S. S. Bajaj

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					                                        S. S. Bajaj
Present                   Chairman,
Affiliation &             Atomic Energy Regulatory Board
Organization              India
Area of Specialization/   Specialisation:
                          • Regulation of Nuclear Facilities
                          • Reactor safety analysis,
Awards                    • Probabilistic safety assessment,
                          • Containment engineering
                          • Professional experience of more than four decades
                          • Fellow of Indian National Academy of Engineering
                          • Indian Nuclear Society (INS) Award for Outstanding
                            Achievement in Nuclear Technology including
                            Nuclear Safety
                          • Life Time Achievement Award from the Society for
                            Reliability & Safety
Title of paper            Issues on Materials for Nuclear Applications:
                          Regulatory Perspectives for India
Authors                   S. S. Bajaj
Issues on Materials for Nuclear Applications:
  egu ato y e spect es o d a
Regulatory Perspectives for India
Second International Conference on Advances in Nuclear
Materials (ANM-2011)
M t i l (ANM 2011)
February 9-11, 2011, Mumbai
                                                                        S. S. Bajaj
                                                               Atomic Energy Regulatory Board

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Nuclear Power Programme in India
Current issues on materials
Future scenario
Way forward

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   Status of Nuclear Power Programme in India
   NPPs in operation

                                                           Year of commissioning
TAPS 1&2           2X160 MWe                        BWR            1969
 RAPS-1                100 MWe                     PHWR            1972
 RAPS-2                200 MWe                     PHWR            1980
MAPS-1&2           2X220 MWe                       PHWR        1983 & 1985
NAPS-1&2           2X220 MWe                       PHWR        1989 & 1991
KAPS-1&2           2X220 MWe                       PHWR         1992&1994
KGS-1&2            2X220 MWe                       PHWR         2000&1999
RAPS-3&4           2X220 MWe                       PHWR         2000&1999
RAPS-5&6           2X220 MWe                       PHWR            2010
TAPP-3&4           2X540 MWe                       PHWR         2006&2005
KGS 3&4            2X220 MWe                       PHWR         2007&2011

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Status of Nuclear Power Programme in India
NPPs Under Construction

      Kalpakkam                     500 MWe           FBR

      Kudankulam                  2X1000 MWe          VVER

     Kakrapar 3&4                  2X700 MWe          PHWR

    Rawatbhata 7&8                 2X700 MWe          PHWR

    Kudankulam 3&4                2X1000 MWe          VVER

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Nuclear Power Programme in India
Current status and key features

   PHWR-centric programme
   PHWR       ti
   Following the ‘Three Stage Nuclear Power Programme’
            g       y
   Consisting mostly of small size 220 MWe units
   Now embarking on medium sized 700 MWe units
   Indigenous efforts on design, safety, materials & manufacturing
   Robust R&D support and industry infrastructure

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Nuclear Power Programme in India
Current issues on materials

   Issues related to ageing and structural integrity
       Pressure Tubes
       PHT f d
       Flow assisted corrosion in high energy piping
       TAPS Reactor Pressure Vessels

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Issues related to ageing and structural integrity
Pressure Tubes

   Earlier     t    l d Zr-2           t b    ith
   E li reactors employed Z 2 pressure tubes with lloose fit GS
   Issues included
       Hydrogen pick up
       Shifting of GS, sag, hydride blister formation
       Reduction in fracture toughness
   Response involved
       Extensive inspections, GS repositioning
       Assessment of material properties and degradation
       Extensive reviews
       Replacement after 10 to 12 Full Power Years
       Presently phased out from all operating units
                     p        g           p
   The issue which kept the regulator occupied for maximum time in the nineties

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Issues related to ageing and structural integrity
Pressure Tubes

                i          l   l Zr 2.5%      P
   All PHWR units presently employ Z – 2 % Nb Pressure
   Tubes with tight fit GS
                                  Zr 2.5%Nb
       Oldest reactor employing Zr-2.5%Nb PTs, KAPS – 2 completed
       more than 12 FPY
       Present concern:        Creep
           Issues of Axial / Diametric creep
           Inspections, material surveillance, modeling
           Materials R & D support in place
           A subject of close regulatory monitoring
       Experience of dealing with the issues of Zircaloy-2 PTs will
       be useful.

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Issues related to ageing and structural integrity
Thinning of PHT Feeder Pipes

   Concern regarding thi i of elbows on outlet side feeders
   C              di thinning f lb           tl t id f d
   Higher rate of thinning than expected
   Flow Assisted Erosion - Corrosion
   Problem was more pronounced in RAPS-2, MAPS, NAPS
   Coverage and scope of In-service Inspection of feeders enhanced
       More number of feeders monitored
       Inspection of straighter portion also in addition to elbows
   En-masse replacement done for RAPS-2, MAPS-1, NAPS-1&2,
       SA – 333 Grade – 6 with higher chromium
       Elbows of higher schedule (160) for increased margins

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                   g g                      g y
Issues related to ageing and structural integrity
Flow Assisted Corrosion in high energy piping

  Issue was hi hli ht d after th iincidents of pipe f il
  I                                                          tJ
            highlighted ft the id t f i failures at Japanese NPP
  Mihama – 3 in August 2004 and KAPS – 2 in February 2006.
  Pipe rupture following material loss and thinning due to Flow Assisted
  Corrosion (FAC)
  Failure downstream of orifices
  Major campaigns for thickness monitoring of vulnerable piping & fittings
  mandated for Indian NPPs, post 2006
  Present action programme of NPCIL involves
       Periodic monitoring program of vulnerable locations
                                          fittings          FAC,               steel.
       Replacement of existing CS pipe / fittings, prone to FAC with low alloy steel
       Use of FAC resistant material, higher corrosion allowance at FAC prone locations
       and improvements in piping layout to minimize flow disturbances for future units

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Issues related to ageing and structural integrity
 TAPS Reactor Pressure Vessels

RPVs has been in operation for more than 40 years
    Irradiation embrittlement of RPV material
    Inability for inspection of welds at critical locations due to inaccessibility

Present Fluence ~23 EFPY against original Design Life of 40 EFPY
Fracture toughness assessment based on surveillance coupon tests confirms
RPV integrity till 40 EFPY
    C t ib ti f t
    Contributing factors:
         Larger Dia. of RPV (designed for 368 fuel assemblies)
         Operation at lower power (since 1986)

Action plan for addressing health of inaccessible welds
    Integrity checks during hydro / leakage tests
    Fatigue analysis
    Inspection of accessible welds & extrapolation of results to infer health of other welds

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Nuclear Power Programme in India
Current issues on materials

   Uncertainties iin materiall b h i iin post-accident (hi h
   U    t i ti         t i behavior         t    id t (high
   temperature) regime
                                        y                         pp
       Issue related to Zirconium alloys for fuel clad and core support
       Experience with PTs show that material properties / behavior is
       influenced by variabilities in the source and manufacturing routes
                    y                                             g
       Present modeling of post-accident material behavior based on
       published information
       Need to establish database on high temperature properties on
       material indigenously.

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Nuclear Power Programme in India
Current issues on materials

Issues of radiation protection
       Cobalt from hard facing material Stellite
            Adjuster rod drive mechanisms in PHWRs
            Valve seats
       Alternate materials
            SS 440 C for Adjuster rod drives
       Antimony 124 activity in primary heat transport of PHWRs
            Leaching of Antimony from carbon impregnated bearings in PCPs and
            subsequent activation
            Needed Antimony free carbon bearings
   Must have special emphasis on ensuring zero potential for
   activation problems during material selection for reactor application

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Nuclear Power Programme in India
Current issues on materials

      Issues of waste management and d
      I       f    t                     i i i
                               t d decommissioning
          Experience during the EMCCR campaigns in PHWRs reveals
          presence of Niobium-94 (41Nb94).
          41Nb has a long half life (20300 yrs, γ of 0.7 & 0.87 MeV)
          Issue limited to irradiated Garter Springs (limited quantity) in
          the EMCCRs so far.
          All the remaining PHWRs have PTs of Zr-2.5%Nb
          EMCCR in these reactors will involve generation of irradiated
          PTs, with 41Nb94.
          Will have waste management implications
          Waste Management solutions need to be evolved.

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Nuclear Power Programme in India
Future Scenario

   New it being l
   N sites b i planned    d
   Significant expansion of capacity on the cards
   New NPPs of advanced designs
   Fast Breeder Reactors
   Imported technology / plants
   Further development following the ‘three stage nuclear programme’

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Nuclear Power Programme in India
Future Scenario

   Plants f di
   Pl t of diverse d i            d         t i l
                      designs, vendors & materials
   The extent of diversity and magnitude will pose major challenges to
   the utility and the regulator
   Many of these reactors employ materials new to us
   There are significant differences in approaches followed
       Health assessment
   Decision making during the plant life cycle will pose challenges

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Way Forward

  Need to ensure availability of knowledge base on materials
     Ensuring vendor support with respect to material related
     information throughout plant lifetime, to facilitate decision making
     is important
     Bilateral and multilateral forums for information exchange and
     Future R & D strategies need to address issues of plants of
             t d designs
     iimported d i
      Initiatives to build knowledge base and experience to support
      decision making will be required within the regulatory body.
  Safety remains paramount consideration for the Regulator
  Conservative approach will be seen as prudent.

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          Thank you!

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PHWR Schematic
                                1    Fuel bundle     8  Fueling machines
                                2    Caladria        9 Heavy water
                                3    Adjuster rods   10 Pressure tube
                                4    Pressurizer     11 Steam going to

                                     Steam              Cold water returning
                                                     12 from turbine

                                     Light Water     13 Containment Building

                                     Heavy water

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Typical PHWR Reactor assembly

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Pressure T b in PHWR
P        Tubes i PHWRs

                                              B k

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PHT feeders

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PHT feeders


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      Pipe Failures due to FAC
                                                                       p    p
                                                    Condensate Water Pipe Rupture in
                                                    Mihama Unit - 3

Feed water pipe rupture in KAPS
unit - 2

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Reactor Pressure Vessels at TAPS

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