Assessment of Internal Exposure following Accidents or Incidents

1. ASSESSMENT OF OCCUPATIONAL EXPOSURE DUE TO INTAKES OF RADIONUCLIDES Assessment of Internal Exposure following Accidents or Incidents

2. Assessment of Internal Exposure following Accidents or Incidents – Unit Outline • Introduction • Post Event Information Requirements • Post Event Monitoring • Follow-up Monitoring

3. Introduction

4. Accident “Any unintended event, including operating errors, equipment failures or other mishaps, the consequences or potential consequences of which are not negligible from the point of view of protection or safety.” BSS Glossary

5. IAEA Accident response experience Under the 1986 Convention on Assistance in the Case of a Nuclear Accident or Radiological Emergency, the IAEA: • makes available appropriate resources for emergency response, • promptly transmits requests for assistance to other States or international organizations which may possess necessary resources, and • may co-ordinate assistance at the international level

6. IAEA Accident response experience • Chernobyl was the most serious accident in Agency history. • IAEA has been involved in investigation of a number of other accidents involving. • loss of control or misuse of radioactive sources, • errors in medical treatment, or • accidental exposure in irradiation facilities.

7. Several situations contribute to accidents • Operational error or equipment failure when transferring large sources; • Interlock failure on high dose rate equipment; • Radiography sources left unshielded; • Equipment failure or operational errors in nuclear facilities. • Medical misuse of sources; and • Criticalities

8. Accidents with ”clinical consequences”* Persons Activityaffected • Nuclear fuel cycle 245 • Industrial uses of radiation 94 • Medical uses of radiation 18 • Tertiary education and accelerators 19 • Other 344 • Total 720 * From 2000 UNSCEAR Report (1975 through 1994)

9. Post Event Information Requirements

10. Introduction • There will be situations involving the use of radioactive material in which the operational controls break down • Accidents or incidents may result in releases of radioactive materials into the working environment with the potential for high doses to the workforce

11. Accidents – Medical treatment first • After an accident, the radiological consequences may be complicated by trauma or other health effects incurred by workers • Treatment of injuries, especially those that are potentially life threatening, generally takes priority over radiological operations • Post-accident exposure assessment should be conducted when the situation has been brought under control.

12. Post-accident – Gather key information • When exposure assessment starts, get as much information as possible • Example - information is needed on; • Time and nature of the incident • Radionuclides involved • Timing of bioassay samples and • Measurements of body activity

13. Post-accident – Gather key information Information is necessary for; • Exposure assessment • Medical assessment, to guide medical treatment of the victim (which may include chelation therapy or wound excision) • Accident reconstruction • Long term medical follow-up of victims Debridement

14. Internal decontamination Soon after ingestion gastric irrigation Nuclides which are hardly absorbed by gastrointestinal tract cathartic Na、K、FWT diuretic FWT volume water intake Cs, Rb Prussian blue→depress reabsoption by small intestine I potassium iodide →depress absoption by thyroid Pb, Cu, Zn、Cd, Cr, Mn, Ni EDTA→ chelator Actinides DTPA →chelator (Ca-DTPA>>Zn-DTPA) approx.10 times

15. Debridement This treatment is seldom done for decontamination recently……

16. Dose reconstruction X-ray tube FOV Distance from the tube Pattern Ⅰ Analysis of the behavior pattern Pattern Ⅱ Pattern Ⅲ Measurement of the dose with the same condition as the accident Pattern Ⅳ

17. Detectors for dose reconstruction For low energy and high dose rate 5KeV-1.3MeV　（Al deposited PET window :3.6μm) For general energy and low dose rate 25KeV-50MeV　（POM window :1mm) 30KeV-50MeV　（POM window :1mm) 30KeV-50MeV　（PMMA window :1mm)

18. Measurement devices for dose reconstruction Reference hygrometer, barometer and thermometer Reference ampere meter hygrometer, barometer and thermometer

19. 24Ｎａ analysis by Ge detector to estimate thermal neutron flux 23Na(100%)： 0.531barn 41K(6.73%)： 1.46barn

20. Long term medical follow-up 23 crews of “No.5 Fukuryu-maru “were exposed by the nuclear test that had been done in Bikini in 1954 . The purpose of this investigation is to examine these victims' health conditions for a long term,and to research the delayed effect. The exposure type was a mixture exposure and the estimated dose was 1.7-6.0Gy. 11 survivors are having their physical condition examined once a year . Fishing vessel,from which radioactivity was detected Fishing vessel and the fish,from which radioactivity was detected Bikini Atoll

21. Long term medical follow-up The contrast medium "Thorotrast" of which the principal ingredient was the thorium dioxide was used for the angiography in Japan from 1932 to 1945. The number is estimated to be 10,000-20,000 people. Thorotrast deposits mainly on the liver and the spleen, then causes the internal exposure for a long term. The purpose of this investigation is to clarify the relation between the deposition amount of Th- 232 and the clinical conditions and also to clarify the influence to human body by a long-term internal exposure. The medical examination is done once a year. Thorotrast Abdomen image by radiography

22. Post-accident information gathering • Accidents or incidents can result in high committed effective doses ( dose limits) • Individual and material specific data are normally needed for exposure assessment • Necessary data include information on; • Chemical and physical forms of the radionuclide(s) • Particle size • Airborne concentrations

23. Post-accident information gathering • Necessary data also includes information on; • Surface contamination levels • Retention characteristics in the individual affected • Nose blows, face wipes and other skin contamination levels and • External dosimetry results

24. Post-accident information gathering • Data may seem inconsistent or contradictory, particularly if the intake period is uncertain • Adequate dose assessments can be made only after; • Considering all of the data • Resolving the sources of inconsistency as far as is possible, and • Deciding most likely and worst scenarios for exposure and magnitude of intake

25. Post Event Monitoring

26. Recommended procedures for monitoring Later actions Low level monitoring if possible & justified Low level of internal contamination Dose estimate based on ICRP models NO Later actions (see below)

27. External contamination interference • Radiological characteristics of the radionuclides determine whether direct, indirect, or both methods should be used • If there is external contamination with gamma emitters, direct measurements should normally be delayed until decontamination • This 1) prevents interference with the measurement and 2) avoids contamination of the direct measurement facility

28. External contamination interference • If urgency of assessment precludes complete decontamination, wrap the individual in a sheet to minimize contamination of the facility • Such initial direct measurement results are upper limits for the body content • More measurements would be needed after further decontamination • External α or β contamination won’t normally interfere with direct measurements, unless bremsstrahlung is produced by the betas

29. Other concerns • External contamination will not interfere with indirect methods • However, care must be taken to avoid transfer of contamination to excreta samples • Rarely, intakes may be so high that special techniques to avoid interference with equipment response, e.g. excessive electronic dead times

30. Mobile Direct Measurement Facilities

31. Mobile Direct Measurement Facilities

32. Analysis of excreta • Analyses of samples of urine and faeces should be considered to verify the intake • These results may be difficult to interpret, because of; • Possible multiple routes of intake and • Imprecise about radionuclide transfer to the blood

33. Analysis of excreta • Early excreta results are generally not useful for intake assessment because of the delay between intake and excretion • Particularly true for faecal excretion • In addition, rapid early components of urinary excretion can be difficult to interpret - not fully defined in some models

34. Analysis of excreta • Nevertheless, all excreta should be collected following an accident or incident • Early detection of radioactivity in urine can be a useful indication of the material solubility and potential for effective treatment • Excreta analyses can be the only reliable method of assessing intakes if large amounts of external contamination interfere with direct measurements.

35. Blood sampling • Emphasize non-invasive procedures. Invasive procedures such as blood sampling are usually justified only in accident situations in which large intakes may have occurred • Blood sampling can provide data on the solubility and biokinetics • Has limited value for quantitative intake estimates because of rapid clearance of most radionuclides to other tissues

36. Workplace monitoring samples • Workplace monitoring samples, e.g. • Air filters • Surface contamination wipes, • Should be analysed to determine; • Radionuclides involved • Isotopic ratios, and • Physicochemical characteristics

37. Follow-up Monitoring