Siting of NPPs and external events

1. Siting of NPPs and external events External events and screening criteria for site suitability including man made hazards- Finnish experience VN/RA/01 Task 1&2 Workshop Hanoi, October 2012 Confidential Ilari Aro STUK

2. What is siting • Siting is the process of selecting a suitable site for a facility, including appropriate assessment and definition of the related design bases. (IAEA Safety Guide NS-R-3, 2003) • Existing sites • site characterization is updated for new units • site related design requirements are determined according to current regulatory requirements • New sites • an extensive siting process • Environmental Impact Assessment (EIA) is part of the siting process • role of EIA depends on national legislation

3. Nuclear power plants in Finland • Olkiluoto NPP (TVO) • 2 operating units - ABB BWRs • New EPR under construction • EIA and DiP completed for a new unit • Loviisa NPP (Fortum) • 2 operating units - VVERs • EIA completed for a new unit • Fennovoima Ltd • EIA and DiP completed for a new unit

4. YVL 1.0 requirement: External events • According to Council of State Decree, the most important nuclear power plant safety functions shall remain operable in spite of any natural phenomena estimated possible on site or other events external to the plant. In addition, the combined effects of accident conditions induced by internal causes and simultaneous natural phenomena shall be taken into account to the extent estimated possible. • Natural phenomena include at least freezing which hinders the operation of the final heat sink or blockage due to some other reason, thunderstorm, earthquake, storm wind, flooding, exceptionally cold or warm weather, exceptionally hard rain or drought and exceptionally low sea level. Other events external to the plant are at least electromagnetic disturbances, oil leaks, crashing aeroplanes, explosions, releases of poisonous gases and unauthorised plant site entry. • Guide YVL 2.6 deals with how earthquakes are taken into account in nuclear power plant design. • Guide YVL 2.8 deals with probabilistic safety analyses (PSA) for nuclear power plants.

5. Safety criteria for siting - severe accidents • In the environment surrounding the nuclear power plant, however, precautions in the form of land use and public protection plans shall be taken with a view to the possibility of a severe accident. This means, among other things, that in the plant's vicinity there may not be facilities or population centres where the necessary protective measures, such as sheltering indoors or evacuation, would be difficult to implement. • In the plant's vicinity, no activities may be carried out that could pose an external threat to the plant. • The general principle in the siting of nuclear power plants is to have the facilities in a sparsely populated area and far away from large population centres. What justifies placement in a sparsely populated area is that emergency planning will then be directed at a smaller population group and will thus be easier to implement.

6. External events affecting safety • The applicant for a licence shall list those external events that could pose a threat to safety at the site in question and shall also assess the risks arising from these events. Effects on the supply of cooling water and on electric power grid connections shall also be considered. • Hazardous industry, traffic and exceptional natural phenomena shall be considered. In Finland, examples of exceptional natural phenomena include • freezing or other clogging of the cooling water intake • storms • snow loads • flood • low sea level • seismic events. • The risks arising from external events are assessed by analyses conducted in accordance with Guide YVL 2.8.

7. Protection against external threats After September 11, 2001: political and public will was expressed to improve protection against terrorist actions • Reconsideration of aircraft crash design basis • consider large passenger and military aircrafts • no immediate release of significant amount of radioactive substances • initiation and maintenance of key safety functions in spite of the direct consequences of the event (penetration of structures by impacting parts, vibration, explosion, fire) • Microwave and biologic weapon consideration

8. Effects of external events in the plant • External events can cause • loss of external electrical net (fire, storm effects) • loss of water cooling channels (ice, algae, mud, oil) • loss of intactness of building (pressure wave), e.g. wall / roof • loss of systems and components because of vibrations • loss of ventilation and cooling e.g. of diesel generator (snow, sand) • high temperature of air or water for cooling • flooding in the buildings • missiles to cause damage (e.g. turbine and tornado caused missiles, airplane engines) • fire in the buildings • poisonous gases, smoke to threat operators’ health • loss of computers or electrical systems (electromagnetic)

9. Finnish experiences • loss of cooling channels because of ice or algae • weakening of cooling chain capacity because of mud in the spring time • loss of diesel generators because of snow blockage of ventilation / air cooling channels • backfitting of accumulator fastening because of seismic vibrations (in the original design not taken into account) • taking oil transport accidents into account in the design (cooling water intake) • tornado design basis is under national study

10. Olkiluoto 1 and 2 operating experience:Blockage of seawater intake by frazil ice(rapid freezing of subcooled water) • Frazil ice has caused partial blockage of seawater intake in Olkiluoto three times, modifications of the plant and operating instructions were implemented • anti-icing line returning warm cooling water to seawater intake • latest partial blockage in 2008 due to failure of one anti-icing pump • Provisions to prevent blockage in OL3 • anti-icing line returning warm outlet water to intake tunnel • heating of bar screens in seawater pumping station • Possibility to take essential seawater from outlet side • Provisions for 72 h loss of ultimate heat sink (large feedwater supply) • air-cooled diesels • air cooled EFW and ECCS pumps (2/4)

11. Olkiluoto 1 and 2 operating experience: Blockage of diesel air intakes • In 1995 snow blocked Olkiluoto diesel generator combustion air intake and diesels failed to start in a test, plant modifications implemented in OL1/OL2 • Provisions to prevent blockage of air intakes in OL3 • structures to protect diesel generator and air cooler air intakes from snow, external fire, pressure wave etc. • heating of intake screens • alternative air intake required for SBO diesels (diverse diesel generators for two safety trains) • note: extreme snowstorm involves risk of simultaneous loss of offsite power and diesel generator unavailability • Additional diversity: Gas turbine plant next to the site with underground cable connection (not part of the plant)

12. Olkiluoto 1, 2 Potential loss of reactor building heating in very cold weather, < -20oC • Risk identified by Swedish operating experience • If ventilation is not turned off, very fast cooling of instrument rooms • Freezing of reactor tank level measurement impulse pipes (core damage assumed) • loss of level measurements is a known vulnerability • need for diversification • Preliminary analysis showed very high risk • Corrective action: operator stops ventilation • Alarm added in control room • Operating procedures, training • Tuning of air flow • More detailed calculations • Current risk estimates very low • Vulnerabilities in all buildings were checked • fire PSA screening studies were utilized in identifying possible vulnerabilities • some temperature alarms were added

13. Site characterization • Geology and seismology • Hydrology • Meteorology • Transport routes (sea, land and air routes, pipelines) • oil and hazardous substances • airports • Industrial activities • production, storage • Agriculture • Population Information on the following topics is required for assessing site suitability and for determining plant design values for external events

14. Meteorology and hydrology (1) Phenomena considered in design of OL3 • Highest and lowest outdoor air temperature • instantaneous, short term, long term • Air humidity • Extreme wind speed • including tornadoes (trombs) and downbursts • Seawater temperature • high temparature • subcooling, frazil ice formation • Seawater level, extreme high and low • all sites are coastal • Ice conditions • Precipitation • Snow load • Lightning peak current, rise time etc.

15. Meteorology and hydrology (2) • No detailed quantitative requirements in current YVL guides • Quantitative risk targets provide some guidance • core damage frequency < 1E-5/a • large release frequency < 5E-7/a • no single factor shall dominate • Intensity-frequency distributions have been determined based on available observations • reliable observations for ~ 100 years • return periods of interest up to 10 000 - 1 000 000 years • uncertainties are very large at high return periods • Combinations of correlated events are potentially important • snow and wind: potential for loss of offsite power and simultaneous failure of diesel generators due to combustion air intake blockage

16. Meteorology and hydrology: OL3 lessons learned (1) • The design values for external events are presented and reviewed in connection with the construction licence application • OL3 design values had been specified in the call for tenders and had become part of the agreement prior to submission of the construction licence application • In STUK’s review supported by expert organizations, some design values were considered insufficient or poorly justified • TVO had not involved all its available expertise • expertise of the Finnish Meteorological and Marine Research Institutes was not fully exploited • insufficient consideration of uncertainties • not enough prior discussions with STUK • Changes in the design bases were difficult to accomplish

17. Meteorology and hydrology: OL3 lessons learned (2) Examples of potential problem areas in the original design as presented in PSAR • Design of air intakes with regard to blockage by snow or ice • redesigned • Provisions for preventing seawater intake blockage by frazil ice • a line for returning heated outlet water to intake • Design basis for • high air temperature • extreme wind • including tornadoes and downbursts • high seawater level

18. Meteorology and hydrology: OL3 lessons learned (3) • Meteorological and hydrological topics have been included in the national nuclear safety research program SAFIR • extreme weather phenomena and seawater level • statistical analysis of recorded data, including older data • physical basis for extreme events • effect of climate change • assessment of the latest IPCC report on the regional scale • co-operation with Sweden • a popular topic in public discussion in the media

19. Example: Recurrence time - air temperature curvemedian and 95 % confidence band source: Finnish Meteorological Institute and TVO • based on digitized data for about 60 years from the neighbourhood of Olkiluoto • median curve used by TVO to justify design basis temperature 36 oC • highest measured value in the region 35.9 oC in 1914 • median curve does not reach 36 oC • confidence band should be considered Temperature (oC) Recurrence time (years)

20. Industrial and transport activities close to sites • No hazardous production plants or storage facilities or pipelines in the vicinity of Olkiluoto site • Shipping lines are not in the immediate vicinity of Olkiluoto site • Sea transport of oil near Loviisa/Ruotsinpyhtää • 30 % of Russian oil exports are transported through the Gulf of Finland • main fairway 40 km from the Loviisa site • a few supertankers and several small tankers per day • transports are increasing rapidly • the possibility of a major oil spill must be considered • risks of oil spills is a common topic in the media • Fennovoima sites • Kemi harbour and industrial area 6 - 8 km from the Simo site • some transports and use of dangerous materials

21. OL3 Risk Profile, CDF  1.8E-06 /a • Transients 45% • Loss of feed water • Component cooling system failures • Loss of Coolant Accidents 24% • Small LOCA being the most important • Loss of off-site power supply 5% • Internal Fires 2% • Internal Floods 2% • External events 16% • Frazil ize • Organic material in sea water • Wind&Snow Low power and shutdown 6% (internal)

22. Use of PSA - Loviisa NPP RiskProfile

23. Use of PSA - Olkiluoto 1/2 RiskProfile

24. Screening criteria for man made hazards • Screening criteria have relationship with PRA in Finland - PRA basis screening is carried out and events are studied and analysed • IAEA Safety Standards Series No. NS-G-3.1 ”External Human Induced Events in Site Evaluation for NPP’s” presents two step approach for screening (no numerical values presented) • Distance • Probability • Hazardous industries and installations need to be considered • explosions • poisonous and / or flammable gas clouds, fluids • Transport routes: roads, railway, waterway, airway, including pipelines and transports need to be considered as above • Design or regulatory criteria need to be established for distance and / or probability: examples e.g. U.S. Regulatory Guide 1.91 (1978)

25. Non-seismic External Events - Screening study • Screening study done by an external consultant • Based on the report Knochenhauer and Louko, Guidance for External Events Analysis, SKI Research Report 02:27 • Screening starts with ~ 50 phenomena • high/low air temperature, wind, lightning, snow, frost ... • high/low seawater level, high seawater temperature, frazil ice • oil and chemical spills, organic material in water (algae) • explosion pressure wave, EM pulses

26. Non-seismic External Events - Screening criteria for single events Source: Areva, Relcon Scandpower: OL3 PSA Ch. 6.2.1, External Events Screening Analysis

27. Non-seismic External Events - Screening criteria for multiple events Source: Areva, Relcon Scandpower: OL3 PSA Ch. 6.2.1, External Events Screening Analysis

28. Non-seismic External Events - Quantification • Preliminary results in 2004 • frazil ice, CDF = 8.3•10-8/year • organic material in seawater, CDF = 1.1•10-7/year • high wind and snow, CDF = 4.3•10-8/year • total 2.4•10-7/year • Updated results in 2005 • frazil ice, CDF = 8.3•10-8/year • organic material in seawater, CDF = 1.1•10-7/year • high wind and snow, CDF = 1.9•10-8/year • more conservative analysis but gas turbines included • total 2.1•10-7/year

29. Examples of external events design basis • Highest outdoor air temperature +36 oC (less than 6h), 27 oC (6 hours to 7 days), and 23 oC (more than 7 days) • Lowest outdoor air temperature -39 oC (less than 6h), -32 oC (6 hours to 7 days), and -29 oC (more than 7 days) • Extreme wind speed 48m/s in the design of safety-critical buildings; the Guide RIL-144 applies with respect to others • Seawater temperature -0.4 oC…+30 oC (as a design basis for safety systems) • Seawater level, normal operation -1.6m…+1.3m (+ wave allowance 0.4m); the function of safety systems will be ensured up to +3.5m • Precipitation 100mm per hour, 400mm per day • Snow load 5 kN/m2 • Lightning peak current 200 kA.

30. Approach to resolve design basis issues related to meteorological events • Exceeding some of OL3 design values can not be excluded with high confidence • It must be shown that exceeding the design values with reasonable amount does not prevent safe shutdown (“cliff edge analyses”) • analysis of actual safety margins in system design • assessment of failure criteria • e.g. effect of high air temperature on residual heat removal • two trains with air cooling (rooms and components) and two trains with seawater cooling • seawater cooled trains are sufficient for residual heat removal in case air cooled trains fail due to high temperature • N+2 failure criterion is not fulfilled, acceptable in a rare situation • air and seawater temperatures are correlated but in practice the design margins are larger in seawater cooled trains

31. Regulatory issues, External events • Estimated risks are low, but uncertainties are high • Some events were screened out based on non-conservative frequency estimates • Frequencies are being updated for the operating license phase PRA • High wind and snow was considered a significant issue • potential for simultaneous loss of off-site power and diesels • new estimate with more conservative data but including on-site gas turbine • Risk informed approach has proven useful • accident chains, dependencies

32. Regulatory issues on external events design values • No detailed quantitative requirements in current YVL guides (except seismic) • Quantitative risk targets provide some guidance • core damage frequency < 1E-5/a • large release frequency < 5E-7/a • no single factor shall dominate • Intensity-frequency distributions have been determined based on available observations • reliable observations for ~ 100 years • return periods of interest up to 10 000 - 1 000 000 years • uncertainties are very large at high return periods • Combinations of correlated events are potentially important • snow and wind: potential for loss of offsite power and simultaneous failure of diesel generators due to combustion air intake blockage

33. STUK statement: extreme weather phenomena • Extreme weather phenomena on the site and extreme seawater levels have been investigated in the risk analyses. Effect of exceptionally high and low temperatures and extreme values and frequencies of local wind (tornados) on the desing have been studied and they can be taken into account in the design of the plant. Variations at sea level are minor and ice conditions are normal in the Finnish coast. • Occurrence of extreme weather phenomena and impact of climate change on them are investigated in the national nuclear research programme. Adequate design of NPP will be studied in the construction license phase.

34. STUK statement: cooling and fresh water • Large volumes of seawater are needed for the cooling of turbines. No obstacles are foreseen in the intake or outlet arrangements. The effects of elevated outlet seawater temperature on the sea have been studied in EIA Report. • The processes of NPP need a lot of purified fresh water. Fresh raw water arrangements are appropriate at the site. Raw water is pumped from the 8 km distance from the river via pipeline. Company has plans for water and they will be reviewed in the construction license phase. • The clogging of seawater systems due to algae, freesing and oil is taken into account in design of NPP.

35. STUK statement: man made hazards • There are no industrial plants, storage facilities, traffic routes or gas pipes near site that could pose a risks to NPP as a result of accidents. • Oil transport routes do not run near the Olkiluoto site. The probability of oil spill affecting the supply of seawater is considered low. • Needed strengthening of national electric grid belongs to Grid Company. A new high voltage line to the site will be constructed. Own emergency generators will be constructed to the site to supply safety systems with the needed power. New lines are taken into account in the land use planning.

36. Conclusions on Finnish projects • Site specific external events have been considered extensively in the design and licensing of OL3 • The experiences from the operating units have been used • operating events • external events PRAs • However, some development areas have been identified • in plant design • in design and licensing processes • most safety issues have been resolved with design modifications or more detailed analyses • OL3 experiences will be considered in new projects • Preparation for new projects have been started • EAIs are have been completed for all three projects • Government and Parliament decision was made in 2010