[en] A containment shell (CS) is used in the localizing safety systems (LSS) and in the sealed enclosure (SE) of the NPP reactor buildings with VVER-1000 reactors to prevent the release of radioactive substances from the reactor building into the environment in the case of a reactor or steam line accident. The reinforced concrete structures of the dome and the cylindrical part of the CS are prestressed with steel strands (PS) to provide the strength and tightness of the CS in the case of an accident. When the strands are tensioned with a force creating stresses in the wires that exceed the low cycle fatigue strength of steel, stress relaxation occurs (loss of forces in the strands) during the operation, which makes it necessary to tension periodically the strands to the design values of the forces. The length of the strand wires increases during the tensioning, which reduces their deformation limit. When the deformation limit is exceeded due to the tensioning of the PS, they can rupture, even if the stress does not exceed the yield strength of steel. The task is to calculate such minimum forces in the PS of the dome and the cylindrical part of the CS that will provide the strength and tightness of the CS in the case of a maximum design basis accident and to create stresses in the PS wires not exceeding the low cycle fatigue strength of steel, or, even better, not exceeding the high cycle fatigue strength of steel. The design model of the protective shell and the reactor compartment in general with the use of shell finite elements on the basis of SCAD SC is developed, which allows you to set any effort in any of 36 reinforcing ropes dome and in any of 96 reinforcing ropes containment cylinder. The calculation of the effort in the reinforcing rope, which provides the strength and tightness of reinforced concrete structures with maximum design basis accident for all combinations of temperatures and excess pressure during 10 hours of the accident. The magnitudes of the forces in the reinforcing ropes, which ensure the strength of reinforced concrete structures in the event of a maximum design basis accident, are determined. It was established that the minimum forces (net) in the reinforcing ropes of the cylinder of the protective shell of the reactor are 7.8 MN, and in the AK dome are 7.6 MN., which provide the strength and tightness of the reinforced concrete structures of the cylindrical part of the protective shell of the reactor VVER-1000 for all possible combinations of temperatures and overpressure within 10 hours of maximum design basis accident. (author)