JCO CRITICALITY ACCIDENT Masashi Kanamori Nuclear Emergency Assistance & Training Center Japan Atomic Energy Agency 11601-13 Nishi-jusanbugyo, Hitachinaka, Ibaraki、JAPAN 311-1206 1

CONTENTS ■ Outline of the criticality accident ■ Criticality accident ■ Emergency environmental radiation monitoring ■ Criticality termination work ■ Countermeasures taken by the related organizations ■ Environmental radiation monitoring after the accident ■ Radiation doses ■ Lessons from the accident and re-arrangements of emergency 　preparedness in Japan 2

Outline of the criticality accident 3

Outline of the criticality accident ■ Criticality accident occurred on September 30, 1999, at the JCO 　　conversion facility at Tokai-mura. ■ The facility was in the operation for the re-conversion of enriched uranium. ■ The excursion continued for　nearly 20 hours ,and the total number of fissions during the criticality accident was estimated to be 2 x 1018. ■ 167 residents were asked to evacuate , and about 310, 000 residents were　asked not to leave their homes. ■ This accident was rated as level 4 on INES scale. 4

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Criticality accident 6

Criticality accident ■ Criticality accident occurred on September 30, 1999, at 10:35 am, at the JCO conversion facility which was in the operation for the re-conversion of enriched uranium. ■ The three workers had used the powdered uranium (U3O8), which is 18.8％enriched-uranium,　and dissolved them in the stainless steel container. Concentration of uranium nitrate solution is about 370gU / l. ■ On September 30, 1999, at 10:35 am,　the 7th solution in a stainless steel container was poured into the precipitation tank and the solution exceeded the critical mass limit lead to the criticality accident. ■ The precipitation tank was not geometrically safe for criticality. So criticality accidents would occur if much more than the criticality mass was poured. 7

■The excursion continued for nearly twenty hours ,and the total number of fissions during the criticality accident was estimated to be 2 x 1018. ■ Exposures were mainly from direct radiations, some rare gases and radioactive iodine were released into the environment, but the effect was small. ■The two workers who received doses of 16 ~ 25GyEq and 6 ~ 9GyEq died. Another worker whose dose was estimated to be between 2 ~ 3GyEq is still living. ■ As the tank and the building were not damaged, most of the fission products were confined in the tank. ■167residents within a range of 350 meters from the criticality tank were evacuated. About 310, 000 residents within a 10km range were asked by the governor not to leave their homes. 8

Time series at the initial stage after the criticality accident (30 September,1999) 10:35　The 7th solution in a stainless steel container was poured into the precipitation tank and the solution exceeded the critical mass limit, so criticality accident occurred. 10:43　JCO notified to fire station of Tokai-mura, saying “This is JCO, 3 workers were down at the conversion facility (“facility”was abbreviated.), please　take them to the hospital in ambulances　immediately.” (In Japanese, the pronunciation of “conversion” is the same as that of “epilepsy”.) 10:46　The rescue team(3persons) arrived at JCO, but they did not know the situation of the accident, so they had any protective measures for radioactive materials. 11:15　JCO notified to STA, saying “Criticality accident possibly occurred.” 9

11:34 JCO notified to Tokai-mura government. 11:40　JCO detected 0.84mSv/h(γ) at the site boundary and informed to STA. 11:52　Sufferers(3 workers) were moved to the hospital by the ambulances. 12:15　Tokai-mura government set up Accident Response Headquarters. 13:55　STA recommended Ibaraki-ken, government that residents near the site remain indoors . 14:30　STA set up Accident Response Headquarters. 15:00　Central government set up Accident Response Headquarters. 15:00　The Mayor of Tokai-mura　recommended that residents living within a 350 m of the JCO plant evacuate. 10

JCO Co Ltd. Tokai-mura Criticality accident JAEA 1km Joban Freeway National Route 6 JR Tokai Sta. JAEA 1km ３０ｋｍ Tokai-mura 11 11

JCO Tokai works JCO Tokai Works National Route 6 12 12

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Precipitation tank 14 14

Precipitation tank 15 15

Situation of work near the tank 6-9 GyEq 2-3 GyEq When the criticality occurred, one of three workers engaged saw a “blue-white glow” and were seriously exposed to radiation. Average dose to the whole-body for workers, Worker-A: 16-25 GyEq Worker-B: 6-9 GyEq Worker-C: 2-3 GyEq 16-25 GyEq 16 16

Sketch of precipitation tank drawn at initial stage of the accident JNC TN8440 2001-018 JCO臨界事故の終息作業について　より引用 17 Sketch of precipitation tank drawn at initial stage of the accident 17

Memorandum based on the hearing results of operator(8:30～10:00p.m.) 18 18

Emergency environmental radiation monitoring 19

Radiation dose around the site ● ： neutron 　　○：　γ 20 20

Radiation dose around the site （Sep.30,10：00 ー Oct.1,7：00） 9/30 10/1 1.0 空間線量の時間変動from安全委 0.1 0.01 21 21

Points of monitoring posts 10 km 8 km 6 km ● 4 km ● 2 km ● ● JCO ● ● ● ● 22 22

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γ-ray measurement results (10:45a.m.) The installation place of 60Co irradiation institution 24 24

The 4th γ-ray measurement results The installation place of 60Co irradiation institution 25 25

Dose measurement results The site boundary and circumference surveillance zone of　processing plant 26 26

Neutron measurement results (17:05p.m.) 27 27

Neutron measurement results 28 28

Criticality termination work 29

Stages of criticality termination work The termination work was performed in three stages: [1] Polaroid photography and preparation, [2] water drainage, [3] addition of boron solution. 30

in criticality termination work 　Policy of dose control in criticality termination work ■The basic concept was prepared based on the ICRP recommendations and 　Japanese regulations. ■Based on the Japanese regulations, the radiation dose limit for employees is 50mSv and the dose limit for emergency exposure situations is 100mSv. ■ It seemed difficult to manage doses under 50mSv, so doses up to 100mSv were considered acceptable. ■The Nuclear Safety Commission agreed with this policy of doses objectives. 31

View of conversion-building (about 11:00p.m.) 33 33

Progress of the accident 0.001 0.01 0.1 1 10 12 14 16 18 20 22 2 4 6 8 Time　 γ- Dose Equivalent Rate (mSv/h) at γ area monitor in 1st fac. 9/30 10/1 Draining Ar Pursing B Pouring Accident occurred. 34 34

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Draining of the cooling water from the tank 36 36

Route of boric acid to the precipitation tank 37 JNC TN8440 2001-018 Route of boric acid to the precipitation tank 37

Pouring of boric acid to the precipitation tank 38 38

Piling up sandbags for shielding 39 39

Countermeasures taken by the related organizations 40

Time　series of criticality accident including countermeasures taken by the related organizations (30 September,1999) 10:35　 Criticality accident occurred. 10:43 　JCO notified to fire station of Tokai-mura 11:15 　JCO notified to STA. 11:34 　JCO notified to Tokai-mura government. 11:40 　JCO detected 0.84mSv/h(γ) at the site boundary and informed to 　　　　　　STA. 11:52 　Sufferers(3 workers) were moved to the hospital by the 　　　　　　ambulances. 41

12:15 Tokai-mura government set up Accident Response Headquarters. 14:30 　STA set up Accident Response Headquarters. 15:00 　Central government set up Accident Response Headquarters. 15:00 　The Mayor of Tokai-mura　recommended that residents living within a 350 m of the JCO plant evacuate. 17:05 　Radiation dose (n) of 4.0mSv/h was detected near the site boundary. 20:30 　Central government set up Local Accident Response Headquarters at JAERI site. 21:00 　Accident Response Headquarters(Head: Prime Minister) was 　　　　　　established. 42

22:30 Ibaraki-ken, government recommended that residents within 　　　　　　a 10 km of the site remain indoors . 23:15 　It was concluded that the cooling water was drained from the jacket surrounding the precipitation tank. ( 1 October,1999) 2:35～6:04 　The work to drain the cooling water from the jacket of the precipitation tank was carried out. 6:15 　The removal of the cooling water from the jacket of the precipitation tank was carried out by forcing the Argon gas. 6:30 　The radiation dose (n) was lowered to the undetectable level. 8:19～8:39 　Boric acid was poured to the precipitation tank. 43

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Countermeasures for residents Evacuation: ■On September 30, at 3:00PM, the Mayor of Tokai-mura recommended that residents living within a 350 m of the JCO plant evacuate. ■The number of persons to evacuate is 161persons(Tokai-mura) and 6persons(Naka-machi). ■Evacuation continued till October 2, at 6:30PM. Sheltering: ■On September 30, at 10:30PM, Ibaraki prefectural government recommended that residents within a 10 km of the site remain indoors . ■The number of persons to remain indoors is about 310,000persons(Tokai-mura, Cities and towns near Tokai-mura) ■Sheltering continued till October 1, at 2:30PM 45

Evacuation for residents （Sep.30 ,15：00 - Oct.1,18：30） Evacuation １６１Persons (Tokai-mura) 46 46

Sheltering (Sep.30, 22：30 - Oct.1,14：30） Sheltering 310,000persons 47

Environmental radiation monitoring after the accident 48

Radiation doses(n,γ） after the accident μSv/h 49 49

Environmental radiation monitoring Neutron, γ-ray (described above) γ-dose rate by released radioactive materials: 0.24 μGy/h (West 8ｋｍ） Detected activated products (AP) and fission products (FP) : Na-24, Mn-56, Sr-91, I-131, I-133, I-135, Cs-138 AP/FP concentration in environmental samples: 　　 negligible value - maximum concentration of I-131 at the site boundary:　　 　 (1.6-44)x10-9 Bq/cm3 << 1x10-5 Bq/cm3 (limit value) - maximum concentration of I-131 in Vegetables (excluding root crop and potato) : 　　　　　　　　　　　　　　 　　0.037 Bq/g <<2 Bq/g (Indices about ingestion restrictions of food and drink prescribed by nuclear safety commission) 50 50

Environmental monitoring 51 51

Radiation survey of residents 52 52

２) Exposures were mainly from direct radiations.) Results of monitoring １）　Some rare gases and radioactive iodine were released into the environment, but the effect was small. ２)　 Exposures were mainly from direct radiations.) 53 53

Radiation doses 54

Estimation of radiation dose ・Estimation of radiation dose of 3 workers 　　- premonitory symptom (vomiting, diarrhea, nausea, trouble of consciousness) - decrease of lymphocyte - check of chromosome - measurement of Na-24 value in blood ・Estimated radiation dose of 3workers Worker-A: 16-20 GyEq Worker-B: 6-10 GyEq Worker-C: 1-4.5 GyEq 55 55

Employees whose dose was actually measured Doses results (1) November 8, 2000 Category People Notes Employees 172 Employees whose dose was actually measured Employees involved in tasks when the accident occurred 3 16~25GyEq or more(Died on December 21, 1999) 6.0~9GyEq(Died on April 27, 2000) 2~3GyEq(Discharged from the National Institute of Radiological Sciences on December 21, 1999) Employees involved in drainage of water, etc. 18 Detected by whole-body counters, individual dosimeters, etc.　Their collective range was 3.8~48mSv(effective dose equivalent). Employees involved in injection of boric acid into the tank 6 Detected by dosimeters, etc. 　Their collective range was 0.7~3.5mSv(effective dose equivalent). Other employees at the site during the accident 49 Detected by whole-body counters and film badges.　Their collective range was 0.6~48mSv(effective dose equivalent). Employees whose dose was estimated 96 Estimated according to location-based radiation dose evaluations and the individual behavior survey conducted by JCO.　 Their collective range was 0.06~17mSv(effective dose equivalent). 16~20 or more 6.0~10 1~4.5 0.6~47.4 0.06~16.6 56 56

Doses results (2) Persons involved in disaster-related tasks November 8, 2000 Category People Notes Persons involved in disaster-related tasks 260 Persons whose dose was actually measured Government-related organizations(Staff of JAERI and JNC) 57→56 Of 206 whose dose was measured by film badges or TLD, exposure was detected on 56. Their collective range was 0.1~9.2mSv(effective dose equivalent). Fire-fighters (involved in rescue tasks related to the accident) 3 Detected by whole-body counters.　Their collective range was 4.6~9.4mSv(effective dose equivalent). Persons whose dose was estimated Self-government bodies related persons 167 Estimated by the behavior survey. 　Their collective range was 0.0002~7.2mSv(effective dose equivalent). State related persons 8 Estimated by the behavior survey. 　Their collective range was 0.49~2.1mSv(effective dose equivalent). Information medium related persons 26 Estimated by the behavior survey. 　Their collective range was 0.014~2.6mSv(effective dose equivalent). 57 57 57

Doses results (3) Residents Category People Notes 234 November 8, 2000 Category People Notes Residents 234 Persons whose dose was actually measured 7 Detected by whole-body counters.　Their collective range was 6.7~16mSv(effective dose equivalent). Persons whose dose was estimated Living or Working persons 199 Estimated by the behavior survey. 　Their collective range was 0.01~21mSv(effective dose equivalent). Momentary staying persons 28 Estimated by the behavior survey. 　Their collective range was 0.01~3.8mSv(effective dose equivalent). 58 58

Lessons from the accident and re-arrangements of emergency preparedness in Japan 59

Lessons learned from the criticality accident ■ Initial responses and communications ■ Authority, responsibility and decision making ■ Radiation measurements and medical responses ■ Regulatory Systems 60

Establishment of the various systems ■ The Special Law of Emergency Preparedness for Nuclear Disaster was enacted in December 1999． ■ The Basic Plan for Emergency Preparedness was revised clarifying roles and responsibilities of the related organizations. ■ An OFC would be designated in a case of emergency as the base for implementing responses. ■ JAEA/NEAT is expected to assist the staff of the OFC as the designated public organization. 61

Legislation in the Special Law of Emergency Preparedness for Nuclear Disaster ■ Assignment of Off-site center ■ Designation of the special nuclear disaster preparedness officer ■ Implementation of nuclear emergency exercises ■ Nuclear emergency plans for nuclear industries ■ Establishment of adequate radiation monitoring systems 62

Actions defined by law Article-10: Disaster preparedness manager shall inform the competent minister, governor and local authorities of the defined incidents. Article-15: In the case of a nuclear disaster the competent minister shall report the situations to the Prime Minister who will in turn declare a disaster. Article-15 Article-10 0.05-0.1 μSv/h (normal dose rate) 5 μSv/h 10 min 500 μSv/h 10 min 63

Organizational arrangements for nuclear emergency response ■ The organizational arrangements in nuclear emergency preparedness in Japan are provided by the Laws. ■ OFC would play an important roll in the negotiations with the related organizations. ■ The government have established the NEAT to fulfill these activities effectively for assisting the OFC. 64

Organizational arrangements for nuclear emergency response Nuclear Emergency Response Headquarters Chairman: Prime Minister Cabinet Office METI MEXT Ministry of Defense Fire and Disaster Management Agency National Police Agency Nuclear Safety Commission ● ● Organization related to disaster preparedness 　　　　　　Police　　　　　　　　　　 JNES 　　　　　　Fire Station　　　　　 NIRS 　　　　　　Self-Defense Forces NUSTEC Local Nuclear Emergency Response Headquarters ● ● Off-site Center The Joint Council of Nuclear Disaster Countermeasures Technical support ＮＥＡＴ　Ｃｅｎｔｅｒ Headquarter of prefecture Headquarter of cities, towns, villages License Holder 65

Off-site center information Local Government Evacuation Sheltering 　　Central Government Specialists Radiation Protection advice Public advice information information instruction Nuclear Safety Commission Nuclear Company Monitoring Specialists NEAT 66

Off-site center and NEAT center Off site center（22 places in Japan）　　 Fukui branch office of NEAT Center (Fukui Prefecture) NEAT Center（Ibaraki Prefecture） is technical assistance base of JAEA 67

Exercises planned by central and local governments ■ Many kinds of exercises and drills are conducted by the related organizations. ■ These exercises are integrated as a full-scale national exercise which is planned and carried out every year. ■ This scheme is shown in the figure on next page . ■ The staff of NEAT attends these exercises and provide technical support by dispatching specialists and providing special vehicles, etc. 68

Over view of annual exercises in Japan Purpose and Feature Cabinet Ministries NISA OFC Local Gov. Annual exercise for all the relevant parties One selected prefecture, with evacuation of residents, Decision maker (utterance based) Full-scale National Exercise Scenario, narrative based stimulated Partial National exercise Prefectural Exercise Annual Prefectural Exercise (one prefecture a year, organized by the prefecture) OFC Drill Mainly decision making process in the Off Cite Center, partial exercise Disaster specialist Drill Disaster specialists drill who have to lead OFC activities Drill for the relevant transport groups Transport Accident Drill Exercises for the facilities regulated by MEXT MEXT Exercise MEXT Exercise Basic training for every function of the full scale National Exercise Basic Training, 69 Exercise for large scale earthquake on DP Day DP Day government exercise DS：Disaster specialist

Legal role of JAEA at nuclear emergency 　■　Designated Public Organizations - Basic Law on Emergency Preparedness 　■　Dispatch of experts and Supplying special equipments 　 ‐Basic Plan for Emergency Preparedness 　■　NEAT　Center is the disaster response support base facilities of JAEA-Nuclear Disaster Countermeasures Manual 70

■ We are continuing to improve the systems in emergency Future issues ■ Functions of Emergency related organizations will continue to be tested in emergency exercises. ■ We are continuing to improve the systems in emergency preparedness and response in Japan. ■ The knowledge gained by the various organizations mentioned above can then be shared with other Asian counties. ■ The IAEA plays an important roll in providing funds and opportunities. ■ It is also important to further our research on such issues as RDD and consolidate our recovery phase programs. 71

Thank you for your attention. 72