CN101105986A

CN101105986A - Reactor reactivity measuring method

Info

Publication number: CN101105986A
Application number: CNA2007100940017A
Authority: CN
Inventors: 蔡光明; 盛春燕
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-08-03
Filing date: 2007-08-03
Publication date: 2008-01-16
Anticipated expiration: 2027-08-03
Also published as: CN101105986B; WO2009018757A1

Abstract

A reactor reaction measuring method is a dynamic response reaction measuring method based on dynamic reversal. Firstly, if needed, the reactor is provided with a quick reaction disturbance so as to obtain a group of neutron flux level measuring data IRPN of dynamic response; the method carries out calculation of dynamic reversal (S=S0,gamma=gamma0,n=IRPN-gamma0) on neutron flux level measuring data IRPN according to reactor dynamics equation to obtain the response pm; and draw the fitting straight line Rhom (IRPN-gamma0)=f(IRPN) with IRPN dynamic response data, and the inclination is the response Rho. Apart from lifting the precision of reaction measurement near the critical status, the method can also make reaction measurement on reactors the secondary critical status. Furthermore, the method can obtain reaction of reactors through simple mathematic treatment, and take into consideration the impact of external neutron source and Gamma current.

Description

Reactor reactivity measurement method

Technical Field

The invention relates to a reactivity measurement of a nuclear reactor, with which the reactor reactivity or the effective multiplication factor can be obtained.

Background

The reactivity measurement of the existing nuclear reactor adopts a point reactor kinetic equation to solve reactivity or an effective multiplication coefficient, which is also called an inverse dynamic method, and the point reactor kinetic equation is as follows:

wherein:

n (t) is the time-dependent neutron density;

ρ is the reactivity of the core;

β _ieff is the fraction of the ith group of effective delayed neutrons;

β _eff is an effective delayed neutron fraction, and

in the case of a heavy water pile,

λ _i is the decay constant of the ith group of delayed neutron precursor nuclei;

C _i (t) is the i-th group precursor core density; for heavy water reactor, 15 groups are used for delayed neutron precursor nucleus;

l is the average generation time of instantaneous neutrons;

s is an external neutron source.

The reactivity meter (or a calculation program of the reactivity meter) is an inverse dynamic method for obtaining the reactivity of the reactor by solving a point reactor kinetic equation.

The inverse dynamic method is a reactivity measuring method widely adopted by a reactivity measuring tool reactivity instrument at present. However, because the external neutron source S and the gamma current gamma are determined by lacking a measurement method, the method generally requires that the neutron flux is in a certain level near the critical point (the general pressurized water reactor requires the intermediate range current to be 10) ^-8 A is more than) The measurement accuracy can be ensured.

In addition, the periodic method is also a widely used reactor reactivity measurement method. However, the method also requires that the measurement accuracy can be ensured under the requirements of being near the critical point, the neutron flux level is higher than the level of an ignorable external neutron source S, the measured reactivity cannot be too large, and the like.

Disclosure of Invention

The invention aims to provide a reactor reactivity measuring method, which has the following measuring principle: dividing lambda in point reactor dynamics equations (1) and (2) _i C _i Item is eliminated, then

Signals I of the out-of-core nuclear measurement System _RPN In addition to the signal generated by neutrons, gamma-generated noise and noise of the measurement system are also included. The noise generated by gamma and the noise of the measurement system are collectively referred to as gamma noise, and then

I _RPN ＝n+γ (4)

In calculating the reactivity with a reactivity meter (or program), let S = S ₀ ，γ＝γ ₀ (S ₀ 、γ ₀ Constant), n = I _RPN -γ ₀ The reactivity thus measured is ρ _m Then, equation (3) becomes:

substituting formula (4) into the left side of formula (3)

When gamma is a constant, the above formula becomes

Then, according to the formulae (3), (5) and (7), there are

Substituting the formula (4) into the above formula, the reactivity measurement formula containing external neutron source effect and gamma current feedback correction is obtained

ρ _m (I _RPN -γ ₀ )＝ρI _RPN +(Sl-S ₀ l-ργ) (9)

In calculating reactivity with a reactivity meter (or program), data for S, γ are generally ignored due to lack of measurement method. I.e. let S in the reactivity calculation ₀ ＝0，γ ₀ If not less than 0, the above formula is changed to

ρ _m I _RPN ＝ρI _RPN +(Sl-ργ) (10)

According to the formula (9), when ρ is constant, ρ is _m (I _RPN -γ ₀ )＝f(I _RPN ) Is a linear function whose slope is the reactivity p.

In the formula derivation process, only the assumption that gamma is a constant is made; in addition, ρ is required to be constant. This method therefore requires below the zero power doppler heating point to be used to accurately measure the reactivity p.

The invention provides a dynamic response reactivity measurement method, which comprises the following steps:

step one, according to the principle, a group of steady-state measurement data cannot be processed to obtain the reactivity (I) _RPN Is a constant or rho _m = 0). If the reactor begins to be in steady state, this requires a reactivity perturbation to obtain a set of dynamically responsive neutron flux level measurements I _RPN . It should be noted that the speed of this reactive perturbation cannot be too slow, otherwise the dynamic response is substantially over after the perturbation is over. General reactionThe stack can be moved to achieve the desired result by continuously inserting or withdrawing control rods and then maintaining the rod positions. When the rod position is unchanged, the reactive perturbation ends. This can be achieved by moving the fuel assembly or by moving the reflective layer.

Measuring data I for neutron flux level according to point reactor dynamic equation _RPN Performing inverse dynamic calculation (let S = S) ₀ ，γ＝γ ₀ ， n＝I _RPN -γ ₀ ) And calculating to obtain the reactivity rho _m 。

Finally, the reactivity is in a constant state _RPN Dynamic response data (making neutron flux level below zero power doppler ignition point), making rho according to equation (9) _m (I _RPN -γ ₀ )＝f(I _RPN ) The slope of the fitted line is the reactivity p.

The dynamic response reactivity measurement method provided by the invention is based on a mature inverse dynamic method, and because the external neutron source S and the gamma current are considered, no requirements are required on the critical state and the neutron flux level of the reactor. Not only can the measurement accuracy of reactivity be improved in the critical state, but also the subcritical degree can be measured even in the subcritical state. The measured reactivity takes the influence of external neutron source S and gamma noise into account, so that the measurement accuracy is high. The reactor is suitable for various reactor types, and has the advantages of high reactivity measurement speed, high precision, good operability and simple data processing.

The reactivity measurement method can perform reactivity measurement under a subcritical state due to dynamic response; therefore, the original reactor physical test which needs to be carried out after the reactor is critical can be moved to be carried out before the reactor is critical, so that the time of occupying major repair critical paths is reduced, and the economic benefit of the nuclear power plant is improved;

in the process of reaching the critical point, the conventional method adopts an inverse counting rate method to reach the critical point. The countdown rate method can only predict the critical point and cannot obtain the reactivity (or the subcritical degree) of the core. And if the traditional countdown rate method is combined with the dynamic response reactivity measurement method in the rod lifting critical process, the reactivity (or the subcritical degree) of the reactor core can be determined, so that the reactor critical process is safer and quicker.

Drawings

FIG. 1 is a response curve of a source range detector after a sub-critical lower plunger;

FIG. 2 is ρ _m I _RPN ＝f(I _RPN ) Straight line fitting (gamma) ₀ ＝0)。

Detailed Description

A reactor reactivity measurement method, comprising the steps of:

step one, according to actual needs, giving a faster reactivity disturbance to a reactor to obtain a group of neutron flux level measurement data I with dynamic response _RPN 。

Step two, measuring data I of neutron flux level according to point reactor kinetic equation _RPN Performing inverse dynamic calculation (let S = S) ₀ ， γ＝γ ₀ ，n＝I _RPN -γ ₀ ) And calculating to obtain the reactivity rho _m 。

Step three, putting the reactivity in a constant state I _RPN Dynamic response data, making rho according to equation (9) _m (I _RPN -γ ₀ )＝f(I _RPN ) The slope of the fitted line is the reactivity p.

FIG. 1 is a response curve of a source range detector after a sub-critical lower plunger. Where the left ordinate is reactivity in pcm (1 pcm =1 × 10) ^-5 ) (ii) a The ordinate on the right side is the control rod position in steps; the ordinate on the right also represents the Source Range (SRC) count rate in CPS. A is a neutron flux level measurement curve; b is reactivity rho calculated without S, gamma correction _m (i.e. let n = I) _RPN S = 0); and C is the control rod position.

FIG. 2 is ρ _m I _RPN ＝f(I _RPN ) Straight line fitting (gamma) ₀ = 0). Where 2A is the measurement data and 2B is the straight line fit to the measurement data.

Reactivity in subcritical conditions (subcritical degree) measurement has been a difficult point in reactor reactivity measurement. To illustrate the advantages of the dynamic response reactivity measurement method, the reactivity measurement in the subcritical state is taken as an example to illustrate the invention.

Step one, according to the principle, a group of steady-state measurement data can not be processed to obtain reactivity, namely I _RPN Is constant or p _m And =0. The reactor therefore inserts control rods at a faster rate, achieving a faster reactivity disturbance, and then maintains the rod position. No other reactivity was introduced during this period. At the same time, in order to obtain better processing result, it can be maintained for above 2 minutes, so as to obtain a group of neutron flux level measurement data I with dynamic response _RPN And the data for neutron flux levels below the zero power doppler heating point can also preferably be more than 2 minutes. The dynamic response curve a, C for the neutron flux level after sub-critical down-rod insertion as shown in fig. 1 is the control rod position.

Step two, measuring data I of neutron flux level according to point reactor kinetic equation _RPN Inverse dynamics calculation was performed (let S =0, γ) ₀ ＝0，n＝I _RPN ) Calculating the reactivity rho _m Such as curve B in fig. 1.

Step three, after the reactivity is in a constant state, I _RPN Dynamic response data (neutron flux level below the zero power doppler heat generation point), as in a of fig. 1, is given as ρ according to equation (10) _m I _RPN ＝f(I _RPN ) And fitting a straight line to obtain a fitted straight line equation of y = -197.95x +119113. I.e. the reactivity p of the reactor was-197.95 pcm (1pcm =1 × 10) ^-5 ) As shown at 2B in fig. 2.

The invention is based on an inverse dynamic response reactivity measurement method, can obtain the reactivity (or subcritical degree) of the reactor through simple mathematical processing, and considers the influence of an external neutron source and gamma current. The method can improve the reactivity measurement precision near the critical state, and the reactor can also carry out the reactivity (or subcritical degree) measurement under the subcritical state.

Claims

1. A method for measuring reactor reactivity, comprising the steps of:

step one, obtaining a group of neutron flux level measurement data I with dynamic response _RPN ；

Step two, making S = S ₀ ，γ＝γ ₀ ，n＝I _RPN -γ ₀ Measuring data I for neutron flux level according to point-pile kinetic equation _RPN Carrying out inverse dynamic calculation to obtain the reactivity rho _m (ii) a Wherein S is an external neutron source, and gamma is gamma noise;

step three, putting the reactivity in a constant state I _RPN Dynamic response data, making rho according to _m (I _RPN -γ ₀ )＝f(I _RPN ) Fitting a straight line with a slope of the reactivity p,

ρ _m (I _RPN -γ ₀ )＝ρI _RPN +(Sl-S ₀ l-ργ)。

2. the reactor reactivity measurement method according to claim 1, wherein: in the first step, a fast reactivity disturbance is given to the reactor to obtain a set of neutron flux level measurement data I with dynamic response _RPN 。

3. The reactor reactivity measurement method according to claim 1, wherein: i after the reactivity is in a constant state in the third step _RPN Dynamic response data doing rho _m (I _RPN -γ ₀ )＝f(I _RPN ) The straight line is fitted when the reactor neutron flux level is below the zero power doppler heat generation point.

4. The reactor reactivity measurement method according to claim 1, wherein: in the first step, the reactor is disturbed reactively in a mode that control rods are continuously inserted or withdrawn, and then the position of the control rods is kept unchanged.

5. The reactor reactivity measurement method according to claim 1, wherein: in step one, the reactor is given a reactivity disturbance by continuously moving the fuel assemblies or moving the reflective layer and then keeping its position.

6. The reactor reactivity measuring method according to claim 4 or 5, wherein: the time for maintaining the reactivity constant is at least 2 minutes.