scholarly journals Investigation of the Status of Unit 2 Nuclear Reactor of the Fukushima Daiichi by the Cosmic Muon Radiography

2020 ◽  
Author(s):  
Hirofumi Fujii ◽  
Kazuhiko Hara ◽  
Shugo Hashimoto ◽  
Kohei Hayashi ◽  
Hidekazu Kakuno ◽  
...  
Keyword(s):  
Pressure Vessel ◽  
Nuclear Power ◽  
Nuclear Reactor ◽  
Fuel Loading ◽  
Concrete Wall ◽  
Cosmic Muon ◽  
Muon Radiography ◽  
Reactor Building ◽  
The Status ◽  
Fukushima Daiichi

Abstract We have investigated the status of the nuclear debris in the Unit-2 Nuclear Reactor of the Fukushima Daiichi Nuclear Power plant by the method called Cosmic Muon Radiography. In this measurement, the muon detector was placed outside of the reactor building as was the case of the measurement for the Unit-1 Reactor. Compared to the previous measurements, the detector was down-sized, which made us possible to locate it closer to the reactor and to investigate especially the lower part of the fuel loading zone. We identified the inner structures of the reactor such as the containment vessel, pressure vessel and other objects through the thick concrete wall of the reactor building. Furthermore, the observation showed existence of heavy material at the bottom of the pressure vessel, which can be interpreted as the debris of melted nuclear fuel dropped from the loading zone.

scholarly journals Investigation of the Unit-1 nuclear reactor of Fukushima Daiichi by cosmic muon radiography

2020 ◽  
Vol 2020 (4) ◽  
Author(s):  
Hirofumi Fujii ◽  
Kazuhiko Hara ◽  
Kohei Hayashi ◽  
Hidekazu Kakuno ◽  
Hideyo Kodama ◽  
...  
Keyword(s):  
Nuclear Fuel ◽  
Pressure Vessel ◽  
Nuclear Power ◽  
Fuel Loading ◽  
Concrete Wall ◽  
Cosmic Muon ◽  
Muon Radiography ◽  
Fuel Assemblies ◽  
Reactor Building ◽  
Fukushima Daiichi

Abstract We have investigated the status of the nuclear fuel assemblies in the Unit-1 reactor of the Fukushima Daiichi nuclear power plant by cosmic muon radiography. In this study, muon tracking detectors were placed outside the reactor building. We succeeded in identifying the inner structure of the reactor complex, such as the reactor containment vessel, pressure vessel, and other structures of the reactor building, through the concrete wall of the reactor building. We found that a large number of fuel assemblies were missing in the original fuel loading zone inside the pressure vessel. The natural interpretation is that most of the nuclear fuel was melted and dropped down to the bottom of the pressure vessel or even below.

Nuclear Power Plant Fires and Explosions: Part IV — Water Hammer Explosion Mechanisms

2017 ◽  
Author(s):  
Robert A. Leishear
Keyword(s):  
Nuclear Power ◽  
Power Plants ◽  
Nuclear Power Plants ◽  
Nuclear Reactor ◽  
Water Hammer ◽  
Compression Process ◽  
Flammable Gas ◽  
Piping Systems ◽  
Fukushima Daiichi ◽  
Accident Conditions

Water hammers, or fluid transients, compress flammable gasses to their autognition temperatures in piping systems to cause fires or explosions. While this statement may be true for many industrial systems, the focus of this research are reactor coolant water systems (RCW) in nuclear power plants, which generate flammable gasses during normal operations and during accident conditions, such as loss of coolant accidents (LOCA’s) or reactor meltdowns. When combustion occurs, the gas will either burn (deflagrate) or explode, depending on the system geometry and the quantity of the flammable gas and oxygen. If there is sufficient oxygen inside the pipe during the compression process, an explosion can ignite immediately. If there is insufficient oxygen to initiate combustion inside the pipe, the flammable gas can only ignite if released to air, an oxygen rich environment. This presentation considers the fundamentals of gas compression and causes of ignition in nuclear reactor systems. In addition to these ignition mechanisms, specific applications are briefly considered. Those applications include a hydrogen fire following the Three Mile Island meltdown, hydrogen explosions following Fukushima Daiichi explosions, and on-going fires and explosions in U.S nuclear power plants. Novel conclusions are presented here as follows. 1. A hydrogen fire was ignited by water hammer at Three Mile Island. 2. Hydrogen explosions were ignited by water hammer at Fukushima Daiichi. 3. Piping damages in U.S. commercial nuclear reactor systems have occurred since reactors were first built. These damages were not caused by water hammer alone, but were caused by water hammer compression of flammable hydrogen and resultant deflagration or detonation inside of the piping.

NERO: A Teleoperated Wall Climbing Vehicle for Assisting Inspection of a Nuclear Reactor Pressure Vessel

1993 ◽  
Author(s):  
B. L. Luk ◽  
A. A. Collie ◽  
T. White
Keyword(s):  
Pressure Vessel ◽  
Nuclear Reactor ◽  
Vertical Surface ◽  
Reactor Pressure Vessel ◽  
Control Console ◽  
The Status ◽  
Walking Mechanism ◽  
Reactor Pressure

Abstract NERO is a series of teleoperated wall climbing vehicles. Each vehicle carries a specific tool for assisting inspection of a nuclear reactor pressure vessel in the U.K. They adopted a simple sliding frame walking mechanism to cope with 250mm head room and 25mm obstacles on the surface. Vacuum suckers are used by the vehicle for climbing vertical surface. The NERO vehicle is driven remotely by an operator via a control console. The status of the vehicle and the control console is displayed on the console’s computer monitor. These vehicles completed their tasks successfully by September 1992.

scholarly journals Structural Modeling and Dynamic Analysis of a Nuclear Reactor Building

2020 ◽  
Author(s):  
Evrim Oyguc ◽  
Abdul Hayır ◽  
Resat Oyguc
Keyword(s):  
Nonlinear Dynamic ◽  
Nuclear Power ◽  
Power Plants ◽  
Nuclear Power Plants ◽  
Nuclear Reactor ◽  
Energy Sources ◽  
Finite Element Program ◽  
Design Spectrum ◽  
Reactor Building ◽  
Set Up

Increasing energy demand urge the developing countries to consider different types of energy sources. Owing the fact that the energy production capacity of renewable energy sources is lower than a nuclear power plant, developed countries like US, France, Japan, Russia and China lead to construct nuclear power plants. These countries compensate 80% of their energy need from nuclear power plants. Further, they periodically conduct tests in order to assess the safety of the existing nuclear power plants by applying impact type loads to the structures. In this study, a sample third-generation nuclear reactor building has been selected to assess its seismic behavior and to observe the crack propagations of the prestressed outer containment. First, a 3D model has been set up using ABAQUS finite element program. Afterwards, modal analysis is conducted to determine the mode shapes. Nonlinear dynamic time history analyses are then followed using an artificial strong ground motion which is compatible with the mean design spectrum of the previously selected ground motions that are scaled to Eurocode 8 Soil type B design spectrum. Results of the conducted nonlinear dynamic analyses are considered in terms of stress distributions and crack propagations.

Nuclear Reactor Pressure Vessel Integrity Assessment: Enhancement Provided by 3D Modeling Flaw Stability Calculations

2013 ◽  
Author(s):  
Adolfo Arrieta-Ruiz ◽  
Eric Meister ◽  
Henriette Churier
Keyword(s):  
Pressure Vessel ◽  
Nuclear Power ◽  
Power Plants ◽  
Nuclear Reactor ◽  
Structural Integrity ◽  
Reactor Pressure Vessel ◽  
Integrity Assessment ◽  
Potential Damage ◽  
Vessel Integrity ◽  
Reactor Pressure

Structural integrity of the Reactor Pressure Vessel (RPV) is one of the main considerations regarding safety and lifetime of Nuclear Power Plants (NPP) since this component is considered as not reasonably replaceable. Brittle fracture risk associated with the embrittlement of RPV steel in irradiated areas is the main potential damage. In France, deterministic integrity assessment for RPV is based on the crack initiation stage. The stability of an under-clad postulated flaw in the core area is currently evaluated under a Pressurized Thermal Shock (PTS) through a fracture mechanics simplified method. One of the axes of EDF’s implemented strategy for NPP lifetime extension is the improvement of the deterministic approach with regards to the input data and methods so as to reduce conservatisms. In this context, 3D finite element elastic-plastic calculations with flaw modelling have been carried out recently in order to quantify the enhancement provided by a more realistic approach in the most severe events. The aim of this paper is to present both simplified and 3D modelling flaw stability evaluation methods and the results obtained by running a small break LOCA event.

The Solenoid Valve for Main Steam Relief Valve Adapted Under Severe Accident

2020 ◽  
Author(s):  
Nobuo Kojima ◽  
Koji Nishino ◽  
Keisuke Sakemura ◽  
Kengo Kobayashi
Keyword(s):  
Nuclear Power ◽  
Main Part ◽  
Nuclear Reactor ◽  
Flow Direction ◽  
Solenoid Valve ◽  
Severe Accident ◽  
Design Specification ◽  
Relief Valve ◽  
Fukushima Daiichi ◽  
Main Steam

Abstract MSSRVs in Boiling Water Reactor (BWRs) can be mandatory opened through a solenoid valve, when a nuclear reactor raises unusual pressure. The solenoid valve consists of a valve main part which forms a flow channel, and a pilot part which controls a flow direction. In the accident of the Fukushima Daiichi nuclear power plant, MSSRVs ware over the design specification of these solenoid valves, and were not able to operate. One of the reason, there is degradation of a sealant and a coil of a solenoid valve. As one of the measures for rebooting the BWRs, the development and verification of a solenoid valve which were applied to the SA condition are required. Since we developed and verified it applied to the SA.condition, we report here.

scholarly journals Imaging the inner structure of a nuclear reactor by cosmic muon radiography

2019 ◽  
Vol 2019 (5) ◽  
Author(s):  
Hirofumi Fujii ◽  
Kazuhiko Hara ◽  
Shogo Hashimoto ◽  
Kohei Hayashi ◽  
Fumiaki Ito ◽  
...  
Keyword(s):  
Nuclear Reactor ◽  
Cosmic Muon ◽  
Muon Radiography

Monitoring of the Recovery Process of the Fukushima Daiichi Nuclear Power Plant from VHR SAR Images

2016 ◽  
Vol 11 (2) ◽  
pp. 236-245 ◽  
Author(s):  
Wen Liu ◽  
◽  
Fumio Yamazaki ◽  
Tadashi Sasagawa ◽  
Keyword(s):  
Power Plant ◽  
Nuclear Power Plant ◽  
Nuclear Power ◽  
Recovery Process ◽  
Sar Images ◽  
Reactor Building ◽  
Building Footprint ◽  
Intensity Images ◽  
Fukushima Daiichi ◽  
Very High

The Mw9.0 earthquake hitting the Tohoku area on Japan's Pacific coast on March 11, 2011, triggered huge tsunamis and a Fukushima Daiichi nuclear power plant breakdown. Due to high radiation levels, plant damage could only be assessed from satellite images. Our study involves four very-high-resolution (VHR) TerraSAR-X/TanDEX-X SAR intensity images taken under different acquisition conditions and used to try and determine reactor building damage. Layover and radar shadow areas were specified first based on building footprint and height, then backscattering patterns in these areas were modeled by introducing sectional views of the target building. Criteria for detecting damage from individual SAR scenes were used to compare simulated backscattering patterns to actual SAR intensity images. Damage to other reactor buildings was then identified based on these criteria. Results were confirmed by comparisons to two optical VHR WorldView-2 images and ground photos.

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