PC-based probabilistic safety assessment in Japan

The role of PC-based programs is becoming important in the area of PSA. The PC-based program QUEST has been developed to perform level-1 PSA at PNC. This program is an effective tool to examine the effects of the change in the plant design and/or operational procedures. Also, as a part of the full scope PSA activity for the prototype liquid metal fast breeder reactor, a systems analysis code network, which involves some PC-based programs, was developed and has been utilized to perform level-1 PSA with less manpower and more consistency. Further, a living PSA tool is currently being developed for the purpose of maintenance of or improvement in operational safety.     

PSA in design of passive/active safety reactors

PSAs in the design of advanced reactors are applied mainly in level 1 PSA areas. However, even in level 1 PSA, there are certain areas where special care must be taken depending on plant design concepts. This paper identifies these areas both for passive and active safety reactor concepts. For example, ‘long-term PSA’ and shutdown PSA are very important for a passive safety reactor concept from the standpoint of effectiveness of a grace period and passive safety systems. External events are also important for an active safety reactor concept. These kinds of special PSAs are difficult to conduct precisely in a conceptual design stage. This paper shows methods of conducting these kinds of special PSAs simply and conveniently and the use of acquired insights for the design of advanced reactors. This paper also clarifies the meaning or definition of a grace period from the standpoint of PSA.     

Methods and practices used in incident analysis in the Finnish nuclear power industry

According to the Finnish Nuclear Energy Act it is licensee's responsibility to ensure safe use of nuclear energy. Radiation and Nuclear Safety Authority (STUK) is the regulatory body responsible for the state supervision of the safe use of nuclear power in Finland. One essential prerequisite for the safe and reliable operation of nuclear power plants is that lessons are learned from the operational experience. It is utility's prime responsibility to assess the operational events and implement appropriate corrective actions. STUK controls licensees' operational experience feedback arrangements and implementation as part of its inspection activities. In addition to this in Finland, the regulatory body performs its own assessment of the operational experience. Review and investigation of operational events is a part of the regulatory oversight of operational safety. Review of operational events is done by STUK basically at three different levels. First step is to perform a general review of all operational events, transients and reactor scram reports, which the licensees submit for information to STUK. The second level activities are related to the clarification of events at site and entering of events' specific data into the event register database of STUK. This is done for events which meet the set criteria for the operator to submit a special report to STUK for approval. Safety significance of operational events is determined using probabilistic safety assessment (PSA) techniques. Risk significance of events and the number of safety significant events are followed by STUK indicators. The final step in operational event assessment performed by STUK is to assign STUK's own investigation team for events deemed to have special importance, especially when the licensee's organisation has not operated as planned. STUK launches its own detail investigation once a year on average. An analysis and evaluation of event investigation methods applied at STUK, and at the two Finnish nuclear power plant operators Teollisuuden Voima Oy (TVO) and Fortum Power and Heat Oy (Fortum) was carried out by the Technical Research Centre (VTT) on request of STUK at the end of 1990s. The study aimed at providing a broad overview and suggestions for improvement of the whole organisational framework to support event investigation practices at the regulatory body and at the utilities. The main objective of the research was to evaluate the adequacy and reliability of event investigation analysis methods and practices in the Finnish nuclear power industry and based on the results to further develop them. The results and suggestions of the research are reviewed in the paper and the corrective actions implemented in event investigation and operating experience procedures both at STUK and at utilities are discussed as well. STUK has developed its own procedure for the risk-informed analysis of nuclear power plant events. The PSA based event analysis method is used to assess the safety significance and importance measures associated with the unavailability of components and systems subject to Technical Specifications. The insights from recently performed PSA based analyses are also briefly discussed in the paper.     

Determination of design alternatives and performance criteria for safety systems in a nuclear power plant via simulated annealing

This study presents an efficient methodology that derives design alternatives and performance criteria for safety functions/systems in commercial nuclear power plants. Determination of the design alternatives and intermediate-level performance criteria is posed as a reliability allocation problem. The reliability allocation is performed in a single step by means of the concept of two-tier noninferior solutions in the objective and risk spaces within the top-level probabilistic safety criteria (PSC). Two kinds of two-tier noninferior solutions are obtained: desirable design alternatives and intolerable intermediate-level PSC of safety functions/systems.The weighted Chebyshev norm (WCN) approach with an improved Metropolis algorithm in simulated annealing is used to find the two-tier noninferior solutions. This is very efficient in searching for the global minimum of the difficult multiobjective optimization problem (MOP) which results from strong nonlinearity of a probabilistic safety assessment (PSA) model and nonconvexity of the problem. The methodology developed in this study can be used as an efficient design tool for desirable safety function/system alternatives and for the determination of intermediate-level performance criteria.The methodology is applied to a realistic streamlined PSA model that is developed based on the PSA results of the Surry Unit 1 nuclear power plant. The methodology developed in this study is very efficient in providing the intolerable intermediate-level PSC and desirable design alternatives of safety functions/systems.     

State of the art in reliability of thermal-hydraulic passive systems

In order to address the issues posed by the development of advanced nuclear technologies, this article endeavours to analyse the current state of the art in reliability of passive systems, for their extensive use in future nuclear power plants. Inclusion of failure modes and reliability estimates of passive components for all systems is recommended in probabilistic safety assessment (PSA) studies. This has aroused the need for the development and demonstration of consistent methodologies and approaches for their reliability evaluation, within the community of the nuclear safety research. This report provides the insights resulting from the survey on the technical issues associated with assessing the reliability of passive systems in the context of nuclear safety, regulatory practices and probabilistic safety analysis. Special emphasis is placed on the reliability of the systems based on thermal-hydraulics, for which methods are still in a developing phase. The main achievements of these studies are presented and a viable path towards the implementation of the research efforts is delineated as well.     

Model-based human reliability analysis: prospects and requirements

Major limitations of the conventional methods for human reliability analysis (HRA), particularly those developed for operator response analysis in probabilistic safety assessments (PSA) of nuclear power plants, are summarized as a motivation for the need and a basis for developing requirements for the next generation HRA methods. It is argued that a model-based approach that provides explicit cognitive causal links between operator behaviors and directly or indirectly measurable causal factors should be at the core of the advanced methods. An example of such causal model is briefly reviewed, where due to the model complexity and input requirements can only be currently implemented in a dynamic PSA environment. The computer simulation code developed for this purpose is also described briefly, together with current limitations in the models, data, and the computer implementation.     

正压浓相恒压输送系统的DCS控制设计及应用

正压浓相气力输送系统是目前国内火电厂应用最为广泛的气力输送系统,该系统对运行的控制流程要求高、逻辑性强;其关键输送技术指标均采用模拟量进行检测,并实时控制.本文介绍的恒压输送系统,除了以上特点外,其独具的输送压力的动态实时调控功能,更是对控制系统提出更高的要求;阐述了DCS用于正压浓相恒压输送系统的典型设计.     

Liposomes as Carriers of Antimicrobial Drugs

Liposome are promising drug carrier systems being developed. Their successful use in the treatment of several diseases demonstrates that a solid rationale for clinical development of liposomes as antimicrobial drug carriers can be established. There are a number of potential drug candidates for liposome encapsulation. The involvement of several biotechnology companies has culminated in the design and licensing of formulations for the treatment of certain microbial infections and cancers. Understanding of liposome behavior in the body and of the physicochemical mechanisms involved in the interaction of liposome, drug, and cellular targets is essential for their future applications.     

Liposomes as Carriers of Antimicrobial Drugs

Abstract

Liposome are promising drug carrier systems being developed. Their successful use in the treatment of several diseases demonstrates that a solid rationale for clinical development of liposomes as antimicrobial drug carriers can be established. There are a number of potential drug candidates for liposome encapsulation. The involvement of several biotechnology companies has culminated in the design and licensing of formulations for the treatment of certain microbial infections and cancers. Understanding of liposome behavior in the body and of the physicochemical mechanisms involved in the interaction of liposome, drug, and cellular targets is essential for their future applications.     

Environmental impact assessment and the planning process of major sports events in Brazil: a case study of the Rio 2007 Pan American Games

This paper investigates the implementation and enforcement of environmental licensing and environmental impact assessment (EIA) regulations and decisions in the context of the Rio 2007 Pan American Games in Brazil. The methodology includes detailed case study analysis involving document analysis and interviews with key stakeholders. The results demonstrate that implementation and enforcement of EIA and environmental licensing still have a long way to go in terms of being fully effective in Brazil. Despite this, in the scope of the case study, the results showed that implementation and enforcement of environmental licensing and EIA regulations and decisions seem to be undertaken according to relevant regulations in the context of the Pan American Village. Finally, recommendations for major sports events and for the Brazilian context to strengthen its regulatory framework for environmental licensing and EIA are developed.     

Probabilistic analysis of accident precursors in the nuclear industry

Feedback of operating experience has always been an important issue in the nuclear industry. A probabilistic safety analysis (PSA) can be used as a tool to analyse how an operational event might have developed adversely in order to obtain a quantitative assessment of the safety significance of the event. This process is called PSA-based event analysis (PSAEA). A comprehensive set of PSAEA guidelines was developed by an international project. The main characteristics of this methodology are summarised. This approach to analyse incidents can be used to meet different objectives of utilities or nuclear regulators. The paper describes the main objectives and the experiences of the Belgian nuclear regulatory organisation AVN with the application of PSA-based event analysis. Some interesting aspects of the process of PSAEA are further developed and underlined. Several case studies are discussed and an overview of the obtained results is given. Finally, the interest of a broad and interactive forum on PSAEA is highlighted.     

Seismic PSA method for multiple nuclear power plants in a site

The maximum number of nuclear power plants in a site is eight and about 50% of power plants are built in sites with three or more plants in the world. Such nuclear sites have potential risks of simultaneous multiple plant damages especially at external events. Seismic probabilistic safety assessment method (Level-1 PSA) for multi-unit sites with up to 9 units has been developed. The models include Fault-tree linked Monte Carlo computation, taking into consideration multivariate correlations of components and systems from partial to complete, inside and across units. The models were programmed as a computer program CORAL reef. Sample analysis and sensitivity studies were performed to verify the models and algorithms and to understand some of risk insights and risk metrics, such as site core damage frequency (CDF per site-year) for multiple reactor plants. This study will contribute to realistic state of art seismic PSA, taking consideration of multiple reactor power plants, and to enhancement of seismic safety.     

Living PSA program: LIPSAS development for safety management of an LMFBR plant

During construction and subsequent operation of a nuclear power plant, many changes occur in components, systems and operating procedures, which continuously modify the configuration of the power plant. The unique ability of PSA techniques to effect of possible changes to baseline system configurations has been noted. A living PSA program can assess and manage safety-related operations and plant changes by adequately reproducing plant models and structured databases corresponding to the changes in system configuration. A living PSA system, LIPSAS, has been developed for the Japanese prototype liquid metal-cooled fast-breeder reactor (LMFBR), Monju, which is in the preoperation functional test stage. In order to utilize the LIPSAS as a risk management tool, equations for the schematic time history of the plant risk level and the relative risk criteria have been developed. Experience with LIPSAS shows that this program is a prospective tool to support decisions that affect plant safety, although a continuing and significant resource commitment of the operations staff at the site is still required.     

Micrometeorite and space debris simulation for columbus hull components

An experimental impact simulation program is currently performed with respect to Columbus hull components. The main objectives are to establish a data base for an optimum design of meteoroid/debris protection shields (MDPS) as well as viewport components, and to obtain input data for numerical models which describe the penetration and perforation processes of meteoroid bumper and viewport systems.

As expected, it has been experimentally demonstrated that protection against particles in the order of 1 cm, at relatively low impact velocities (around 3 km/s), is extremely problematic.

Applying usual dual-plate Al bumper techniques would require unrealistically thick and heavy systems in order to safety stop such particles, which are expected to occur within the low earth orbit space debris complex.

Preliminary results obtained with multiplate Al targets as well as hybrid target systems (Al-ceramics, Al-Kevlar) indicate that the situation can be considerably improved with respect to the shielding efficiency at a given areal material density.

These investigations are still in progress. Results of the test series performed with Al dual-plate systems and with laminated glass targets as viewport components are reported and discussed.     

Risk perception, safety goals and regulatory decision-making

Deciding on ‘how safe is safe enough?’ includes value judgements with implications of an ethical and political nature. As regulators are accountable to governments, parliaments and the general public, regulatory decision-making should be characterized by transparency with respect to how such value judgements are reflected in risk assessments and regulatory decisions. Some approaches in this respect are discussed in the paper, based on more than fifteen years of experience in nuclear regulatory decision-making. Issues discussed include: (1) risk profiles and safety goals associated with severe reactor accidents—individual health risks, societal risks and risk of losing investments; (2) risk profile-based licensing of the Swedish SFR final disposal facility for low and intermediate level radioactive waste.     

The rise and fall of nuclear power in the United States and the limits of regulation

This paper documents the rapid growth of nuclear power in the United States and its subsequent decline in the late 1970s. It demonstrates that the increase in numbers of new orders for nuclear plants created pressures for additional licensing complexity to insure safety and provide public intervenors with opportunities to participate in the regulatory process. The resulting protraction of the licensing process combined with increasing political opposition to nuclear power caused construction delays and bureaucratic bottlenecks at a time when soaring interest rates and double-digit inflation have pushed the cost of building new facilities out of the reach of the financially battered utility industry. Together with a downturn in demand for electricity and increasing uncertainty over nuclear power, no reactor orders have been placed since late 1978. It is argued that renewed growth of nuclear power in the United States is unlikely, especially in a regulatory environment which fosters increased costs of electricity to consumers and a simultaneous abrogation of the economies of scale. The consequences of the impending atrophication of the nuclear industry in America and its effects on future energy mixes and long-term national interests must be considered in future nuclear policies and reforms.     

Snow Leopard terminates Eltron agreement

Canada’s Snow Leopard Resources Inc has terminated its efforts to reach a definitive agreement with US company Eltron Research Inc on licensing sulphur mitigation technology developed by Eltron.This is a short news story only. Visit www.filtsep.com for the latest filtration industry news     

Development of a digital reactor control and protection system

For automation of routine monitoring and control duties and for retrofitting the aging control and protection system of the 33-year-old swimming-pool reactor SAPHIR at PSI, a digital data aquisition and control system, based on microprocessors with intelligent and remote multiplexing capabilities and strictly cyclic and deterministic signal processing is being developed.The implementation of this functionally and geographically distributed system leads to an improved man/machine interface and is welcomed by the Swiss regulatory authorities as a contribution to the nuclear qualification of digital reactor protection systems for future reactor facilities like district heating reactors or gas-cooled high temperature reactors. The demonstration and testing on an already operating research reactor with a proven, conventional protection system as a backup has the benefit of not being subject to the time critical licensing procedures for new reactors.