Communicating Bad News

Chapter-7

visual examination for leakageKhurram Shahzad AhmadPrincipal EngineerNCNDT-SES Dte.1Periodic System Pressure TestSystem pressure tests Class-1, 2 and 3 components shall be conducted in accordance with the Examination Categories identified as following:

2system pressure testingClassExamination CategoryExamination area1B-P Pressure Retaining Components2C-HAll Pressure Retaining Components3D-BAll Pressure Retaining ComponentsPeriodic System Pressure TestPiping that penetrates a containment vessel is exempt from the periodic system pressure test when the piping and isolation valves perform a containment function and the balance of the piping system is outside the scope of this Division.

3system pressure testingSystem Test RequirementPressure retaining components within each system boundary shall be subject to the following applicable system pressure tests under which conditions a VT-2 visual examination is performed to detect leakage: System Leakage TestA system leakage test conducted while the system is in operation, during a system operability test, or while the system is at test conditions using an external pressurization source.

4system pressure testingSystem Test RequirementSystem Hydrostatic TestA system hydrostatic test conducted during a plant shutdown at an elevated test pressure. System Pneumatic TestA system pneumatic test conducted in lieu of either of the above system pressure tests for Class 2 or Class 3 components.

5system pressure testingSystem Test RequirementBuried ComponentsFor buried components surrounded by an annulus, the VT-2 visual examination shall consist of an examination for evidence of leakage at each end of the annulus and at low point drains.For buried components where a VT-2 visual examination cannot be performed, the following requirements shall be met:For buried components that are isolable by means of valves that are required to be essentially leak tight, the examination requirement shall be satisfied by performing a test that determines the rate of pressure loss or a test that determines the change in flow between the ends of the buried components. The acceptance rate of pressure loss or flow shall be established by the Owner.6system pressure testingSystem Test RequirementBuried ComponentsFor buried components that are not isolable by means of valves that are required to be essentially leak tight, the examination requirement shall be satisfied by performing a test to confirm that flow during operation is not impaired.Test personnel need not be qualified for VT-2

7system pressure testingThe holding time after pressurization to test conditions, before the visual examinations commence, shall be as follows:For the system leakage tests the following shall be met.For Class 1 components (Examination Category B-P), no holding time is required after attaining test pressure.For Class 2 (Examination Category C-H) and Class 3 (Examination Category D-B) components not required to operate during normal plant operation, a 10 min holding time is required after attaining test pressure.For Class 2 (Examination Category C-H) and Class 3 (Examination Category DB) components required to operate during normal plant operation, no holding time is required, provided the system has been in operation for at least 4 hr for insulated components or 10 min for noninsulated components.8Test Condition Holding TimeFor system pressure tests, a 10 min holding time for noninsulated components, or 4 hr for insulated components, is required after attaining test pressure. For system pneumatic tests, a 10 min holding time is required after attaining test pressure.

9Test Condition Holding TimeInsulated and Non insulated ComponentsThe VT-2 visual examination shall be conducted by examining the accessible external exposed surfaces of pressure retaining components for evidence of leakage.For components whose external surfaces are inaccessible for direct VT-2 visual examination, only the examination of the surrounding area (including floor areas or equipment surfaces located underneath the components) for evidence of leakage shall be required.Components within rooms, vaults, etc., where access cannot be obtained, may be examined using remote visual equipment or installed leakage detection systems. 10VISUAL EXAMINATIONInsulated and Non insulated ComponentsEssentially vertical surfaces need only be examined at the lowest elevation where leakage may be detected. Discoloration or residue on surfaces shall be examined for evidence of boric acid accumulations from borated reactor coolant leakage.

11VISUAL EXAMINATIONInsulated and Non insulated ComponentsFor insulated components in systems borated for the purpose of controlling reactivity, insulation shall be removed from pressure retaining bolted connections for VT-2 visual examination. Insulation removal and VT-2 visual examination of insulated bolted connections may be deferred until the system is depressurized. When corrosion resistant bolting material with a chromium content of at least 10%, such as SA-564 Grade 630 H1100, SA-453 Grade 660, SB-637 Type 718, or SB-637 Type 750, is used, it is permissible to perform the VT-2 visual examination without insulation removal.

12VISUAL EXAMINATIONInsulated and Non insulated ComponentsEssentially horizontal surfaces of insulation shall be examined at each insulation joint if accessible for direct VT-2 examination.When examining insulated components, the examination of the surrounding area (including floor areas or equipment surfaces located underneath the components) for evidence of leakage, or other areas to which such leakage may be channeled, shall be required.

13VISUAL EXAMINATIONA PWR is a nuclear power reactor, which uses light water as the coolant and moderator. The high temperature and high pressure coolant (i.e., primary system: reactor coolant system) from the core (RPV) is sent to the steam generators (S.Gs) of this primary system, to generate steam of the secondary feedwater coolant. Then, the steam is ultimately sent to a turbine generator system to generate electricity. In the state of high temperature and high pressure, there is no boiling of the coolant in the reactor core.14Plant system and componentsContainment BuildingThe entire reactor coolant system is located in containment building, which isolates the radioactive reactor coolant system from the environment in the event of a leak. The containment building is designed to contain the pressure produced by the complete blow down of the reactor coolant system inside the containment building as a result of a system piping rupture. The containment also contains accumulators for injecting the borated water into the RCS during accidents.

15Plant system and componentsControl BuildingThe control building contains the central control room with its console and control panels, as well as the relay room with its relays and controllers. The control building houses the main control room, the cable spreading room, auxiliary instrument room, and computer.

16Plant system and componentsAuxiliary BuildingSafety related and potentially radioactive auxiliary system are located in auxiliary building which is located between the control building and the containment. It houses the residual heat removal system, the safety injection system, the component cooling system etc. A fuel storage area (part of the auxiliary building) is provided for handling and storage of new and spent fuel.

17Plant system and componentsTurbine BuildingThe turbine building contains all the power conversion system. The main turbines and turbine auxiliaries, moisture separator / reheaters, feedwater heaters, main condenser, condensate booster and feedwater pumps, etc., are all located in the turbine building.

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Basic Configuration of PWRsThe PWR consists of a primary system (reactor system) and a secondary system (steam system) in order to keep radioactive materials in the primary system. The reactor coolant in a reactor vessel of the primary system is pressurized so that it circulates with reactor coolant pumps without boiling, and the high temperature and high pressure reactor coolant moves from a reactor core to steam generators (primary side) for effective heat transfer. Within the steam generators, heat exchange occurs at heat transfer tubes transporting the heat from the primary side to the secondary side, and steam is generated. 20Plant system and componentsBasic Configuration of PWRsThis steam is sent to a turbine to drive a generator, condensed in condensers to water, and sent back to the steam generators (secondary side) with main feedwater pumps (feedwater).PWR Major systemsPrimary Cooling System,Chemical and Volume Control System,Emergency Core Cooling System,Containment Spray System,Residual Heat Removal System,Turbine generator System, etc.21Plant system and componentsPrimary Cooling System (RCS)The PWR cooling system is provided, for the following functions:To circulate the reactor coolant heated within the reactor core, to transfer heat to S.G., and to generate high temperature and high pressure steam, which is ultimately discharged to drive a turbine,To provide adequate core cooling, in order not to cause any core damage during reactor operation,To be a coolant pressure boundary that is a barrier to prevent leakage of radioactive materials contained in the reactor coolant to the outside,22Plant system and componentsPrimary Cooling System (RCS)To be moderator and reflector, and to contain the reactor coolant that has a role of solvent of the boron neutron absorber, and To control the primary system pressure constant with a pressurizer.Major Equipments of Primary Cooling System are:Reactor Coolant Pumps (RCPs)Steam Generators (SGs)PressurizerPiping23Plant system and componentsChemical and Volume Control System (CVCS)The CVCS extracts some part of the primary coolant from one primary coolant cold leg and returns it to another primary coolant cold leg, after passing it through a makeup line, and consists of components, piping and valves. Functions: (supporting to RCS)Makeup of the primary coolant (if any), in order to maintain the required coolant inventory in RCS, by maintaining the required water level in the pressurizer. Removal of fission and corrosion products, from coolant, Adjustment of the boric acid concentration in coolant, and Supply of the water to the shaft seal area of the RCPs, etc.24Plant system and componentsEmergency Core Cooling System (ECCS)In case of the primary coolant loss from the reactor core, due to pipe break accident of a reactor cooling system (i.e., LOCA), this system is provided to prevent the fuel failure.Containment Spray System (SCS)After LOCA accident, the temperature and pressure in the reactor containment rise due to fuel decay heat. A radioactive iodine removal chemical is added in the borated water of Refueling Water Storage Tank. 25Plant system and componentsContainment Spray System (SCS)The SCS sprays borated water through spray nozzles installed in the upper part of the containment for inside cooling of the containment in order to:Cool down and condensate the steam in the containment.Reduce its internal pressure.Absorb iodine and reduce its concentration with the spray water droplet.To provide long time continuous spray, the recirculation line from the reactor containment sump is provided.26Plant system and componentsContainment Spray System (SCS)The main functions of SCS are:To reduce the temperature and pressureTo remove radioactive materials, such as iodine, in the air.To prevent release of radioactive materials to the outside of the reactor containment.27Plant system and componentsResidual Heat Removal System (RHRS)The main functions of RHRS are:To remove the residual decay heat from the reactor core,To cool down the nuclear reactor during plant shut down and refueling, andTo provide low pressure coolant injection in case of LOCA.Turbine Generator SystemThe PWR plant is separated completely into the primary system and the secondary system. Since the steam generated in a S.G. does not contain radioactivity, the turbine generator system is almost the same to that of the conventional thermal power plant. The steam generated within the S.G. is ultimately sent to a turbine generator system to generate electricity.28Plant system and componentsThank You for Your Attention29