In recent time requirements for security of building constructions, an internal inventory and personnel at action of special inertial reaction taking into account increase in their predicted intensity are toughened. It is possible to carry to similar special types of loadings: seismic influence, blow of the plane, the fire, a loading of designs air shockwaves, the unauthorized armed attacking actions and so forth. These circumstances cause need of identification of stocks of design durability, the detailed description of features of formation of zones of destruction, distribution of indignations for the actual designs including equipped with tools shock-, vibration- and fire-protection. The central element of design protection of the modern NPP is the pressure-tight cover of the reactor (containment) capable to maintain not only extreme external mechanical influences (earthquakes, hurricanes, plane crash, etc.), but also intrinsic pressure up to 0,4 MPa. However, at damage of building constructions because of emergence of cracks, through holes, a dehiscence of a reinforcing layer mechanical strength and a limit of their fire proofness can change considerably. Thus, preservation of a wholeness of building constructions of the NPP becomes one of decisive factors for safety of operation of the reactor in the conditions of emergency situation. Now new approaches to increase in design protection of envelopes of the NPP are developed. In particular, tests of perspective concrete goods with “non-contact” joints of fittings are carried out (like loopback joints, and also direct or bent restart-up with various anchor devices). Within the pilot studies full-scale tests of reinforced concrete linear elements with unwelding joints of metal mountings in various conditions were carried out. Tests were carried out at the hydrostatic stand of LLC “Stroydinamika”. Sizes of models 4700´400´400 mm. The class of durability of concrete of reinforced concrete models declared by the manufacturer is B25. The generalized test data for option of multiple sign-variable mechanical influence are provided on the chart “loading movement”. During tests for the first time it was succeeded to investigate features of destruction of a loopback joint on slanting section. Destruction of a loopback joint on slanting section is reached only at a unilateral loading in the conditions of the application of loading immediately near a joint. The crack arises at loadings 0,7-0,8 from maximal. For development of recommendations about application, calculated justification and designing of the offered options of a joint tests of designs on the inertial unidirectional and reversal load began. These tests are intended to give the answer to a question of effectiveness of use of loopback joints of metal mountings for decrease in intensity of destructions at shock and explosion.