JPS5943384A - Control rod device for fast breeder - 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 The present invention relates to a control rod device for a fast breeder reactor using a control rod incorporating a /ζ neutron absorber for reactivity control.

In fast breeder reactors that use liquid metal sodium as a coolant, control rods containing neutron absorbers are usually inserted into and withdrawn from the reactor core from above to control the reactivity of the reactor. FIG. 1 is a conceptual diagram showing the positional relationship between a fuel assembly and a control rod during insertion and withdrawal in a typical conventional fast breeder reactor. In FIG. 1, the right figure shows the fuel assembly, the center figure shows the control rod in a fully withdrawn state, and the left figure shows the control rod in a fully inserted state.

1 is a fuel assembly, 2 is a neutron absorber built into the control rod, 3 is a fuel rod in the fuel assembly 1, 4 is a fissile material loaded in the fuel t-1 rod 3, 5 and 6 are J and upper and lower axial blankets respectively loaded in the fuel rods 3, 7 is the gas p/num in the fuel rods that accommodates the volatile materials produced by nuclear fission, 8 is! 1il1 clause 11 rod guide tube.

As shown in Fig. 1, conventionally, an effective neutron absorbing material section 2 (hereinafter abbreviated as control salary effective section) is built into a control rod.
is the length that covers the entire area of the fissile material loading part 4 (hereinafter referred to as F, ・Fuel effective part) in the fuel rod 3 in the fuel rod 3 in the fuel rod 3 in the fuel rod 1 in the fully inserted state. The lower end of the control rod effective section 2 is located at the upper end of the fuel effective section 4 when the trench is fully withdrawn. Therefore, in the fully withdrawn state, a part of the control rod effective section 2 is present at the position of the upper axial plunket 5 marked on the upper part of the fuel effective section 4.
During normal operation, neutrons are wasted and absorbed, resulting in poor neutron economy. Also, in order to sew this, the effective part of the control rod was pulled up above the seventh part of the fuel rod b-direction blanket.
It is conceivable to use one moxibustion stroke per stroke, but this would require the use of a ti control keyaki controller drive mechanism installed at the top of the reactor core, which would eventually lead to an increase in the size of the reactor vessel and containment vessel, reducing construction costs. resulting in a significant increase.

The purpose of the present invention is to eliminate the above-mentioned conventional drawbacks, and to increase the length of the control rod drive 1 + J + stroke, i.e., to eliminate wasteful absorption of neutrons during normal operation without increasing the size of the reactor vessel or containment vessel. The object of the present invention is to provide a control rod device capable of improving the economy of a nuclear reactor and, ultimately, the economic efficiency of a nuclear reactor.

In order to achieve the above object, the control rod device for a fast breeder reactor of the present invention provides a control rod effective section length that is given by the neutron absorbing material built into the control rod, by using the fissile material built into the fuel rod. The length of the effective fuel 77B is shorter than the length of the effective fuel 77B, and the lower end of the control rod effective part is positioned above the upper end of the upper part (1 fuel A: 1 effective part) when the control rod is completely withdrawn. It is characterized by:

FIG. 2 illustrates the length relationship between the control rod effective part and the fuel assembly and the positional relationship thereof when the control rod is inserted and withdrawn according to the present invention.

In this figure, what the right, center, and left figures represent,
Also, each symbol indicates the same as in FIG. As is clear from Fig. 2, the length of the control rod effective section 2 is
It is made shorter than the width of the fuel effective section 4, and the lower end of the control rod effective section 2 does not touch the lower end 1 of the fuel effective section 4 in the fully inserted state, and also does not touch the lower end 1 of the fuel effective section 4 in the fully withdrawn state. 1. than the upper end. I have one device in place.

This J match is completely inserted ↓? There may be concerns that the fact that the upper end of the control rod effective section 2 does not reach the lower end of the fuel effective section 4 may cause local distortion of the neutral f east distribution (or power distribution) during that time. , in the high-bed reactor, the mean freedom of the neutral r- is the same as <-i, so no local distortion occurs in the - of the neutral r- as seen in thermal neutron reactors. In addition, by shortening the length of the control rod fT effect section 2, the total reactivity is lowered, and the concentration of the medium F absorbent in the control rod fr'kh section 2 is increased. This can be dealt with by

Next ((-・to invention),
Ii'i', by taking the middle + '1 child economy 1-
Which one has the advantage of 1 adventure?
41, let us clarify the desirable range of control 'l (I rod A 1 effective part t) in Figure 3 with 8 light L2.

Figure 3 Q'1, R11l flD'stick! Control σ11 due to insertion of effective part 2 (this control '111I river function reaction rl
The axis to 11 is 0 and 17. The insertion depth is expressed as a relative value, and the vertical axis is the relative value of controllable reactivity. It represents. In the figure, the solid line is for the conventional example, and the broken line is for the present invention.
As is clear from the -10 solid line graph, in the conventional example, the insertion depth is 0%, that is, the fully pulled out state is 4.
3. Even if the control rod is fully inserted, the controllable reactivity of the control rod remains 2% of the reactivity when fully inserted, and this is due to the neutron absorption when fully inserted. Is it true that the two channels are being absorbed in vain even during redundant extraction? taste. This is an electrical output of 1 million k.
W N (7) 413fJJ, target high speed increase <11+
Based on the absolute value of the reactor I,'r reaction 18°, the total control rod iiJ' reactivity is 10 to 12 chi Δ.
The controllable reactivity of waste absorption is about 0.
2 to 0.24% Δ.

On the other hand, there are considerable differences in the degree of lumen needed to convert a nuclear reactor to IM for one year depending on the core configuration (1-1, 2-2).
It is about 5-6% Δ, whereas no 11i1
<Absorption will account for 3 to 10 inches. Assuming that the reactor installation f:h utilization rate is 80, and if this waste absorption is calculated as 1j11 transfer days, it will amount to 9 to 30 days. If we consider the electricity transmission sales price to be about 15 i'J/kW-hr, this means a decrease in sales of 300 million to 10 Qf per year.

and 5 for 5 z, as is clear from the broken line graph,
+ In the 11th position according to the invention, the control 1 ear function JX 1. which is outside the control in the completely withdrawn state 1 regardless of the insertion depth 0. (Since it is extremely small, it is possible to avoid wasteful neutron absorption such as the ringing in the conventional example described above, a decrease in the number of days of operation due to the noise, and a decrease in the number of unloaded units.) can.

On the contrary, if you consider the same number of driving days, fuel and FI
In the effective part 4 (the 4 knee!I basket of the fissionable substance ′ν↓ is anti-161JQ, lf* ;'), f is reduced by 3 to 10 chi (the advantage of 8 is obtained). are doing.

In Figure 3, by inserting the solid line graph to the negative side of the insertion depth, in order to take advantage of the neutron 1j4', t'ik absorption reduction effect, the control rod effective section 2 is changed to the fuel effective section. 4
Than which culm Sho's t + t no shaku - 111, 1 after Bayoi! 'j'Th'E limit Vf-value is obtained. According to Figure 3, this t(z scaling limit value is -15%
It can be seen that the hardness (corresponding to the insertion depth) is shortened. Is this 1゛] thinking-ko, υ1jI(!I
Target f! , as 1 and 11 of Gao Ke I breeder reactor, fuel Ij'no part 4 f-j sa l 00 an % upper ¥XB
Assuming a core of 1it-+ direction blunt foot 5, the length of the control rod effective section 2 will be approximately 15 m, that is, approximately 15 m or more than the length of the -L section blanket, and -r' will also be approximately It can be seen that this does not lead to further improvement in the effect of reducing wasted neutron absorption. That is,
In order to achieve the effect of reducing wasted neutron absorption, control rod effective section 2
is the granket 5 in the direction of the upper axis lj compared to the fuel effective part 4.
It can be seen that it is sufficient to shorten the length by a length smaller than lA of zero intensity 1. Furthermore, although volatile substances generated by nuclear fission are stored, the sprenano 7 is placed on one side of the fuel effective part 4. In a reactor core in which the upper part uses Szolenum type fuel rods, the entire effective fuel section 4 is located lower than in the case of Figures 1 and 2, so there is a restriction on the drive stroke of the control rods. Generally, it has been tried that there is a tendency for the control f+QI rod effective part to be slightly reduced by −+11 in the fully withdrawn state, but according to the present invention, the control f+QI rod effective part is The lower end of the neutron effective part 4 can be placed at the upper end of the effective part 4 than the lower end of the effective part 4, and as a result, wasteful absorption of neutrons can be prevented.
;can.

Furthermore, it goes without saying that shortening the length of the control rod core (11 part 2) will also have the effect of reducing the amount of radioactive waste.

μ Explanation l, 2/Thus, according to the present invention, in a fast breeder reactor, i[V! Medium PI at the time of normal/military transition: ``Because wasteful intake IIy is reduced'', about typical nuclear reactors 9
~10 days of reactor operation 16 + r, 1%, which is l (10, -fj For a kW class reactor, 11113 Of, α ~ 10 billion yen increase in income. [0]
It is said that if the number is increased, it is possible to reduce the loading of fissile material ef by 1 (11 points).Furthermore, the 4 inventions are , it also has the effect of making it possible to reduce the amount of physical damage.

[Brief explanation of drawings]

Figure 1 1j % 7x)': Useful for the next high-speed soybean fermenter:
ttll i'flll Zaikato・l? ,! yi:111
Figure 2 shows the length and positional relationship between the two parts.
Figure 1 shows the system in the actual 1KIi example of the invention (the length of the combination of Iil Keyaki and 1Iryo 1p, and the complete relationship of II'h).
J-it't, sudden turn, s''■s Figure 3 is subordinate/K example-1?
111 of the invention (this i4;
jlil accompanying people, control rod control Ij ■ ability reaction 11 (
It is a graph showing a change in the ratio zt of -. 1... Combination of 4 fuel rods, 2... Deposit (I rod effective part, 3... Fuel rod, 4... Fuel effective part,
5...L section axial blank cut, 6...Lower 'l'lll force direction blanket, 7...
are Splenano 2, 8... control rod' inner tube. t・,I generation pH person Tota・small ++ □°,'1-1 sword 2nd figure

Claims (1)

[Claims] 1. In a control rod device for a fast breeder reactor that uses a control rod with a built-in neutron absorber for reactivity control, the effective part of the control rod provided by the neutron absorber built into the control rod is The length is made 5 shorter than the length of the effective fuel section given by the fissile material contained in the fuel rod, and when the control rod is fully withdrawn, -f2Nc. A control rod device for a fast breeder reactor, characterized in that the lower end of the control rod effective section is located at a distance from one end of the twisted effective section. 2. The difference between the length of the effective fuel part and the length of the control rod effective part is less than half the length of the two-part axial blanket provided in the upper part of the fuel effective part. [The control frame for fast breeder reactor according to claim 1]