JPS6049274B2 - Method and device for measuring reactivity of fuel assembly - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for measuring the reactivity of a fuel assembly.

Knowing the reactivity of a fuel assembly (hereinafter abbreviated as fuel assembly) is important for criticality safety during storage of the fuel assembly.
- Engineering Li'', ■ -ι赳, 4', 1-÷↓μm-L7=
Small - TL to each: 4 to -k; / above is very important.

For example, if reactivity can be measured quickly, the fuel assemblies can be reloaded into the reactor core in a pre-planned manner during refueling, or removed from the reactor and stored in a designated storage location.
, you can see whether it is okay or not. Also, in the case of a new fuel body,
It is determined whether the fuel body has a predetermined reactivity. The present applicant has already published Japanese Patent Application No. 51-126804 (Japanese Unexamined Patent Application Publication No. 53-197) regarding a method and apparatus for measuring the reactivity of fuel bodies.
-52893)).

In this invention, firstly, a method for measuring the reactivity of a standard fuel body using a relatively troublesome operation called the standard fuel body reactivity measurement method is shown, and then the reactivity obtained by the above method is measured using a standard fuel body reactivity measurement method. A so-called comparison method is shown in which the reactivity of another fuel is determined by comparing it with the former. Since this comparative method measures neutrons spontaneously emitted from the fuel body (the emission rate is low), there was a limit to the ability to quickly measure the reactivity of the fuel body. J An object of the present invention is to provide a method and apparatus for quickly measuring the reactivity of a fuel body, eliminating the drawbacks of the comparative method.

First, the method of the present invention will be explained using mathematical formulas.

Name the standard fuel assembly A) and the measured fuel assembly B. The spontaneous neutron emission rate of both fuel bodies is S? , Sg) The multiplication factor is KA,
k8, reactivity ρA, and ρ8, and neutron fluxes at arbitrary positions on the side surface of the fuel body are φ8 and φg. When an external neutron source with intensity Sx is placed on the side of the fuel bodies A and B, the neutron flux at the position is φ, φ? Then, the following formula holds true. α here.

, βu is a proportionality constant. From these equations, the following equation can be easily derived.

The reactivity of fuel bodies A and B is ρA, and ρ8 is Therefore, equation (3) can be transformed as follows.

(4) In the formula, ρ6 is a known quantity, and φQ, φ8, φ? φg
Since is a measurable quantity, ρ8 is calculated using equation (4). In other words, the difference in neutron flux between the state where an external neutron source is placed on the side surface of the fuel body A whose reactivity is known and the state where the external neutron source is not placed is φ
The reactivity of the fuel body B to be measured is determined by dividing φ8 by the difference in neutron flux between the state where an external neutron source is placed on the side of the fuel body B to be measured and the state where it is not placed. I know that it will happen. Next, the apparatus used in the above method will be described in detail with reference to the drawings. FIG. 1 shows an embodiment showing the configuration of a measuring device.

In the figure, a first neutron detector 2 and a second neutron detector 3 are attached to the side surface of a mounting box 1 that holds a fuel assembly. A fuel body (not shown) is inserted into the interior 4 of the mounting box 1, and an irradiation box 5 is provided on the opposite side of the first neutron detector 2 across the fuel body. A neutron source (not shown) is housed inside the irradiation box 5 and is fixed so as to irradiate the fuel body. The second neutron detector 3 is arranged at a position that cannot be reached by neutrons emitted from the neutron source, for example, at a position at least about 50 cm away from the irradiation box 5. Therefore, the neutron flux φ in equation 4, φ? is measured by the first neutron detector 2, and the neutron fluxes φ8 and φ8 are measured by the second neutron detector 3. Reference numeral 6 denotes a mounting portion for mounting the mounting box 1 at an appropriate position.

Signal cables 7 and 8 send electrical signals sent from the neutron detectors 2 and 3 to the measurement section.

The signals sent through the signal cables 7 and 8 are measured by the measuring section, then temporarily stored in a storage device, and used for reactivity calculation in a calculation device after an appropriate period of time has elapsed. Second
The figure is a perspective view of another embodiment of the device of the present invention.

This embodiment differs from the embodiment shown in FIG. 1 in that a second irradiation box 9 is provided on the opposite side of the second neutron detector 3 across the fuel body, and an external neutron source is These are two points where a guide tube 10 is provided to move between the irradiation boxes 5 and 9. In this device, either the first neutron detector 2 or the second neutron detector 3 determines the neutron flux φS, φg: φ via, φ? may be measured, or these neutron fluxes may be measured alternately. As explained above, according to the present invention, since an external neutron source of arbitrary strength is used, it is possible to measure the neutron flux φ and φ with high accuracy in a short period of time, so the reactivity of the fuel body can be measured quickly. can be done.

[Brief explanation of the drawing]

1 and 2 are perspective views of a measuring device according to the present invention, respectively. 1... Mounting box, 2, 3... Neutron detector, 4... Inside the mounting box, 5, 9... Irradiation box, 6... ... Mounting part, 7, 8 ... Signal cable, 10 ... Guide tube.

Claims (1)

[Claims] 1. Measure the neutron flux with and without an external neutron source placed on the side surface of a standard fuel assembly whose reactivity is known, and then place the external neutron source on the side surface of the fuel assembly to be measured. Measure the neutron flux between a state in which a neutron source is placed and a state in which a neutron source is not placed, and calculate the difference between the neutron flux measured in a standard fuel assembly and the neutron flux measured in the fuel assembly to be measured. A method of determining the reactivity of a fuel assembly by determining the ratio. 2. An irradiation box containing an external neutron source is placed on one side of the mounting box across the mounting box in which the standard fuel assembly or the fuel assembly to be measured is attached, and a first neutron detector is arranged on the other side. At the same time, a second neutron detector is further placed at a position where the emission rate of neutrons emitted from the external neutron source is sufficiently smaller than the emission rate of neutrons emitted from the standard or the fuel assembly to be measured. A fuel assembly reactivity measuring device characterized by: