By focusing on NPPs of Western design (e.g. PWR and BWR), the first author (G. Saji) has established that ‘long cell action’ corrosion plays a pivotal role in practically all unresolved corrosion issues for all types of nuclear power plants as presented in a series of papers already published (1–9). The authors believe that a similar study of NPPs of Russian design, with their unique scientific and technological basis compared to Western plants, are important to illustrate that this mechanism can occur even with different materials, welding technology or operation (e.g. water chemistry control). Among all the differences, it is important to note that PWSCC per se does not seem to be occurring in VVER plants, although no specific reason has yet to be identified. In this paper, a detailed electrochemical assessment is first made on the behavior of ammonia-potassium water chemistry and structural materials at the normal operational temperature in the primary water of VVERs. The chemical and electrochemical characteristics of the ammonia in VVERS were found to be significantly different from those of PWRs which use the hydrogen water chemistry. However, the water chemistry of RBMK is not fundamentally different from that of the Western BWR and therefore the previous studies on SCC of BWRs are generally applicable. On the bases of these studies, various corrosion issues commonly experienced in NPPs of Russian design (VVER and RBMK) are briefly reviewed. They include: (i) pitting corrosion in un-clad VVER-440 RV; (ii) corrosion cracking at the transition welding joints of RV nozzles and piping; (iii) corrosion issues in PGV-440 steam generator collectors; (iv) steam generator tube and collector corrosion; (v) IGSCC in RBMK with austenitic steel piping; (vi) FAC (E-C) in the secondary system of VVERs; and (vii) Anomalous corrosion products sedimentation in the core region in some VVERs. Since the long cell action hypothesis does not seem to contradict the various corrosion activities being experienced in NPPs of Russian design, the first author invites further study on the potential involvement of this mechanism since this hypothesis provides new insight into many of the unresolved corrosion issues. More specifically, the VVERs’ ammonia-potassium water chemistry has theoretically been identified as playing a key role in the prevention of PWSCC, which is one of the most troublesome mechanism of corrosion degradation in many Western PWRs. In view of this significance, the authors proposed an urgent international joint initiative to prove or disprove this mechanism’s existence in nuclear power systems.
Temperature conditions in the RBMK spent fuel pool in the event of disturbances in its cooling mode
