Operational Safety Requirements Research Articles

Protecting Remotely Located Motors: Application Issues and Solutions to the Technical Challenges

The basic goals of motor protection are allowing the motor to operate as close to thermal limits as possible and isolating the motor when actual failures occur. The basic principles for performing this protection are well known. In most installations, the motor is located close to the protective relay and interrupting device, be it a contactor, starter, or circuit breaker. However, the motor may sometimes be located remotely from the protective relay due to the needs of the physical process or due to operational safety requirements. Distances of 1,0002,000 ft between the motor location and the protective relay are common. This large distance does not change the motor protection used, but it does require careful application engineering to ensure reliable protection performance.

Analysis on Strength, Stiffness and Stability for Shippment Structure of Hull Subsection

In allusion to the safety problems of the shippment structure of hull subsection at area B in a Shipyard Co., Ltd., Guangdong, in this paper, a solid model for a proposed shippment structure of hull subsection was established by using a finite element software ANSYS which is a common software, the internal force (stress), deformation and stability of components under various actual working conditions were calculated, and then the checks of strength, stiffness and stability were performed on the basis of the national regulations. The results show that both strength and stability can meet the safety requirements of operation, but stiffness is insufficient, because the horizontal displacement of steel pillars in shippment structure oversteps the specified value of the national standards of China. The conclusion provides a theoretical foundation for the safety use of shippment structure of hull subsection and the optimization and improvement of the structure.

Configuration and operation of detritiation systems for ITER Tokamak Complex

The ventilation systems design for the ITER nuclear buildings ensures radioactive contamination is confined so that workers, the public and the environment are protected. Nuclear buildings are divided into confinement sectors which connect to the Heating, Ventilation and Air Conditioning (HVAC) system and detritiation system (DS). The Tokamak Complex DS provides centralized air purification for the building confinement sectors. A distributed arrangement of ventilation piping provides networks necessary for two key functions, these being Vent Detritiation (VD), to maintain sub-atmospheric pressure, and Air Detritiation (AD) to collect tritium released into the confinement sector. For the VD function, air extracted from the particular confinement sector is directed to the DS for processing prior to exhaust to the environment. This paper presents the configuration of the DS of the Tokamak Complex and addresses details of the design of the distributed piping network. Dynamic flow and pressure drop modelling has been applied to support the development of the system configuration and provide data for sizing the system and selecting components. Further design development is discussed in view of the safety requirements for operation of the system during design basis events such as earthquake or fire.

Importance measures-based prioritization for improving the performance of multi-state systems: application to the railway industry

The railway industry is undertaking significant efforts in the application of reliability-based and risk-informed approaches for rationalizing operation costs and safety requirements. In this respect, importance measures can bring valuable information for identifying the actions to take for most effective system improvement. In this paper, the railway network is modelled within a multi-state perspective in which each rail section is treated as a component, which can stay in different discrete states representing the speed values at which the section can be travelled, depending on the tracks degradation and on the traffic conditions. The Monte Carlo method is used to simulate the complex stochastic dynamics of such multi-state system. A prioritization of the rail sections based on importance measures is then used to most effectively improve the performance of the rail network, in terms of a decrease in the overall trains delay. High-importance sections, i.e. with highest impact on the overall delay, are considered for a relaxation of their speed restrictions and the proposed changes are then verified, from the risk-informed perspective, to have negligible impact on the risk associated to the rail infrastructure.

The Mrázovka tunnel in Prague before completion

Prague, the capital of the Czech Republic, lies in the heart of Europe. It is exceptional not only by its beauty, but also due to the fact that the planned system of main urban roads has not been completed yet. Currently the most topical issue is the Mrazovka tunnel being in the process of completing the works, with the scheduled inauguration in August 2004. The Mrazovka tunnel is 1300 m long in total. It consists of two tubes with one-way traffic (the ETT and WTT). Three-lane mined tunnels form the major part of the tunnel structure. In terms of length and cross sections, the Mrazovka tunnel tubes are the largest and technically most difficult project implemented till now in the Czech Republic using the New Austrian Tunnelling Method. The difficulty followed from the longitudinal profile of the tunnel route, the geology encountered and existence of residential buildings above the tunnels. The most difficult sections of the drive were the three-lane tubes at the portal North under Mrazovka Hill, the excavation under the buildings existing at locations with shallow rock cover, and the excavation of bifurcation chambers with a cross section up to 324 m2. The tunnel excavation and primary lining were completed in April 2002. Casting of final lining started in April 2001, the work was finished in August 2003. In terms of the approved traffic study, various profiles of the mined tunnels, i.e., profiles for three-lane and two-lane tunnels, bifurcation chambers, tunnel ramps and cross passages had to be carried out at the Mrazovka tunnel. The structural design of the final liner was significantly affected by the longitudinal profile of the tunnel too. It called for application of a closed waterproofing system and for the liner proportioning counting with a full hydrostatic head from groundwater level found up to 30 m above the tunnel crown. The waterproofing is provided along the entire circumference of all mined profiles. In terms of structural analysis the most interesting were the design of final lining of the three-lane tunnel with the slab under the roadway participating in a composite action with the liner as a tension member, and the design of final lining for a bifurcation chamber having an internal width and height of 20.5 and 11.4 m, respectively. The original design of equipment for the Mrazovka tunnel was elaborated in compliance with recommendations and conclusions of the PIARC conferences held in Marrakechi in 1991 and in Montreal in 1995. At the time when the design had already been completed, the contractor selected, and civil and mining work on the Mrazovka tunnel started, the opinion on the active and passive operational safety in road tunnels changed substantially all over the world. This change took place in the nineties, after several conflagrations in tunnels with catastrophic consequences. For the above reason the already designed Mrazovka tunnel equipment had to be redesigned. The new system designed was based on the requirement for intensive evacuation of smoke from the fire vicinity, within a length of about 400 m. The PIARC recommended suction performance for a three-lane tunnel was 120 m3/s in 1999. Functionality of the newly designed system was verified by mathematical and physical modelling. A study on operational safety in tunnelled sections of the City Ring Road in Prague was developed in 2002, using acknowledged world-wide parameters. It proved that the operating Strahov tunnel, Zlichov tunnel, the Mrazovka tunnel being currently completed, and the other three tunnels on the City Ring Road being designed, satisfy the operational safety requirements. Currently the Mrazovka tunnels are in the phase of equipment installation. The required term of bringing the Mrazovka tunnel into service is August 2004. (A). Reprinted with permission from Elsevier. For the covering abstract see ITRD E124500.

Dependability and Safety for Megajoule Laser Operations and Maintenance

Risk assessment of a complex system that uses new technologies is described: the MegaJoule Laser (LMJ). The steps to obtaining the safety and security goals for LMJ are highlighted, i.e., to ensure safe operation, to put in place detection systems and means to prevent or limit serious accidents, and to limit the consequences to the environment and the workers. The objective is to show what has been done during LMJ design and construction to prevent serious accidents during routine operations and maintenance.The risks during operations and maintenance of the LMJ facility are identified by a preliminary risk analysis. The safety management to address adequately the protective features is described. As an example, a main accidental scenario in the LMJ target area is emphasized: workers’ exposure to hazardous levels of nuclear radiation. The LMJ operation and maintenance safety requirements that must be taken into account by the industrial firms to which LMJ contracts have been awarded are discussed.

Roughness growth on tread-braked railway wheels: e u r o s a b o t theoretical studies

Rail and wheel surface irregularities are the main source of rolling noise. One of the main causes for wheel surface roughness is tread braking. Wheels braked by the most common tread brakes—cast iron blocks—have high roughness levels and, as usual, corrugation with wavelength of 30–100 mm. The Brite Euram research project EUROSABOT deals with new solutions for tread brakes, which would lower the roughness level, prevent the buildup of periodic roughness, and consequently reduce the rolling noise, and at the same time would follow the safety requirements of railway operation. Field measurements, discussed in detail by Stefan Buehler in a companion presentation, in parallel with laboratory studies has distinguished that the interaction of thermo-elastic and vibrational instabilities is the main reason for corrugation generation. Computer simulations describing simultaneously thermodynamical, structural, and acoustic processes of the braking operation have proved to be unpractical for parametric studies and, instead, several simplified models are used. These models have shown that the main parameters affecting roughness growth are Young’s modulus and coefficient of thermal expansion of the block material and damping of the system.

Portable instantaneous mass monitor for coal mine dust.

A battery-operated portable coal mine dust mass monitor has been developed based on the measurement of beta-radiation absorption by the aerosol particles collected by inertial impaction on a thin polyester film substrate. The nonrespirable fraction of the dust is retained by a cyclone precollector, and the respirable particles, down to almost 0.4 µm in diameter (unit density), are collected by the impactor mass-sensing stage. Each measurement-sampling run is performed in 1 minute, at the end of which the mass concentration (milligrams per cubic meter) during that period is displayed automatically on a digital semiconductor readout. The displayed output is proportional to the ratio of the logarithms of the initial to the final beta-pulse rate resulting in a measurement that is independent of beta-source decay, variations of substrate thickness and barometric pressure, changes in detector sensitivity, etc. The mass concentration range of the instrument is 1 to 50 mg/m3, at a sampling flow rate of 2 liters/min. Timing and signal processing are performed by means of solid-state analog-digital circuitry. The instrument is designed to meet the U.S. Bureau of Mines intrinsic safety requirements for operation in coal mine environments.

Interior Arrangements

THE basic layout of the Trident flight compartment is designed to facilitate the eventual introduction of a fully automatic landing system, ‘Autoflare’ being the initial step towards this concept. Close collaboration has been maintained from the project stage with pilots and engineering staffs of airlines specializing in short/medium haul networks. The result is a flight compartment which is simple, spacious and adequately meets the operational safety requirements of a high speed civil airliner designed to achieve all‐weather utilization.