitor, at the Cs-137 energy, is suggested. In addition, a study was conducted to evaluate the theoretical importance of this effects and to find an acceptable procedure in making the approximations

[en] The paper presents the main aspects of spent fuel and radioactive waste management strategy proposed for Cernavoda NPP taking into account the level of radioactive waste management in Romania and in E.U. The following problems are tackled: - Radioactive waste and spent fuel management practice; - Sources and types of wastes (radioactive wastes and spent nuclear fuels); - Present status of the objectives concerning Cernavoda NPP (radwaste repository, spent fuel interim-storage and disposal facility)