1 Factors Contributing to the Reduction of Occupational Exposures at Czech NPPs Karla Petrová, Libor Urbančík, Dagmar Fuchsová State Office for Nuclear Safety Vladimír Kulich ČEZ, a.s ISOE EUROPEAN SYMPOSIUM 25 – 27 June 2008, TURKU, FINLAND

2 Collective Effective Doses at Czech NPPs

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4 Collective Effective Doses at Czech NPPs – Distribution

5 Collective Effective Doses at Czech NPPs What is the cause of such low doses?

6 Collective Effective Doses at Czech NPPs What is the cause of such low doses? Answer is not simple.

7 Collective Effective Doses at Czech NPPs What is the cause of such low doses? Answer is not simple. There is a concurrence of many factors.

8 Occupational Exposure Reduction Factors Contributing to the Exposure Reduction Objective causes:Objective causes: General arrangement General arrangement Structural materials Structural materials Fuel integrity Fuel integrity Specific causes influenced by the state regulation:Specific causes influenced by the state regulation: Legislative support Legislative support Operational safety culture Operational safety culture Well-thoughtout system of radiological monitoring Well-thoughtout system of radiological monitoring Effective radiological event feedback Effective radiological event feedback Effective education and training Effective education and training Specific causes uninfluenced by the state regulation:Specific causes uninfluenced by the state regulation: Modified water chemistry of the primary circuit adopted by the licensee Modified water chemistry of the primary circuit adopted by the licensee Licensee’s system of radiation work debriefing Licensee’s system of radiation work debriefing

9 Objective Causes General Arrangement

10 Objective Causes General Arrangement

11 Objective Causes Structural Materials Low cobalt content in reactor structural materials is one of the major causes of low doses at the Czech VVERs. Low cobalt content in reactor structural materials is one of the major causes of low doses at the Czech VVERs. Real content of cobalt in the steels and alloys used varies in range from to %. Real content of cobalt in the steels and alloys used varies in range from to %. Czech technical standards allow for cobalt concentration in materials < 0.05 %. Czech technical standards allow for cobalt concentration in materials < 0.05 %.

12 Objective Causes Low Content of Cobalt Table 1: Primary coolant samples from Dukovany NPP Unit 1 and Temelin NPP Unit 1 Radionuclide Volume activity [Bq/l] Dukovany NPP Temelin NPP 110m Ag Co Co Cr Fe Mn Nb Zr Sb < Sb < 2 615

13 Objective Causes Low Concentration of Cobalt in Coolant

14 Objective Causes Low Content of Cobalt

15 Objective Causes Low Content of Cobalt

16 Objective Causes Fuel Integrity

17 Objective Causes Fuel Integrity

18 Specific Causes Influenced by the State Regulation Legislative Support In order to maintain the favorable circumstances leading to a low cobalt concentration in structural materials of the Czech NPPs, the SONS has adopted a special chapter in the decree on technical safety in nuclear facilities related to cobalt contents in these materials.In order to maintain the favorable circumstances leading to a low cobalt concentration in structural materials of the Czech NPPs, the SONS has adopted a special chapter in the decree on technical safety in nuclear facilities related to cobalt contents in these materials. Another example of the state’s involvement in reducing workers’ exposure to radiation is the presence of radiation officers directly at classified activities in controlled areas of the Czech NPPs. In 2002 and 2005 the SONS adopted amendatory acts to the existing decrees that strengthened the role of radiation officers.Another example of the state’s involvement in reducing workers’ exposure to radiation is the presence of radiation officers directly at classified activities in controlled areas of the Czech NPPs. In 2002 and 2005 the SONS adopted amendatory acts to the existing decrees that strengthened the role of radiation officers.

19 Specific Causes Influenced by the State Regulation Operational Safety Culture Table 2: Number of events and number of unplanned scrams at the Dukovany and Temelin NPP units INES = 0 21/-17/-12/2613/3412/4219/4214/3119/24 INES = 1 0/-1/-2/11/20/10/30/11/2 INES > 1 0/-0/-0/00/00/00/00/00/0 Scram number 1/-0/-0/-1/130/21/00/12/1

20 Specific Causes Influenced by the State Regulation Radiological Monitoring 1.Workplace Monitoring Program 2.Personal Monitoring Program 3.Monitoring of Discharges Program 4.Vicinity NPP Monitoring Program 1.Docs on Radiation Safety Procedures (DR series) 2. Operating Procedures (P series) Documentation Approved by the SONS Implementing Rules Operational Instructions 1.Program of Radiation Protection at Work 2. Radiation Protection Assurance Procedures

21 Specific Causes Influenced by the State Regulation Monitoring of the Workplace

22 Specific Causes Influenced by the State Regulation Monitoring of the Workplace

23 Specific Causes Influenced by the State Regulation ALARA Implementation

24 Specific Causes Influenced by the State Regulation Effective radiological event feedback Every event is notified by the licensee to Every event is notified by the licensee to the SONS through the daily notification system. the SONS through the daily notification system. Classified events are submitted to the Classified events are submitted to the investigation group (INES < 0). investigation group (INES < 0). Significant events go to the Event Committee (INES ≥ 0 and Near Miss events with INES < 0). Significant events go to the Event Committee (INES ≥ 0 and Near Miss events with INES < 0). SONS regularly performs inspections over licensee’s events categorization and investigation. SONS regularly performs inspections over licensee’s events categorization and investigation. There is a rule of openness and trust between the regulator and licensee in their relations. There is a rule of openness and trust between the regulator and licensee in their relations.

25 Specific Causes Influenced by the State Regulation Effective radiological event feedback The relationship between regulator and licensee should have a common goal in the field of radiation protection: Effective and reasonable protection of people and the environment. Radiological event feedback serves that goal.

26 Specific cause uninfluenced by the state regulation Modified water chemistry Table 3: High-temperature pH 300 value limited in TechSpecs (TS) of Dukovany NPP Operational pH value 1 st intervention level for pH 2 nd intervention level for pH 7.1 – – 7.1; 7.3 – Optimum 7.2 Restore specified optimal value up to 48 hrs. Recover value into the 1 st intervention level up to 24 hrs.

27 Specific cause uninfluenced by the state regulation

28 Specific cause uninfluenced by the state regulation Is collective effective dose reduction really depending on pH value regulation?

29 Specific cause uninfluenced by the state regulation Is collective effective dose reduction really depending on a state intervention?

30 Conclusions 1. Activatedcorrosion products are the main contributors of surface activity and they build up radiation fields during outages. 1. Activated corrosion products are the main contributors of surface activity and they build up radiation fields during outages. 2. Dominant contribution of 58 Co is caused by low cobalt content in reactor system materials. 3. Modified primary water chemistry is only one of factors affecting radiation fields buildup. 4. Uncompromising ALARA implementation realized by CEZ plc with high safety culture are those essential factors significantly affecting occupational doses.

31 Factors Contributing to the Reduction of Occupational Exposures at Czech NPPs Any questions?