The nuclear accident that occurred in Tokai Village, Japan, is a very famous incident. Due to this accident, the surrounding area was exposed to radiation, and three individuals near the accident site were exposed to a tremendous amount of radiation. Among them, two suffered unimaginable pain and eventually died. This accident is recorded as a Level 4 incident on the International Nuclear Event Scale. Today, let's take a closer look at the Tokai Village radiation accident.

About 25 years ago, on September 30, 1999, the Tokai Village radioactive leak accident occurred at the JCO uranium processing facility in Tokai Village, Nakagun, Ibaraki Prefecture, Japan. To understand the incident of that day, one must know the uranium processing process. Uranium initially exists in the form of a mineral called uraninite. So, first, this mineral form of uranium is mined, and then impurities are removed.

We enter the process of extracting pure uranium through the enrichment process. When the enrichment process is completed, the pure uranium consists of about 99.3% uranium-238 and the remaining approximately 0.7% is uranium-235. This 0.7% of uranium-235 is the key fuel for nuclear power generation. Therefore, it is necessary to increase the proportion of uranium-235 to about 3 to 5% while reducing the proportion of uranium-238 to about 97 to 95%. This is known as uranium enrichment. To simply explain this process, it involves selectively extracting only uranium-235 from the pure uranium. Then, if we assume we have collected 5 units of uranium-235, we would combine that with 95 units of uranium-238. This results in uranium that is enriched in a 95 to 5 ratio. The enriched uranium is then used for various purposes.

Through the process, small cylindrical chunks, known as fuel pellets, are compressed. These fuel pellets are then placed inside metal fuel rods, which are bundled together to form a fuel assembly that is used in the reactor. This is how nuclear fuel is produced through the nuclear fuel processing process, and it is then inserted into the reactor to generate electricity. This is the overall nuclear fuel processing procedure.

Now, let's return to the day of the accident at the JCO uranium processing facility. This facility is where uranium that has undergone enrichment is converted into fuel. However, on September 10, 1999, an unusual task that had never been seen before was assigned here. The task involved processing 57 kg of highly enriched nitric acid uranium fuel, which was intended for Japan's experimental reactor, Joyo. Three workers were assigned to this task: Ochi Sashi, Shihara Masato, and Yokokawa Yutaka. All of them were experienced.

They had over ten years of experience as workers. The tasks assigned to them that day were not the usual ones. The workers had been processing low-enriched uranium fuel for light water reactors, with less than 5% uranium content. However, the materials they handled that day were a high-concentration uranium solution containing 18.8% nitric uranium. This was the first time the workers dealt with nitric uranium, and they had no prior experience. However, the management did not communicate any precautions during the work and did not warn them about the risks of criticality accidents. The most critical aspect of the manufacturing process is to be cautious about criticality accidents. So, what is a criticality accident? It refers to the minimum mass of fissile materials, such as uranium and plutonium, needed to sustain a chain reaction. Now, let's say I gathered 100 kg of pure uranium and shaped it into a sphere. In the case of uranium, if you just leave it alone...

Nuclear fission occurs when uranium naturally undergoes fission. Of course, the probability of uranium spontaneously causing nuclear fission is not very high. However, if it surpasses the critical mass, the probability of uranium undergoing fission increases drastically. The critical mass varies depending on numerous factors such as the purity of the material, its form, density, reflectors, and absorbers. 

Now, imagine we gather 100 kg of pure uranium and exceed the critical mass. At this point, the uranium splits into various substances, releasing two or three neutrons. These emitted neutrons can then strike other uranium atoms, causing them to split as well, leading to a chain reaction. During this process, light, heat, and radiation are generated. If there are people nearby, they would be almost certainly facing a life-threatening situation, as they would be exposed to a significant amount of radiation.

the surrounding environment can be destroyed. When the mass exceeds the critical limit, an unintended nuclear fission chain reaction occurs, which is known as a criticality accident. Now that we understand the manufacturing process and what a criticality accident is, let's go back to the day of the Tokai Village incident. Until September 30, the second day of the operation, no significant problems had arisen. The work was nearing its final stages. These three individuals mixed nitric acid with enriched uranium powder at a concentration of 18.8% to create uranyl nitrate. According to JCO regulations, the amount of enriched uranium was limited to below 2.4 kg to prevent a criticality accident. Therefore, they mixed 2.3 kg into the bucket. The maximum amount of uranyl nitrate that can be produced in one batch is 2.3 kg. The three workers poured the resulting uranyl nitrate into a precipitation tank, and the work continued. However,

When the amount of uranyl nitrate that entered the settling tank reached about 16 kg, it began to emit a blue light and released an enormous amount of radiation. An uncontrolled nuclear chain reaction criticality accident occurred. The critical mass of pure uranium-235 is about 52 kg. However, the uranyl nitrate worked on this time had an enrichment ratio of 18.8%. Normally, neither the workers nor JCO had ever handled such a high concentration of uranium. Moreover, since uranyl nitrate was in a solution state, a criticality accident could occur with a mass smaller than the critical mass. All these conditions aligned, leading to the criticality accident. The workers' process was completely chaotic. Normally, the amounts of uranium powder and nitric acid should be precisely calculated in advance to ensure that the volume of the solution does not exceed the critical mass.

Next, we mixed 2.3 km at a time, little by little, very slowly, without mixing it all at once. When mixing nitric acid and uranium powder, we had to use a special container designed to be resistant to corrosion and to prevent criticality accidents, rather than a stainless steel bucket. However, due to the ease of cleaning and the reduction in work time, the workers would likely opt for the stainless steel buckets. Additionally, to minimize worker involvement during the mixing process, it should be conducted as automated as possible. But on that day, all the work was done manually. Once the nitric uranium was fully mixed, it had to be poured very slowly into the dissolution tank. However, that day, the workers directly inserted it into the precipitation tank without going through the nitric uranium dissolution tank. The process of ensuring the materials were well mixed was also done carelessly. After mixing in the nitric uranium precipitation tank, they would roughly stir it with something like a stick.

제시는 이 모든 것에 대해 안전 교육 감독도 소홀히 했습니다. 이 모든 것은 해류 제작 공정 과정을 최대한 단순하게 만들어서 비용을 줄이겠다는 목적이었어요. 시의 도카이촌 해결 가공 시설에서는 이미 이런 말도 안 되는 위법한 우라늄 연료 작업이 일상화되어 있었던 거죠. 언젠가는 일어날 수밖에 없었던 사고인 겁니다. 임계 사고가 일어난 시점, 세 명의 작업자들은 카론 소리와 함께 푸른 섬광을 목격합니다. 핵분열이 일어날 때 생기는 체렌코프 현상이었고, 공장에는 즉각 감마선 경보가 울리기 시작했습니다. 임계 경보가 울리는 것을 들은 요코카와는 소리를 듣자마자 링카이 다니게로!라고 외쳤고, 다들 즉시 방사선 관리 구역 바깥까지 도망갔습니다. 하지만 이미 상황은 늦었습니다. 정말 불행하게도 가장 가까이서 작업하던 두 사람, 우치 이사시와 신아라 마사토는 사태가...

As it occurred, they were exposed to an enormous amount of radiation. Ouchi lost consciousness and collapsed, while Shinohara repeatedly called out Ouchi's name in an attempt to bring him back to awareness. The three individuals who were exposed immediately exhibited symptoms such as pain, nausea, difficulty breathing, and headaches. These were typical signs of radiation exposure. A tremendous amount of radiation began to spread to the surrounding area. One minute after the incident, around 10:36, at the Naka Research Institute, located approximately 1.7 kilometers west of the site, a neutron dose of 6.3 microsieverts per hour was detected. Shortly after the incident, at 10:43, a request for dispatch was made to the fire department, and firefighters arrived in about three minutes to transport the three workers. However, when Shiga initially contacted the fire department, he did not mention anything about radiation exposure, and the firefighters had no information regarding the incident.

Because they did not hear, the three firefighters who jumped into the scene were later informed that the firefighters had been exposed to radiation due to an accident. The chain reaction continued until the next day. The radiation level in the air was 0.84 MW per hour, which was 20 to 30 times higher than the normal range. Jessie had to find a way to stop the chain reaction. Therefore, at 1:40 AM the day after the accident, Sio equipped 16 staff members with protective suits and sent them to the accident site. To stop the chain reaction, they first needed to drain the cooling water from the sedimentation tank. However, the radiation was so strong that the working time was limited to just 10 minutes. So, once a person entered to work, they had to return after exactly 10 minutes to switch with the next worker, and this process continued with each worker entering and returning within that 10-minute limit.

Among the people involved in the operation, six were exposed to radiation exceeding 50 millisieverts. For the workers, this was a significant amount, as they received this dose in just one day, making it quite dangerous. Among the workers, there was even one who was exposed to a maximum of 120 millisieverts. However, thanks to the workers who bravely broke pipes with hammers and injected gas into the settling tank, risking exposure, they were able to successfully remove all the coolant. This occurred around 5 AM. Then, boric acid water, which absorbs neutrons, was injected into the settling tank, and 19 hours and 40 minutes after the accident began, the situation was finally brought under control. Immediately after the accident, among the 21 radiation detection devices around the factory, about two recorded radiation levels exceeding 4,000 times the normal measurement, at 0.84 millisieverts. Those exposed to radiation during the accident...

It was initially reported that 49 people were affected, but later it was revealed that including the surrounding residents, the number increased to 66. Among the residents, the most exposed individual was a typical person who was exposed to radiation while working with a 25 mm sheet. The annual exposure limit for an ordinary person is only 1 mm, and those who exceeded this limit amounted to 112 people. The most severely affected individuals were, of course, the workers at the time. Uchi Shishin had an exposure of about 18 sieverts, while Masato Yokokawa was exposed to about 10 sieverts, and Yutaka was exposed to around 1 to 40 sieverts. The person with the highest exposure was Uchi, who, interestingly, was reported to be walking around normally at first. The reason Uchi appeared fine initially is that radiation exposure at levels exceeding a thousand sieverts does not cause any injuries from shock. Therefore, the doctors and nurses at Tokyo University Hospital were extremely...

Seeing the seemingly intact state of Ouchi, I was puzzled but thought, Could this possibly be treatable? However, that hope was soon shattered. In fact, Ouchi's chromosomes were completely shattered. This photo was taken on the day of exposure, capturing Ouchi's chromosomes under a microscope. The Japanese specialists who examined this photo concluded that although Ouchi's body appeared to be alive at that moment, it was essentially no different from being dead. Let's take a look at some excerpts from a book that details the situation very thoroughly, titled 83 Days. Chromosomes contain all genetic information; they can be likened to the blueprint of life. Typically, they are composed of two pairs, but in Ouchi's case, it was nearly impossible to identify which chromosomes were present. The chromosomes were scattered so much that it became impossible to create new cells.

The moment of exposure meant that Otsu's body lost its blueprint. Once destroyed, chromosomes cannot be healed by current human technology. This is where the problem begins. The human body continuously undergoes a process where old cells die and new cells regenerate throughout a person's life. In just one day, approximately 50 billion cells die and are reborn in an adult's body. Moreover, more than 2 billion cells die and regenerate every hour. However, if all chromosomes are completely destroyed due to such a powerful radiation exposure, it is akin to the entire body rotting alive. Otsu's condition rapidly deteriorated due to exposure to radiation at a level of 18. White blood cells were wiped out, causing the immune system to collapse, and all skin began to decay without being regenerated.

I lost everything. Because of this, the moisture in my body evaporated, making me vulnerable to external infections. I even lost the ability to blink due to the loss of eye moisture, which led to blindness. All my internal organs were damaged. I couldn't eat food at all, so I was given nutritional supplements, but since I couldn't digest them, everything was expelled from my body in the form of diarrhea. During this process, I lost up to 10 liters of fluid and blood each day. I was unable to breathe on my own and had to rely on a machine for assistance. Ouchi suffered from extreme pain and eventually saw the doctor, but his once strong spirit completely collapsed, leading him to refuse surgery and treatment, causing chaos. On the fifth day after the exposure, organ cells failed to regenerate, resulting in bleeding from most of my organs. It seemed that the muscles were damaged, and in a situation where there was no hope left, Ouchi's suffering increased.

The family members and medical staff, who could no longer bear to watch, decided not to resuscitate him when the third cardiac arrest occurred. Ochi died on the 83rd day after the exposure due to multiple organ failure. Ochi is recorded as the first fatality from a critical incident in Japanese history. The condition of Shinnohara, who was closest to Ochi at the work site, was also very poor. While the extent of Shinnohara's chromosomal damage was somewhat less severe, unfortunately, there was almost no chance of resuscitation. After arriving at the Shinwa Hospital and beginning treatment, he started to lose consciousness. In particular, his salivary glands, which are sensitive to radiation, were damaged, leading to a lack of saliva. Because of this, Shinnohara was unable to eat food and had to receive nutrition through a feeding tube. A week later, Shinnohara's white blood cell count...

Lymphocytes decreased, and skin cells began to necrose without regeneration. Shin Ah-ra's family hid the death of Otsu for about two weeks without informing Shin Ah-ra. Later, when Shin No Ah-ra heard about Otsu, she thought, I also had a similar prescription. Shin Ah-ra successfully received skin grafts on her torso, face, legs, and arms, and she also succeeded in bone marrow transplantation. This allowed her to replace the bone marrow that had been exposed to radiation and generate new blood cells. Shin Ah-ra's blood production capacity significantly recovered. Additionally, her condition seemed to improve gradually. On January 1, 2000, she celebrated the millennium by taking a walk in the park with her family, joking around, and she was even able to move around in a wheelchair. However, hope did not last long. The transplanted skin began to fall off, and bleeding occurred in several organs of Shin No Ah-ra.

Shortly thereafter, Ciara's condition rapidly worsened. She contracted hepatitis, was placed on a ventilator, and underwent 24-hour dialysis, with all her organs deteriorating. Ultimately, seven months after exposure to radiation, she experienced cardiac arrest. Ciara's family, seeing her condition, decided not to pursue any further resuscitation efforts. On April 27, Ciara Masato passed away. In fact, Ochi also received skin grafts and stem cell transplants before his death. However, the transplanted skin fell off within a few days, and the hematopoietic stem cells were quickly destroyed due to the intense radiation emanating from Ochi's body. The third individual in the workshop was Yoko Kawau Yutaka. He was in a different room and was far from the settling tank, resulting in an exposure of about 30 to 40 rads. However, even this amount was significant.

In 2003, Yokokawa's white blood cell count had dropped to an extremely low level, but fortunately, after a successful stem cell transplant, he recovered and was discharged on December 20, 82 days later. In March 2003, Yokokawa faced trial along with five executives from the company. He was charged with negligent homicide and negligent injury, receiving a sentence of two years and six months, with a four-year probation. It is said that Ouichi and Shinohara had a very close relationship, enjoying fishing together after work every day. Yokokawa was so friendly that he would lend his jumper to Shinohara when the weather was cold. Therefore, Yokokawa and Ouichi would regularly visit Shinohara's grave every few months. After the accident, he was fined.

부과받고 문을 닫고 맙니다. 하지만 이미 사고 때문에 돌이킬 수 없는 피해가 발생한 다음이었습니다. 시간과 비용 절감 같은 생산성을 우선시한다면, 어떤 치명적인 결과를 초래할 수 있는지를 보여주는 상징적인 사건으로 남았습니다. 그럼 지금까지 리뷰 형이었습니다.

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