JPH049698A - Annihilation treatment of transuranic element - Google Patents

Abstract

PURPOSE:To make annihilation treatment of transuranic elements (TRU) by arranging TRU assemblies contg. the many TRUs on the outer side of a reactor core part and operating a fast breeder to irradiate the TRU assemblies with neutrons, then rearranging the TRU assemblies in the reactor core part. CONSTITUTION:The reactor is operated after 103 pieces of the TRU assemblies contg. the <237>Np at a high ratio in the outer part 2 of the reactor core part 1. The TRU assemblies B arranged in the outer part 2 are irradiated in this way with the neutrons deceleratively leaking out of the reactor core part 1. The core fuel of the reactor core part 1 in the above-mentioned irradiation is replaced with 1/3 each at every one year irradiation. On the other hand, the TRU assemblies B are irradiated for total 4 years while being disposed in the outer part 2. Thereafter, 103 pieces of the TRU assemblies B in the outer part 2 are moved and rearranged to the TRU loading region 3 in the reactor core part 1 and the reactor is operated for 4 years. At this time, 103 pieces of the next fresh TRU assemblies B are previously arranged in the outer part 2. The above-mentioned operations are thereafter repeated and the annihilation treatment of the TRU is thus executed.

Description

Detailed Description of the Invention [Object of the Invention] (Industrial Application Field) The present invention relates to transuranium elements (Trans-Ura+tiu
The present invention relates to the annihilation processing power method for annihilation of TRUs (hereinafter referred to as 1.rTRUJ), and particularly relates to improvements in the processing method for annihilation processing of TRUs in fast reactor cores.

(Conventional technology) Spent nuclear fuel contains high-level radioactive waste such as Nejitirano, 237 (2”7Np) and Americiut 241.
(241Am), Amerin Uno, 243 (243
Am) and other TRUs, and the half-lives of these nuclides are extremely long, 2.14 million years, 432 years, and 738 C1 years, respectively, so it is desirable to eliminate them in a short period of time through nuclear transmutation, etc. There is.

One of such extinction processing methods is the conventional one, for example, the document ``Study of the Actinide-only Fast Reactor Concept'', Osugi et al., JAERI-M 83-217.1, 983, or the document rFBR NyorT RLJ’s extinction process”
, Sasahara, Matsuzai, ['' Motohara Ryoka Society, Autumn 1988 P Paper Collection F7. As shown in 1988, TRU is used in fast reactor cores where neutron energy is extremely high compared to thermal neutrons. A method has been proposed for annihilating TRUs by loading them with nuclear fission.

This extinction treatment method uses the fourth
By causing nuclear transmutation shown in Figures (a), 4(b), and 4(c) in the fast reactor core,
This eliminates the nuclide. This method is applicable because the neutron energy of the fast reactor core is high.
Am.

Neutron capture such as 243Am is difficult to occur, and the negative impact on the reactor's neutron economy due to TRU loading is relatively small (
Generally, the neutron capture cross section decreases as the neutron energy increases, as shown in FIG. )thing,
In fast reactor cores, neutron flux levels are generally about an order of magnitude higher than in thermal neutron reactors, so even though the energy-averaged TRU fission and neutron capture cross sections are small,
This takes advantage of the characteristics of fast reactor cores, such as the ability to obtain high TRU extinction efficiency due to high neutron energy.

(Problems to be Solved by the Invention) By the way, as mentioned above, when the TRU is annihilated by loading it into the fast reactor core, the main target nuclides of the TRU annihilation process are Np, Am,
The influence on the neutron economy of the reactor when Am is loaded into the fast reactor core is as follows.

For example, the number of neutrons newly generated due to the presence of 237Np in the fast reactor core, per unit time and per unit volume, can be approximately expressed by the following equation.

However, N237: the number of 237Np atoms per unit volume ν237, the number of neutrons generated per one nuclear fission when 2B7Np undergoes nuclear fission, 237, 237σr, the energy-averaged fission cross section φ of Np: Neutron Flux On the other hand, due to the presence of 237Np in the fast reactor core, the number of neutrons absorbed by 237Np and annihilated per unit time and unit volume can be approximately expressed by the following equation.

N ・(σ 1σ )・φ ・eyes・(2)
f' c 237, 237 However, σ, the energy-averaged neutron capture cross section of Np. Therefore, the influence of the presence of Np in the fast reactor core on the neutron economy of the reactor, that is, the generation and extinction of neutrons, is taken into consideration. The amount of change in the net number of neutrons is 1.237, . 237
+ (a237 +, 237 , ,, (3°f'
It will be proportional to f c . When the value of the above equation (3) is positive, loading 237Np into the fast reactor core is preferable from the viewpoint of neutron economy, and conversely, when the value of the above equation (3) is negative, loading 237Np into the fast reactor core. It can be said that loading the reactor core is not desirable from the viewpoint of neutron economy.

Here, when we actually calculate the value of equation (3) above, the system
is about 3.0, σ237 is about 0.3 burns, and σ237 is about 1.6 burns, so the value of (3) 20 becomes -1.0 burns, which is negative. That is,
Loading Np into the fast reactor core has a negative impact on neutron economics.

Similarly, when the values similar to the above equation (3) are calculated for Am and 243Am, which are the main target nuclides of the annihilation process other than Np, the following equation is obtained.

However, when ν241, 241Am undergoes nuclear fission, the number of neutrons generated per nuclear fission, the energy-averaged fission cross section of 41, 241Am, the energy-averaged neutron capture cross section of ν243, 243Am, is The energy averaged neutral f capture cross section of the fission cross section σ2 J3, which is the number of neutrons generated per nuclear fission during nuclear fission, 243 A, that is, 24.1 A''] and 243 An1 are both, As with 237Np, loading into the fast reactor core can have a negative impact on neutron economics.

Therefore, in the conventional method of eliminating T R, U using a fast reactor core, the loading of T RU into the reactor core has a negative impact on the neutron economy and degrades the criticality of the reactor.
The amount of TRU11 that can be loaded into the core is limited, which is a factor that limits the rate of TRU extinction.

The present invention has been made with these points in mind.
It is an object of the present invention to provide a method for annihilation of transuranium elements that can increase the number of TRUs that can be loaded into the reactor core and further enhance the annihilation efficiency of TRUs.

(Structure of the Invention) (Means for Solving the Problems) The present invention provides, as a means for achieving the above-mentioned L1 goal, a fast reactor in which nuclear fission is caused by fast neutrons,
TRtJ, which contains many transuranium elements with atomic number 93 or higher
5! Operate the fast reactor by placing the coalescence outside the reactor core,
After irradiating the TRU assembly with neutrons leaking from the reactor core, this TRU1,J assembly is relocated within the reactor core to operate the fast reactor (7. The feature A is that the conversion is performed.

(Function) In the transuranium element extinction treatment method according to the present invention, T
The RU assembly is first placed outside the reactor core to operate the fast reactor, and then relocated inside the reactor core to operate the fast reactor.

By the way, the main target nuclide of TRU's extinction process is
Np, Am, and 243Am have small energy-average fission cross sections and are nuclides that are difficult to fission. On the other hand, ζ is 237Np.

241, 243 Atn, Am captures neutrons, resulting in plutonium-238 (238Pu), plutonium-23
9 c2”9Pu), Americani Uno, 242m (Arn
), Amerishiuno, 242 c242Am) 42m Curiolium, 245 (245Crn)"4 is a nuclide that has a large energy-averaged fission cross section and is easily fissionable.

On the other hand, the neutron capture cross section generally increases as the neutron energy decreases, and the average energy of neutrons existing in a fast reactor is lower outside the core than in the core.
The energy-averaged neutron capture cross section of Np, A, m243Am, etc. is larger outside the core than in the core.

(7 Therefore, Nl is the main target nuclide for extinction treatment),
A fast reactor is operated by first placing a TRU assembly containing a large amount of Am, AlTl, etc. outside the reactor core.

As a result, the neutrons decelerated and leaked from the reactor core were irradiated, resulting in a pressure of 237N.

24+ 243 A m, A m, etc. efficiently capture neutrons, and P u, P u are easily fissionable.

242m 242 245 It is converted into Am, Am, Cm, etc.

Therefore, this TRU assembly is then relocated within the reactor core and the fast reactor is operated. As a result, the 238Pu
Fission-prone nuclides such as fission efficiently cause fission [1,
TRU will be destroyed. So [7, at this time,
The number of 237Np, which has a negative impact on the neutron economy, has decreased, and on the contrary, the amount of fissile materials such as 238Pu, which are easily fissionable, has increased, so the negative impact on the reactor's neutron economy is reduced compared to the conventional method. In some cases, the neutron economy of the reactor will also be 11J.

(Example) Hereinafter, the present invention will be explained with reference to the drawings.

FIG. 1 is a horizontal sectional view of a fast reactor core in which the TRU extinction processing method according to the first embodiment of the present invention is implemented, and shows a TRU assembly 1 containing a large amount of 237N, which is the target for extinction processing.
As shown by the symbol B in Fig. 1, the 03 core is not placed in the reactor core 1, where most of the nuclear fission occurs, but in the outer part 2 outside the core.
Place [5] and operate the furnace. As a result, the neutral f, which is decelerated and leaks from the core part 1, is placed in the outer part and is thermally radiated from the TRU assembly.

The reactor core 1 is loaded with a mixed oxide fuel 1 of Brutcoum and uranium, which is used as the core fuel of a normal fast reactor, and its plutonium enrichment is 20%.

In the irradiation, one-third of the core fuel in the core part 1 is replaced every year of irradiation, and the TRU assembly B is irradiated for 14 years while remaining in the outer part 2.

Thereafter, the outer part 2, 1.0' three TRU assemblies were moved and relocated to the 'l' RIJ loading area 3 in the thermal reactor core, and the reactor was operated for four years. 2, place the next new TRU aggregate heat 03 and set aside.

Thereafter, the above operation is repeated to perform the disappearance process of TR and U.

Tokoro-〇, the main target nuclide of TRU's extinction process is C237
241, 243 The nuclear fission cross-sections of Np, Am, and Am whose energies are averaged by 4 are approximately 0.3 bar and approximately () and approximately 0.3 bar and 0.3 bar, respectively, in the upper part 1 of a fast reactor. .2
It is a nuclide that is extremely small and difficult to undergo nuclear fission.

As shown in Figure 4 (C), Np241
24.3 A m, A nl or neutron-captured bridge 238 239 242m 242A
In, a certain Pu Pu, Am or 245 ('m, etc.) energy averaged 2. Nuclear fission cross section in the core 1 of the fast reactor C1 about 141 burns, about 1.9 burns 1 about 3. [1...-1 about 3.2 burns 1 about 2.6 burns, and is a nuclide that is easily fissionable.In addition, in Fig. 4(a)...(C), F',
P is a fission product (Fission Pro mountain) ct
, ), and the nucleus 14, not shown in a single frame, undergoes nuclear fission at 11, relative to the neutral 3' energy in a fast reactor, I6. The energy averaged fission cross section must be approximately 1 burn or more. Also, Fig. 4(a) to (e)
Nakano 238Np1242AII].

``The half-life of ρ decay of Am is extremely short, so we can almost ignore it and get it.

As shown in FIG. Since Np, Am,
The energy-averaged neutron capture cross section of Am'4 is
The outer part 2 is larger than the core part 1. Typical T
The following table shows the results of actually calculating the neutron capture cross sections of RU elements in the core and outside the core.

From Table 1, N is the main target nuclide for extinction treatment.
T containing many p, Anl, Arn, etc.
By first arranging the R,U assembly B in the outer part 2 of the reactor core and operating the reactor, the neutral r or'r R[1 Np, which is irradiated to aggregate B and is contained in this TRU aggregate,
Am, Am, etc. will efficiently capture neutral f. As a result, Np, Am, Am, which are difficult to undergo nuclear fission, are included in the TRU collection & body B.
etc., subject to nuclear transmutation, susceptible to nuclear fission P u
P u211.2 [11242245 Am, Am, converted to Cn1'@-.

In addition, during the above-mentioned period of irradiation,
The number of Np, Am, Am, etc. atoms present in the nuclear reactor is increased until a sufficient number of atoms are converted into nuclides that are easily fissionable.

At 12, the thermal side of the TRU aggregate? If neutrons are irradiated sufficiently at , then this T R
The U assembly B is relocated I2 into the reactor core 1 and the reactor is operated.

As a result, 3 dot product 23g within the TRU aggregate
239 242n+ 24.2 P
u, Pu, Am, Am245
Nuclides that are easily fissionable, such as 0m, efficiently cause nuclear fission, resulting in the disappearance of TRU. At this time, 237Np, A, which has a negative impact on the neutron economy of the reactor.
The number of TRU aggregates such as m, Am, etc. is small -9 and 23g 2
39 On the contrary, it is easy to undergo nuclear fission Pu, Pu242
m 242 245 A port 1. Since the amount of fissile materials such as Arri and Cm is increasing, the negative effects of 4 on the reactor's neutral f-economy are reduced compared to conventional annihilation processing, and in some cases, 2"C (i) It is also possible to improve the neutral F economy of the furnace.

Figure 2 shows TRU East Combined B as the outer part? Place, place.

This figure shows the change in the amount of 23" PuO produced as a result of neutron capture by 237Np and 237N, which are included in the TRU aggregates, when irradiation with neutral energy is carried out in a neutral state. In the evaluation, for simplicity, N
Changes in the content due to nuclear fission, etc. of p and 2:3Fy,1 were ignored.

As is clear from Fig. 2, the initial amount of 237Np decreased by approximately 2796 1 after 4 years of irradiation in the sound side part 2 of the TRU aggregate, and as a result, the amount of 238P1'' decreased by approximately 2796% among all TRUs. It makes up for 27% of the population.

In other words, when 2""Pu is loaded into the TRIJ loading area in the reactor core 1, the influence of Taking into account 2S of annihilation, the amount of change LL in the number of neutrons is obtained in the next generation.

Tata,, ν23g, 238Pu or nuclear fission,
, f: L, '? ; the number of neutrons that t41 per fission C238,2381), the energy averaged P,), the fission cross section σ238, the neutron capture cross section averaged by J energy I of 238Pu Therefore, when irradiating for 4 years in the outer part', 2 and relocating it to the TR'UJ loading area-3 in the TRU aggregate B central part, the The influence of the contained 237Np and 238Pu on the neutron economy of the reactor is expressed by the value obtained by averaging the results of equations (3) and (5) above according to the ratio of the content of C1237Np and 238Pu. The value is calculated using the following formula % 1, or 1. In advance, the TRU aggregate sound side part 2'
By irradiating C for 4 years and leaving it at 2, T RU aggregate B
The negative impact on the neutron economy of the reactor when loading the T RU assembly 4J region 3 of the reactor core section 1 is 0 compared to the conventional method in which the RU assembly B is pre-irradiated in the outer section, 2. .3/ -ko, o-o, y3...
(7), it can be seen that it has decreased to about one-third.

This means that it is easier to maintain the criticality of the reactor compared to conventional methods] 7. This reduces the concentration of fissile material loaded into the reactor core 1, reducing fuel costs. It is possible to improve economic efficiency by

In addition, by not reducing the concentration of fissile material loaded into the reactor core 1, the breeding characteristics can be reduced by the reactivity loss 4 that accompanies the operation of the 1-11 reactor, making long-term continuous operation possible. .

In other words, the equipment 61 of the TRUi tone body B in the case of the conventional method
'A:RL in the TRU aggregate core 1- until the impact on the neutral r-economy of the furnace by J.

In this case, compared to the conventional method, 110.3 to 33 times as many RU aggregates B can be loaded into the reactor core 1 at the same time. In addition, by using this method, the TRU extinction efficiency can be reduced to about 3 times compared to the conventional methodZ).

In addition, the TRU aggregate sound 37 loaded into the reactor core 1 causes nuclear fission and is converted to about 2790 Np, which is difficult to cause nuclear fission, or 238P11, which is easy to cause nuclear fission. It is possible to improve efficiency. il, te, 'r T included in RU aggregate B
Nuclear fission of RLJ; more C5TRU sound collector B
Since the output of λ- is increased by one more and the output share of the normal core fuel is reduced accordingly, the thermal margin of the normal core fuel can be increased.

FIG. 3 shows a second embodiment of the present invention.
Unlike the first embodiment, the irradiation period falling on the side part N of the aggregate aggregate is set to 1 square, and FIG. 11
) and 238P.

The influence of 237Np and 238Pu contained in TRU assembly B on the neutron economy of the reactor when TRU assembly B is loaded in the TRU equipment area 3 in the reactor core is calculated as shown in equation (6) above. As is clear from Figure 3, the amount of 237NpO in all TRUO is approximately 459
(1% PuO amount is about 535)%, so 1, (',)Xo, 451-1.6x0.55=+Q,
43 burn...(8).

By the way, in the plutonium-uranium mixed fuel used for normal fast reactor core fuel, the value corresponding to the above equation (8) for the mixed fuel nuclide of plutonium and uranium when the plutonium enrichment is 20% by weight is: It is about 0.4 burn.

Therefore, in the case of this embodiment, the T loaded in the reactor core 1
It can be said that the TRU components of RIJ assembly B are equivalent to normal fast reactor core fuel in terms of reactor neutron economy. Therefore, it is possible to maintain the criticality of the reactor by irradiating the outer part 2 for 0 hours and by using only the TRU assembly B.

Also, in this embodiment, due to the operation l'T), there is no need to combine the normal core fuel f in the entire area of the core 1, and the outer part 2 has a T increased in the year
From the RU assembly B's
Since the cooling process reduces the amount of heat generated by heating, the i' RU extinction cost can be reduced and economical efficiency can be improved since core fuel is no longer required.

In both of the above embodiments, "C" is the nuclide to be annihilated by TRU.
41 243 244c, 242. ,,,
etc., but A m, A m.

It can be applied to all nuclides that have a relatively small fission cross section and can be converted to fissile nuclei S by transmutation of neutral j' capture.

Furthermore, in both of the above embodiments, TRU disappears using two fast reactors. For example, 1'R of the outer part 2-47 outside the core part 1
, U assembly B may be irradiated and the reactor core 1 after relocation may be irradiated using different furnaces 5, and similar effects can be expected in this case as well.

〔Effect of the invention〕

As explained above, in the present invention, the TRU assembly is placed outside the reactor core, the reactor is operated, and after converting nuclides that are difficult to fission into nuclides that are easy to fission,
Relocating the U assembly to the core]2. This reduces the negative impact on the neutron economy when loading T R, U-' into the reactor core, and reduces the
The RTJ loading amount can be increased, and the TRU extinction efficiency can be improved.

In addition, since the breeding characteristics of the reactor fuel can be improved, long-term continuous operation is possible, and the power sharing by TRLl is reduced, so the power sharing of the core fuel used for reactor operation is reduced, and the reactor The thermal margin of the fuel can be increased.

Furthermore, the amount of fuel such as plutonium required for reactor operation can be reduced or eliminated, making it possible to reduce TRU extinction costs and improve economic efficiency.

[Brief explanation of the drawing]

FIG. 1 is a horizontal sectional view showing a fast reactor core in which the transuranium element extinction treatment method according to the first embodiment of the present invention is implemented;
The figure is a graph showing changes in the amount of TR,U contained in one TRU assembly according to the first embodiment according to the irradiation period outside the core. Figures 2 and 4 (a) to (c) show typical transmutation buses of TRU elements, and Figure 5 shows neutron energy and neutron capture cross sections. FIG. 1... Core part, 2... Outer part, 3... TRU equipment G1
Area, B...TRLI aggregate.

Claims (1)

[Claims] In a fast reactor in which nuclear fission is mainly caused by fast neutrons, the fast reactor is operated with a TRU assembly containing a large amount of transuranium elements having an atomic number of 93 or higher placed outside the reactor core, and the TRU assembly is attached to the reactor core. After being irradiated with neutrons leaking from the reactor core, the TRU assembly is relocated in the reactor core to operate a fast reactor and transmute the transuranic element. Disappearance processing method.