Inspection and Repair Stands for Power-Grade Reactor SFAs
The stands is designed for inspection and repair of spent fuel assemblies (SFA) in VVER-1000 cooling pools. They provide on-line data on the in- and post-operation health of spent fuel assemblies to facilitate upgrades to the fuel design and fabrication quality management.
The stand is located in the emergency defueling section of the cooling pool. The control system electronics is deployed next to the pool. The stand can be completely dismantled for emergency reactor defueling or repair of the pool lining.
- SFA visual inspection by radiation-resistant camera providing nonstop recording,
- length measurements of the fuel assembly and its elements,
- measurements of the SFA flat-to-flat dimensions,
- measurements of the SFA bend and twist,
- remote removal and mounting of the SFA head and simultaneous check of SFA head springing,
- ultrasonic detection of leaky fuel rods,
- removal of a leaky fuel rod with the pullout force controlled,
- installation of a dummy fuel rod to replace the leaky one,
- visual inspection and eddy-current flaw detection of the fuel rod removed.
A measuring module is used to carry out non-destructive examinations. It locates and moves measuring instruments along SFAs both vertically and horizontally.
Specifications of the measuring module:
|Maximum overall dimensions (LxWxH), mm||1000x900x6167|
|Operating environment||cooling pool water|
|Vertical stroke of carriage, mm||4500|
|Horizontal stroke of table, mm||498|
|Linear speed of vertical stroke of carriage, mm/s||0.125–12.5|
|Linear speed of horizontal stroke of table, mm/s||0.1–10|
|Motor voltage, VDC||90|
The measuring module is assigned safety class 4 to NP-001-97 and seismic category III to NP-031-01.
The measuring instruments are intended SFA visual examinations, dimensional measurements, cladding leak detection and eddy-current flaw detection.
A radiation resistant TV camera enables visual examinations along the entire length of a fuel assembly communicating videos to a video recorder and a computer. The same TV camera makes dimensional measurements of the fuel assembly and its components (height of the fuel assembly and external fuel rods, distance between spacer grids, etc.). The SFA length is determined as the difference between the height coordinates when pointing the TV camera at the boundaries of the object under examination.
The SFA width across flats, bend and twist are measured by contact differential transformer transducers.
The eddy-current flaw detection equipment identifies defects (cracks, corrosion, hydrogenation, etc.) on the outer and inner surfaces of fuel rod claddings. The fuel rods undergo eddy-current testing after having been taken out of a fuel assembly. The instrumentation sensitivity conforms to foreign standards (ASTM E426-98, JIS G 0583-2004, etc.).
The cladding leak tests are performed ultrasonically by detecting water under the fuel rod cladding. An ultrasonic sensor excites and registers ultrasonic waves that go all the way through the cladding from the fuel rod upper plug to the lower one and back. With water under a leaky cladding, additional absorption of the wave energy occurs in the fuel rod and the reflected signal abruptly falls in magnitude. A fuel assembly is searched for leaky fuel rods after its head has been removed. The cladding leak test equipment detects leaky fuel rods in a fuel assembly with a burnup of up to 30 MW*day/kgU. The method for detection of leaky fuel rods in spent fuel assemblies is covered by patent Rus.Fed. 2262757.
The measurements are performed with a manipulator with 52 ultrasonic sensors inside. Inspection of all 312 fuel rods requires a consecutive installation of the manipulator in six different orientations, each time with a 60° rotation about the fuel assembly. A computer program controls the consecutive connection of the ultrasonic sensors to the measurement system, as well as measurements of the sensor signal amplitude. The software prints out or stores the examination results as an SFA cross-section chart indicating tight and leaky fuel rods. The design of the cladding leak test manipulator is covered by patent Rus. Fed. 139831.
In 2009, in cooperation with OKB "GIDROPRESS", Afrikantov OKBM, and SSC RIAR, Sosny R&D Company introduced a system for ultrasonic leak testing and eddy-current flaw detection for TVSA spent fuel rods at the Kalinin NPP, as well as an ultrasonic system for leak testing of individual fuel rod claddings for the TVSA-T inspection and repair stand at the Temelin NPP, the Czech Republic.
The SFA inspection and repair stands developed jointly with OKB "GIDROPRESS", ATOMMASHEKSPORT for NPP-2006 project were suplied to Unit 1 of the Leningrad NPP-2 and Units 1, 2 of the Novovoronezh NPP-2. In 2017, SFA inspection and repair stands were commissioned in Unit 1 of the Leningrad NPP-2 and Unit 1 of the Novovoronezh NPP-2.
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