USE AND QUALIFICATION OF THE UMAE UNCERTAINTY METHODOLOGY HAVING AS BASIS THE CATHARE2 CODE
by Francesco D'AURIA, Maurizio INGEGNERI

Abstract: The present paper deals with the use of the UMAE (Uncertainty Methodology Based on Accuracy Extrapolation). This methodology allows the calculation of uncertainty in the prediction by thermal-hydraulic system codes of transient scenarios relevant to Nuclear Power Plants.
The UMAE has been applied in an international exercise promoted by OECD/CSNI (OECD Committee on the Safety of Nuclear Installations), called UMS (Uncertainty Method Study); the qualification of uncertainty methodology constitutes one of the main purposes of UMS. The methodology has been applied in the proposed study having as the basis both the Relap5/mod2 and the Cathare2 codes calculations. In this paper, the results obtained by the use of Cathare2 code are discussed.
One small break Loss of Coolant Experiment performed in the Japanese LSTF (Large Scale Test Facility) has been taken as reference test in relation to which code uncertainties have been predicted. The results of the application proved the capabilities of UMAE in predicting uncertainties at least in the considered scenario.

Key words: uncertainty, accuracy, scaling, extrapolation, Cathare

THE SLOWING DOWN OF FISSION NEUTRONS
by Dušan STEFANOVlĆ

Abstract: The investigations are presented from the general point of view of slowing down of fission neutrons in different media and different geometries. The analytical method for solving the neutron slowing down equation is given. The solution obtained has been extended to a cylindrical reactor cell. This solution has also been interpreted by the mathematical phenomenology. A presentation is given of the application of the multi-group approximation to solving the problem of energy distribution of neutrons in a reactor cell. This contribution considers an analytical procedure for solving the problem of neutron dependent anisotropy of elastic scattering. An interesting set of results for fast neutron fields at the RB reactor is given.

Key words: fission neutrons, slowing down, analytical solution, energy distribution, reactor cell, fast fission ratio, energy dependent anisotropy, fast fission fields, reactor RB

OPTIMIZATION OF ²⁰¹Tl PRODUCTION PARAMETERS REGARDING ITS ROUTINE PRODUCTION AT THE TESLA ACCELERATOR INSTALLATION
by Marko DAKOVIĆ, Jožef J. ČOMOR

Abstract: In addition to chemical biological and radiochemical requirements, radionuclidic purity is a very important parameter of the quality of cyclotron produced radio-pharmaceuticals. The radionuclidic purity of a product is governed by several radiophysical production parameters, including target content, target thickness, and projectile type and impact energy. A numerical procedure is presented that can be successfully used for the prediction of thick target yields of nuclear reactions. Its applicability is demonstrated by optimizing the radiophysical production parameters of ²⁰¹Tl. Concerning the required yields, radionuclidic purity, and available proton beams extracted from the VINCY Cyclotron, the following production parameters were selected: 50 mm target made of thallium enriched in ²⁰³Tl to 98.36 %, irradiated by 36 mA proton beam at a glancing angle of 7° with an impact energy of 28.5 MeV.

Key words: Tl-201, radiopharmaceutical, radioisotope production, process optimization

LARGE HADRON COLLIDER PROJECT AT CERN
by Petar ADŽIĆ

Abstract: The Large Hadron Collider (LHC) is the latest scientific project in the world of particle physics launched by European Organization for Nuclear Research (CERN) nearby Geneva. The construction of the main components of this complex synchrotron ring where two proton beams will be accelerated up to energies of 7.7 TeV and then brought into collision, is well underway and the first installation of these components is expected to take place by the end of 2000. As a successor of the existing LEP machine and taking over a significant part of its infrastructure, when completed and commissioned in 2005, the LHC complex will represent the most sophisticated and the largest project ever undertaken in the world of science. This machine has an ambitious task to offer the most contemporary and highest quality programmes in particle physics for scientists from all over the world. Its design and construction make use of the latest achievements in modern technologies, material sciences, engineering, computers, electronics and employing world wide experts and specialists of various profiles. At the same time, the LHC project ought to enable CERN and European scientists to maintain the world leading role in the field of particle physics in the next century.

Key words: proton synchrotron, hadron collider, superconducting magnet, particle physics, center-of- mass energy, luminosity, fundamental interactions, standard model

PLANNING AND PERFORMING DECOMMISSIONING OF A RESEARCH NUCLEAR REACTOR
by Milena MATAUŠEK

Abstract: Immediate action to adopt the global strategy of decommissioning the research reactor RA at the VINČA Institute of Nuclear Sciences and to perform the preliminary planning of particular activities is necessary independently on the decision of the future status of this reactor, namely even in the case that it is decided to complete its modernization and to use the reactor again.
In this paper some basic definitions are given which should make it possible to understand better the decommissioning process. The necessary requirements which have to be fulfilled before the decommissioning is started are summarized and some experiences from other countries, relevant for the case of the RA research reactor, are given.
Finally, conclusions have been made concerning the decommissioning strategy for the RA reactor, the necessary prerequisites and the optimal decommissioning time schedule.

Key words: decommissioning of research nuclear reactors, reactor RA, storage of radioactive waste, storage of spent nuclear fuel, safety aspects of decommissioning

Note: Full text published in Serbian