JPS59193394A - Reactor - 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] [Industrial application field] The present invention relates to nuclear reactors.

[Technical background of the invention]

When the nuclear power plant is completed, fuel will be loaded into the two reactors. The fuel that is loaded into the reactor for the first time is called the initial loading fuel. When a nuclear reactor starts operating and burns fuel, the fissile material is gradually consumed.

Along with this, the reactivity of the furnace decreases. Due to this, the output is reduced. IU: To avoid any disturbance, the blade is usually replaced once a year. After replacing the combustor (1) From the start of operation, the next replacement must be done on the driving route J') 1. Drive all 1'+j cycles → Noikle or simply one cycle and jl・PfJ- Make it.

Figure 1 (1,''; represents the change in the delayed neutron generation rate β throughout the cycle. In this figure, the curve n represents the first cycle, and the curve t) represents the equilibrium cycle. The delayed neutral r shown in this figure
The occurrence rate β is obtained by averaging the values of each nuclide using the fission rate of each nuclide as a weight. The following table shows the delayed neutral 1'-dukol fraction β of major fissile materials.

1st Table Now, in the 1st@Noikle, 'i:1111'J of the nuclear reactor is performed using only the initial loading fuel. Therefore, the fissile materials in the early stage are only 2350 and 238U, and the rate of delayed neutron generation is relatively large. This rate of delayed neutron generation is probably due to a decline in the combustion rate in the neucle. This is 2'. U's neutral understanding
[Due to the accumulation of 239p, Δ・3.

, - In the equilibrium cycle after many replacements of moi'to with Renie 1, approximately 2/3 of the total
About 3/4 of the fuel is present from the previous cycle -C
As a result, we have already experienced combustion. , - in the equilibrium force cycle, from the beginning, 23 as fissile material
This means that 9 p u exists, and the delayed neutron generation rate β has a considerably small value from the beginning of the cycle.

By the way, the delayed neutron generation rate β causes a problem in the safety of the nuclear reactor unless its value is small to some extent. This will be explained in conjunction with FIG.

FIG. 2 shows the behavior of a nuclear reactor after a positive or negative reactivity is applied. In the figure, the horizontal axis is time t
It shows the progress of storage when reactivity is applied at = 0. l: The vertical axis is L = Q 1. 'X
IJ+gero neutral J'-! , 'i', : degree n ([) )
, and at the time of , ki, during the game ('1 double density + l (t
) represents a ratio of 4. Since the original J'(), i 0) output is proportional to the neutron density, the 1
Change in neutron density after lIi point n(L)/nU
By examining N, you can get some output 4 (11th festival - j-4) of D, rj 'gi.

Now, the positional displacement curve (, in the figure shows the case where a reactivity ρ of +lE is applied, and the curve d located on the i side is ('j O,) anti-L1 degree -ρ The curves c and d such as
: It was determined by the /J culm formula.

... (1) However, in the figure, it is assumed that a Sdenob-shaped reactivity ρ is applied at each step 1-0, and! (J is the prompt neutron lifetime, J, and λ is the decay constant of the delayed neutron first nucleus.

Now, let's assume that an accident has occurred in which the number of voids suddenly increases in the reactor core3.This kind of ``J1 failure'' may be due to some reason, for example, due to the pump that circulates the cooling.
:111-(Pump) tJ Tsubu) Shi, cooling flow 1
It can be assumed that jλ is ejaculated and 《〈J〉 is exhausted. Normal nuclear reactors are designed so that the void coefficient is negative. In such a nuclear reactor, the reactivity is low F'L, and a negative reactivity ρ is applied. , time t-
When a negative reactivity ρ is applied to 0, the power of the reactor decreases rapidly once for a short period of time to J+='7iS. The difference α is given by the following formula.

54. )) It is preferable from the safety point of view of the reactor that the output is reduced by applying negative reactivity -p.

If the low -1'- ratio of the 1-force/j7 output is small, the heat generation of the fuel (J) will decrease immediately after the accident, and the fuel (J)7'5 cooling capacity will decrease without it. A situation has occurred in which there is a sudden drop in J: -c L, -J, U. For example, dirt may be combusted by overheating of the fuel. 0) 11.11 The sound is expressed by the formula (?) -3-(constant", 1, ro3.(疋-, -C' h
：The generation rate β is small, and the raw J' reactor (J's value is 1\!l'!i is the 1st 'recycle 0' with the curve F1-C). Since it is relatively large, it is necessary to take safety measures (] 1 river-4-ru・Milakura or J-+-J.

11th aspect of the invention The present invention takes into consideration the circumstances such as Io) and calculates the 1'l-'j'-proportion of 11-ratio β during the delayed onset in the first cycle.
The purpose is to provide an atom 1; Then, Brtonium l is attached to the atom '41 (::f), and the delayed neutron generation rate β is lowered from the beginning of the first cycle.

The present invention will be described in detail in Example 1 below.
Harvest at dawn.

FIG. 3 shows a typical relationship between the burn-up of 2 (jli' + IO and the delayed onset 11j' - onset) 1 ratio H.

Figure C' 1111 line 0 is 1 degree 3, O%
The uranium fuel diagram 1-1 curve [:) shows a fuel with a mixture of 8% plutonium and natural uranium. The delayed neutron hole 〈1-proportion β of the uranium oxide S+;
is small, and the combustion change becomes small -C.

In this reactor, the plutonium-mixed fuel and the uranium fuel are loaded with fissile material using the following formula: Fig. 7, 1, F, 1 shows how the delayed neutron generation rate H changes in this example. N-Q' a-) A) 11th song j special g is Uya 1 → Noik/l, J< shi, and curve 11 is j
17: 7fii-IJ cycle is J<shi. , In the second embodiment, the total neutron generation rate β at the beginning of the first cycle or each equilibrium cycle β Ikuru's first 111+ i Kooi-C is also in equilibrium → the safety of the same H+7 as Noikuru should be maintained., Tokoro-(Ko・Hatsuta+; ii Bretoniut in fuel
If the ratio of ・ is made even larger than in this example, the first →
The neutron generation rate β is in equilibrium at the initial −C'N of the Noicle →
It becomes 0 smaller than that of Noikl, and in the final stage it takes a value even smaller than the ratio shown by curve g.

In this way, the delayed neutron generation rate β becomes smaller than that of the equilibrium cycle, which means that if an accident occurs in which a positive reactivity 1) is applied to the reactor, a favorable IJ2L <No. When a positive reactivity ρ is applied, the ?th ? After a very short period of time, as shown by curve C in the figure, the reactor power decreases to ρ/
(β-ρ), and during this increase, when the reactivity ρ is equal, the delayed neutron generation rate β becomes larger as the delayed neutron generation rate β becomes smaller. Therefore, the proportion of plutonium in the initial fuel is given by Eq.
-(kiru 0-order pull+-=-Reflect on the lower limit of the ratio of Udo.ItE reactivity ρ or LIJ is added.'';
Assuming this, it is necessary to limit the delayed neutral j'-occurrence ratio β to an extent that does not become too small. For this, the fourth
As shown by curve 1 in the figure, it is necessary to reduce the delayed neutralization rate β at the end of the first cycle to at least the same degree as that of the equilibrium cycle.

The mixing ratio of uranium and plu-nium in the initially loaded fuel shown by curve 1 is as follows.

The safety design of each nuclear reactor is not necessarily the same, and there may be cases where it is necessary to consider safety more in the event of an accident where negative reactivity is applied, or vice versa. In some cases, it may be necessary to give greater consideration to safety in the event of an accident. Therefore, in general, depending on the actual situation of each nuclear reactor, it is not shown in the following formula; Good.

・ ・(5) Effects of the invention] As explained above, according to the present invention, plutonium is loaded as a part of the first fuel in the first cycle, and the balance is changed to neucle. 52 and 52, which simplify the control system that controls each transfer→noicle, can be obtained by setting the close!lt property.

4 Drawing 0) 1 in the cylinder 1 Etsumei 11 ri 1 represents the change in the neutron generation rate β between the first cycle and the equilibrium cycle in a conventional nuclear reactor] - +, 1j, gender diagram, 2nd The figure is a characteristic diagram showing the change in neutron density when positive reactivity and negative reactivity are applied, respectively. Figure 4 shows the delayed neutron generation rate in the first cycle of the initially loaded fuel loaded with plutonium. ＞Change and ・V fWi cycle, respectively, are represented,! ,
Sol', 'Ji'l: 3° application which is l's 1
Person 11 Nuclear Business Co., Ltd. Representative Person Br J! l! Shi Yamauchi +fii) AI
D.

driving wallet 2nd group t (Sa゛)

Claims (1)

[Scope of Claims] 1. lj;j characterized in that it is loaded with fuel containing -i'i+t of the initially loaded fuel, and -C pull 1-niul;
]! -Furnace. . 2. The nuclear reactor according to claim 1, wherein plutonium and uranium are contained in the initially loaded fuel within the range of .