JPH0718940B2 - High conversion high combustion pressure tube reactor - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

TECHNICAL FIELD The present invention relates to a heavy water moderator pressure tube reactor capable of achieving high conversion and high burnup in order to effectively utilize nuclear fuel.

[Prior art]

In a heavy water moderator reactor that uses heavy water, which has the best nuclear characteristics among many moderators, as a moderator, if the coolant is other than heavy water, it is necessary to separate the coolant from the moderator. It has been publicly known that the form of a pressure tube type heavy water reactor is adopted. Normally, the pressure tube type heavy water reactor is
A calandria tank containing a heavy water moderator and an inert gas inside, a calandria tube arranged in a large number in the longitudinal direction of the calandria tank, and a heavy water moderator distributed through the inside of the calandria tube. It has a furnace body composed of a pressure tube for driving and a fuel assembly inserted in the pressure tube. In the pressure tube type heavy water reactor described above, in order to achieve high conversion of the new fissile material created by the neutron absorption reaction, it is necessary to harden the neutron energy spectrum, specifically, to reduce the lattice pitch or void the heavy water moderator. Although it is necessary, reducing the grid pitch makes it difficult to install pressure pipes, and it is difficult to void all heavy water moderators due to the problem of criticality, and partial voiding becomes a problem in terms of core stability. . On the other hand, in order to increase the burnup of nuclear fuel, it is necessary to increase the amount of heavy water moderator, but in this case, the void coefficient of the coolant deteriorates, which is a safety problem. If both high conversion and high burnup are to be achieved at the same time, the core configurations will be different. Therefore,
Heretofore, a method has been considered in which the core is divided into an inner gas region and an outer heavy water region, and a fuel assembly highly converted in the inner gas region is highly burned in the outer heavy water region.

[Problems to be Solved by the Invention]

As described above, in order to divide the core into two parts, the inner gas region and the outer heavy water region, it is necessary to have a double tank structure, but since the range occupied by the core expands and the pressure vessel is enlarged, There was a structural problem. In addition, there is a problem in the neutron economy, in which it is important to eliminate unnecessary absorption and leakage of neutrons. It is an object of the present invention to provide a high conversion / high combustion pressure tube type reactor capable of effectively utilizing fuel without changing the structure of the normal pressure tube type heavy water reactor.

[Means for Solving the Problems]

In order to achieve the above-mentioned object, in the present invention, the fuel assembly inserted into the pressure pipe has a structure in which an upper fuel assembly and a lower fuel assembly are axially detachably stacked via a connecting portion. In the calandria tank, the high conversion area and the high combustion area are arranged above and below the inert gas area and the heavy water moderator area. It is advisable to form a connecting portion at the upper and lower ends of each fuel assembly so that other fuel assemblies can be connected.

[Work]

The upper fuel assemblies arranged in the inert gas region without heavy water are highly converted by neutrons having high energy, and the lower fuel assemblies arranged in the heavy water region are highly burned by neutrons having low energy. By changing the water level of the heavy water moderator in the calandria tank, the ratio between the high conversion area and the high combustion area arranged above and below can be changed. When the upper fuel assembly, which has been highly converted in the inert gas region above the core, is next recombined with the placement position of the lower fuel assembly and reloaded, high combustion occurs in the heavy water region below the core, so high conversion・ High burnup can be achieved.

【Example】

In the embodiment shown in the drawings, a heavy water moderator region 5 and an inert gas region 6 such as helium and nitrogen are provided in the calandria tank 1 which is surrounded by a heavy water reflector 2. A fuel assembly 7 is arranged in a pressure pipe 4 inserted in a large number of calandria pipes 3 penetrating in the vertical direction of the calandria tank 1, and flows into the pressure pipe 4 from an inlet pipe 8 at the lower part of the core. The coolant boils in the core and flows out from the outlet pipe 9. A fuel exchange device installed below the nuclear reactor and a seal plug attached to a lower end portion of the pressure pipe 4 for enabling refueling during operation are not shown. In the fuel assembly 7 in the pressure pipe 4, an upper fuel assembly 7a and a lower fuel assembly 7b are stacked in two stages via a connecting portion 10. The connecting portion 10 is provided for each fuel assembly 7a, 7b for the reason described below.
It may be formed on the upper and lower ends of the. In the figure, the connecting portion 10 is arranged so as to approximately match the boundary between the heavy water moderator region 5 and the inert gas region 6 in the calandria tank 1, that is, the water level of the heavy water moderator in the calandria tank 1. However, the water level of the heavy water moderator can be changed appropriately. As a result, the upper fuel assembly 7a in the gas region 6 which is subjected to a high conversion action
The ratio between the portion and the portion of the lower fuel assembly 7b in the heavy water moderator region 5 that is subjected to high combustion action can be changed appropriately. When the connecting portion 10 is formed at the upper and lower ends of each fuel assembly 7a, 7b, the lower fuel assembly 7b is taken out and used when the fuel is changed by the fuel exchange device during the reactor operation or the reactor shutdown. Placed in the spent fuel pool (not shown), then take out the upper fuel assembly 7b that has been converted to a higher level, mount a new fuel assembly on it, and reload it in the core. The burned upper fuel assembly 7a can now be highly burned. Incidentally, when mainly aiming at a high conversion, it is not necessary to rearrange the upper fuel assembly 7a in the upper part of the core. I took out that samurai and reprocessed it to make a high conversion.
Obtain Pu and supply this Pu as fuel for other reactor type.

【The invention's effect】

According to the present invention, since the high conversion area and the high combustion area are arranged above and below, the reactor structure may be the same as the conventional one, and the structural structure when the core has a double tank structure is used. Problems and neutron economic problems will be resolved. Moreover, by adjusting the water level of the heavy water moderator in the calandria tank, the upper fuel assembly portion disposed in the inert gas region and subjected to a high conversion action, and the lower fuel assembly portion disposed in the heavy water region and subjected to a high combustion action. The ratio of the fuel assembly portion can be changed appropriately. Furthermore, since the upper fuel assembly, which has been highly converted in the inert gas region above the core, can be rearranged and placed in the heavy water region below the core, a high burnup can be achieved, thus achieving high conversion and high burnup. it can.

[Brief description of drawings]

The figure is an illustration of a high conversion, high combustion pressure tube reactor according to the present invention. 1 ... Calandria tank, 3 ... Calandria tube, 4
...... Pressure tube, 5 ... Heavy water moderator area, 6 ... Inert gas area, 7 ... Fuel assembly, 7a ... Upper fuel assembly, 7b ...
… Lower fuel assembly, 10… Connection.

Claims (2)

[Claims] 1. A calandria tank for accommodating a heavy water moderator and an inert gas therein, a plurality of calandria pipes arranged in a longitudinal direction of the calandria tank, and a calandria pipe penetrating the inside of the calandria pipe. In a pressure tube type reactor having a reactor body composed of a pressure tube for circulating a coolant and a fuel assembly inserted in the pressure tube, the fuel assembly inserted in the pressure tube is an upper fuel assembly. The upper fuel assembly and the lower fuel assembly are the structure in which the upper body and the lower fuel assembly are detachably stacked in the axial direction via the connecting portion. A high-conversion high-combustion pressure tube reactor, wherein a high-conversion region and a high-combustion region are arranged above and below the region. 2. A high conversion, high combustion heavy water moderator pressure tube reactor according to claim 1, wherein the upper and lower ends of each fuel assembly are formed with connection portions capable of connecting other fuel assemblies.