During the shutdown stage, liquid radioactive waste (LRW) and, partially, solid radioactive waste (SRW) should be removed from a power unit’s systems. Currently, there is a significant quantity, more than 21,000, of spent fuel assemblies (SFA) at Unit 1 (in the reactor and cooling pools), Unit 2 (in cooling pools), Unit 3 (in the reactor and cooling pools), and also in the operating facility designed for the spent nuclear fuel wet storage (SNFSF-1). The SFA should be further transferred to a special facility for preliminary processing and long-term safe storage. The most of major activities that should be performed at the stage for ChNPP Units 1,2 & 3 shutdown and at the stage of the Shelter Object (SO) transformation into ecologically safe system have much to do with management of the previously accumulated RAW and the radioactive waste that is being currently formed.
As for now, only short-lived low-level and medium-level solid radwaste, including contaminated soils of the Chornobyl NPP site, are dispatched for disposal. The liquid radwaste accumulated at the ChNPP is under control being in the drums of the two storage facilities available at the ChNPP industrial site. The solid radioactive waste is stored in the existing solid radioactive waste storage facility. The whole bulk of the accumulated RAW is to be processed and dispatched for disposal; and high-level and long-lived waste is to be transferred for interim storage. It should be noted that:
- radwaste in Ukraine may be disposed in solid condition only;
- long-lived radwaste in Ukraine must be disposed in stable geological formations;
- currently, there is no site available in Ukraine for RAW disposal in stable geological formations; according to NASU assessments, its organization will require significant costs and at least 10-15 years for design and research effort.
The Law of Ukraine ‘On RAW Management’ forbids corporate bodies and natural persons that accumulate RAW as a result of their activity, supply and use radioactive agents and nuclear facilities, performance of activities related to RAW disposal. The SSE ‘Complex’ located within the Exclusion Zone implements disposals at the disposal site. The liquid radioactive waste accumulated as a result of previous operation is stored in the two storage facilities existing at the ChNPP industrial site and interconnected by special pipelines designed for the waste transportation.
The Liquid Radioactive Waste Treatment Plant (LRWTP) was constructed to process the liquid radioactive waste accumulated at the Chornobyl NPP industrial site (including the SO operational LRAW) and planed for processing during 10 years. Design life of the plant shall be at least 20 years, i.e. after the period of 10 years, the LRWTP will be able to process the liquid radioactive waste that will be further formed during the ChNPP power units decommissioning and the Shelter Object transformation into ecologically safe system. The LRWTP commissioning will allow stepwise conversion of liquid RAW into a solid form by cementing following prior steaming of still liquor as well as separation of perlite and ion exchange resins. The LRWTP is an industrial complex that includes:
- equipment for LRAW removal from LRAW storage tanks;
- equipment for LRAW preliminary processing and volume-reduction;
- equipment for the waste conditioning performed with the objective to obtain solidified LRAW.
Characteristics of the LRAWTP end product (packages) match the waste acceptance criteria that shall be established for disposal in the near-surface storage facility for low and medium-level short-lived RAW (Lot 3) of the Industrial Complex for Solid Radioactive Waste Management ( ICSRWM). Thus far, 2,500 m 3 of solid radioactive waste (SRAW) with total activity exceeding 130 Т Bq are accumulated in the solid waste storage facility (SWSF) that is being constructed by ICSRWM. The latter is designed to remove and process/condition the following:
- solid waste accumulated during ChNPP operation;
- operational SRAW of the power units and the Shelter Object;
- SRAW that is being formed as a result of decommissioning activities.
The interim surface storage site for Group 3 SRAW and the long-lived waste located within the ChNPP area is rated to accept 13,000 primary packages (storage drums of 200 liters capacity comprising 165 liter drums), this will allow acceptance of the ICSRAWM products during the period of 10 years. Further, after a 30-year temporary storage of the indicated categories of the radwaste, a decision should be made regarding organization of a disposal facility in deep geological formations or dispatch of the waste to another interim radioactive waste storage unit.
For the period of ICSRAWM construction, SSE ChNPP has developed and concurred with the regulatory authority a decision to provide a site for the interim storage of shielding containers with high-level waste (HLW). The decision meets the regulatory requirements regarding environmental isolation, availability of physical protection, and possibility to further remove the HLW.
The following important issues related to the RAW management at the SSE ChNPP should also be noted.
The long-lived SRAW include the reactors’ graphite stack, which mass at the 3 units as a whole exceeds 5,000 tons. The most acceptable decision at this time is conservation and further cooling of the graphite as a part of the reactor during the period not shorter than 100 years.
Group 3 SRAW include the process channels (PC) of Units 1, 2 & 3 now and will include them over a long period of time in future. As far as these SRAW are concerned, there are several possible options:
- conservation and further cooling of PC as a part of a reactor during a period no shorter than 100 years;
- PC removal from a reactor after nuclear fuel unloading with further cooling in near-reactor vaults and cooling pools;
- PC removal from a reactor after nuclear fuel unloading with further compacting and transference for interim storage and disposal.
Management of the radioactive agents deposited in the cooling pond as a result of the Chornobyl accident happened in 1986 is another major task of great importance.
While future disposal of high-level and long-lived waste in deep geological formations, it must be taken into account that in-pile absorbers and structural elements of fuel assemblies made of non-retentive fissionable material should to be disposed following their cooling in a dry storage facility for spent nuclear fuel.
As for the power units decommissioning process, development of RAW and SNF management infrastructure is a crucial task.
(The answer to the question is based on the reports presented by A.I. Savin, Deputy Technical Director for RAW Management, SSE Chornobyl NPP, and A.V. Shatsman, Director for Human Resources, SSE Chornobyl NPP, at the 7-th International Scientific and Practical Conference ‘Nuclear Facilities: Reliability and Safety’.
For more detailed information on RAW processing at the ChNPP refer to the official web-site of the State Specialized Enterprise ‘Chornobyl NPP’ at www.chnpp.atom.gov.ua)