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National Institute of Radiological Sciences

Past radiological accident handled by QST

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Radiation exposure accident with Ir source for non-destructive test (1971/9)

Ir-192 source (190 GBq) for non-destructive test was found in a shipyard in Chiba prefecture, Japan, in September 1971. A worker brought it back to his house and he, together with his five friends were exposed at his home.

The shipyard realized the loss of the source two days later and reported to the authority. The workers were notified that they handled a radiation source with exposure and the six worker admitted to the NIRS hospital for dose assessment and treatment. The doses were assessed by physical method and cytogenetic method. The maximum average whole body dose was 1.3 Gy. Two fingers of one of the patients had atrophy and necrosis and were amputated 20 years later.


Contamination survey for tourists who returned from around Chernobyl nuclear accident site (1986/5)

Chernobyl nuclear power plant accident was occurred in April 1986. A massive amount of radioactive substances was released to outside due to the reactor damage by explosion and fire.  

The former NIRS (current QST) conducted health check of 118 passengers on the three flight came from Kiev area at the Narita International Airport in May 1986, according to the Government’s request.

No passengers had health problems. The passengers had significant residual contamination changed the clothes and were decontaminated after explanation. Health check of some of the return tourists from Soviet Federation or East Europe was continued until August.


Criticality accident in Tokai-Village (1999/9)

On September 30, 1999, at around 10:35, criticality accident occurred in a uranium conversion test plant of the JCO Ltd., in Tokai・mura, Ibaraki Prefecture, Japan.

When two workers (A and B) were pouring uranyl nitrate into a precipitation tank, the solution emitted a flash of blue light and the alarms went off to warn against gamma rays. Another worker (C) who was in the corridor next to the room immediately recognized that a criticality accident had taken place and ordered the two workers to evacuate. The three workers had been exposed to high doses.

Worker A and B vomited and Worker A had diarrhea while they were being transferred to the hospital. The 3 patients received first aid treatment in the National Mito Hospital. However, since the patients showed symptoms of high dose exposure and radio-activities were detected from the surface of their bodies, it was decided that they were transferred to the hospital of the NIRS (current QST), which was a third level hospital for Radiation Emergency Medicine.

The experts on dose assessment of the NIRS determined that the accident was a criticality accident and estimated that Patient A received 16-25 GyEq or over, when converted into a gamma-ray dose (Gy equivalent to gamma-ray). Patient B was exposed to radiation of 6-9 GyEq and Patient C received a dose of 2-3 GyEq based on clinical symptoms, the amounts of 24Na in vomit and blood specimens, lymphocyte counts and chromosome analyses. NIRS decided the need of bone marrow transplantation for Patient A and B, and they were transferred to University Tokyo for the treatment.

Later, Patient A received a peripheral blood stem cell transplantation from his sister. Patient B received cord blood stem cell transplantation. Despite intensive care, Patient A died on the 83rd day after the accident (December 21, 1999) due  to dermal injuries and multiple organ failure, including renal insufficiency. The bone marrow of Patient B was restored and cadaver allografts and cultured autografts were transplanted to treat the skin injuries on the face, legs and arms, which engrafted well. However, Patient B died on the 211th day (April 27, 2000) due to pulmonary and renal insufficiencies and bleeding from the digestive tract. Patient C was treated in a sterile room in the NIRS to prevent infection, administered with cytokines to restore his bone marrow and left the hospital on December 20, 1999. He has been periodically examined in the QST and in a regional hospital.

This criticality accident changed the consciousness of the public and municipal or local governments on radiation. The NIRS receives increasing numbers of requests for people to give lectures on radiation emergency medicine. Municipal governments that do not have nuclear facilities also feel the necessity for educating their people about radiation. For the NIRS, the criticality accident emphasized the importance of establishing radiation emergency medicine capacity against this kind of accident.


Local radiation exposure accident with soft X-ray at electronic factory  (2000/6)

Radiation exposure accident with soft X-rays of non-destructive test due to interlock cancellation was occurred at an electronic parts factory in June 2000.  Three workers were exposed on their right hands.

They were suffered with radiation skin injury and were introduced to former NIRS (current QST) for dose assessment and specialized therapy. NIRS conducted measurement on the accident site and dose reconstruction based on interview and the estimated dose to their right hand were over 40, 50, and 60 Gy, respectively. The whole body doses were not significant.

They admitted to the NIRS hospital and were treated for skin lesion in the acute phase.


Plutonium inhalation accident at Oarai Research and Development Center of the Japan Atomic Energy Agency (JAEA)(2017/6)

Five workers were exposed with radiation at Plutonium inhalation accident in the Oarai Research and Development Center of the Japan Atomic Energy Agency (JAEA) in June 2017. Internal contamination with large amount of radio activities was suspected in early time. However, over estimation by lung monitor with residual body surface contamination was revealed after reexamination and dose assessment at QST. DTPA was administered as a decorporation therapy. A part of the patients were followed up continuously.