Shield assemblies

Prior to placing in dock, Lenin NIB reactors were defueled, and shielding assembly was imloaded from Reactor 1. Electromotors of the primary coolant pump were made dead, automatic power supply was cut off and sealed, drives of control rod groups and actuators of emergency protection system were dismantled and removed from both reactors. The primary circuit was filled with bi-distilled water under a pressure of 15 kgf/cm (reactors 1) and 9 kgf/cm (reactor 2). The third-circuit system was filled with atmospheric-pressme water. 

Figure 11. Group 5 suppressive shield assembled, ready for test...

The eflFect of the various strategies used to shield the main detector from external environmental radiation eflEects can be appreciated if one notes the various counting rates found during the development of the early detectors. Libby reports the background rate for an unshielded screen-wall counter at about 500 counts per min (cpm). Placing the detector in the 8-in. steel shield assembly reduced the rate to about 100 cpm. The use of the coincidence principle reduced the background rate to about 5 cpm (27). 

Cycle time Number of cavities Operator required Size and type of press Ability to use regrind Can aluminum be used Slides and cams Dimensional concerns Painting or shielding Assembly required Fasteners required How many parts ... 

Glass window assembly Lens bonding Polycarbonate shield assembly... 

The seismic analysis of LMR core structures is a complex problem involving the dynamic interaction of many hundreds of individual fuel, blanket, and shield assemblies m a sodium environment. To simplify the core seismic problem, the cluster modeling technique sho vn in Fig. 14 for a diametral row of the core is used. The clusters of assemblies are assumed to have no relative motion between the assemblies within a cluster. The diametral row modeling approach gives conservative results and it is easier to evaluate the core seismic behavior compared to a full core model using the cluster technique. 

In 900MWe units, the capsules are irradiated along the outer surface of the thermal shield assembly. In 1300 and 1450 MWe units, the capsules are directly attached to the core barrel. In the case of Chooz-A, the thermal shield assembly was removed in 1970 and the surveillance capsules were then located under the core. The capsules are equipped with neutron dosimeters and thermal monitors, with some variations according to the reactor series. In all cases, activation dosimeters of nickel, copper and cobalt, as well as fissile dosimeters of uranium-238 and neptunium-237 are used. This instrumentation is complemented by iron and cadmium-shielded cobalt dosimeters in most cases and, in the most recent plants, also by niobium dosimeters. Each capsule contains temperature detectors based on eutectic alloys with melting points generally of 304 and 310 °C. 

The core design aims at passive shutdown capability based on the features of metallic fuel and the small-size core. A homogeneous core is used to achieve the compact radial core size which has a marked influence on the vessel size. The core consists of driver assemblies, blanket assemblies, shielding assemblies, control rods and in-vessel storage (for spent fuel). A quarter of the core (drivers and blankets) is changed every two years. 

The 9- to 3-in. sphere ratio became smaller as the distance from tlie bare and steel-shielded assembly was increased, but remained fairly constant behind the concrete shield. The albedo results obtained were within 25% of the expected dose received by the phantoms. 

The PRISM core has a heterogeneous layout of fuel, blanket, control, reflector, and shield assemblies. Three hundred and ninety-one core assemblies are broken down into 192 fuel assemblies in two TRU enrichment zones, 114 reflector assemblies, 66 shield assemblies, 6 GEMs, 9 control assemblies, and 3 ultimate shutdown assemblies. The baseline core configuration is shown in Figure 6.16. 

Sixty-six shield assemblies are located about the core to absorb neutrons and prevent excessive irradiation damage. 

Core FAs Radial blanket FAs Steel shielding assembly... 

Boron shielding assembly 0 Passive emergency protection rod... 

The reactor is a pool type (integral type) as all primary components are installed inside the reactor vessel (RV). Major primary components are the IHX, primary EM pumps, moveable reflectors which form a primary reactivity control system, the ultimate shutdown rod which is a back-up shutdown system, radial shielding assemblies, core support plate, coolant inlet modules and fuel subassemblies. 

The primary sodium circulates from the EM pumps downward, driven by pump pressure, and flows through radial shielding assemblies located in the region between the RV and the cylindrical dividing wall. The coolant flow changes its direction at the bottom of the RV and then goes upward, mainly into the fuel subassemblies and partly into the movable reflectors. 

Implementation of a supplementary surveillance programme is being considered at some plants to reduce uncertainties due to deficiencies found. In order to prevent embrittlement, flux reduction measures (low leakage loading pattern, dummy shielding assemblies) have been introduced. To reduce PTS loads due to cold water injection, heating of ECCS water has been recommended. Annealing was conducted at the Loviisa plant in 1996. 

Radial blanket PAs Steel shielding assembly Boron shielding assembly Passive emergency protection rod Reactivity compensating rod Control rod... 

The core includes fuel assemblies with MOX fuel (Fig. XXI-5), fuel assemblies of the internal blanket, fuel assemblies of the side blanket, shielding assemblies containing natural boron carbide, and cells for in-reactor storage. Design characteristics of the BMN-170 core and fuel assemblies are presented in Table XXI-2. 

Thanks to the lead interposed between the enlarged lower portion and the cote, the amphora-shaped inner vessel is subject to lower neutron damage, and this allows the eUm-ination of the numerous shielding assemblies that worrld otherwise be necessary. The eUm-ination of these shielding assemblies allows the reduction of the diameter of the inner vessel in its upper part, leaving a greater radial space for the installation of the SGs and allowing the reduction of the diameter of the reactor vessel. 

An integral primary system layout is employed (Fig. 12.4), ie, reactor core, variable frequency submersible coolant pumps, intermediate heat exchanges, safety system heat exchangers, and cold trap filters. The reactor vessel is enclosed in a guard vessel. There are no auxiliary sodium systems in the primary circuit. The reactor core consists of fuel assemblies, boron shield assemblies, and absorber rods. The central part of the core consists of wrap-spaced hexagonal fuel assemblies and cells with absorber rods. The spent fuel is stored in the reactor vessel for up to 2 years, which facilitates spent fuel cooling and eliminates the need for spent fuel storage casks. Assemblies with boron carbide are placed behind the spent fuel to protect the reactor vessel. 

The core consists of driver fuel assemblies, internal blanket assemblies, radial blanket assemblies, control rods, ultimate shutdown system (USS) assembly, gas expansion modules (OEMs), reflector assemblies, B4C shield assemblies, shield assemblies, and in-vessel storages (IVSs). There are no upper or lower axial blankets surrounding the core. A fission gas plenum is located above the fuel slug and sodium bond. The bottom of each fuel pin is a solid rod end plug for axial shielding. The reflector assemblies contain solid Inconel-600 rods. The control assemblies use a sliding bundle and a dashpot assembly within the same outer assembly structure as the other assembly types. 

We will discuss here hardware that may be found between the source and the detector a shutter or chopper, folding mirrors, windows and spectral filters, cold-shield assembly, and additional baffles to reduce stray light. We will also discuss determination of the distance between the source and detector. 

We use a cold aperture to limit the energy reaching the detector. The aperture is usually mounted in afield-of-view shield assembly, also known as a FOV shield, or cold shield. Our calculations normally assume that the energy reaching the detector... 

Simple cold shield assembly for a test dewar. (Courtesy of SE-IR Inc., Goleta... 

Figure 14.19 Aperture stop, field stop, and glare stops of a cold-shield assembly in a test dewar, without a lens.

Another application is in ferroelectric devices used to bond electrode terminals to the crystals in stacks. These adhesives replace solders and welds where crystals tend to be deposited by soldering and welding temperatures. Bonding of battery terminals is another application when soldering temperatures may be harmful. Conductive adhesives form joints with sufficient strength, so they can be used as structural adhesives where electrical continuity, in addition to bond strength, is required, as in shielded assemblies [37]. Sharpe [38] has pubhshed an excellent comprehensive review of electrically conductive adhesives. 

The gas is transported to the Brayton conversion loop(s) around or through a shield assembly designed to protect the spaceship from neutron and gamma radiation produced by the reactor. 

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