Tokaimura Criticality Accident of September 30, 1999

1
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

2
Definitions
3
Definitions - Continued
4
Definitions - Continued
5
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 ()

6
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.

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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.

8
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.

9
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.

10
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'.

11
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

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The Accident

• At about 1035 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.

13
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

14
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

15
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.

16
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

17
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 0920 October 1st.

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Response to the Accident

• There is no indication that the process had a CAS
• Presumably the areas 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

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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

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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

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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

22
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

23
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

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Response to the Accident - Continued

• Other in-field and city responders were from the
  civil police, civil firefighters, and army. The
  armys role is not indicated but their chemical
  warfare unit responded
• Finally, the Prime Minister ate lunch made from
  local products to reassure residents

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Results of the Accident
26
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

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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

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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

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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

30
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.