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
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.