Views from the Nuclear Industry on the Implementation of the 2007 Recommendations ~Focusing on the optimization process using dose constraints

Transcription

1 Views from the Nuclear Industry on the Implementation of the 2007 Recommendations ~Focusing on the optimization process using dose constraints OECD/NEA The 5 th Asian Regional Conference Chiba, Japan 4 September, 2009 The Federation of Electric Power Companies Sakae MUTO

2 (Source : Graphical Flip-chart of Nuclear & Energy Related Topics

3 Regarding the 2007 Recommendations of the ICRP The three fundamental principles for radiation protection are maintained The three basic principles for radiation protection - Justification, Optimization, and Application of Dose Limits - are maintained The values of nominal risk factor were confirmed to be low based on the latest scientific knowledge and that the dose limits of the 1990 Recommendations are maintained The optimization of radiation protection Using dose constraints in the optimization process is emphasized

4 Regarding dose constraints Dose Limits Dose Constraints Restrictions of individual dose received from all sources Restrictions of individual dose received from a single source Dose constraints (key descriptions in ICRP) Used in conjunction with the optimization of protection to restrict individual dose An upper bound on the predicted dose in the optimization of protection for that source (It is a level of dose above which it is unlikely that protection is optimized ) and for which, therefore, action must almost always be taken Ensuring that the optimization process did not create inequity Not to be used or understood as prescriptive regulatory limits

5 Dose control of workers in NPS Dose limits (50mSv / year, 100mSv / 5 years) To keep the dose limit, detailed control is implemented when the screening level is exceeded Screening levels (ex. 18mSv / year, 80mSv / 5 years) Established by the nuclear operators on a voluntary basis ALARA Radiation work admission Planned total dose + Total dose +Maximum individual dose( per day) + Maximum individual dose(total) 0.1 msv / Work 0.2 msv / Work 0.5 msv / Work Plan for implementing measures to reduce dose

6 examples of occupational exposure in NPS Outage Worker Inspection of piping Inspection of pumps Reactor Worker Reactor Building Patrol (Plant operator) Turbine Turbine Building Dose rate of the turbine is low in outage. In operation Inspection of piping : radiation Pumps Reactor Reactor Building Patrol (Plant operator) Turbine Turbine Building Dose rate of the turbine is high in operation.

7 The radiation exposure dose registration management system and the radiation work passport system The Radiation Dose Registration Center for Workers (RADREC) was established in 1977 with an objective to collectively control the dose data of radiation workers Related NPS and dose data is recorded for each individual The radiation work passport are issued to individuals and necessary information such as the history of radiation exposure is recorded RADREC Confirm individual dose NPS (A) Dose Data Confirm individual dose NPS (B) Dose Data Radiation work passport Work for Work for

8 Status of radiation exposure of radiation workers(fy2007) Dose distribution of radiation workers (total of nuclear power stations, etc.) Number of Workers 60,000 50,000 40,000 30,000 20,000 10, ,678 9,584 1 or less Over 1 to 5, incl. 3,055 Over 5 to 10, incl. Max. of individuals:21.1msv Average dose : 1.2mSv 1, Over 10 to 15, incl. Over 15 to 20, incl. Over 20 Dose distribution(msv) (Source : Radiation Effects Association News)

9 Protection for public Design stage Safety review As to radiation protection, facilities are designed based on the concept of ALARA Annual dose of neighboring public is evaluated based on the estimated annual release Confirmation of the status that ALARA is achieved Review by the regulating authority Operation stage Nuclear Safety Commission Target dose values for discharge (guideline) 50μSv / year Safety regulations Discharge control target values are determined from the estimated annual release Measures are taken so that Discharge control target values are not exceeded (control) Confirmation by environmental radiation monitoring Approval by the regulating authority Dose received by public discharge(gaseous,liquid) from NPS <0.001 msv ( FY2007)

10 Dose constraints for Occupational exposure and Public exposure(1) Occupational exposure Monitoring is possible by using dosimeters for individuals Possible to control individual dose directly Public exposure Monitoring of individuals is not possible More important to restrict each source individually Occupational exposure Public exposure Source Source Source Source Source Monitoring :possible Source Important to restrict each source individually Monitoring :impossible

11 Dose constraints for Occupational exposure and Public exposure(2) The Role of Dose Constraints Descriptions about "dose constraints" ICRP 2007 para.233 Occupational exposure the dose constraint is a value of individual dose used to limit the range of options such that only options expected to cause doses below the constraint are considered in the process of optimization Tools for optimizing protection Public exposure the dose constraint is an upper bound on the annual doses that members of the public could receive from the planned operation of a specified controlled source Assign doses to each source for observing individual dose limits

12 View about applying Dose Constraints to Occupational exposure The Role of Dose Constraints Tools for optimization Status of radiation control at nuclear power plants Planning Radiation work admission for each work Individual dose control using screening levels Achieve Optimization of Protection There is a structure for observing dose limits and optimizing protection based on experience in Occupational exposure at NPS, so the necessity to introduce dose constraints is minimal

13 View about applying Dose Constraints to Public exposure In order to ensure the dose below dose limit (1mSv/year ), it would be meaningful to introduce dose constraints with the aim of assigning doses to facilities related to radiation at each source In this case, the following points should be taken into consideration. Dose constraints should not be set lower than required Clarify the positioning so that dose constraints are not treated as a limit It would be necessary to coordinate with the existing Target dose values (for discharge)

14 Radiation protection in the future - What is expected - Dose per person received from natural and man-made radiation sources ( Average in Japan) (Units: msv / year) Medical Other 3.8mSv annually per person Cosmic rays Terrestrial Radon Internal Fallout Airplane use Occupation General consumable items Nuclear facilities Note 1: Radon is a gas generated when a very small amount of uranium or thorium is found in the earth or in building materials. Note 2: Fallout refers to radioactive fallout from nuclear weapon tests. [Source] Environmental Radiation in Daily Life, Former Science and Technology Agency Taking into consideration a balance with radiation exposure from other sources and with other risks such as caused by chemical substances

15 Conclusion In order to promote the use of nuclear power and radiation, we hope for Flexible recommendations that enable full use of operating experience Scientifically reasonable radiation protection balanced with other risks