Hideo Ohashi, Prof. Emeritus

University of Tokyo & Kogakuin University
The Window to Society after Retirement from Engineering Education


 This top page is to transmit the proof that I am still alive and enjoying retired life, mainly to my relatives, friends and former students. A story or an event is selected from daily life and my thoughts and experience are introduced.

From Daily Life - 93: Fukushima accident and hydrogen explosion

 As a nuclear power technology advisor for the former Ministry of International Trade and Industry, I assisted in the safe operation of nuclear power plants for 16 years until 1999. During that time, I visited all nuclear power plants scattered from Hokkaido to Kyushu to confirm that the work of regular inspection had been completed according to the reports after the completion. Therefore, I feel a sense of responsibility for the unpredictable accident at the Fukushima No. 1 Nuclear Power Plant in 2011, and I am filled with regret. The deep scars left by the widespread diffusion of radioactivity remain unhealed.
 Recently, my old acquaintance, Michio Ishikawa, published a new book on the core meltdown and hydrogen explosions of the Fukushima accident. He joined the Japan Atomic Energy Research Institute in the early days of nuclear power generation, experienced the construction and operation of Japan's first power reactor, JPDR, and then conducted fuel destruction experiments using the NSRR test reactor, which studies runaway reactors. He later worked on the decommissioning of JPDR, thus accumulating extensive experience and research from the birth to the end of a nuclear reactor. After leaving the Japan Atomic Energy Research Institute, he served as a professor at Hokkaido University and has authored many books. Below, I will consider what we should learn from the Fukushima accident, primarily based on excerpts from his new book.
 The greatest challenge in the use of nuclear power lies in how to contain the radioactivity produced as a result of nuclear fission. The fuel pellets that cause the nuclear reaction in a reactor are small ceramic cylinders, approximately 1 cm in diameter and height, made by sintering uranium dioxide. Radioactivity is isolated from the outside by the following five barriers:
 1. It is contained within the ceramic of the fuel pellet.
 2. It is contained within the zirconium alloy fuel rods that enclose and seal numerous fuel pellets.
 3. It is contained by the reactor that houses the fuel rods.
 4. It is contained by the containment vessel that houses the reactor.
 5. It is sealed by the building that covers the containment vessel.
 In the Fukushima accident, all five of these barriers were destroyed by hydrogen explosions in the three operating nuclear power plants, allowing the release of radioactivity into the environment. The zirconium rods enclosing the fuel pellets has the property that when they come into contact with water at temperatures exceeding 900 degrees Celsius, the oxide film covering the rods breaks down, allowing direct contact between the zirconium and water. This causes the zirconium to deplete the oxygen in the water, resulting in explosive combustion and the generation of a large amount of hydrogen. The book explains in detail the conditions under which this occurs.
 It may seem like hindsight, but if the knowledge of hydrogen explosions caused by the zirconium-water reaction described in the book had been possessed beforehand, even if a core meltdown had occurred, the hydrogen explosion could have been prevented. If the spread of radioactivity had been limited to a localized area within the power plant, the influence of the accident would have been far more limited.
 Nuclear safety is guaranteed by many regulations. The purpose of these regulations is to ensure that equipment maintains a sound operating state within planned operating conditions, and that even in the event of an unplanned situation, the reactor can be immediately shut down, and that the decay heat generated after the shutdown is reliably cooled.
 However, in Fukushima, the cooling of the reactor after the emergency shutdown was interrupted, resulting in the start of a core meltdown. When this situation arose, there were no documents at the time instructing appropriate operations. Core meltdown means the death of the reactor, and its recovery is impossible. If the death of a reactor with the release of a large amount of radioactivity into the environment is called an "ugly death," then ending with the radioactivity remaining inside by continuing cooling down can be called a "graceful death." The difference lies in preventing a hydrogen explosion, which is possible.
 For enhanced nuclear safety in situations where a reactor faces unforeseen difficulties and begins a core meltdown, the reactor must undergo a "graceful death" by preparing appropriate operation manuals that prevent widespread contamination like in Fukushima from happening again. I hope this book will serve as a catalyst for the preparation.



→ Past Top Pages

   
"From Daily Life"
        
1: Tracing family roots
        
2: The second last car
        
3: August 15. my memorial day
        
4: Battlefield rations
        
5: Begginer at the gym
        
6: Fuji View Hotel
        
7: Lesson in Hiragana writing by brush
        
8: Moving from old to new smartphone
        
9: Living alone in my second year
        
10: Welcomed by cherry blossom
        
11: Eden of peach blossom
        
12: Tama River Walk
        
13: Chichibu Pilgrimage
        
14: Bonds with local community
        
15: About my homepage
        
16: Annual report of athletic gym
        
17: Pilgrimage to Mt. Tsukuba
        
18: Reunion of alumni and classmates
        
19: Braking by left foot
        
20: Battlefield rations in the sequel
        
21: Granddaughter has come!
        
22: Visit to Kobayashi Residence
        
23: Wake-up exercise
        
24: Digital photo album
        
25: Seven tools for brushing teeth
        
26: Ambulance
        
27: Quick report on drive monitoring
        
28: Hearing aid
        
29: Jindai Botanical Park
        
30: 2020, a historic year
        
31: Topics of eye
        
32: Final report on drive monitoring
        
33: Cognitive ability test
        
34: PCI to prevent heart infarction
        
35: Ashikaga Flower Park
        
36: 90 years old supported by medication
        
37: 3 years with Subaru
        
38: 45 years living in Seijo
        
39: Caspian Sea yogurt
        
40: Home Museum of Aunt Zschäbitz
        
41: Reunion of university classmates
        
42: Okutama spar tour
        
43: New Year's greeting card
        
44: Implant
        
45: Fuchu Forest Park
        
46: Grave closing
        
47: Walking group of local community
        
48: How-to books for the elderly
        
49: Home altar
        
50: Such a life
        
51: Knee of the elderly
        
52: Metropolitan Kinuta Park
        
53: Shirakaba Art Museum of Kiyoharu
        
54: Haiku; Metasequoia
        
55: Three years with COVID-19
        
56: Battlefield rations in the 6th year
        
57: Hearing impairment
        
58: Shinjuku Station
        
59: Haiku with photograph
        
60: Moving to 5G smartphone
        
61: History of private cars
        
62: Setagaya Art Museum
        
63: FreeCell
        
64: Turbo
        
65: Hinata Temple of Yakushi
        
66: Moving of home computer
        
67: Amakusa tour
        
68: Hand craft as a hobby
        
69: Kitami Community Square
        
70: Photo-Haiku 2
        
71: Support scam abusing Trojan Horse
        
72: Bedside gym
        
73: Metropolitan Nogawa Park
        
74: Family funeral
        
75: Sudoku (Number Place)
        
76: Photo-Haiku 3
        
77: Ohyama Afri Shrine
        
78: Kunisaki Peninsula tour
        
79: The old school system is far away
        
80: Cooking group of local community
        
81: Motor fan group of local community
        
82: Directories disappear!
        
83: Tunnel ventilation
        
84: Hearing aid renewal
        
85: Photo-Haiku 4
        
86: Digital records of life
        
87: 80 years after the ceasefire
        
88: Diagnosis of walking ability
        
89: Tracing back in time
        
90: Tour around castles and potteries
        
91: Asset management
        
92: Email - Part 1
        
93: Email - Part 2

   
"Memorable Scenes"
          Series 1: Parade with Doctor hat on the head
          
Series 2: Calligraphy in a frame
       
Series 3: A young man from the Orient
        Series 4: Sumo-stamping
        Series 5: Waiting room of Shanghai Station
        Series 6: Let's Walk Festival
       
Series 7: Last long-distance drive
          Series 8: My Car No. 3
          
Series 9: Ski camp
          
Series 10: Safari experience
        
Series 11: First encounter with dogwood
        Series 12: Mt. Fuji

   
"Treasure Box of Words"
          Series 1: Virtue brings profit
          Series 2: Wait for a ripe moment
          Series 3: Catch the symptoms
          Series 4: Words are selected metaphors
          Series 5: Start with two humans
          Series 6: Optimism is a will, pessimism a mood
          Series 7: Atop a summit, and another becomes visible
          Series 8: We see only what we want to see
        Series 9: Chanllenge is the privilage of the young
        Series 10: Today is the first day of my life

   
Engineer Series 1: Who's engineer, juveniles' answer
          Series 2: Corus of "We raise engineers!"
          Series 3: From Nobel Prize to Gold Medal
          Series 4: Professionals in three categories
          Series 5: Various tasks in engineering
          Series 6: Classification of EPs by IEA
          Series 7: Science, technology and related professionals
          Series 8: Proposal for the classification of engineers
          Series 9: Revised proposal for the classification of engineers
          Series 1 - 10: Whole Series including summary and remarks

    Cartoon Series 1: Mechanism of viscosity
          Series 2: Mechanism of loss generation
          Series 3: Commuter packer and enthalpy
          Series 4: Skinny grasshopper and fat pupa
          Series 5: From hand-drawn picture to ready-made clip art
          Series 6: Why do you learn? - 1
         
Series 7: Why do you learn? - 2
          Series 8: Two Sciences
         
Series 9: Scientist and Engineer
          Series 10: Science and Non-science
        Series 11: Structure of human relations
        Series 12: Oriental subconsciousness

   
Nostalgia Series 1: The first own car
          Series 2: The first driver's license
          Series 3: Comparison of German and Japanese Diploma
          Series 4: The first air travel
          Series 5: Tachometer used 60 years ago
          Series 6: The three sacred calculators
          Series 7: The first home computer
          Series 8: Sentimental journey to Nordkapp
          Series 9: Change of photograph
          Series 10: Story of passport

   
The others

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Let's find facts!  Final version revised in August, 2016.

Japanese universities found in statistics

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Brief Self Introduction
Mail address: PGA02322@nifty.com
Place of residence: Tokyo, Japan

Major Past Activities

Membership of Academic/Professional Societies

Curriculum Vitae

Recent Publications

The center of gravity of recent publications has been shifting from those with the topics in fluids engineering to those in engineering education. Please refer to Publications List of the recent papers written in English.