Liquid SNF Removal and Decommissioning of IIN-3M Research Reactor

Denis V. Derganov, Ilia V. Kuzmin (SOSNY R&D Company, Russian Federation), Sapar A. Baitelesov, Fakhrulla R. Kungurov (Institute of Nuclear Physics, Academy of Sciences of the Republic of Uzbekistan), Vladimir Mikhal, Umar S. Salikhbayev (Division of Nuclear Fuel Cycle and Waste Technology, IAEA)

European Research Reactor Conference (RRFM-2020), 12–15 October, 2020 (onlain)

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The Radiation and Technological Complex (RTC) was operated by JSC 'Foton' (Tashkent, the Republic of Uzbekistan) from 1975 to 2015. It included several radiation-hazardous facilities, such as the IIN-3М reactor facility, two gamma-irradiation facilities (ISSLEDOVATEL and RKhM), an isotope storage facility, and auxiliary systems and equipment. In 2012, a decision was taken to remove the liquid spent nuclear fuel (LSNF) from the site and decommission the JSC 'Foton' RTC. A rapid elimination of the RTC site to ensure the unrestricted use of the area was considered the first choice.

The main tasks were to dismantle all buildings and facilities on the RTC site, remove all radioactive and household waste, and reconvert the land for further economic use. The paper gives a brief description of the JSC 'Foton' RTC, the tasks solved during the liquid SNF removal and decommissioning of the radiation-hazardous facilities, the scope of work performed, the technologies used and the project output.

1. Introduction

Since 1975, JSC 'Foton' RTC had operated the Radiation and Technological Complex (RTC) incorporating several radiation-hazardous facilities. Among them was the IIN-3M research reactor consuming an aqueous uranyl sulphate solution enriched up to 90% in uranium-235.

In 2012, the Cabinet of Ministers of the Republic of Uzbekistan decided on decommissioning of the JSC 'Foton' RTC to enhance radiation safety of the city of Tashkent and the Republic of Uzbekistan and to mitigate the non-proliferation threat. The first step was removal of the spent nuclear fuel (SNF) under the Russian Research Reactor Fuel Return (RRRFR) Program initiated by the U.S. DOE, the IAEA, and Russia. Uzbekistan joined the Program in 2002.

In spite of the fact that Russia has reactors consuming the liquid nuclear fuel, no technology for the transport of the liquid spent nuclear fuel (LSNF) had ever been developed. In addition, the aqueous uranyl sulphate solution was not actually among the fuels reprocessed at Mayak PA. So, the Uzbek Government brought into view heavy requirements to ensure safety during the fuel discharge from the reactor, temporary storage and loading into a shipping cask.

The Institute of Nuclear Physics, Academy of Sciences of the Republic of Uzbekistan was appointed the organization responsible for the LSNF removal. Sosny Research and Development Company was engaged in solving this task as a company with wide experience in preparation and transportation of the spent fuel.

Preparation of the IIN-3M liquid spent fuel for the removal and reprocessing required designing dedicated equipment for the LSNF discharge from the reactor into temporary storage canisters, and then, into transport canisters and a SKODA VPVR/M cask. This also required special equipment to receive the LSNF-containing canisters at Mayak PA. It was mandatory to develop a technology and perform a safety analysis of the LSNF discharge from the reactor, reprocessing and handling the post-reprocessing products at Mayak PA.

Development of the JSC 'Foton' RTC Decommissioning Plan was started in parallel with the LSNF removal and with the technical assistance of the IAEA. The Decommissioning Plan addressed various decommissioning strategies. A rapid elimination of the RTC site to ensure the unrestricted use of the area was selected as the best option. Thus, the main decommissioning tasks were to dismantle all buildings and facilities on the RTC site, remove all radioactive and industrial waste, and reclaim the land for further use in the national economy.

2. Description of RTC Site

The JSC 'Foton' RTC was in Tashkent, Uzbekistan with an area of 27 000 m². The RTC site had 10 buildings and facilities (Fig.1). The IIN-3M reactor was located in a laboratory building. The reactor was designed solely for research, not for power production. The reactor (Fig. 2) had a high-pressure vessel 450 mm in diameter and 1835 mm long. It was installed in a heavy-concrete shielding box with the wall thickness of up to 3 m.The neighboring rooms housed process systems and a control panel. The building also incorporated laboratories for radioactive material studies.

The gamma-irradiation facilities ISSLEDOVATEL and RKhM were located in a separate building. All gamma radiation sources had been removed from the facilities to be disposed before the RTC decommissioning activities were started.

The isotope storage facility was used to store solid radioactive waste (SRW) accumulated during the reactor operation period. The maximum equivalent dose rate for the SRW was up to 30 µSv/h.

Some of the rooms in the laboratory building and the isotope storage facility had surface contamination including that with alpha emitting sources.

3. LSNF Removal from IIN-3M Reactor

Preparation of the IIN-3M liquid spent fuel for the removal to Russia for reprocessing included the following activities:

• development, fabrication and testing of the equipment for the LSNF discharge from the reactor into temporary storage canisters,
• discharge of the LSNF from the reactor into temporary storage canisters and characterization of the spent fuel,
• development, fabrication and testing of the equipment for loading the LSNF into transport canisters,
• development, fabrication and testing of the equipment for loading the transport canisters into a SKODA VPVR/M cask at UJV Rez, the Czech Republic and the IIN-3M reactor site,
• development, fabrication and testing of the equipment for the LSNF receipt at Mayak PA,
• research activities to develop and adjust reprocessing operations, preparation of a safety analysis report and licensing Mayak PA for the LSNF receipt and reprocessing.

Particular attention was given to the safety of the LSNF handling operations at each stage of the project.

3.1. LSNF Discharge from Reactor

 After the reactor shutdown, the liquid spent fuel was stored in the reactor vessel (about 23 L), and in containers in a safe box of the isotope storage room (about 1 L).

Special equipment was designed and fabricated for the discharge and temporary storage of the uranyl sulphate solution, such as:

• equipment for the fuel batch discharge and loading into six temporary storage canisters with simultaneous measuring of volumes of the liquid,
• equipment for temporary storage of the fuel before shipping,
• equipment for the fuel batching and loading from the temporary storage canisters into shipping canisters.

All the equipment ensured nuclear safety and personnel protection against ionizing radiation. It also prevented unauthorized access to the uranyl sulphate solution during its temporary storage.

In designing, the equipment was subject to a detailed safety analysis including nuclear, radiation, fire and explosion (hydrogen accumulation) safety aspects, as well as an analysis of possible accidents. The nuclear safety expert assessment reports issued by a Russian expert organization and the Uzbek regulatory authority confirmed compliance of the equipment with the applicable Uzbek rules and regulations.

The equipment for the LSNF discharge and temporary storage was designed for the use in the IIN 3M reactor hall (Fig. 3). It was tested at Sosny R&D Company's production facility, delivered to JSC Foton in October 2013, installed and commissioned in January 2014 upon completion of the personnel training.

In September 2014, upon multiple tests of the equipment and personnel training, the uranyl sulphate solution was discharged from the reactor core and measured using the equipment for the LSNF discharge and temporary storage in accordance with a specifically developed procedure. The fuel was placed in the temporary storage canisters.

The personnel exposure during these operations was significantly less than the allowable values.

3.2.  LSNF Loading into SKODA VPVR/M Cask and Air Shipment

 A transport and handling plan for the liquid spent fuel shipment from Uzbekistan to Russia was prepared basing on the multi-modal principle and included the following operations:

• loading the LSNF-containing canisters into the SKODA VPVR/M cask, the SKODA VPVR/M cask into the ISO container, the ISO container on a dedicated truck on the IIN-3M reactor site, and delivery of the cargo to Tashkent airport by road;
• enclosing the SKODA VPVR/M cask in a special overpack to build up the Type C package ТUК-145/С at the airport (the dedicated truck is Mayak PA property that is delivered to the airport by air beforehand together with the overpack); loading the truck together with the ТUК-145/С package on board the aircraft, and delivery of the cargo to the Russian Federation;
• offloading the truck with the ТUК-145/С package from the aircraft at Ekaterinburg airport and delivery of the ТUК-145/С package by road to Mayak PA.

A special canister was designed to ensure safe transportation of the liquid spent fuel. The canister consists of a body and a cap (Fig. 4). The canister body is an air-tight cylindrical weldment. A shielding lead plug at the top of the canister protects the personnel from ionizing radiation in the vertical direction during installation and removal of the canister cap, connection of the canister to the systems for pouring the LSNF in/out of the canister and performance of the leak tests. There are two adapters (fuel and gas) in the canister neck. The gas adapter is intended for vacuuming the canister to fill it up with the liquid spent fuel, as well as for follow-on gas purging and leak testing. The gas adapter is a quick-release fitting with a shutoff valve installed in the gas tube. The gas tube goes through the lead plug to connect the gas adapter with the inner cavity of the canister.

The analysis of the LSNF-containing canister after a bottom drop onto a solid target from a height of 1.7 m (the maximum possible drop hight for the canister being loaded into a cask) demonstrated that the integrity and containment of the canister were maintained under such accident conditions, thus preventing a spill of the liquid spent nuclear fuel from the canister.

The LSNF-containing canisters were transported in the TUK-145/C packaging previously used for air shipments of RR SNF from Vietnam and Hungary. The SKODA VPVR/M cask was upgraded for that particular shipment to include polyethylene impact absorbers in vacant cells of the cask, as well as above and under each canister to provide additional dynamic protection of the radioactive contents.

The package design was subject to a series of numerical computations to analyze the impact of the TUK-145/C containing the canisters with the liquid SNF onto a solid target at a velocity of 90 m/s. The LSNF-containing canisters inside the SKODA VPVR/M cask were proved to maintain their integrity and containment under aircraft accident conditions in all cases considered (top, bottom, side, and corner drops) preventing the spill of the liquid SNF from the canisters into the SKODA VPVR/M cask.

Nuclear safety of the package design and shipment was confirmed by state expert assessment reports.

The discharge of the liquid SNF from the IIN-3M reactor was conducted according to the specifically developed procedure:

• batch loading of the uranyl sulphate solution from the temporary storage canisters into the transport canisters,
• leak tests and weighing of the transport canisters,
• loading of the LSNF-containing canisters into the SKODA VPVR/M cask using a transfer cask.

In October 2014, UJV Rez, the Czech Republic, tested the equipment for compatibility with the SKODA VPVR/M cask.

After testing, the equipment was shipped off to Uzbekistan, whereto the second batch of the equipment designed by Sosny R&D Company was delivered at the same time. It included ramps, an electric pallet truck, a leak detection system, a vacuum reservoir, a weighing unit, and transport canisters. Installation of the equipment was followed by personnel training. The equipment was commissioned after the acceptance tests in March 2015.

Safety of the equipment for loading the liquid SNF into the transport cask and its compliance with applicable  Uzbek regulations and standards were confirmed by expert assessment reports.

3.3. Equipment for LSNF Receipt at Mayak PA

In 2013, an LSNF receipt, temporary storage and reprocessing plan was elaborated, uranium extraction parameters were optimized, corrosion remedies were developed, and characteristics of the post-reprocessing radioactive waste were updated for Mayak PA to receive the new type of the spent fuel.

For this purpose, special equipment was designed including a grapple and a fixing plate for unloading the LSNF from the transport canister and a manifold for the discharge of the liquid spent fuel into a reprocessing vessel. The safety justification included a design analysis, fire, explosion, radiation and nuclear safety calculations.

In the course of 2014, equipment for the LSNF receipt, interim storage and handling at Mayak PA was fabricated. Once fabricated, installed and tested, the equipment was commissioned.

3.4. Summary of LSNF Removal from IIN-3M Reactor

In September 2015, the LSNF-containing  canisters were loaded into a shipping cask on the IIN-3M reactor site. The liquid spent nuclear fuel was shipped by air for the first time ever. The LSNF was transferred to the Radiochemical Plant at Mayak PA for reprocessing.

4. Foton RTC Decommissioning

On request of the Cabinet of Ministers of Uzbekistan and with financial support from international donors, the IAEA put out the RTC decommissioning to tender. An international consortium of the Institute of Nuclear Physics of Academy of Sciences, Uzbekistan, and Sosny Research and Development Company, the Russian Federation, won the tender and took on the RTC decommissioning plan in August 2015.

The milestones of the RTC decommissioning are:

1) preparatory activities including elaboration of design documentation, safety analysis, development, fabrication and delivery of equipment, and personnel training,

2) radiation-hazardous operations, i.e. dismantling of the reactor vessel and contaminated equipment, decontamination of the RTC facilities, removal of the radioactive waste,

3) the RTC regulatory clearance, demolition of the buildings and facilities on the RTC site, and the initial land rehabilitation.

4.1. Preparatory activities

The preparatory activities included:

• project management and quality assurance,
• comprehensive engineering and radiation survey (CERS) of the RTC site,
• developing a draft detailed design and a risk register,
• decommissioning safety analysis,
• environmental impact assessment,
• developing a waste management plan,
• developing a radioactive waste database,
• designing, fabrication and delivery of the non-standard equipment for handling the reactor vessel, and start-up activities,
• procurement of equipment, tools and materials,
• developing/updating administrative and technical documents,
• personnel training and examination.

The Complex Engineering and Radiation Survey (CERS) was intended to determing conditions of the structures, systems, elements of the RTC site, contamination survey, characterizing and identifying the stocks of radioactive waste and other hazardous waste accumulated over the period of operation.

The CERS outcome  demonstrated that the reactor vessel, the liquid SNF draining equipment, the activated concrete in the reactor box, the gas suction and removal system of the reactor vessel and the remaining SRW fragments in the isotope storage facility were the main sources contributing to the gamma-radiation dose rate on the RTC site. During the CERS, the volume and category of the solid and liquid radioactive waste were identified, the surface contamination data were acquired and integrated for all the RTC buildings and facilities, the soil and groundwater radiation characteristics were studied, and the condition of the buildings, equipment and systems was evaluated. All the radioactive wastes were preliminary categorized as low-level. The maximum equivalent dose rate for the reactor vessel was up to 260 µSv/h. The volume of activated concrete to be removed was estimated to be 40–50 m³.

The developed detailed design identified specific activities, technologies and sequence of their implementation, human, time and material resources required, as well as measures to ensure safe work implementation.

The safety predictions demonstrated that annual effective doses for the personnel and the public would not exceed the limits as a result of the RTC decommissioning. The ones in case of design-basis and beyond-design-basis accidents would not exceed the limits, either.

The environmental impact assessment included a comprehensive analysis of various environment components (soil, water, air, flora, fauna, etc.) that might be impacted by the RTC decommissioning. Measures to mitigate the human impact on the environment were specified.

The waste management plan identified the waste sources, quantity, specific operations with radioactive and nonradioactive waste. It also described a procedure for the RW characterization, accounting and control and criteria of the waste regulatory clearance.

At the initial stage, the RTC decommissioning equipment was designed and fabricated for hands-on operations:

• equipment and materials for reactor vessel handling, including supports, a ramp, auxiliary handling equipment and materials,
• upgrades to the active ventilation system,
• equipment and materials to decontaminate the buildings, i.e. jack hammers, a dry electric diamond cutter, a concrete mill, an industrial vacuum cleaner, a recipro saw);
• equipment to characterize the radioactive waste and RW packaging;
• personal protection equipment and other materials.

The personnel involved in hands-on operations were grouped, assigned jobs to perform activities in specific areas (a characterization group, a dismantling group, etc.) and trained in efficient and safe operation methods.

Following the results of the preparatory activities, the Uzbek regulatory body authorized hands-on activities at the Foton RTC.

4.2. Dismantling reactor vessel and contaminated equipment, decontamination of buildings and facilities on RTC site

Radiation hazardous activities were carried out on the RTC site in the following sequence:

1) dismantling the equipment for the discharge and interim storage of the uranyl sulphate solution,

2) discharge of the cooling water from the reactor cooling system,

3) dismantling the IIN-3М reactor vessel externals,

4) dismantling and preparation of the reactor vessel for transportation to the disposal site,

5) dismantling the contaminated equipment in the laboratory building and the isotope storage facility,

6) collecting solid radioactive waste,

7) removal of activated concrete from the reactor box in the laboratory building;

8) removal of surface contamination from the building structures and equipment,

9) fragmentation, packing, characterization and preparation of the SRW for shipping and disposal, taking SRW inventory,

10) transportation of the SRW packages to a disposal site and the LSNF packages to a reprocessing site.

The reactor vessel was removed as a whole through existing rooms and door ways. For this purpose, the reactor vessel was detached from the supports first, and then removed from the reactor box with an existing hoist, loaded on two forklifts equipped with special rotary transport supports and moved out over the ramp to the characterization area (Fig. 5). There, the reactor vessel was embedded in concrete in a steel container and transported to the disposal site.

The concrete walls of the reactor box were activated as deep as 1 m. The activated concrete was demolished with jack hammers and diamond cutters, loaded into 200 L barrels, removed from the reactor box with a standard winch and transferred to the characterization area.

The total number of packages removed from the RTC site was 518. The activated concrete made up 90 % of the total RW weight.

The total activity of the radioactive waste was 64 MBq. Main dose forming radionuclides were Cs-137, Co-60 and Eu-152.

As a result of the activities, all buildings, rooms and structures were decontaminated, the radioactive material, equipment, building structures and all types of the waste were removed from the RTC site.

The individual doses received by the personnel during these operations were two orders of magnitude less than the conservative estimates in the safety analysis. The cumulative equivalent dose made up around 43 mSv during the entire campaign.

The Uzbekistan National Center for Sanitary and Epidemiological Supervision that took charge of safety surveillance detected no radiation and industrial safety breach.

4.3. RTC release from regulatory control, demolition of buildings and facilities and initial rehabilitation

 This milestone covered the final RTC radiation survey. It demonstrated that there were no radioactive substances, waste or contamination remaining on the RTC site. The radiation parameters in the rooms, buildings, facilities and on the RTC site did not exceed the admissible levels stipulated by the Uzbek radiation safety regulations. The EDR in the reactor box did not exceed 0.3 µSv/h, and the average specific activity of the concrete was less than 1 Bq/g.

The RTC radiation survey outcomes were confirmed by the radiation data for the RTC site provided by the Uzbekistan National Center for Sanitary and Epidemiological Supervision, as well as by the results of the independent radiation survey performed by an IAEA inspector.

Analysis of the survey data gave grounds to the Uzbek regulatory body to release the RTC site from regulatory control. The buildings and utility systems were demolished and the primary land rehabilitation was performed. Thus, the Foton RTC ceased to be a radiation hazardous facility in fact and in law.

5. Conclusions

For the period of 2012–2018, by efforts of the international consortium of INP, Uzbekistan, and Sosny R&D Company, Russia, and with the financial support of the IAEA and the U.S. DOE, the full range of activities (from the government decision to the land rehabilitation) was performed to abandon a radiation-hazardous site including the IIN-3M research reactor. The milestones of the project included removal of the liquid spent nuclear fuel from the IIN-3M research reactor and decommissioning of the Foton RTC in Tashkent. The project has returned the site "greenfield" status, thus making it appropriate for unrestricted use in the national economy.

The technologies developed for preparation of the Uzbek LSNF for shipping and reprocessing can be used for Russian solution reactors, as well. They can also be extended over to shipments of other high-level uranium solutions to Mayak PA for reprocessing.

The experience gained demonstrates that an international consortium of a local company having all necessary licenses, human and technical resources, and a foreign partner developing a proper technology and ensuring technical support can effectively meet a radiation-hazardous facility decommissioning challenge.