Search

The paper analyzes the prospects for using applied mathematical and algorithmic support for the study of the sealing ability of contact sealing connections of isolation valves. To ensure the operability of the equipment, it is necessary to determine the required level of sealing forces (contact pressures) that affect the weight and size characteristics of the product. The relevance of the study is related to the task of reducing the amount of time and material resources at the stage of design and experimental testing of pipeline fittings. The purpose of this work is to develop methods for automated assessment of the tightness of contact sealing connections to develop proposals for reducing the required level of contact pressures and weight and size characteristics of isolation valves. The paper presents an overview and analytical study of methods for determining the tightness of contact sealing connections, as well as a mathematical apparatus for modeling surface irregularities and defining sealing characteristics of isolation valve connections. An algorithm for evaluating these parameters has been developed, which modules can be further implemented as software for automating the assessment of the tightness of contact sealing connections at various stages of designing isolation valves. The developed algorithm makes it possible to filter out irrelevant sets of design parameters at the early stages of design without the need for their experimental verification, which will reduce the total amount of time and material resources in the development of isolation valves of pipelines.

Multiple failures of main steam isolation valve (MSIV) stem components have occurred at nuclear power plants. Stems are typically composed of ASM SA564 Grade 630 precipitation hardened steel, commonly known as 17-4 PH steel, in the H1100 condition. Several past valve stem failures have been attributed to thermal embrittlement, a condition under which the stem base material exhibits degraded mechanical properties due to microstructural changes induced by long-term exposure to a temperature range of approximately 260–316 °C (500-600 °F). Failure mechanisms of embrittled MSIV stems include sudden fracture due to loads from test actuations during plant outages as well as in-service fatigue crack growth (FCG) caused by vibrations from the steam flow. Three MSIV stems were removed from service after nine years in a pressurized water reactor (PWR) and were metallurgically and mechanically evaluated to determine the severity and extent of thermal embrittlement present. Findings from these evaluations were used to develop a condition-based projection of risk over time of the embrittlement-induced failure of the stems. It was found that the stem material removed from service did not exhibit significant metallurgical or mechanical evidence of embrittlement and that the probability of failure of the material in its current aged condition was small.

The isolation valves are crucial components of water distribution systems (WDS) that are used to shut down a segment of the network to repair or replace failed pipes. In this paper, an algorithm to...

In order to improve the safety and reliability of the Chinese nuclear power plants (NPP), an innovative passive nuclear safety design, the secondary passive residual heat removal system (SPRHRS) is proposed for the light water reactors in China. Previous research work has shown that under design-basis accidents, SPRHRS can mitigate the results by partially or completely replacing the traditional emergency water cooling system. However, the Fukushima Daiichi nuclear power plant accident implies necessity of further assessments of NPPs capability to withstand threats resulting from accidents beyond design-basis accidents. In this study, the nodalization of a 1000 MW class PWR with the SPRHRS design was conducted using RELAP5/MOD3.4. Responses of the PWR under the loss of heat sink accident caused by the station blackout (SBO) was analyzed. The results showed that the residual heat can be effectively removed by the SPRHRS under SBO. In addition, sensitivity studies about the effects of the coolant tank volume and the isolation valve opening condition of the SPRHRS on its residual heat removal capability were also performed. The results indicate that these two main design elements have significant influence on the operation characteristics of SPRHRS. For the SPRHRS design in this study, the appropriate value of the coolant tank volume is 400 m3 and the appropriate valve opening signal is set to be triggered when the SG shell side collapsed liquid level drops lower than 20% of its full value. The present work would be instructive for the design of passive safety systems of Chinese NPPs.

This paper describes the development and field deployment of a new downhole isolation valve system called the Retrievable, Instrumented & Tandem Downhole Deployment Valve (RIT-DDV). The purpose of this technology is to provide a temporary mechanical barrier to isolate and monitor the well during drilling operations in an environment where a full column of single-phase fluid cannot be maintained. The RIT-DDV is based on predominantly used downhole isolation valve (DIV) design and technology, which is a hydraulic flapper-type isolation device installed in the casing that seals the open hole during pipe tripping operations. The key features of the new RIT-DDV systems are dual flapper valves with three downhole pressure and temperature gauges to take measurements above, between, and below the flappers. The advantage of this configuration is that it enhances safety by enabling double-block-and-bleed system functionality, providing valve redundancy, and moreover allowing for continuous real-time monitoring of downhole well conditions. In addition, the RIT-DDV is designed to be reusable and can be tested upon installation and replaced if necessary. The RIT-DDV system enabled the operator to isolate and monitor the well while drilling through a depleted formation that prevented drilling with a full column of single-phase drilling fluid. The RIT-DDV was successfully trialed in western Kazakhstan and demonstrated the potential of this technology to enhance the safety of drilling heavily fractured carbonate formations with reservoir fluids containing hydrogen sulfide (H2S) / carbon dioxide (CO2) that are prone to total loss of circulation. The downhole pressure / temperature monitoring capabilities that the system provides within the casing string helped drill through the depleted fractured carbonate reservoir section without incurring non-productive time (NPT).

The main steam system is an important system connecting the primary and secondary loop of the nuclear power plant. It transports the steam generated by the steam generators to the steam turbine to drive the turbine to turn and do work. The main steam isolation valve (MSIV) is important safety devices in nuclear power plant. Its safety function is to automatically shut down under the accident condition of large break in the main steam pipe or main water supply pipe in order to limit the steam leakage and mitigate the consequences of the accident. The main steam partial shutdown test is a test to periodically verify the operability of the MSIV during the power operation of the nuclear power plant. The test period is usually once a month. However, during the test, there may be shutdown events caused by the mistakenly close of the MSIV, so the test is a high-risk periodic test. At the same time, due to the limitations of field condition and space, there are so many industrial risks and the risk of accidental collision leading to shutdown during the test. At present, the probabilistic safety analysis (PSA) is widely used in operation guidance, maintenance rules and many other fields of nuclear power plants. PSA has gradually developed into an important tool for safety evaluation and decision making. With the development and improvement of PSA technology, risk-informed safety management has been widely used. The this paper, the use of risk-informed PSA method to demonstrate the extension of periodic test period will be introduced. And taking FJS Nuclear Power Plant as an example, the extension of the periodic test period of the partial closing test of the MSIV is demonstrated.

The main steam isolation valves are safety valves installed in nuclear power plants designed for high energy line break of the steam pipeline, the main steam collector or the steam generator feedwater pipeline. During the regular shutdowns, the radial cracks regularly situated around the circumference in hardfacings of wedges were observed some of which were assessed as non-permissible. The primary objective of the solution is to develop and verify a suitable methodology, based on which it will be possible to decide on the operability of wedges. However, the solution aims at the potential risk prediction of brittle fracture or fatigue cracks growth under the operational loading during the period between regular diagnostics or until the end of the planned service life of the valves. The paper deals with the computational analysis of cracks focused mainly on the abovementioned fracture failures. It is also dedicated to comparing the acquired results from the analyses computed by finite element method (ANSYS) with classical analytical models and experimental testing, respectively.

The functional requirements of Main Steam Isolation Valves (MSIVs) provided in the Boiling Water Reactor (BWR) nuclear power plants in Japan have been previously evaluated via seismic tests and so forth. However, since the response acceleration has increased in line with a recent reassessment of standard earthquake ground motions, it is necessary to evaluate seismic operability with respect to high acceleration. In addition, from the viewpoint of equipment fragility in seismic PRA, it is necessary to determine practical seismic operability limits. We used a resonant shaking table in the Central Research Institute of the Electric Power Industry (CRIEPI), which is capable of seismic tests at acceleration levels previously unachievable, and in seismic tests carried out on an MSIV, we obtained results confirming that validated seismic operability was possible even at response accelerations as high as 15 × 9.8 m/s2. The seismic operability results obtained for this MSIV will be applied to a fragility analysis of seismic PRA.

This study investigates the effect of applying scenario-based phase designs for isolation valve installation by developing an optimal multiphase valve design model while previous research f...

The current paper reports on a case study investigating water distribution system management in emergency conditions when it is necessary to seal off a zone with isolation valves to allow repair. In these conditions, the pressure-driven analysis (PDA) is considered to be the most efficient approach for the analysis of a water distribution network (WDN), as it takes into account whether the head in a node is adequate to ensure service. The topics of this paper are innovative because, until now, previous approaches were based on the analysis of the network behaviour in normal conditions. In emergency conditions, it is possible to measure the reliable functioning of the system by defining an objective function (OF) that helps to choose the optimal number of additional valves in order to obtain adequate system control. The OF takes into account the new network topology by excluding the zone where the broken pipe is located. The results show that the solution did not improve significantly when the number of valves reached a threshold. The procedure applied to other real case studies seems to confirm the efficiency of the methodology even if further examination of other cases in different conditions is necessary.

The ITER project is under construction in Cadarache, France, to assemble and operate an experimental nuclear fusion facility. The aim of this paper is the description of the implementation of the French Order of February 7, 2012, concerning Basic Nuclear Installation (also called “INB” Order) [1] within the European Union Domestic Agency (EU-DA), specifically on the Electron Cyclotron Upper Launcher (EC UL). The EC UL will be used for the control and heating of the ITER plasma. The launcher includes the port plug and related in-vessel items (nuclear shielding, blanket module, and optics) and the ex-vessel first confinement items (diamond window, isolation valve, waveguides, miterbends, tapers and port plug back end).

The equipment capability curve is one of the bounding elements of the freeze-drying design space, and understanding it is critical to process design, transfer, and scale-up. The second bounding element of the design space is the product temperature limit beyond which the product collapses. The high cost associated with freeze-drying any product renders it crucial to operate using the most efficient cycle within the limits of the equipment and the product. In this work, we present a computational model to generate the equipment capability curve for 2 laboratory scale freeze-dryers and compare the results to experimentally generated equipment capability curves. The average deviations of the modeling results from the experiments for the 2 lyophilizers modeled are −4.8% and −7.2%. In addition, we investigate the effect of various numerical and geometric parameters on the simulated equipment capability. Among the numerical parameters, the chamber wall thermal boundary conditions exert the largest influence with a maximum value of 12.3%. Among the geometric parameters, the inclusion of the isolation valve reduces the equipment capability by 23.7%. Larger isolation valves, required for controlled nucleation technology, choke the flow in the duct at lower sublimation rates, thereby lowering the equipment capability limit.

In the present work, the conventional chemical oxygen iodine laser (COIL) source has been technologically upgraded and successfully tested after implementation of decoupling interface between laser cavity and resonator. In the technique, anti-reflection coated fused silica windows mounted in suitable mechanical assemblies are placed between resonator mirrors and laser cavity in such a way that the generated laser beam is out coupled through the resonator during the laser operation. The implemented decoupling assemblies isolate the caustic environment produced in low pressure laser cavity from that of resonator mirrors. Thus requirement of using isolation valves and cavity limbs between laser cavity and resonator as in conventional COIL source is eliminated. Such decoupling mechanism therefore effectively reduces the number of associated components as well as overall length of the laser source which in turn further reduces the overall weight of the laser making it suitable for use onto a mobile platform. Moreover the technique provides accrued benefits in terms of reduction in readiness time and checking of optical alignment of the laser source at will in practical operation scenarios.

Anticipated Transients without Scram (ATWS) are evaluated to demonstrate the capability of the barriers to prevent fission product release. Swiss nuclear authority guidelines allow the use of best-estimate codes and methodologies for beyond design basis events analyses, such as ATWS, to simulate more realistic plant responses. Thus, realistic initial and boundary conditions may be applied so that all systems unaffected by the event are credited and no independent single failures need to be assumed. The RELAP5-S3K coupled thermal-hydraulics/neutronics code was used for KKM (Muhleberg BWR-4 NPP) ATWS analyses. The KKM RELAP5-S3K model was demonstrated to be valid for a wide range of transients including Loss of Coolant Accident (LOCA) and ATWS. Two ATWS cases, a main steam isolation valve (MSIV) closure and a loss of offsite power (LOOP), were simulated to demonstrate the KKM plant capability. The MSIV closure is a limiting ATWS event for reactor pressure vessel (RPV) overpressure and torus pressure and temperature. After closure of the MSIV, all RPV outlet flow is directed to the torus through the safety relief valves resulting in limiting torus pressures and temperatures comparable to other events. The LOOP event can be a limiting ATWS event for peak cladding temperature (PCT) if insufficient makeup water is available. The simulation results showed that the ATWS acceptance criteria for PCT, reactor peak pressure, and torus temperature and pressure are satisfied. The RELAP5-S3K results have been compared to the ATWS results from KKM’s fuel vendor, General Electric-Hitachi (GEH), using their TRACG code (TRACG being perhaps the most advanced system code available for BWRs). The plant response predicted by the RELAP5-S3K model is similar to that reported by GEH. Variations between the two are attributed to (1) code differences in modeling of the physical phenomena and (2) different levels of detail in modeling the KKM plant and core parameters, e.g. cross-sections. Considering that an independently developed model using the RELAP5-S3K code predicts plant behavior during an ATWS similar to the state-of-the-art code TRACG, it is concluded that the KKM ATWS analysis with RELAP5-S3K provides trustworthy information for comparison against safety criteria.

Isolation valves are critical for reliable functioning of water distribution networks (WDNs). However, it is challenging for utilities to prioritize valve rehabilitation and replacement given it is often unclear if certain valves are operable in a given WDN. This study uses the Gomory-hu tree of the segment-valve representation (or dual representation) of WDNs to obtain logical implications of inoperable valves (i.e., which segments would be isolated and merged unnecessarily due to valve inoperability). Multi-objective optimization is then used to identify the critical valves based on selected attributes (e.g., social vulnerability, flow volume) of segments that would be unnecessarily isolated as a result. This study developed three multi-objective formulations: first, deterministic; second, accounting for uncertainty; and third, accounting or both uncertainty and likelihood of failure of pipes within segments. Identified critical valves are compared between the three developed formulations and a method considering only a single objective. Results demonstrated that the multi-objective optimization provided additional information that can be used to discern valve importance for utilities in comparison with using a single objective. Further, though there was overlap between the results from the three formulations, the third formulation provided the most insight without overwhelming decision-makers with a large number of identified valves.

Because consideration of segments and valves is essential for evaluating the reliability and resilience of water distribution networks (WDNs) when shutdowns are required, a quick method of ...

An intervention operation in the Gulf of Mexico used a novel method with an electric-line powered shifting tool to reliably locate and latch onto the shifting profile of the intended completion isolation valve successfully completing the shifting operation. Locating and latching onto the lower shifting profile of a completion isolation valve is often a challenging operation with slickline or conventional electric-line shifting tools. It relies on the weight of the downhole tool to provide the downward force to drive the shifter to latch onto the shifting profile. Numerous parameters such as the well deviation, the friction force of the shifter keys with the tubing, and the pull from the cable highly affect this downward force. Accurate positioning of the downhole tool with respect to the completion is even more challenging in deep water wells because the long cable stretch can result in several feet of uncertainty. The novel method used in this operation consisted of using the shifter, linear actuator, and anchor modules to move in an inchworm motion after tagging the closed ball valve. The tag was used as a reference point to accurately locate the position of the shifter with respect to the valve opening shifting profile. While moving toward the profile, the position of the shifter was maintained at all times using the accurate linear position measurement of the tool. The linear actuator has a limited stroke, but it can be compounded to achieve a much longer measurement. Because the tag position of the shifter was only a few linear actuator strokes away from the opening profile, the operation was extremely efficient. The intervention operation was successfully completed in a few hours using this method. The signals were measured downhole and reported in real time to surface, enabling accurate monitoring of the progress and indicating the position of the tool with respect to the valve opening profile at all times. While moving toward the profile after tagging the ball, the shifter was used to probe for diameter changes. This measurement provided an additional confirmation of the position of the shifter, which was able to sense passing through the profile. Finally, after passing the profile and reversing direction, a controlled increase in the linear actuator axial force confirmed the latch onto the opening profile. This seek method enabled latching onto the opening profile and confirmed without doubt that the shifter keys were engaged in the profile before proceeding to increase the forces to shift the ball open. While the ball valve was shifted open, the downhole measurements recorded an axial force vs. displacement footprint that is characteristic of the opening of the ball valve, giving confirmation that the operation was successfully completed without having to physically pass through the ball valve to confirm. This was the first time that this method, consisting of moving in an inchworm motion after tagging the ball, had been used for locating and latching onto the shifting profile of a completion isolation valve. This novel method eliminated uncertainty from conventional methods that use the cable overpull and head tension as a latch indicator.

The number of isolation valves installed in a water distribution pipe network is typically based on conservative rules of thumb that have been propagated throughout the water industry. Howe...

Currently, for the EU DEMO, two Breeding Blankets (BBs) have been selected as potential candidates for the integration in the reactor. They are the Water Cooled Lithium Lead and the Helium Cooled Pebble Bed BB concepts. The two BB variants together with the associated ancillary systems drive the design of the overall plant. Therefore, a holistic investigation of integration issues derived by the BB and the installation of its ancillary systems has been performed. The issues related to the water activation due to the 16N and 17N isotopes and the impact on the primary heat transfer systems have been investigated providing guidelines and dedicated solution for the integration of safety devices as isolation valves. The tritium retention and the permeation rates through the blanket and its ancillary systems have been also assessed taking into account different operating points both for the BB and ancillaries and comparing, when possible, the releases with the operating and safety limits. Moreover, the issues related to the tritium start-up inventory as well as the uncertainties on the Tritium Breeding Ratio (TBR) due to the integration of the auxiliary systems within the Vacuum Vessel have been also studied. Finally, the impact of the BB concepts on the safety systems like the Vacuum Vessel Pressure Suppression System is described with a particular focus on the different measures that should be implemented according to the considered concept. All these aspects are then taken into account to drive future developments during the Concept Design Phase., peer-reviewed

En este trabajo se propone una metodología para la sectorización óptima de redes de distribución de agua impulsadas por bombas y, además, se analiza el rendimiento de las soluciones obtenidas. El algoritmo de sectorización consta de dos etapas. La primera se plantea como un problema de optimización de múltiples objetivos y consiste en identificar una estructura de comunidades que privilegian la conectividad interna sobre la externa. La segunda etapa consiste en determinar la ubicación óptima de los dispositivos a instalar (válvulas y caudalímetros) en los cortes virtuales establecidos en las soluciones de la primera etapa. Para analizar el rendimiento de las soluciones se evalúa la variación del índice de resiliencia frente a incrementos en las demandas de un número fijo de nodos para cada una de las configuraciones de sectorización obtenidas.

Water network partitioning (WNP) represents an efficient strategy to improve management of water distribution networks, reduce water losses and monitor water quality. It consists in physically dividing of a water distribution network (WDN) into districted metered areas (DMAs) through the placement of flow meters and isolation valves on boundary pipes between DMAs. In this paper, a novel methodology for designing DMAs is proposed that provides districts with quite similar node elevations and minimizes the number of boundary pipes in order to simplify pressure management and reduce the number of devices to place into the network.

Subsurface barrier valves such as a formation isolation valves (FIVs) isolate the formation from the production bore after the first perforation and the lower completion has been installed. This enables installation of the upper completion and in some cases multiple perforation runs before the well starts producing. During this time, they protect the formation from fluid loss and pressures by acting as a bi-directional fluid barrier. In addition to reduced rig time, a key advantage of FIVs is reduced intervention costs. FIVs can be openend and closed multiple times as required, mechanically with an intervention tool such as a primary shifting tool (PST) (Fig. 1). The conveyance method for PSTs can be on coiled tubing, work string, perforating string, or wireline (using a tractor and stroker) to open and close FIVs. PSTs then must reliably engage and release from shifting profiles in the FIVs to operate the valve and release from the profile after successful valve actuation. Hence design of the PST is critical for relaible FIV operation. In the event of an emergency where the shifting profile in the tool is unable to release from the engaging profile in the FIV, it is critical to have an emergency release feature inherent in the PST that can enable release of the tool yet not damage the FIV. A novel methodology was developed to design PSTs to enable emergency release if required, through controlled plastic deformation at loads below work string shear limitation. This methodology also avoids fracturing of PST components as free-hanging pieces could be caught in the wellbore while pulling out the tool from the well after emergency release.

Within the framework of the activities foreseen by the EUROfusion action on the cooling water activation assessment for a DEMO reactor equipped with a Water Cooled Lithium Lead Breeding Blanket (WCLL BB), the University of Palermo is involved in the assessment of dose rates induced by the decay of nitrogen radioisotopes produced by water activation, nearby the main components (e.g. isolation valves) of both First Wall (FW) and Breeder Zone (BZ) cooling circuits. In particular, the aim of this work is to evaluate the spatial distribution of nitrogen isotopes (16N and 17N) in the WCLL BB cooling circuits. To this purpose, a coupled neutronic/fluid-dynamic problem is solved following a theoretical-numerical approach and adopting an integrated computational tool mainly relying on the use of MCNP6 and ANSYS CFX codes. The operative procedure adopted foresees the assessment of the production rate distributions of nitrogen isotopes within FW and BZ cooling channels and tubes by means of totally heterogeneous neutronic analyses. A fully 3-D fluid-dynamic approach is, then, used to compute the nitrogen isotope concentrations within the In-Vessel complex flow domain, while a 1-D lumped parameters approach is adopted to calculate their distribution along the Ex-Vessel BB Primary Heat Transfer System. The results obtained, herewith presented and critically discussed, provided the necessary data to perform dedicated neutronic and photonic transport analyses and, hence, to assess the dose rates in the aforementioned target locations.

As DEMO is the first European device planned to produce electricity from fusion, the volume of its Primary Heat Transfer Systems (PHTS) will be consistently larger if compared to present or next-generation tokamaks such as ITER. The consequences of an in-vessel Loss-Of-Coolant Accident (LOCA) would then be more important, and within the EUROfusion Consortium different possible mitigation measures are being investigated. Among these, the introduction of Isolation Valves (IsoVs) on the main cooling loops of the Breeding Blanket is being considered, in view of the many benefits they would introduce, not only in case of accidents, but also e.g. during the maintenance of the in-vessel components. Fast-closing IsoVs on the PHTS would help in relaxing not only the requirements of the VV pressure suppression system (VVPSS) design, but also those related to the expansion volumes that shall accommodate the contaminated coolant discharged from the PHTS after a LOCA. In the present work, the GETTHEM code, the system-level thermal-hydraulic model developed for the EU DEMO at Politecnico di Torino, is used to assess the beneficial effects of the introduction of the IsoVs. The effects of the actuation time of the IsoVs and of their location are parametrically investigated, considering both water and helium as PHTS coolants, with particular reference to the reduction of the in-vessel space-averaged pressure and of the suppression system size.

In the frame of the EUROfusion consortium activities the Helium Cooled Pebble Bed (HCPB) and the Water Cooled Lithium Lead (WCLL) concepts are being developed as possible candidates to become driver Breeding Blanket (BB) for the EU DEMO, which aims at the tritium self-sufficiency and net electricity production. The two BB design options encompass water or helium as coolants and solid ceramic with beryllium/beryllides or PbLi as tritium breeder and neutron multipliers. The BB segments have evolved towards a more stable conceptual design taking into account multiple feasibility aspects and requirements imposed by interfacing systems. Possible solutions to improve shielding capabilities of Helium cooled BB are investigated and the impact of water coolant activation is assessed by studying the spatial distribution of 16N and 17N isotopes dose rates, in particular in proximity of isolation valves. The reference and back-up technologies for the Tritium Extraction and Removal (TER) from the helium purge gas and the PbLi are developed addressing key feasibility aspects and implications on the tokamak layout and with considerable R&D efforts. As the BB internals offer an ideal environment (high temperatures, thin structural material) to promote the tritium permeation, studies are devoted to establish a tritium balance in the different systems during operation, with special care to the permeation rate and inventory in the coolant. Those are the key parameters for the feasibility assessment and technology selection for the Coolant Purification Systems (CPS).

An inspection and replacement policy for a protection system is described by a mathematical model that incorporates multiple aspects of maintenance quality. A three-state component failure model is assumed, with a defective state preceding failure. The quality of maintenance intervention is modelled by supposing that inspections may misclassify defects (false positives and false negatives) and further that an inspection may induce a defect. The quality of replacement is modelled by supposing that a component arises from a heterogeneous population, composed of weak and strong items and with the mixing parameter determining quality. Isolation valves used in water distribution systems motivate the model development, and a case study is considered in this context. We evaluate the impact of these aspects of the quality of maintenance upon cost and production losses. Defect induction is found to be a key determinant of the cost-optimal policy. The proposed model allows us to verify conditions that justify investment in higher quality maintenance, and thus to provide guidance for prioritization of this investment.

A Quantitative Microbial Risk Assessment model was developed to assess the infection risk due to faecal contamination events after repairs of drinking water mains. Ingress was modelled per section between isolation valves; transport of pathogens and consumed dose were modelled with a hydraulic network model and stochastic drinking water demand patterns. Dose response models were then used to calculate the risk of infection. The sensitivity analysis showed that the contamination concentration is the most important parameter for the ingested dose, while the choice of dose response relation highly impacts the resulting infection risk. The time of day that valves are opened after repairs, releasing the contamination, in combination with the time that drinking water is withdrawn from the tap influences the amount of contamination consumed versus flushed away through non-exposure uses such as toilet flushes and showering. A standard QMRA approach that typically neglects the diurnal consumption pattern may underestimate the risk. The consumption volume is less important. Issuing a boil water advice and opening only one valve before “releasing” the isolation section are effective mitigation options to reduce the infection risk per event by 50% to 80%. The statutory Dutch sampling protocol requires E. coli analysis of a 100 ml sample taken the day after the repair. The modelled probability of detecting a contamination under these circumstances is approximately 25%, because the contamination rapidly leaves the drinking water distribution system through the customers’ taps, toilets and showers. If a sample is taken 1–4 hours after the repair the modelled probability of detection exceeds 80% when taken at the optimal location.

An embodiment of the structure and control algorithm of the isolation valve of multi-section mobile car refueling. It is shown that this option provides the most energy efficient and rational option for refueling consumers. The calculation of the most rational pressure, number and volume of sections is performed. The algorithm of control is based on the modified algorithm of multicriteria selection of the Edgeworth-Pareto.

There is a safety hazard in the interlock control logic of the second circuit main steam isolation valves of the CPR1000 nuclear power unit. During reactor power operation, any abnormal full-close limit switch signal of valves may lead to a reactor shutdown event or even a Safety Injection of nuclear reactor. In this Paper, the control strategy of the second circuit main steam isolation valves is analyzed and demonstrated, and after Probabilistic Safety Assessment(PSA), a feasible improvement plan is proposed, which effectively improves the control reliability of the second circuit system in nuclear power plants.

All advanced NPPs are required to improve safety strategy to cope with design extension condition (DEC) after Fukushima accident. One design improvements for HPR1000 is adoption of secondary Passive Residual Heat Removal System (PRS) to cope with station blackout accident together with loss of all feedwater, which can help to strengthen defense in depth capability and enrich DEC mitigation measures. To make the best use of PRS decay heat removal capability, investigation of PRS startup performance and decay heat removal capability after MFLB accident are investigated based on HPR1000 RELAP5 model. PRS startup response featured by pressure, mass flow rate and void fraction are investigated under three startup strategies. Strategy 3(backflow valve open strategy) is recommended due to minimum fluctuation during initiating stage, in which strategy steam isolation valve is normally open and backflow isolation valve is used to initiate PRS. Then Main Feedwater Line Break (MFLB) accident was simulated with the assumption of loss of auxiliary feedwater. Response characteristics in primary loop and PRS are investigated. After PRS being initiated after scram with 60 s delay, natural circulation in PRS will establish rapidly, and decay heat will be removed under natural circulation operation mode. No overall boiling occurred in primary circuit before isolation of affected SG. Secondary PRS is adequate to remove decay heat after DEC.

The ITER Electron Cyclotron Heating Upper Launcher (ECHUL) will be used to drive current locally inside magnetic islands located at the q = 2 (or smaller) rational surfaces in order to stabilize neoclassical tearing modes (NTMs). Each of the fours antennas consists of eight beam lines, totaling 12.8 m that are designed for the transmission of up to 1.5 MW of mm-wave power at 170 GHz, with at least 90% of the power in the main HE11 mode. Each transmission line consists of a Z shaped set of straight corrugated, aluminum alloy waveguides connected by miter bends with a nominal inner diameter of 50 mm. The FCS system also encompasses intrinsic components such as: closure plate, mm-waveguide taper, isolation valve, diamond window and an EU-US interface waveguide. All FCS components are connected via a dedicated flange coupling, with a bolted connection, comprising of two concentric metallic seals in order to satisfy the SIC-1 requirements. The coupling shall be capable of resisting the applied external loads and displacements, including thermal cycles due to ohmic losses in the transmission line, and also adhere to the matting of different materials (EN AW-6082, CuCrZr, SS 316L) while maintaining ultra-high vacuum tightness (10 −8 mbar). The present study will use a dedicated experimental apparatus for the characterization of the mechanical and vacuum properties of a single metallic seal under compression, with applied heat flow. In order to ensure reproducibility of the components mechanical characteristics, randomly chosen metallic seals of each diameter have been tested from two independent manufactures (A and B).

Dividing a water distribution network (WDN) in the optimal district metered areas (DMAs) formation is one task that usually troubles water utility managers. The present paper utilizes optimization methods to achieve desired segmentation conditions in terms of (a) operating pressure reduction, thus reducing the system's real water losses and (b) residual chlorine concentration reduction thus preventing disinfection byproducts' growth. Exploiting the numerous possibilities offered by the inter-connection of Matlab and EPANET software tools, an algorithm is developed in C++ language. The algorithm reads all significant data of a WDN as an output of EPANET. The first algorithm calculates the optimal allocation of a given number of closed isolation valves in terms of water losses' reduction, considering restrictions for network's proper operation. The second algorithm calculates the optimal formation of DMAs in terms of water quality improvement. Both algorithms can be applied in any WDN. The outcome is the optimal set of closed pipes that leads to the optimal formation of DMAs in a given network. The closing of pipes (by installing isolation valves) determines the optimal formation of DMAs. The basic concept of both algorithms and their application in a case study network's hydraulic model are presented.

The driving device of the main steam and feed water isolation valves is one of the most important electromechanical equipment in nuclear power plants, and its motion performances are related to the safety of nuclear power plants. This article proposes an optimization methodology to research the motion performances. In the methodology, inputs are the motion performance indexes and the major influencing parameters with no need for complex mathematical models of the electromechanical equipment; the co-simulation model or the prototype are adopted to illustrate the influence rules of major parameters on the motion performance indexes; objective functions for optimization, which combine motion performances with weight factors, can reveal the influence rule curves. Then based on the methodology, motion performances of the equipment are analyzed and the key indexes are selected. Besides, the maximum pressure of the driving device is chosen as the major parameter and a dimensionless objective function synthesizing the motion performance indexes is proposed. Finally, the influence rule curve where the dimensionless function varies with the maximum pressure is obtained by the co-simulation and the experimental study on the prototype verifies the results, which provides references for the further research and development in the engineering application. For other electromechanical equipment, the method is an efficient tool to design, verify, and optimize the performances.

The simulation of hydraulic behaviour of water distribution networks (WDN) needs to develop and implement a mathematical model that is able to consider a wide range of control devices of complex systems. A literature overview is primarily provided for the solution procedures of steady state simulation of nonlinear pipe network hydraulics. Typical elements of pressure regulating valves are conceptually described and differentiated into their functional characteristics to incorporate their hydraulics in the simulation model. They are explored by considering their possible topological positions and operating states. A novel efficient methodology using an unknown head-loss function is initially presented for the hydraulic simulation of network flow problems containing static and/or dynamic closed pipes. Closed pipes can be mainly obtained in the distribution networks either by turning off the isolation valves at a pipe segment or as a result of the operating state of unidirectional control devices depending on the pressure distribution in the pipe network. Thereupon, this approach is extended to integrate the control elements of pipe networks such as check valves, pressure reducing (PRV) and safety valves as well as booster/pumping stations. An iterative numerical algorithm is applied to solve the loop equations using the Newton-Raphson method for the linearised energy equation, where Hardy-Cross technique is locally used to correct flow rates of loops containing closed pipes in the iteration procedure. The developed hybrid approach demonstrated robust and very fast converging behaviour for real-world pipe network applications. Moreover, it can consider a variety of combinations of control devices in different network configurations. Several empirical head loss formulas can be additionally used in combination with the commonly known equations such as Hazen-Williams and Colebrook-White head loss formulas. The application of the algorithm will be briefly demonstrated by discussing some simulation results from example and real world large scale WDN.

This paper proposes a model of inspection of a\ud protection system in which the inspection outcome provides\ud imperfect information of the state of the system. The system itself is required to operate on demand typically in emergency situations. The purpose of inspection is to determine the functional state of the system and consequently whether the system requires replacement. The system state is modeled using the delay time concept in which the failed state is preceded by a defective state. Imperfect inspection is quantified by a set of probabilities that relate the system state to the outcome of the\ud inspection. The paper studies the effect of these probabilities on the efficacy of inspection. The analysis indicates that preventive replacement mitigates low quality inspection and that inspection is cost-effective provided the imperfect-inspection probabilities are not too large. Some derivative policies in which replacement is “postponed” following a positive inspection are also studied. An isolation valve in a utility network motivates the modeling.