1 Fire Probabilistic Safety Assessment for Kudankulam NPP in India Gennady Tokmachev, PhD Atomenergoproekt, Moscow, Russia orc.ru Web:

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3 Presentation Outlines Introduction Plant design features Methodology Fire hazards assessment Fire frequency Probabilistic model Results Conclusions

4 Background Atomenergoproekt – main design architecture of VVERs PSA studies – since 1988 Fire analyses – since 1994 Fire studies performed – for Balakovo 1-4, Novovoronezh- 3,4, Kalinin, Rostov, Smolensk NPPs in Russia, and Bushehr plant in Iran The first phase of the fire PSA for Kudankulam NPP was conducted at the PSAR stage in 2002 <= contractual terms Now this is Regulatory requirement in Russia

5 Plant Design Features Safety systems comprise new passive technologies, e.g. emergency residual heat removal is fulfilled by passive and active diversified redundant systems Four safety trains of 100% capability Substantial physical separation of cables and systems High degree of fire resistance of structural elements of safety and normal operation systems. Fire barriers between redundant trains have a minimum fire resistive rating of 3 hours Implementation of weakly combustible cable insulation Use of fire resistant control circuits at control rooms, etc

6 Methodology -1 The fire PSA involved building and room analyses (incl. fire hazards assessment), determination of fire-induced events and fire related accident sequences, quantification of CDF, uncertainty, sensitivity and importance analyses The study was performed in a highly iterative manner The general approach to conducting a fire PSA was little changed due to lack of data, e.g. operating procedures

7 Methodology - 2 Uncertainties associated with the results of the fire PSA are relatively high Carrying out the fire PSA from the very beginning of the design development gave the benefit of modifying plant design easily to mitigate fire consequences More comprehensive PSA for internal fires will be performed during the detailed design

8 Fire Hazards Assessment (FHA) -1 FHA - comprehensive assessment of potential fire hazards throughout the plant and the effect of potential fires on the safety-related plant areas Essential fundamental part of the fire PSA Fire containment approach - the design basis: all combustibles within fire compartment can be consumed regardless of operation of fire suppression systems Fire propagate issues were addressed FHA established the failure modes of equipment and especially electrical circuits as a result of a cable failure

9 Fire Hazards Assessment -2 FHA resulted in physical changes to the plant. Examples: Constructing fire barrier walls between redundant cables to divide the containment annulus into smaller compartments Providing cooling for those compartments Reinforcing fire-rated doors in some compartments of the auxiliary reactor building Replacing surplus fire doors by fire-rated walls in cable shafts Enclosing cables in conduit to prevent cables from contacting other equipment in the fire compartment

10 Fire Frequency Statistical basis - operational experience of all the 18 units with VVER-1000 reactors in Russia and Ukraine Data on fire incidents that occurred during calendar years, including years at power Fires at VVER-1000 plants are relatively rare => involving data on both fires and ignitions at VVER-1000 plants Probability of the ignition-fire transition was derived from operational experience Since the mid-1980s substantial effort has been made to upgrade fire safety at VVER plants => the estimates can be considered as conservative ones for the current state

11 Frequency of Fires at Operating NPPs with VVER-1000 Equipment becoming an ignition sourceFrequency of large fires per plant-year Turbine, generator, exciter2.9Е-3 Turbine driven pump8.3Е-4 Motor driven pump, including oil ignitions3.5Е-3 Switchgear, including circuit breakers1.4Е-3 Electrical components (transformers, etc.)1.4Е-3 Cable1.1Е-2 Transient fuel2.7Е-4

12 Probabilistic Model Small event trees / large fault trees Computer code RISKSPECTRUM Fire PSA relied on the plant response probabilistic model developed for the internal IEs Review of any simplifications in the internal event PSA to confirm their applicability for the fire risk assessment Fire-induced event were incorporated using house events: Additional failures Modified CCFs The factor of a fire impact on operators, etc

13 Results Overall fire-induced CDF for Kudankulam NPP - 9.1Е-9/a Six times lower than CDF addressed in the internal PSA The largest contribution to the total CDF - fires in diesel generator buildings UKD and relevant cable tunnels UKZ Inadvertent openings of safety/relief valves due to hot shorts - dominant contributors NB! Since the mechanisms leading to spurious actuation of equipment are not well understood, much uncertainties are associated with scenarios involving such failure modes

14 Results. Contribution to CDF

15 Conclusions Passive safety features incorporated in the design of Kudankulam NPP assure reliable fire resistance of the plant Results of the fire PSA give confidence that the design of the Kudankulam plant will comply with the probabilistic safety goals established for future plants Although the numerical results of the fire PSA at the PSAR design stage are associated with high uncertainties, the fire PSA including FHA can provide an extremely cost- effective approach to fire protection improvement

16 Thank you very much for your attention! Questions?!