IAEA International Atomic Energy Agency Cytogenetic Dose Estimation in the Criticality Accident in...
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IAEAInternational Atomic Energy Agency
Cytogenetic Dose Estimation in the Criticality Accident in Tokaimura
LectureModule 13
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 (235U) 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
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IAEA
Pacific Ocean
Tokyo
Mito
Japan
Pacific Ocean
Ibaraki Prefecture
Mito
The JCO is located at Tokai-mura, Ibaraki Prefecture, which is about130 km northeast of Tokyo.
Tokai-mura
Where did accident occur?
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Diagram of the accident
W
A
B
C
Wall
Floor
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Chronology of accident
Time EventsTime after accident
(min)
Symptoms
A B C
Vomiting Diarrhea Vomiting Nausea
10:35 Criticality occurred 0
10:43 Ambulance was called 8
10:46 Ambulance arrived 11
11:27 Workers on the ambulance 52
11:49 Ambulance left 74
12:07 Arrived at National Mito Hospital
92
13:43 Left National Mito Hospital 188
14:16 Helicopter left Mito Heliport 221
14:45 Helicopter arrived at Chiba 250
14:58 Left Chiba Heliport 263
15:25 Workers arrive at NIRS 2905
loss of consciousness
JCO
NIR S
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Blood Cells Counts 2-3 h after accident
WorkerWBC
(cells/mm3)
RBC
(×104cells/mm3)
PLT
(×104cells/mm3)Hb
(g/dl)
Gra
(cells/mm3)
Lymph
(cells/mm3)
A 22,800 533 16.118. 0
21,888
(97%)684(3%)
B 12,700 424 15.9 14.312,446
(98%)127(1%)
C 11,500 558 16.5 18.310,005
(85%)1,495(13%)
From J Radiat Res 2001 42 Suppl S157-166
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Chromosome Preparations
7
8mlperipheral
blood
RPMI-164020% FCS2% 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
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First Performed PCC-ring Analysis
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Prematurely condensed chromosomes having PCC-rings (white arrow) in a lymphocyte of patient A
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Metaphase Chromosomes in Patient B
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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
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Metaphase Chromosomes in Patient A
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Metaphase chromosomes having severe chromosome aberrations in a lymphocyte of patient A
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Frequency of Chromosome Aberration in Lymphocytes
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Patient AberrationFrequency of aberration/cell after accident
9 hrs 23 hrs 48 hrs Total
ADic 445/50 197/20 73/8 715/78
Dic+R 563/50 250/20 90/8 903/78
BDic 199/75 127/50 153/50 479/175
Dic+Rc 224/75 147/50 166/50 537/175
C Dic+Rc 63/100 64/100 64/100 191/300
Dic: dicentric chromosomeR: ring chromosome with/without centromereRc: ring chromosome with centromere
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PCC-ring in vitro calibration curve
A
B
C
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Dose-response Curves
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Dose-response curve (Y=2.31 x 10-2D + 6.33 x 10-2D2) of Dic+Rc for 60Co 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 (∆).
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Comparison of Doses Estimated by Various Indicators
PatientEstimated Dose (GyE, GyE’, or GyE”)* by
PCC-ring Dic Dic+R/Rc 24Na**
A > 20 22.6 24.5 17-24
B 7.4(6.5-8.2) 8.3 8.3 8.7-13
C 2.3(1.8-2.8) 3.0(2.8-3.2) 2.5-3.6
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* Equivalent dose to X or γ-rays** Ishigure et al, when neutoron’s RBE is 1.5-2.0.
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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
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