Combined Use of Probabilistic and Deterministic Methods in External events PSA

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Combined Use of Probabilistic and Deterministic
Methods in External events PSA

• Vladimir Morozov, Head of Safety Analysis
  Division
• Gennady Tokmachev, Chief Engineer of Safety
  Analysis Division,
• Igor Kalinkin, Head of EE Department in Safety
  Analysis Division
• JSC Atomenergoproekt, Moscow, RF

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About

• JSC Atomenergoproekt is an engineering company,
  General Designer of nuclear power plants.
• The company developed the designs of the majority
  of NPPs in Russia, Eastern Europe and CIS
  countries. JSC Atomenergoproekt is the General
  Designer of the Bushehr NPP in Iran, Kudankulam
  NPP in India, Akkuyu NPP in Turkey.
  Atomenergoproekt is the General Designer and
  General Contractor of the Novovoronezh-2 NPP

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About

• PSA division (bureau) has over 25 year experience
  in developing PSA for units with WWER power
  reactors.
• Operation conditions include power operation and
  shutdown states.
• At present time the scope of development include
  internal level 1, level 2 and external events PSA.

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Internal events PSA aids design and operation

• Aid to justification of design basis
• Initiating events selection and categorization
• Provide input to categorisation of SSC
• Aid to optimisation of system configurations
• Helps to provide justification of conditions for
  safe operation (STI AOT)

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Requirements of regulatory documents

• It should strive to have PSA estimated value for
  severe BDBA frequencies less than 10-5 1/year
  (NP-001-97- General provisions to ensuring NPP
  safety) for the whole scope of events
• PSA for external events must be developed to
  obtain NPP accident risk assessment due to
  external events (NP-064-05 Analysis of effects
  of natural and man-induced external events on
  nuclear energy objects.)

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The scope of external events analysis

• Extreme natural events
• Seismic events
• High winds and tornadoes
• Extreme air and water temperatures
• External floodings, fires
• Extreme precipitation
• External man-induced events
• Air, road, water transportation incidents
• Industrial facility incidents

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General procedure for external events analysis

• Is defined by national safety guide RB-021-01
  Evaluation of reactor severe core damage due to
  external events (at present time under revision)
• It include
• Events selection and screening
• Hazard analysis
• Plant walkdowns
• Plant response and fragility analysis (if
  required)
• Bounding or detail analysis of accident sequences
  based on modified level 1 models, core damage
  estimation.

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Event selection and screening

• Development of preliminary generic list of
  external events
• Analysis of site characteristics, preliminary
  screening using RB-021-01 criteria A (distance
  event cannot occur close to the site) ,B
  (inclusion event is included in definition of
  another event which already have been analyzed)
  ,C (time event is slow developing and plant
  operating personnel have enough time to prevent
  its consequences)
• At preliminary stage only deterministic criteria
  are used

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Hazard analysis(seismic)

• Design base estimation is deterministic aimed to
  conservative assessment of maximum design
  earthquake (MRZ once per 10 000 years) and
  design earthquake (PZ once per 1000 years)
  according to NP-031-01 (Norms for design of
  seismic resistant NPP)
• Seismic hazard curves are developed according
  classical PSHA approach
• Along with seismic hazard response spectra is
  also estimated
• Global seismic hazard program results
  (http//www.seismo.ethz.ch/static/GSHAP/) and
  local seismological, tectonic and geological data
  are used to develop models for analysis

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Hazard analysis(seismic)

• Aleatory uncertainties include
• Attenuation law variabilities
• Seismic source characteristics (magnitude-length)
• Source location inside source zone
• Epistemic uncertainties (require development of
  logic tree)
• Source characteristic (active/not, linear or area
  source, maximum magnitude determination)
• Selection of attenuation law type
• Selection of parameters for source magnitude
  occurrence rate law
• Others

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Example of logic tree for seismic hazard
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Hazard curves after logic tree quantification
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Example of percentile and mean hazard curves
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Example hazard curve for maximum air temperatures
(Gumbel)
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Uncertainty in hazard curve for minimum air
temperatures (Weibull)
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Plant walkdown and seismic margin evaluation
(deterministic procedures)

• plant walkdowns in according to GIP-WWER
  procedures (Balakovo unit 1)
• Seismic margin evaluation using CDFM
  (conservative definition of failure margins)
  using EPRI NP-6041 SL1

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Conditional failure probability (fragility)

• For seismic PSA using hybrid approach
• IAEA TECDOC-1487 Annex 1
• Kennedy, R.P., Overview of Methods for Seismic
  PRA and Margin Assessments Including Recent
  Innovations, Proceedings of the OECD-NEA Workshop
  on Seismic Risk, Tokyo, Japan, August 1999
• Load strength model or FORM (first order
  reliability methods) for others

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Some results for EE PSA (Balakovo unit1
Novovoronezh-2 unit 1)
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• Thank you for attention !

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