Inventory Limits Research Articles

Tritium and dust source term inventory evaluation issues in the European DEMO reactor concepts

Fusion reactors represent a future evolution of the nuclear technology improving the world-wide energy portfolio. The experimental fusion reactor under construction (ITER) and the planned industrial fusion reactors (DEMO) are large and complex facilities. For their operation it is necessary to ensure safety limiting of radiological and mobilizable source terms inventory, such as tritium and radioactive dust.The source term inventories shall be assumed in the establishment of operational and safety requirements for DEMO, as well as performing safety analyses for commercial fusion devices. In the last few years a methodology for evaluation of tritium and dust source term inventory has been proposed in the framework of the EUROFusion project. The basis of the methodology is a semi-empirical approach to scale the radioactive inventory limits implemented in ITER. The source term amounts derived for DEMO will supply a guidance for safe operation of future fusion reactors. The development of methodology has to be completed and refined because of the lack of validation versus adequate experimental data and rules for extension to different scenarios.The aim of this work is assessment of the developed methodology for evaluation of the source terms inventory versus JET operating limits for tritium and versus the dust control strategy adopted in ITER for the dust. The updating of the methodology for the dust and T inventory was carried out in line with the current DEMO design. The new values of the in-VV source terms were achieved. These values are recommended to be used for the safety assessment of the fusion reactor. Calculated DST and TST inventories’ values show a reasonable agreement with scaled ITER or assessed JET limits.

Inventory Planning with Method Q and Method P for Probabilistic Demand on Chrysanthemum Seeds at PT Transplants Indonesia

Fluctuating and uncertain demand is a problem faced by manufacturing firms. The problem can be mitigated by the availability of inventory systems. This inventory serves to ensure the availability of appropriate resources in the right quantity and at the right time, so as to minimize the costs incurred. PT. Transplants Indonesia is a company engaged in the business of chrysanthemum flower in Indonesia. PT. Transplants Indonesia is a subsidiary of Okinawa Flower Agricultural Cooperative Association (OKF) in Okinawa, Japan. The purpose of this company establishment is to meet the demand of farmers who are members of the OKF. In the case of backorder, on Q method with probabilistic request the size of the lottery (Q) is always fixed for every time the order is made and the order is made if the amount of inventory system has reached a certain level (r) called the reorder point. In method P with probabilistic order requests made according to a fixed interval of time (T) and the ordering does not exceed the maximum inventory limit (R). Total Inventory cost incurred by the company using the method used by the company amounted to Rp.74.995.360,84. The inventory model using the Q method generates a total inventory cost of Rp.70.253.291,46. Meanwhile, inventory model using P method resulted in total inventory cost of Rp.71.529.327,17. So economically, the selected inventory model is the inventory model with the Q method which has a lower total inventory cost value than using the P method.
 
 Keywords— Inventory system, Probabilistic, Backorder, Method Q, Method P, Reorder point.

A multi-scenario and multi-objective scheduling optimization model for liquefied light hydrocarbon pipeline system

The mixed transportation mode based pipeline system plays a significant role in the supply chain of liquefied light hydrocarbon. Inefficient scheduling may lead to problems of frequent pump stoppage/restart, high energy consumption, and frequent pressure fluctuation. To avoid these problems, this paper implements the discrete-time representation to develop a multi-scenario and multi-objective mixed integer nonlinear programming model to minimize the pump operation cost and the number of the switching operation. In the model, several factors, such as transportation mode, inventory limits of injection stations, flow rate and pressure limits of pipeline segments, are taken into consideration. Additionally, the uncertainty of the liquefied light hydrocarbon production is described by scenarios. The improved augmented ε-constraint method is implemented to solve this model. Finally, the model is successfully applied to a multi-source single-sink liquefied light hydrocarbon pipeline system in Daqing oilfield in China. The experimental results show that the proposed model outperforms another two available models in profit, safety, and robustness aspects.

A robust optimization model for the maritime inventory routing problem

Uncertainty is a highly important aspect of maritime transportation. Unforeseen occurrences related to environmental conditions, poor weather, vessel reliability, or port congestion are frequent and have a non-negligible impact on the total time required for vessels to perform (un)loading operations at ports. We study a special case of maritime transportation named the maritime inventory routing (MIR) problem, in which one must determine the routings of vessels while keeping the inventory levels at ports within the operational limits. In this paper, we propose a robust optimization approach that considers the uncertainty in the total time spent by vessels at the ports. This approach allows the trade-off between the risk of infeasibility (i.e., violating inventory limits at ports) and the increase in operational costs due to the protection against uncertainty events to be assessed. To test the proposed methodology, we used a real-world instance based on the MIR problem faced by a Brazilian petroleum company. In this problem, violating the inventory limits at ports causes considerable financial losses due to consequent interruptions in crude oil production. Our approach supports the decision maker to devise more robust plans in which the risk of violating inventory limits is acceptable. In other words, despite the increase in the operational costs associated with more robust solutions, the approach enables the decision maker to avoid much larger potential costs. For the problem considered, we observed that the probability of infeasibility of the proposed solution may be reduced from 87% to 2%, depending on the level of robustness adopted by the decision maker. However, this increased protection causes an increase of up to 13% in the overall costs.

Multiproduct pipeline scheduling integrating for inbound and outbound inventory management

This paper addresses the operation of a unidirectional multiproduct pipeline system integrated with inventory tanks management at the refinery and distribution center. A Mixed Integer Linear Programming (MILP) formulation is proposed to model the scheduling of a pipeline operation consisting of a single source node and a single destination node representing a refinery and a distribution center, respectively. Different operational aspects such as product availability, inventory limits, product quality, forbidden sequences, transition between different products injected into the pipeline and tanks inventory management are considered. Time synchronization among refinery, pipeline, and distribution center is guaranteed enhancing the model representation of real operations. Additionally, a solution procedure is developed to improve the model solution performance that explores the reduction of the number of variables and constraints. Different examples based on a real world case are solved showing the model's applicability, which proves to be effective in generating feasible solutions in reasonable computational times.

Impact of RFID technology on inventory control policy

RFID application can improve operation performance in a supply chain by reducing or eliminating inventory misplacement and shrinkage. In this paper, we present a periodic review inventory model to investigate and characterize the multiperiod inventory control policies in both non-RFID and RFID cases when the firm encounters misplacement and shrinkage. The optimal inventory control policy is proved to be a two-control limit policy. The control limits in both the non-RFID case and the RFID case are analyzed and examined, while considering the impact of shrinkage and misplacement on inventory policies. A critical inventory level is determined to identify the relationship of higher inventory level control limits between the RFID case and the non-RFID case. An intensive numerical study with sensitivity analysis of selling price, misplacement rate, shrinkage rate, inventory recovery rate, and tag price is conducted. We find that when RFID technology is adopted, the inventory control policy in the RFID case is much more stable than that of the non-RFID case, as the misplaced inventory can be recovered perfectly and instantly for sale and the inventory shrinkage can be reduced by RFID technology. In addition, one of our intriguing findings is that when the shrinkage rate is below a threshold value which is independent of parameters, RFID application has no effect on inventory control policy if the misplaced inventory can be recovered in a timely manner by physical audit, which has not been revealed in previous studies.

Efficiency of thermal outgassing for tritium retention measurement and removal in ITER

As a licensed nuclear facility, ITER must limit the in-vessel tritium (T) retention to reduce the risks of potential release during accidents, the inventory limit being set at 1kg. Simulations and extrapolations from existing experiments indicate that T-retention in ITER will mainly be driven by co-deposition with beryllium (Be) eroded from the first wall, with co-deposits forming mainly in the divertor region but also possibly on the first wall itself. A pulsed Laser-Induced Desorption (LID) system, called Tritium Monitor, is being designed to locally measure the T-retention in co-deposits forming on the inner divertor baffle of ITER. Regarding tritium removal, the baseline strategy is to perform baking of the plasma-facing components, at 513K for the FW and 623K for the divertor. Both baking and laser desorption rely on the thermal desorption of tritium from the surface, the efficiency of which remains unclear for thick (and possibly impure) co-deposits. This contribution reports on the results of TMAP7 studies of this efficiency for ITER-relevant deposits.

Simultaneous scheduling of front-end crude transfer and refinery processing

Scheduling of front-end crude-oil transfer and refinery processing are two critically important and challenging tasks to petroleum refineries. However, the simultaneous scheduling of front-end crude-oil transfer and refinery operations has never been considered in previous studies due to the large scale and complexity of the resultant optimization problem. In this paper, a systematic methodology for simultaneous scheduling of front-end crude transfer and refinery processing has been developed. It provides a large-scale continuous-time based scheduling model for crude unloading, transferring, and processing (CUTP) to simulate and optimize the front-end and refinery crude-oil operations simultaneously. The CUTP model consists of a newly developed refinery processing sub model, a crude processing status transition sub-model, and a borrowed front-end crude transferring sub model. The objective is to maximize the total operational profit while satisfying various constraints such as operation and production specifications, inventory limits, and production demands. The efficacy of the proposed scheduling model has been demonstrated by an industrial-scale case study.

A practical model for managing inventories with unknown costs and a budget constraint

The economic production quantity method is one of the simplest models to control production and inventory. However, the assumptions on which it is based make its application difficult in practical situations. In most companies, set-up and inventory costs are unknown, or may not even exist as such, although other data are known, such as available capacity in machining hours and limits set by the financing subsystem. The present work offers a multi-item inventory model that sets reference values using known values such as inventory investment limits and production capacity. In order to confer the proposed model’s larger practical content, a spreadsheet available to be downloaded has been implemented. Finally, the model dynamics is illustrated as a numerical example obtained from a real company.

An iterative two-phase hybrid matheuristic for a multi-product short sea inventory-routing problem

This paper considers a multi-product short sea inventory-routing problem in which a heterogeneous fleet of ships transports multiple products from production sites to consumption sites in a continuous time framework. A many-to-many distribution structure is taken into account, which makes it extremely hard to even compute feasible solutions. We propose an iterative two-phase hybrid matheuristic called Hybrid Cargo Generating and Routing (HCGR) to solve the problem. In the first phase the inventory-routing problem is converted into a ship routing and scheduling problem by generating cargoes subject to inventory limits through the use of mathematical programming. In the second phase, an adaptive large neighborhood search solves the resulting ship routing and scheduling problem. The HCGR heuristic iteratively modifies the generated cargoes based on information obtained during the process. The proposed heuristic is compared with an exact algorithm on small size instances; computational results are also presented on larger and more realistic instances.

Combined ship routing and inventory management in the salmon farming industry

We consider a maritime inventory routing problem for Norway’s largest salmon farmer both producing the feed at a production factory and being responsible for fish farms located along the Norwegian coast. The company has bought two new ships to transport the feed from the factory to the fish farms and is responsible for the routing and scheduling of the ships. In addition, the company has to ensure that the feed at the production factory as well as at the fish farms is within the inventory limits. A mathematical model of the problem is presented, and this model is reformulated to improve the efficiency of the branch-and-bound algorithm and tightened with valid inequalities. To derive good solutions quickly, several practical aspects of the problem are utilized and two matheuristics developed. Computational results are reported for instances based on the real problem of the salmon farmer.

Inventory Management Practices and Its Effects on Vendor Managed Inventory Performance

The Vendor Managed Inventory (VMI) has long been implemented by many corporations due to its various positive effects it has towards the company’s performance.At the same time, a number of success stories of VMI program have also been discussed by numerous authors.However, until now, there is no concrete conclusion on VMI has been clarified. Therefore, this study tries to shed the lights on the effects of inventory management practices, which include visibility of demand, replenishment decision, inventory ownership, inventory location, and inventory control limits on VMI performance.Quantitative methodology was chosen as the method to gather the data where those manufacturing companies being selected according to the list from the Federation of Malaysian Manufacturer (FMM).The data was gathered from 101 manufacturing companies whose manufacturing based located in Malaysia. Data analysis was conducted by employing descriptive analysis, factor analysis, reliability analysis, and a simple multiple regressions.The findings showed that visibility of demand and inventory control limits were the main predictor of service performance. Meanwhile, only inventory location contributes to cost performance of VMI. Manufacturing companies should urge their customer to share demand information and setting appropriate min–max limits of inventory levels in order to get benefits from VMI program.It was suggested for companies to consider to setup inventory storage or warehouse near to their customer’s premises especially when engaging with abroad customers.

Difference Evolution Algorithm for Batch Scheduling in Chemical Flow Shop

Batch production in chemical flow shop is conducted with batch as processing unit. It is characterized by multi-stage production flow, intermediate inventory limit as well as product switching time. This paper presents heuristic difference evolution algorithm which adopts 2-D codes to represent batch size constraint. The experimental results show that the model and algorithm put forward in this paper has good performance.

How do small business owners manage working capital in an emerging economy?

PurposeThe purpose of this study was to examine the actions owner‐managers of small businesses undertake in managing working capital.Design/methodology/approachThe study adopted an exploratory research design. The point of saturation was achieved after ten owner‐managers were interviewed. Data were analyzed using content analysis technique with the aid of NVivo software. Verbatim texts were used to explain the emergent themes.FindingsThe findings indicate that in the absence of systems, structures and procedures, small business owner‐managers intuitively plan, monitor and control their working capital. The activities undertaken include; reliance on memory and oral agreements, informal planning, assuming inventory limits, unconventional record keeping, cash flow based information management and giving credit to close associates.Research limitations/implicationsA more detailed investigation of the steps in the action sequence ma y advance our understanding of the process. Future studies need to test the effect of personal characteristics on working capital management process.Practical implicationsOwner‐managers of small businesses do not require the same degree of sophistication employed in planning, monitoring and controlling working capital. They require soft skills. Therefore, academicians, practitioners and policy makers need to emphasize knowledge management and cash accounting.Originality/valueThis study examines the process perspective of working capital management, an aspect that has not been adequately highlighted in previous studies.

Management Insights

Management Insights

Hydrogen isotope exchange in tungsten: Discussion as removal method for tritium

Hydrogen isotope exchange in re-crystallized polycrystalline tungsten was investigated at 320 and 450K. In a first step the tungsten samples were loaded with deuterium to a fluence of 1024D/m2 from a low-temperature plasma at 200eV/D particle energy. In a second step, H was implanted at the same particle energy and similar target temperature with a mass-separated ion beam at different ion fluences ranging from 2×1020 to 7.5×1023H/m2. The analytic methods used were nuclear reaction analysis with D(3He,p)α reaction and elastic recoil detection analysis with 4He. In order to determine the D concentration at depths of up to 7.4μm the 3He energy was varied from 0.5 to 4.5MeV. It was found that already at an H fluence of 2×1020H/m2, i.e. at 1/5000 of the initial D fluence, about 30% of the retained D was released. Depth profiling of D without and with subsequent H implantation shows strong replacement close to the surface at 320K, but extending to all analyzable depths at 450K especially at high fluences, leading to higher release efficiency. The reverse sequence of hydrogen isotopes allowed the analysis of the replacing isotope and showed that the release of D is balanced by the uptake of H. It also shows that hydrogen does not diffuse through a region of filled traps into a region were unfilled traps can be encounter but transport is rather a dynamic process of trapping and de-trapping even at 320K. Initial D retention in H loaded W is an order of magnitude higher than in pristine W, indicating that every H-containing trap is a potential trap for D. In consequence, hydrogen isotope exchange is not a viable method to significantly enhance the operation time before the tritium inventory limit is reached but should be considered an option to reduce the tritium inventory in ITER before major interventions at the end of an operation period.

INCAP – applying short-term flexibility to control inventories

Inventory based capacity control (INCAP) is a very simple method that allows inventory levels to be effectively controlled by using short-term capacity flexibility in make-to-stock settings. Moreover, INCAP can be used for finished goods inventories as well as for semi-finished goods inventories. The basic idea is to define upper and lower inventory limits and to adjust capacities if the inventory level reaches either limit. Should the inventory fall below the lower limit, capacity is increased to prevent stock-outs. Similarly, in order to avoid excess inventories the capacity is decreased should the inventory rise above the upper limit. INCAP is thus able to control inventory levels within a defined inventory range. In order to do so, it applies short term measures like over-time or extra shifts to increase capacities and cancels work hours or shifts to decrease capacities. Simulation experiments based on data from the automotive industry show that INCAP is able to improve the performance of a manufacturing system in that it significantly reduces the inventory levels necessary for guaranteeing a satisfactory service level. Overall, INCAP is found to be a straightforward but powerful method, able to cope both with uncertainties in production output as well as with varying demand. However, some restrictions do apply: INCAP depends not only on a minimum level of short-term capacity flexibility, but also in the standard set-up presented here it is limited to make-to-stock environments with similar products.

Dust in ITER: Diagnostics and removal techniques

Dust will be present in ITER and will be an issue in terms of safety. The ITER strategy for dust management is based among others on the definition and respect of dust inventory limits. To ensure that the safety limits are fulfilled, dust diagnostics and removal techniques need to be developed considering the Tokamak environment constraints (magnetic field, radiation, vacuum and temperature). This paper presents possible dust inventory build-up monitoring strategies for different periods of the machine operation (during/between pulses and during short or long maintenance periods). The strategies rely on the use of a set of complementary techniques for dust diagnostics and removal.

Refurbishment of the Tritium Laboratories at SCK•CEN

The SCK•CEN tritium laboratories were commissioned in 1975 for a maximum tritium inventory of 37 TBq. With an aim to improve the infrastructure, the capabilities and safety, SCK•CEN’s general management decided to refurbish the laboratories. A new ventilation system, including a stack and gloveboxes equipped with a detritiation installation, will allow a higher tritium inventory limit of 0.37 PBq. This paper discusses the ongoing refurbishment of the two neighboring tritium laboratories. Currently one laboratory has been denuclearized whilst the other is still in operation. Nevertheless a number of conclusions can already be drawn. We succeeded in denuclearizing most of the equipment and infrastructure without personnel receiving measurable tritium doses. If the free released metals had been disposed off at a nuclear melting facility, 22% of the costs could have been saved, however free release is more socially acceptable.

STAR Facility Tritium Accountancy

The Safety and Tritium Applied Research (STAR) facility has been established to provide a laboratory infrastructure for the fusion community to study tritium science associated with the development of safe fusion energy and other technologies. STAR is a radiological facility with an administrative total tritium inventory limit of 1.5g (14,429 Ci)[1]. Research studies with moderate tritium quantities and various radionuclides are performed in STAR. Successful operation of the STAR facility requires the ability to receive, inventory, store, dispense tritium to experiments, and to dispose of tritiated waste while accurately monitoring the tritium inventory in the facility.This paper describes tritium accountancy in the STAR facility. A primary accountancy instrument is the tritium Storage and Assay System (SAS): a system designed to receive, assay, store, and dispense tritium to experiments. Presented are the methods used to calibrate and operate the SAS. Accountancy processes utilizing the Tritium Cleanup System (TCS), and the Stack Tritium Monitoring System (STMS) are also discussed. Also presented are the equations used to quantify the amount of tritium being received into the facility, transferred to experiments, and removed from the facility. Finally, the STAR tritium accountability database is discussed.