User:Satoan321/sandbox/Fixed-Bed Nuclear Reactor

The Fixed Bed Nuclear Reactor (FBNR) is a small (40 MWe) source of power mainly developed by the Federal University of Rio Grande do Sul, Brazil. In comparison to other reactors, the FBNR is inherently safe because most of its switches will not turn on unless all the signals from all the safety detectors show safe operational conditions. In addition to having a low impact on the environment, it is the first of its kind not to need on-site refueling since it has a has a long fuel cycle time (it can operate without refueling and reshuffling of fuel for a long period of time). It uses a technology called the Pressurized-Water technology (in which water is heated to an extremely high temperature by fission, kept under high pressure and converted to steam by a generator). This technology is combined with the HTGR type fuel elements (high-temperature reactor that can reach high outlet temperatures, up to 1000 °C) making it a proliferation resistant and passively cooled reactor.

Multiple institutions have shown interest in working on the project such as The Imperial College of London, The Institute of Theoretical and Experimental Physics (ITEP) and the Institute of Physics and Power Engineering (IPPE).

Reactor Description

Schematic Design of FBNR.

The Fixed-Bed nuclear reactor is a specific case of the fluidized bed concept . The fuel elements, which are called pebbles, are held in place in the core by the flow pressure (approx. 10 bar). They then become fluidized in the fuel chamber and exit when the velocity reaches 1.4 m/sec. After that, they go to the core and remain in a fixed place while the flow velocity is 7 m/sec.

The reactor has a core and a steam generator in the upper section and a fuel chamber in the lower section.

The Core

The basic geometrical sketch of the FBNR core.

The core is made up of two circular perforated zircaloy tubes with diameters of 31 cm and 171 cm, respectively, inside which the spherical fuel elements are held together by the coolant flow in a fixed bed configuration, forming a suspended core, during reactor operation. The coolant rises vertically into the inner perforated tube, then passes horizontally via the fuel elements and the outer perforated tube before entering the outer shell and rising vertically to the steam generator.

The Reserve fuel chamber

The reserve fuel chamber is a 60-centimeter-diameter tube constructed of a high-neutron-absorbing alloy that is attached immediately beneath the core tube. The fuel chamber is made out of a helical 40-centimeter-diameter tube that is flanged to the reserve fuel chamber and sealed by national and international authorities. The fuel elements are held in place within the tube by a grid at the bottom. In the upper half of the module, a shell-and-tube steam generator is included. For fine reactivity adjustments, a control rod can be slid within the core's center.

Pressurizer System

A pressurizer system is installed in the reactor to keep the coolant at a consistent pressure. The coolant is circulated inside the reactor by the pump, which moves it up through the fuel chamber, core, and steam generator. After that, the coolant returns to the pump via the concentric circular route. The water coolant carries the 15 mm diameter spherical fuel elements from the fuel chamber up into the core at a flow velocity known as terminal velocity. In the reactor, a fixed suspended core forms. The suspended core breaks down in the shutdown situation, and the fuel elements leave the core and fall back into the fuel chamber due to gravity.

Characteristics

Charecteristic	Explanation
Small in size	The reactor is small with an optimum size of 40 MWe. The maximum size the Fixed Bed Nuclear Reactor can have is 60 MWe and that can only happen at the cost of a lower thermodynamic efficiency.
No need for on-site refueling	Each module is fuelled in the factory, sealed and then transported to and from the site. The FBNR has a long fuel cycle time and, therefore, does not need on­ site refuelling.
Long fuel cycle time	The length of the fuel cycle depends on the economic analysis of the fuel inventory for particular situation of the reactor and its application. The HTGR fuel elements have high burn up capacity. The replacement of fuel chamber is done at any desired time interval and could be set at every 10 years or for the reactor lifetime.
No fuel reshuffling	The reshuffling of fuel is not necessary because the fuel elements go from the fuel chamber to the core and vice versa without the need of opening the reactor.
Easy transportation	The reactor is about 2 m in diameter and 6 m high, with a fuel chamber that is only 2 m in diameter and 1 m high. Therefore, the transportation to and from the site and return are very easy and convenient.

Technical Data

The table below contains technical information about the FBNR as a whole and its specific components.

Technical Data Table for the FBNR

General Plant Data		Reactor Core		Primary coolant system
Reactor thermal output	218 MWth	Active core height	2 m	Primary coolant flow rate	1060 Kg/s
Power plant output, gross	72 MWe	Equivalent core diameter	1.7 m	Reactor operating pressure	16 MPa
Power plant output, net	70 MWe	Average fuel power density	28 KW/KgU	Core coolant inlet temperature	290 °C
Power plant efficiency, net	33%	Average core power density	45 MW/m3	Core coolant outlet temperature	326 °C
Mode of operation	Baseload	Fuel material	CERMET	Reactor pressure vessel
Plant availability target	> 95%	Fuel element type	Spherical	Inner diameter of cylindrical shell	214 mm
Primary coolant material	Light Water	Cladding material	Zircaloy-4	Wall thickness of cylindrical shell	15 mm
Moderator material	Light Water	Outer diameter of elements	15 mm	Total height, inside	6000 mm
Type of cycle	Indirect	Fuel cycle length	25 Months	Transport weight	5 t
Thermodynamic cycle	Desalination	Mode of reactor shut down	Turn off the coolant pump	Active/passive systems	Passive

Advantages of the FBNR

The Fixed-Bed Nuclear reactor has multiple advantages especially for being its size.

Advantages for developing countries

• It provides electricity generation combined with seawater desalination, which meets the urgent needs of many developing countries.
• It can be used in countries with small electric grids and insufficient infrastructure.
• It can be perfect for countries with limited capacities for investment, especially in relation to hard currency, and small turnover of capital in the electricity market
• It does not release carbon dioxide, hence it will contribute to sustainable development in both developing and developed countries through power generation and process heat applications.

Non Proliferation aspect of the reactor

The non proliferation aspect of the reactor is based on two principles:

• Sealed reactors
• Isotope denaturation

Its small spherical fuel elements are contained in a fuel chamber that only the authorities can seal. Also, the only component that needs to be transported from the fuel factory to the site and back is the fuel chamber. On the other hand, there is no way to irradiate any external fertile substance with neutrons. Proliferation resistance is significantly increased by isotopic denaturing of the fuel cycle, whether in the U-233/Th or Pu-239/U cycle. Therefore, both the fact that it can only be sealed by authorities and that it can’t irradiate neutrons make it a non-proliferation reactor

External links

• FBNR website