Assessment of the safety upgrading for Unit 2 of Armenian NPP I

1
Assessment of the safety upgrading for Unit 2 of
Armenian NPP IC related issues

• Tsolak Malakyan, Nuclear Radiation Safety
  Centre (NRSC)
• Gagik Matnishyan, Armenian Nuclear Regulatory
  Authority (ANRA)

Regional Workshop on Modernization Projects of
NPP Instrumentation and Control Systems Related
to Power Uprates and Licence Renewals Project
(RER/4/027)Portoroz, Slovenia14-18 April 2008
2
Introduction

• Performed modernizations for IC improvement for
  ANPP were based on recommendations coming from
  IAEA-TECDOC-640
• NRSC with GRS sponsorship in 2006 provided
  assessment of the safety upgrading of Unit 2 of
  Armenian NPP. General objective of the project is
  complex assessment of performed/planned
  safety-related modernisations for Armenian NPP
  Unit 2. To reach declared project goal following
  two stages/tasks were implemented
• Task A Adaptation and completion of safety
  issues list presented in IAEA TECDOC 640 (Ranking
  of safety issues for WWER-440 model 230 NPP) was
  performed.
• Task B Detailed analysis was performed for
  safety issues selected by GRS experts generally
  based on rank of particular issue presented in
  IAEA TECDOC-640 (mostly analysis was performed
  for III and IV category issues).

3
Task A Adaptation and completion of safety
issues list related of IC

• 16 safety related issues for IC were assessed
• 12 safety related issues from IAEA TECDOC-649
• 3 additional safety related issues proposed by
  GRS/Riskaudit experts

• And 1 additional safety related issue selected
  from IAEA TECDOC 1044 (IAEA Generic safety
  issues )

4
Task A Adaptation and completion of safety
issues list related of IC

• Conclusion of this stage are that all considering
  issues escape of 1 are relevant for ANPP initial
  design

5
Task B Detailed analysis safety issues list
related of IC

• The goals of task B2 is development of technical
  report with assessment of technical solutions
  completeness for elimination of safety
  deficiencies.
• Here only information related safety issues of
  categories IV and III are presented
• Reliability of IC Equipment (III)
• IC Redundancy, Separation and Independence (IV)
• IC / Electrical Equipment Qualification (III)
• Control Room Habitability/Shutdown Panel (III)

6
Task B Detailed analysis safety issues list
related of IC

• Reliability of IC Equipment (III)
• Issue description IC equipment still used is
  very old fashioned (e.g. electrochemical
  switches, relays) and its reliability is
  questionable. The causes include deterioration
  with age, difficulty of maintenance and testing
  and the need for frequent attention.
• Modernisation
• The replacement of non-seismic relays in
  emergency protections and interlocks circuits was
  performed with seismic relays at ANPP.
• The non-seismic sensors and secondary instruments
  operated in protection and interlock circuits
  were replaced with seismic ones.
• New digital instruments were installed at MCR of
  Unit 2
• network frequency, current frequency on 28NA,
  29NA buses
• Unit total electrical output
• measuring sets of TG-3,4 revolutions
• electrical capacity of TG-3,4.
• The instrumentation stock of ANPP main and
  auxiliary systems was significantly renewed
• Additional P measuring instruments were
  installed in SG-RCP compartment and in this
  connection new interlocks on confinement
  ventilation systems were implemented.
• The number of H measuring channels in 2SG-1?6
  was significantly increased.
• Additional ?P measuring sets (two sets for
  every RCP) were installed on 2RCP-1?6 and in this
  connection the EP-III actuation logic was
  modified by 2 out of 3 logic.

7
Task B Detailed analysis safety issues list
related of IC

• Reliability of IC Equipment (III)
• Modernisation
• Additional ?P between SG and MSH and P
  instrument sets were installed in MSH (to provide
  channelling principle).
• The differential transformer sensors and
  transmitters were replaced with 0?5mA standard
  output sensors.
• All IC sensors and instruments were replaced on
  DG-3, 4, 5, 6.
• All protection removal keys were eliminated from
  reactor protection generation circuits.
• Safety parameters display system were
  implemented at Unit 2 with their individual
  sensors qualified for operation in environmental
  and seismic conditions.
• Physical and galvanic isolation of measuring
  channels was performed though there are still
  common circuits left.The whole instrumentation
  stock is subjected to departmental and laboratory
  tests in compliance with annual test schedule.
• Modernization of SG level regulators (performed
  during 2006 outage)

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Task B Detailed analysis safety issues list
related of IC

• Reliability of IC Equipment (III)
• Modernisation
• Replacement of source range neutron flux
  monitoring instrumentation (performed during 2006
  outage)
• There were installed four sets for level
  controlling and four sets of four-meter level
  controllers on each SG.
• Upon the installation of these instruments the
  interlock and protection set-points were isolated
  though there are still some common circuits.
• Modernization of old automatic reactor power
  regulation (ARM) system
• Effectiveness of modernization
• It is necessary to identify those IC which have
  significant influence on NPP safety and perform
  measures to increase their reliability. This
  analysis could be done using PSA model developed
  for ANPP.

9
Task B Detailed analysis safety issues list
related of IC

• IC Redundancy, Separation and Independence (IV)
• Issue description There are numerous instances
  where redundancy, physical and electrical
  separation and independence of safety related
  instrumentation channels are not adequately
  provided
• Modernisation
• The type of activation logic is that all the
  channels of emergency protection system are
  designed with logic 2 out of 3 (or 2 out of 6 for
  the steam generator protection for all 6 loops).
• They mainly use de energize-to actuate technique.
  Only one channel (delta pressure on reactor
  coolant pump) use energize-to actuate technique.
• All protections and interlocks of reactor are
  powered from six buses of 220V DC (3 bushings
  from 2BAB-1 and 3 bushings from BAB-2), the loss
  of even 4 corresponding bus wont effect the
  safety system operation.
• The Unit 2 MCR, the process alarm circuits are
  powered from two I category reliability buses
  (according to Automatic Stand-by Start-up
  circuit) of 28NA and 29NA AC buses.
• Modernization is foreseen in 2008 aimed to
  separation (physically and electrically) of
  emergency protection systems channels as
  possible (during implementation of modernization
  ANPP will fully follow and respect the
  international design rules (diversity,
  redundancy, physical separation etc.))
• Effectiveness of modernization
• Foreseen modernizations will increase
  independence of the existing safety related
  instrumentation, however modernization needs to
  include measurements which will assure total
  independency between A and B channels of
  emergency protection system. Otherwise planned
  modernization only partially will cover this
  issue.

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Task B Detailed analysis safety issues list
related of IC

• IC / Electrical Equipment Qualification (III)
• Issue description At the time the design was
  made, the environmental and seismic qualification
  of instrumentation and electrical equipment was
  not addressed, and there was no backfitting
  program developed in that field up to now.
• Modernisation
• Measures are foreseen aimed to safety-related
  equipment qualification. It is planned to perform
  this work in 2008 based on current international
  qualification standards
• The Engineered Seismic Protection System is
  replaced with a new Engineered Seismic Protection
  System-2, interlocking logic is simplified for
  the functioning of ESPS.
• Cable lines, supply systems, protections,
  interlocks and other consumers of safety systems
  and safety related systems are reconstructed in
  the form of two divergent category I and II power
  supply systems.
• Seismic non-qualified relay, detectors and gauges
  are replaced with seismic-resistant ones.
• ANPP put into operation new diagnostic systems
• acoustic primary leak detection system (ALUS)
• primary loose object detection system (KUS).

11
Task B Detailed analysis safety issues list
related of IC

• IC / Electrical Equipment Qualification (III)
• Modernisation
• Feasibility study has been done for replacement
  of an old ??-500?? information computing system
  with an advanced complete set that meets the
  current seismic requirements.
• Cables and communication instrumentation of the
  unit were analysed in the view of their
  resistance to short circuits, recommendations
  were developed on improvement of reliability and
  thermal resistance of cables and instrumentation
• automatic fire alarm for switchboard rooms,
  intake air-ducts of MCR, ECB implemented on the
  basis of seismic qualified components was
  documented
• documentation was developed and ANPP
  reconstructed the snubber displacement control
  system
• rooms containing IC and safety related electric
  equipment are seismic qualified against current
  requirements
• up to 1976 both IC, electric equipment and
  switchboards were tested against seismic
  resistance.

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Task B Detailed analysis safety issues list
related of IC

• IC / Electrical Equipment Qualification (III)
• Modernisation
• The tests were performed on vibration stand in
  the frequency range of 0?30Hz and peak ground
  acceleration (0.4g and 1.08g). In 1976-1977 the
  second phase of tests was performed on vibration
  stand for seismic resistance of IC, electric
  equipment and switchboard devices with due
  consideration of their reinforcement and
  anchoring which demonstrated their seismic
  resistance.
• seismic tests resulted in replacement of CK-40
  type batteries with seismic resistant VARTA
  type, mounted on seismic resistant stacks.
• In 1998 motors on all Main Stop Valves were
  replaced with impermeable motors.
• Effectiveness of modernization
• A performed modernization allows qualifying
  seismically IC/Electrical equipment at ANPP.
  However other environmental hazards were not
  considered.

13
Task B Detailed analysis safety issues list
related of IC

• Control Room Habitability/Shutdown Panel
• Issue description There is insufficient
  provision to maintain control room habitability.
  In case of main control room inhabitability or
  unavailability, there is no other centralized
  location from where a safe shutdown can be
  performed .
• Modernisation
• In case of shut down and MCR unavailable, it is
  possible for the operators to monitor the plant
  with following parameters Level in SG-1-6,
  Primary pressure, Level in Prz, Temperature in
  cold and hot legs, Temperature difference between
  hot and cold legs, Temperature in Prz. Neutron
  flux could be monitored from reactor building
  central hall (Shelter room - reserve emergency
  cooldown panels IC is qualified as
  safety-related equipment), from the shelter room,
  which is located in the reactor building. These
  parameters are displayed in MCR during normal
  operation (same sensors used for MCR and reserve
  emergency cooldown panel)
• Implementation of adequate air filtering,
  supplied to MCR is foreseen in 2009 as well as
  flying objects protection installation
• Implementation of reserve control panel is
  foreseen in 2009

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Task B Detailed analysis safety issues list
related of IC

• Control Room Habitability/Shutdown Panel
• Modernisation
• By design following measures were implemented to
  address this issue
• Separation of scram buttons - MCR, SUZ-2 panel
  and Central control panel.
• Measures are taken for rooms and buildings
  seismic stability increase.
• Replacement of single-wing doors in cable tunnels
  and in turbine hall on the door with 90 min.
  fire-resistance is performed.
• Gas masks, air bottles, and communication are
  existing at MCR.
• Emergency personnel protection procedures are
  developed related
• Effectiveness of modernization
• The original design of MCR at ANPP provides
  sufficient base to maintain control room
  habitability in case of main control room
  inhabitability or unavailability.
  Implementation of reserve control panel will
  allows performing safe shutdown in case of
  unavailability of MCR.

15
Conclusion

• Performed modernizations for IC improvement for
  ANPP were based on recommendations coming from
  IAEA-TECDOC-640
• Most of recommendations for III and IV category
  issues were addressed
• Implementation of the rest recommendations is
  included in modernization program for 2006-2016
• Further modernizations on IC will be developed
  based on safety assessments (SAR and PSA results)