MAJOR TECHNICAL PARAMETERS
Parameter Value
Technology developer, country of origin
NIKIET, Russian Federation
Reactor type Integral PWR
Coolant/moderator Light water / light water Thermal/electrical capacity,
MW(t)/MW(e)
28.4 / 6.6
Primary circulation Forced and natural circulations NSSS Operating Pressure
(primary/secondary), MPa
14.7 / 4.7 Core Inlet/Outlet Coolant
Temperature (oC)
270 / 310
Fuel type/assembly array UO2 pellet / hexagonal Number of fuel assemblies in
the core
163 Fuel enrichment (%) 19.7 Core Discharge Burnup
(GWd/ton)
up to 160
Refuelling Cycle (months) 72 (96 for SHELF-M) Reactivity control mechanism Control rod driving mechanism Approach to safety systems Combined active and passive Design life (years) 60
Plant footprint (m2) 8000
RPV height/diameter (m) Power capsule:
14 / 8 (12 / 8 RF only) RPV: 3 / 1.2
RPV weight (metric ton) 340
Seismic Design (SSE) SSE 8 (MSK-64) Fuel Cycle Requirements /
Approach
6 years (8 years for the modernized SHELF-M) Distinguishing features Power source for users in remote
and hard-to-reach locations as both floating and submerged nuclear power plants Design status Detailed design underway
1. Introduction
A power unit with the SHELF reactor is designed as a local power source for users in remote and hard-to-reach locations. SHELF is an integral-PWR based power capsule to generate 6.6 MW(e). The power capsule is developed in two options: containing only all reactor components, and the capsule of a bigger size that includes also the turbine generator package (TGP), the automated and remote-control system, monitoring and protection system and the electricity output regulation. SHELF power capsule can be used as both floating and submerged nuclear power plants. The engineering design of SHELF is similar to the marine propulsion nuclear power plants. The power unit is delivered as a single module with all of its components accommodated inside a high- strength containment vessel. This ensures high quality of the module fabrication at a specialized machine- building plant. The reactor is refuelled, exhausted equipment is repaired or replaced during its lifecycle, and decommissioned at the end of service life at a specialized plant.
With the capability for long-term unattended automated operation, the TGP and other equipment inside the SHELF module eliminates the need for plant operators inside the power unit and keeps the module unmanned during the automated operation period up to 8000 hours. Within the period of automated operation, the scheduled maintenance is conducted once a year for a duration of 15 days.
2. Target Application
SHELF is designed for a source of power in remote and hard-to-reach locations with decentralized power supplies including the sites on Arctic shore regions. The power of the single-unit plant is 6.6 MW(e) from 28.4 MW(t). Depending on the consumer requirements, SHELF plant can provide direct heat supply to resident and production premises with a capacity of 12 Gcal/h or a desalination plant with a capacity of 500 m3/h of fresh water. For land-based use, the heat is removed by external heat exchangers cooled by mechanical air pumping.
The SHELF plant does not require local water sources. Decay heat removal for submerged deployment is provided by the sea water.
3. Main Design Features
Design PhilosophySHELF is a water-cooled reactor of integral layout with a combined forced and natural coolant circulation modes. The fuel campaign is six (6) years with the design capacity factor of 80%. The reactor components are assembled inside a cylindrical power capsule with 8 m in inner diameter and 14 m long. The reactor equipment is installed in the rear portion of the capsule and the TGP equipment is installed in its front. Besides the power capsule, there is a compact module that houses the auxiliary systems including an air conditioning system to maintain the ambient temperature in the module less than 50oC. The unit’s external systems include an automated instrumentation and control system (AICS), uninterrupted power supply systems, as well as the reactor facility and TGP auxiliary systems, including a ventilation system.
Nuclear Steam Supply System
The reactor uses a traditional two-circuit heat removal system. The reactor's steam removal system is designed to transport the steam generated in the reactor to two turbines. In normal operation, steam is supplied from the reactor to each of the turbines via steam pipelines. Shut-off valves are provided on steam lines both in the sealed volume and outside it. In addition, the reactor plant provides an emergency cooling system. The emergency cooling system is passive and does not require a command to activate.
Reactor Core
The core is of the heterogeneous cartridge type and consists of 163 hexahedral fuel assemblies (FA) of three different types. A number of FAs contains burnable poison and control absorber rods. Absorber rods for reactivity control are united in six identical shim groups. The fuel composition are governed by the maximum fuel load needed for the reactor core life with less than 20% enrichment; fuel composition consists of uranium dioxide in a silumin matrix in the form of cylindrical fuel elements. The ammonia addition is used to generate hydrogen in water to prevent corrosive oxidative radiolysis products generation. The reactor operating time with one fuel load is 5.6 years, with no scheduled maintenance outages for maintenance, and the reactor core life is 40 000 h. This factor is favourable for core self-regulation and safety improvement. Reactor refuelling is performed on the specialized enterprise basis.
Reactivity Control
The core contains two independent reactor shutdown systems. Functionally, the rods are divided into emergency protection rods and control rods. The material of the absorber is boron carbide and titanium diboride. Control rods are grouped in clusters to reduce the number of actuators. Additionally, an emergency system for filling the core with boron carbide solution is provided.
Reactor Pressure Vessel and Internals
The reactor pressure vessel (RPV) accommodates the core and the reactor internals, including heat exchanger (HX) and emergency HX, each consists of 4 sections. The RPV has an elliptical bottom, cylindrical shells, and two reactor cover (central and peripheral). The RPV outer diameter is 1300 mm and height 3000 mm.
Reactor Coolant System
SHELF’s thermal-hydraulic circuit consists of two self-sustained systems: nuclear steam supply system (NSSS) and a turbine generator system. NSSS comprises the primary circuit system, secondary circuit system, emergency core cooling system (ECCS), emergency cooldown system (ECS), makeup, dual and emergency absorber injection system, equipment cooling system, reactor overpressure protection system, SG overpressure protection system, safeguard vessel and containment overpressure protection system and instrumentation and control system.
Power Conversion System
The SHELF two-circuit integral-PWR consists of a reactor and associated systems required for its normal operation, emergency cooling, emergency protection and maintenance in a safe condition. The primary circuit system removes heat from the reactor core and transfer it to the secondary circuit fluid in the SG. The secondary circuit system generates superheated steam from feedwater and transfers heat to the turbine generator plant.
The secondary circuit system comprises a steam generator installed inside the reactor vessel and pipelines with valves (outside the vessel).
Steam Generator
The once-through steam generator (SG) is part of the SHELF reactor and is designed to generate superheated steam in the process of the reactor operation and to remove heat from the primary circuit system during the reactor cooldown. The SG comprises a tubing, collection and distribution chambers installed in the annulus above and below the tubes, steam and feedwater lines installed inside the reactor vessel, steam and water risers installed on the reactor vessel flange, and outside steam and feedwater lines with shutoff and isolation valves.
The SG’s heat transfer surface is divided into four independent sections cut off, when required, by the shutoff and isolation valves.
Pressurizer
The design includes an overpressure protection system as an additional engineering approach for the management of beyond design-basis accidents and serves to prevent, in such cases, the primary circuit system boundaries from breaking down or being loaded with forces in excess of those permitted. The system incorporates two parallel initiation lines.
4. Safety Features
SHELF achieves high level of reactor safety through the following aspects.
1. Use of an integral water-cooled water-moderated reactor with well-developed intrinsic self-protection properties and the following inherent features:
2. A defence-in-depth system of barriers to the spreading of ionizing radiation and radioactive products of uranium fission into the environment, as well as a combination of implemented engineering and organizational measures to protect these barriers from internal and external impacts. Safety barrier system includes fuel matrix, fuel cladding, leak tight primary circuit-reactor vessel, safeguard vessel, confinement valves and containment.
3. Application of passive safety systems and features that operate based on the natural processes without energy supply from outside. Such systems are as follows:
i. Structure of CPS drive actuators;
ii. Decay heat removal system (DHRS); Emergency core cooling system (ECCS);
4. Safety system reliability:
High reliability level of safety systems is achieved through implementing the following principles:
i. Passive operation not requiring any actions for initiation; Diversity of safety systems and devices achieved through the use of different operating principles of systems (e.g., use of the CPS electromechanical drives for the emergency shutdown of the reactor.
5. Protection against external impacts:
The reactor facility’s containment ensures that the reactor components inside the containment and the safeguarded vessel are not damaged in the event of external impacts, including typhoon, hurricane, snow and icing, as well as of helicopter or airplane impacts on the SHELF NPP.
Key systems of the SHELF reactor facility:
1) To atmosphere;
2) ACS;
3) Pressurizer;
4) Shim group and EP;
5) ECCS;
6) Makeup;
7) Containment;
8) To TGP;
9) Absorber tank;
10) SG;
11) Core;
12) IBS
Engineered Safety System Approach and Configuration
One of the major principles of safety systems design is the requirement that they should operate at any design- basis initiating event and during failure of any active or passive component with mechanical parts independently on the initiating event (single failure principle).
Decay Heat Removal System
The decay heat removal system is designed to remove heat from the reactor core during unexpected operational occurrences and events caused by a loss of heat removal due to the feedwater supply and steam discharge
systems failure. The system ensures the nuclear fuel cooling function. The system is based on a passive principle of action with heat removed from the reactor through natural circulation.
Emergency Core Cooling System
The emergency core cooling system is designed to supply the in-vessel natural circulation circuit with water during accidents with loss of the primary circuit integrity. The system uses passive principle of action to organize the coolant movement. The emergency mitigation of the primary coolant loss is ensured passively by draining water from the emergency cooldown tanks into the reactor due to the gravitation because of the difference in the tank and reactor elevations.
Containment System
Reactor is located inside several steel containments. The containment serves to localize accidents and withstands a total pressure in the reactor coolant. They form an additional barrier to leakage of radioactive materials into the environment while limiting the coolant loss during a reactor vessel break.
5. Plant Safety and Operational Performances
The electric power of one SHELF unit is 6.6 MW(e), and the thermal power is 28.4 MW(t). The current supplied to the consumer system is alternate and three-phase (voltage 0.4 kV ± 2 %, frequency 50 Hz ± 1 Hz).
The nuclear plant base operation mode is power operation in a range from 20 to 100% full power with the capability to vary the consumed power daily and annually. The power increase and decrease rate is 1% (forced primary coolant circulation) and 0.3% (natural primary coolant circulation). The time of the reactor operation with one fuel load is 40 000 effective hours.
6. Instrumentation and Control Systems
The automated process control system (APCS) of a nuclear plant with the SHELF reactor is to control the major and auxiliary electricity generation processes in all modes of the unit operation:
1. Normal operation comprises of phased automated initiation, operation at steady power levels in a range of 20 to 100% Nnom with forced primary coolant circulation, operation at steady power levels in a range of 20 to 40 % Nnom with natural primary coolant circulation, switchovers from one steady power level to another in the above power ranges at a preset rate, switchover from natural primary coolant circulation to forced circulation and scheduled automated deactivation.
2. Anticipated operational occurrences like emergency power reduction and operation with a decreased steam supply due to failures of the reactor facility’s key components or feedwater supply and steam receipt systems.
3. Emergency: Emergency deactivation in the event of reactor facility parameters deviating beyond the safe operation limits or in the event of equipment failures leading to the safe operation limits being violated.
7. Plant Layout Arrangement
The undersea power unit module is an energy capsule which accommodates all components of the reactor facility, the TGP, and the unit equipment automated and remote control, monitoring and protection systems, including the electricity output regulation, monitoring and control equipment. The unit’s land based installation includes the AICS equipment, the AICS undersea equipment uninterruptible power supply systems, as well as auxiliary systems to support the reactor facility and TGP operation, including the ventilation system, the negative pressure system and others.
8. Design and Licensing Status
The licensing of the nuclear plant design is scheduled for 2019-2020.
9. Fuel Cycle Approach
The duration of the campaign reactor core is 6 years (8 years for the modernized version of SHELF-M).
10. Waste Management and Disposal Plan
Fuel handling is based on the traditional scheme implemented for the marine-based prototype reactor. Fuel processing and disposal will take place at a specialized enterprise.
11. Development Milestones
2012-2016 Preliminary studies and technological innovation (using previously developed patents).
2017-2019 Pre-conceptual design and technology validation.
2019-2021 Design phase.
2022-2024 Detailed Design
2025 - 2028 Projected deployment (start of construction) time.
2030 Operation testing