JPH05240982A - Fuel assembly for variable pressure loss pressurized water reactor - Google Patents

Abstract

PURPOSE:To increase flow rate of coolant in the core center with high power, mitigate power peaking limit and obtain a fuel loading pattern with improved neutron economy. CONSTITUTION:On the lower surface of lower nozzle 1 on a fuel assembly, a pressure loss control plate 3 is fixed with fixing screws 6 in the four corners detachably. By attaching the pressure loss control plates 3 to the fuel assemblies, water channel cross sctional area is reduced to increase the pressure loss. This fuel assembly with the pressure loss control plate 3 is arranged in the core periphery where power is low and heat removal is not a problem. By this, the coolant flow is increased in the fuel assembly in the core center where power is high to mitigate power peaking limit and a fuel loading pattern with improved neutron economy is obtained. As the pressure loss control plate is detachable, it can be removed when the assembly is used in the core center with high power in the next cycle.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure water reactor fuel assembly having an adjustable pressure loss.

[0002]

2. Description of the Related Art In a pressurized water reactor (PWR),
The inlet flow rate to each fuel assembly is uniform, and the pressure loss of each fuel assembly is also equal, so that the flow rate is almost equal regardless of the output level. Therefore, it was not possible to increase the flow rate to a specific fuel assembly in which heat removal is a problem. Further, if the structure of the lower nozzle is changed, the position of the fuel assembly will change at the time of refueling, so the core distribution of pressure loss cannot be adjusted freely and appropriately according to the power peaking situation. was there.

Further, in the PWR, by devising the fuel loading pattern of the core, the amount of neutron leakage is reduced, the output in the peripheral portion of the core is low, and the output in the central portion of the core is high in many cases. Has become a problem, and the limitation of local heat removal has been a problem in reactor operation.

[0004]

The problem to be solved is to variably adjust the pressure loss of the PWR fuel assembly at the time of refueling so as to increase the cooling water flow rate of the fuel assembly having a large output peaking and It is possible to realize a safe loading pattern with little leakage.

[0005]

In order to solve the above problems, the present invention is directed to a lower nozzle 1 (P in FIG. 2) of FIG.
A pressure loss adjusting plate 3 (having a diameter substantially the same as that of the water flow hole 2 of the lower nozzle and having a water passage hole 5 at the center thereof) is arranged in the lower nozzle of the fuel assembly F for WR. The fixing screw holes 6 are provided at the four corners) to the fixing screw holes on the lower surface of the lower nozzle 1 so as to be removably attached. The pressure loss adjusting plate is attached to the fuel assembly to reduce the cross-sectional area of the water channel to increase the pressure loss, and the fuel assembly to which the pressure loss adjusting plate is attached has a low output and the core peripheral portion where heat removal is not a serious problem. I decided to place it.

[0006]

[Function] By arranging the fuel assembly having the pressure loss adjusting plate in the peripheral portion of the core where the output is low and heat removal is not a serious problem, the flow rate in the peripheral portion of the core is reduced, and the reduced amount is attached to the pressure loss adjusting plate. Since it is related to the heat removal of the fuel assembly in the central part of the core, which has a high output, the margin for the thermal limitation of the entire core becomes large.

Since this pressure loss adjusting plate can be removed, it can be removed and used at the time of refueling when it is loaded in the central portion of the core where the output becomes high in the next cycle.

[0008]

EXAMPLE A reactor having three primary and secondary cooling heat exchange systems, namely a three-loop core (consisting of 157 fuel assemblies), has a pressure loss of 5 at the lower nozzle of the outermost fuel assembly 36.
According to the analysis when increasing by 0%, the flow rate of the central fuel assembly is increased by about 10%, and the output peaking limit can be relaxed by about 5%. This makes it possible to adopt a fuel loading pattern with improved neutron economy with less neutron leakage without reducing the thermal safety margin.

The pressure loss adjusting plate has an outer size that can be attached to the lower surface of the lower nozzle 1 (FIG. 1A) as shown in FIG. 1B, and the adjusting plate 3 has a lower nozzle size. A hole is provided at a position corresponding to the water flow hole 2, and a cylindrical shape having an outer diameter that can be fitted into the water flow hole 2 and a required inner diameter according to the amount of increasing the pressure loss is provided on the upper surface of the hole. A large number of pressure loss adjusting elements 4 are fixed.

The pressure loss adjusting plate 3 may be attached to the lower nozzle 1 by, for example, fixing it to the lower surface of the lower nozzle with screws. For this reason, there are fixing screw holes 6 at the four corners. To remove it, just unscrew this screw when refueling. It goes without saying that the pressure loss adjusting plate is not limited to this example, and various forms can be considered depending on the shape of the lower nozzle.

[0011]

As described above, according to the fuel assembly for variable pressure loss PWR of the present invention, the one having the pressure loss adjusting plate attached to the lower surface of the lower nozzle is arranged in the outermost fuel assembly having a low output, so that the fuel output can be improved. It is possible to increase the flow rate of the cooling water in the central part of the high core, relax the restriction of power peaking, and obtain a fuel loading pattern with improved neutron economy.

[Brief description of drawings]

FIG. 1A is an explanatory diagram of a lower nozzle for mounting a pressure loss adjusting plate.

FIG. 1 (B) is a structural explanatory view of a pressure loss adjusting plate.

FIG. 2 is an explanatory diagram of a PWR fuel assembly.

[Explanation of symbols]

 1 Lower Nozzle 2 Lower Nozzle Flow Hole 3 Pressure Loss Adjusting Plate 4 Pressure Loss Adjusting Element 5 Water Passage Hole for Pressure Loss Adjusting Element 6 Fixing Screw Hole F PWR Fuel Assembly

Claims (1)

[Claims] 1. A fuel assembly for a pressurized water reactor,
A pressure loss adjusting plate having a cylindrical pressure loss adjusting element having a water passage hole at the center is detachably attached to the lower surface of the lower nozzle having a plurality of water flow holes by using screw holes provided in the adjusting plate. A variable pressure loss pressurized water reactor fuel assembly characterized in that: