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

2. 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

3. Outline of the criticality accident3

4. 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

5. 5

6. Criticality accident 6

7. 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

8. ■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

9. 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

10. 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

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

12. JCO Tokai works
JCO Tokai Works
National Route 6 12 12

13. 13 13

14. Precipitation tank 14 14

15. Precipitation tank 15 15

16. 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: GyEq
Worker-B: 6-9 GyEq
Worker-C: 2-3 GyEq
16-25 GyEq 16 16

17. Sketch of precipitation tank drawn at initial stage of the accident
JNC TN 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

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

19. Emergency environmental radiation monitoring19

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

21. 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

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

23. 23 23

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

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

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

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

28. Neutron measurement results28 28

29. Criticality termination work29

30. 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

31. 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

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

34. 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

35. 35 35

36. Draining of the cooling water from the tank36 36

37. Route of boric acid to the precipitation tank37
JNC TN
Route of boric acid to the precipitation tank 37

38. Pouring of boric acid to the precipitation tank38 38

39. Piling up sandbags for shielding39 39

40. Countermeasures taken by the related organizations40

41. 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

42. 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

43. 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

44. 44 44

45. 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

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

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

48. Environmental radiation monitoring after the accident48

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

50. 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

51. Environmental monitoring51 51

52. Radiation survey of residents52 52

53. 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

54. Radiation doses 54

55. 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: GyEq
Worker-B: GyEq
Worker-C: GyEq 55 55

56. 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

57. 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 ~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

58. 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

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

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

61. 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

62. 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

63. 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
μSv/h (normal dose rate)
5 μSv/h 10 min
500 μSv/h 10 min 63

64. 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

65. 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

66. 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

67. 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

68. 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

69. 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

70. 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

71. ■ 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

72. Thank you for your attention.72