In 2012-2013 two precise automated systems for the hot cell were developed. This work was performed under the contract with Afrikantov OKBM as a part of development of equipment for the hot cell of the BN-800 reactor at Beloyarsk NPP. As a result, the item prototypes were developed and a set of documents for batch fabrication of the systems to be used to control the condition of elements of the spent BN-800 reactor fuel assemblies.
Automated non-destructive assay system is designed for the following types of post-irradiation examination of spent fuel rods and absorbers:
- measurement of the outer diameter;
- monitoring of the gamma-radiation intensity;
- search for defects in the cladding;
- search for changes in the cladding thickness.
This is a module-based system including the equipment for above examination, a set of grapples, a radiation-resistant video surveillance of the equipment operation, a set of certified defect standards and methodical support.
The design of the system allows for performing several types of measurement simultaneously. If necessary, the system design can be changed; the measuring modules shall be replaced remotely using the standard manipulators and lifting equipment of the hot cell.
The replaceable measuring modules are stored in the special tight cases that can be used for storage at the site, transportation to the operation site and decontamination.
The in-cell equipment is remotely operated from the automated workplace of the control room. The actuators of the control system and the front ends of the precise sensors are in the air-tight enclosure with the individual ventilation system located in the repair room. The equipment is arranged channel-by-channel in sub-blocks and mounted on two racks installed in the enclosure.
The main component of the in-cell system is a transport-operation module that is designed for securing, alignment, vertical transfer and rotation of objects under testing. The module is a bearing and guiding structure with mechanisms for securing, vertical transfer and rotation of tested objects with the max. length of 2500 mm and max. diameter of 32 mm. The error of vertical alignment of object under testing is not more than 0.15 mm and the speed of vertical transfer is up to 3 m/min.
The channel for measuring the diameter of the fuel rod/absorber cladding is designed to determine the cross dimensions of the object under examination in two mutually perpendicular sections simultaneously using two pairs of linear transducers. The module of the channel for measuring the diameter of the fuel rod/absorber cladding can be provided in two designs: for measuring in a start-stop scan mode with the error of not more than ±10 µm or in a continuous scan mode with the error of not more than ±20 µm.
The channel for monitoring the gamma-radiation intensity is designed to measure the relative gamma-radiation intensity of radioactive isotopes during the vertical transfer of the object under examination. The in-cell part of the channel is a collimator with the remotely adjustable slot providing an error of the curtains positioning of not more than 50 µm. The channel is based on a HPGe-detector and a multichannel analyzer that would make a spectrum in relation to the interest in selected nuclides with the energy line of 1332 keV (60Со) but no less than 1.8 keV and the input static load up to 1x105 s-1.
The eddy-current flaw defection channel is designed for monitoring the cladding condition of the fuel rods under testing in order to detect a leaky cladding or one with the abnormal structure. The pulse method of eddy-current detection is based on a high-performance PCI and a special pulse driver. The eddy-current differential and transformer transducers are optimized for their remote installation into the unified module of the eddy-current flaw defection channel using the manipulators of the hot cell. The channel can determine the coordinates of outer defect, inner defect, penetration defect and magnetic inclusion with an error of not more than ±2 mm. The object under testing can be scanned in the continuous magnetic field for improvement of the results informational contents.
The channel for search for changes in the fuel rod cladding thickness is designed for monitoring the cladding condition of the fuel rods and determination of coordinate of the local changes of the cladding thickness. Since the channel realizes the harmonic method of the eddy-current defectoscopy with the combined transmission eddy current transducer, the cladding thickness can be determined in addition to the local changes coordinates. The coordinate of change in the cladding thickness of the object under testing is not less than 50 µm and has an error of not more than ±2 mm.
The system software provides the examination, setup and configuration of the system, development and realization of the programs for the automated researches, viewing, analyses and initial processing of the data.
The system is equipped with a set of standards for diameter, thickness, defects, gamma-radiation sources and dummy objects to be used to verify the system operability and perform its maintenance, adjustment and verification of metrological characteristics. These standards are certified in the Voluntary Certification System and verified in the All-Russian Research Institute of Metrological Service (VNIIMS).
Puncture system is designed for puncturing the cladding of the fuel rod of BN-800 reactor in the hot cell in order to determine the pressure and volume of internal gas. The leak tightness of the fuel rod under examination is concluded basing the measurement results.
This system is designed jointly with RIAR specialists to perform the following functions:
- fuel rod cooling;
- mechanical puncture of the fuel rod cladding in the gas plenum;
- determination of the pressure and volume of internal gas before puncturing the cladding of the fuel rod under examination basing the results of measurement of temperature and pressure of internal gas after the cladding puncturing;
- recording and storing the measurement and calculation results;
- sampling the internal gas for subsequent analysis of its content;
- accumulation and temporary storage of internal gas.
According to the design, the in-cell part of the system can be mounted at two heights for better visibility inside the hot cell when the parameters of internal gas are not determined.
The system can be used to determine the absolute gas pressure under the fuel rod cladding in the range from 0.1 to 0.5 MPa with an error of not more than ±30 % and in the range from 0.5 to 3 МPa with an error of not more than ±10 %. The gas volume under the fuel rod cladding can be measured in the range from 0.02 to 1.00x10-3 m3 with an error of not more than 10 %.
Measurement (control) procedures for all research equipment (automated non-destructive assay system and puncture system) were developed by the Sosny R&D Company and certified by relevant organizations, such as All-Russian Research Institute of Metrological Service (VNIIMS), Specialized Scientific and Research Institute of Instrumentation (SNIIP), State Moscow Region Center for Standardization, Metrology and Testing (TsSM of Moscow Region).
Acceptance tests of equipment were held on December 16-19, 2013 with participation of specialists from Afrikantov OKBM and Beloyarsk NPP. The test results proved that the research equipment prototypes are ready for their operation in the hot cell of BN-800 reactor.
Nuclear Measurement and Information Technologies, No.4 (52), 2014: Automated System for Post-Irradiation Examinations of BN-800 Spent Fuel Elements
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