IAEAInternational Atomic Energy Agency

Cytogenetic Dose Estimation in the Criticality Accident in Tokaimura

LectureModule 13

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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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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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