JPS6250796B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pool type liquid metal cooled fast breeder reactor structure.

A pool liquid metal cooled fast breeder reactor structure includes a nuclear fuel assembly submerged in a pool of liquid metal coolant within a primary vessel, which is suspended from a containment chamber roof structure. Existing pool-type liquid metal cooled fast breeder reactors are relatively small; for example, the structure known as the prototype fast reactor (PFR) at Dounreay in Scotland has a power output of 600 MW (t). occurs. Although the PFR fuel assemblies are supported from the roof structure by a series of ties, one newly proposed structural design supports the fuel assemblies from the walls of the primary vessel. A typical structure of this type is disclosed in the applicant's Japanese Patent Application No. 52-96518 for a 1300 MW (t) nuclear reactor, in which the fuel assembly is separated from the wall of the primary vessel by a skirt. Supported by a solid bottom. The primary vessel and solid bottom are made of austenitic stainless steel;
In the case of a primary vessel, it receives the dead weight caused by the coolant pool and the weight of the fuel assembly, and in the case of a solid bottom, it takes the dead weight caused by the weight of the fuel assembly. The primary vessel and solid bottom are also subject to pressure loads and temperature gradients. Furthermore,
Welds in these structures are also subject to internal stresses caused by the welding process. Temperature and radiation effects alter the fracture strength properties of austenitic metals, so even small defects in welds can rapidly propagate through cracks and cause catastrophic failure of the components. There are concerns. The size and rate of progression of these defects suggests that conventional means of detecting the onset of failure through periodic inspection are insufficient to ensure the integrity of austenitic stainless steel structures. There is. Therefore, it is believed that other design principles must be used such that the structures forming part of the primary load line between the fuel assembly and the roof structure are resistant to at least some damage. This principle forms the basis of the invention.

According to the present invention, in a pool type liquid metal cooled fast breeder reactor structure, the primary vessel incorporates an annular yoke formed of arcuate segments, and this yoke is disposed outside the primary vessel. It is suspended from the roof structure of the containment chamber by a first annular series of tie straps, while the solid bottom on which the fuel assembly rests inside the primary vessel is yoke by a second series of tie straps. The yoke has upwardly and downwardly extending legs which are respectively extended by the upper and lower skins of the primary container. The present invention provides that the welds in the primary load line between the containment roof structure and the primary vessel and solid bottom are discontinuous and that any cracks in the welds will be prevented by one connecting strap. It is based on the damage-resistant design principle of attaching the connecting straps so that they are limited to These straps have their loads constantly monitored and failures easily detected. 2 due to cracks in welds
Although it is unlikely that one or more straps will be damaged at the same time, a design factor of safety should be considered to withstand crack damage to multiple straps until a critical event occurs.

In a preferred construction, the arcuate segments of the yoke are forgings or extrusions of "K" cross-section, and the yoke is connected to the roof structure of the containment chamber by means of tie straps secured to upwardly extending vertical legs. The bottom, which is suspended from the body and is rigid, is supported by tie straps secured to downwardly extending slanted legs, while downwardly extending vertical legs and upwardly extending slanted legs are respectively attached to the lower and upper portions of the primary container. Fixed to the upper skin.

The structure of a pool type liquid metal cooled fast breeder reactor according to the present invention will be described below as an example with reference to the accompanying drawings.

FIG. 1 shows a pool type liquid metal cooled fast breeder reactor consisting of fuel assemblies 1 submerged in a pool 2 of liquid sodium coolant in a primary vessel 3.
have. The primary container has an open top, is suspended from the roof of the storage chamber 4, and is provided with a plurality of coolant pumps 5 and heat exchangers 6. Only one coolant pump and one heat exchanger are shown in the accompanying drawings. The fuel assembly 1 mounted on the grid 7a and supported by a solid bottom 7 is housed together with the heat exchanger in an internal tank 8, while the pump 5 for delivering coolant to the grid is located outside this internal tank 8. be done. The fuel assembly 1 consists of a plurality of sub-assemblies,
These subassemblies stand upright from the diamond in a closely spaced side-by-side array, and the fuel assembly is surrounded by a neutron shield 9. Control rods 10 and instrumentation 11 penetrate the roof of the containment chamber.

During operation of the reactor, relatively cool coolant drawn from a pool area outside the core tank by the pumps 5 is directed upwardly through the fuel assembly in heat exchange with the fuel assembly by the diamond grid 7a; It is then discharged back to the outer area of the pool through the heat exchanger 6. A secondary coolant is caused to flow from outside the containment chamber in heat exchange with the pool coolant through a heat exchanger and to a steam generator (not shown).

The primary container 3 incorporates an annular yoke 12 made of arcuate segments shown in detail in FIGS. 2 and 3, which yoke forms a first annular structure located outside the primary container. It is suspended from the containment chamber roof structure by a series of tie straps 14. The fuel assembly and rigid bottom are supported from the yoke by a second series of tie straps 15. The yoke has upwardly and downwardly extending legs which are respectively extended by the upper and lower skins of the primary container. Now referring to Figures 2 and 3, the yoke is a forged or extruded K
It can be seen that it is composed of arcuate segments 13 of the letter-shaped section, these segments having the reference numeral 1
As shown in 6, the ends are also butt welded. Vertical leg 17 extending above the K-shaped section
has a tapered upper edge 18 to which the end of the connecting strap 14 is butt welded. The downwardly extending beveled leg 19 is wedged at its lower edge 21 and the end of the connecting strap 15 is butt welded to its protrusion. The downwardly extending vertical leg 22 of the K-shaped section is extended by lower plates 23, 24 of decreasing thickness, which extend longitudinally over a number of segments and which include a primary container. A hemispherical bottom area 25 is attached. The upwardly sloping legs 26 of the K-shaped section are extended by plates 27, 28, which are connected to the intermediate member 2 of chevron-shaped cross section.
a vertically oriented upper skin 30 of the primary container extending longitudinally over a number of segments with 9;
is welded to plate 28. Legs 17, 19, which carry large loads, are reduced in impact with corresponding legs of adjacent segments, as indicated by reference numeral 20 in FIGS. 2 and 3, to reduce the thickness of the material to be welded.

In the construction described above, the large loads of the fuel assembly and solid bottom are transferred to the connecting straps 14,
15 and yoke 12 from the roof structure of the containment chamber. The path of this load is between the connecting straps 14, 15 and the legs 17 and 1 of the K-shaped section.
It only includes intermittent welds, such as the end welds between the straps 9 and 9, so that even if a crack in the weld propagates, the spread of the defect is limited to one strap. Other seam welds of the primary container,
Although the weld between the yoke and the primary vessel skin is continuous in nature, it is relatively lightly loaded and does not constitute a significant weld line.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a liquid metal cooled fast breeder reactor according to the present invention, FIG. 2 is a partial view of the inner surface of the primary vessel,
FIG. 3 is a partial view of the outer surface of the primary container. 1...Fuel assembly, 2...Liquid sodium coolant pool, 3...Primary container, 4...Accommodation chamber, 5
...coolant pump, 6 ... heat exchanger, 7a ... diamond grid, 7 ... solid bottom, 8 ... internal tank, 9 ... neutron shield, 10 ... control rod,
12... annular yoke, 13... arcuate segment,
14, 15... Connecting strap, 17... Vertical leg extending upward, 19... Inclined leg extending downward, 22... Vertical leg extending downward, 23,
24... lower plate, 25... hemispherical bottom area of the primary container, 26... upwardly sloping legs, 2
7, 28... plate, 29... intermediate member.

Claims (1)

[Scope of Claims] 1. A concrete containment chamber; a primary vessel containing a pool of liquid alkali metal coolant contained within the containment chamber; and a nuclear fuel assembly submerged in the pool of coolant and supported by the solid bottom, the primary vessel incorporating an annular yoke made of arcuate segments, the yoke comprising: Suspended from the roof structure of the containment chamber by a first annular series of bonding straps located on the exterior of the primary vessel, while the rigid bottom is suspended from the yoke by a second series of bonding straps. a liquid metal cooled fast breeder, wherein the yoke has upwardly and downwardly extending legs, the legs being respectively extended by the upper and lower skins of the primary vessel. Furnace structure. 2 The arcuate segments of the yoke are of K-shaped cross-section, and the yoke is suspended from the roof structure of the containment chamber by means of tie straps fixed to vertical legs extending above the yoke and connected to the solid bottom of the yoke. is supported by a connecting strap secured to a downwardly extending sloping leg, and a downwardly extending vertical leg and an upwardly extending sloping leg are respectively secured to the upper and lower skins of the primary container. A fast breeder reactor structure according to claim 1. 3. The free ends of the upwardly extending vertical leg and the downwardly extending sloping leg of the yoke arcuate segment are slotted and the ends of the connecting straps are butt welded to their projecting ends. Fast breeder reactor structure described in Section 1. 4. The fast breeder reactor structure according to claim 3, wherein the upwardly extending vertical legs and the downwardly extending inclined legs of the arcuate segments are prevented from coming into contact with corresponding legs of adjacent segments. 5. The fast breeder reactor structure according to claim 4, wherein the arcuate segment of the yoke is a forged body. 6. The fast breeder reactor structure according to claim 4, wherein the arcuate segment of the yoke is an extrusion.