The construction of a centralized spent fuel storage facility (CSFSF) in the Chernobyl Exclusion Zone is a resonant issue. The facility is constantly in the focus of attention of scientific and public organizations, industry experts, and the media.
Currently, the stage of actual implementation of this project is initiated, in this connection the interest to the most important its component safety level and this level acceptability from the viewpoint of up-to-date requirements is extremely heightened.
We decided to talk with the experts of the State Scientific and Technical Center for Nuclear and Radiation Safety (SSTC NRS), who directly participated in analyzing documents that justify CSFSF safety.
Scientific Director Oleksiy Dybach, Head of the Decommissioning Department Serhiy Kondratiev, veteran of the Ukrainian nuclear industry Viktor Shenderovych presented the information on how safety was justified, what documents were considered during the process, what was SSTC NRS role in the activities related to CSFSF licensing.
Dybach Oleksiy Scientific Director
– What is CSFSF role in the energy production cycle using nuclear fuel?
– Spent nuclear fuel (SNF) is an integral component of electric energy production cycle using nuclear technologies, including those for the main facilities of this production in Ukraine: nuclear power plants. After SNF storage in spent fuel pools, which are components of the complex of each NPP unit, a subsequent decision on SNF management should be implemented within 5-7 years.
The management may be conducted in two ways. The first is the so-called “deferred” decision with the arrangement of intermediate long-term storage. The second is SNF reprocessing for subsequent use of reprocessing products, storage; disposal of radioactive waste generated during reprocessing.
In Ukraine, at the level of state documents, a “deferred” decision on SNF management was made. It implies the arrangement of intermediate long-term storage of SNF. A reserve period will provide an opportunity to adopt a justified and economically acceptable option for subsequent actions with SNF. Among them: reprocessing, whose products may be used also for the production of other nuclear fuels, as well as SNF disposal with the formation of a geological repository.
At the same time, it should be noted that this decision is aimed at increasing the energy independence of Ukraine, since it excludes dependence on the Russian Federation regarding the need to export spent nuclear fuel for storage and reprocessing.
Such a decision also provides the necessary economic efficiency, since technical and economic indicators of the constructed long-term intermediate storage facility CSFSF show unconditional economic advantages compared to the expenses Ukraine incurs when sending SNF to Russia.
Currently, the issue of possible SNF reprocessing in Ukraine or using capabilities of other countries (except Russia) is not considered as realistic in the near future.
In implementing the above concept, the CSFSF is of key importance, since according to this project it is possible to store SNF from operating power units of KhNPP, RNPP, and SUNPP for up to 100 years.
At the same time, the CSFSF has technical capabilities to store additional SNF amount if a decision is made to construct new power units (within implementation of the energy strategy of Ukraine until 2035 and beyond) by appropriate expanding.
It is necessary to pay attention to the following. Recently, some media highlighted again ungrounded statements about the storage of spent nuclear fuel in the CSFSF from reactors of other countries. This information has no basis, since the CSFSF project and the safety justifications performed do not consider the possibility to store any spent nuclear fuel, except that from Ukrainian NPPs.
Thus, if the DSFSF is available at ZNPP, it may be assumed that regarding SNF for a long-term perspective, the independence of Ukraine's nuclear energy is provided taking into account the simultaneous provision of economic benefits.
– What are the main features of SNF management technology adopted under establishing the CSFSF?
– Storage of SNF in the CSFSF is provided in HI-STORM metal-concrete containers located at open storage site.
The whole SNF management cycle starts from NPP units where SNF is reloaded into special containers after which they are transferred to transport containers for transfer to the CSFSF.
On CSFSF territory, with the help of reloading equipment containers are transferred to reinforced concrete containers at specially equipped CSFSF site.
A technology of SNF management developed by Holtec International (USA) including development of the necessary special equipment for the whole SNF management chain was accepted for the implementation. At the same time, it is necessary to pay attention that in the beginning, the HI-STORM storage containers will be supplied by Holtec International, and then containers will be manufactured in Ukraine.
It should also be noted that SNF storage technology developed by Holtec International is used in projects of different countries.
– What documents on CSFSF construction were analyzed by the regulatory body and SSTC NRS?
– The CSFSF is a nuclear facility in accordance with the laws of Ukraine and regulatory documents in the field of nuclear energy, and therefore documents on nuclear and radiation safety justification of the facility at all stages of its establishment should be developed.
The SSTC NRS considered and conducted the NRS review of the feasibility study for CSFSF construction, facility construction project, technical specifications for equipment important to safety and necessary support documents, as well as various documents on testing programs for special equipment.
Technical specifications are documents developed for each type of equipment and define requirements, main technical characteristics, safety and reliability criteria and other parameters.
During the review, the following documents were considered as the most important: safety analysis report of the facility as a whole, safety reports for the most important equipment including design and other necessary justifications, as well as quality assurance documents for equipment manufacturing.
In the future, it is assumed to perform analysis and review of documents related to the requirements for equipment testing, testing results under manufacturing equipment, as well as final technical specifications for equipment.
Assessment of various programs including testing programs at the CSFSF site, commissioning, etc. is also envisaged.
An important stage will be consideration and review of the safety report developed taking into account conducted construction, mounting, precommissioning activities and commissioning as one of the documents required to obtain a license for operation.
Head of the Decommissioning Department
– What documents should be considered from the viewpoint of implementing the adopted SNF management technology in relation to activities at NPP sites?
– As stated above, SNF management activities start at NPP sites at each power unit where SNF is loaded to special containers.
The analysis and review of all applied equipment were performed during the review of CSFSF documents that was also mentioned above.
At the same time, there are a number of issues including those related to ensuring safety, which are developed within modification projects of the SNF management system for each power unit, NPP. These projects take into account power unit features at each site and necessary interconnections with available power unit systems
These modification projects and corresponding safety analysis reports will also be analyzed by the SSTC NRS.
– Why exactly SSTC NRS performed the nuclear and radiation safety review?
– The SSTC is a recognized expert organization in nuclear and radiation safety, which has a high level of competence in the entire range of issues on NRS of nuclear power facilities and nuclear industry. The SSTC conducts reviews of all significant activities related to NPP construction and operation. In addition, the SSTC is involved in many international projects implemented at ChNPP including those on SNF and radwaste management.
Without bias it may be stated that there is no another expert organization on a comprehensive assessment of NRS with the same level of competence and activity experience in Ukraine.
– Are documents provided for reviews sufficient to draw conclusions on the safety of SNF storage for the environment and the public?
– During the review, the client involving the developers of the Holtec International technology provided all the documents and justifications necessary to conduct the review. In the course of its performance, necessary meetings and consultations were held, required additional documents were provided.
Regarding individual private issues, decisions should be detailed and specified at subsequent stages, but this does not affect the conclusion on NRS at the stage of granting the permit for construction.
The results of the completed assessments on nuclear and radiation safety confirm the necessary safety level of the facility in accordance with national regulatory documents, as well as IAEA recommendations.
The environmental impact assessment was carried out at the stage of feasibility study including assessment of transboundary transfer and specified in the design.
The documents on environmental impact assessment were reviewed by relevant institutions with making a conclusion on the compliance of the design with the requirements of current regulatory documents.
– What is the basis of SSTC NRS conclusions regarding CSFSF acceptable safety level?
– Firstly, full compliance with all the requirements set forth in current regulatory documents of Ukraine on NRS.
Secondly, meeting the requirements of IAEA documents.
Thirdly, meeting the most important requirements of U.S. documents related to SNF management systems. Regarding this issue attention should be paid to the following. The equipment of SNF management system, which is developed for the CSFSF is manufactured by Holtec International taking into account the requirements of American standards (since the company is American). In this regard, taking into account the requirements of Ukrainian regulatory documents, the SSTC NRS carried out a special study to compare relevant regulatory documents of Ukraine and the United States.
The study showed comparability of the majority of requirements and separate additional requirements of U.S. documents for the issues not reflected in Ukrainian regulatory documents. In addition, certain provisions were identified according to which Ukrainian regulatory documents were stricter in comparison with U.S. documents.
The decisions developed for the CSFSF including those related to equipment take into account meeting additional requirements, in terms of both U.S. documents and Ukrainian regulatory documents.
The analyses performed confirm CSFSF reliability and safety under all operational modes including emergency ones. At the same time, all extreme natural and man-caused hazards typical for CSFSF site and their combinations were considered.
Natural hazards were considered based on the occurrence frequency of once per 10 000 years, as well as hypothetical accidents, for example aircraft fall.
To confirm analyses results in some cases the SSTC NRS performed alternative calculations.
The analyses confirmed the required safety level and low level of environmental impact even under accidents (actual absence of additional environmental impact under accidents outside the exclusion zone)
An important factor is ensuring operation reliability during the scheduled lifetime: up to 100 years.
Now, there is no operation experience for these storage facilities for such a long period. However, there are studies conducted in the United States for dry storage containers, which confirm storage reliability for up to 50 years and it is planned to continue studies in this area.
The results of these studies are proposed to consider in CSFSF long-term operation.
CSFSF safety is also determined by high quality requirements for equipment manufacturing, control of handling operations on SNF management, as well as availability of monitoring systems in the storage area of HI-STORM containers at the CSFSF site.
When assessing CSFSF safety, it is necessary to take into account positive operational experience of ZNPP DSFSF storage system (storage technology similar to the Holtec International technology).
At the same time, it should be noted that a number of additional requirements was taken into account in the CSFSF system compared to the ZNPP DSFSF aimed at safety improvement of storage. First, we are talking about a double safety barrier in a container, a storage basket.
– Why the technology with a double wall of container, basketwas selected?
– The defense-in-depth principles providing safety barriers on the path of radioactive release and radiation spread are among the key ones in the NRS philosophy, they are specified in international and national regulatory documents.
When designing SNF management equipment, the barriers implemented in the equipment are components of this defense. Consequently, the number of barriers increases the efficiency of the defense-in-depth. In accordance with national regulatory requirements, a double barrier is required to store SNF. This provision is more conservative in comparison with the requirements of other countries including the United States. This requirement, of course, is aimed at safety improvement, but it is associated with additional costs to manufacture containers
Taking into account importance of the safety factor, it was accepted as a boundary condition to design container, basket.
– How safe storage of nuclear fuel at the CSFSF will be ensured?
– Consideration of all the factors listed above ensures safe storage conditions for the planned period up to 100 years. In case of obtaining additional information and data, including those related to storage duration, they will be taken into account during operation considering the necessary measures (if needed).
During operation, SNF storage will be monitored by certain monitoring systems for individual parameters of storage containers and parameters of radiation situation at the storage site, as well as provisions of operational documents that will be developed for the operation stage.
veteran of the Ukrainian nuclear industry
– Will Westinghouse SNF received under using FA-W at Ukrainian NPPs be stored at the CSFSF?
Yes. Design solutions and safety justifications are developed considering this fuel.
– What is the protection of SNF from intentional actions? What is envisaged in case of earthquake, flood, fire and other man-made hazards?
– With regard to possible intentional actions, a physical protection system is implemented at the CSFSF, which is developed taking into account all national provisions and requirements
With regard to protection against natural and man-made hazards, consideration of all external hazards is envisaged when developing technical solutions. Moreover, earthquakes based on occurrence frequency of once per 10000 years, possible flooding proceeding from extreme showery rains, etc. are taken into account.
An analysis of possible fires and explosions outside and within the CSFSF site was performed considering possible sources of such hazard.
Consequences of all these events do not affect facility safety.
– Is it possible to remove SNF safely from storage containers after a certain storage period for further disposal or reprocessing?
– Yes, such operations may be implemented. At a certain stage of long-term storage, a decision may be made on the subsequent stage of SNF management: reprocessing or disposal. In this case, decisions should be made on the types of containers for transport, disposal and vehicles for implementation, appropriate documents and procedures should be developed.
– Will the radiation background change in CSFSF area when its operation starts?
– Under normal and abnormal operation the radiation background outside the CSFSF site will practically not change.
– Is SNF transport from nuclear power plants to the CSFSF safe? Does the radiation background increase on the road on which SNF is transported?
– In Ukraine, there are special regulatory documents that regulate requirements for transport of radioactive materials, in particular SNF. All these requirements are taken into account in designing and manufacturing transport containers for transfer, as well as forming trains. Meeting these conditions ensures no adverse radioactive effects during SNF transport.
It should be noted that in Ukraine there is a successful experience of SNF transport from NPPs by public roads.
– What in your opinion should the public know about the CSFSF?
– Since the CSFSF is a facility for storage of potentially radiation hazardous materials, irrespective of a considerable number of documents proving its safety, the public is recommended to have information on CSFSF location, boundaries of the control and observation areas. If you want and have the opportunity, you may visit the site and see everything with your own eyes.