Control rod guide tube

Each fuel assembly that makes up the core rests on an orificed fuel support mounted on top of the control rod guide tubes. Each guide tube, with its fuel support piece, bears the weight of fuur assemblies and is supported by a control rod drive penetration nozzle in the bottom head of the reactor vessel. The core plate provides lateral guidance at the top of each control rod guide tube. The top guide provides lateral support for the top of each fuel assembly. 

Another generic problem has been the development of cracks in the control rod guide tubes of inconel which penetrate a PWR pressure vessel head. Such cracks are difficult to locate and repair because of the confined space between the tubes. After some time leaks usually develop when the cracks grow larger, ultimately requiring replacement of the vessel head. Crack formation can probably be prevented by a proper selection of material, its pretreatment and meticulous adjustment of the water chemistry. 

Besides it was required to develop and modify core components (fuel sub-assemblies, control rod guide tubes and control rods), to explore and modify electrical drives of sodium pumps, to modify a reactor refuelling system, to construct advanced failed fuel detection systems, to design and construct advanced reactor vessel integrity inspection systems, reactor vessel and auxiliary primary sodium pipeline displacement measurement systems, to remarkably improve water-sodium reaction detection systems of the water-sodium steam... 

Install the control rod guide tubes and seal the shield sections together so that they represent a continuous gas-tight disc except for the control and uranium rod openings. 

Mini multichannel analyzers connected to CdZnTe detectors (MMCC) are the preferred instruments for fi"esh fuel verification giving more credible results than Nal-based systems (Arlt et al. 1993,1997). The probe of the CdZnTe based system is less than 1 cm in diameter and can be inserted into the water tube or control rod guide tube of fuel assemblies and can therefore be implemented entirely in situ without any problems arising from interference resulting from radiation emitted by adjacent fuel assemblies. 

Control Rod Guide Tube Levd Mdnitrv Temporaiy-Modificatioo 92-020 ... 

Bayonet coupling type internal CRD blowout support (to control rod guide tube base coupling)... 

The UIS is a cylindrical structure located above the core It supports the control rod guide tubes and instrument wells in the event of an earthquake The cylindrical drum is made of 316FR with no vertical weld seam, to allow it to withstand the thermal stress due to the axial temperature distribution near the liquid surface, which changes as the liquid level changes The surface of the UIS near the core outlet is covered with Alloy 718 as a measure against thermal striping, similar to the design of the prototype reactor "Monju"... 

The core plate consists of a circular plate with round openings. The core plate provides horizontal support and guidance for the control rod guide tubes, incore flux monitor tubes, peripheral fuel supports, and startup neutron source holders. The last two items are also supported vertically by the core plate. The entire assembly is bolted to a support ledge in the core shroud. The core plate also forms a portion within the core shroud, which causes the recirculation flow to pass into the orificed fuel support and through the fuel assemblies. 

The control rod guide tube extends from the top of the control rod drive (CRD) housings up through holes in the core plate above the core plate. The control rod guide tubes, control rod drive (CRD) housings and RPV stub tubes (shown in Figure 2-10) provide an assembly of components at symmetric locations below the core which support the weight of the fuel (except for some peripheral bundles supported by the core plate) and allow the movement of control rods into and out of the reactor core to achieve reactivity control. 

The orificed fuel supports (OFS) are stainless steel castings which rest on the top of a control rod guide tube as shown in Figure 2-10. Each OFS supports the weight of four (4) fuel bundles. 

CONTROL ROD GUIDE TUBE DOWNCOMER BOTTOM PLATE... 

FIG. 2-10. Control rod guide tube and fuel support assembly. 

There have been no reported cracks in control rod guide tubes. 

The inspections (extent and point in time) depend on the event (e.g. dismantling of internal axial pumps, control rod guide tubes or edge fuel assembly elements) and shall be determined for each facUity. 

Fig. 9.3. Sectional view of the Sequoyah pressurized water reactor (courtesy of Nuclear Engineering International). A, Control rod drive head adaptors B, instrumentation ports C, thermal sleeves D, upper support plate E, support column F, control rod drive shaft G, control rod guide tube H, internals support ledge J, inlet nozzle K, outlet nozzle L, upper core plate M, baffle and former N, fuel assemblies O, reactor vessel P, thermal shield Q, access port R, lower core plate S, core support T, diffuser plate U, lower support column V, radial supports W, instrumentation thimble guides.

Fuel assembly total length Arrangement of rods Number of fuel assemblies Number of fuel rods/assembly Number of control rod guide tubes Number of grids per assembly Cladding tube material Cladding tube wall thickness... 

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