CN101105986B - Reactor reactivity measuring method - Google Patents

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 measuring method

Technical field

The present invention relates to the reactivity measurement of nuclear reactor, utilize this method can obtain pile reactivity or effective multiplication factor.

Background technology

The reactivity measurement of existing nuclear reactor adopts point-reactor kinetic equation to find the solution reactivity or effective multiplication factor, claims the inverse method again, and point-reactor kinetic equation is as follows:

$\frac{\mathrm{dn}\left(t\right)}{\mathrm{dt}}=\frac{\mathrm{\ρ}-{\mathrm{\β}}_{\mathrm{eff}}}{l}n\left(t\right)+\underset{i=1}{\overset{6}{\mathrm{\Σ}}}{\mathrm{\λ}}_i{C}_i\left(t\right)+S---\left(1\right)$

$\frac{d{C}_i\left(t\right)}{\mathrm{dt}}=\frac{{\mathrm{\β}}_{\mathrm{ieff}}}{l}n\left(t\right)-{\mathrm{\λ}}_i{C}_i\left(t\right)---\left(2\right)$

Wherein:

N (t) is the neutron population with time correlation;

ρ is the reactivity of reactor core;

β _IeffIt is i group effective delayed neutron fraction;

β _EffBe effective delayed neutron fraction, and ${\mathrm{\β}}_{\mathrm{eff}}=\underset{i=1}{\overset{6}{\mathrm{\Σ}}}{\mathrm{\β}}_{\mathrm{ieff}};$ For heavy water reactor, ${\mathrm{\β}}_{\mathrm{eff}}=\underset{i=1}{\overset{15}{\mathrm{\Σ}}}{\mathrm{\β}}_{\mathrm{ieff}};$

λ _iIt is the disintegration constant of i group delayed-neutron precursor;

C _i(t) be i group pioneer cuclear density; For heavy water reactor, delayed-neutron precursor is used 15 groups;

L is that prompt neutron is on average for the time;

S is outer neutron source.

Reactivity meter (or reactivity meter calculation procedure) is by finding the solution point-reactor kinetic equation, obtain the reactivity of reactor, i.e. the inverse method.

Above-mentioned inverse method is that reactor current reactivity measurement instrument reactivity meter institute extensively adopts reactivity measuring method.But determine outer neutron source S and gamma electric current γ owing to lack measuring method, so this method generally requires near critical, (the general middle range electric current of presurized water reactor requirement is 10 in certain level for neutron flux ^-8More than the A) above could guarantee measuring accuracy.

In addition, periodic method also is widely used reactor reactivity measuring method.But this method also requires near critical, more than the level of neutron-flux level neutron source S outside can ignoring, measured reactivity can not be too big etc. requirement, could guarantee measuring accuracy.

Summary of the invention

The object of the present invention is to provide a kind of reactor reactivity measuring method, its measuring principle is as follows: with the λ in point-reactor kinetic equation formula (1), (2) _iC _iThe item cancellation then has

$\frac{\mathrm{dn}}{\mathrm{dt}}+\frac{\mathrm{dC}\left(t\right)}{\mathrm{dt}}=\frac{\mathrm{\ρ}}{l}n+S---\left(3\right)$

The signal I of out-pile nuclear examining system _RPNExcept comprising the signal that produces by neutron, the noise of γ generation and the noise of measuring system have also been comprised.Here the noise that γ is produced and the noise of measuring system are referred to as gamma noise, then

I _RPN＝n+γ (4)

Calculating in the reactive process, make S=S with reactivity meter (or program) ₀, γ=γ=γ ₀(S ₀, γ ₀Be constant), n=I _RPN-γ ₀, the reactivity that measures thus is ρ _m, then formula (3) becomes:

$\frac{d(I_{\mathrm{RPN}}-{\mathrm{\γ}}_0)}{\mathrm{dt}}+\frac{\mathrm{dC}\left(t\right)}{\mathrm{dt}}=\frac{{\mathrm{dI}}_{\mathrm{RPN}}}{\mathrm{dt}}+\frac{\mathrm{dC}\left(t\right)}{\mathrm{dt}}=\frac{{\mathrm{\ρ}}_m}{l}(I_{\mathrm{RPN}}-{\mathrm{\γ}}_0)+S_0---\left(5\right)$

With formula (4) substitution formula (3) left side

$\frac{\mathrm{dn}}{\mathrm{dt}}+\frac{\mathrm{dC}\left(t\right)}{\mathrm{dt}}=\frac{{\mathrm{dI}}_{\mathrm{RPN}}}{\mathrm{dt}}-\frac{\mathrm{d\γ}}{\mathrm{dt}}+\frac{\mathrm{dC}\left(t\right)}{\mathrm{dt}}---\left(6\right)$

If γ is a constant, then following formula becomes

$\frac{\mathrm{dn}}{\mathrm{dt}}+\frac{\mathrm{dC}\left(t\right)}{\mathrm{dt}}=\frac{{\mathrm{dI}}_{\mathrm{RPN}}}{\mathrm{dt}}+\frac{\mathrm{dC}\left(t\right)}{\mathrm{dt}}---\left(7\right)$

Then, according to formula (3), (5), (7), have

$\frac{\mathrm{\ρ}}{l}n+S=\frac{{\mathrm{\ρ}}_m}{l}(I_{\mathrm{RPN}}-{\mathrm{\γ}}_0)+S_0---\left(8\right)$

With formula (4) substitution following formula, then just obtained comprising the reactivity measurement formula of outer neutron source effect and the correction of gamma current feedback

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

Calculating in the reactive process with reactivity meter (or program), measuring, generally ignoring the data of S, γ owing to lack method.Promptly in calculating, reactivity makes S ₀=0, γ ₀=0, then following formula becomes

ρ _mI _RPN＝ρI _RPN+(Sl-ργ) (10)

According to formula (9), when ρ is constant, then ρ _m(I _RPN-γ ₀)=f (I _RPN) be linear function, its slope is exactly reactive ρ.In the derivation of equation process, only being γ is the hypothesis of constant; Also needing ρ in addition is the requirement of constant.Therefore this method requires below zero energy Doppler heat generating spot, just can be used for accurately measuring reactive ρ.

Dynamic response reactivity measurement method provided by the invention may further comprise the steps:

Step 1, according to above-mentioned principle, the measurement data of one group of stable state is can't handle to obtain reactive (I _RPNBe constant or ρ _m=0).If reactor is initially located in stable state, this needs a reactivity disturbance, to obtain the neutron-flux level measurement data I of one group of dynamic response _RPNThe speed that it is pointed out that this reactivity disturbance can not be too slow, also is through with basically otherwise disturbance finishes the back dynamic response.General reactor can obtain needed result by mobile control rod, promptly inserts continuously or the extraction control rod, keeps excellent invariant position then.When excellent invariant position, reactivity disturbance finishes.Also can realize by modes such as mobile fuel assembly or mobile reflection horizon.

Simultaneously according to point-reactor kinetic equation to neutron-flux level measurement data I _RPNCarry out inverse and calculate, (make S=S ₀, γ=γ ₀, n=I _RPN-γ ₀), calculate reactive ρ _m

At last reactivity is in the I behind the constant state _RPNDynamic response data (making neutron-flux level below zero energy Doppler heat generating spot) are ρ according to formula (9) _m(I _RPN-γ ₀)=f (I _RPN) fitting a straight line, its slope is exactly reactive ρ.

Dynamic response reactivity measurement method provided by the invention is based on the inverse method of maturation, owing to considered outer neutron source S and γ electric current, therefore critical conditions, the neutron-flux level to reactor does not all require.Not only under critical conditions, can improve reactive measuring accuracy, even and under subcritical state, also can measure subcriticality.The reactivity of measuring has been considered the influence of outer neutron source S and gamma noise, so the measuring accuracy height.Go for various heap types, reactivity measurement speed is fast, precision is high, and operability is good, data processing is simple.

Because dynamic response reactivity measurement method can be carried out reactivity measurement under subcritical state; Therefore, can move on to the reactor physics that need after reactor is critical, carry out originally test and carry out before critical, so just reduce the time that takies the overhaul critical path, improve the economic benefit of nuclear power plant;

In reaching critical process, traditional method is to adopt the rate Fa Laida that counts down critical.The rate method of counting down can only be estimated critical point, and can't obtain the reactivity (or subcriticality) of reactor core.And if reach in the critical process with the traditional rate that counts down method again in conjunction with using dynamic response reactivity measurement method at rod withdrawal, just can determine the reactivity (or subcriticality) of reactor core, thereby it is safer, faster to make reactor reach critical process.

Description of drawings

Fig. 1 is subcritical plunger opisthogenesis range explorer response curve down;

Fig. 2 is ρ _mI _RPN=f (I _RPN) fitting a straight line (γ ₀=0).

Embodiment

A kind of reactor reactivity measuring method may further comprise the steps:

Step 1, is according to actual needs given one in reactor reactivity disturbance faster, to obtain the neutron-flux level measurement data I of one group of dynamic response _RPN

Step 2, according to point-reactor kinetic equation to neutron-flux level measurement data I _RPNCarry out inverse calculating and (make S=S ₀, γ=γ ₀, n=I _RPN-γ ₀), calculate reactive ρ _m

Step 3, reactivity is in I behind the constant state _RPNThe dynamic response data are ρ according to formula (9) _m(I _RPN-γ ₀)=f (I _RPN) fitting a straight line, its slope is exactly reactive ρ.

Fig. 1 is subcritical plunger opisthogenesis range explorer response curve down.Wherein the ordinate on the left side is reactive, and unit is pcm (1 ρ cm=1 * 10 ^-5); The ordinate on the right is control rod rod position, and unit is the step; The ordinate on the right is also represented source range (SRC) counting rate, and unit is CPS.A is that neutron-flux level is measured curve; B is the reactive ρ without S, γ corrected Calculation _mEven (n=I _RPN, S=0); C is control rod rod position.

Fig. 2 is ρ _mI _RPN=f (I _RPN) fitting a straight line (γ ₀=0).Wherein, 2A is a measurement data, and 2B is the fitting a straight line of measurement data.

It is the difficult point that pile reactivity is measured that reactivity under the subcritical state (subcriticality) is measured always.For the advantage of dynamic response reactivity measurement method is described, be example explanation the present invention with the reactivity measurement under the subcritical state.

Step 1, according to above-mentioned principle, the measurement data of one group of stable state be can't handle obtain reactive, i.e. I _RPNBe constant or ρ _m=0.Therefore reactor inserts control rod with fast speeds, realizes reactivity disturbance faster, keeps excellent invariant position then.There is not other reactive introducing in the meantime.In order to obtain better result, preferably can keep more than 2 minutes, simultaneously to obtain the neutron-flux level measurement data I of one group of dynamic response _RPN, and the data of neutron-flux level below zero energy Doppler heat generating spot preferably also can be had more than 2 minutes.Neutron-flux level dynamic response curve A behind the subcritical plunger down as shown in Figure 1, C are control rod rod positions.

Step 2, according to point-reactor kinetic equation to neutron-flux level measurement data I _RPNCarry out inverse calculating and (make S=0, γ ₀=0, n=I _RPN), calculate reactive ρ _m, as the curve B among Fig. 1.

Step 3, reactivity is in I behind the constant state _RpNDynamic response data (neutron-flux level is below zero energy Doppler heat generating spot) as the A among Fig. 1, are ρ according to formula (10) _mI _RPN=f (I _RPN) fitting a straight line, the fitting a straight line equation that obtains is y=-197.95x+119113.The reactive ρ that is reactor is-197.95pcm (1pcm=1 * 10 ^-5), as the 2B among Fig. 2.

The present invention is based on the dynamic response reactivity measurement method of inverse, handle just to obtain the reactivity (or subcriticality) of reactor by simple mathematical, and considered the influence of outer neutron source and gamma electric current.Near the reactivity measurement precision of this method improving critical conditions, and reactor also can carry out reactivity (or subcriticality) measurement under subcritical state.

Claims (7)

1. reactor reactivity measuring method is characterized in that may further comprise the steps:

The neutron-flux level measurement data I of step 1, one group of dynamic response of acquisition _RPN

Step 2, make S=S ₀, γ=γ ₀, n=I _RPN-γ ₀, according to point-reactor kinetic equation to neutron-flux level measurement data I _RPNCarry out inverse and calculate, calculate reactive ρ _mWherein, S reflects outer neutron source effect, and γ is the gamma electric current;

Step 3, the reactive ρ of reactor core is in I behind the constant state _RPNThe dynamic response data are ρ according to following formula _m(I _RPN-γ ₀)=f (I _RPN) fitting a straight line, its slope is the reactive ρ of reactor core,

ρ _m(I _RPN-γ ₀)＝ρI _RPN+(Sl-S ₀l-ργ)

S ₀, γ ₀Be constant.

2. reactor reactivity measuring method according to claim 1 is characterized in that: in the described step 1 by to one in reactor reactivity disturbance faster, to obtain the neutron-flux level measurement data I of one group of dynamic response _RPN

3. reactor reactivity measuring method according to claim 1 is characterized in that: in the described step 3 reactivity is in the I behind the constant state _RPNThe dynamic response data are ρ _m(I _RPN-γ ₀)=f (I _RPN) fitting a straight line, be below zero energy Doppler heat generating spot, to carry out at the pile neutron flux level.

4. reactor reactivity measuring method according to claim 2 is characterized in that: be in the described step 1 mode of a reactivity disturbance of reactor, insert continuously or the extraction control rod, keep excellent invariant position then.

5. reactor reactivity measuring method according to claim 2 is characterized in that: giving the mode of a reactivity disturbance of reactor in the described step 1 is that continuous mobile fuel assembly or mobile reflection horizon keep its invariant position then.

6. reactor reactivity measuring method according to claim 4 is characterized in that: the time of the excellent invariant position of described retentive control was at least 2 minutes, promptly kept the reactive constant time of reactor core to be at least 2 minutes.

7. reactor reactivity measuring method according to claim 5 is characterized in that: the time of described maintenance assembly or reflection horizon invariant position was at least 2 minutes, promptly kept the reactive constant time of reactor core to be at least 2 minutes.

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