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Ultrasonic rail inspection system
ENew equipment Graphite
brick tests
Under a contract from Nuclear Electric plc, supported by Scottish Nuclear, graphite moderator bricks and slices of bricks, typical of those which are interlocked in layers to construct the cores of Advanced Gas-cooled Reactor (AGR ) power stations, are being subjected to an extensive series of tests to provide more comprehensive information on the strength of the bricks. The results of these tests will be used in conjunction with sophisticated finite element analysis calculations to increase accuracy in formulating the safety case for core integrity. The tests are being carried out at the Risley Laboratory of AEA Reactor Services and will examine the effects of stresses within bricks caused by external loads and a sequence of stresses arising from the complex shrinkage behaviour of the graphite over the operating lifetime of the reactor. Radiation dose rates across the cores are not uniform, and this causes differential shrinkage and distortion of the graphite components. As a consequence the bricks start by shrinking more on the inside adjacent to the fuel than on the outside. Later this is reversed as the graphite on the inside characteristically stops shrinking and begins to expand. Towards the end of the reactor lifetime this process leads to a build-up of internal stress at the roots of the keyways by which the bricks are interlocked. These keyway roots are the most stressed parts of the graphite core bricks. The core design mainly compensates for the graphite dimensional changes and the necessary movements due to temperature changes during operation by having the individual bricks loosely keyed together in an arrangement which permits expansion and contraction of the whole core without affecting its stability or integrity.
110
Graphite
moderator
bricks being measured
as part of an assessment
Large-scale tests using full-scale core bricks and brick slices of thicknesses up to 250 mm will push and pull the specimens in order to determine the ability of bricks to withstand external loads. In other tests graphite slices are being subjected to bending forces designed to mimic the stresses imposed on the keyways during the lifetime of the reactor, to test the resilience of the bricks to this type of stressing. As it is not practicable to replace damaged graphite, AGR station operation depends on maintaining satisfactory integrity of the bricks and their keyways. An extension to the graphite core lifetime would have enormous implications for the economics of nuclear power generation since the stations have high capital costs but low marginal fuel costs. AEA Technology, Ride y, Warrington, Cheshire WA3 6A T, UK
Ultrasonic inspection
rail system
RMK’s Zenica rail fabrication plant in Yugoslavia is the first purchaser of the Micro Plus ultrasonic inspection system from Sonomatic. The plant
of the effects
of stresses
manufactures rail for Yugoslav railways, and is gearing up to export to other European countries. To do this, the plant will have to demonstrate its quality control procedures and the consequent quality of its product. The Micro Plus system will provide continuous, full-volumetric inspection for internal flaws, and will eventually be able to handle five different rail profiles, using the non-contact immersion technique which has proved successful for the inspection of round and square steel billet and bar. The system was developed from Sonomatic’s Midas ultrasonic inspection and data acquisition system, and is based around a 386 computer. The Micro Plus is a multi-channel inspection system with an array of ultrasonic transducers which examine the rail as it passes through a water-injected stuffing box at line speeds up to 1.5 m s-‘. The water acts as an ultrasonic couplant, and consequently the inspection heads do not touch the surface of the rail. This means that there is no wear and the system is very reliable. The 32-channel will be installed
system which at Zenica will
N DT & E International
April 1991
brick tests
Under a contract from Nuclear Electric plc, supported by Scottish Nuclear, graphite moderator bricks and slices of bricks, typical of those which are interlocked in layers to construct the cores of Advanced Gas-cooled Reactor (AGR ) power stations, are being subjected to an extensive series of tests to provide more comprehensive information on the strength of the bricks. The results of these tests will be used in conjunction with sophisticated finite element analysis calculations to increase accuracy in formulating the safety case for core integrity. The tests are being carried out at the Risley Laboratory of AEA Reactor Services and will examine the effects of stresses within bricks caused by external loads and a sequence of stresses arising from the complex shrinkage behaviour of the graphite over the operating lifetime of the reactor. Radiation dose rates across the cores are not uniform, and this causes differential shrinkage and distortion of the graphite components. As a consequence the bricks start by shrinking more on the inside adjacent to the fuel than on the outside. Later this is reversed as the graphite on the inside characteristically stops shrinking and begins to expand. Towards the end of the reactor lifetime this process leads to a build-up of internal stress at the roots of the keyways by which the bricks are interlocked. These keyway roots are the most stressed parts of the graphite core bricks. The core design mainly compensates for the graphite dimensional changes and the necessary movements due to temperature changes during operation by having the individual bricks loosely keyed together in an arrangement which permits expansion and contraction of the whole core without affecting its stability or integrity.
110
Graphite
moderator
bricks being measured
as part of an assessment
Large-scale tests using full-scale core bricks and brick slices of thicknesses up to 250 mm will push and pull the specimens in order to determine the ability of bricks to withstand external loads. In other tests graphite slices are being subjected to bending forces designed to mimic the stresses imposed on the keyways during the lifetime of the reactor, to test the resilience of the bricks to this type of stressing. As it is not practicable to replace damaged graphite, AGR station operation depends on maintaining satisfactory integrity of the bricks and their keyways. An extension to the graphite core lifetime would have enormous implications for the economics of nuclear power generation since the stations have high capital costs but low marginal fuel costs. AEA Technology, Ride y, Warrington, Cheshire WA3 6A T, UK
Ultrasonic inspection
rail system
RMK’s Zenica rail fabrication plant in Yugoslavia is the first purchaser of the Micro Plus ultrasonic inspection system from Sonomatic. The plant
of the effects
of stresses
manufactures rail for Yugoslav railways, and is gearing up to export to other European countries. To do this, the plant will have to demonstrate its quality control procedures and the consequent quality of its product. The Micro Plus system will provide continuous, full-volumetric inspection for internal flaws, and will eventually be able to handle five different rail profiles, using the non-contact immersion technique which has proved successful for the inspection of round and square steel billet and bar. The system was developed from Sonomatic’s Midas ultrasonic inspection and data acquisition system, and is based around a 386 computer. The Micro Plus is a multi-channel inspection system with an array of ultrasonic transducers which examine the rail as it passes through a water-injected stuffing box at line speeds up to 1.5 m s-‘. The water acts as an ultrasonic couplant, and consequently the inspection heads do not touch the surface of the rail. This means that there is no wear and the system is very reliable. The 32-channel will be installed
system which at Zenica will
N DT & E International
April 1991