JPH0385496A - fast breeder reactor - Google Patents

Abstract

PURPOSE:To enable detection of delayed neutrons within a predetermined time interval at any place by providing delayed neutron detection (a DN method) units of a single point sampling method, placed at a periphery of a reactor core side coolant inlet window of an intermediate heat exchanger and between the most departed heat exchangers. CONSTITUTION:In case that reactor core fuels are damaged at parts facing intermediate heat exchangers 3a to 3d, precursor nucleons of discharged delayed neutrons can be detected by DN method units 21a to 21d provided at a periphery of a reactor core 5 side coolant inlet window 7 of each heat exchanger 3a to 3d. Also, in case that the reactor core fuels located at parts between the most departed heat exchangers 3a and 3b, and 3c and 3d, are damaged, the precursor of delayed neutrons in the coolant, can be detected by the DN method units 21e and 21f provided between the heat exchangers 3a and 3b, and, 3c and 3d. Accordingly, for fuel damages in any place in the reactor core 5, the precursor of discharged delayed neutrons can be detected within a predetermined time interval and a trip signal is generated and therefore safety and reliability are much improved. Furthermore, as the units 21a to 21f are made to be of a single point sampling type, they can be withdrawn from the reactor core, and maintainability is also much improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Field of Application) The present invention relates to fast breeder reactors, and particularly to means for detecting damaged fuel.

(Prior Art) A tank-type fast breeder reactor that uses liquid metal such as liquid sodium as a coolant has a plurality of holes on a roof slab 2 that closes the upper opening of a reactor vessel 1, as shown in FIGS. 5 and 6. Intermediate heat exchanger 3a.

3b, 3c, 3d and coolant circulation pumps 4a, 4b.

4c and 4d are mounted alternately on the same circumference, and above the reactor core 5 housed in the reactor vessel 1 is a core upper mechanism 6 containing a control rod drive mechanism, etc. There is. and the intermediate heat exchangers 3a, 3b+3c,
3d is provided with a coolant inlet window 7 through which the coolant flows;
From this coolant inlet window 7 to intermediate heat exchangers 3a, 3b, 3c.
, 3d is heat-exchanged with the secondary coolant through the heat transfer tube, and flows out into the cold plenum 8 at a low temperature. On the other hand, the coolant inside the cold brenum 8 is supplied by coolant circulation pumps 4a and 4b.

4C* is sucked into 4d, flows into the reactor core 5 through the in-furnace piping 9 and the high-pressure blemish 10, is heated to a high temperature while rising in the reactor core 5, and flows out into the hot blemish 11. Then, the coolant flowing out from the core 5 to the hot blemish 11 is returned to the intermediate heat exchangers 3a and 3b through the coolant artificial window 7.
, 3c, and 3d, and circulate through the above-mentioned channels.

In addition, in the fast breeder reactor configured in this way, each unit is equipped with a delayed neutron detection unit (hereinafter referred to as a DN method unit) 12 that detects delayed neutron leading nuclei emitted from the damaged fuel in order to detect damage to the core fuel. Intermediate heat exchanger 3a, 3b, 3
It is provided near c and 3d. This DN method unit 12 is composed of a ring-shaped sampling tube 13 disposed around the coolant population window 7, and a unit body 14 that analyzes the coolant sampled by the sampling tube 13. As shown in the figure, the coolant in the reactor is introduced into the sampling chamber 16 through the sampling tube 13 by the electromagnetic pump 15, and the delayed neutron leading nuclei in the coolant introduced into the sampling chamber 16 are detected by the neutron detector 17. By the way, among the coolant flowing out from the core 5 of such a fast breeder reactor, the intermediate heat exchanger 3 a r 3 b r3
The coolant flowing out from the portions facing c and 3d directly flows into the coolant artificial windows 7 of the intermediate heat exchangers 3a, 3b, 3c, and 3d, but the coolant flowing out from other portions flows into the reactor vessel wall. After flowing toward the reactor vessel wall, it rises to near the coolant liquid level, and then flows from the reactor vessel wall to the intermediate heat exchangers 3a and 3b.

The flow becomes horizontal toward 3c and 3d. For this reason, for example, the intermediate heat exchangers 3a, 3b, and 3c that are farthest apart
If the core fuel located between
There was a problem that it took a long time to reach neutrons c and 3d, and it was difficult to detect delayed neutron leading nuclei in the coolant and issue a reactor trip signal within a predetermined time due to the functions required by the DN method. .

Further, the conventional DN method unit 12 includes an intermediate heat exchanger 3a,
Ring-shaped sampling tube 1 around 3b, 3c, 3d
3 was installed, so if the 10,000-DN method unit 12 failed, it could not be removed from the furnace.

The present invention has been developed in view of these circumstances, and is capable of detecting delayed neutron leading nuclei emitted from the damaged fuel within a predetermined time no matter where fuel damage occurs in the reactor core.
An object of the present invention is to provide a fast breeder reactor in which a method unit can be pulled out from inside the reactor.

[Structure of the Invention] (Means for Solving the Problem) In order to achieve the above object, the present invention provides a nuclear reactor and a plurality of intermediate units disposed around the reactor core housed in the reactor vessel. In a fast breeder reactor having a heat exchanger, a plurality of coolant circulation pumps arranged between these intermediate heat exchangers, and a core upper mechanism provided above the reactor core,
A DN method unit for detecting delayed neutron leading nuclei released from the damaged fuel of the reactor core is a one-point sampling method,
This one-point sampling type DN method unit is installed near the coolant inlet window on the core side of each intermediate heat exchanger and between the two intermediate heat exchangers that are farthest apart.

(Function) That is, in the present invention, by making the DN method unit a one-point sampling method, even if the DN method unit breaks down, it can be pulled out from the furnace, and the maintainability of the DN method unit can be improved. can. In addition, by installing a single-point sampling DN method unit near the coolant inlet window on the core side of each intermediate heat exchanger and between the two intermediate heat exchangers that are farthest apart, it is possible to Even if a fuel failure occurs in a nuclear reactor, delayed neutron precursor nuclei emitted from the damaged fuel can be detected within a predetermined time, thereby increasing the safety and reliability of the nuclear reactor.

(Example) Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 and FIG. 2 show an embodiment of the present invention, and in this embodiment, coolant artificial windows on the core 5 side of each intermediate heat exchanger 3a, 3b, 3c, 3d mounted on the roof slab 2 are shown. A one-point sampling type DN method unit 21d is installed near 7, and a one-point sampling type DN method unit 21e is installed between the two intermediate heat exchangers 3a and 3b and 3C and 3d that are the most distant from each other. , 21f are installed to detect fuel damage.

According to such a configuration, among the coolant flowing out from the core 5, the coolant flowing out from the portions facing the intermediate heat exchangers 3a, 3b, 3C*3d is as shown in FIGS. 3 and 4. and an intermediate heat exchanger 3a.

Intermediate heat exchangers 3a, 3b, 3c because the coolant is directly sucked into the inlet windows 7 of 3b, 3c, 3d.

When the reactor core fuel is damaged in the part opposite to the reactor core 3d, the delayed neutron leading nuclei released from the damaged fuel are transferred to the vicinity of the coolant inlet window 7 on the core 5 side of each intermediate heat exchanger 3a, 3b, 3c, and 3d. DN method units 21a, 21b, 21 installed in
c, 21d. In addition, the two intermediate heat exchangers 3a and 3b and 3c and 3 that are the most distant from each other are
If the core fuel located between can be detected.

Therefore, in this embodiment, even if fuel failure occurs at any position in the reactor core 5, it is possible to detect delayed neutron leading nuclei emitted from the damaged fuel within a predetermined time and issue a reactor trip signal. The safety and reliability of nuclear reactors can be improved. In addition, in this embodiment, the DN method unit 2
1&, 21b.

Since 21c, 21d, 21e, and 21f are of the one-point sampling method, the DN method unit 21a.

21b, 21c, 21d, 21e, and 21f can be pulled out from inside the furnace, and the DN method unit 21a.

The maintainability of 21b, 21c, 21d, 21e, and 21f can be improved.

[Effects of the Invention] As explained above, according to the present invention, continuous neutrons emitted from the damaged fuel can be detected within a predetermined time no matter where fuel damage occurs in the reactor core. Since it can be extracted from the reactor, the safety and reliability of the nuclear reactor can be improved, and the maintainability of the DN method unit can be improved.

[Brief Description of the Drawings] Fig. 1 is a longitudinal sectional view of a fast breeder reactor showing an embodiment of the present invention, Fig. 2 is a plan view thereof, and Figs. 3 and 4 are explanatory diagrams of the operation of the same embodiment. , Figure 5 is a vertical cross-sectional view of a conventional fast breeder reactor.
FIG. 6 is a configuration diagram of the -MI4=DN method unit. 1... Reactor vessel, 2... Roof slab, 3a-3
d... Intermediate heat exchanger, 4a to 4d... Coolant circulation pump, 5... Core, 6... Core upper mechanism, 7...
Coolant inlet window, 8...Cold blennium, 9...In-furnace piping, 10...High pressure blennium, 11...Hot blennium, 21a to 21f...DN method unit.

Claims (1)

[Claims] A reactor vessel, a reactor core housed within the reactor vessel,
a roof slab that closes the upper opening of the reactor vessel;
A plurality of intermediate heat exchangers mounted on the roof slab and disposed around the core, a plurality of coolant circulation pumps disposed between these intermediate heat exchangers, and a plurality of coolant circulation pumps disposed around the core. In a fast breeder reactor having an upper core mechanism installed above, the DN method unit for detecting delayed neutron leading nuclei emitted from the damaged fuel in the core is of a one-point sampling method, and the DN of this one-point sampling method is A fast breeder reactor, characterized in that a method unit is installed near the coolant inlet window on the core side of each of the intermediate heat exchangers and between the two intermediate heat exchangers that are farthest apart.