Reflector Movement

The assumption is that once the feedback associated with temperature is known the negative feedback coefficient for the reactor can be estimated. This will determine if sufficient excess reactivity is present for the desired mission lifetime. The dimensions of the reactor when heated to the operating temperatures of 1300 K for peak fuel temperature and 860 K in the pressure vessel are shown in Table 5-2  

This ensures that while the volumes of components in the core are changing, the mass of each material remains constant. Finally, the cross sections of the materials being used in the core were corrected to those at operating temperature The vast majority of the materials in the core do not have readily available cross sections at the desired temperature. The NJoy code was used to generate cross sections for the different materials in the reactor [MacFarlane, 1994]. The temperatures used were the peak values from the FEPSIM model. These temperatures are probably somewhat high, but are a much better approximation than using room temperature cross sections. This run resulted in a k-effective of 1.022 0.001. The net reactivity swing of the system was 2. With a total excess reactivity of 5.7 this leaves another 3.7 for bumup and other losses. 

Increasing the thickness of both the rhenium liner and the uranium nitride pin were required in the reactor design to meet the safety conditions. During normal operations the rhenium had a negative effect on the k-effective but was countered by the extra fuel in the core. In two of the three accident scenarios, the neutron spectrum is more thermal than during normal operation due to the addition of water to the core. For the dry sand accident case, the spectrum is faster than the normal operation case. For the accident scenarios, the extra thermal absorption of neutrons from the additional rhenium dominated the effects from the additional fissionable fuel. 

In this scenario the reactor is immersed in water, and the gas flow region is flooded. It is assumed that the radial reflectors are all removed by any splashdown into water. This scenario results in the moderation of the fast neutrons and normally the increase in cross section with decreased neutron energy would result in an increase in reactivity. The inclusion of rhenium in the core between the fuel and the NblZr cladding negates this effect, as it is a Spectral Shift Absorber. SSA s are materials that are relatively transparent to neutrons in the fast spectrum but a massive absorber at the lower end of the energy spectrum [King, 2005]. 

The neutron multiplication factor (k-effective) was 0.964 0.001, well below the desired value of 0.985. 

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The exact position of reflectors within the weld volume is calculated by means of the known probe position plus weld geometry and transferred to a true-to-scale representation of the weld (top view and side view). Repeated scanning of the same zone only overwrites the stored indications in cases where they reach a higher echo amplitude. The scanning movement of the probe is recorded in the sketch at the top, however, only if the coupling is adequate and the probe is situated within the permissible rotation angle. 

The 4S employs a reactivity control system with an annular reflector in place of the control rods and driving mechanisms which traditionally require frequent maintenance service. Reactivity is controlled only by the vertical movement of the annular reflector during plant startup, shutdown and power generation, thus eliminating the necessity for complicated control rod operations. Although this reactivity control method using a reflector has been studied in some projects using this method for the core bum-up phase is a new approach. 

The reflector is moved upward by the hydraulic pump during start up. During power operation, the reflector is held by the hydraulic system and gradually moves up for bum-up compensation at a constant speed of Imm/day without any speed control system. To attain this very slow speed, a reduction mechanism composed of paradox planetary gears is installed. The technical reliability of the gears has been demonstrated elsewhere. However, a spare set of gears is installed in the 4S in case of trouble. To shut down the reflector, the scram valve is opened in the hydraulic circuit. When the reflector lowers Im, the core reaches the subcritical cold shutdown state. The length of the downward movement of the reflector is determined by the capacity of the hydraulic cylinder. It cannot move otherwise. 

One of the excellent features of the 4S is that it is simple to operate. There are no feedback control systems and no human intervention is required. All reactivity control is performed by the automatic movement of the reflector as shown in Fig. 13. 

Figure 15 shows the changes in system parameters as a function of time in the event of a sudden 20% loss of power. It takes 10 minutes for the reactor to shift to the new plant conditions corresponding to the load since each system or component has a time lag due to thermal inertia. No movement of the reflector is required. 

All reactivity during plant operation is controlled just by moving the reflector without feedback control systems. TTius, a fine movements of the reflector are required. The technologies proposed for this purpose are all new to the nuclear industry, but are tried and tested in other fields. Reliability experiments are needed. 

The machine configuration XCFZ determines the placement of the LT on the rotary table associated with the movement of rotation axis around the z-axis. Meanwhile the reflector will occupy the position reserved for the tool (Fig 4). 

The LT is a measuring instrument that tracks the movement of a reflector and calculates its position in spherical coordinates. The distance to the reflector (d) can be measured by an interferometer (IF) or by an absolute distance meter (ADM), while the inclination angles (cp) and azimuthal (6) are measured by two angular encoders. The reflector returns the laser beam, where the beam strikes a position sensor (PSD) that detects any change in position causing the movement of the axes of LT so that the laser beam is incident on the optical center of the reflector. Thus the LT head constantly monitors the position of the reflector. 

Description Trucks or tractor-trailer combinations, due to their length and lower maneuverability, may be struck by other vehicles because the other driver does not see the vehicle and its movement in time. Such drivers can be assisted by making sure that the truck s lighting system and reflectors are adequate. The truck driver should use extra care in crossing traffic lanes and making turns during adverse visibility conditions. 

Applications and uses automotive components, electrical equipment subjected to high temperatures, parabolic reflectors, solar energy systems, movement sensors, surfboards, golf cars, lawn and garden equipment, sporting goods, automotive exterior parts, safety helmets, and building materials. 

Figure 4.23 Experimental realization of SHG (013 = 2wi) in NLO crystals, (a) Collimated input beam (b) focused input beam (c) external cavity enhancement of input beam Mj, M2 are high reflectors for oji, but M2 is transmitting for 0)3. In the centre part, beam walk-off compensation is indicated, by counter-angular (-0) movement of a glass block. On the right, co and 2(u wave separation by a blocking filter (top), a polarizing beam splitter (PBS, middle), ora prism (bottom) is indicated...

The 4S reactor employs a burnup control system with an annular reflector in place of the control rod and its living mechanism. Burnup control by vertical movement of the annular reflector eliminates the necessity for complicated control rod operations. 

The length of the downward movement of the reflector is determined by the capacity of the hydraulic cylinder. It cannot move further. 

The 4S-LMR incorporates neutron reflectors to control the core reactivity without neutron absorber rods. The reflectors are driven from outside the reactor vessel and move very slowly the movement speed is below 1 mm/day. Electromagnetic pumps are used for primary coolant circulation. Incorporation of these design features eliminates fast moving or rotating components, contributing to a decreased component failure and reduced maintenance. 

Core burn-up reactivity compensation system Annular reflector upward movement with a very low speed, below 1 mm/day... 

The unprotected transient overpower (UTOP) events were analyzed to estimate the allowable external reactivity insertion. In the 4S-LMR, slow upward movement of the reflector is used to compensate the bum-up reactivity loss. An UTOP is then the event initiated by an inadvertent reflector lifting without scram. The analytical assumptions used for the reference UTOP case are summarized below ... 

The 4S has a long-life core and an innovative core burn-up control system based on upward movement of the reflectors surrounding the core these are essentially innovative features never applied in commercial power reactors before. A demonstration of these features in the operating prototype reactor would be required before the 4S-LMR can be licensed for commercial operation. 

Vertical movement of the annular reflector during plant operation, including the start-up and shutdown, is the only mechanism for reactivity control provided for in the 4S-LMR. The reflector is installed inside the reactor vessel and heat generated in the reflector is removed by sodium. 

These corner-cube reflectors guarantee that the incoming light beam is always reflected exactly parallel to its indicent direction, irrespective of slight misalignments or movements of the travelling reflector. The two partial beams (BS1-T1-M3-M4-T2-BS2 and BS1-P-T3-P-BS2) for the reference laser interfere at the detector PDl, and the two beams BS2-T2-M4-M3-T1-BS1 and BS2-P-T3-P-BS1 from the unknown laser interfere at the... 

The upper core restraint (UCR) blocks could also be realized with C/C materials. The functions of UCR are to limit the lateral movement of the replaceable reflector and fuel columns at the upper end of the reactor core, thus ensuring a uniform flow of primary coolant gas. High temperature strength and stiffness are required for these components [20]. The lower floor blocks (LFBs) are located toward the bottom of the reactor and must support its weight, as well as ensure its vertical and lateral positioning. C/C materials could constitute two of the three layers of the LFB structure. 

A reflector made up of twelve segments (sliders) is assumed for reactivity control. Each segment is controlled individually by a stepper motor. Only one segment is moved at a time. The assumed increment of movement is one millimeter per step. 

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