Manufacturing of PCFS hydroaccumulators

The passive core flooding system (PCFS) refers to NPP passive safety systems and is designed to remove residual heat of the reactor primary circuit coolant. The system includes 8 hydroaccumulators of 120 cubic meters each. During operation at the NPP, the hydroaccumulators store the boric acid water solution heated to a temperature of about 60 degrees. When the pressure in the primary circuit drops below a certain level, the solution is automatically supplied to the reactor and the core cools down.

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Manufacturing of shells

Assembly of semi-bodies

Fabricattion of embedded components

Quality control

Shells used for assembling the bodies of hydroaccumulators are manufactured in the assembly and welding production area of Petrozavodskmash. Each PCFS accumulator consists of three shells and two heads. The shells are made of 60-mm thick stainless steel sheets. For one accumulator, a cylinder of 4.3 m diameter is made of a 2.5 m wide and 13 m long blank on a bending machine. For a set of eight PCFS accumulators, 24 shells are required.

Three PCFS shells are assembled and welded to the head by circumferential welded joints. In the resulting semi-bodies, internals, floorings and ladders made of round bars are installed. One flooring reaches 4 m in diameter and more than 400 kg in weight. Each accumulator accommodates three such structures. At the end, the top head is welded. After hydraulic tests, the accumulators are cleaned and prepared for painting. Painting, preservation and packaging complete the procedure of manufacturing the accumulators.

Embedded components and fasteners are metal annular supports made of steel sheets with a diameter of about 5 meters and weight of 9 and 18 tons each, respectively. The embedded components are concreted into the NPP ceilings; the fasteners are attached to them, and the hydroaccumulatos are installed on the fasteners. To fix eight hydroaccumulators at the NPP, eight embedded components and eight fasteners are required. The total weight of the equipment is 220 tons

Before shipment, the PCFS accumulators undergo several checks such as load tests, hydraulic tests, and visual inspection. The hydraulic tests are used to check the finished structures for strength and tightness. The quality of the welded joints is controlled by dye penetrant test. In addition, outer surfaces of the hydroaccumulators are visually inspected for deformations and leakage.

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Quality control

Dye penetrant test.

Ultrasonic test

Radiographic test

Shipment and delivery

The PCFS hydroaccumulators are oversized for road vehicles, so, when possible, they are transported by water. The road transportation to the Petrozavodskmah's berth is carried out along a special road and is accompanied by respective services and traffic police.