JPS60388A - Nuclear reactor fuel aggregate - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a nuclear reactor fuel assembly that improves the performance of a nuclear fuel assembly, particularly a blanket fuel assembly of a fast reactor.

[Technical landscape of invention and its problems]

For example, plutonium is the most effective fuel for fast reactors in terms of breeding rate, but this plutonium is extracted from the reprocessing of fuel used in U.S. reactors such as light water reactors. Because plutonium fuel is used as a fuel source, the plutonium fuel cycle is heavily dependent on the operation of conventional reactors, both electrically and cost-wise.

By the way, the core of a fast reactor is a core fuel assembly.

It consists of a blanket fuel east combination, control rod 9 reflector, etc. Pu--U mixed oxide is used as the core fuel assembly, and depleted uranium oxide is used as the blanket fuel assembly. Conventional blanket fuel assemblies are constructed in such a way that a plurality of fuel rods are arranged regularly within a coolant flow channel box (2). Even if the aggregate is loaded into a fast reactor, as described above, depleted uranium < u23J is 0.
Since U238) is used, the remaining amount is less than 3%, so 4
In the early stages of M (-), there is almost no heat generation, but for 2 to 5 years in the furnace (21). (The fuel rod begins to generate heat, and at the end of its life, the fuel rod has an average power of about 100 WA.
Reach XrL.

- As mentioned above, the heat removal from the fuel rods that generate heat (2) The flow t of the necessary coolant (sodium) is determined by the orifice hole at the entrance nozzle of the Plunket fuel collector. The coolant is kept constant throughout the reactor life (2 is fixed, so there is almost no heat generation), so that the cold coolant passes through the fuel assembly as it is and reaches the reactor outlet (1). In order to reduce the coolant flow temperature of the entire furnace (two effects), and in the final stage of combustion of the fuel assembly (two), a considerable amount of U238 is
, and generates fission heat, so it is predicted that it would be difficult to cool the entire reactor to a predetermined temperature if the orifice hole was kept constant as described above.

[Purpose of the invention]

The present invention has been made in view of the above circumstances, and its purpose is to reduce the increase in heat generation during the life of the blanket fuel assembly.
=Providing a nuclear reactor fuel assembly equipped with a flow rate adjustment function for adjusting the coolant flow rate (there are two types).

[Summary of the invention]

In order to achieve the object (1), the present invention provides a channel box having a coolant inlet and an outlet, a plurality of fuel rods arranged in the channel box, and a lower part of the channel box. A fixed part vane is disposed above the flow path box and holds the fuel rod, and a variable flow A is disposed above the flow path box to increase the amount of neutron irradiation (1) and increase the coolant gap flow path. The reactor assembly book (1) with grooves, the variable flow control, and the It also has a column made of a material with large radiation swelling, and the upper end of this column (=fixed flow wJ adjustment body) with a groove bottom.

Next (2) The variable R and adjustment mechanism according to the present invention will be explained.

Figure 1 shows the relationship between the amount of neutron irradiation at the degree of processing of stainless steel material and body swelling due to swelling.

As the amount of neutron irradiation increases, the swelling expansion also increases. This means that the neutron irradiation amount is the operating time (
You can think of it as increasing in two proportions. In addition, this Swelling J carving is made of materials and the degree of processing (although the two are different,
The calorific value of the fuel rods is proportional to the operating time (as the increase in power increases). (
2 becomes an increasing characteristic.

In the middle, the fuel rod output is W, and the fuel output is υ′l c′4
Assuming that the coolant flow rate is Q and the fuel assembly outlet temperature is T, the output/temperature characteristics of a conventional fuel assembly, which is obtained by keeping the coolant flow rate Q constant from the beginning of use to the end of use (-), are shown in Figure 2. (2) As shown in (2), the fuel assembly outlet temperature T increases (2) as the output W increases (1).On the other hand, the output/temperature characteristics of the fuel assembly using the variable flow adjustment mechanism of the present invention are Figure 3 (
As shown in (2) (2) Since the coolant flow rate Q flowing through the fuel assembly is increased due to an increase in the output W (1), the fuel assembly outlet temperature T is kept constant from the beginning of use to the end of use (M).
-Can be done.

[Practice of the invention 1] An embodiment of the present invention will be described with reference to the drawings.

FIG. 4 is a vertical cross-sectional view of a nuclear reactor fuel assembly according to the present invention.As shown in FIG. At the bottom of each fuel rod 2, the end plug 3 is fixed to a fixing member, for example, a fixing rod 4.In addition, the inner surface (two The lower end of the support column 5, which is made of a material with large neutron irradiation swelling, such as stainless steel, is fixed to the rod. No. 4 is fixed at the y center part (2) and the flow rate regulator 6 is placed at the upper end thereof.

At this time, the support 8 is arranged between the fuel rod 2 and the opening 7 so that the support 5 maintains the central axis (2,000 lines). On the other hand, the opening 7 is configured to form an annular gap flow path 11 along the conical surface (=) of the flow adjustment body 6. A handling head 9 for handling is provided with a coolant outlet 12.A lower end portion (2) is provided with a coolant inlet 10.

Therefore, as mentioned above (2), since the support column 5 is made of a material with large neutron irradiation swelling, it will expand as the amount of neutron irradiation increases.
The gap between the opening 7 and the miscarriage regulator 6 changes to increase. In this way, the opening 7, the flow path adjustment body 6, and the struts 5 that support the flow path adjustment body 6 constitute a variable t&adjustment mechanism that adjusts the flow rate of the coolant. In addition, in this example? As a means of fixing J several fuel rods 2, the end plugs 3 are used as fixing rods 4 (
= Fixed, but the end plug 3 may be fixed by passing through the fixing rod 4 (2), and the upper end of the fuel 2 is fixed, and the flow adjustment part is provided at the lower end. You can also do that.

The operation of the reactor fuel assembly according to this embodiment (2) will be explained in two parts.Reactor fuel assemblies are usually arranged around the core of a fast breeder reactor. In this case, the fuel rods 2 are made of 414 depleted uranium, so the yield is small, for example, about 25 w/c on average in the longitudinal direction.
It is about TL. FIG. 4 shows the mutual positional relationship between the opening 7 and the flow-in style sock 6 at the initial stage of use. At this time, all of the coolant introduced from the coolant intake port 10 flows out through the gap flow path 11 in the direction of the arrow (1st flow 11. The gap flow path 11 is small, and the longitudinal average heat generation of the fuel rods 2 is reduced by 7.
W/lx (2°C average outflow coolant is about 600°C
(So that (= coolant flow rate is A node). Therefore,
At the end of the life of the fuel rod 2 (U2 in the fuel rod 2)
The equivalent ship of 38 was converted into two to generate heat of C nuclear fission (29), and the average heat value in the longitudinal direction of the fuel rods 2 was approximately 100 Wμ. Therefore, the average outflow coolant temperature of the fuel assembly should be approximately 600'C12 (the coolant flow must be approximately four times the initial temperature of the fuel assembly). When the rod 2 is used, the strut 5 expands due to neutron irradiation swelling ≦2, and this (=therefore iN,
The gap flow path between the N adjustment body 6 and the opening 7 is set from 1 to 5 in FIG.
As shown in l' in the figure, the coolant flow rate increases accordingly, and at the end of the life of the fuel rod 2,
It becomes possible to flow approximately four times as much coolant as at the beginning of use.

Therefore, according to the fuel assembly book (2) of the present invention, the conventional blanket fuel assembly (2)
= Low-temperature coolant flows out from the reactor exit side (2) to lower the reactor exit temperature, and low-temperature coolant flows to the upper part of the reactor core (14).
This does not necessarily cause problems such as thermal stress in the structure, and the average temperature at the exit of the fuel assembly can be maintained constant by continuously increasing the coolant flow rate of the fuel assembly to 1i14 throughout its life. .

〔Effect of the invention〕

According to the present invention, the increase in heat generation during the life of a nuclear reactor fuel assembly (1 accompanied by the cold flowing through this fuel assembly) continuously adjusts the flow rate of the stamping material (2) to It is possible to provide a nuclear reactor fuel assembly that maintains a constant average temperature at the outlet of the reactor fuel assembly.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between neutron irradiation amount and swelling due to degree of processing of stainless steel, Figure 2 is a diagram of output temperature characteristics of a conventional fuel assembly, and Figure 3 is a diagram of the present invention. Fig. 4 is a vertical cross-sectional view of one embodiment 111 of the present invention, and Fig. 5 is a slope fIrlJTi diagram of the fuel assembly in the final stage of combustion in Fig. 4.1. ...biE road dance, 2...fuel rod 3...end plug,
4... Fixed rod 5... Strut, 6... Bloodshed adjustment rod 7... Opening, 8... Support 9... Handling head, 10... Inflow port 11.
...Annular gap flow path, 12...Outlet (8733) Agent: Yoshiaki Inomata, patent attorney (and one other person) Fig. 1φt(/(r”w#Iri Fig. 3) 7 Blade 1 Figure 4 Figure 5

Claims (1)

[Claims] (1) A channel box having a coolant inlet and an outlet;
Inside the flow path box (= a plurality of arranged fuel rods and the flow iJ
! A fixing member that holds the fuel rods is provided below the R box (and in front +F), and a variable member is provided above the channel box that increases the coolant gap flow path t4 as the neutron irradiation rate increases. 12) The variable flow control mechanism is equipped with a flow control mechanism and a flow control mechanism. A column made of a material with a large irradiation swelling than the material of the lees, and the upper end of the column (= fixed flow path A joint) nuclear reactor fuel assembly.