Compatibility with Reactor Coolant

Materials of Construction Compatibility with Reactor Coolant... 

Because thorium metal is unattacked by sodium at temperatures up to 500°C, it is compatible with the coolant in sodium-cooled reactors. 

Plutonium dioxide is the form of plutonium most commonly specified for fuel for power reactors. It has the same general features already described for pure UO2 fuel, such as high melting point, irradiation stability, compatability with metals and with reactor coolants, and ease of preparation. In most designs of plutonium-fueled power reactors the fuel is a mixture of uranium and plutonium oxides. 

Special attention should also be paid to the selection of materials and to the coolant chemistry, which also make an important contribution to the reliability of the steam supply system for the nuclear plant. The compatibility of materials and coolant, which is of the utmost importance to minimizing the amount of maintenance, repair and statutory inspection necessary for primary circuit components, should be given careful consideration. Only those materials should be used that have been shown to be compatible with the coolant under the conditions (of temperature of coolant and material and coolant composition) that will prevail in the reactor. A specific concern is the possible occurrence of intergranular stress corrosion cracking. 

The first one is related to the maximum temperature of the cycle. As stated above, the maximum chemical fluid temperature used in our flow sheet (in the S03 decomposition reactor) is around 850°C. Quite interestingly, increasing this maximum temperature does not lead to reduced heat requirements (Buckingham, 2009). It is therefore not necessary to have the hottest possible heat source, which is good in terms of feasibility. The V/HTR operation temperature just needs to be compatible with a 850°C fluid temperature, which implies an outlet temperature of about 950°C if 50°C pinches are assumed (between the primary coolant and the secondary loop, and between the secondary loop and the chemical fluids). 

Fusion Reactors. The development of fusion reactors requires a material exhibiting high temperature mechanical strength, resistance to radiation-induced swelling and embrittlement, and compatibility with hydrogen, lithium and various coolants. One alloy system that shows promise in this application, as well as for steam-turbine blades and other applications in nonoxidizing atmospheres, is based on the composition (Fe,Co,Ni)3V (30). 

The fuels for fast breeder reactors include alloys such as U-Pu-Zr and the ceramic materials UO2-PUO2, UC-PuC, and UN-PuN, but the mixed oxides, UO2-PUO2, are the choice for prototype fast breeder fuel elements because of their high melting temperature, compatibility with cladding and coolants, and relatively good irradiation stability and fission product retention. The disadvantages are the relatively low metal density, the... 

Oxide fuels have demonstrated very satisfactory high-temperature, dimensional, and radiation stability and chemical compatibility with cladding metals and coolant in light-water reactor service. Under the much more severe conditions in a fast reactor, however, even inert UO2 begins to respond to its environment in a manner that is often detrimental to fuel performance. Uranium dioxide is almost exclusively used in light-water-moderated reactors (LWR). Mixed oxides of uranium and plutonium are used in liquid-metal fast breeder reactors (LMFBR). 

The LS-VHTR uses the same type of coated-particle graphite-matrix fuel that has been successfully used in high-temperature gas-cooled reactors such as the Peach Bottom Reactor, the Fort St. Viain Reactor (FSVR), the Arbeitsgemeinshaft Versuchsreaktor (AVR), and the Thorium High-Temperature Reactor (THTR). At this time, graphite-based fuels have been demonstrated to be compatible with only two coolants helium and fluoride salts. 

Salt selection. Unlike the reactor coolant salt, the secondary salt has no requirement for low nuclear cross sections to minimize neutron absorption. A variety of chloride and fluoride salts are potential candidates. Studies have not yet been conducted to define the preferred salt based on cost and performance requirements (compatibility with coolant salt and melting point). If appropriate low-cost salts are found, the option exists for the secondary-salt inventory to absorb days to weeks of decay heat. 

A. The material used to manufacture the flywheel of the reactor coolant pump motor will be produced by a commercially acceptable process that minimizes flaws, such as the vacuum melt and degassing process. This provides adequate fracture toughness properties under reactor operating conditions. The acceptance criteria for flywheel design will be compatible with the safety philosophy of the Pressure Vessel Research Committee (PVRC) of the Welding Research Council (WRC) primary coolant pressure boundary criteria as appropriate considering the inherent design and functional requirement differences between the pressure boundary and the flywheel. 

As for the coolant, helium, a chemically inactive gas, is used. It is compatible with the structural material and graphite, and it contributes to the reactor s high-temperature features. 

A molten salt reactor (MSR) is a reactor in which fluorides of fissile and fertile elements such as UF4, PuFg, and/or Thp4 are combined with carrier salts to form a fluid fuel. MSRs can operate as simple burner reactors with high fuel economy or with the addition of online fission product removal and can achieve breeder status. Typical operation sees molten salt flowing between a critical core and an intermediate heat exchanger. A secondary coolant salt then transfers heat to a steam or closed gas cycle. The majority of work has involved fluoride salts, as corrosion-resistant alloys have been shown to be compatible with these salts. 

Only one type of nuclear fuel has been fully demonstrated for use in high-temperature reactors for commercial applications the graphite-matrix coated-particle fuel. Although helium has historically been the coolant used in high-temperature reactors, graphite-based fuel is also compatible with one other type of coolant molten fluoride salts. For example, for over a century the aluminum industry has produced aluminum by electrolytic methods in graphite baths filled with molten fluoride salts at 1000°C. The AHTR uses a low-pressure molten fluoride salt with a boiling point of 1400°C. 

The materials used for reactor internals are chosen to be compatible with the primary coolant chemistry and, as far as is possible, to be free from elements such as carbon or cobalt, which are prone to activation. Full details of the materials used, as well as the controls on fabrication, are provided in Section 4.5 of Reference 6.1. 

Three types of metals are used exclusively stainless steels, nickel-chromium-iron alloys and, to a limited extent, cobalt-based alloys. These materials have provided many years of successfiil operation in similar control rod drive mechanisms. In the case of stainless steels, only austenitic and austenitic stainless steels are used. Where low or zero cobalt alloys are substituted for cobalt-based alloy pins, bars, or hard facing, Ihe substitute material is qualified by evaluation or test. The materials used for reactor internals are chosen to be compatible with the primary coolant chemistry and, as far as is possible, to be free from elements such as carbon or cobalt, which are prone to activation. Full details of the materials used, as well as the controls on fabrication, are provided in Section 4.5 of Reference 6.1. 

The materials used in the reactor coolant pressure boimdary conform to the applicable ASME code rules. A full list of the materials used, and a discussion of die compatibility of those materials with the primary coolant chemistry and the containment building environmental conditions, is provided in Section 5.2.3 of Reference 6.1. That same section also describes the fabrication process, which meets the requirements of ASME E, El and IX. 

The chemical and volume control system valves are stainless steel for compatibility with the borated reactor coolant. All the isolation valves are actuated by the containment isolation system in addition, they can all be actuated manually from the main control room. The containment isolation valves are described in Section 9.3.6.3.7 of Reference 6.1 a summary description is provided below. 

The CARA fuel design is adjusted to the conditions of the operating NPPs, mainly the coolant flow and hydraulic channel pressure drop, and is mechanically compatible with the refuelling machines of the vertical and horizontal channel reactors. 

Two Reactor Coolants are Chemically Compatible with Graphite-Matrix Fuel... 

Mononitride UN and UPuN fuel was initially tested in the BR-10 and BOR-60 reactors at 350—1045 W/cm and 4—9% bumup. Both showed good resistance to irradiation and low reaction rates with liquid metal coolants. They are also compatible with ferritic—martensitic steels, eg, EP-823 and EP-450 up to 800°C for 2000 h and 1200-1300°C for 5 h (Filin, 2000). In 2014-2015, hot cell examinations of UPuN fuel rods irradiated in BOR-60 and BN-600. Irradiation experiments on UPuN FAs for BREST and BN have started (Nikitin, 2015). The main design characteristics of the BREST-OD-300 are given in Table 12.7. 

A high thermal conductivity material must have a low neutron absorption cross section depending on the reactor (HoUenbach and Ott, 2010). In addition, it must have a high melting point and be chemicaUy compatible with the fuel, the cladding, and the coolant. The need to meet these requirements narrows the potential materials to SiC, beryllium oxide (BeO), and C. The following sections provide a Uterature survey on UO2 fuels composed of SiC, C, and BeO. 

Good compatibility with Pb (a potential Generation IV reactor coolant) has been reported for Ti2AlC at 650 and 800°C [137]. 

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