M. Varvas and H. Putnik
AS ALARA
6, Kiriku Str, Tallinn, EE0100 Estonia

F. Hodson
BNFL Engineering Ltd.
The Victoria, Salford Quays, Manchester, M5 2SP, UK

S. Pettersson
SKB
Box 5684, SE-10240 Stockholm, Sweden.

The questions related to the safe handling of radioactive waste from previous USSR navy nuclear submarine training facility will be discussed. A first step towards the retrieval and storage of the radioactive wastes, an interim waste storage facility, capable for storage of 720 concrete or steel waste containers, was constructed in the site. After that the next step was to condition all radioactive waste from the site and store it into this interim storage, until the final repository will be available in Estonia. At the moment most of the liquid waste in the site were already purified, there are still some sludges and remaining liquids, which need to be solidified in future. Currently most efforts are directed into the solid waste retrieval and conditioning project. The aim of it is to remove and condition the radioactive waste from the Solid Waste Storage. It consists of a concrete structure, divided into 10 compartments. Three of these were used for the storage of radioactive waste. One of the compartments is already emptied and from two remainings the most active items - 20 control rods - removed and placed to the specially designed and manufactured waste packages - Control Rod Containers (CRC).

There are still a lot of problems associated with the safe handling of radioactive waste on the Paldiski site. Estonia does not have an indigenous nuclear power industry and therefore does not have the means to generate capital for investment and decommissioning from the sale of electrical power. Also there is a very large information/experience gap, which is being addressed, again within the constraints of budgetary and manpower resources. Also there is a great void in the information available from the former site occupiers, the Russian Navy.

In the early 1960's a nuclear facility was constructed for the USSR Navy at Paldiski, Estonia. Two scaled submarine mock-ups, each containing full-sized nuclear reactors of 70 and 90 MW respectively, were used for the training of navy staff in the safe operation of reactor systems. The site plan is presented in Figure 1.

After Estonia's re-proclamation of independence in 1991 and following the withdrawal of Russian troops from its territory in 1994, the transferring of ownership of the Paldiski site became a subject of negotiations between Russia and Estonia. As a result, both reactors were defuelled by the Russians and the spent fuel was returned to Russia in October 1994. The reactors were prepared for safe storage by enclosing them in concrete sarcophagi. This work was carried out by Russian personnel. After that the ownership and control of the site was officially transferred to the Republic of Estonia on September 26, 1995. For the purpose of managing the site AS ALARA, a state owned company, was established by the Estonian government.

A detailed description of the situation, a conceptual decommissioning plan together with efforts already undertaken or planned, in the national level as well as by the Paldiski International Expert Reference Group (PIERG), were summarized in our WM'96 presentation (Putnik et. al., 1996). The current paper is focusing on the problems related to the safe handling of radioactive waste, remaining in the area of the facility.

Most of the operational radioactive waste on the site was concentrated in the SWS (Solid Waste Store), LWS (Liquid Waste Store) and LWTF (Liquid Waste Treatment Facility). Also there are some contaminated rooms, equipment etc. in a few other buildings. The final goal of decommissioning is to condition all radioactive waste from the site into an internationally accepted form, suitable for long term storage and possible transport to a repository. It is yet to be decided upon the site for such a repository.

It was decided that as a first step towards the retrieval and storage of the radioactive wastes, part of the MTB (Main Technological Building) of the site, where both training reactors were housed, would be converted into an interim waste storage facility. It has been decided for the interim/long term storage of the recovered radioactive wastes that concrete or steel containers with the outer dimensions 1.2xl.2xl.2 m³, will be used. Because the generation of radioactive waste in industry, medicine and scientific research is rather small in Estonia, this interim store will also house the spent sources from those facilities.

The construction of the interim storage facility within the MTB started in December 1996 and was completed in February 1997. The storage consists of two compartments, each of which can store 360 waste containers. If additional storage capacity is required in the future, it will be possible to construct more such storage compartments inside the MTB. Additionally, a change room facility complete with personnel contamination control, showering facilities and the active laundry for contaminated personal protective clothing was also completed recently in the annex of the MTB.

The layout of the annex and the northern part of the main hall of the MTB can be seen on Figure 2. Both interim storage compartments are situated inside the main hall of the building, which also houses both sarcophagi containing the two reactors. The hall is 190 metres long, 20 metres wide and 22 metres high. The height of the interim waste storage compartments is 10 meters and the thickness of their reinforced concrete walls is 25 cm. The loading of the waste containers into the storage compartments is achieved by using the overhead crane. The interim storage compartments are open from the top, but it will be possible to cover them with concrete slabs in the future, if found to be necessary.

The liquid waste, which was stored in the tanks of the LWS and the LWTF, was treated in 1995 by IVO International Ltd., Finland, using their transportable liquid waste treatment system, NURES. As a result, about 80% (760 m³) of all radioactive liquid waste on the site has been processed. Characterization of the tank sludges and cost estimations for sludge conditioning has also been carried out.

A request for financing of the proposed solidification of the remaining liquids and sludges has been send out in May 1997. AS ALARA has received some replies, but none has come up with proposals for financing the work. In the last PIERG meeting, October 20-22, 1997, the proposal was made to split the project into smaller work packages in order to make funding somewhat easier. Accordingly, the solidification of the residues, treatment of the remaining water followed by decontamination work, will be done as separately funded projects. Preferably the spent resins, sludges, sand etc. would be solidified in a cement matrix. AS ALARA will provide the waste containers and most of the staffing required for work on the site.

A feasibility study of the dismantling of the LWTF facility, financed within the EC PHARE activities, started in January 1998.

At the moment, most efforts are directed into the solid waste retrieval and conditioning project. The aim of it is to remove and condition the radioactive waste from the SWS, then to decontaminate, declassify and eventually dismantle the facility.

The SWS consists of a concrete structure, divided into 10 compartments. Three of these, cells 1, 4A and 5 were used by the Russian Navy for the storage of radioactive waste. According to information supplied by the Russian Navy, cell 4A was used mainly for disposing of soft materials with very low activity, whilst the other two were filled with metal scrap, wood and other heavy items. Among other general waste there were eight steam generators and 20 control rods all from reactor 1. Waste had been dumped into the SWS without any conditioning and packaging and without any inventory being kept. The estimated waste volume in the SWS is about 100 m³.

As the first step in the project, the waste was characterized by remote visual inspection and radiation measurements in April 1996. Results showed, that while the dose rate in the cell 4A did not exceed 20 m Sv/h, in the cells 1 and 5 it reached up to 200 mSv/h and 10 Sv/h respectively. According to gamma spectroscopic measurements, the predominant radionuclides were Cs-137 and Co-60 in cell 4A and Co-60, Eu-152 and Eu-154 in cells 1 and 5. Somewhat surprisingly, only low levels of contamination have been found to date.

It was decided to build a "shelter building" covering the SWS compartments containing waste. This was constructed in order to enable better working conditions when opening the cells, removing the waste and preventing the spread of possible airborne contamination, whilst at the same time giving a degree of shelter to the people carrying out this work.

A plastic tent with a step over function equipped with ventilation system and HEPA filters was constructed above the cell 4A before the waste retrieval started. Cell 4A, where the radiation level was lowest, was emptied first during March and April 1997. From this cell waste was removed manually. Soft material was packaged into 200 litre drums and compacted using an in-drum compactor. After nuclide specific measurements, these drums will be placed into waste containers, one per container. Low activity scrap metal will also be placed into these containers to fill the void as completely as possible. The remaining voidage will be filled by concrete manufactured on site and utilizing contaminated sand also removed from the cells of the SWS. This will make a monolithic waste residue.

During the work in cell 4A a lot of wooden and metallic items, of an assortment of shapes and sizes, were discovered. The presence of these, as well as a remarkably high degree of decomposition of the waste, complicated their retrieval and segregation. Very unexpectedly, 35 unshielded radiation sources were found. This considerably slowed down the work and lead to an inevitably higher than unexpected radiation dose to the workers. Altogether 13 ManmSv were received by 8 persons.

After removing the waste from cell 4A this compartment was decontaminated and transformed into an air locked receipt and despatch facility. This is necessary for taking the empty waste containers into the shelter building and removing full waste containers from cells 1 and 5 as well as the previous arisings from cell 4A.

Figure 3 shows the SWS and "shelter building" during the removing of waste from compartment 1.

Due to the high radiation levels encountered in cells 1 and 5, remote handling techniques were developed and utilized for the removal of highly radioactive items (mostly control rods) from these cells. It was decided to recover them remotely from their haphazard storage positions, and cut them into pieces with an approximate length of 1 metre. The cut pieces were placed in specially designed concrete containers called Control Rod Container (CRC). The CRCs are constructed from the pipe which once fed one of the cooling water circuits to the reactors. Concentrically there is an inner steel tube which guides the tube into which the cut pieces of the control rods will be placed (collecting tube). The inner part of the CRC consists of a metal cylinder into which the cut control rod pieces are placed. The CRC inner tube is manually winched into the outer CRC when full of cut control rod pieces. The annular space between the inner and outer CRC tubes is filled with concrete (thickness approximately 50 cm). The total weight of the CRC is approximately 6.5 tonnes. Figure 4 shows the CRCs and the concrete waste container used at Paldiski.

Cutting of the control rods was performed in compartments 1 and 5 using remotely operated manipulator crane and cutter. Both of these items are hydraulically operated and the manipulator crane, like the main crane in the SWS, is radio controlled. The CRC was placed on top of the SWS and the inner tube winched down into the compartment for filling. All of the control rods have been identified, retrieved and cut from both compartments 1 and 5. The cut control rod pieces have been placed into the CRCs which have been moved into two previously unused pool, purpose built for holding steam generators, in the main hall of MTB as the interim storage.

Altogether four CRCs were manufactured and used on the Paldiski site. Three were used to contain the "active" ends of the control rods and a fourth, slightly modified, CRC was used to contain the "inactive" ends of the control rods. This fourth CRC was also constructed from the reactor cooling water pipe but the internal arrangements were constructed from contaminated steel tubing which was formerly the Russian Navy control rod transfer cask.

It was also decided to handle the eight steam generators from reactor 1, which were disposed in compartment 1, as separate waste packages. An unused pond, designed to accept a reactor pressure vessel, is being used as their interim storage place. At the moment two of the steam generators have been already lifted up and surveyed. They are constructed of stainless steel, having a length of approximately 2.2 metres, diameter 0.8 metre and weight of 2.8 tonnes. Surprisingly, each of them also contained some 500 litres of water. One of them did not have its connecting pipework seal welded. They are being drained, their surface decontaminated, monitored and wrapped in PVC prior to being stored. The slightly contaminated water from these steam generators is being used to make an "active" grout to encapsulate waste in the concrete waste containers.

The other radioactive waste remaining in cell 1 was removed manually like it was done in cell 4A. It can be stated, that as a result of removing the control rods from compartment 1, the dose rate decreased remarkably (below 100 m Sv/h), thus enabling people to work there. Further remote operations continue in Compartment 5 to remove active sources and other waste because the radiation levels, whilst remarkably lower, are still too high to allow man access. Once the high radiation items have been removed, then this cell too will be cleaned and decontaminated as previous ones.

There is a very large information/experience gap within AS ALARA. It had been recognized that the handover of the facility to Estonia by the Russian Navy had been a largely political one, which left the personnel at the site without the same level of nuclear knowledge and experience. Also there is a great void in the information available from the former site occupiers, the Russian Navy. This has hindered operations through not knowing what to expect when recovery operations have been undertaken and also caused the necessity to halt operations and re-evaluate and modify plans when certain discoveries have been made.

Also the lack of funding causes problems in the provision of items required for the work and in the timing of the projects. The same equally apply to systems for planning, management, quality assurance, compliance with necessary Estonian radiological and non-radiological regulations. There were no systems established which could be useful. The setting up of systems, training of operators and managers in both systems/systems requirements and the technical requirements of radioactive and non-radioactive waste management all take time, money and people resources, all of which are in considerable short supply to AS ALARA.

Table I shows the time schedule for the main steps of radioactive management in Paldiski site. In addition to the retrieval, packing, conditioning and storage of the known radioactive wastes on the Paldiski site, buildings and facilities will have to be radiologically surveyed. Once any decontamination has been carried out then these facilities could be demolished in a controlled and progressive manner.

In future also the reactor compartments sealed within sarcophagi will be eventually dismantled and decommissioned.

1. H. Putnik, T. Grochowski, S. Pettersson, 1996. Decommissioning planning activities for two Russian Navy land based nuclear submarines at Paldiski, Estonia Proc. WM '96.

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