MHTGR-10
General Characteristics:
Type:Mobile nuclear reactor
Length:12.19 m
Width:2.44 m
Height2.87 m
Mass:30,000 kg
Reactor Characteristics:
Thermal power:22 MWth
Power output:10 MWe
Core diameter:2.3 m
Core length:3.9 m
Coolant gas:Helium
Moderator:Graphite
Operating lifetime:60 years (2 refuelings)
Fuel:QUADRISO
Fuel mass:384 kg
Fuel enrichment:15%
Core mass:10,700 kg
Overview:
The MHTGR-10 (Mobile High Temperature Gas-cooled Reactor - 10 MW) is a mobile nuclear power plant designed by SDI Power Systems. The entire MHTGR-10 reactor is designed to fit within a standard 40-foot ISO container which lets it be easily transported by ship, rail, truck, or air to remote locations to provide power for airbases, naval installations, and other military or civilian facilities located in remote areas. Using 15% enriched fuel the reactor has a design fuel life of 20 years and and can be refueled twice to to give it a total operational life of 60 years.
Reactor core:
MHTGR-10 burns QUADRISO fuel particles which consists of a Tristructural-isotropic (TRISO) fuel particle with an additional burnable neutron poison layer. TRISO fuel particle consists of a uranium dioxide (UO2) enriched to 15% U235 surrounded by four layers; a dense inner layer of pyrolytic carbon (PyC), a layer of silicon carbide (SiC) which increases the structural integrity of the particle and enable it to retain fission products at high temperatures, and another layer of pyrolitic carbon which forms the outer shell of the fuel particle. Each QUADRISO particle, which is approximately 650 microns in diameter, is formed by surrounding the TRISO particle with a layer of erbium as the burnable neutron poison which acts to compensate for the depletion of the TRISO fuel. After being irradiated the erebium poison depletes and neutrons stream into the fuel kernel and induces fission reactions which compensates for the fuel depletion of the TRISO fuel. The individual QUADRISO fuel particles are loaded into sealed fuel cartridges designed for a maximum fuel temperature of 1,600°C. The core has a total of 151 hexagonal fuel assemblies surrounded by identically sized hexagonal beryllium reflector elements which form the outer reflector assembly. Each fuel assembly consists of a hexagonal graphite block with 54 helium coolant channels and 19 Zircaloy-4 lined fuel channels for the QUADRISO fuel cartridges. The coolant is helium gas at 7.0 MPa pressure which enters the core at 460 °C and exits at 850 °C with a total coolant flow rate through the core of 22.75 kg/s. Reactor control is provided by a total of 18 control rods (three for dynamic power changes and fifteen safety rods used for shutdown) which employ europium oxide as the neutron poison. The three power changing control rods are actuated by a closed-cloop hydraulic control circuit which insert and retract them from core while the fifteen safety rods are normally held outside of the reactor core under spring pressure by a series of clock-type springs wound by a hydraulic motor which actuates through an electromagnetic clutch, ensuring the rods will spring back into the reactor and initiate scram if the reactor suddenly loses power or if the scram control is remotely activated. Core shielding designed to protect the compressor, turbine, and electrical equipment from radiation damage consists of side and axial composite shields 5.0 centimetres thick made from 50% boron carbide (B4C) and 20% grade 316 stainless steel. To save weight and allow the reactor to be more easily transported the MHTGR-10 does not include any biological shield and should be employed with a 150 meter personnel exclusion zone while in operation.
Turbomachinery & Power Conversion Equipment:
The MHTGR-10 employs a closed-cycle brayton power cycle with the reactor essentially functioning as a large nuclear-powered single-spool turboshaft engine. Helium working fluid at 3.2 MPa and 58 °C is compressed by the 18-stage axial compressor to a pressure of 7.1 MPa where it then passes through a recuperator and enters the core at a pressure of 7.0 MPa and a temperature of 460 °C. The helium working fluid then absorbs heat from the nuclear fuel elements and leaves the core at a pressure of 6.8 bar and a temperature of 850 °C. The helium is then expanded through a six-stage turbine employing uncooled IN-100 nickel alloy blades which drives both the compressor and two 5 MWe generators though a single shaft. The helium leaves the turbine with a pressure of 3.5 MPa and a temperature of 620 °C where it then passes through the recuperater where it exchanges heat into the helium entering the reactor core and then into a a precooler which uses a series of helium-to-water heat-exchangers running along the entire sides and top of the reactor module to reject heat from the helium working fluid into the environment, returning the helium to a pressure of 3.2 MPa and temperature of 58 °C where it then again enters the compressor.
Electrical power is provided by two 5 MWe 4-pole, 6-phase helium-cooled permanent magnet generators located on either end of the reactor which are direct-driven by the compressor-turbine spool at a speed of 15,000 RPM. Each generator is supported by a pair of active magnetic bearings and employs a rare-earth permanent magnet rotor and a fully encapsulated stator with hermetically sealed stator winding cooled using bleed helium from the compressor. Each generator operates with a rated line-line voltage of 6.6 kV and a frequency of 666 Hz and is coupled to power conversion unit (PCU) with a rectifier and an inverter unit which converts the generator output to 60 Hz 3-phase AC for power distribution.