JP5090687B2 - PWR nuclear fuel rod-based BWR square nuclear fuel assembly manufacturing method and nuclear fuel assembly - Google Patents

Description

The present invention relates to a square nuclear fuel assembly that can be loaded into a boiling water reactor.

FIG. 1 is a schematic perspective view of a conventional square nuclear fuel assembly (30) containing nuclear fuel material to be loaded into a boiling water reactor (BWR) (Patent Document 1). A conventional square nuclear fuel assembly (30) includes a cylindrical nuclear fuel rod (31) enclosing a number of nuclear fuel materials arranged in a square lattice, and an upper side supporting the upper and lower ends thereof. A coupling plate (32) and a lower coupling plate (33), and several spacers (34) which are positioned in the middle of the height of the nuclear fuel rod (31) and regulate the distance between the nuclear fuel rods (31); It is composed of a structural material with a channel box (35) that covers four sides. The spacer (34) has a square shape with a spacer outer frame (36) having an appropriate rigidity and thickness δ.
Fig. 2 is an overview of a conventional boiling water reactor nuclear fuel rod (31). A cladding tube (41) made of Zircaloy 2 which is an alloy of zirconium, an upper end plug (42) and a lower end plug (43) for hermetically closing the upper and lower opening ends of the cladding tube (41), a spring (45), , Composed of a structural material composed of an upper plenum (48) and a large number of nuclear fuel pellets (44) formed by cylindrically sintering concentrated uranium oxide as a nuclear fuel in a cladding tube (41) .
A cross-sectional view of a conventional square nuclear fuel assembly (30) at a height where the spacer (34) is not located is shown in FIG. 3 (Non-Patent Document 1). The control rod side leakage water passage (51) and the control rod opposite leakage water passage (52) are arranged in a lattice shape. A cooling water passage (49) is provided between the nuclear fuel rods (31). Fast neutrons generated by fission are decelerated by water, causing fission of uranium 235 (U235) violently. Therefore, the concentration of U235 can be reduced as the nuclear fuel rod (31) comes closer to the control rod side leakage water passage (51) or the leakage water passage (52) opposite to the control rod. You can save U235. U235 enrichment example
The enrichment of nuclear fuel rod (1) with enrichment No. 1 is 4.9wt%.
Concentration No. 2 nuclear fuel rod (2) has a U235 enrichment of 3.6 wt%.
The enrichment of nuclear fuel rod No. 3 (3) has a U235 enrichment of 3.0 wt%.
The U235 enrichment of the nuclear fuel rod (4) with enrichment No. 4 is 2.3 wt%.
The gadolinia-added nuclear fuel rod (5) has a U235 enrichment of 3.0wt% and a gadolinia addition ratio of 4.5wt%.
It is.
One of the measures to reduce power generation costs is to burn nuclear fuel assemblies for a long time. Therefore, I want to increase the U235 enrichment. Gadolinium is added to U235 as a flammable poison with a large thermal neutron absorption effect because the initial excess reactivity cannot be suppressed with the existing control rod alone. Gadolinium that has absorbed neutrons has a smaller thermal neutron absorption effect.
The water rod (6) is a hollow Zircaloy tube for enhancing the fast neutron moderating action at the center of the conventional square nuclear fuel assembly (30), and low-speed water flows therethrough.
FIG. 4 shows a core plan view in which a conventional square nuclear fuel assembly (30) is disposed at a height where the spacer (34) is not located when the reactor is shut down where the control rod (60) is inserted. . The distance P between adjacent nuclear fuel rods (31) is set to P = D + Δ in consideration of the nuclear fuel rod interval Δ of 1 mm or more. The unit cell width L surrounded by the dotted line is half the distance LL between adjacent control rod centers. Therefore, the channel box width CL must be less than or equal to L. If the channel box thickness is Σ and the spacer outer frame thickness is δ, then the channel box side width CL is CL> P × (m-1) + D + if the arrangement of nuclear fuel rods (31) is m × m δ × 2 + Σ × 2. Assuming that half of the control rod thickness is S, the gap between the control rod surface and the channel box is h, and the half of the adjacent channel box gap is g, the channel box width CL is LShg>CL> P × (m-1 ) + D + δ × 2 + Σ × 2 makes it possible to load a conventional BWR defined by a square unit cell width L.
Fig. 5 shows the main specifications of PWR and BWR using uranium oxide (UO2) as nuclear fuel. The column “BWR square nuclear fuel assembly” is the main specification of the conventional square nuclear fuel assembly (30) cited from Non-Patent Document 2.
: Sho 61-37591, "Nuclear Fuel Assembly" ： Japan Atomic Energy Research Institute, 2001, JAERI-Research 2001-046 “Proposal and analysis results of benchmark problems related to reactor physics of light water reactor next generation fuel” : Journal of the Atomic Energy Society of Japan, 2004, Vol46 ~ 47 “Series Lecture Basics of Nuclear Fuel Engineering”.

The mainstream nuclear power reactors in the world are pressurized water reactor (PWR) and boiling water reactor (BWR).
The “PWR nuclear fuel rod” column in FIG. 5 shows the main specifications of the PWR nuclear fuel rod, but the difference is small compared to the “BWR square nuclear fuel assembly” column. If any one of U235 enrichment, cladding inner / outer diameter, length, material, and pellet diameter is the same, the cost can be reduced by scale.
In particular, when a mixed oxide (MOX) of plutonium (Pu) and uranium (U) is used as a nuclear fuel, the reprocessing cost of Pu is high, so the cost reduction of the MOX fuel assembly is required.

The square nuclear fuel assembly for BWR is the same as the nuclear fuel rod for PWR, “U235 enrichment, pellet shape, inner and outer diameter nuclear fuel rods” are arranged in a square shape, fixed with spacers and upper and lower fittings, and enclosed in a channel box. To do. The length of the cladding tube is adjusted according to the BWR core. In the channel box, the side width CL of the square is adjusted according to the unit cell width L so that it can be loaded on the BWR loaded with the conventional square nuclear fuel assembly (30).
In the MOX core, BWR has voids, so the effect of gadolinium is small because the neutron moderation effect is not as good as PWR. Therefore, what is called a so-called combustible poison and moderator, which has a large thermal neutron absorption effect and changes to a large neutron moderation effect when absorbing thermal neutrons, is loaded. For example, natural lithium (Li) includes lithium 6 (Li6) and lithium 7 (Li7) that are slightly different in weight. Li7 has a small neutron absorption effect and acts as a moderator. Li6 has a large neutron absorption effect, and when it absorbs neutrons, it becomes helium (He) and gaseous tritium (T). T has a large neutron moderating action. If there is zirconium (Zr) which is a hydrogen storage metal nearby, T is stored in Zr and fixed there. However, since Zr becomes brittle, it is difficult to coexist with the nuclear fuel that generates heat. Therefore, the Li-containing material enclosed in the Zr capsule is filled into the cladding tube (41).
Natural boron (B) includes boron 10 (B10) and boron 11 (B11) that are slightly different in weight. B11 has a small neutron absorption effect and acts as a moderator. B10 has a large neutron absorption effect, and when it absorbs neutrons, it becomes helium (He) and Li7. If there is oxygen in the vicinity of Li7, it is fixed as lithium oxide.
In the future, if the core design of both BWR and PWR is modified to increase the number of common parts, further cost reduction is expected.

  The BWR square nuclear fuel assembly can be manufactured from the same nuclear fuel rods that make up the PWR nuclear fuel assembly, which not only enables mass production, but also reduces the manufacturing cost of the PWR nuclear fuel assembly. Cost can be reduced.

  We were able to provide a square nuclear fuel assembly with low power generation costs and high safety.

FIG. 6 is a schematic view of a square nuclear fuel assembly (230) using PWR nuclear fuel rod elements of the present invention. The main specifications are shown in the column of “Invention BWR Example 1” in FIG. The shape and dimensions of the conventional square nuclear fuel assembly (30) for BWR are not changed, the material of the cladding tube (41) is Zircaloy 4 which is the same as PWR, and the enrichment of U235 is used in PWR `` 4.8wt % Or 4.1 wt% or 3.4 wt% "was used. The nuclear fuel pellet radius loaded on the nuclear fuel rod is rp,
The U235 enrichment of the No. 1 pellet-filled nuclear fuel rod (231) will be 4.8 wt% used in PWR from the original 4.9 wt%. Since the output decrease is about 4.8 / 4.9, the change is small.
The U235 enrichment of enrichment number 2 double-pellet-filled nuclear fuel rod (232) compensates for the decrease in U235 enrichment of enrichment-number 1 pellet-filled nuclear fuel rod (231) to 3.7 wt% from the original 3.6 wt% In order to increase it, the U235 concentration 4.1 wt% uranium oxide powder used in PWR is used as a raw material to produce a cylindrical green pellet before sintering with an outer diameter of rp and an inner diameter of 0.756 x rp. U235 oxide powder with a concentration of U235 of 3.4 wt% is loaded into a cylindrical green pellet, which is sintered into a 3.7 wt% double pellet. Since the output rise is about 3.7 / 3.6, the change is small.
The U235 enrichment of the double pellet-filled nuclear fuel rod (233) with the enrichment number 3 is 3.0 wt%, the same as the original. Made from uranium oxide powder with U235 enrichment of 3.4 wt% used in PWR as raw material, cylindrical green pellets before sintering with outer diameter rp and inner diameter 0.385 × rp are made with natural U concentration 0.7 wt% uranium oxide powder Loaded into cylindrical green pellets and sintered into 3.0wt% double pellets.
The U235 enrichment of No. 4 double pellet-filled nuclear fuel rod (234) is 2.3 wt%, the same as the original. Made from uranium oxide powder with U235 enrichment of 3.4 wt% used in PWR as raw material, cylindrical green pellets with an outer diameter of rp and an inner diameter of 0.638 x rp are made and sintered with uranium oxide powder with a natural U concentration of 0.7 wt%. Loaded into cylindrical green pellets and sintered into 2.3 wt% double pellets.
The U235 enrichment of gadolinia-added nuclear fuel rods (235) will be changed from the original 3.0 wt% to 3.4 wt% used in PWR. The output increase of about 3.4 / 3.0 times is sufficiently small by gadolinia in the early stage of combustion. Even at the end of combustion, it is smaller than the double-pellet-filled nuclear fuel rod (232) with enrichment of U235 enrichment of 3.7 wt%, so the increase in pellet center temperature due to the decrease in heat conduction due to the addition of gadolinia impairs the integrity of the nuclear fuel rod It is not a thing. Zircaloy 4 water rod (236) is made of Zircaloy 4 same as PWR and enhances neutron moderation effect like conventional water rod (6).
In this example, in order to obtain the required U235 enrichment, it can be achieved by mixing the U235 enrichments used in the PWR or by adding and mixing natural uranium, but it is somewhat difficult to mix uniformly. . The high concentration of U235 on the side of the cladding tube to which heat is removed, as in this example, lowers the pellet center temperature. Good for fuel integrity.

FIG. 7 is a schematic view of a PWR nuclear fuel rod multi-element utilization type square nuclear fuel assembly (240) of the present invention. Main specifications are shown in the column of “Invention BWR Example 2” in FIG. The shape and dimensions of the conventional square nuclear fuel assembly are not changed, and the enrichment of U235 is 4.8wt%, 4.1wt% or 3.4wt% used in PWR, and the cladding tube material is the same as PWR. Zircaloy 4 is characterized in that the length, outer diameter, and inner diameter of the cladding tube are the same as those used in the PWR. The nuclear fuel rod arrangement can be made 12 × 12, the output per nuclear fuel rod can be reduced, and the safety can be further improved.
The enrichment No. 1 PWR same cladding tube nuclear fuel rod (241) has the same U235 enrichment as 4.8 wt% as PWR. The enrichment No. 2 PWR identical cladding nuclear fuel rod (242) has a U235 enrichment of 4.1 wt%, the same as PWR. The enrichment No. 3 PWR identical cladding tube nuclear fuel rod (243) has U235 enrichment of 3.4 wt%, which is the same as PWR. The PWR same cladding tube nuclear fuel rod (244) with gadolinia added is a nuclear fuel rod in which gadolinia is added to Uwt. Inside the zircaloy 4 frame (246) made of zircaloy 4, a gadolinia-added zircaloy 4 lining (247) is applied to further reduce the initial excess reactivity. The inside is slow running water (248).
Most of the elements use PWR elements, so the cost can be reduced by mass production.
If the width of the channel box (35) is increased by about 0.5 cm, the nuclear fuel rod arrangement can be made 13 × 13, and the output per nuclear fuel rod can be further reduced, thereby further improving the safety.

In recent years, a nuclear fuel assembly using MOX, which is a mixed oxide of U and Pu, as a nuclear fuel has been designed to burn off surplus Pu.
Figure 8 shows a conventional BWR MOX square nuclear fuel assembly (300) loaded on a D-lattice BWR with a nuclear reactor structure where the control rod side leakage water passage (51) is wider than the leakage water passage (52) opposite to the control rod. FIG. Fig. 9 shows the main specifications of PWR and BWR using MOX as nuclear fuel. An example of the specification of a conventional nuclear fuel assembly using MOX for BWR square is shown in the `` Conventional BWRMOX '' column, and an example of a specification of a conventional fuel rod using MOX for PWR is shown in the `` Conventional PWRMOX '' column (non-patent Reference 3). Note that the gap between the pellet and the inner side of the cladding tube is approximately absent, but in practice, it is almost the same as the value shown in FIG.
The inner width and outer width of the channel box (35) of the conventional MOX square nuclear fuel assembly (300) for BWR are the values described in the column of `` Conventional BWR square nuclear fuel assembly '' in FIG. The same.
The nuclear fuel rod (301) with the Pu enrichment number 5 has a Pu enrichment of 4 wt%.
The nuclear fuel rod (302) with Pu enrichment number 4 has a Pu enrichment of 6 wt%.
The Pu enrichment No. 3 nuclear fuel rod (303) has a Pu enrichment of 10 wt%.
The Pu enrichment No. 2 nuclear fuel rod (304) has a Pu enrichment of 12 wt%.
The Pu enrichment No. 1 nuclear fuel rod (305) has a Pu enrichment of 16wt%.
The gadolinia-added nuclear fuel rod (306) has a Pu enrichment of 4 wt%.
In the center, a large square water rod (307) is arranged to enhance the deceleration effect.
Since Pu emits stronger radiation than U, storage management is difficult. Therefore, the manufacturing cost is increased. We want to simplify production as much as possible and reduce manufacturing costs. Therefore, the nuclear fuel assembly manufacturing cost will be reduced by incorporating as many nuclear fuel rod elements as possible in the MOX nuclear fuel assembly for PWRs and expanding the scale.
FIG. 10 is a cross-sectional view of a square nuclear fuel assembly (310) utilizing MOX nuclear fuel rod elements for PWR of the present invention. As shown in the column “Invention BWRMOX1” in FIG. 9, the inner diameter and diameter of the cladding tube are the same as the nuclear fuel rod for PWR using MOX as the nuclear fuel.
The Pu enrichment of P1 nuclear fuel rod (315) is for 19.1 wt% PWR.
The Pu enrichment of P2 nuclear fuel rod (314) is for 14.4 wt% PWR.
Pu enrichment of P3 nuclear fuel rod (313) is for 7.5 wt% PWR.
Zirconium boride-added MOX rod (316) is coated with the same specifications as the P1 nuclear fuel rod (315), etc., and indented bottom-bottomed zirconium boride (two boron (B) and one zirconium (Zr ZrB2 consisting of), melting point of 3200 ° C.) and vibration-filled double pellets of MOX powder with Pu enrichment of 7.5 wt%. Add the dish and chamfer.
The Li2O rod (311) is a Zr capsule containing only sintered pellets of lithium oxide (Li2O, melting point 1570 ° C) consisting of two Li and one oxygen in a cladding tube of the same specifications as the P1 nuclear fuel rod (315) etc. Enclosed and filled. The four corners, which are strongly influenced by water in the leaked water passage, contain only nuclear fuel, and output fluctuations are large and undesirable in terms of fuel integrity. Therefore, only Li2O, which is a flammable poison and moderator, was used. Four centers with less thermal neutrons were concentrated by Li to enhance the moderation effect. Fast neutrons are decelerated by Li7 and Li6 to become thermal neutrons. Thermal neutrons are absorbed in the early stage of combustion with a large amount of Li6, and the excess reactivity is suppressed. At the end of combustion, when Li6 is exhausted, thermal neutrons from Li7 activate fission of surrounding Pu and increase the reactivity. Zirconium boride (ZrB2 having a melting point of 3200 ° C. or ZrB12 composed of 12 B and 1 Zr having a melting point of 2300 ° C.) may be used instead of the Li-containing material as a flammable poison and moderator. Although the present invention can be loaded on the C lattice BWR, it can also be applied to the D lattice BWR.
FIG. 11 is a cross-sectional view of a zirconium boride-type square nuclear fuel assembly (320). As shown in the column “Invention BWRMOX2” in FIG. 9, the inner diameter and diameter of the cladding tube are the same as the nuclear fuel rod for PWR using MOX as the nuclear fuel.
The Pu enrichment of P1 nuclear fuel rod (315) is for 19.1 wt% PWR.
The Pu enrichment of P2 nuclear fuel rod (314) is for 14.4 wt% PWR.
Pu enrichment of P3 nuclear fuel rod (313) is for 7.5 wt% PWR.
Zirconium boride rod (321) is a zirconium boride containing a combustible poison and moderator boron (B) in a cladding tube of the same specification as P1 nuclear fuel rod (315) (melting point 3200 ° C ZrB2 or melting point 2030 Only pellets of ZrB12) at ℃ are filled.
The zirconium boride outer layer (335) is coated with zircaloy 4 and fixed to the channel box (35) opposite to the control rod (or suspended on the channel box (35) like a curtain).
The center with few thermal neutrons was concentrated by boron to enhance the moderation effect by boron. Fast neutrons are decelerated by B11 and B10 and become thermal neutrons. Thermal neutrons are absorbed at the early stage of combustion with a large amount of B10 and the excess reactivity is suppressed, and thermal neutrons from B11 activate the fission of surrounding Pu and increase the reactivity at the end of combustion when the B10 component disappears. A zirconium boride liner (335) is placed to further reduce the initial excess reactivity.
The nuclear fuel rods at the corners on the control rod side were made of zirconium boride rods (321) containing only zirconium boride, because inclusion of nuclear fuel causes a large output fluctuation and is not preferable in terms of fuel integrity.
Built-in zirconium boride, which is a flammable poison and moderator with a very high melting point, reduces the possibility that the neutron absorption function will be impaired even if a major accident occurs at high temperatures. Boron carbide (B4C) may be used as a flammable poison and moderator with a very high melting point.
If there is a lot of B10, use natural boron from the production area with low B10 content, or use degraded boron with low B10 concentration produced when producing high-performance control rod concentrate B10.
FIG. 12 is a cross-sectional view of a reduced-speed square nuclear fuel assembly (330). The specifications are as shown in the column “Invention BWR Reduction Fast Reactor” in FIG. PWRMOX combined nuclear fuel rods (334) filled with MOX for PWR with Pu enrichment of 14.4wt% were arranged in 12x12 in the cladding tube for PWR with MOX having a cladding tube diameter of 0.952cm as nuclear fuel. The inner width of the channel box is 13.4cm, which is the same as the conventional square nuclear fuel assembly (30) so that it can be loaded into a conventional BWR. In particular, if Pu, which has a low decontamination factor, is used as a nuclear fuel in order to reduce costs, minor actinides (MA) such as neptunium (Np), americium (Am), and curium (Cm) are included, and MA absorbs thermal neutrons. Since it is easy to do, it has the function of suppressing excess reactivity. Therefore, only the zirconium boride lining (335) is sufficient to suppress the initial excess reactivity. In the place where water originally existed, boron and Zr, which are not as much as hydrogen, were laid, so there is little neutron moderating action. It is a nuclear fuel assembly for a reduced-speed reactor (Non-patent Document 4) that focuses on the properties of Pu that fissions efficiently against fast neutrons.
Note that Gilro and stainless steel are considered as PWR cladding tube materials, but they will be incorporated in the present invention when they are used.
： Japan Atomic Energy Research Institute, 2001, JAERI-Research 2001-046 “Proposal and analysis results of benchmark problems related to reactor physics of light water reactor next generation fuel” : Journal of the Atomic Energy Society of Japan, 2006, Vol48, Tsutomu Okubo et al.

In recent years, reduction of nuclear power generation costs has become an urgent issue. It is possible to reduce the cost of scale by incorporating a large number of PWR nuclear fuel rod elements into a square nuclear fuel assembly. In the future, standardization will be made so that there is a great deal in common with both PWR design and BWR design taken into consideration, thereby achieving a global unification of light water reactors and further reducing power generation costs.
Although the use of Li is important in the present invention, Li6 is an important fuel for fusion power generation that is expected to be fully introduced in the 23rd century. Extracted Li from discarded lithium batteries and concentrated Li6 for fusion power generation can be used for the remaining Li7-rich degraded lithium.
As for the deteriorated boron, there is no anxiety in supply because the deteriorated boron is a waste of B10 enriched boron, which is an important control material for the fast breeder reactor, which is expected to be introduced in the 22nd century.
The low-speed slow reactor will be an important energy source until the full-fledged fast breeder reactor and fusion power generation expected after the 22nd century.

The schematic perspective view of the conventional square nuclear fuel assembly (30). Overview of a conventional nuclear fuel rod (31). Sectional drawing in the height in which the spacer (34) in the conventional square nuclear fuel assembly (30) is not located. FIG. 3 is a core plan view in which a conventional square nuclear fuel assembly (30) is disposed at a height where the pacer (34) is not located when the reactor is shut down. Main specifications of BWR and PWR with uranium oxide (UO2) as nuclear fuel. FIG. 2 is an overview of a square nuclear fuel assembly (230) using a nuclear fuel rod element for PWR according to the present invention. FIG. 2 is a schematic view of a PWR nuclear fuel rod multi-element utilization type square nuclear fuel assembly (240) of the present invention. Sectional view of a conventional MOX square nuclear fuel assembly (300) for BWR. Main specifications of BWR and PWR with MOX as nuclear fuel. It is sectional drawing of the MOX nuclear fuel rod element utilization type | mold square nuclear fuel assembly (310) for PWR. FIG. 3 is a cross-sectional view of a zirconium boride-type square nuclear fuel assembly (320). FIG. 6 is a cross-sectional view of a low-deceleration type square nuclear fuel assembly (330).

Explanation of symbols

1 is the nuclear fuel rod with the highest concentration.
2 is a nuclear fuel rod of enrichment number 2.
3 is a nuclear fuel rod of enrichment number 3.
4 is a nuclear fuel rod No. 4 enrichment.
5 is a gadolinia-added nuclear fuel rod.
6 is a water rod.
30 is a conventional square nuclear fuel assembly.
31 is a nuclear fuel rod.
32 is an upper coupling plate.
33 is a lower coupling plate.
34 is a spacer.
35 is a channel box.
Reference numeral 36 denotes a spacer outer frame.
41 is a cladding tube.
42 is an upper end plug.
43 is a lower end plug.
44 is a nuclear fuel pellet.
45 is a spring.
46 is a lower end plug insertion port.
47 is a coolant inlet.
48 is the upper plenum.
51 is a control rod side leakage water passage.
52 is a leakage water passage opposite to the control rod.
60 is a control rod.
230 is a square nuclear fuel assembly utilizing the PWR nuclear fuel rod element of the present invention.
231 is a pellet-filled nuclear fuel rod with the highest enrichment.
232 is a double pellet-filled nuclear fuel rod No. 2 enrichment.
233 is a double pellet-filled nuclear fuel rod of enrichment number 3.
234 is a double pellet-filled nuclear fuel rod No. 4 enrichment.
235 is a gadolinia-added nuclear fuel rod.
236 is a Zircaloy 4 water rod.
240 is a square nuclear fuel assembly utilizing the PWR nuclear fuel rod multi-element type of the present invention.
241 is the enrichment No. 1 PWR same cladding nuclear fuel rod.
242 is an enrichment No. 2 PWR same cladding nuclear fuel rod.
243 is the enrichment No. 3 PWR same cladding tube nuclear fuel rod.
244 is gadolinia-added PWR same cladding nuclear fuel rod.
246 is Zircaloy 4 frame.
247 is a gadolinia-added Zircaloy 4 lining.
248 is low-speed running water.
300 is a conventional MOX square nuclear fuel assembly for BWR.
301 is a nuclear fuel rod of Pu enrichment number 5.
302 is a nuclear fuel rod of Pu enrichment number 4.
303 is a nuclear fuel rod of Pu enrichment number 3.
304 is a nuclear fuel rod of Pu enrichment number 2.
305 is the number 1 Pu enrichment nuclear fuel rod.
306 is a gadolinia-added nuclear fuel rod.
307 is a square water rod.
310 is a square nuclear fuel assembly utilizing MOX nuclear fuel rod elements for PWR of the present invention.
311 is a Li2O stick.
313 is a P3 nuclear fuel rod.
314 is a P2 nuclear fuel rod.
315 is a P1 nuclear fuel rod.
316 is a MOX rod containing zirconium boride.
320 is a zirconium boride-type square nuclear fuel assembly of the present invention.
321 is a zirconium boride rod.
Reference numeral 330 denotes a reduced-speed square nuclear fuel assembly according to the present invention.
334 is a nuclear fuel rod for PWRMOX.
335 is a zirconium boride outer coating.

Claims (2)

A square nuclear fuel assembly for a BWR adjacent to a cross-shaped control rod arranged in a square grid is
A large number of cylindrical nuclear fuel rods (31) containing a large number of nuclear fuel pellets (44) formed by sintering nuclear fuel in a cylindrical shape in a zirconium alloy cladding tube (41). And several spacers (34) which are positioned in the middle of the height of the nuclear fuel rods (31) and regulate the spacing between the nuclear fuel rods (31), and made of a zirconium alloy covering these on four sides It consists of a channel box (35)
In order to reduce manufacturing costs in the square nuclear fuel assembly for BWR,
“U235 enrichment or Pu enrichment of nuclear fuel pellets and geometry”, “cladding tube material, inner diameter and outer diameter D”, and “channel box material” are the same as the nuclear fuel rod for PWR, 1mm or more When the distance P between adjacent nuclear fuel rods taking into account the nuclear fuel rod interval Δ is P = D + Δ, the channel box thickness is Σ, the spacer outer frame thickness is δ, and half of the control rod thickness is S, If the gap between the control rod surface and the channel box is h, half of the gap between adjacent channel boxes is g, and the arrangement of the nuclear fuel rods is m × m, then the channel box side width CL is LShg>CL> P × (m -1) A BWR square nuclear fuel assembly manufacturing method characterized in that it can be loaded on a conventional BWR with a square unit cell width L by + D + δ × 2 + Σ × 2. In the BWR square nuclear fuel assembly produced by the manufacturing method according to claim 1,
Li2O rod (311) or zirconium boride rod (321) or zirconium boride added MOX rod (316) or boron filled with flammable poison and moderator lithium oxide (Li2O) or zirconium boride (ZrB2 or ZrB12) A square nuclear fuel assembly using MOX as a nuclear fuel, characterized in that it has a built-in zirconium oxide outer layer (335).

Images