Radiation Protection of the Emergency Workers Regaining Control over Radioactive Material Inside Destroyed Unit IV of the Chernobyl NPP

Transcription

1 International Conference on Global Emergency Preparedness and Response, Vienna, October 2015 Radiation Protection of the Emergency Workers Regaining Control over Radioactive Material Inside Destroyed Unit IV of the Chernobyl NPP Vladimir Kutkov, NRC Kurchatov Institute, Russian Federation

2 Recovery of the Chernobyl NPP 1. To prevent development of catastrophic conditions on the ChNPP site. 2. To establish emergency management. 3. To regain control over the emergency situation on the site and in vicinity. 4. To re-establish the Defence-in-Depth of the ruined Unit IV and regain control over about 6.6E+20Bq of fission and activation products inside. 5. To return the Chernobyl NPP in operation. 2

3 Ruined Unit IV of ChNPP in May,

4 Secured Unit IV in November,

5 Phase 1 of the Recovery Operation April 1986 (days D1-D2) Objective: To prevent development of catastrophic conditions and establish emergency management. Fire on roof of Unit IV and Joint Turbine hall was put out in5 hoursafter start of the accident; Units I-III in cold shutdown in 3-25 hours; The Governmental commission was established and deployed to city of Pripyat in 18 hours; About 50,000 citizens of city of Pripyat were evacuated 27 April, 39 hours. 5

6 Phase 2 of the Recovery Operation 28 April -22 May (days D3-D27) Objective:To regain control over the emergency situation on the site and in vicinity. About 100,000citizens were relocated from the ChNPP 30-km zone and other contaminated territories in Belarus and Ukraine on 2-6 May; Clean-up works on the site started; Strategyfor regaining control over radioactive material and returning the ChNPP into operation was issued on 22 May. 6

7 Milestones of Recovery Strategy (Decree of CCCPSU and the CMSU on 22 May 1986) Milestone PLANNED REACHED Repopulate the 30-km zone Dec Revoked Secure the ruined Unit IV Sep Nov Decontaminate the ChNPP site Sep Dec Return the Unit I in operation July 1986 Oct Return the Unit II in operation July 1986 Nov Return the Unit III in operation Aug Dec Resume constructing Stage 3 Oct Revoked 7

8 Phase 3 of the Recovery Operation 23 May 30 November (days D28-D219) Objective: To re-establishthe Defence-in-Depth of the ruined Unit IV and regain control over about 6.6E+20Bq of fission and activation products inside. 30 November 1986 Object Ukrytie securing the ruined Unit IV was commissioned; 1 October 1986 Unit I returned to operation, 5 November 1986 Unit II returned to operation, and 31 December 1987 Unit III returned to operation. 8

9 1986 Chernobyl emergency workers 9

10 1986 Chernobyl emergency workers (2) Cohort IDM Size, Mean dose, persons msv C1A Witnesses: Victims 134 3,400 C1B Witnesses: Recov. 2, C2 Early Military EmWrk 21, C3 Late Military EmWrk 61, C4 ChNPP staff 2, C5 ChNPP supporters 2,000 ND C6 Construction Work. 21,

11 Chernobyl NPP site in April

12 Witnesses of the Accident 12

13 Radiation Safety Provisions in Exposure Situations PLANNED Each planned exposure should be justified The doses of planned exposure situation should be kept As Low As Reasonably Achievable The sum of doses in a planned exposure situation should be kept below specified dose limits EMERGENCY Each protective action should be justified in context of protective strategy The protective strategy should be optimized The residual dose after implementation of protective strategy should be kept under specific reference levels 13

14 GSR Part 3 and GSR Part 7: Exposure of Emergency Workers In an emergency exposure situation, the relevant requirements for occupational exposure in planned exposure situationsshall be applied for emergency workers, in accordance with a graded approach. Response organizations and employers shall ensure that no emergency worker is subject to an exposure in an emergency in excess of 50 msvother than those whose perform exceptional tasks. 14

15 ChNPP Staff: «Normal Operations» 15

16 Works at the Roof of Unit III/IV K* max = 4 Gy/h K* min = 0.2 Gy/h Dose limitation for Emergency Workers H WB = 250 msv, including 200 msv in one operation 16

17 Conditions of Generic Optimization The radiation protection framework established in US-605 for protection of emergency workers (Cohort C6) was optimized under following conditions: The object Ukrytie shall be completed by 1 October 1986; The individual dose of emergency worker shall not exceed 250 msv; The collective dose of emergency workers should be minimised; Civil and military workforce is limited. 17

18 Chernobyl Construction Workers 18

19 1986 Civil Emergency Workers 19

20 Summary About 110,000 emergency workers were involved in 1986 in 216 days operation on regaining control over the radioactive material in destroyed Unit IV of the ChNPP. Average whole body dose equivalent of gammaradiation in 1986ChNPP emergency workers is 170 msv. 300 msv was exceeded in about 3,500 workers, 1000 msv was exceeded in about 500 workers. 20

21 Summary (2) Exposure of accident witnesses in Cohort C1 who worked at ChNPP site 26 April -1 May provides example of unrestricted exposure of emergency workers in emergency exposure situation. That exposure provides the lognormal distribution of individual does, which is expected. Exposure of ChNPP in Cohort C4 who worked at ChNPP site after 1 May provides example of regulated exposure of emergency workers in emergency exposure situation. That exposure provides the restricted lognormal distribution of individual does as expected. 21

22 Summary (3) Exposure of construction workers in Cohort C6 who built the object Ukrytie at ChNPP site 20 May 30 November to rebuilt Defence-in-Depth of ruined Unit IV and secure about 6.6E+20Bq of fission and activation products. That works were performed under the strict radiation control and exposure was optimised on the way specific for planned activities in emergency exposure situation. The optimization under limited resources provides the cut-off type of distribution, which should be taken into account in application of principle of optimization in emergency exposure situation. 22

23 Thank you for your attention! 23