1. Riser shroud 2. Pool metallic liner
3. Core supporting plate with control lead tubes
4. Reactor core 5. Plenum 6. Check valve
7. Secondary water inlet 8. Secondary water outlet 9. Primary pump
10. Primary HX 11. Upper header 12. Control rod drives 13. Isolation plate
MAJOR TECHNICAL PARAMETERS
Parameter Value
Technology developer, country of origin
NIKIET,Russian Federation
Reactor type Pool-type
Coolant/moderator Light water / light water Thermal/electrical capacity,
MW(t)/MW(e)
70 / NA
Primary circulation Natural (below 30% of rated power)/forced (for 30-100%
of rated power) NSSS Operating Pressure
(primary/secondary), MPa
Atmospheric pressure at reactor poll water surface Core Inlet/Outlet Coolant
Temperature (oC)
75 / 102
Fuel type/assembly array Cermet (0.6 UO2+ 0.4 Al alloy) / hexagonal Number of fuel assemblies in
the core
91
Fuel enrichment (%) 3.0
Core Discharge Burnup (GWd/ton)
25-30 Refuelling Cycle (months) 36
Reactivity control mechanism Control rods Approach to safety systems Passive
Design life (years) 60
Plant footprint (m2) 100 000 RPV height/diameter (m) 17.25 / 3.20
Seismic Design (SSE) > 0.8g (automatic shutdown) Fuel cycle requirements /
Approach
Once-through fuel cycle with UO2 fuel
Distinguishing features Design capable for
radioisotopes production for medical, neutron beams for neutron therapy and industrial purposes
Design status Conceptual design
1. Introduction
RUTA-70 is a multi-purpose water-cooled water-moderated integral pool-type reactor serving as a Nuclear Heating Plant (NHP) of 70 MW(t) thermal capacity for district heating, desalination and radioisotopes production for medical and industrial purposes. It has no power conversion system. In the primary cooling circuit, the heat from the core is transferred to the primary heat exchanger (HX) by forced convection at full power and by natural convection at power below 30% of the rated power. Forced coolant circulation using pumps for operations at power levels of 30% to 100% rated power increases the coolant flow rate in the primary circuit and raises the down-comer temperature. RUTA-70 can perform continuous operation without any maintenance for about one year. RUTA-70 reactors can be located in the immediate vicinity of the heat users.
2. Target Application
The conceptual design of RUTA is primarily developed to provide district heating in remotely isolated areas.
Continuous increase of the organic fuel costs in the country essentially enhances the prospect of RUTA as a heating reactor. In addition, RUTA can also perform seawater and brackish water desalinations based on distillation process.
3. Main Design Features
Design PhilosophyThe basic design principles of this reactor are design simplicity and a high safety level due to a low pressure and a large coolant inventory in the primary system. The design aims for low cost of plant construction and operation, high level of safety achieved through specific features and inherent safety mechanisms. The reactor facility is a ground based nuclear heating plant (NHP) designed similarly to pool type research reactors.
Nuclear Steam Supply System
RUTA-70 has a two-circuit layout. The primary circuit is an in-pile reactor core cooling circuit and the secondary circuit is an intermediate one that removes heat from the reactor and transfers it to the third circuit, which is the consumer circuit, i.e., to the heating network. Most of the plant equipment, including the primary- to-secondary side heat exchangers (HX-1/2) resides at dry boxes outside the pool.
Reactor Core
The reactor core is placed in the lower part of the reactor vessel, the vault, in the shell of the chimney section.
The core is designed with the ‘Cermet’ fuel rods that contribute to the reactor safety due to a high thermal conductivity of the fuel matrix and its role as the additional barrier to the fission products release. The reactor core consists of 91 fuel assemblies (FA) of hexagonal geometry with 120 fuel rods per each FA. The height of reactor core is 1400 mm or 1530 mm depending on the fuel rod type. The core equivalent diameter is 1420 mm. In the radial direction, the design of the RUTA-70 fuel assembly is similar to that of the VVER-440 fuel assembly.
Reactivity Control
In the RUTA-70 design, the following mechanisms of reactivity control and power flattening are applied:
optimization of refuelling, use of burnable poison, profiling of fuel loading and movable control rods. The reactivity control is performed by regulating the control rods and using burnable poison. The reactivity margin is partly compensated by the burnable absorber (gadolinium) incorporated into the fuel rod matrix in a way to improve a core power distribution. The rest of the reactivity margin is compensated by the control rod groups.
Reactor Coolant System
The primary coolant forced circulation is provided by two main circulation pumps - one pump per each of two reactor loops. Two MCPs of axial type are installed in the bypass lines of the main circulation loop close to the down-comer inlet. The loop arrangement of the primary circuit components, with the secondary circuit pressure exceeding the pool water pressure, ensures that the reactor coolant is localised within the reactor tank.
Steam Generator
The turbine and associated systems (including steam generator) are not used in the NHP RUTA-70.
Primary Cooling Mechanism
The heat from the core to the primary heat exchanger (HX) is transferred by forced convection of the primary water coolant at full power operation but by natural convection under operation conditions below 30% of the rated power. The application of forced coolant circulation using pumps for operations at power levels of 30%
to 100% rated power increases the coolant flow rate in the primary circuit and raise the down-comer temperature by reducing the water thermal gradient in the reactor core. The distributing header is placed in the upper part of the shell of the chimney section. Pipelines of water supply to the primary HXs are connected to the header from both sides. Downstream of the HXs, coolant is directed via the suction header to the circulation pump that supplies water to a group of heat exchangers located at one side of the pool. Water is returned from the pump head via the supply header. Pumps are connected to the bypass line of the natural convection circuit and are placed in a special compartment in close vicinity to the reactor pool.
4. Safety Features
The high safety level of pool reactors is achieved through their design features, which make it possible to resolve some of the major safety issues through the employment of the naturally inherent properties of the reactor. The safety concept of the RUTA-70 is based on the optimum use of inherent safety features, consistent implementation of defence in depth strategy and to perform the functions based on principles such as multi- channelling, redundancy, spatial and functional independence, application of a single failure criterion and diversity.
Engineered Safety System Approach and Configuration
The RUTA-70 uses mostly passive systems to perform safety functions such as: air heat sink system for emergency cooldown (ASEC), gravity driven insertion of the control rods in the core as reactor safety control system, the secondary circuit overpressure protection system, the overpressure protection system for air space in the reactor pool and pre-stressed concrete external impacts protection system. In case of multiple failures in the reactivity control systems and devices, safety can be ensured by self-control of reactor power (boiling - self-limitation of power), i.e. through the inherent safety features of the reactor. There is a stabilisation of
reactivity feedbacks determined by negative fuel and coolant temperature reactivity coefficients and by the positive density reactivity coefficient.
Decay Heat Removal System
Natural circulation in the secondary circuit provides for residual heat removal from the shutdown reactor and passive cooldown of the reactor facility in blackout emergency situation. The passively actuated ASEC provides residual heat removal to the ultimate heat sink (atmospheric air). ASEC is envisaged for reactor cooldown in case of loss of auxiliary power. Each loop of the secondary circuit has an ASEC subsystem (train);
the ASEC is connected at the bypass line of the network heat exchangers. If all controlled trains of heat removal are lost, heat losses via the external surface of the reactor pool to the surrounding environment (ground) are considered as an additional safety train. Residual heat is accumulated in the pool water. The transient of pool water heat-up in the aqueous mode before the onset of boiling takes several days. As soon as boiling starts, steam goes to the reactor hall where it is condensed by passive condensing facilities. A reactor boil-off without makeup takes 18 to 20 days. Upon completion of this period residual heat is balanced by heat transfer to the ground. Core dry out is avoided. Moderate temperatures are not exceeding the design limits characterize fuel elements.
Emergency Core Cooling System
In emergency situations, residual heat is transferred by natural circulation of the coolant in the reactor tank and in the secondary circuit in station blackout condition. Heat is removed from the secondary circuit convectors using the ASEC under forced or natural circulation of air in the convector compartments. Direct-acting devices open air louvers of the ASEC passively. The system for emergency makeup of the primary and secondary circuits is an active system.
Reactor Pool
The reactor pool consists of reactor core and internals, control and protection system, distributing and collecting headers and a large amount of water. Big amount of water in the reactor pool ensures slow changing of coolant parameters and reliable heat transfer from the fuel, even if controlled heat transfer from the reactor is not available. Fuel temperatures are moderate.
Containment System
The inner surfaces of the pool concrete walls are plated with stainless steel.
5. Plant Safety and Operational Performances
The NHP RUTA-70 may operate in both the base load and load follow modes. Two independent systems based on diverse drive mechanisms are provided for safe reactor shutdown and ensure the reactor power control. One system acts as an accident protection system, while the actuated second system is designed to provide guaranteed sub-criticality for an unlimited period of time and to be able to account for any reactivity effects including those in accidental states. Either system can operate under the failure of a minimum of one rod with maximum worth. In case of loss of power to the reactor control and protection system (RCP), all rods of this system can be inserted in the core under the effect of gravity.
6. Instrumentation and Control Systems
RCP actuators based on two diverse principles of action have been chosen for the RUTA70:
- Multi-position mechanical RCP actuator for automatic (ACR) and manual control rods (MCR);
- Two-position hydrodynamic RCP actuator for scram rods (SR).
In the core there are 42 reactor control and protection system (RCP) rods composing two shutdown systems with diverse actuators. One of these systems intended specifically for core emergency protection (EP) includes 12 rods. The second shutdown system performing the concurrent functions of shutdown and control includes a group of six (6) automatic regulators (ACRs) and four (4) groups of a total of 24 control rods, for remote manual reactivity control (manual rods MCRs). In response to the scram signal, all control rods of the second shutdown system also perform the functions of emergency protection. MCRs are used to compensate for relatively fast reactivity changes such as heat up and xenon poisoning of the reactor therefore, most of MCRs will be withdrawn under nominal operating parameters. MCRs and scram rods may take the intermediate position in the core performing the functions of power control and forming the radial power profile. The slow transients of reactivity change (such as burn-up of fuel and burnable poison) are also controlled by the group of ACRs plus the required groups of MCRs.
7. Plant Layout Arrangement
Reactor BuildingThe protective flooring composed of slabs is installed above the reactor pool to avoid possible damage to the primary components from external impacts. To prevent gas and vapour penetration to the reactor hall from the upper part of the reactor, joints of the protective slabs are gas-tight.
1. Core, 2. Primary heat exchanger 3. Check valve, 4. Pump
5. Primary Circuit distributing header 6. Secondary circuit inlet pipeline 7. Secondary circuit outlet pipeline 8. SCS drives, 9. Upper slab
Control Building
The smallest staffing of the operating shift is four persons. These are the NDHP shift supervisor, the chief reactor control engineer, a fitter-walker for normal operation systems and a duty electrician to attend to electrical devices and systems, instrumentation and control. A supervising physician and a refuelling operator are added to the regular shift staff for the core fuelling, first core critical mass attaining, power start up and refuelling periods. The total personnel number including regular engineers, technicians and administrative staff may reach up to 40 persons.
Balance of Plant
The turbine and associated systems are not used in the NHP RUTA-70. Such scheme in spite of some reduction of autonomy of district heating system (in comparison to high-temperature reactors) possesses several major advantages: Increase in reliability of heat supplying due to diversification of heat sources, provide redundancy required by relatively cheap heat sources and increase of economic effectiveness of heat production.
1. Reactor pool, 2. Reactor Core
3. Primary heat exchanger, 4. Concrete vessel 5. Soil, 6. Purification system,
7. Ventilation system, 8. Secondary circuit
9. Containment, 10. Residual heat removal system 11. Secondary circuit circulation pump,
12. Secondary circuit pressurizer, 13. Secondary heat exchanger
14. Peak/backup heat source, 15. Control valves
16. Grid circulation pumps, 17. Grid water, 18. Consumers
8. Design and Licensing Status
To provide an operating reference for the reactor, in 2004, the feasibility study was carried out jointly by NIKIET, IPPE, and Atomenergoproekt (Moscow). This study showed that RUTA-70 could be deployed along with the non-nuclear sources of power operating in peak and off-peak mode.
9. Fuel Cycle Approach
The standard fuel cycle option for the RUTA70 NHP is a once-through fuel cycle with uranium dioxide fuel.
The alternative fuel cycle option is a once-through cycle with cermet fuel (microparticles of fuel in a metallic matrix). Standard fuel reprocessing method as used for VVER type reactors could be applied. In this, fuel reprocessing can be made centralized. According to the design of the NHP RUTA70, spent fuel assemblies should be stored in the cooling pond for 3 years after discharge from the reactor core and then transported to the fuel reprocessing plant without further long-term on-site storage.
10. Waste Management and Disposal Plan
Radioactive waste is to be transferred to the ‘National Radioactive Waste Management Operator’ for subsequent disposal.
11. Development Milestones
1990 Conceptual design of the 20 MW(t) RUTA heating plant
1994 Feasibility study ‘Underground NHP with 4 × 55 MW(t) RUTA reactors for district heating in Apatity-city, Murmansk region’
2003 Technical and economic assessments for regional use of the 70 MW(t) RUTA reactor to improve the district heating system
6
2 5 10
4
9
1 3
8 7
MAJOR TECHNICAL PARAMETERS
Parameter Value
Technology developer, country of origin
National Research Centre
‘Kurchatov Institute’ (RRC KI),Russian Federation
Reactor type PWR
Coolant/moderator Light water / light water Thermal/electrical capacity,
MW(t)/MW(e)
3.3 / 0.068 Primary circulation Natural circulation NSSS Operating Pressure
(primary/secondary), MPa
19.6 / 0.36 Core Inlet/Outlet Coolant
Temperature (oC)
311 / 328
Fuel type/assembly array UO2 pellet; MOX is an option Number of fuel assemblies in the
core
109
Fuel enrichment (%) 15.2
Core Discharge Burnup (GWd/ton)
57 600 / 27 390 Refuelling Cycle (months) 300
Reactivity control mechanism Control rods and absorber rods Approach to safety systems Passive
RPV height/diameter (m) 3.7/1.25 Seismic Design (SSE) VIII (MSK-64) Fuel cycle requirements /
Approach
Initial factory load for the entire lifetime
Distinguishing features 25 years without refuelling, passive reactivity control and unattended operation
Design status Conceptual design
1. Introduction
The ELENA nuclear thermoelectric plant (NTEP) is a direct conversion water-cooled reactor without on-site refuelling capable of supplying 68 kW(e) of electricity and 3.3 MW(t) of heating capacity for 25 years without refuelling. The technology and techniques were developed incorporating experience from the construction and operation of the GAMMA reactor for marine and space application. The ELENA NTEP is designed as an
"unattended" nuclear power plant (NPP), requiring nearly no operating or maintenance personnel over the lifetime of the unit. The conceptual design was developed by the National Research Centre “Kurchatov Institute” (NRC KI). The ELENA NTEP is a land-based plant; however, in principle it is also possible to develop underground or underwater versions. The reactor and its main systems are assembled from factory- fabricated finished components or modules, whose weight and dimensions enable any transport delivery method for the complete plant, including helicopter and ship. The specific features of the design include capability of power operation without personnel involvement, compensation of burn-up reactivity swing and other external reactivity disturbances without moving the control rods and the use of thermoelectric energy conversion to produce electricity.
2. Target Application
The unattended ELENA NTEP plant is designed to produce heat for towns with a population of 1500–2000 and located in remote areas where district heating is required. Since it is auxiliary in nature, the electricity generation of 68 kW could be used for the in-house power needs of the plant and to supply electricity to consumers requiring a highly reliable power supply, such as hospitals, etc. A desalination unit can be used in combination with the ELENA NTEP.