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Tokaimura Criticality Accident of September 30, 1999. S. T. Almodovar Senior Technical Advisor Fluor Daniel Hanford With acknowledgement of Valerie Putman (INEEL) for providing much of the accident information. Definitions. Definitions - Continued. Definitions - Continued.

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Tokaimura criticality accident of september 30 1999

Tokaimura Criticality Accidentof September 30, 1999

S. T. Almodovar

Senior Technical Advisor

Fluor Daniel Hanford

With acknowledgement of Valerie Putman (INEEL) for providing much of the accident information

Definitions continued2
Definitions - Continued

  • Low enriched uranium (LEU) = less than 10% enriched

  • Intermediate enriched uranium (IEU) = 10-60% enriched

  • All times are Tokaimura local

  • Uncertain and speculative information, and comments, are often marked with brackets ([])

Definitions continued3
Definitions - Continued

Radiation dose values:

1 Sv (Sievert) is 100 rems

1 Gy (Gray) is 100 Rads

20 mSv is the worker annual dose limit, according to JCO

7 Sv is considered lethal, according to interviewed Japanese medical personnel

Note: It is not the intent of this presentation to delve into health physics any deeper than what is stated above.

Conditions before the accident
Conditions Before the Accident

  • Corporate Safety Culture - Perhaps a Case of Bottom Line Driven Safety

    • JCO asserted that a criticality accident was not possible. Titanic thinking: This ship is unsinkable, therefore, why obstruct the view of the first class passengers with unneeded life boats

    • Documents submitted by JCO Co Ltd, the plant operator, said there was no need to prepare for a "criticality accident" -- a nuclear chain reaction similar to what occurs in a nuclear reactor -- because safety precautions would prevent it

    • JCO has acknowledged that it “skirted official procedures for years to save time, and news reports said the company had secret manuals for employees instructing them to use shortcuts.”

Conditions before the accident continued
Conditions Before the Accident - Continued

  • Corporate Safety Culture - Perhaps a Case of Bottom Line Driven Safety, Continued

    • “Before the accident, supervisors and, possibly, managers directed personnel to take shortcuts to accelerate processing further. Workers were directed to use the buckets, overbatch, and, possibly, skip other steps.”

    • “Workers also have decided to skip more steps than their oral directions specified.”

    • One of the three workers told police: ”We talked, and decided to finish the work quicker.” The Oak Ridge Y-12 workers call this a “Bubba said.”

Conditions before the accident continued1
Conditions Before the Accident - Continued

  • Bad Conduct of Operations - Inadequate Safety Training

    • “It appears that the workers did not even understand what the word 'criticality' meant.”

    • “Interviewed workers and supervisors said they knew nothing about the dangers of overbatching. Some management personnel agreed, indicating worker training included almost nothing on criticality accident consequences and did not emphasize criticality accident prevention.”

    • “The Asahi newspaper, citing unidentified police sources, reported Monday that one of the workers had ordered two colleagues to speed the process along by skipping even more steps.”

Conditions before the accident continued2
Conditions Before the Accident - Continued

  • Bad Conduct of Operations - Inadequate Safety Training, Continued

    • Investigations to date have revealed the existence of an “illegal operations manual”, and one of the three workers who suffered severe radiation exposure has told police that his team violated even the “unauthorized procedures”.

    • “Even the unauthorized operating manual required them to pour the mixture first into an intermediary tank, which had a 'criticality control' function.”

    • The investigation has confirmed that the plant operator, JCO, “deliberately ignored the official operational manual approved by the government, and dissolved uranium oxide (U3O8) powder in stainless steel buckets, rather than in a purpose-built 'dissolver'.”

Conditions before the accident continued3
Conditions Before the Accident - Continued

  • Inadequate Human Factors

    • Equipment design and location did not make it cumbersome to do the wrong thing: That is make the peg square, the hole round, and do not have “unlike” processes in the same area

  • Transition Operation - Felt and Looked Like a “New” Process

    • The conversion of fuel for Joyo was the first such operation in three years and only began again on September 22

The accident
The Accident

  • At about 10:35 a.m. on September 30, Japan's first criticality accident occurred at a nuclear fuel conversion facility in the village of Tokai, Ibaraki Prefecture.

  • The accident happened at the experimental conversion building in the Tokai Works of the JCO Co. Ltd

  • The experimental conversion building, where the accident occurred, handles uranium of higher enrichment than that for ordinary light water reactors.

The accident continued
The Accident - Continued

  • At the time the accident took place, the facility was processing the nuclear fuel component for the Japan Nuclear Cycle Development Institute's experimental fast breeder reactor (FBR), Joyo

  • At the point in the process where the accident occurred, the volume of uranium liquid fed into a container is supposed to be limited to about 2.4 kg

  • According to the workers who were exposed, however, 16 kg of liquid -- almost seven times the proper amount -- was fed into the sedimentation tank

The accident continued1
The Accident - Continued

  • The accident involved 18.8% enriched uranium

  • For the three previous years, the facility processed 5% enriched uranium

  • On Wednesday, workers poured about 9.2 kg uranium from four buckets into the sedimentation tank

  • On Thursday workers added about 6.9 kg uranium from three buckets

  • Process

The accident continued2
The Accident - Continued

  • Workers were most likely aware of the total accumulated mass Thursday

  • The resultant solution, or reflected slurry, went critical

  • One email indicates the solution was approximately 370 g/L uranium with, possibly, 1 mole/L nitric acid

  • The system pulse between super- and sub-critical states for more than 17 hours.

The accident continued3
The Accident - Continued

  • A stirring device in the tank and further U3O8 dissolution might have contributed to the phenomena

  • Available reports do not indicate the number of pulses, their magnitude, or their frequencies

  • Fission yields are not yet reported for any pulse or for the reaction duration

The accident continued4
The Accident - Continued

  • Measured radiation dose-rate values at the nearest site boundary seem fairly steady for hours, indicating pulse frequency was probably rapid enough to overwhelm radioactive decay evidence

  • It took about 3 hours on October 1st to drain cooling water from a water jacket around the tank

  • Boron was added to the system

  • System safely subcritical at 09:20 October 1st.

Response to the accident
Response to the Accident

  • There is no indication that the process had a CAS

  • Presumably the area’s gamma alarms activated, and everybody in the area left as quickly as they could

  • The radius for this initial evacuation is not reported. Most plant personnel were probably first evacuated to the further plant boundaries if not to offsite locations

  • There are no indications that there were any emergency plans in the sense of our emergency planning

Response to the accident continued
Response to the Accident - Continued

  • Although the building was not damaged, all fission products were released to the atmosphere. [Room and building filters either failed or were not designed to handle fission products.]

  • News reports indicate some 7000 people were checked for radiological exposure

  • Significant exposures were apparently limited to the three workers in the room, 36 other plant workers, three firemen [ambulance crew?], and up to seven residents who were near site boundaries at the time

Response to the accident continued1
Response to the Accident - Continued

  • Firemen [ambulance crew?] were exposed when they entered the area without appropriate personal protective equipment. Apparently they were not advised of conditions or accident type before they entered

  • Plant personnel completed initial notifications to JCO officials within ten minutes

  • Some notification information was not clear because at least one company official did not understand they were dealing with a criticality accident

Response to the accident continued2
Response to the Accident - Continued

  • Apparently none of these officials instructed plant personnel to notify and/or establish communications with city or regulatory authorities.

  • City authorities were notified approximately one hour after the initial pulse. They apparently determined response actions for residents on their own, or with a little help from plant personnel Residents were notified up to 2.5 hours after the first pulse

Response to the accident continued3
Response to the Accident - Continued

  • About 160 people within a 350m radius were evacuated until the afternoon of October 1st. However, after a night in temporary shelters, some evacuated residents reportedly returned home to care for pets and/or retrieve fresh clothing

  • Authorities advised people within 10km to shelter (stay inside with doors and windows closed) at least until the evening of October 1st. Apparently others stayed inside as well because the city is said to have resembled a ghost town

Response to the accident continued4
Response to the Accident - Continued

  • Authorities also warned people they should not eat produce or drink milk from the area until testing was complete. That ban was lifted by October 4th. [authorities may have attempted to scale reactor-accident guidance to this accident]

  • It now seems responders were notified and activated separately from authority notifications. Notifications to offsite responders might have warned offsite authorities. Initial radiological responders were apparently from plant personnel but, as response continued, they might have been supplemented by personnel from other plants

Response to the accident continued5
Response to the Accident - Continued

  • Other in-field and city responders were from the civil police, civil firefighters, and army. The army’s role is not indicated but their chemical warfare unit responded

  • Finally, the Prime Minister ate lunch made from local products to reassure residents

Results of the accident continued
Results of the Accident - Continued

  • It is now widely accepted that the Chernobyl nuclear disaster has led to a massive increase in thyroid cancers in the three countries most affected

  • Already, 680 cases of thyroid cancer have been recorded in Belarus, Russia and Ukraine. Belarus has shown a 100-fold increase, from 0.3 per million in 1981-85 to 30.6 per million in 1991-94

  • Problems of the nervous and sensory organs have increased by 43%; disorders of the digestive organs by 28%; and disorders of bone, muscle and the connective tissue system have increased by 62%

Results of the accident continued1
Results of the Accident - Continued

  • The yen fell Thursday (September 30, 1999) against other currencies for the first time in a week

  • “This accident will have a strong political impact in Japan, because (Prime Minister Keizo) Obuchi has always supported nuclear power despite strong opposition”

  • Sumitomo, owner of JCO Co. Ltd. which runs the plant, will pay any compensation exceeding its insurance of one billion yen (9.5 million dollars)

  • Standard and Poor's warned Monday (October 4, 1999) it was monitoring the credit rating of Sumitomo Metal Mining Co. Ltd. for a possible downgrade

Results of the accident continued2
Results of the Accident - Continued

  • Investigators from the Science and Technology Agency on Sunday began raiding the offices of JCO Co. Ltd., the operator of the uranium processing facility

  • The investigation started just after 4 p.m. Six agency officers entered the firm's plant in Tokaimura, Ibaraki Prefecture, and four went to JCO headquarters.

  • The European press on Friday splashed huge, emotional headlines about the incident, in which mishandled nuclear material went briefly into chain-reaction, exposing 49 workers to radiation and forcing the evacuation of local residents

Results of the accident continued3
Results of the Accident - Continued

  • Kazuo Sato, chairman of the Nuclear Safety Commission, said on Sunday that the commission would look into whether there had been lax supervision by the central government

  • "This accident is not about technical failure, but about a sheer lack of safety culture and poor morale at the plant," said Keiji Naito, an emeritus professor of nuclear engineering at Nagoya University

Results of the accident continued4
Results of the Accident - Continued

  • "The company lacks both fundamental knowledge of nuclear matters and safety measures and it is mind-boggling to think how both the JCO and the government allowed this to happen," Nobuo Oda, an emeritus professor of radiation physics at Tokyo Institute of Technology, said.

  • JCO "must have been run by amateurs," said the Tokyo Institute of Technology expert. The accident demonstrated "gross amateurism and low morale among plant workers," professor Oda said.