Conceptual design of the hot cell facility universal docking station at ITER

Between main shutdowns of the ITER machine, in-vessel components and Iter Remote Maintenance System (IRMS) are transferred between the Tokamak complex and the Hot Cell Facility using different types of sealed casks. Transfer Casks have different physical interfaces with the Vacuum Vessel, which need to be the same at the docking stations of the HCF. It means that in-vessel components and IRMS are cleaned in the same cells, which is in fact not convenient. Furthermore, logistic studies showed that the use rate of the cells is very inhomogeneous. In order to have dedicated cell for decontamination of Remote Handling tools, in order to increase the operability efficiency and to removes the hot cell docking operation from the critical path, the concept of a universal docking station has been investigated. Based on an existing design, the work was focused on a review of requirements, the re-design and the integration within the HCF layout. The universal docking station has been proposed and is now integrated in HCF design.     

Preliminary assessment for dust contamination of ITER In-Vessel Transporter

After plasma operations of ITER, radioactive dust will have accumulated in the vacuum vessel (VV). The In-Vessel Transporter (IVT) will be introduced into the VV to remove the shield blanket modules for maintenance or replacement and later reinstall them. The IVT itself also needs to undergo regular maintenance in the Hot Cell Facility (HCF). It is assumed that maintenance workers will be exposed to radioactive dust that has adhered to the surfaces of the IVT. In this study, the areas of the IVT that may be contaminated by dust are evaluated to assess the level of exposure to workers during maintenance work in the HCF. Decontamination processes for the IVT, such as a combination of vacuuming and brushing, were investigated and the dose rate after these processes was evaluated. Even though dust was removed from surfaces where decontamination was possible, the dose rate was very high at some assessment points. To decrease the dose rate in accordance with ALARA policy, a decontamination plan and a maintenance plan, which includes the removal of dust, a radiation shield system, and a reduction in working time are proposed.     

Description of the shuffle design software MARLA

MARLA is the Studsvik software for the automated design and analysis of a fuel shuffle. The software is currently being applied to Boiling Water Reactors, but will eventually be extended to all Light Water Reactor types. MARLA performs all tasks related to planning the fuel shuffle, including the optimisation of the fuel movement schedule, a complete shutdown margin analysis of all intermediate core configurations using the licensing-grade SIMULATE-3 nodal code, and generation of the official Fuel Movement Checklist used by the crane operators during core alterations. Shutdown margin analysis is interactive with the shuffle design and takes place during the planning stage – not after the sequence has been planned. In addition, MARLA provides the means to manage all fuel pools and nuclear components on site, as well as optimise the choice of bundles to be loaded into dry storage casks to open space in the storage pools to meet future storage needs. This paper describes the software in superficial detail.     

The remote handling compatibility analysis of the ITER generic upper port plug structure

The ITER diagnostics generic upper port plug (GUPP) is developed as a standardized design for all diagnostic upper port plugs, in which a variety of payloads can be mounted. Here, the remote handling compatibility analysis (RHCA) of the GUPP design is presented that was performed for the GUPP final design review. The analysis focuses mainly on the insertion and extraction procedure of the diagnostic shield module (DSM), a removable cassette that contains the diagnostic in-vessel components. It is foreseen that the DSM is a replaceable component – the procedure of which is to be performed inside the ITER hot cell facility (HCF), where the GUPP can be oriented in a vertical position.The DSM removal procedure in the HCF consists of removing locking pins, an M30 sized shoulder bolt and two electrical straps through the use of a dexterous manipulator, after which the DSM is lifted out of the GUPP by an overhead crane. For optimum access to its internals, the DSM is mounted in a handling device. The insertion of a new or refurbished DSM follows the reverse procedure.The RHCA shows that the GUPP design requires a moderate amount of changes to become fully compatible with RH maintenance requirements.     

ITER Hot Cell process operability analysis using discrete event simulation tools

This paper reports on the use of Discrete Event Simulation tools for operability analysis of the Iter Hot Cell (HC) design. A simulation model representing the operation of the ITER Hot Cell has been created. The model incorporates the process logic for ITER components that are required to be refurbished, maintained and disposed of within the Hot Cell. This paper presents some results of the simulation indicating the performance of the Hot Cell for Divertor and Port Plug refurbishment. The results show that based on the established task durations a full 54 cassette Divertor refurbishment takes 4536 h, longer than the planned 6-month shutdown scheduled for the task. The simulation provides a platform to accurately size the capacity of process equipment with respect to given budgetary constraints and to identify opportunities to smooth the process flow. Effects of parameters such as human resource shift patterns, equipment mean time between failure and random variability in process times on overall Hot Cell productivity have been studied. The simulation model is flexible, capable of evolving in parallel with the Hot Cell design as more detailed input data becomes available thereby providing a valuable decision making and design optimisation tool throughout the development of the Hot Cell and beyond that into operation.     

Evolving the JET virtual reality system for delivering the JET EP2 shutdown remote handling tasks

The quality, functionality and performance of the virtual reality (VR) system used at JET for preparation and implementation of remote handling (RH) operations has been progressively enhanced since its first use in the original JET remote handling shutdown in 1998. As preparation began for the JET EP2 (Enhanced Performance 2) shutdown it was recognised that the VR system being used was unable to cope with the increased functionality and the large number of 3D models needed to fully represent the JET in-vessel components and tooling planned for EP2. A bespoke VR software application was developed in collaboration with the OEM, which allowed enhancements to be made to the VR system to meet the requirements of JET remote handling in preparation for EP2. Performance improvements required to meet the challenges of EP2 could not be obtained from the development of the new VR software alone. New methodologies were also required to prepare source, CATIA models for use in the VR using a collection of 3D software packages. In collaboration with the JET drawing office, techniques were developed within CATIA using polygon reduction tools to reduce model size, while retaining surface detail at required user limits. This paper will discuss how these developments have played an essential part in facilitating EP2 remote handling task development and examine their impact during the EP2 shutdown.     

Evaluation of operators’ mental workload of human–system interface automation in the advanced nuclear power plants

It has been expected that the automation of certain tasks in a control room would help decrease operators’ mental workload, enhance situation awareness, and improve the whole system performance. However, there have been too many automation-induced system failures that would warrant a fresh look on the influences of automation. Automation problems include the reduction in the operator's system awareness, an increase in monitoring workload, and the degradation in manual skills. This study evaluates operators’ mental workload and system performance during a human–system interface (HSI) automation in an advanced nuclear power plant (NPP). The reactor shutdown task and alarm reset task simulations were conducted in this study to evaluate operators’ mental workload and performance. The results of this study indicated that for ensuring safe operating in NPPs, the design of automation needs to be carefully implemented. Task characteristics and degrees of automation should be carefully evaluated while designing HSIs. The reactor shutdown tasks studied in this paper suggest that a high level of automation design for the long period and low workload would be sufficient. On the other hand, the degree of automation of alarm reset task does not show a significant difference to the operator's mental workload. In conclusion, the human–system interface automation in advanced NPPs is suggested to be more flexible and needs to be continually improved.     

How to make a fuel rod modelling code meet the requirements of design applications

The tasks of the fuel rod designer and the resulting requirements on fuel rod modelling codes are described in the first part. These requirements have increased during recent years in connection with the goal to increase the burnup. Cutting of overconservatism can contribute to this goal, but this needs good and accurately calibrated models. The second part of the paper discusses the special rules which control the use of a fuel rod modelling code in design applications. It is demonstrated how an uncontrolled piling-up of scatter bands and parameter bounds will very rapidly end in hypothetic results. Only a reasonable coordination of unfavourable input parameters leads to “realistic” conservatism from an engineer's point of view. A sound data base is the prerequisite for the respective methods. Further efforts will be necessary to qualify codes and procedures for future probabilistic methodologies.     

ITER Upper Port Plug handling cask system assessment and design proposals

The current design of the ITER cask for Upper Port Plugs has been evaluated. Careful reduction of the number of mechanical degrees of freedom is an opportunity to relax the tolerances in the design, resulting in cost reduction and reliability increase. A new kinematical design for the tractor module has a higher stiffness to weight ratio, reduces actuator forces by a factor four and minimizes cross-talk between lift and rotation motion. Non-cantilevered handling is recommended to reduce wheel loads on the tractor by a factor six and to simplify guidance. At the system level the tubular guide (TG) is proposed, a semi-permanent 3.5 m long tube which is an extension of the Upper Port. Cask docking is simplified and the risk of the cask tilting is prevented. Redesigning the system concept is recommended and the TG looks promising. Since a system level redesign impacts the external interfaces, overall feasibility has to be investigated.     

Fusion Specific Features in ITER Accident Analysis

Fusion specific features like inherent plasma shutdown, low decay heat densities, cryogenic temperatures, and limited source terms were considered during the safety design process of ITER. Uncertainties in plasma disruptions motivates a robust design to cope with multiple failures of in-vessel cooling piping. A vacuum vessel pressure suppression system mitigates pressure transients and effectively captures mobilized radioactivity. In case of pump trips or ex-vessel coolant losses in the divertor the plasma needs to be actively terminated in a few seconds. Failure to do so might damage the divertor but radiological consequences will be minor due to the intact first confinement barrier. Tritium plant inventories are protected by several layers of confinement. Uncontrolled release of magnet energy will be prevented by design. Postulated damage from magnets to confinement barriers causes fluid ingress (air, water, helium) into the cryostat. The cold environment limits pressurization. Most tritium and dust is captured by condensation.     

High level integration of remote handling control systems at JET

To reduce the timescale of the JET Enhanced Performance 2 (EP2) shutdown, two multi-jointed Booms instead of one will be used for maintenance and upgrades inside the JET vessel. To fully utilize this new configuration, the control systems of the Booms have been modified at a high level to allow quick and safe interactions between them. This paper will discuss how the control systems of the Booms have been integrated to exploit the increased mechanical functionality of the Octant 1 Boom, and will demonstrate how this has improved safety, utility and efficiency for the remote handling operators during the EP2 shutdown. Other operational streamlining functions will be mentioned, as well as a look to the future of Remote Handling at JET.     

Analysis and validation center for ITER RH maintenance scenarios in a virtual environment

A facility for detailed simulation of maintenance processes in the ITER Hot Cell Facility (HCF) has been taken into operation. The facility mimics the Remote Handling (RH) work-cells as are presently foreseen. Novel virtual reality (VR) technology, extended with a physics engine is used to create a realistic setting in which a team of Remote Handling (RH) operators can interact with a virtual Hot Cell environment. The physics engine is used to emulate the Hot Cell behavior and to provide tactile feed-back of the (virtual) slave. Multi-operator maintenance scenarios can be developed and tested in virtual reality. Complex interactions between the RH operators and the HCF control system software will be tested. Task performance will be quantified and operational resource consumption will be estimated.     

Tritium and heat management in ITER Test Blanket Systems port cell for maintenance operations

Three ITER equatorial port cells are dedicated to the assessment of six different designs of breeding blankets, known as Test Blanket Modules (TBMs). Several high temperature components and pipework will be present in each TBM port cell and will release a significant quantity of heat that has to be extracted in order to avoid the ambient air and concrete wall temperatures to exceed allowable limits. Moreover, from these components and pipes, a fraction of the contained tritium permeates and/or leaks into the port cell. This paper describes the optimization of the heat extraction management during operation, and the tritium concentration control required for entry into the port cell to proceed with the required maintenance operations after the plasma shutdown.     

Water hydraulic manipulator for fail safe and fault tolerant remote handling operations at ITER

Department of Intelligent Hydraulics and Automation (IHA) of Tampere University of Technology has been involved in the European Fusion program since 1994 within the ITER reactor maintenance activities. In this paper we discuss the design and development of a six degrees of freedom water hydraulic manipulator with a force feedback for teleoperation tasks. The manipulator is planned to be delivered to Divertor Test Platform 2 (DTP2) during year 2008. The paper also discusses the possibility to improve the fail safe and redundant operation of the manipulator. During the design of the water hydraulic manipulator, special provisions have been made in order to meet the safety requirements such as servo valve block for redundant operation and safety vane brakes for fail safe operation.     

Remote handling installation of diagnostics in the JET Tokamak

The requirement for an upgrade of the diagnostics for the JET ITER Like Wall (ILW) while maintaining personnel exposure to contamination as low as reasonably practicable or ALARP, has necessitated the development of a bespoke set of diagnostic components. These components, by virtue of their design and location, require a versatile yet comprehensive suite of remote handling tools to undertake their in-vessel installation. The installation of the various diagnostic components is covered in multiple tasks. Each task requires careful assessment and design of tools that can successfully interface with the components and comply with the handling and installation requirements. With remote maintenance a requirement, the looms/conduits were designed to be modular with connections which are electrically connected when the module is fitted or conversely disconnected when removed. The shape of each complex and often bulky component is verified during the design phase, to ensure that it can be delivered and installed to its specified location in the torus. This is done by matching the kinematic capabilities of the remote handling system and the path of the component through the torus by using a state of the art virtual reality system.     

Development and application of high volume remote handling systems in support of JET and ITER

The Joint European Torus (JET) Remote Handling System has evolved from a small scale maintenance capability to one of high efficiency large volume installations. The Enhanced Performance 2 shutdown 2010–2011 for example, required the replacement of many thousands of components ranging from about 100 g to 130 kg in weight. The scale of this type of operation and the necessity to maximise operational availability intensified the demands for high productivity whilst maintaining the necessary high standards for precision, reliability, cleanliness, and operational security.This paper discusses the developments in design, control, maintenance, preparation and operation of the current state of the art remote handling facilities at JET. It explores how the experience of over 20,000 h of operations has developed the applied methodology and how this could be appropriate to ITER and other facilities requiring complex remote maintenance, where extensive, high productivity remote handling operations will be essential. It also discusses the advances that have been made in management and presentation of operational data within the command, control and human machine interfaces (HMI) systems, along with the supporting operational databases.     

Nuclear design of a heliotron-H fusion power reactor

Nuclear analysis was carried out for the heliotron-H fusion power reactor employing anl=2 helical heliotron field. The neutronics aspects examined were (a) tritium breeding capability, (b) shielding effectiveness for the superconducting magnet (SCM), and (c) induced activity after shutdown. In this reactor design of the heliotron-H, the space available for the blanket and shield is limited due to the reactor geometry. Thus, some parametric survey calculations were performed to satisfy the design requirements. The nucleonic design features of the heliotron-H are as follows. An adequate tritium breeding ratio of 1.17 is obtained when a 10-cm thick Pb neutron multiplier and a 40-cm thick Li₂O breeding blanket are used. In this case, the total nuclear energy deposition is 16.10 MeV per 14.06 MeV incident neutron. The performance of the SCM is assured during 2 yr of continuous operation using a 20-cm thick tungsten shield. Biological dose rate behind the SCM at 1 day after shutdown is too high for hands-on maintenance.     

Risk-Based,genetic algorithm approach to optimize outage maintenance schedule

A huge number of components are typically scheduled for maintenance when a nuclear power plant is shut down for its planned outage. Among these components, a number of them are risk significant so that their operability as well as reliability is of prime concern. Lack of proper maintenance for such components during the outage would impose substantial risk on the nuclear power plant (NPP) operation.     

AP1000核电厂灵活循环燃料管理策略研究及应用

我国核电装机容量逐年稳步扩增,核电厂参与电网调峰愈加频繁,固定的换料周期逐渐难以满足核电厂经济运行的需求。本文基于AP1000核电厂18个月堆芯装载方案,设计了±1个月和±2个月的灵活周期堆芯装载方案,完成方案的安全性限值与燃料经济性评价,开展完整的安全分析。结果表明,堆芯设计满足安全相关验收准则的要求,全面论证了灵活循环燃料管理策略的安全性和可行性。本研究为AP1000核电厂灵活循环周期运行提供了技术支撑,灵活循环周期运行即将在海阳核电厂中工程应用。