Tomsk Polytechnic University has joined Russia’s project on the experimental determination of the radiation characteristics of the irradiated graphite from uranium-graphite reactors. Unit 1 of the Leningrad NPP – a 1,000 MWe RBMK reactor now closed for decommissioning – is the subject of the research.

Leningrad in Sosnovy Bor (Leningrad Region), which began construction in – 1967, started operation in 1973. Currently Leningrad NPP has four units in operation – units 3&4 with RBMK-1000 reactors, as well units 5&6 with new VVER-1200 units (also known as Leningrad-II 1&2). Units 5&6 replaced units 1&2 with RBMK-1000 reactors, which were decommissioned in 2018 and 2020.

Earlier an agreement for R&D was signed between Rosatom’s Experimental & Demonstration Centre for the Decommissioning of Uranium-Graphite Reactors (ODTs UGR – Opitno-Demonstratsionni Tsentr vivoda iz expluatatsii Uran Grafitovikh Reaktorov) and nuclear utility Rosenergoatom. This envisaged implementation of R&D on the experimental determination of the radiation characteristics of the irradiated graphite, which was used as moderator in the RBMKs. Among the main characteristics to be determined are the isotope composition, specific activity, spatial distribution of radionuclides in the graphite stacks from the reactors.

Scientific organisations with experience in sampling and measuring the radiation characteristics of irradiated graphite are involved in carrying out this large-scale and interesting work,” said Alexander Pavlyuk, acting head of ODTs UGR. “Tomsk Polytechnic University was involved as a co-executor. An agreement was concluded between the university and ODC UGR for research and development work on the development of methods for the experimental determination of the radiation characteristics of the irradiated graphite.”

As part of the work, it is planned to adapt and improve the instrumentation and methodological base for the tasks of studying the peculiarities of the localisation of radionuclides in the graphite stacks of RBMK-1000 reactors.

Pavlyuk noted that Russia’s existing nuclear fleet includes 11 RBMK reactors at the Leningrad, Smolensk and Kursk NPPs. Such reactors “are distinguished by having the highest power, energy intensity of the core, thermal neutron flux values, and duration of the operating period,” he said.

To date, four RBMKs have been closed down – Leningrad 1&2 and Kursk 1&2 Final shutdown involves work to prepare the reactor for decommissioning, including unloading nuclear fuel from the core and removing nuclear fuel and other nuclear materials from the site. Closure of all reactors of this type is planned to be completed by 2038. The Leningrad reactors are considered as an a pilot project for the decommissioning such reactors. However, to obtain a decommissioning licence, it is first necessary to determine the content of radionuclides in the graphite stacks, Pavlyuk explained.

Project participants plan to test methods previously developed for examining graphite stacks of uranium graphite reactors, and also improve them taking into account the specifics of the RBMK. Technicians as part of the scientific group plan to test the scanning devices and develop all the necessary methods and recommendations.

“Moreover, this work, as a pilot project, also involves analysing the applied approaches, methods, hardware and methodological base in order to universalise their use when planning and performing similar work at the remaining RBMK-1000 reactor plants and reactor plants of other types,” Pavlyuk noted.

Employees from the Institute of Physics & Chemistry of the Russian Academy of Sciences, Prolog LLC, and Sibnuklon LLC were also involved in the work. The project will be carried out as part of the R&D programme to develop innovative technologies for NPP decommissioning. The contract is designed for two years. Previously, at Tomsk Polytechnic University a research and development centre for decommissioning was opened with the support of Rosatom fuel company TVEL and Moscow Lomonosov State University. The new structure is being developed within the framework of the Ministry of Education & Science’s Priority 2030 programme.

Image: The reactor hall of the Leningrad 2 RBMK light water graphite-moderator reactor unit near St Petersburg (courtesy of Rosenergoatom)