Development of Decommissioning Engineering Support System ...

Journal of NUCLEAR SCIENCE and TECHNOLOGY, Vol. 41, No. 3, p. 367–375 (March 2004)

TECHNICAL REPORT

Development of Decommissioning Engineering Support System (DEXUS) of the Fugen Nuclear Power Station Yukihiro IGUCHI1; , Yoshiki KANEHIRA1 , Mitsuo TACHIBANA2 and Terje JOHNSEN3 2

1 Japan Nuclear Cycle Development Institute, Tsuruga-shi, Fukui 914-8510 Japan Atomic Energy Research Institute, Shirakata-Shirane, Tokai-mura, Naka-gun, Ibaraki 319-1195 3 Institutt for energiteknikk, P.O.Box 173, N-1751 Halden, Norway

(Received July 18, 2003 and accepted in revised form November 18, 2003) The Fugen Nuclear Power Station (NPS) was shut down permanently in March 2003, and preparatory activities are underway to decommission the Fugen NPS. An engineering system to support the decommissioning is being developed to create a dismantling plan using stateof-the-art software such as 3-dimensional computer aided design (3D-CAD) and virtual reality (VR). In particular, an exposure dose evaluation system using VR has been developed and tested. The total system can be used to quantify radioactive waste, to visualize radioactive inventory, to simulate the dismantling plan, to evaluate workload in radiation environments and to optimize the decommissioning plan. The system will also be useful for educating and training workers and for gaining public acceptance. KEYWORDS: Fugen, ATR, decommissioning, system engineering, CAD, virtual reality, radiation dose, visualization, data management

I. Introduction Fugen (ATR: Advanced Thermal Reactor) is a 165 MWe, heavy water moderated, light-water cooled, pressure-tube type reactor. The development was promoted by Power Reactor and Nuclear Fuel Development Corporation (PNC) as a Japanese national project since 1967. The construction started in December 1970 and Fugen received a final license for operation in March 1979. As a thermal reactor, Fugen has been positively utilizing mixed uranium and plutonium oxide fuel (MOX fuel). Since then, Fugen has been operating about 24 years and attained ca. 21 TWh of power generation, ca. 130,000 hours of total operation time and 62% as an average load factor. In February 1998, the Atomic Energy Commission of Japan decided to end the mission of ATR development and introduced a new policy that development and research of decommissioning of Fugen should be promoted in order to carry out the decommissioning smoothly after the shutdown in 2003. Several strategies for the preparations have been evaluated since 1998.1) It is important to execute the decommissioning economically and rationally. Therefore, a systems engineering approach is necessary in order to optimize the workload, exposure dose, waste mass and cost by selecting appropriate dismantling plan at the planning stage of the decommissioning. Because the nuclear facilities have a large number of components and structures, it is necessary to evaluate the process effectively and precisely before the dismantling is initiated in reality. For this reason, in order to make an efficient decommissioning plan, we have been developing an Engineering Sup-



Corresponding author, Tel. +81-770-26-1221, Fax. +81-770-268129, E-mail: [email protected]

port System for decommissioning by adopting new information technologies such as 3-dimentional computer aided design (3D-CAD) systems and virtual reality (VR) systems. This paper describes the status of the development of the system for the Fugen Nuclear Power Station (NPS).

II. Outline of the Engineering Support System at Fugen The systems engineering approach is a method to optimize the workload, exposure dose, waste mass and cost by selecting appropriate dismantling plan at the planning stage of the decommissioning. For this purpose, Decommissioning Engineering Support System (DEXUS) is under development by using 3DCAD, VR and visualization technology.2,3) As illustrated in Fig. 1, DEXUS consists of database system, evaluation and optimization system, VR and visualization system, and data management system. The CAD data, volumetric data and activity inventory data is input to the visualization system to show the complex structure and radioactivity. The data is also related to the decommissioning plan evaluation and optimization system. The output of the decommissioning plan is also visualized by the system. Moreover, an advanced simulation such as interference checking during the dismantling plan is realized. This means we can expect more precise evaluation of workload, simulation of workers and safety check at the dismantling plan by using virtual reality technology and the result can be reflected on the evaluation system. These sub-systems are used for the planning stage of decommissioning project. In the future, a data management system (project and waste data management) at the real dismantling phase is necessary. This sub-system will be developed at a later stage.

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Decommissioning Engineering Support System Database System Activity Inventory Visualize

Data

Evaluation and Optimisation

Volumetric Data (Weight, Volume, Surface etc.) 3-dimensional CAD Data

VR & Visualization Activity Visualisation

Manpower Analysis

Dismantling Simulation Data

Dismantling Method

Planning and Training Visualize

Radiation Dose

Tele-robotics Visualize

Data

COSMARD (Developed by JAERI)

PA Presentation

Data Reflect

Waste Mass

Data Management (Future Plan) Project Management Waste Data Management

Fig. 1 Conceptual design of DEXUS

1998

Plant Status

1999

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Operation

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2004

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2006

2007

Preparation Period (ca. 10 years) Shutdown (March 2003)

Activity Inventory Assessment Data Reflection

Database System

Reactor and Auxiliary Building Turbine and Fuel Pool Building Outside Equipment and Data Finishing

3D-CAD, Volumetric Data

Evaluation & Optimisation

Data Reflection Introduction to Fugen Assessment of the Decommissioning Plan

COSMARD

VR & Visualization

Feedback and Optimization Reflection

Planning Phase-I

Tools Development

Exposure Dose Evaluation System

Phase-II

Integration with Planning System Further Development

Fig. 2 Development schedule of the DEXUS

The development of the system was started in 1998. The CAD data, database of mass and radiation activity are currently completed. Some commercial software tools were introduced for the dismantling scheduling and visualization as well as newly developed systems. In the first step of the planning stage of the decommissioning, the planning support system will be completed in 2004. The system and sub-systems work on PCs in a networked environment. The sub-systems related to 3D-CAD require much computing resources (memory and processing speed, e.g. 2 Giga Byte memory and 2 Giga Hertz CPU) but the database system is available on standard PCs connecting with the powerful database server PC. The maintenance of the system is relatively easy to accomplish and all the employees at the Fugen NPS can easily access the system thorough the network.

Figure 2 shows the development schedule of DEXUS of the planning support system.

III. Database Connection and Simulation by 3DCAD Data The 3D-CAD data of the reactor, auxiliary, turbine buildings, etc. is prepared and the property data of the component such as weight, material, activity, contamination, radiation dose rate is stored in the database system in order to evaluate the mass and level of the waste. Visualization software to show 3D-CAD data is also prepared as shown in Fig. 3. This visualization system also displays the property data of each component by connecting the object in CAD with the data in the database as shown in Fig. 4. It is possible to color the objects according to the radioactivity level in JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY

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Development of Decommissioning Engineering Support System (DEXUS) of the Fugen Nuclear Power Station CASE-1

Before

Tank Removal Interference CASE-2 (Alternative way) Outlook of Fugen

Piping

Cut View of Reactor

Fig. 3 Example of visualized equipment Hx.1 Removal Component and Activity Database

Hx.2 Removal

No Interference

Fig. 6 Visualization of dismantling movement

Cut Surface Connection with Design Data and P&ID

Cut 3D CAD Data P&ID Data Visualisation

Wire Frame Radioactivity

Cut Option

Fig. 4 Database connection from CAD data

Attribute before Cutting

Attribute after Cutting

Fig. 7 Cutting simulation in 3D-CAD

1.Removal of piping

2.Removal of Hx. 1

3.Removal of Hx. 2

Schedule

piping Hx. 1 Hx. 2 Tank

Work Area Setting

1.

2.-3.

4.

4.End of Dismantling

Overlap between work area and plant Evaluation Results (CSV format)

Fig. 5 Dismantling scheduling simulation

the database. Moreover, by selecting an object of 3D-CAD, the symbol in the P&ID (Piping and Instrumentation Diagram) that contains the object is highlighted in a drawing. The schedule simulation and animation movement enables the visualization of the dismantling process with commercial software (Figs. 5 and 6). The schedule simulation is connected with software scheduling or project management software. The components disappear according to the schedule in the CAD system. The animation system can be used for the dismantling plan in detail by making each movement of components or parts. This system is useful for route finding or interference avoidance. A customized cutting function was developed. Virtual cutVOL. 41, NO. 3, MARCH 2004

Selection of evaluation item

BUD_ID Compornect Room (PlantSp Type1 ID ace) (PlantSpace) 1106 24 CONC 1105 25 CONC 1102B 26 CONC 1104 29 CONC 1105 30 CONC 1102B 31 CONC 1106 34 CONC 1105 35 CONC

ID

Area(m2) 24 25 26 29 30 31 34 35 -

25.92 25.92 28.8 25.92 25.92 25.92 29.92 29.92

Vol.(m2) 5.76 5.76 7.2 5.76 5.76 5.76 6.72 6.72

Fig. 8 Mass evaluation in 3D-CAD

ting is available in the 3D-CAD software, and the attributes of the original object and new identification numbers are attached to the cut objects as shown in Fig. 7. This function is important to secure the traceability of waste. Furthermore, the user can define a specific area and obtain the data in the area such as total mass volume, weight, surface etc. as shown in Fig. 8. Piping and ducts are automatically cut at the border of the area. This data can be used for the planning of workload of dismantling work as described in the next part.

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IV. Development of Dismantling Plan Evaluation System

V. Development of an Exposure Dose Evaluation System with Virtual Reality (VRdose)

In order to make an optimized dismantling plan, we have adopted Computer Systems for Planning and Management of Reactor Decommissioning (COSMARD)4,5) developed by Japan Atomic Energy Research Institute (JAERI) based on the experience of the decommissioning of the Japan Power Demonstration Reactor (JPDR). COSMARD enables evaluation of workload, radiation exposure dose, waste mass and schedule of the dismantling process as shown in Fig. 9. The input data such as weight, radioactivity, and radiation dose rate, come from our component database and 3D-CAD. This system connects with other sub-systems, evaluates the dismantling cost and finally produces an economical and reasonable decommissioning plan. The workload is evaluated using a model that describes the relationship between physical characteristics such as weight, location, radiation, type, material etc. of the components and manpower. The same model can be applicable for the common components as JPDR; however, a special evaluation is necessary for the unique components of Fugen such as heavy water system or reactor core as described in Fig. 10. The calculation is now initiated and the models are being verified.

1. Background In nuclear installations, in service and after service, some areas are inaccessible because of higher radiation and surface or air contamination. VR technology can be a very useful solution for planning operations in such restricted areas. When planning the decommissioning of an NPP, high importance lies on balancing cost reduction and safety. Having access to planning tools using computer simulation technology such as VR is very effective for optimization of this kind of questions. Since 1999, a VR tool named VRdose has been developed for simulation and planning of dismantling work in an environment with presence of radioactivity.6) It is possible to evaluate the workload of the dismantling of the general component by COSMARD based on the experience of decommissioning of existing plants. However, equipment such as the reactor core or heavy water system, which is unique to Fugen, requires a special evaluation as described. Moreover, intensive training before the real dismantling plan is effective for reducing radiation exposure dose, workload and for improving safety. For example, mock-up training will be replaced with a computer simulation system. For this reason, a dismantling work simulation system based on VR technology and 3D-CAD data seems very useful.

Input(Main) Work Breakdown Structure

Dose

Volume Data Weight, Activity Inventory etc.

Manpower

Schedule

Environment Dose rate

:Fugen’s Original Data :JPDR Experience

Work Model

2. Outline of the System VRdose is a simulation system of human movements, which evaluates workload and exposure dose. A set of virtual humans, manikins, can move around in the VR space, which in the Fugen case has been derived from 3D-CAD data. The manikins can perform sequential work operations, interacting with and waiting for each other. The manikins and their operations may be recorded as work scenarios. Based on a work scenario the system outputs work-time and exposure dose for each worker. Scenarios may be played back, discussed and edited, helping to arrive at a reasonable work process. The flow of the system concept is shown in Fig. 11. Figure 12 shows a snapshot from the user interface. In the

Fig. 9 Function of COSMARD 3D CAD Data

Visualisation Image of Radiation Dose Rate

Components of Fugen Common Components

• Piping • Pump, Motor • Hx, Tank • Duct, Cable Tray

Decontamination

Unique Components Condition is Special (Common components)

Special structure

• Reactor • Heavy water system • Steam drum • Fuel handling sys.

Tritium decon.

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Independent Estim.

3D-CAD Data (VRML2.0) Editor of Work Scenario and Radiation Dose Rate (JAVA)

Image of Scenario Editor

Radiation Dose Rate Data Base Work Scenario Data Base

Additional model

Work and Dose Rate Visualisation

Calculation of Labour and Exposure Dose

COSMARD Output

Total man power, Total occupational dose

Fig. 10 Application model of COSMARD

Fig. 11 Concept of VRdose

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Development of Decommissioning Engineering Support System (DEXUS) of the Fugen Nuclear Power Station Planning and play back

Scenario Radiation (2D-map)

History of radiation dose rate

Tool selection

Radiation (landscape)

Fig. 12 User interface of VRdose

default set-up VRdose comes with four work areas for use in standard mode of the program, representing different sets of windows interfacing with the VR model of the work environment and with sets of radiation information. In addition, VRdose has a full screen stereoscopic demonstration mode, allowing for use in an immersive VR facility. This system is developed in cooperation with the Institute for Energy Technology (IFE) in Norway, which is the host of the OECD/NEA Halden Reactor Project in Norway.

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and selected. Any pre-defined object in a model may be moveable. In scenario recordings, manikins can access these objects, and they can also be moved to different locations. When generating a VR model, the developer decides which objects should be moveable. The navigator, as well as the rest of VRdose has been developed using Java and the Java 3D API (Application Protocol Interface). The geometries are made in VRML. Dose-rate visualization is an important feature of VRdose, and various ways of visualizing the radiation situation are available. In Fig. 13 an example situation is shown. The bright green area at the bottom left of the main window indicates that some source of high radiation is present somewhere on the reactor top. The same information can be extracted from the overview map (upper left window). The dosimeter surface plot, at the bottom left in Fig. 13, shows the dose-rate level at chest height of the virtual spectator on a 50  50 m2 area. The pole indicates the position of the VR camera through which the scene in the navigation 3D window is viewed.

3. The Navigation Area For most users, the first approach to VRdose will be the set of tools available in the Navigation Area. The main window in this workspace is the 3D Navigation window, to the right in Fig. 13. Virtual Environments (VEs) described in the Virtual Reality Modelling Language (VRML, ISO/IEC 14772-1: 1997) format can be loaded and a set of navigation functions allows the user to move through and explore the selected VE in various ways. The navigator has a 3D radiation visualization tool, and in Fig. 13 this tool has been activated. It also has a tool for selecting objects or positions. Inside the VR model, individual objects can be identified

4. The Scenario Recording Area Planned work operations can be recorded in the Scenario Work Area. This area is shown in Fig. 14. The user may record work scenarios on selected locations in the VE. A scenario consists of one or more workers, each with a work task that can include walking routes, simplified work animations and operations as well as coordination of the different actions with the other participants in the work scenario. Scenarios can be recorded, edited and stored to Extended Mark-up Language (XML) files. In Fig. 15 the list of work actions of the two participants in a demonstration scenario is shown. For this demonstration, one manikin is given the assignment engineer and the other is a mechanic. The user can switch between the manikins or participants while recording, and a pointer always indicates the selected manikin. After the scenario has been recorded, its various tasks can be assigned to real staff whose relevant data have previously been entered into the system database. For each work task in

Fig. 13 User interface in the navigation work area

Fig. 14 The scenario work area

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Mechanic Position Walk Path

Engineer

Synchronize

Position

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Work Work Synchronize Walk Path

dose-rate / time

Fig. 15 Two workers and scenario

Fig. 17 The dose evaluation area

Worker Id

Worker Name

Description

dose-rate / distance

Real World Dose

Show All Worker

Fig. 16 Virtual storage house

the scenario, the estimated dose-rate is computed, and the workers accumulated dose in the task can be visualized as graphs and tables. The manikin workers need dismantling tools. A selection of pre-defined dismantling tools such as a band saw, cutting torch, dust box, scaffold etc. have been modeled and can be inserted into any VE from the Virtual storage house (see Fig. 16) A manikin can pick up a tool, carry it around and use it in work operations. This function gives the user a realistic impression of the dismantling plan. The user can build work scenarios step by step. This may require much effort if the scenario consists of many actions and tasks of many workers. A Scenario Wizard is therefore being developed, and can be applied for all or part of the scenario creation. The scenario wizard utilizes templates or libraries of tasks to produce the scenario semi-automatically. The templates for the decommissioning are configured based on the work breakdown structure from COSMARD. 5. The Dose Evaluation Area When a scenario has been recorded, it can be examined in the dose evaluation area shown in Fig. 17. This area has dose and dose-rate graphs of each of the participants in the scenario, as well as a combination of radiation visualization tools. It will often be useful to move between the dose evaluation area and the scenario area while evaluating the best way to perform the work.

Fig. 18 The database interface

6. The Worker Data Area The fourth area is the interface to the worker database on another PC server. From this data area information from real life workers can be inserted into the database, and recorded scenarios can be assigned to them. The database may record real life doses as well as assigned computer generated doses, and general staff information can be entered. For every task that has been assigned to a real worker the occupational dose and dose-rate is stored. This information is displayed as tables and graphs in the Worker Data work area as illustrated in Fig. 18. From this worksheet reports can also be automatically generated, stating some workers dose history or giving an overview of the dose-rate exposure associated with a certain task. 7. Stereoscopic Projection System (VENUS) Even though for many purposes, the VR models and animations of VRdose can and will be viewed on normal office PCs and laptops, the extra 3D effects of a stereoscopic system with large screen projection is sometimes needed. In a stereoscopic view, the left and right eye get different visual input, e.g. by the use of polarized glasses. This adds depth to the VE, and gives the spectator an increased sense of presence in the virtual world. VRdose is now available on a multipurpose visualization JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY

Development of Decommissioning Engineering Support System (DEXUS) of the Fugen Nuclear Power Station

Fig. 19 Projectors of VENUS and discussion of dismantling plan

system at Fugen named Virtual Engineering and Navigation with a Universal Visualization System (VENUS), which was installed in March 2002. It is possible to see stereoscopic view by using 4 high-resolution projectors and polarized glasses. This system is at present used both in the evaluation and testing of VRdose, and in actual applications of the system. One present application is in the job briefing to engineers as shown in Fig. 19. VENUS will also be used for the public relation purposes. 8. Applying VR Decommissioning Tools There are several application areas for VRdose in a decommissioning process. A virtual reality illustration of a scenario has several advantages over that of a picture or a video. A VR decommissioning tool can offer radiation visualization inside a model of the NPP. This may contribute to improving radiation awareness as well as to provide a better estimation of radiation conditions in the work areas. In addition, radiation computations are performed for all recorded work scenarios. In VRdose, all work operations are represented as scenarios including a number of participants. Each of these participants actions in the scenario may later be linked to a selected real life worker previously entered into the database. Based on these dose-rate scenarios, the sequence of dismantling and work operations can be planned with regard to minimizing radiation exposure involved. Further, the use of staff can always be planned according to the expected dose connected to the work task, aiming both at keeping the staffs doses as low as possible and at efficient use of working power. Once a work plan has been made, VRdose also provides an effective tool for job briefing to the staff involved. Unlike videotapes, it is possible in VR to move around during playback, allowing the spectator to view the scenario from any angle. In VRdose a 2D map is also available, to make orientation and precise movement easier. Once the work plan has been confirmed, VRdose can be used for training purposes. One may rehearse and demonstrate complex scenarios without exposing the trainees to any radiation. The operations that require much safety attenVOL. 41, NO. 3, MARCH 2004

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tion can be performed in a secure environment, and the operations that will be done in a high radiation area can be practiced in VRdose at any time and as frequently as necessary and at low cost. The possibility of training for the work tasks in advance, along with better planning and briefing should lead to an optimization of the radiation dose and minimization of workload and consequently result in cost reduction. The economical benefit gained from using the VRdose system will compensate the cost of the development and introduction of this software. The results could be reflected in the work plan itself. VRdose can also provide the public with illustrating and comprehensible information of the decommissioning process. This will help to prevent misunderstandings about the decommissioning process. The minimizing of radiation exposure is also an important issue to both the public in general and the environmental organizations in particular. Briefings to authorities and the press can be made much clearer, directly and convincingly when using the virtual reality tool. 9. Application Test VRdose has been applied for a part of the dismantling process. In 2001 at the Fugen site, a replacement work was conducted after piping corrosion of the helium circulation system, which is connected to the heavy water system (helium is used as a cover gas in the reactor core). A pipeline was laid out in a higher radiation area and it was cut and removed for the replacement. A part of this work was evaluated by using VRdose system after the job was finished. The evaluated area includes one air valve, 9 straight pipes, 4 elbows and 2 tees. The average radiation dose-rate was 0.1 mSv/h. Eight workers were involved and it took three days to remove the piping. The number of cutting places was 15 and band saws and saber saws were used. Figure 20 shows a photograph of a part of the area. The model of this area was extracted from 3D-CAD data and converted to VRML files including scaffolds, structure, walls and other piping and equipment as obstacles. A scenario was made based on the results of the work.

Fig. 20 Evaluation area of piping removal

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on COSMARD for more accurate evaluation. In near future, some of the functionality mentioned above will be included in the system and applied to real cases of dismantlement planning and training. This may effectively lead to a reduction in the total cost of decommissioning as well as to safety improvements during dismantlement. VRdose and similar systems have applications in nuclear decommissioning. Moreover, VR technology could be used as an effective planning and training tool for facility maintenance work. The procedure is planning of work operation, personnel assignment and job briefings just like a real world decommissioning situation. VRdose also provides a possibility for training operations involved in high radiation area work without expensive special training equipment, and can be a very helpful tool in training for handling extreme situations.

VI. Conclusion Fig. 21 Simulation of piping removal work

The simulation produced a reasonable animation of the work of three days. In principle, the system should be used at the job planning stage but this trial usage gave us a good practice of the system application. First, even though it is a single job, the scenario of the job consists of many tasks. These tasks should be presented in the scenario wizard. Secondly, waiting time in the simulation is longer than the time it takes to do the actual cutting. During this time the workers are wearing special protective clothing to prevent radioactive tritium intake. The other time spent was for approach and withdrawal movement, preparation of tools, discussion among workers or idling. In the simulation, these are represented as waiting time. Some waiting time is actually necessary. It should be included into the simulation based on the outcome of the real experience. However, part of the waiting time can be eliminated using this system and job briefing for workers before they perform the real job. A part of the simulation is shown in Fig. 21. 10. Future Plans and Possibilities of VRdose The present version of VRdose simulates external exposure dose. In the new version, radioactive tritium (beta emitter) intake is also considered, as cutting of the heavy water or helium system may release vapor with tritium, derived from heavy water. The intake exposure will be calculated based on the concentration of tritium in air and on efficiency of protective clothing. Moreover, in the dismantling process, some radioactive materials or shielding materials might be moved. This leads to changing of radiation dose-rate in the work area. Simulation of dynamic radiation dose rate transition is still challenging, mainly because of the required computing power. However, the situation is improving due to a favorable price to performance ratio in hardware technology. The scenario wizard is still limited. The wizard will be extended to include more information about the dismantling work after a number of tests in realistic situations. The final outcome of the workload estimates should be reflected later

The decommissioning engineering support system (DEXUS) for the Fugen decommissioning project was developed and it is expected to be useful for the planning of the dismantling process. The system enables data retrieval from the component database, estimation of waste amount, visualization of radioactivity, scheduling of dismantling and a number of other useful capabilities. Moreover, by using virtual reality technology, it is possible to evaluate exposure dose more accurately and to estimate the workload of dismantling work in the radiation environment more easily. In the future, this system will be expanded to be useful for training system, coupled with a remote control system, database and project management. The system will quite effectively lead to the reduction of the total cost of the decommissioning and the improvement of safety during the dismantlement.

Acknowledgments We are grateful to Dr. Satoshi Yanagihara of Japan Atomic Energy Research Institute for the co-operation work by using COSMARD (Computer Systems for Planning and Management of Reactor Decommissioning) and many suggestions to the engineering support system. We also express our grateful to Ms. Grete Rindahl, Mr. Michael Louka and Fridtjov
wre of Institutt for Energiteknikk–OECD Halden Reactor Project for the development of the virtual reality system. We also thank Mr. Masahiro Chujou for his enthusiastic contribution of the test and evaluation of the system.

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Development of Decommissioning Engineering Support System (DEXUS) of the Fugen Nuclear Power Station neering support system of the Fugen NPS,’’ ICONE11-36270, (2003). 4) S. Yanagihara, ‘‘COSMARD: Code system for management of JPDR decommissioning,’’ J. Nucl. Sci. Technol., 30[9], 890 (1993). 5) S. Yanagihara, et al., ‘‘Development of computer systems for

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planning and management of reactor decommissioning,’’ J. Nucl. Sci. Technol., 38[3], 193–202 (2001). 6) G. Rindahl, et al., ‘‘Virtual Reality Technology and Nuclear Decommissioning,’’ Proc. Int. Conf. on Safe Decommissioning for Nuclear Activities, IAEA, Berlin, (2002).