## 1 Introduction  
Corrosion of reinforcement in reinforced concrete structures is a main mechanism of their degradation [1; 2; 3; 4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18]. Reinforced concrete structures where nuclear and radioactive materials are handled are not an exception in this case [19]. Reinforcement corrosion is the main cause of aging of concrete structures of nuclear power plants (NPPs), according to [20]. Nevertheless, reinforcement corrosion in concrete is an electrochemical process encompassing the anodic dissolution of iron and the cathodic reduction of oxygen in the absence of chlorides in the external environment [8; 21; 22]. In the case of their presence, the process encompasses absorption of a chloride ion and formation of soluble ferrous chloride from insoluble ferrous oxide [21; 23; 24; 25; 26]. This type of corrosion is usually local, unlike oxygen-induced corrosion [21; 22; 24; 25]. The general mechanism of reinforcement corrosion is triggered in reinforced concrete structures in the case of degradation of the depassivation layer at the interface between a steel rod and concrete, whose pH has high alkalinity [7; 8; 21; 26; 27; 28; 29; 30] due to the contact between and the intake of carbon dioxide or chloride ions [7; 21; 24; 26; 27; 28; 29; 30]. In the case of carbonization, it is assumed that corrosion is triggered at the moment when carbonization reaches the boundary of reinforcement. That is when the pH value of the protective layer becomes neutral [7; 30]. The case of the presence of chlorides is characterized by the recurrent restoration of the layer previously lost to depassivation due to changes in conditions of penetration of chlorides into the structure (clogging of pores with carbonization products; closure of cracks developed under the action of temperature or loading, when the structure is deloaded, etc.). In this case, corrosion is continuous only if chlorides accumulate in the body of the structure [7; 29]. As time progresses, corrosion triggers deterioration of the strength characteristics of reinforced concrete structures; it reduces their ability to resist operational and potential special effects due to a reduction in their diameter [1; 2; 3; 4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 24]. Hence, it is necessary to ensure the predictability of this process as early as at the stage of design of structures and, in some cases, at the time of their regular inspections. In addition, according to [31; 32; 33; 34], reinforced concrete structures of buildings and facilities, where nuclear and radioactive materials are handled, need simple practical methods of justification of design solutions, including the methods that are licensed by authorized state and supervisory (regulatory) authorities in accordance with the pre-set procedure. At present, appropriate models are available. They simulate corrosion of reinforcement in concrete for design conditions to ensure the durability of reinforced concrete structures [21; 35; 36; 37; 38; 39; 40; 41; 42; 43; 44]. However, advanced methods of predicting radiation-induced corrosion of building structures at stages of design [45; 46; 47] and operation [48] are highly conservative. Therefore, radiation-triggered corrosion changes (i) in structures of buildings and facilities where radioactive and nuclear materials are handled, and, (ii) in some cases, in materials for radiation and nuclear waste packaging, are underestimated in terms of the effect of gamma radiation on their future operational degradation, as evidenced by a number of scientific studies [30; 45; 49; 50; 51; 52; 53; 54; 55; 56; 57; 58; 59; 60; 61; 62], including the dissertation study [63]. Gamma radiation accelerates corrosion of steel elements and reinforcement in reinforced concrete structures [56; 57; 58; 60; 61; 64; 65; 66; 67; 68; 69].