• Wide scope of application. This simulator can evaluate SA in reactor operating condition and in reactor shutdown condition.
• It is easy to prepare the operating environment. The simulator can be used with normally available PC.
• User can use the simulator without expert knowledge of analysis code such as MAAP. This simulator has user friendly Graphic User Interface (GUI) and feature to make SA scenario with flowchart.
• The evaluation result of the simulator is equivalent to the analysis result by MAAP.

The background of the development of the simulator is described below.

The necessity of updating the Emergency Operating Procedures and Accident Management Guidance (EOPs/AMG) by extending the scope of accident scenarios including SA in the spent fuel pool (SFP) in reactor shutdown condition is recognized as one of lessons from the Fukushima accident. On the other hand, the use of simulator is described as one of possible methods of validating the EOPs/AMG in IAEA safety guide.

From now on, it is expected that the opportunity of using SA analysis code and simulator for validating procedure / education training would increase.

However, the specification of most of conventional simulators does not include the SA in reactor shutdown condition in where the reactor node and SFP node are connected via wet well filled with water. This type of accidents cannot be evaluated with MAAP alone. In addition, special knowledge is needed to handle SA analysis code.

Under such circumstances, a simulator that can easily handle SA codes like MAAP interactively in real time is developed by using the software "DesignEP", a GSE product. The main screen of the simulator is shown in Fig.1. It is easily possible confirm the condition of the nuclear power plant and the operational state of the equipment by a variety of graphical expression. In addition, the simulator can handle simultaneous accidents like in the PCV and SFP in a nuclear power plant or furthermore in multiple units, since the DesignEP can control multiple codes simultaneously. This simulator can be used without special knowledge of MAAP by user friendly graphical user interface.

The evaluation with the simulator is based on the output result from MAAP calculation. The evaluation result of the simulator has been examined under the evaluation condition that can be also evaluated by MAAP alone. It is confirmed that the evaluated result by the simulator is equivalent to the evaluated result by MAAP alone [5]

Fig.1 Main screen of the simulator

Phase 2 : Industrial Confirmation Phase

1. (1) Components:
   ABWR plant

1. (2) Location:
   N/A

1. (3) Materials:
   N/A

1. (4) Condition:
   N/A

• Enable to simulate various SA.

It can evaluate the SA in reactor operating condition and in reactor shutdown condition. In addition, it can evaluate simultaneous accidents in PCV and SFP which are difficult to evaluate with a single SA analysis code. (Fig.2)
This simulator enabled to evaluate SA in reactor shutdown condition by using the MAAP v.5.04. And, the evaluation of simultaneous accident in reactor and SFP was realized by calculating to evaluate mutual influence from MAAP calculations for reactor and SFP.
Using similar method, it is also possible to evaluate multi-unit accidents.

Fig.2 Scope of the simulator

• User friendly GUI design

User can easily check the state of the whole reactor building visually by GUI. This simulator consists mainly of the main screen and SFP screen.

Main screen

Alerts, historical trend graph, status of the reactor building, and the equipment status are displayed on the main screen. (Fig.3)



Fig.3 Constitution of main screen




In the simulator, the reactor building is divided into eleven nodes. Conditions of 12 different parameters in each node like gas temperature and pressure and so on, are visible as change of color. Detailed information is displayed as parameters list by clicking the node icon. The status to be displayed as color can be switched by the button on the main screen. (Fig.4)



Fig.4 Switching status on main screen




Fuel conditions both in RPV and SFP are displayed on the main screen, and the melting state is displayed in 5 stages. (Fig.5)



Fig.5 Status of fuel




Equipment icons display the operational statuses of the equipment and are used to turn on and off these equipment’s. User can control the equipment at arbitrary timing by click the button on the equipment icon.
Alerts and trend graphs can be displayed according to any parameters and conditions.

SFP screen

Gas phase temperature, water level and spent fuel condition are displayed on the SFP screen. (Fig.6) The view of spent fuel condition can be switched between melting degree and fuel temperature. More detailed information can be displayed by clicking on the spent fuel icons. (Fig.7)



Fig.6 Constitution of SFP screen



Fig.7 Detail information of spent fuel



• Accident scenario setting with flowchart.

It is possible to create accident scenarios with flowchart. The Flowchart can be created by dragging and dropping prepared process icons which deal with various processes like branching by specified conditions, parallel processing, and repeating process and so on, as shown in the Fig.8. Even those who are not familiar with the MAAP code can also create the accident scenarios easily by combining these process icons.



Fig.8 Flowchart of accident scenario



• Wide operational environment

This simulator is able to run on a PC not need special spec. This simulator is able to run in both stand-alone and online. And it is possible to run the simulator by web browser online. (Fig.9)



Fig.9 Wide operational environment

This simulator consists of two MAAP servers and one client. The MAAP server consists of the MAAP, database and interface code. These are used for accessing variables in MAAP code, and used for drawing GUI objects. One MAAP server is to evaluate the accident in reactor, and the other is to evaluate the accident in SFP.

The client summarizes the results of the calculation from both servers, and evaluates mutual influence based on the each results (coupling calculation), and feedbacks them to each MAAP servers.

The software DesignEP, a GSE’s product, is used for this simulator. The DesignEP is software which can integrate the SA analysis code MAAP into the interactive real time simulation environment. It has functions such as access to variables in MAAP code and control of multiple MAAP calculations. (Fig.10)

Fig.10 System configuration

• • Verification of the effectiveness of the nuclear reactor safety system It is easily possible to verify the effectiveness of the nuclear reactor safety system with this simulator. Any nuclear reactor safety systems can be activated/un-activated by user manipulation at arbitrary timings, and the effect of these safety systems is reflected in the evaluation. The simulator allows user to easily check the state of the nuclear power plant and to operate the nuclear reactor safety system easily.


• • Explanatory materials to third parties It is easily possible to check the state of the nuclear power plant by using the GUI of the simulator. Therefore, the evaluated result by this simulator can be utilized as one of the materials to explain the accident countermeasure to third party.


• • Support the judgment of the accident countermeasures The simulator can support the judgment of the accident countermeasures under the SA situation such as the decision making of the possibility of entering the operation floor by predicting the accident progress.


• • Verification of EOPs It is easily possible to set up and understand the accident scenario of the EOPs by the simulator. The EOPs is usually described as flowchart. It is possible to implement such procedures described in EOPs as flowchart in the simulator, though these procedures are needed to be edited as text in conventional analysis code like MAAP, Therefore, it is very easy to understand and verify the EOPs.

1. 1.OSART評価報告書, IAEA-NSNI/OSART/183/2015 , IAEA(2015)
2. 2."Good practices with respect to the development and use of nuclear power plant procedures”, IAEA-TECDOC-1058, IAEA(1998)
3. 3.杉浦, 藤原, 久保田, 他,"原子炉及び燃料プール同時過酷事故進展を扱うプラントシミュレータの開発;（1）全体計画", 日本原子力学会2017年春の大会予稿集, 2M05, 2017.
4. 4.杉浦, 藤原, 久保田, 他,"原子炉及び燃料プール同時過酷事故進展を扱うプラントシミュレータの開発;（2）原子炉停止時におけるプラントシミュレータの仕様及び機能", 日本原子力学会2017年秋の大会予稿集, 1C05, 2017.
5. 5.坂本, 杉浦, 藤原, 他,"原子炉及び燃料プール同時過酷事故進展を扱うプラントシミュレータの開発; (3)ベッセルオープン時のSFPとの結合計算", 日本原子力学会2017年秋の大会予稿集, 1C06, 2017.

Japan Society of Maintenology (ejam@jsm.or.jp)