Core Shroud

The reactor vessel is a pressure vessel with a single full-diameter removable head. The base material of the vessel is low alloy steel, which is clad on the interior except for nozzles with stainless steel weld overlay to provide the necessary resistance to corrosion. Since the vessel head is exposed to a saturated steam environment throughout its operating lifetime, stainless steel cladding is not used over its interior surfaces. 

Two ring spargers, one for LPCS and the other for HPCS, are mounted inside the core shroud in the space between the top of the core and the steam separator base. The core spray ring spargers are provided with spray nozzles for the injection of cooling water. The core spray spargers and nozzles do not interfere with the installation or removal of fuel from the core. A nozzle for the injection of the neutron absorber (sodium pentaborate) solution is mounted below the core in the region of the recirculation inlet plenum. 

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Reactor Assembly. This assembly (Fig. 3) consists of the reactor vessel, its internal components of the core, shroud, top guide assembly, core plate assembly, steam separator and dryer assemblies and jet pumps. Also included in the reactor assembly are the control rods, control rod drive housings and the control rod drives. 

Fig. 25 Plots of the concentrations of oxygen (ppb), hydrogen (ppb), and hydrogen peroxide (ppb), and the calculated ECP (mVsHE) at the top inner surface of core shroud as a function of time along the CEP. Note that the concentration of hydrogen is considerably lower than the feedwater hydrogen, because of the mixing of flows from the lower plenum and because hydrogen is stripped from the coolant by boiling in the core.

At this point, it is worth enquiring if these calculations have any relationship to reality. While it is very difficult to obtain information on crack extension in reactor coolant circuits for a variety of reasons, Tang etal. [63] published the data shown in Fig. 35. The data refer to the extension of a crack adjacent to the H-3 weld on the inner surface of the core shroud of a GE BWR in Taiwan. The authors had monitored the growth of the crack as a function of time after the eleventh outage for refueling. The reactor model was the same as that employed in our previous modeling and the coolant chemistry conditions could be estimated with sufficient accuracy to make a comparison between the observed and calculated crack extensions... 

S. Suzuki, K. Kumag yi, C. Shitara, J. Mizutani, A. Sakashita, H. Tokuma, H. Yamashita, Introduction of repair and maintenance technology against SCC in core shroud, Maintenology 3 (2004) 65—70. 

For the general investigation of core seismic responses, the harmonic excitations subjected to ngid core shroud and core support plate are used in the analyses considering conservative excitation conditions. Table 1 shows the input loading conditions. 

For example, ageing of reactor internals is in almost all cases associated with irradiation assisted stress corrosion cracking. For Boiling Water Reactors (BWR) the 2 major corrosion concerns at present are indeed cracking of the core shroud/plate and possible cracking in the lower plenum region. 

TAPS-l was under annual shutdown from July 1996 to mid January 1997 for mandatory regulatory inspection of core shroud and other systems. 

Core shroud Control blade (absorber tubes)... 

Baffle thickness (ia) Core shroud Radial reflector 0.875... 

The jet pumps (Figure 3.9) are located in the annular region between the core shroud and the vessel inner wall. Each pair of jet pumps is supplied driving flew from a single riser pipe. The jet pump assembly is composed of two jet pumps and contains no moving parts. 

The core structure supporting the reactor core is located inside the reactor pressure vessel. The lower core support structure mainly serves to support the weight of the fuel assemblies, align and position the assemblies, absorb the impact of the control rods in the event of a reactor trip, and channel the flow of coolant in the reactor pressure vessel. It comprises the lower core support with flow distribution plate, the core barrel and the core shroud with core formers, and it defines the geometry of the reactor core. It remains in the reactor pressure vessel during refu-... 

Inside the reactor pressure vessel, the reactor core is fixed in position by the core internal structure consisting of the core shroud and an upper and lower core grid plate (see Fig. 1.3.). In a 1300 MWe plant the reactor core itself consists of 193 fuel assemblies arranged in a geometrical pattern inside the reactor pressure vessel as an example, a core scheme also containing mixed-oxide fuel assemblies is shown in Fig. 1.8. 

Radionuclides are also produced by neutron activation in the core support structures, the core shroud and, finally, in the wall of the reactor pressure vessel. The relative proportions of the induced radionuclides depend on the particular type of material used (mild steels and stainless steels), while their activity concentrations are much lower than in the core inner materials, due to the much lower neutron flux to which these components are exposed. 

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