JPH07191170A - Minor actinide burner reactor - Google Patents

Abstract

PURPOSE:To provide a minor actinide (MA) burner reactor which can consume MA with high efficiency, can operate for a long period stably. and is embodied in a simple structure. CONSTITUTION:Nitride of minor actinide extracted from a spent fuel is inserted in a metal cover pipe to form a MA type fuel 2 in pin shape, and a number of such fuel pins are arranged in ring form to constitute a reactor core 3. A neutron absorbing material 4 is arranged in the center opening of this core 3, and a reflector 5 is installed outside of the core 3. The core 3 is cooled by a cooling material made in sodium Na or lead Pb.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to neptunium Np extracted in a spent fuel reprocessing step of a light water reactor or a fast breeder reactor,
Actinide elements such as Americium Am and Curium Cm (hereinafter collectively referred to as minor actinides, M
(Sometimes abbreviated as A)) for a minor actinide combustion furnace that burns at a high concentration or a high ratio.

[0002]

2. Description of the Related Art Consuming minor actinides extracted from spent fuel in light water reactors and reusing them as much as possible has high energy utilization efficiency and has been drawing attention from the viewpoint of treating high-level waste liquid. As a minor actinide special-purpose furnace that specially burns this minor actinide, it is cooled by liquid sodium (Na) and plutonium (P
u-) and a minor actinide (MA) mixed Pu-
A minor actinide combustion furnace with a core using MA type metal fuel has been proposed (Japan Atomic Energy Research Institute FR '
91, Kyoto International Conference Material 19.6).

On the other hand, a minor actinide combustion furnace having a core using a MA type fuel consisting of only a minor actinide is also used from the viewpoint that a pure MA type fuel has a higher MA consumption efficiency than a Pu-MA type fuel. Proposed (Proceedings of the 1991 Autumn Meeting of the Atomic Energy Society of Japan)
A71).

The MA type fuel minor actinide special combustion furnace is an annular type fast reactor that performs batch type fuel exchange, uses a metal fuel, and arranges a blanket around the core to form a liquid metal (Na) core. Is cooled by. The proposed minor actinide firing furnace has a heat output of about 500 MWt.

FIG. 10 shows a plane of a general core structure of the conventional minor actinide firing furnace. Figure 10
, A core 21 is arranged in the center of the reactor, and the core 21 has a large number of hexagonal Np-Pu-Zr type fuels 22.
The Np-Pu-Zr type fuel 22 has a predetermined number of control rods (C / R) 23 inserted therein. A blanket 24 made of an AmCm-Pu-Y rod is arranged around the core 21. A reflector 25 made of stainless steel (SUS) is provided on the outer side of the blanket 24.

In the above-mentioned conventional minor actinide firing furnace, under control of the control rod (C / R) 23, the Np-Pu-Zr type fuel 22, which is a metallic fuel mixed with plutonium, is burned, and this Np-Pu-Zr is burned. The neutrons generated by the mold fuel 22 generate new Pu and Np in the blanket 24 to continue the operation.

[0007]

However, the above-mentioned conventional minor actinide firing furnace has the problems of fuel, blanket,
There was room for improvement in terms of operating cycle, void reactivity of coolant, and efficiency of MA consumption.

That is, although the metal fuel can be loaded with a high fuel density, the melting point is lowered, and the maximum linear output is limited. For example, the design limit value of the maximum line power of Pu-U type metallic fuel is about 500 w / cm, while M
The maximum line output design limit value of the A type metal fuel is about 300 w / cm, which is about 40% lower than that of the Pu-MA type metal fuel. In addition, metal fuels generally have a problem of increasing Na void reactivity.

In addition, since the blanket arranged around the core of the conventional minor actinide firing furnace produces Pu and MA in the blanket, it is possible to reduce the combustion defect reactivity during the operation of the furnace. In the first place, the minor actinide special-purpose firing furnace is aimed at consuming MA.
The production of MA reduces the consumption efficiency of MA.

Further, although the conventional minor actinide firing furnace performs fuel exchange by a batch system, it has been desired to develop a minor actinide firing furnace that can be continuously operated for a longer period of time.

In addition, the MA type fuel minor actinide firing furnace, which was announced in the proceedings of the 1991 Autumn Meeting of the Atomic Energy Society of Japan, has an effective multiplication factor Keff of the time passage, as described in the proceedings. Since it is decreasing with
It seems that the MA concentration in the core is not so high. In this case, the transition core from the start core of the nuclear reactor (the core of the starting configuration) to the equilibrium core (core in which the fuel component reaches a certain state) must use Pu-MA type fuel. Presumed. As described above, the core that uses fuels having different configurations at the start time, the transition time, and the equilibrium time is uneconomical because the fuel manufacturing process is complicated. Also, the low concentration of MA means that
Therefore, the development of higher concentration MA type fuel is required.

In the conventional minor actinide combustion furnace using the MA type fuel, the core shape is an annular type in order to reduce the void reactivity of the Na coolant, and the reactor output is a relatively low level of 500 MWt. However, when Na void reactivity is converted into economic units ($), the ratio βeff of effective delayed neutrons, which is a conversion coefficient, is Pu.
Since it is much smaller than about 0.4% of -U type fuel core, further reduction of void reactivity of the coolant has been desired.

Therefore, an object of the present invention is to solve the above-mentioned problems of the conventional minor actinide special-purpose kiln and to provide a simple minor-actinide special-purpose kiln capable of efficiently consuming MA and stably operating for a long period of time. To provide.

[0014]

In order to achieve the above object, the minor actinide combustion furnace of the present invention comprises a large number of pin type MAs in which a minor actinide nitride extracted from a spent fuel is inserted into a metal cladding tube. Type fuel is annularly arranged to form a core, a neutron absorber is arranged in the central opening of the core, a reflector is arranged outside the core, and the core is made of sodium Na or lead Pb. It is characterized by being cooled by a metal coolant.

[0015]

[Operation] MA of the minor actinide special-purpose firing furnace according to the present invention
By using a nitride fuel, the type fuel has an advantage that there is little problem of lowering the melting point and a high linear output can be achieved at a high concentration.

That is, the MA type nitride fuel is Pu-
Line output of U-type nitride fuel (design limit value approx. 850 w / c
m) must be reduced by about 40% as in the case of metal fuel, but the design limit value of the line output is about 500 w / cm with respect to the above 850 w / cm, which is higher than that of metal fuel Can obtain a high value.

Further, the nitride fuel generally has a lower void reactivity of Na than the metal fuel, and has an advantage that the Na void can be reduced.

In the minor actinide firing furnace of the present invention, the MA extracted from the spent fuel is made of stainless steel (SU).
By using the pin type MA type fuel inserted into the metal clad tube such as S), it is possible to have good coexistence with Na through stainless steel (SUS).

Further, the minor actinide firing furnace according to the present invention has the reflector placed directly around the MA type fuel and does not use a blanket. Since this blanket is not used, in the minor actinide special-purpose firing furnace of the present invention, new MA is not generated, and high consumption efficiency of MA can be obtained. Further, the structure of the core becomes simple, and further, the combustion reactivity swing does not increase due to the blanket, and a combustion furnace with easy operation control can be obtained.

Further, since the minor actinide combustion furnace of the present invention uses the high-concentration MA fuel extracted from the spent fuel, when the reactor is operated in the equilibrium core, fissile nuclides are generated in the MA fuel, The effective multiplication factor Keff is increased to 1
The operating period per cycle can be extended. By utilizing the fact that fissionable nuclides are generated during the operation of the nuclear reactor, it is possible to construct a one-batch core that does not require refueling, and it is possible to further extend the continuous operation. Such a long continuous operation brings advantages such as a reduction in the number of fuels manufactured during the life of the nuclear reactor plant, a reduction in the amount of radioactive waste associated therewith, a reduction in the fuel cycle cost, and the like.

[0021]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a longitudinal section of a core in a first embodiment of a minor actinide combustion furnace according to the present invention. In FIG. 1, a minor actinide combustion furnace 1 has an annular core 3 composed of a large number of pin type MA fuels 2.
have. A neutron absorber 4 is arranged inside the center opening of the annular core 3. Furthermore, core 3
A reflector 5 made of stainless steel (SUS) is arranged around the. The core 3 is cooled by Na (not shown).

The pin type MA type fuel 2 of this embodiment is
Only MA extracted from the spent fuel of the light water reactor is inserted into a stainless (SUS) cladding tube. Here, the MA is extracted from a spent fuel having a burnup of about 33 Gwd / t in a light water reactor, and has a composition of 52% Neptunium Np, 45% Americium Am, and 3% Curium Cm. ing.

The main items of the minor actinide special-purpose firing furnace 1 are shown below. Main features of minor actinide firing furnace Electric output approx. 150,000kWe Heat output approx. 400MWt Core shape Annular type core height 30cm Core equivalent radius approx. 40cm outside approx. 160cm Core fuel volume ratio approx. 48% Operating period 25 months Fuel exchange 3 batch fuel Type Nitride Number of control rods 30 Average line power About 160 w / cm Coolant Na As noted above, the core 3 of this example has an electrical output of about 150,000 kWh (heat output of about 400 MWt) and a core height Is 30 cm, the core equivalent radius is 40 cm on the inside, and 160 cm on the outside, which is a flat annular core. The MA fuel is a nitride (NpN, AmN, Cm).
N) is used, regardless of whether it is a start core, a transition core or an equilibrium core (neptunium Np52%, americium A)
m 45%, curium Cm 3%), and MA in volume ratio
It has a composition of 48% fuel, 30% coolant, and 22% structural material. The MA fuel having a smear density of 80% is used.

The minor actinide firing furnace 1 is operated for one cycle of 25 months, and the fuel is exchanged in three batches. The average line power is the normal core (about 250 w / c
m), about 160 w / cm. As the coolant, sodium Na is used.

FIG. 2 shows the change over time in the effective multiplication factor Keff from the start of the reactor of the minor actinide combustion furnace 1 of this embodiment to the equilibrium core. As shown in FIG. 2, in the core 3 of the present embodiment, fissionable nuclides such as Pu238 are generated from MA when the operation of the reactor is started, whereby the effective multiplication factor Keff is increased, and the equilibrium core from the start of the reactor. BOEC (Beginning of Equilibriu)
The increase of Keff up to m Cycle) is about 4% Δk.
This amount of increase is a value that can be sufficiently controlled with 30 control rods. In this way, the effective multiplication factor Keff increases, so that in the minor actinide combustion furnace 1 of this embodiment, unlike the normal core, the control rod is pulled out to control the output.

Further, in the minor actinide combustion furnace 1 of this embodiment, the combustion reactivity swing in the equilibrium core is about 1% Δk, which is a sufficiently small value that is easy to control. Here, the combustion reactivity swing is represented by the following formula, where Kmax is the maximum value of Keff and Kmin is the minimum value thereof during the operation period of the reactor.

Combustion reactivity swing = (Kmax-Kmin
) / (Kmax.Kmin) Further, the maximum line output of the minor actinide combustion furnace 1 of this embodiment is about 310 w / cm at the time of starting the reactor, and about 300 w / cm at the beginning of the equilibrium core, and at the end stage. Approximately 290 w / cm, which is below the line power design limit of approximately 500 w / cm.

The reactivity of Na voids used as a coolant is about 2.3% Δk for all core voids. This Na void reactivity can further increase the maximum line output of the core 3 and reduce the core volume to increase and further reduce the leakage of neutrons.

The amount of MA consumed in the minor actinide combustion furnace 1 of this embodiment calculated by the above specifications is about 27 in the equilibrium core.
The amount of MA consumed is 0 kg / year, which is almost the same as the amount of MA consumed when a MA of 10% is loaded in a normal fast reactor having 1,000,000 kWh and MOX fuel core.

As described above, according to the minor actinide combustion furnace 1 of the present embodiment, MA can be consumed with high efficiency by one type of MA fuel through the start core, the transition core, and the equilibrium core.

As described above, the minor actinide combustion furnace according to the present invention has an increased effective multiplication factor Keff during operation. Therefore, the same configuration as that of the minor actinide combustion furnace 1 does not require refueling for a long time. It is possible to construct a one-batch core capable of continuous operation.

FIG. 3 shows an effective multiplication factor Keff of the second embodiment of the present invention in which a minor actinide combustion furnace having the same structure as the minor actinide combustion furnace 1 is continuously operated without refueling.
Shows the change over time. As indicated by the curve of Keff of the nitride fuel core shown by the solid line in FIG. 3, the minor actinide combustion furnace of this example has a continuous operation period of 26 years, and the combustion reactivity swing during that period is about 5% Δk. is there. The value of the combustion reactivity swing is a value that can be sufficiently controlled by the number of 30 control rods in the minor actinide exclusive combustion furnace 1.

Further, the maximum line output in the continuous operation period of this embodiment is as shown by the solid line (nitride fuel core) in FIG.
It tends to decrease gradually with the passage of time, reaching a maximum of about 310 w / cm at the start of the reactor, and has a sufficient margin until reaching the line power design limit value of 500 w / cm. According to this embodiment, there is no need to refuel for a long period (26 years).

In the minor actinide combustion furnace of the first embodiment, MA type fuel consisting of one kind of composition is used through the start core, the transition core, and the equilibrium core, but Pu etc. are used in the start core and the transition core. It is also possible to use mixed fuels. The third embodiment of the present invention is different from the minor actinide firing furnace 1 of the first embodiment in MA
The fuel volume ratio is made smaller and the core fuel volume ratio is set to about 46%.
%. In addition to the core fuel volume ratio, the minor actinide combustion furnace of this embodiment has the same configuration as the minor actinide combustion furnace 1. In this case, the combustion reactivity swing, the maximum line output, etc. of this minor actinide combustion furnace are almost the same as those of the minor actinide combustion furnace 1 of the first embodiment.

Next, a fourth embodiment of the present invention in which the core is divided into two regions having different concentrations of MA fuel will be described. The core of the minor actinide combustion furnace of this example has an annular shape similar to the core 3 of the first example, and is divided into two regions, an inner core and an outer core (inner core area: outer core area = about 3: 2), M with 65% fuel smear density in the inner core
A fuel and MA fuel having a fuel smear density of 80% are arranged in the outer core. No neutron absorber is arranged in the central opening of the core, and the fuel volume ratio of MA is about 50%. The main features of the other reactors described above are almost the same as those of the minor actinide combustion furnace 1 of the first embodiment.

In the minor actinide combustion furnace having the above-mentioned configuration with an electric output of 150,000 kWh, the combustion reactivity swing is about 1% Δk per cycle, which can be sufficiently controlled by 30 control rods. The maximum line output is about 4
00w / cm, and the line output design limit value (500w / c
There is a sufficient margin up to m). In addition, Na
The void reactivity was about 2% Δk in all core voids.

When the electric output is 250,000 kW, the core height is 50 cm, and the fuel smear density is 150,000 kW as described above.
65% in the inner core and 80 in the outer core, similar to the core of e.
%. In this case, it is possible to operate only with the MA fuel from the start of the reactor, the reactivity to be controlled accompanying combustion is about 6% Δk, and the combustion reactivity swing in the equilibrium core is about 1% Δk / It was a cycle.
These reactivities are controllable and the maximum line power is about 4
It is 50 w / cm, which is lower than the line output design limit value. The Na void reactivity was about 3.5% Δk.

In each of the above-mentioned embodiments, the minor actinide firing furnace using the nitride fuel was used. Next, the fifth embodiment of the present invention using the metal fuel will be described.

When using the MA metallic fuel, the fuel composition is (Np, Am, Cm) -10% Zr. In this case,
The fuel volume ratio is about 45%. The fuel smear density is 75%. The other main features of the minor actinide firing furnace are almost the same as those of the minor actinide firing furnace of the first embodiment.

In the case of the minor actinide combustion furnace of this embodiment, it is possible to use only MA type fuel from the start of the reactor, the reactivity to be controlled is about 5% Δk, and the equilibrium core is used. Combustion reactivity swing of about 1%
Δk / cycle. The maximum line output is about 300w.
/ Cm, which can sufficiently satisfy the line output design limit value.

According to the core of the present embodiment, the operation of one batch system is possible, and in this case, the time change of the effective multiplication factor Keff and the time change of the maximum line output during one continuous operation period are shown in FIG.
4 is shown by a broken line. From FIG. 3, it is possible to use 2 in case of metal fuel
It can be seen that continuous operation for 6 years is possible, and the combustion reactivity swing of the equilibrium core is about 6% Δk. Also, FIG.
Therefore, the maximum value of the maximum line output is about 300 w / cm,
It can be seen that the line output design limit value is satisfied.

Next, a sixth embodiment of the present invention using an oxide fuel will be described. A minor actinide combustion furnace using this oxide fuel has an electric output of 250,000kWe.
In the case of, the core height is 50 cm, and NpO2, AmO2
, CmO2 MA oxide is used, and the fuel volume ratio of MA is 44% and the fuel smear density is 92%.

In the minor actinide combustion furnace of the present embodiment, the starting core and the transition core use Pu-MA type fuel in which MA and Pu are mixed, and the equilibrium core uses only MA type fuel.

In this embodiment, the combustion reactivity swing in the equilibrium core is about 0.5% Δk / cycle, which can be sufficiently controlled. Also, the maximum line output is 320 w / cm
Which is higher than the line output design limit value of 260 w / cm (about 60% of about 430 w / cm of Pu fuel), the problem can be solved by reducing the average line output. Further, the Na void reactivity in this example was about 3% Δk in all core voids.

In the minor actinide combustion furnace with an electric output of 150,000 kWh according to this embodiment, the fuel volume ratio is about 55%. In this case, a ductless assembly is used to construct a core using MA oxide. can do.

Next, a seventh embodiment of the present invention using MA extracted from spent fuel of a light water reactor having a high burnup of about 55 Gwd / t will be described.

While the MA fuel of the first embodiment extracted from the spent fuel of the light water reactor with the burnup of about 33 Gwd / t has the composition of Neptunium Np52%, Americium Am45% and Curium Cm3%, MA of this embodiment
Fuel is Neptunium Np43%, Americium Am4
It has a composition of 5% and curium Cm 12%. MA
As the fuel, MA nitride is used.

In this embodiment, the electric output is 150,000 kW.
When constructing the core of e, the fuel volume ratio of MA is about 43
%, And the fuel smear density is 80%. This minor actinide combustion furnace can be operated using only MA type fuel from the start of the reactor to the equilibrium core. At this time, the reactivity to be controlled over the entire equilibrium core from the start of the reactor is about 2% Δk, and the combustion reactivity swing in the equilibrium core is about 2.5% Δk.
/ Cycle and their reactivity is well controllable. Further, the maximum line power shows a maximum value at the time of starting the reactor and is about 300 w / cm, which is sufficiently smaller than the line power design limit value.

Also in the minor actinide firing furnace of this embodiment, a one-batch type core can be constructed. In that case, the period of continuous operation is about 14 years, the combustion reactivity swing is about 2% Δk, and the maximum line output is about 300 at the beginning of operation.
w / cm.

Next, an eighth embodiment of the present invention will be described in which a Na layer is arranged between the core and the upper reflector in order to reduce the Na void reactivity.

FIG. 5 shows that Na is present between the core and the upper reflector.
The longitudinal section of the core of the minor actinide firing furnace in which the layers are arranged is shown. The minor actinide firing furnace 11 of the present embodiment comprises a core 12, a neutron absorber 13 and a reflector 14, and a thickness of 1 is provided between the core 12 and the upper reflector 14a.
It has a Na layer 15 of 5 cm. In addition to having the Na layer 15, the minor actinide special-purpose firing furnace 11 has substantially the same specifications as the minor actinide special-purpose firing furnace 1.

The Na layer 15 is formed in the core 1 when Na is voided.
The leakage of neutrons from 2 can be increased, which can reduce the Na void reactivity. As a result, Na
The void reactivity is 2% Δk, which is improved over the Na void reactivity of the first embodiment.

In addition to this, by increasing the thickness of the Na layer 15, or by dividing the small flat annular type core into upper and lower parts or modularizing it, N
The a void reactivity can be suggested.

Next, a description will be given of a ninth embodiment of the present invention in which lead Pb is used as a coolant in order to reduce the Na void reactivity. The minor actinide combustion furnace of this embodiment uses lead Pb as a coolant and has a fuel volume ratio of 44%, and the specifications are the same as those of the first embodiment.

As a result of analysis in this example, it was found that the Pb void reactivity was 1.4% Δk, which was about 40% lower than the Na void reactivity.

Minor actinide special-purpose firing furnace 11 of this embodiment
Fig. 6 shows the time change of Keff from the start of the reactor to the equilibrium core at. The solid line in FIG. 6 is one cycle 25.
The graph shows the time-dependent change of Keff in the case of months, and the figure shows that the increase in Keff in this case is about 8% Δk. This increase in Keff of about 8% Δk is expected to be difficult to control with 30 control rods. In such a case, control becomes possible by increasing the number of control rods or shortening the period per cycle.

Therefore, in FIG. 6, the time change of Keff in the case of 12 months in one cycle is shown by a broken line in comparison with the case of 25 months in one cycle. From the broken line in the figure, it can be seen that the increase amount of Keff is about 5% Δk in the case of 12 cycles per cycle. The increase amount of Keff can be sufficiently controlled by 30 control rods.

The maximum line output of this embodiment is about 300.
Since it is w / cm, it is sufficiently smaller than the line output design limit value.

According to the minor actinide special-purpose firing furnace of this embodiment, a one-batch type core can be constructed. FIG. 7 shows the time change of Keff during the entire operation period during the operation of the one-batch system. It can be seen from FIG. 7 that the operating period of the minor actinide special-purpose firing furnace of this example is 30 years, and the combustion reactivity swing is about 11% Δk. The combustion reactivity swing of about 11% Δk is dealt with by setting the number of control rods to about 45.

As is clear from the above description, when the minor actinide combustion furnace of the ninth embodiment is operated in the one-batch system, the combustion reactivity swing is relatively large. On the other hand, combustion reactivity swing can be reduced by inserting fuels having different fuel volume ratios several years after the start of operation. That is, as shown in FIG. 8, one-third of the initial fuel (fuel volume ratio 44%) is calculated 3 years after the start of operation.
Is replaced with fuel having a fuel volume ratio of 40% to operate. In this case, although the total operation period is shortened by about 1 year, the combustion reactivity swing can be reduced by about 1.5% Δk.

Further, in the above operating method, by further substituting the fuel during the operation, the entire operating period can be extended without increasing the reduced combustion reactivity swing. That is, as shown in FIG.
By recharging the core with the initial fuel taken out 3 years after the start of operation 6 years before the end of the operation, the total operation period can be extended by about 5 years.

Further, by making the time point of reloading the initial fuel earlier than in the case of FIG. 8, the entire operation period can be further extended. Further, since the fuel taken out at the time of reloading in FIG. 8 is the fuel having a large fuel volume ratio that has been loaded in the core from the initial stage of operation, the fuel loaded from the initial stage is replaced with the fuel loaded three years after the start of operation. If the fuel having a low fuel volume ratio is taken out, the entire operation period can be further extended.

Next, in the minor actinide special-purpose firing furnace of the present invention, an extremely long life FP (Fiss
The operation method to eliminate the ion product) in the core is explained. In general, ultra long life F such as Te99 and I129
When P is to be extinguished in the minor actinide combustion furnace, it is necessary to increase the fuel volume in order to maintain the core criticality. However, by inserting the fuel mixed with the ultra long life FP in the middle of the reactor into the core, the ultra long life FP can be eliminated without increasing the fuel volume ratio.

That is, in FIG. 8, a pin type MA in which Te99 metal with a volume ratio of 10% is inserted into a stainless (SUS) cladding tube as the fuel to be inserted 3 years after the start of operation.
Mix mold fuel. In this case, the time change of Keff is almost the same as that of FIG. 8, and the total operation period is about 29.
Was the year.

The above-mentioned Te disappearance amount is about 160 in 26 years.
It is kg, and this amount corresponds to the amount produced by six 1.1 million kWh light water reactors in one year.

Next explained is the tenth embodiment of the invention in which the Doppler coefficient is increased. Generally, in a minor actinide combustion furnace using MA type fuel consisting of MA only, the value of Doppler coefficient is small, and increasing this coefficient is preferable for improving safety. Therefore, in this embodiment, zirconium hydride ZrH2, which is a neutron moderator, is mixed in the MA type fuel. Figure 9
The Doppler coefficient when the zirconium hydride ZrH2 is mixed at a volume ratio of 1% and 2% is theoretically calculated, and the Doppler coefficient for zirconium hydride ZrH2 having other volume ratios is interpolated.

When the volume ratio of zirconium hydride ZrH2 was 1% and 2%, the fuel volume ratio of MA was 47% and 50%, respectively, and the fuel volume ratio was higher than that in the case where zirconium hydride ZrH2 was not added (fuel volume ratio 44%). Although increased, the fuel specifications do not change significantly. As is clear from FIG. 9, when the zirconium hydride ZrH2 is added, the Doppler coefficient increases, and especially when the zirconium hydride ZrH2 is 2
In terms of% volume ratio, the Doppler coefficient is about twice as large as that without addition.

That is, according to this embodiment, the Doppler coefficient can be increased and the safety of the nuclear reactor can be improved without significantly changing the fuel specifications.

[0070]

EFFECTS OF THE INVENTION As is apparent from the above description, the minor actinide combustion furnace of the present invention constitutes the core with the MA type fuel into which the high concentration MA fuel extracted from the spent fuel is inserted, without providing a blanket. Since the MA fuel is burnt, the MA fuel can be efficiently consumed.

Further, since the high-concentration MA fuel increases the effective multiplication factor Keff during combustion, it is possible to operate with the same kind (composition) of fuel from the start of the reactor to the equilibrium core, and the operation cycle is extended. Therefore, it is possible to provide a minor actinide combustion furnace that can be operated without refueling for a long period of time.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a core portion of a minor actinide firing furnace according to a first embodiment of the present invention.

FIG. 2 is an effective multiplication factor Kef from the reactor start to the equilibrium core of the minor actinide combustion furnace according to the present invention.
A graph showing the time variation of f.

FIG. 3 is a graph showing a change with time of an effective multiplication factor Keff in one batch operation of a core using a nitride fuel and a metal fuel.

FIG. 4 is a graph showing a change in reactor operating time of maximum line power in one batch operation of a core using a nitride fuel and a metal fuel.

FIG. 5 is a vertical cross-sectional view of a core portion of an eighth embodiment of the present invention provided with a Na layer for reducing Na void reactivity.

FIG. 6 is a graph showing the time change of Keff from the start of the reactor to the equilibrium core of the ninth embodiment of the present invention using lead Pb coolant and nitride fuel.

FIG. 7 is a graph showing a change in reactor operating time of Keff in a one-batch system operation of a ninth embodiment of the present invention using a lead Pb coolant and a nitride fuel.

FIG. 8 is a graph showing the time change of Keff according to the operating method for reducing the combustion reactivity swing and the operating method for extending the total operating period of the reactor in the one-batch system operation of the ninth embodiment.

FIG. 9 is a graph showing changes in the Doppler coefficient of the tenth embodiment of the present invention in which zirconium hydride ZrH2 is added.

FIG. 10 is a plan view of a core portion of a minor actinide combustion furnace using a conventional Pu-MA type fuel.

[Explanation of symbols]

 1 Minor actinide firing furnace 2 MA fuel 3 Core 4 Neutron absorber 5 Reflector 11 Minor actinide firing furnace 12 Core 13 Neutron absorber 14 Reflector 14a Top reflector

Claims (6)

[Claims] 1. A core is constructed by arranging a large number of pin type MA type fuels in which a nitride of a minor actinide extracted from a spent fuel is inserted in a metal cladding tube in an annular shape, and inside the center opening of this core. A minor actinide firing furnace characterized in that a neutron absorber is arranged in the core, a reflector is arranged outside the core, and the core is cooled by a metal coolant made of sodium Na or lead Pb. 2. The minor actinide combustion furnace according to claim 1, wherein the core comprises an outer core and an inner core having different fuel smear densities. 3. The minor actinide combustion furnace according to claim 1, wherein the MA type fuel is a metal fuel in which a mixture of minor actinide and zirconium Zr is inserted into a metal cladding tube. 4. The minor actinide combustion furnace according to claim 1, wherein the MA type fuel is a metal fuel in which an oxide of minor actinide is inserted into a metal cladding tube. 5. The minor actinide special-purpose firing furnace according to claim 1, further comprising a Na layer disposed between the core and an upper portion of the reflector. 6. The minor actinide firing furnace according to claim 1, wherein the MA type fuel contains zirconium hydride ZrH2 as a neutron moderator.