[en] With the publication of the PRA Policy Statement and recent regulatory guides, the U.S.NRC makes a continuous approach towards risk-informed regulations with the goal of establishing an overall framework for risk-informed decisions in all regulatory activities as well as plant specific licensing issues. Faced with the changing environment of deregulation of the electricity generation market, the licensee's effort to reduce design margins to enhance flexibility and to relieve unnecessary regulatory burdens have been focused on the control and reduction of plant operating costs. The risk-informed approach provides a structured, systematic, and defensible method that can be applied not only to rulemaking, but also to licensing, inspection, enforcement, and performance assessment, as well as provides basis for prioritization in the establishment of programs and the allocation of resources. This report describes the current regulatory environment of transitioning to risk-informed regulations with an emphasis on its background, concepts, regulatory guides, proposed options for modifying the 10CFR50, and risk-informed applications in U.S.A. Review of the risk informed applications utilizing the information provided by the PRAs and their insights in the U.S.NRC and nuclear industry will provide the insights of predicting the expected regulation changes in Korea. Also it could provide the applicable methods or guides for the implementation of the risk-informed applications in plant design and operations. (author)

No abstract available

[en] The annual activities report of 1998 of Control Licensing Superintendency (SLC/CNEN) - Brazilian organization - introduces the next main topics: main attributions; managerial units - reactors coordination, nuclear facilities coordination, raw materials and minerals coordination, radioactive facilities coordination, radioactive wastes coordination; laboratory coordination of Pocos de Caldas; technical management; and international cooperation

[en] A PC window-based computer code, CONPAS (CONtainment Performance Analysis System), has been developed to integrate the numerical, graphical, and results-operation aspects of level 2 probabilistic safety assessments (PSA) for nuclear power plants automatically. As a main logic for accident progression analysis, it employs a concept of the small containment phenomenological event tree (CPET) helpful to trace out visually individual accident progressions and of the detailed supporting event tree (DSET) for its detailed quantification. For the integrated analysis of Level 2 PSA, the code utilizes five distinct, but closely related modules. Its computational feasibility to real PSAs has been assessed through an application to the UCN 3 and 4 full scope Level 2 PSA. Compared with other existing computer codes for Level 2 PSA, the CONPAS code provides several advanced features: (1) systematic uncertainty analysis / importance analysis / sensitivity analysis, (2) table / graphical display and print, (3) employment of the recent Level 2 PSA technologies, and (4) highly effective user interface. The main purpose of this paper is to introduce the key features of CONPAS code and results of its feasibility study. (author)

[en] Under contract to the Austrian Federal Chancellory, directorate VI, the radioecological prediction code OECOSYS was implemented by the Austrian Research Center Seibersdorf on a VAX computer using VAX Fortran in 1989. Successively, in 1992 the program OECOSYS was implemented - in the version of 1989 - on PC's in Seibersdorf and the Ministry using OS/2 and Microsoft-Fortran. In 1993, an update of data sets and program structures which had become necessary by new data and improvements in modelling, was realized for the same customer. In 1998 the new version of the code in form of an EXCEL-version under MS Windows 95 was installed and adapted according to the Austrian parameters. With this version the calculation of two test scenarios in the context of the emergency exercise Hollabrunn was performed. They comprised an accident scenario in the NPP Dukovany. The assumption for the exercise was a severe accident with the failure of all cooling systems and furthermore the failure of the sprinkler system and the barbotage system after 1 hour. The assumptions were independent of the credibility of the accident scenarios with the aim of creating a useful exercise scenario. Two prognosis calculations were performed, one assuming completely dry deposition and one assuming a predominantly wet deposition. (author)

[en] In this paper, verifications of the new computer codes VEGA in connection with KENO-V.a from SCALE4.3 package and benchmark code MCNP4B2 are carried out against the evaluated critical experiments of the RB reactor low enriched (2%) metal uranium - heavy water lattices. Results of validation of new neutron continuous-energy library - VMCCS, developed in the Vinca Institute for the MCNP code, at the same benchmark experiments are shown as well. (authors)

[en] The term 'cindynics' was introduced about ten years ago to describe the sciences of hazards together with a will to approach the problem of hazard as a whole taking into account all its dimensions (technical, functional, human behaviour, management procedures, goals, regulations etc..). The cindynics concern the situations having a potential or a real form of hazard and try to answer the need for a more complete representation of the hazard space in order to group together in a coherent way the formalisms and methods of observation, understanding and management of hazard situations. Such situations can be encountered in any domain of our society (work place, environment, air and railway transport..) and in any industrial activity (nuclear, chemical, food etc..). The aim of this book is to aware the reader of the complexity of hazards evaluation and management threw the observation, the analysis, the evaluation and the management of hazard situations. The book is divided into 3 parts dealing with: the danger scene (autopsy of some major catastrophes, study of a danger scene: the case of a complex commercial area, the urban metropolis and the hazards), the methodological approach of cindynics (cindynics: an historical and conceptual perspective about hazard sciences, methods for the operation safety of industrial systems, an economical analysis of hazard for an intelligent selection of prevention efforts), management of hazard situations (danger management and civil security, decision making and hazard, experience feedback and the help for its use, hazards management and computer-aided management). (J.S.)

[en] JNC (Japan Nuclear Cycle Development Institute) has been promoting the fellowship program for young scientists to encourage their expertise from 1997. The objective of this program is to raise the talented persons for future JNC activities. This report summarized the status on the 17 themes of researches implemented by young research fellows in 1999. The report includes the list of individual titles and the site and supporting staffs of JNC. The individual reports given by 17 authors describe its time schedule, status, achievements and own publications in the prearranged format. Topics include the followings; Those are giant resonance structures of short lifetime nuclei, growth of cavities in structural materials, calculation methods of photonuclear interaction cross-section, stability and radioactivity diffusion of bentonite, plant ecology of radioactivity in uranium mines, numerical simulations on the TRUEX process, advanced nondestructive testing of materials, physical properties of actinides obtained by band theory, de-oxidisation capability in pyrite to decrease oxygen in bentonite, investigation on equilibrium fast reactor recycling, behaviors of underground water in the Tono Mine, effects of radiation induced educts on swelling, simulation on fuel-coolant interaction after severe accidents, and resonance ionization mass spectrometry for the JOYO reactor to detect failed fuel locations. (Tanaka, Y.)

[en] This paper gives a priori estimates on asymptotic polynomials of solutions to parabolic differential equations at any points. This leads to a pointwise version of Schauder estimates. The result improves the classical Schauder estimates in a way that the estimates of solutions and their derivatives at one point depend on the coefficient and nonhomogeneous terms at this particular point

[en] Atucha-I is a pressure-vessel PHWR 335 MWe nuclear power plant, fuelled with natural uranium, cooled and moderated with heavy water and installed with an on-line refuelling system. Its commercial operation started in 1974. The core includes 253 fuel elements, each one of them located within a vertical coolant channel. On August 11, 1988, the NPP was operating at full power when a slow decrease in thermal power, due to the insertion of negative reactivity and non compensated by the gradual with-drawal of the regulating control rods, was observed. The resulting reduction in steam pressure shut the turbine off and, automatically, disconnected the unit from the grid. The partial insertion of control rods produced a further reduction in thermal power and, when the regulating rods reached the limit extraction position, the operator decided to produce a manual reactor scram, following operational procedures. The NPP was maintained in its hot shutdown condition (220 centigrade, 115 bar) for investigation purposes. Initially, it was assumed that such abnormality had been caused by light water injection or by the non-displayed insertion of a control rod. Chemical analyses demonstrated the absence of neutron poison and the tests performed on the control rods provided normal results. Therefore, on August 13, the NPP was started up again, but, as a precaution, the power to be gradually reached was limited to 70 %. However, after attaining criticality, a decrease in the moderator's cooling pressure and a increase in its temperature were observed. A thermohydraulic testing programme was initiated. On August 14, an increase in the total activity of the primary circuit was detected, indicating the presence of, at least, one broken fuel element. Simultaneously, oscillations were observed when the neutron flux corresponding to a given coolant channel was measured. Considering that the insertion of the fuel element in that channel on August 7 had caused perturbations, this element was taken out and a reduction of the oscillations was verified. Further on, remote visual inspection confirmed that the channel was broken and measurement in the refuelling system showed that the corresponding fuel element was also broken. The NPP was maintained in its cold shutdown condition (50 centigrade, 0 bar) in order to start an inspection programme aimed at assessing the extent of the damage. After a five-month inspection work, the damage in the reactor, the moderator tank and their internals was completely identified. The repair work was performed by specialised teams coordinated by the Responsible Organisation and, along with the associated inspection, kept the plant off the grid for 16 months. (author)