Assessment of the behavior of spent nuclear fuel in Ukraine
Authors: Dolin Viktor V. , Lo Frano Rosa , Kopylenko Olexandr L. , Cancemi Salvatore A. 
Published: September 2023

Abstract. Before June 2023 the Zaporizhzhya Nuclear Power Plant, which is the
largest nuclear facility in Europe, had suffered a complete loss of external
power seven times since the beginning of the Russian invasion. This forced
it to rely on emergency diesel generators to guarantee the safety and
security functions of the plant, such as reactor cooling. From that, it
appears of meaningful importance to evaluate the performance of all its
nuclear facilities, among which the building where the spent fuel storage
pool (SFP) is located, to assess what consequences anomalous/abnormal or
accident events may determine. Contrary to dry storage, the dry cask/packaging system is stored on open
concrete pads within a protected area of the plant site; the wet storage
requires a hydraulic environment such as the water pools where SF is safely
stored. The hydraulic effluent and the physical containment barriers act as
confinement and shielding, guaranteeing safety criteria are fulfilled. In this preliminary study, the attention is thus paid to the SFP; for this
reason, a description of its behavior and filling status must be provided.
Since 2001, spent nuclear fuel (SNF) from 6 VVER (water–water energy reactor)-1000 units has been stored in the dry storage
facility at the Zaporizhzhya Nuclear Power Plant. This means that, despite radioactive
decay, the total activity of such inventory may exceed 30 times that of the
fourth damaged Chornobyl unit at the time of the accident, and this is due to
long-lived actinides (2 × 1019 Bq), 137Cs (1 × 1019 Bq) and 90Sr (9 × 1018 Bq). Continued damage caused by a missile attack on the SFP (e.g., cyclic, dynamic, and thermal loadings) may increase the risk of loss of integrity, because, as it is widely known, concrete has low resistance under tension. In this assessment,
an evaluation, therefore, the radiological risk is addressed.
For such an evaluation, it is considered that an SFP in VVER-1000 is designed
to store 687 fuel assemblies and 670 in VVER-440. When it is half full,
which is the case for 15 Ukrainian units, it will store about 2200 t U,
containing up to 1 × 1019 Bq of 137Cs, 7 × 1018 Bq of 90Sr and 1 × 1019 Bq of TUE. Moreover, if it is considered that the spent fuel pool represented the Achilles' heel of the nuclear power plant during the 2011 Fukushima accident, it appears quite obvious that there is a need to evaluate the threat associated with the SF storage
condition in order to prevent the occurrence of a new severe accident or
other challenging situations that the armed conflict has created and may
create. The results of the analysis of the Zaporizhzhya Nuclear Power Plant behavior suggest firstly that the plant was/is subjected to high stresses its structures may not withstand for a long time. Secondly, damages may impact SFP instrumentation, which is used for monitoring, for example, radiation or hydrogen formation, leading to loss of control of the SFP facility. Further, it is shown that to prevent the global nuclear threat, nuclear safety and security systems must be maintained and upgraded with at least the introduction of new technical and environmental devices.