1. IAEA International Atomic Energy Agency Cytogenetic Dose Estimation in the Criticality Accident in Tokaimura Lecture Module 13

2. IAEA Criticality Accident in Tokai-mura, Japan On 30 September 1999, at 10:35, a criticality accident occurred at the uranium conversion facility in Tokai-mura, a village 130 km northeast from Tokyo, Ibaraki Prefecture, Japan The criticality event occurred when a worker was pouring a solution of enriched uranium ( 235 U) into a precipitation tank directly He bypassed a dissolution tank and buffer column supposed to be used in order to avoid criticality The amount of uranium poured was several times more than the specified mass limit 2

3. IAEA The JCO is located at Tokai-mura, Ibaraki Prefecture, which is about 130 km northeast of Tokyo. Tokai-mura Where did accident occur? 3

4. IAEA Diagram of the accident 4

5. IAEA Chronology of accident TimeEvents Time after accident (min) Symptoms ABC VomitingDiarrheaVomitingNausea 10:35Criticality occurred0 10:43Ambulance was called8 10:46Ambulance arrived11 11:27Workers on the ambulance52 11:49Ambulance left74 12:07Arrived at National Mito Hospital 92 13:43Left National Mito Hospital188 14:16Helicopter left Mito Heliport221 14:45Helicopter arrived at Chiba250 14:58Left Chiba Heliport263 15:25Workers arrive at NIRS290 5 loss of consciousness JCO NIRS

6. IAEA 6 Blood Cells Counts 2-3 h after accident Worker WBC (cells/mm 3 ) RBC (×10 4 cells/mm 3 ) PLT (×10 4 cells/mm 3 ) Hb (g/dl) Gra (cells/mm 3) Lymph (cells/mm 3 ) A 22,80053316.1 18. 0 21,888 (97%) 684 (3%) B 12,70042415.914.3 12,446 (98%) 127 (1%) C 11,50055816.518.3 10,005 (85%) 1,495 (13%) From J Radiat Res 2001 42 Suppl S157-166

7. IAEA Chromosome Preparations 7 8ml peripheral blood RPMI-1640 20% FCS 2% PHA Mononucleated cells 37ºC 48h incubate 0.3μg Colcemid 500nM Okdaic acid (last 1h) Centrifugal sedimantation Add 75mM KCL 37ºC 20min Fixed with 1:3 acetic alcohol (three times) -20ºC 3h Air-dry slides 37ºC 48h incubate Scoring Dic+R PCC-ring analysis

8. IAEA First Performed PCC-ring Analysis 8 Prematurely condensed chromosomes having PCC- rings (white arrow) in a lymphocyte of patient A

9. IAEA Metaphase Chromosomes in Patient B 9 Metaphase chromosomes having dicentric chromosomes (black arrows), a tricentric chromosome (short arrow) and a ring chromosome with centromere (white arrow) in a lymphocyte of patient B

10. IAEA Metaphase Chromosomes in Patient A 10 Metaphase chromosomes having severe chromosome aberrations in a lymphocyte of patient A

11. IAEA Frequency of Chromosome Aberration in Lymphocytes 11 PatientAberration Frequency of aberration/cell after accident 9 hrs23 hrs48 hrsTotal A Dic445/50197/2073/8715/78 Dic+R563/50250/2090/8903/78 B Dic199/75127/50153/50479/175 Dic+Rc224/75147/50166/50537/175 CDic+Rc63/10064/100 191/300 Dic: dicentric chromosome R: ring chromosome with/without centromere Rc: ring chromosome with centromere

12. IAEA PCC-ring in vitro calibration curve A B C 12

13. IAEA Dose-response Curves 13 Dose-response curve (Y=2.31 x 10 -2 D + 6.33 x 10 -2 D 2 ) of Dic+Rc for 60 Co γ-rays, dose-response curves of Dic+R, Dic+Rc, and Dic for 1.9 MeV x-rays (after Norman and Sasaki, 1966), and the estimated dose of patients A (□) and B (∆).

14. IAEA Comparison of Doses Estimated by Various Indicators Patient Estimated Dose (GyE, GyE’, or GyE”)* by PCC-ringDicDic+R/Rc 24 Na** A> 2022.624.517-24 B7.4(6.5-8.2)8.3 8.7-13 C2.3(1.8-2.8)3.0(2.8-3.2)2.5-3.6 14 * Equivalent dose to X or γ-rays ** Ishigure et al, when neutoron’s RBE is 1.5-2.0.

15. IAEA Conclusion It was difficult to collect sufficient number of lymphocytes due to severely high dose exposure High-yield chromosome preparation method was used to collect lymphocytes Dose estimation was made by two method: PCC-ring analysis Analysis of dicentric and ring chromosome 15