The role of I

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The role of IC systems in power uprating
projects
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Why to uprate?

• Market changes induce the claim to operate the
  plants in an ever increasing efficiency.
• Efficiency can be increased either by a better
  utilization of existing capacities or by
  increasing the capacities.
• The utilities are aiming for additional
  production through the better utilization of
  available assets.
• Gaining public acceptance to increasing existing
  nuclear power plant capacity is significantly
  easier than that to constructing a new NPP.

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Conditions enabling power uprating

• The average age of the nuclear units operating
  for the time being is above 20 years.
• The units were designed in the mid-seventies.
• Today, there is a more accurate knowledge on the
  behavior of structural materials and integrated
  effects of external and internal factors exerted
  on the components.
• Today demands affecting components during
  transients can be defined more exactly,
  uncertainties of calculations can be reduced,
  and, as a result, the conservatism applied in the
  original design can be reduced.
• Today more accurate and reliable control and
  assessment methods are available (accuracy of
  measurements, reduction of detection thresholds,
  etc)
• Knowledge related to nuclear fuel and core
  thermal hydraulics also had a considerable
  development. Fuel utilization arose to one and a
  half times of that in the eighties.

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Definition of power uprate

• The process of increasing the maximum licensed
  power level at which a commercial nuclear power
  plant may operate is called a power uprate.
  (Definition from the U.S. NRC)
• Types of power uprates
• measurement uncertainty recapture power uprates
• stretch power uprates
• extended power uprates

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Basic ways of power uprating

• Reducing uncertainty
• Improving efficiency
• Increasing thermal power

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Measurement uncertainty recapture uprates

• The reactor thermal power is validated by the
  nuclear steam supply system energy balance
  calculation.
• The reliability of this calculation depends
  primarily on the accuracy of feedwater flow,
  temperature, and pressure measurements.
• Because the measuring instruments have
  measurement uncertainties, margins are included
  to ensure the reactor core thermal power does not
  exceed safe operating levels.
• 10 CFR, Part 50, Appendix K (1973), required
  licensees to assume a 2.0 percent measurement
  uncertainty for the reactor thermal power.
• The current rule (2000) allows licensees to
  justify a smaller margin for power measurement
  uncertainty when more accurate instrumentation is
  used to calculate the reactor thermal power.

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Measurement uncertainty recapture uprates 2.

• Measurement uncertainty recapture (MUR) power
  uprates are achieved by implementing enhanced
  techniques, such as the improved performance of
  plant equipment both on the primary and secondary
  side, protection and monitoring system, operator
  performance, etc. These uprates are less than 2
  measured in electrical output power.
• The use of state-of-the-art feedwater flow
  measurement devices that reduce the degree of
  uncertainty associated with feedwater flow
  measurement can be an example.

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Measurement uncertainty recapture example
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Stretch power uprates

• Uprates are typically up to 7-percent and are
  within the design capacity of the plant. The
  actual value for percentage increase in power a
  plant can achieve and stay within the stretch
  power uprate category is plant-specific and
  depends on the operating margins included in the
  design of a particular plant.
• Stretch power uprates usually involve changes to
  instrumentation setpoints, but do not involve
  major plant modifications. This is especially
  true for boiling-water reactor (BWR) plants.
• In some limited cases where plant equipment was
  operated near capacity prior to the power uprate,
  more substantial changes may be required.

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Extended power uprates

• Extended power uprates are greater than stretch
  power uprates and are usually limited by critical
  reactor components such as the reactor vessel,
  pressurizer, primary heat transport systems,
  piping etc., or secondary components such as the
  turbine or main generator. To cope with these
  limitations, extended uprates usually require
  significant modifications to major
  balance-of-plant equipment such as the
  high-pressure turbines, condensate pumps and
  motors, main generators, and/or transformers.
  Extended power uprates have been approved for
  increases as high as 20 percent.

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Power uprates and IC

• Necessary modifications in the instrumentation
  and control systems in relation to power
  upratings are usually not very substantial. The
  following preconditions must be fulfilled in the
  frame of IC
• sufficient measurement ranges
• sufficient accuracy of process parameter
  measurements
• sufficient calculation algorithms to indicate
  credible reactor thermal power
• sufficient possibilities for the adaptation of
  new limit values in the Reactor Protection
  System, limitation systems and control systems

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Typical examples of IC changes

• Modification of specific control systems to
  enable operation under different conditions.
• Inclusion of additional process sensors
• Replacement of sensors by ones with improved
  accuracy
• Optimised calculation of the measurement
  uncertainties permitting a reduction in the
  margin applied to the measurement of reactor
  thermal power.
• Modification of the reactor protection system
  setpoints
• Changes in the appropriate HSIs to accurately
  assess the current state of the plant
• Changes in alarm setpoints
• Changes in the instrument calibration procedures
• Adjustment of the plant computer and safety
  parameter display system
• Development of additional instrument validation
  processes

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Power Uprating inthe Paks NPP
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Early activities (uprate from 440 to 465 MW)

• High Pressure Turbine
• Blades of all stages of the High Pressure Rotor
  the 1st stage excepted were exchanged.
• From the diaphragms in the HP housing, stages No.
  5 and 6 were exchanged. As for the diaphragms of
  stages No. 2, 3 and 4, only the projections above
  the bandage were replaced.
• Final (end) - and diaphragm sealing were
  exchanged from flat springs to spiral ones.
• Low Pressure Turbine 
• Blades of rotor stages No. 1, 2, 3 and 4 were
  exchanged.
• From diaphragms of LP housing, those of stages
  No. 1, 2, 3 and 4 were exchanged.
• Having the steam separator exchanged, steam
  intake of the LP housing was modernized.
• Final (end) - and diaphragm sealing were
  exchanged from flat springs to spiral ones.
• Took place from 1997 to 2001

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The replacement of the turbine rotor
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Modifications for the new, 8 power uprating

• New fuel
• Primary circuit
• Core monitoring (VERONA)
• Secondary circuit
• Electrical systems
• IC systems
• No feedwater flow measurement problems

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The specific modifications
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The specific modifications (contd)
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The new encased bus bar for Units 1 and 2
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The new encased bus bar for Units 1 and 2
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Implementation of power uprating in Paks

• The first modified fuel was loaded in 2005 in
  Unit 4 (one third of the core). In 2006, when the
  Unit 4 reactor contained two loads of the
  modified fuel, the 108 power could be attained.
• The stepwise increase of power, however, required
  a test run at about 104 for several months
  thus, the further increase up to 108 took about
  four months from the unit restart, and was
  reached on 28 September, 2006.
• As for Units 1-3, operation of the fuel
  assemblies that are suspected to contain deposits
  will be terminated probably in 2006 in Unit 1,
  and in 2008 in Unit 2. Power uprating in a core
  loaded with fuel assemblies with deposits is not
  considered.

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Main parameter changes after power uprating
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Primary circuit pressure control improvement
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Physical parameters limiting thermal power

• Maximum allowable temperature at the core
  sub-channel outlets 325 oC
• Corresponding primary circuit pressure 120,57
  bar

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The saturation temperature and pressure
bar
0C
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The saturation temperature and pressure
bar
Real operating temperature
0C
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Characteristic of the old pressure controller
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Primary circuit pressure at a regular weekend
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Physical parameters limiting thermal power

• As a result of power increase, the core outlet
  temperature increases, nearly proportionally with
  the power increase, thus it gets nearer to the
  saturation temperature.
• The primary circuit pressure control system must
  ensure a finer maintenance of the primary circuit
  pressure, the margin of saturation shall be kept
  at the required level.
• The operating pressure must be maintained at a
  stable 123.0 bar with an accuracy of /- 0.25 bar.

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The saturation temperature and pressure
bar
Real operating temperature
0C
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The saturation temperature and pressure
bar
Real operating temperature
0C
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Static characteristic of the new controller
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The structure of the new system
Pressurizer vessel
FieldPLC-1 (WAGO 750)
Injection valves-1
Pressure transmitter (Rosemount 3051)
FieldPLC-2 (WAGO 750)
Injection valves-2
FieldPLC-3 (WAGO 750)
Solid state switch
Electricalheaters
Network switch (Hirschman)
Process computer-1
Process computer-2
Supervisor Notebook
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The main controller
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Electrical heater solid state controller
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The injection valve controller
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IAEA TECDOC onThe Role of IC Systemsin Power
Uprating Projectsin NPPs
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IAEA TECDOC
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TECDOC contents

• Introduction to power uprating
• Limits, margins and their relevance to IC
• Calculation of thermal power
• Impact of power uprating on plant IC
• Human and training aspects
• Regulatory aspects
• IC implementation guidelines for power uprating
• IC benefits and lessons learned from power
  uprating
• Key recommendations
• References
• Glossary
• Country reports

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Key recommendations

• It is important to fully understand the safety
  and technical bases for the claimed margins and
  limits.
• It is important to fully evaluate the areas of
  potential measurement uncertainty.
• Power uprates could potentially lead to various
  unwanted effects. It may be necessary to add new
  instrumentation to ensure that the operating
  conditions at the higher power level are
  adequately monitored and controlled.
• A power uprating could provide the opportunity
  for a wider modernisation of the plant IC
  systems.
• A comprehensive analysis should be undertaken
  covering all aspects of plant behaviour in all
  operational modes to provide input for the
  modified IC design.
• It is important to consider the changed (possibly
  more severe) operating conditions for IC
  equipment, qualification, etc.

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Key recommendations (contd)

• Particular attention should be paid to the design
  of the HSI modifications (if any), and of
  integration of this with the existing HSI, to
  ensure that operating staff performance is
  enhanced rather than degraded.
• In terms of the licensing application for a power
  uprate project, it should be noted that the
  Regulatory Authority will require the licensing
  submission to positively demonstrate that the
  existing safety level has been maintained or
  preferably increased, including all the IC
  aspects and consequences of it.
• Experience feedback from past power uprate
  projects has shown that some plants have incurred
  serious problems with their implementation (e.g.
  inadvertent violation of licensed power limits),
  due to instrumentation issues. Lessons learned
  from other PU projects should be considered.

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Thank you for your attention!

• Any questions?

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