Tighteners

VVER 440 and VVER 1000 reactor main flange joint stud tensioner

ŠKODA JS manufactures fully automated nut tensioners for the main flange joint of a reactor pressure vessel. In cooperation with the company Siempelkamp Tensioning Systems, four sets of new-concept tensioners were manufactured for Czech and Slovak nuclear power plants.

The device is used for hydraulic pre-tensioning of the main flange joint studs and for tightening / loosening of nuts of the VVER 1000 (or VVER 440) reactor. It consists of a support ring with a hydraulic unit with distribution and fifty-four (or sixty) stud bolt tightening units. The studs are pre-tensioned by means of hydraulic tightening units. Subsequently, the tensioning nuts of each stud are tightened. This fixes their pre-tension, which ensures the tightness of the joint during the reactor operation. The elongation of each bolt is detected by a sensor and displayed on a control panel located outside the reactor cavity. The loosening procedure is similar.

The tensioner allows to perform all operations with high precision and in short time, the design of the device allows to tighten / loosen all nuts simultaneously on one clamping.

Tightening units for reactor upper block flange joints

For VVER 1000 reactors, a combined device (tightener) was originally used to tighten and loosen the flange joints of the reactor head penetrations for thermocouples (TK), neutron flux measurement channels (KNI) and linear step drive housings (LKP). However, the operation of this tightener was complicated, the work with it was time consuming and the correct tightening of the joints was not guaranteed.

ŠKODA JS therefore proposed the modernization of the flange joint tightener. As part of the modernization, the universal flange joint tightener was replaced by two special tighteners supplemented by state-of-the-art technology. It is a “tensioning” tightener for flange joint nuts of TK, KNI and LKP housings and a torque tightener for TK joint thrust bolts.

The tighteners are easy to operate, speed up the tightening time and increase the operational safety of VVER 1000 reactors.

In 2003 – 2022, ŠKODA JS delivered a total of 9 sets of these tightening units to the Czech, Ukrainian, Bulgarian, Russian and Chinese VVER-1000 NPP units.

For VVER 440 reactors, the flange joints were originally tightened by hand using torque wrenches. Thanks to the universal electronically controlled tightening units developed by ŠKODA JS, the complexity of the tightening has been significantly reduced. The time required for tightening is significantly reduced and so is the length of the power plant maintenance outage.

Since 2003, ŠKODA JS has supplied a total of 11 sets of these tightening units to the Czech, Slovak, Hungarian and Finnish VVER-440 NPP units.

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