Olena Mykolaichuk State Nuclear Regulatory Inspectorate of Ukraine Chairperson

Transcription

1 Olena Mykolaichuk State Nuclear Regulatory Inspectorate of Ukraine Chairperson

2 Chernobyl NPP as of 25 April 1986: 4 Units RBMK-1000 in operation, 2 more under construction Unit 1 was commissioned in 1977, Unit 4 in 1984 Major nuclear accident at Chernobyl-4 started at 1:26 a.m. 26 April 1986 and resulted in Unit destruction and large radioactive release estimated as 1,4x10 19 Bq, major releases continuing for 10 days and including radioactive gases, aerosols and fuel particles; All operating units at Chernobyl site were shut down on 26 April but restarted in few months Confinement over destroyed reactor (Shelter Object) was erected by 30 November 1986 Remediation works resulted in about 800 disposal sites within and around exclusion zone Authorities introduced a set of large-scale protective measures for the members of general public

3 In few days, starting 2 p.m. 27 April, a vast territory around NPP was evacuated (more than people), nowadays known as the exclusion zone; About hectares of agricultural land were removed from service in 3 countries, and timber production was halted for about hectares of forest; Later on affected territories were graduated by 4 categories, so called people protection measures were established by Law for each category: Exclusion zone - 1; Zone of obligatory relocation - 2; Zone of voluntary ensured relocation - 3; Zone of observation - 4 Real exposure situation differs from established categorization, however no attempt on re-categorization has been succeeded yet Five million people continue to live in areas contaminated above 37 kbq/m 2 of 137 Cs and about residents still receive more than 1 msv annually from the Chernobyl fallout

4 Public should be educated using different means on real protective measures, including iodine medicines use For any accident scenario a clear role for each actor should be prescribed, giving more powers to those who have proper knowledge and skills and preventing unsubstantiated uneducated interventions Emergency drills should cover all levels of decision-making to be involved Public communication should be prompt and not limited to public notification and information

5 Sound dose estimation in short term means more effective public protection so instruments and experts to do it promptly are to be available Optimization of remediation measures means both less real dose and less radioactive waste Decreasing dose and mitigating health effects instead of establishing socio-economic bonuses means real socio-economic benefits in long run Basis for immediate counter measures optimization (cost-risk analyses) should be prepared in advance to provide quick expert decisions

6 Linear-non-threshold (LNT) model A dose-response model which is based on the assumption that, in the low dose range, radiation doses greater than zero will increase the risk of excess cancer and/or heritable disease in a simple proportionate manner. Use of LNT model is considered by the ICRP to be the best practical approach to managing risk from radiation exposure and commensurate with the precautionary principle (UNESCO, 2005). The ICRP considers that the LNT model remains a prudent basis for radiological protection at low doses and low dose rates (ICRP, 2005).

7 Dose limits are not used in emergency exposure situations The optimization of protection and safety in emergency exposure situations primary aims the prevention of tissue reactions: acute health effects with the dose threshold; LNT model is not used for these purposes; The optimization of protection and safety of in areas with low dose/dose rates is based on LNT model The optimization of protection requires judgements to be made about the relative significance of various factors, including: the number of people (workers and the public) who may be exposed to radiation; the likelihood of their incurring exposures; the magnitude and distribution of radiation doses received; and economic, social and environmental factors. The optimization of protection also means using good practices and common sense to avoid radiation risks as far as is practical

8 The low levels of routine radioactive discharges of NPPs and the associated low levels of the public exposure are warranted by the design and technology features; many such design features are related to the accidental conditions or are not connected with radiological requirements at all The reactor containment intended for accidental conditions, but also provide a positive side effect : it play a key role in minimization of routine atmospheric discharges The are alternatives to the LNT-based principle of optimization (ALARA): e.g. BAT or Zero Discharge, both are widely used for regulation of chemical discharges, but may be expensive or not feasible for NPPs; NB: many chemical substances have proved threshold effects; A modification of the LNT risk extrapolation model and even a discovery of solid scientific evidences of the threshold will not lead to relaxation of requirements on levels of routine discharges because of indicated above factors and public perception! LNT-based principle of optimization does not pose a substantial burden on the nuclear industry in planned exposure situations

9 Proper consideration of human factor and optimization preparedness are important factors for emergency planning Linear-non-threshold model may be far from ideal, however to start changing approach to radiation protection we need to achieve a wide international consensus based on radiobiological studies and supported by UNSCEAR and ICRP judgments