Plant Shutdown Research Articles

How Dependent Are European Power Systems and Economies on Natural Gas?—A Macroeconomic Optimization for Security of Electricity Supply

How dependent are European power systems and economies on natural gas? To answer this pressing question, we coupled a simulation model for assessing security of electricity supply and an economic optimization model. With this, we were able to analyze different reduction scenarios of the amount of gas utilized in the power sector. Our results show that reducing the amount of natural gas in the European power sector by up to 30% has a relatively moderate impact on the security of electricity supply. Restrictions of 40% or more result in substantially higher reductions in electricity demand shortfall and are associated with economic costs of more than EUR 77 billion. Furthermore, we demonstrate that a close coordination of gas distribution on a European level would be instrumental in mitigating negative economic consequences. Finally, it can be deduced that a coordinated delay of planned power plant shutdowns could effectively compensate for reduced gas volumes in the electricity sector.

Strategy to coordinate actions through a plant parameter prediction model during startup operation of a nuclear power plant

The development of automation technology to reduce human error by minimizing human intervention is accelerating with artificial intelligence and big data processing technology, even in the nuclear field. Among nuclear power plant operation modes, the startup and shutdown operations are still performed manually and thus have the potential for human error. As part of the development of an autonomous operation system for startup operation, this paper proposes an action coordinating strategy to obtain the optimal actions. The lower level of the system consists of operating blocks that are created by analyzing the operation tasks to achieve local goals through soft actor-critic algorithms. However, when multiple agents try to perform conflicting actions, a method is needed to coordinate them, and for this, an action coordination strategy was developed in this work as the upper level of the system. Three quantification methods were compared and evaluated based on the future plant state predicted by plant parameter prediction models using long short-term memory networks. Results confirmed that the optimal action to satisfy the limiting conditions for operation can be selected by coordinating the action sets. It is expected that this methodology can be generalized through future research.

Effect of Salinity on Stomatal Conductance, Leaf Hydraulic Conductance, HvPIP2 Aquaporin, and Abscisic Acid Abundance in Barley Leaf Cells.

The stomatal closure of salt-stressed plants reduces transpiration bringing about the maintenance of plant tissue hydration. The aim of this work was to test for any involvement of aquaporins (AQPs) in stomatal closure under salinity. The changes in the level of aquaporins in the cells were detected with the help of an immunohistochemical technique using antibodies against HvPIP2;2. In parallel, leaf sections were stained for abscisic acid (ABA). The effects of salinity were compared to those of exogenously applied ABA on leaf HvPIP2;2 levels and the stomatal and leaf hydraulic conductance of barley plants. Salinity reduced the abundance of HvPIP2;2 in the cells of the mestome sheath due to it being the more likely hydraulic barrier due to the deposition of lignin, accompanied by a decline in the hydraulic conductivity, transpiration, and ABA accumulation. The effects of exogenous ABA differed from those of salinity. This hormone decreased transpiration but increased the shoot hydraulic conductivity and PIP2;2 abundance. The difference in the action of the exogenous hormone and salinity may be related to the difference in the ABA distribution between leaf cells, with the hormone accumulating mainly in the mesophyll of salt-stressed plants and in the cells of the bundle sheaths of ABA-treated plants. The obtained results suggest the following succession of events: salinity decreases water flow into the shoots due to the decreased abundance of PIP2;2 and hydraulic conductance, while the decline in leaf hydration leads to the production of ABA in the leaves and stomatal closure.

Emergency shutdowns of propylene production plants: Root cause analysis and availability modeling

Unplanned shutdown events in chemical process plants cause revenue losses due to production curtailments, repair costs, and harmful environmental and safety effects on plant personnel and the surrounding community. Several recent studies have used news articles and databases to perform statistical analyses and modeling of the causes and consequences of chemical process accidents, but these studies do not analyze the operating deviations that led to shutdowns. This work structures narratives about unplanned shutdown events into data, analyzes the causes of those events, and uses the collected data to model the failure probability of process plants. A case study comparing two propylene production technologies, steam cracking and propane dehydrogenation is developed. We use a set of 118 shutdown events reported in four sources across a five-year span for 7 propylene production plants. Using this data, the three leading causes for unplanned shutdowns in both propylene production technologies were determined to be: equipment trips/shutdowns, utility supply interruptions, and weather-related events. A power law process (PLP) for data from multiple repairable systems is used to model the failure behavior for both technologies. For the data collected, this procedure indicated an increasing failure intensity function for both technologies, with propane dehydrogenation increasing more significantly. In addition, both maximum likelihood estimates (MLEs) and confidence intervals for the PLP parameters are presented. Since these are repairable systems, an estimated inherent availability is determined for both technologies. Finally, recommendations that address how to reduce the occurrence of these events and mitigate their consequences are discussed.

Effects of temperature shock on the survival of different life stages of large yellow croaker (Larimichthys crocea) by simulated power plant cooling water

Seawater temperatures have increased with global climate change. Coolant water discharged from coastal nuclear power-generating and coal-powered plants, coupled with already increasing seawater temperatures, can adversely affect local fish communities. A sudden drop in temperature caused by the winter shutdown of power plants can also affect fish health and behavior. To assess the effects of temperature change on fish populations, we subjected early life stages of the once commercially important large yellow croaker (Larimichthys crocea) to various water temperature experiments. Fertilized eggs showed the highest hatching rate at 23.4°C and the lowest rate of deformity in hatched larvae at 23.0°C. We determined the incipient lethal temperature for each life stages using derivation models. Ranges between the upper and lower incipient lethal temperatures increased during development from yolk-sac larvae to juveniles, especially in response to cold shock, indicating that later developmental stages in this species are more tolerant of temperature fluctuations. However, thermal tolerance is not solely determined by life stage. Our results suggest that rapid changes in seawater temperature caused by power plant coolant water discharges may significantly affect early developmental stages of fish. Critical thermal maximum tests indicate that the seawater heating rate is significantly negatively correlated with survival time and affects the critical thermal maximum value of L. crocea. On the basis of our determination of incipient lethal temperatures, emergency measures could be taken to avoid adverse economic and ecological impacts due to changes in seawater temperature caused by coolant water discharges.

How Does Misinformation and Capricious Opinions Impact the Supply Chain - A Study on the Impacts During the Pandemic.

Misinformation or fake news has had multifaceted ramifications with the onset of the Covid-19 pandemic, creating widespread panic amongst people. This study investigates the impact of misinformation/ fake news (on internet platforms) on consumer buying behavior, impact of fear (created by fake news) on hoarding of essential products and consumer spending and finally impact of misinformation-induced panic buying on supply chain disruptions. It draws upon the consumer decision theory and the cognitive load theory for explaining the psychological and behavioral responses of consumers. The study follows an inductive approach towards theory building using a multi-method approach. Initially, a qualitative research method based on interviews followed by text-mining has been used followed by analysis using python for topic modelling using Latent Dirichlet Allocation (LDA). The findings revealed several prominent themes like consumer shift to online buying, two contrasting spending intentions namely financial security and compensatory consumptions, irrational panic buying, uncertainty/ambiguity of government protocol and norms, social media fraudulent practices and misinformation dissemination, personalized buying experience, reduced trust on news and marketers, logistics and transportation bottlenecks, labor shortage due to migration and plant closures, and bullwhip effect in supply chains.

Koskien valjastamisesta patojen purkuun

The latest phase of river restorations is the closure of small hydroelectric plants. The precedent of this stage in Finland is the Hiitolanjoki river, which is a transboundary river crossing the Finnish-Russian border before flowing to Lake Ladoga. This article focuses on the shift in the hydrosocial rhythm of the Hiitolanjoki river from industrial to post-industrial rhythm. In a waterbody with the industrial rhythm, dams regulate the flow and speed of water in line with the demand for electricity. Current dismantling of dams and restoring its original rhythm is a result of the persistent work of local actor-network which has been able to create a wide supporting network including actors from the Hiitolanjoki river to the European Union’s and the Finnish government’s water and fish stock policies. The case of Hiitolanjoki river shows that achieving results requires an active and committed local network of actors.

Development of an End State Vision to Implement Digital Monitoring in Nuclear Plants

Nuclear plant sites collect and store large volumes of data gathered from various equipment and systems. These datasets typically include plant process parameters, maintenance records, technical logs, online monitoring data, and equipment failure data. The collection of such data affords an opportunity to leverage data-driven machine learning (ML) and artificial intelligence (AI) technologies to provide diagnostic and prognostic capabilities within the nuclear power industry, thus reducing operations and maintenance (O&M) costs. In this way, nuclear energy can become more economically competitive with other energy sources, and premature plant closures can be avoided. From a maintenance standpoint, savings can be achieved by leveraging ML and AI technologies to develop data-driven algorithms that better diagnose and predict potential faults within the system. Improved model accuracy can help reduce unnecessary maintenance and foster more efficient planning of future maintenance, thereby lowering the costs associated with parts, labor, and costly planned, forced, or extended outages. From an operations perspective, cost savings can be generated by shifting from routine-based monitoring to online monitoring by taking advantage of advancements in sensors and wireless communication technologies. Advancements in data storage, mapping, management, and analytics would inform the transition from onsite- to cloud-based computing and storage services. Online monitoring would reduce the number of operator manhours required for taking routine measurements, while cloud computing services would generate cost savings by reducing the amount of hardware needing to be purchased and maintained all while scaling to both computational and storage demands. This paper summarizes an end state vision of how to shift from costly, labor-intensive preventative maintenance to cost-effective predictive maintenance.

Features of the presence of precious metals in the zinc production clinker

The paper considers the features of gold deportments in technogenic raw materials – aged clinker of zinc production at the Belovsky zinc plant (Belovo, Kemerovo Region). The Belovsky plant operated from 1930 to 2003 using zinc concentrates from the Salairsky ore mining and processing plant. After the plant shutdown, clinker dumps were stored at the plant’s mill site and were repeatedly washed with acidic solutions to isolate copper. This form of storage and leaching led to the transformation of precious metal deportments in clinker, which currently makes it difficult to extract gold. The gold content in clinker is at the level of 2–3 g/t, which makes gold recovery profitable. The presence of carbon in clinker complicates the use of known methods of both analytical detection of gold and its recovery. A method is proposed for determining the deportment and content of gold taking into account the fact that gold may be present in the form of free fine gold, as well as gold finely disseminated in iron and its oxides, in sulfide phases, in the quartz-silicate part of clinker and in the carbonaceous phase. It was shown that gold deportments in clinker change depending on the storage conditions and preceding acid treatment, and this affects the choice of the material processing flow chart. The share of gold available for leaching is at least 40 %. The increased associativity of gold with the coal (flotation-active) phase and the sorption activity of coal significantly interfere with the study into the properties of gold deportments in clinker, which requires preliminary carbon removal.

Spreading pathways of Pilgrim Nuclear Power Station wastewater in and around Cape Cod Bay: Estimates from ocean drifter observations

Near-surface drifter observations were used to study the spreading pathways in and around the Cape Cod Bay from a source region located just offshore of the Pilgrim Nuclear Power Station. The study was motivated by the recent closing of the power plant and a possible release of accumulated wastewater. The investigation applies several different techniques to the drifter data set to estimate and quantify various aspects of the circulation and spreading. Our goal was two-fold: first, to better understand and predict the fate of the Pilgrim wastewater should it be released; and second, to review, compare, and contrast several useful techniques that can be applied to drifter datasets in other parts of the global ocean. Our analysis suggests weaker spreading of the wastewater plume inside the Bay than outside, and sensitivity of the advection pathways to the location of the release. Statistical techniques predicted that part of the plume would likely be advected cyclonically around the inner coastline of the Bay towards the more quiescent eastern regions, while another part of the plume would likely pass close to the tip of Cape Cod and the beaches of the Outer Cape. For the soluble radionuclides, the levels observed in our statistical model offshore of Provincetown and Dennis/Brewster will be at least 100 times smaller than the initial concentrations.

Green synthesis of TiO2 nanoparticle from Plumeria rubra L. leaves for anticorrosive application

Corrosion may cause the shutdown of plants, loss of essential resources, contamination of the product, reduce the efficiency, high maintenance, and excessively expensive design. It can also jeopardize security of the people and prevent technological advances. The effect caused by corrosion that includes the cost of highway bridges, controlling and appliances airplanes, automobiles, industrial plants such as energy distribution systems and production.Nanoparticles surface coatings provide tremendous ability for various applications, their unique traits that aren’t usually found in regular coatings. This task headed toward developing a nano coating layer that of Titanium dioxide nano-powder which was extracted from chafa (Plumeria rubra L.), corrosion resistant/antifouling resistance residences for a coating. The nanoparticles were sent for TGA/DTA, XRD, FTIR, and SEM analysis. The project is about the discussion on the behavior of corrosion on epoxy- titanium dioxide in various mediums by calculating its corrosion rate. Iron nails were is used as substrates for the epoxy--titaniumoxide coating. The behavior of corrosion of iron nail was studied in different media, NaCl solution, tap water, sulphuric acid and sodium hydroxide solution. The Immersion/dive test is done and after taking observations it is studied for 15–20 days on a daily time frame, with weekly immersing and weighing. The rate of corrosion is calculated and compared. The nanocoating layer successfully passed the chemical resistance test and can be further sent to advanced tests and applications.

Late-career unemployment and cognitive abilities

We study the effect of unemployment on cognitive abilities among individuals aged between 50 and 65 in Europe. To this end, we exploit plant closures and use flexible event-study estimations together with an experimentally elicited measure of fluid intelligence, namely word recall. We find that, within a time period of around eight years after the event of unemployment, cognitive abilities only deteriorate marginally — the effects are insignificant both in statistical and economic terms. We do, however, find significant effects of late-career unemployment on the likelihood to leave the labor force, and short-term effects on mental health problems such as depression and sleep problems.

People, performance and transition: A case study of psychological contract and stakeholder orientation in the Toyota Australia plant closure

AbstractOperations managers often manage in times of change that exert pressure on values and methods usually developed during more stable eras. With increasing global volatility, companies open and close plants because of demand shifts, cost and reshoring considerations, and government‐induced and market forces. Impacts of plant closures on local communities, employees, suppliers, and other stakeholders have been documented, but plant closure processes have not been extensively studied. This paper describes an engaged research study of Toyota Australia's manufacturing closure processes. We apply psychological contract theory, particularly of contract breach, to examine the “respectful” approach Toyota used to close its assembly operation in Melbourne. We examined the role that stakeholder theory plays in describing managerial motivations. Toyota allocated resources beyond typical expectations to prepare its workforce for their post‐Toyota careers and lives. During the 4‐year transition process, employee performance, and engagement improved, supporting propositions that reserves of employee goodwill can come into play when a psychological contract breach occurs. Further, leadership actions can moderate the negative impacts predicted by that theory, beyond outcomes that more transactional views would predict. Our study offers an elaborated model of psychological contract breach that future researchers can apply to plant closures and related operational contexts.

Murine Hepatitis Virus, a Biosafety Level 2 Model for SARS-CoV-2, Can Remain Viable on Meat and Meat Packaging Materials for at Least 48 Hours.

ABSTRACTIn 2020 and 2021, many meat processing plants faced temporary closures due to outbreaks of COVID-19 cases among the workers. There are several factors that could potentially contribute to the increased numbers of COVID-19 cases in meat processing plants: the survival of viable SARS-CoV-2 on meat and meat packaging materials, difficulties in maintaining workplace physical distancing, personal hygiene, and crowded living and transportation conditions. In this study, we used murine hepatitis virus (MHV) as a biosafety level 2 (BSL2) surrogate for SARS-CoV-2 to determine viral survival on the surface of meat, namely, stew-cut beef and ground beef, and commonly used meat packaging materials, such as plastic wrap, meat-absorbent material, and Styrofoam. From our studies, we observed the infectivity of MHV inoculated on ground beef and stew-cut beef for 48 h and saw no significant loss in infectivity for MHV from 0 to 6 h postinoculation (hpi) (unpaired t test). However, beginning at 9 hpi, viral infectivity steadily decreased, resulting in a 1.12-log reduction for ground beef and a 0.46-log reduction for stew-cut beef by 48 hpi. We also observed a significant persistence of MHV on meat packaging materials, with Styrofoam supporting the highest viability (3.25 × 103 ± 9.57 × 102 PFU/mL, a 0.91-log reduction after 48 hpi), followed by meat-absorbent material (75 ± 50 PFU/mL, a 1.10-log reduction after 48 hpi), and lastly, plastic wrap (no detectable PFU after 3 hpi, a 3.12-log reduction). Despite a notable reduction in infectivity, the virus was able to survive and remain infectious for up to 48 h at 7°C on four of the five test surfaces. Our results provide evidence that coronaviruses, such as SARS-CoV-2, could potentially survive on meat, meat-absorbent materials. and Styrofoam for up to 2 days, and potentially longer.IMPORTANCE The meat industry has been faced with astronomical challenges with the rampant spread of COVID-19 among meat processing plant workers. This has resulted in meat processing and packaging plant closures, creating bottlenecks everywhere in the chain, from farms to consumers, subsequently leading to much smaller production outputs and higher prices for all parties involved. This study tested the viability of meat and meat packaging materials as potential reservoirs for SARS-CoV-2, allowing the virus to survive and potentially spread among the workers. We used murine hepatitis virus (MHV) as a biosafety level 2 (BSL2) surrogate for SARS-CoV-2. Our results suggest that ground beef, stew-cut beef, meat-absorbent material, and Styrofoam can harbor coronavirus particles, which can remain viable for at least 48 h. Furthermore, our study provides evidence that the environmental and physical conditions within meat processing facilities can facilitate the survival of viable virus.

Geothermal reservoir characterisation of Devonian carbonates in North Rhine-Westphalia (W. Germany): Mineralogy- and depofacies-related extrapolation of petrophysical parameters

Across Germany, coal-fired power plants will be shut down not later than 2038. In the Rhine-Ruhr area of western Germany, their waste heat is the main supply for one of Europe’s largest district heating networks. Because of the projected shutdown of coal-fired power plants, sustainable alternatives must be implemented. This paper evaluates the hydrothermal potential of Devonian carbonates. A depofacies and mineralogy model is proposed and discussed. Tentative conclusions are drawn based on petrophysical laboratory tests. Extrapolating the thermal and hydraulic rock properties into geothermal reservoir depths offers constraints for associated reservoir simulations. This task applies existing and derived extrapolation equations taking local pressure and temperature gradients into consideration. The change from a non-linear to a linear development at the critical crack-closure pressure provides evidence regarding the petrophysical in-situ reservoir conditions. Results show a positive effect of increased dolomite volumes on reservoir properties. The spatial distribution of fracture networks significantly affects the geothermal reservoir potential, whereas the impact of regionally distributed depofacies variations is moderate. The critical crack-closure pressure equals 40MPa for limestones and 60MPa for dolomitic limestones, as well as dolostones, representing depths of approx. 3.6 and 5.4km, respectively. At depths of 6km, non-linear and linear extrapolation principles must be applied accordingly. At that depth, the thermal conductivity decreases by 14 to 20% compared to the outcrop values, depending on the sample category. The equivalent decrease in porosity amounts to one to two orders of magnitude. The permeability decrease equals three to four orders of magnitude. The petrophysical values of outcrop samples discussed here plot, within the error range, in the same domain as those of the Malm carbonates in the Munich area. Results are considered encouraging for those concerned with the sustainable transition of the district heating network in the Rhine-Ruhr area. Side-strands of regionally important fault systems, often characterised by hydrothermal dolomitisation, combine tectonic and petrophysical aspects that are advantageous and highly relevant for hydrothermal operations.

Risk Assessment of Delay for CEMS and WHRU Installation Project on Plant Shutdown at Central Processing Gas Gundih

This paper addresses a risk assessment of delay for installation of Continuous Emission Monitoring System and Waste Heat Recovery Unit as an effort to fulfil compliance with the Regulation of the State Minister of the Environment Number 13 of 2009 concerning Quality Standards for Emissions from Immovable Sources for Oil and Gas Businesses and Activities. The installation of the unit consists of three steps, pre-shutdown, window shutdown and post shutdown. In accordance with Gas Sale Agreement, that the entire period of normal maintenance work that causes gas to not flow, should not be more than 15 (fifteen) days every year. The planning and implementation of maintenance is very important by utilizing the condition of the window shutdown to avoid material and non-material losses. Reviewing the vulnerability of this project, it is necessary to conduct research that assesses the level of risk of project delays using the ISO 31000:2018 risk management concept approach, through identification of risk variables from several literature studies, risk analysis through Group Discussion Forums, and risk management efforts to reduce risk of delays in the installation project. From the risk identification, 30 risk variables that affect project delays consist of 2 High categories, 3 Medium to High categories, 15 Medium categories, 6 Low to Medium categories and 4 Low categories. The Risk Treatment carried out in the high and Medium to high categories resulted in 9 mandatory RCOs to reduce delays and 1 RCO to speed up the implementation schedule from 19 days to 13 days and earn a profit of $615,000 because the process of selling gas to consumers can be accelerated by 2 days.

Heat treatment optimization of 13Cr4Ni stainless alloy used as hydro turbine materials

In Nepal and the regions along with the Andes, sediment erosion is one of the major causes of the failure of hydro turbines. Every year lots of the components of turbines exposed to sediment-laden water got eroded resulting unexpected shutdown of the power plants. The cheapest method of repairing these eroded runners and other components of turbines are welding which may induce residual stress, embrittlement, and increase carbide content. Therefore, post welding heat treatment especially stress relieving annealing is always carried out to reduce the induced residual stresses, enhance strength and other mechanical properties as well as reduce the risk of cracking. As heating time is relative of low importance, great care should be taken during heat treatment to maintain the soaking time and cooling rate. Holding time for heat treatment will vary with the thickness of casting sections involved, but should be sufficiently long enough to heat all sections to a uniform temperature throughout. The cooling rate determines the material properties at room temperature and rapid cooling avoids the formation of chromium carbide. In this paper, the post-weld heat treatment used for repair and maintenance of turbines in Nepal is studied along with the investigation of heat treatment conditions on mechanical properties and microstructures of 13Cr4Ni stainless steel used as turbine materials to optimize the heat treatment itself. First of all relative analysis of five different heat treatment conditions with respect to ‘no heat treatment’ regarding mechanical properties i.e. toughness, hardness, and fatigue life was carried out. Heat treatments of the specimen were done in a muffle furnace. Hardness, toughness, and fatigue strength of the specimen using the Rockwell Hardness Test, Charpy Impact Test, and Fatigue Life Test were conducted respectively. Subsequently, microstructures of all the heat treatment conditions are closely examined using the metallurgical microscope. It was observed that holding time plays a great impact on improving mechanical properties.

Cursed forever? Exploring socio-economic effects of nuclear power plant closures across nine communities in the United States

Nuclear energy occupies a conspicuous place in the global energy transition. In the United States, civilian nuclear power plants are shutting down before their licenses expire, leaving nuclear host communities struggling to cope with the unexpected change. This study focuses on the socio-economic dimensions of the effects of nuclear power plant shutdowns in nuclear host communities in the United States. Our study attempts to strike a balance between intensive case studies, which often fail to disentangle place-specific factors from broader trends and to put observations in perspective, and large-sample-based quantitative analyses, which seeks a general impact of decommissioning without paying sufficient attention to local variations. We adopt a quasi-experimental approach, which compares communities with decommissioned plants to their control neighbors, to assess the diverse trajectories of socio-economic well-being of nuclear host communities before and after plant closure. These communities are analyzed in terms of their population, per capita income, education, poverty levels, and unemployment. The findings provide a starting point from which more detailed case studies can be conducted, and nuclear host communities can better navigate the decommissioning process.

Implementation of a plant shutdown in times of pandemic

Implementation of a plant shutdown in times of pandemic

Hydro-abrasive erosion modelling in Francis turbine at different silt conditions

Hydro-abrasive erosion creates problems for the safe and effective running of hydropower projects. This is of even greater concern in hilly regions. The huge losses in the revenue of the hydropower plant have become a burden on the hydropower project developers. These losses are mainly due to the reduced capacity of the generation of electricity units (kWh). The high amount of silt entering the plant, especially in the monsoon season causes heavy hydro-abrasive erosion in the turbine and other underwater components. The deterioration of underwater plant equipment due to this kind of erosion can also lead to a total shutdown of the hydropower plant. In the current scope of the study, efforts have been made to validate the existing erosion models for the Francis turbine with the operational hydropower plant and carry out the numerical erosion modelling in the Francis turbine to predict the turbine efficiency losses at maximum and part-load conditions. Various developed erosion models are analyzed for the study period of FY 2018–19 based on influencing parameters like silt concentration, silt size, hardness, and site-specific flow constant. The site chosen for this purpose was the MB-II hydropower plant, a 304 MW hydropower project having four generating units of Francis turbine located at the foot of the Himalayan hills in the Uttarkashi district of Uttarakhand, India. The calibration factor is calibrated for the MB-II hydropower plant using GRG Nonlinear algorithm using a multi-start solver.