Off-Gas Purification System for BN-350 Reactor Sodium Processing Facility
Upgrade of the Off-Gas System for the BN-350 Reactor Sodium Coolant Processing Facility
Tech Area / Field
- FIR-DEC/Decommissioning/Fission Reactors
8 Project completed
Senior Project Manager
Zalouzhny A A
Nuclear Technology Safety Center, Kazakstan, Almaty
- National Nuclear Center of the Republic of Kazakstan / Institute of Atomic Energy (2), Kazakstan, Kurchatov
- Argonne National Laboratory (ANL) / West, USA, ID, Idaho Falls\nRWE NUKEM limited, UK, Dors, Winfrith Newburgh
Project summaryIntroduction and Overview
The nuclear power engineering development as one of the most promising branches of heat and electric power generation is directly related to solving a set of tasks aimed at enhancement of efficiency and safety of nuclear power facilities and nuclear waste recycling, reprocessing and disposal. Recently, nuclear waste recycling, reprocessing and disposal has become highly acute as the number of nuclear power facilities steadily goes up and nuclear facilities commissioned in the past require either reconstruction, improvement or decommissioning, and following facility conservation.
This is in full valid for the Republic of Kazakhstan that has a fast neutron reactor with sodium coolant - BN-350 research. This reactor was constructed and commissioned in 1972, when Kazakhstan was still a part of the Soviet Union. It was the primary power and heat supply source in Aktau town, underpopulated western Kazakhstan region, Caspian shore. It was also used to breed weapon-grade plutonium accumulated in special fuel assemblies (blankets).
Considering the fact that the operational life of BN-350 is over and that Kazakhstan has undertaken obligations on nuclear weapon and its component non-proliferation the BN-350 reactor decommissioning is an urgent task. Joint Kazakhstan-American program on BN-350 decommissioning commenced in Kazakhstan touches upon a wide range of issues to be solved in the course of its implementation. Considering specific physical/chemical features of sodium and nature of using it as a coolant, the processing procedure consists of a number of major stages:
1. Decontamination of the first loop sodium coolant, i.e. removal of the most active and long-lived fission products, in particular Cesium-137.
2. Sodium discharge from the primary and second circuits into special tanks for temporary storage.
3. Low-active metal sodium processing into a chemically inactive substance suitable for safe long-term storage or disposal.
4. Safe long-term storage of low-active sodium processing products for 50 years and more, means to control and monitor the state of the substance stored being provided.
According to main technology adopted for the BN-350 reactor the metal sodium is turned to sodium hydroxide in a chemical reactor by means of interaction with water. A reaction occurs in closed volume with boost nitrogen charging, at temperature of hydroxide boiling. The forming off-gas mixture is continuously removed from a reactor to provide for constant pressure in technological volume. The mixture consists of contaminated water vapors, sodium and potassium hydroxide vapors, hydrogen, and technological nitrogen. All mixture components are hazardous substances and its content in nitrogen discharged into atmosphere is strongly limited. Their collection and removal shall be carried out by special purification system, which task is to provide for environmental safety and explosion-safety of processing. The similar works on treatment are first executed in the Republic of Kazakhstan, and the technologies and work execution experience are absent. Because of it the technologies used in other countries shall be analyzed and accepted as initial information: USA – ANL-West technology, approbation on 16,6 tons of the EBR–I and EBR–II reactors’ coolant; France – NOAH technology, approbation on 37 tons of the Rapsodie facility wastes. The main task of this work is adaptation of selected technologies to production in Aktau. Some of purification technological process stages – which are vapor condensation, filtration, reburning, or hydrogen dilution – are widely used in ordinary chemical technologies, for example, in caustic production in Kazakhstan. There are consumable supplies and commodity nomenclature for these productions, some of which can be used for sodium processing facility. Their use in the purification system sufficiently reduces the price of the project, simplifies an operation process. Moreover, different countries have different quotas of permissible discharges. Thus, the content of some mixture components during discharge according to Kazakhstan regulation is lower than in ANL-West or NOAH technologies, while the content of other mixture components is higher than in these technologies. In this situation the changes shall be done in the purification system structure for production in Aktau. For instance, a number of filters shall be increased or decreased, what entails pipeline diameter changing.
Institute of Atomic Energy of National Nuclear Center of the Republic of Kazakhstan (IAE NNC RK) has wide experience in development of simulator/training complexes for prototypes of nuclear rocket engines with a closed exhaust system, radioactive gas and aerosol trap system, development and operation of high pressure gas, including hydrogen, systems. Specialists of IAE NNC RK and other appropriate Kazakhstan organizations, including MAEC, in cooperation with US specialists are able to assure this project’s implementation.
Nuclear Technology Safety Center (NTSC) coordinates activities on development of a liquid-metal coolant processing facility at BN-350 carried out under the US assistance programs for BN-350 decommissioning. These activities include design, fabrication and utilization of cesium traps to remove the radioactive cesium from the first loop sodium coolant, design and fabrication of a facility to drill and drain the reactor vessel to remove residual sodium from the reactor core, design and fabrication of a facility to process sodium into a substance suitable for storage or disposal with no threat to the environment. To perform these activities requires participation of many Kazakhstan institutions and NTSC will assure coordination of work on design and development of the sodium process facility, for review and approval of incoming scientific and technical documentation by all Kazakhstan institutions interested and the US collaborators.
Expected Results and Their Application
The research under the present project falls under the technology area of fission reactors decommissioning (FIR-DEC).
As a result of this project, a technical design is expected for the off-gas purification system for the sodium processing facility in Aktau. The design will comply with all regulating documentation currently in force in the Republic of Kazakhstan. The knowledge and experience of solving these tasks can be used in practice in chemical enterprises of the Republic of Kazakhstan, as well as in foreign countries for decommissioning the fast breeder reactors with sodium coolant.
Meeting ISTC Goals and Objectives
This project has the following as its objects: reorientation of scientists and engineers formerly engaged in nuclear weapon developments, particularly in design and operation of weapon-grade breeding facilities or in researches of nuclear weapon components and elements to an area of activities related to their knowledge and expertise application to solve tasks in peaceful Kazakhstan economy. This area includes the tasks directly related to nuclear power plants safety development, design and implementation of decommissioning and reconstruction projects and programs for served-out reactors, particularly, BN-350.
New knowledge and expertise gained in the course of this project implementation will be useful in the world engineering practice to solve tasks related to nuclear power engineering.
Scope of Activities
Design and development of different-purpose technological systems are connected with existing technology study, selection of system functional scheme, calculations of technological process in accordance with selected structural scheme, selection of standard and non-standard equipment, construction of separate technology components and equipment type connections. Thus, the order of project implementation can be presented as step-by-step solving the following tasks:
Task 1 – Task description: study of composition of off-gas fraction and determination of required purification factor
In the context of this task the study of qualitative and quantitative content of off-gas, the study and analysis of regulatory requirements to define the necessity and purification degree of all pollutants containing in the off-gases are conducted, technical requirements to the off-gas system of LMC processing facility are formulated, as well as its functional structure is defined. The process of hydrogen removal is defined. The analysis of existing methods of aggressive steam-gas mixture cleaning is conducted.
Content of the stage activities is:
- Study of qualitative and quantitative content of off-gases
- Study and analysis of regulatory requirements to define the necessity and purification degree of all pollutants containing in the off-gases
- Defining the necessity of dilution and reburning of combustible components of off-gases
- Analysis of disadvantages of the existing off-gas systems
- Development of initial requirements and parameters of off-gas system for the BN-350 reactor SPF.
Task report shall include: Technical Task for the off-gas system design.
Task 2 – Development of the conceptual design
The following issues are considered in the framework of this task: mass-transfer and cleaning mathematical model and structural scheme are developed, the main equipment is selected. This equipment is required for realization of mathematical models, which simulate the purification technological process operation. The following activities are conducted:
- Patent studies of the existing technologies for purification of the similar content off-gases to use such technologies for the system
- Defining the mixture treatment procedure - drying, filtration of mechanical impurities, aerosol recovery, etc.
- Patent studies of equipment for purification of the similar content off-gases to select the effective and safe equipment meeting the specific parameters: pressure, temperature, consumption, medium, etc.
- Patent studies of constructional and filtering materials resistant to sodium hydroxide impact at given parameters (pressure, temperature, etc.)
The report should represent conceptual design, including:
- Purification technology of similar content gases
- System structural scheme
- Equipment for off-gas purification and drying, which will meet all required parameters
- List of prospective suppliers
- Draft of the system equipment location
- Selection of structural and filtering materials resistant to impacts of concentrated sodium hydroxide solution vapors and other off-gas components
Task 3 – Technical Design Development
The following activities are conducted in the framework of this task:
- Defining the detailed equipment allocation order according to purified gas moving
- System equipment arrangement and adjustment to the BN-350 reactor processing facility building
- Heat and hydraulic calculations of all system track
- Determination of equipment operating parameters
- Strength calculations of the equipment and pipelines
- Calculation and development of heating subsystem to keep the system operation optimal modes, determination of its electrical parameters
- Development of monitoring system for technological process of off-gas cleaning
- Providing for the work safety while day-to-day operation and system maintenance
- Development of explanatory note to the project.
The report shall include: Final technical design of the system for off-gas purification of the BN-350 reactor coolant processing facility
Task 4 – Contract administration
This task involves an activity related to the present project work coordination between the executors, technical and administrative control and analysis of deliverables, translation of deliverables into English, drawing up of and payment for purchasing the materials and equipment required for the present project implementation, organization and holding the scientific-technical workshops in the framework of the project, as well as financial administration related to this project. Nuclear Technology Safety Center is responsible for this task implementation in the framework of the present project.
Role of Foreign Collaborators/Partners
For a long time, the US and Argonne National Laboratories (ANL) in particular, take an important part in implementation of different-nature projects related to BN-350 reactor decommissioning. Since ANL is widely experienced in the fast (breeder) sodium-cooled reactors designing, construction, operation, deactivation and decommissioning, the ANL leading role in the implementation of projects related to BN-350 reactor decommissioning is invaluable. After the Soviet Union collapse, Kazakhstan relations with Russian construction enterprises were lost. In view of the above, USA provides Kazakhstan with support in implementation of projects and programs related to creation of an infrastructure concerned with safety assurance at nuclear facilities available in Kazakhstan. When Kazakhstan declared its intention to decommission BN-350 reactor and put it into a safe storage state, an inquiry was made for provision of US/ANL support to Kazakhstan. ANL and other experts in the area of sodium-cooled reactors are eager to share their knowledge and expertise with Kazakhstan specialists in the field of fast (breeder) reactors decommissioning on the basis of implementation of appropriate programs, projects and R&D seminars.
Technical Approach and Methodology
The off-gas purification system will be developed on the basis of the system used at the EBR-II reactor sodium processing facility constructed in the Argonne National Laboratory – West – this project collaborator. This system operation experience will be taken into consideration and design measures on increasing the system reliability and operation safety will be undertaken.
It is proposed to implement the work in the following way. Firstly, information on same content off-gas purification technologies should be collected worldwide and the experience gained by the project collaborator, Argonne National Laboratory, at the sodium processing facility in Idaho Falls should betaken into consideration. A result of this work implementation will be an issue of the project technical order. Then the system conceptual design will be developed, discussed at a seminar and approved with the collaborator. Then a full-scale design will be developed. The design will include safety analysis, quality assurance program and environment safety assessment report while operating developed equipment. Then the design will be integrated into sodium processing facility design implemented in the framework of other project. The separate stage will be the project administration, which will be implemented by the project leading institution – Nuclear Technology Safety Center.
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