- Status
- Closed
Background
As a consequence of the Chernobyl accident, a lot of various contaminated material was generated, mostly considered as radioactive waste. In relation to decommissioning of three shut down units and especially as a result of retrieval of waste from several hundreds of temporary storage facilities and the whole complex of further activities with conservation and/or dismantling of the 4-th unit, another extremely big amounts of various types of radioactive waste will be generated and shall be processed for long time storage or disposal.
A significant part of the radioactive waste is contaminated metal. Its processing is complicated and very limited volume reduction factor can be achieved using standard waste processing technologies. Melting of the metal waste is considered as a progressive processing technology, providing for reasonable volume reduction, additional decontamination of processed metal and partially, after proper processing, even reusing of the remelted metal in nuclear industry.
In view of this situation, the feasibility study was initiated within the TACIS programme on the cleaning of the Chernobyl area from radioactively contaminated metallic material using melting process including recycling measures. The feasibility study was developed at the end of 1993 and beginning of 1994.
Main objectives of the feasibility study was the on-site evaluation of the metallic inventories, the basic design of a melting plant, the selection of an optional site, cost estimation and a proposal for the project realization concept.
In continuation of these works, the next step of the project – detailed analysis of the safety conditions for building and operation of the melting facility and preparation of necessary licensing documents - were initiated and accomplished within a separate contract.
Objectives
An overall objective of the project was to contribute to progress of decontamination, cleaning and disposal works performed at Chernobyl NPP site through the development of a feasibility study for the application of progressive technology for contaminated metal waste processing.
Specific objectives of the project were:
- Evaluation of radioactively contaminated metallic material with regard to masses, specific activity and nuclide spectrum stored/disposed of within the 30 km-zone
- Basic design of a melting plant to be erected on site for treatment of contaminated metals
- Proposal for recycling of remelted material
- Selection of an optional site for melting plant
- Inquiry on licensing conditions
- Estimation of the overall project costs
- Know-how transfer concept
- Proposal for the project realization concept.
Results
Project results are documented in a final project report. Subsequent steps related to safety and licensing procedures are described in a separate report issued at the beginning of 1996 under separate contract.
CONTAMINATED METALLIC MATERIAL INVENTORY
Mass, specific activity and nuclide spectrum of metallic waste stored within the 30 km Chernobyl exclusion zone was estimated based on published data, records on inventory of the metal scrap stored in temporary storage facilities and other available information.
The total mass of on-site stored contaminated metal scrap was estimated as 100.000 tons. About 50% of this amount belongs to big size equipment, which has to be cut for further handling. About 30 % represent small size scrap which could be, eventually, packaged/encapsulated into proper matrix.
Maximum specific activity of 400 Bq/g was found using dose rate measurement and samples and smears radionuclide analysis. Main observed radio nuclides were Cs-137, Sr-90, Ru-106 and Pu-241.
BASIC DESIGN OF THE MELTING FACILITY
Based on estimated metal waste inventory a melting facility with approximate 10 tons per year throughput has been proposed. Basic technological cycle was proposed as follows:
- Size reduction of bulk pieces (cutting) for transport to the facility
- Radiological check, pre cleaning and pre-decontamination
- Size reduction for melting facility
- Melting in one of the furnaces (induction or arc furnace)
- Formation of the output product (ingot, granulated material, etc.) and exit check
- Packaging (including secondary waste) and delivery for further storage and/or disposal.
Basic concept of the melting plant, including location plan of the furnace and the whole complex of supporting facilities and handling and storage premises is described in sufficient detail in the final project report.
Basic technological equipment and systems for blasting, size reduction, material handling as well as radiation control and protection, air filtration and ventilation were identified. To ensure a high degree of availability and flexibility, two different types of furnaces have been proposed as a core of the technological line: electric arc furnace and induction furnace. Induction furnace allows the continuous melting regime, but also a separate melting of metal mix, when stepwise increasing temperature facilitates melting and separation of metal mix components. Electric arc furnace allows only batch loading and the melting temperature cannot be adjusted. On the other side, the last furnace allows to melt bigger pieces of metal.
Most of contaminants from the metal are concentrated in slag. About 500 tons per year of highly active secondary waste, mostly slag from the melting process, will be generated and stored in 200 L drums until final decision.
SITE SELECTION
A suggested facility size is about 200x 470 m. Three options have been proposed for siting of the facility: directly at the ChNPP site, at the river Pripyat bank (close to former fleet repair facility, where a lot of bulk waste is stored) and out of the 30 km exclusion zone. Two first option were preferred for in the report.
REMELTED METAL UTILIZATION CONCEPT
Several options for utilization of still slightly contaminated remelted metal were proposed. Most of them consider using of remelted metal for containers manufacturing and shielding purposes, especially for wide application at the ChNPP site, including Unit 4 shelter.
ESTIMATION OF THE OVERALL PROJECT COSTS
Construction costs as well as operational costs estimation has been elaborated, however the prices must be actualized at the time of facility construction.
LICENSING PROCEDURE
Licensing procedure was briefly described in the final project report.
To facilitate the administrative and legal realization of this project the counterparts expressed their mutual readiness for an intensive know-how- exchange in the field of licensing conditions and procedures.
In the follow up step, as a continuation of the project works, the detailed analysis of the safety conditions for building and operation of the melting facility and preparation of necessary licensing documents were initiated and accomplished within a separate contract. The results are described I na separate report, issued at the beginning of 1996.