CN1881481A - Inverse dynamic rod-drop method - Google Patents

Abstract

The invention relates to a reverse dynamic rod-drop method, which collects the nuclear power change data (dl) in the rod-drop process, uses the point stack power module to solve the reaction property or the change curvatures (p1, p3) of effective increment factor along the time, uses least square method to treat data (p2), and uses reaction balance formula (p30 and the nuclear design report data (d4), to obtain the needed reaction stack reaction property (or effective increment factor d6) and the reaction stack control rod value (d5).

Description

Inverse dynamic rod-drop method

Inverse dynamic rod-drop method is by gathering the nuclear variable power data in the rod motion, find the solution with point-reactor kinetic equation and to obtain reactivity or effective multiplication factor curve (inverse method) over time, use the Least Square in Processing data then, with reactive balance equation and nuclear design report data, obtain required pile reactivity (or effective multiplication factor) and reactor control rod and be worth at last.

(1) technical field:

The present invention relates to the reactivity measurement (G21C 17/104 measures reactive (5)) of nuclear reactor, utilize this method can obtain pile reactivity (or effective multiplication factor) and reactor control rod value.

(2) background technology:

1) point-reactor kinetic equation is found the solution reactivity or effective multiplication factor (inverse method)

Off-line digital reactivity meter program (ODRM) is according to a heap kinetic model, is used for calculating the reactive calculation procedure of a reactive off-line.Point-reactor kinetic equation is as follows:

$\frac{\mathrm{dn}\left(t\right)}{\mathrm{dt}}=\frac{k_{\mathrm{eff}}\left(t\right)(1-{\mathrm{\β}}_{\mathrm{eff}})-1}{l_0}n\left(t\right)+\underset{i=1}{\overset{6}{\mathrm{\Σ}}}{\mathrm{\λ}}_i{C}_i\left(t\right)+S---\left(1\right)$

$\frac{d{C}_i\left(t\right)}{\mathrm{dt}}=\frac{k_{\mathrm{eff}}\left(t\right){\mathrm{\β}}_{\mathrm{ieff}}}{l_0}n\left(t\right)-{\mathrm{\λ}}_i{C}_i\left(t\right)---\left(2\right)$

Wherein:

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

k _Eff(t), effective multiplication factor;

β _Ieff, i organizes effective delayed neutron fraction;

β _Eff, effective delayed neutron fraction; Wherein ${\mathrm{\β}}_{\mathrm{eff}}=\underset{i=1}{\overset{6}{\mathrm{\Σ}}}{\mathrm{\β}}_{\mathrm{ieff}};$ Annotate: for heavy water reactor, because the influence of photoneutron should add 9 groups of delayed photoneutron parameters again;

λ _i, the disintegration constant of i group delayed-neutron precursor;

C _i(t), i group pioneer cuclear density;

l ₀, the prompt neutron mean lifetime;

S, outer neutron source.

Off-line digital reactivity meter program (ODRM) obtains effective multiplication factor k by finding the solution point-reactor kinetic equation _Eff(t), obtain reactivity according to reactive definition at last.

2) reactive balance equation:

Only about 2s of the time interval between two state points (beginning fall the rod point 1 and the rod point 2 that falls fully) of this paper research, and the variation of moderator medial temperature is very little, and the changes of reactivity that moderator temperature effect, axial flux redistribution effect and cavity effect are introduced can not considered; Boron concentration is constant; The changes of reactivity that poison, burnup are introduced can not considered yet.The reactive balance equation that obtains two state points thus is:

Δρ＝Δρ _RCCA+Δρ _DOP+Δρ _MOT (3)

In the formula:

Δ ρ, the excellent forward and backward pile reactivity variable quantity that falls, Δ ρ=ρ ₂-ρ ₁

Δ ρ _RCCA, the changes of reactivity amount that the excellent forward and backward control rod that falls is introduced, Δ ρ _RCCA=ρ _RCCA2-ρ _RCCA1

Δ ρ _DOP, the changes of reactivity amount that the excellent forward and backward Doppler effect that falls is introduced, Δ ρ _DOP=ρ _DOP2-ρ _DOP1

Δ ρ _MOT, the changes of reactivity amount that the excellent forward and backward moderator temperature effect that falls is introduced,

Δρ _MOT＝ρ _MOT2-ρ _MOT1；

The preceding reactor of the rod that falls is kept critical conditions, i.e. ρ ₁=0, the reactivity that the rod back that then falls (rod point 2 fully falls) control rod is introduced is:

ρ _RCCA2＝ρ ₂-(Δρ _DOP+Δρ _MOT)+ρ _RCCA1 (4)

The zero energy of the rod that falls when being to(for) original state is measured, and does not then carry out Doppler effect and the correction of moderator temperature effect, and following formula also can be reduced to:

ρ _RCCA2＝ρ ₂+ρ _RCCA1 (5)

3) least square method

Do fitting a straight line with least square method, can effectively reduce the influence that measuring error is calculated reactivity on the one hand; The extension of the fitting a straight line reactivity of rod point that just can obtain to fall fully farthest reduces the influence of γ electric current on the other hand.

(3) summary of the invention:

Inverse dynamic rod-drop method is used for reactivity measurement, the following (see figure 1) of the method for its data processing and process:

3.1 reactive calculating

At first utilize data acquisition system (DAS) to obtain the nuclear variable power curve that rod causes, data acquisition time should be lacked at interval as far as possible.When choosing power history data, should choose preceding the 2～3min data of rod at least, with assurance reactor core stable equilibrium's reactor core state that before the rod that falls, is as the criterion.ODRM calculates with delayed neutron parameter and the nuclear variable power data chosen and just can obtain reactivity curve over time then.

Fall into the reactor core initial stage at control rod, if put aside the influence of poison, the reactivity of reactor should be near a horizontal linear; And it is close to 0 rapidly in time by the reactivity of ODRM calculating.This is to can not ignore and influenced reactive calculating owing to the rod back γ electric current that falls.The value of γ electric current is difficult for determining, and it also changes in time after the shutdown, and correction is not easy to do.In addition, the reactivity that the rod back ODRM that falls calculates is bigger along a center curve oscillation amplitude, this be since measuring error when low-power during than high power (relatively) to reactivity calculate influence bigger.

Process studies show that to the responsiveness curve characteristics to the about 40～50s in rod back that falls, center curve can the near linear processing from the rod back that falls.Therefore to doing fitting a straight line to the changes of reactivity curve of the about 40～50s in rod back that falls with least square method, can effectively reduce the influence that measuring error is calculated reactivity on the one hand from the rod back that falls; The extension of the fitting a straight line reactivity of rod point that just can obtain to fall fully farthest reduces the influence of γ electric current on the other hand.

After obtaining fitting formula with least square method, with following principle determine to begin to fall excellent some time and falling the excellent some time fully:

● excellent point (2D) selection principle begins to fall: reactive calculating shows near reactive slightly the vibration 0 or near slightly vibration mean value of nuclear power, be that reactor core is in critical conditions (or reactive calculating show near a reactive slightly vibration constant, promptly reactor core is in subcritical state or supercriticality); Near the excellent point that falls, can judge from reactive or nuclear variable power as far as possible.

● excellent point (2E) selection principle fully falls: constantly begin from the rod that begins to fall, reactive calculating shows that reactive absolute value increases gradually, and reaches or near peak point; And the rod point that falls fully constantly should be greater than beginning the excellent rod drop time (can obtain from the rod test that falls) that constantly adds that falls.

Begin to fall after the excellent some time determines with the excellent some time that falls fully, then just can calculate the reactivity that the rod that falls is fully put according to fitting formula.

3.2 measure excellent value calculation

According to reactive balance equation,, obtaining surveying excellent control rod worth with regard to processing with excellent reactor core reactivity of putting and the data that the nuclear design report provides of falling fully.

3.3 inverse dynamic rod-drop method and existing technology are relatively

Present commercial nuclear power station mainly adopts transfers boron method (inverse method) to measure the reactor core control rod worth, be characterized in that precision is higher, but measuring speed is slow.Naval reactor mainly adopts rod drop method to measure the reactor core control rod worth, be characterized in that measuring speed is fast, but precision is relatively poor.And experimental reactor also has other multiple reactivity measuring methods, and these methods respectively have relative merits.As, the commercial nuclear power station of part adopts the patent of invention DRWM method of Westinghouse Electric at present, and it adopts two cover inverse to calculate, can be than transferring the fast velocity survey reactor core control rod worth that manys of boron method.

Therefore, inverse dynamic rod-drop method and existing technology relatively have following characteristics:

1. compare with transferring the boron method, described method reactivity measurement speed is fast, owing to do not need to regulate boron concentration, has reduced the generation of boron water in addition, so good economy performance.

2. compare with transferring the boron method, described method can be measured big reactivity.

3. present commercial nuclear power station adopts transfers the boron method to measure control rod worth, because the requirement of technical manual also can't be carried out the measurement of all control rod total values.Compare with transferring the boron method, described method can be measured all control rod total values.

4. traditional rod drop method is owing to done multiple simplification hypothesis, and the reactivity measurement precision is limited.Therefore, compare described method reactivity measurement precision height with rod drop method.

5. described method can be used for various heap types, and reactivity measurement speed is fast, precision is high, and operability is good.

6. described method can be used for carrying out on the various initial power level reactivity measurement.But in order to guarantee precision, initial power should be on the level that can ignore neutron source.

Inverse dynamic rod-drop method is the same with traditional rod drop method, and the differential of energy measurement control rod is not worth.But, be to be used for the design of checking nuclear because commercial nuclear power station is measured the control rod worth fundamental purpose, the integration of measuring control rod is worth enough.Therefore commercial used in nuclear power station inverse dynamic rod-drop method replaces transferring the boron method to measure control rod worth, can obtain huge economic benefit.

(4) description of drawings:

Fig. 1 is inverse dynamic rod-drop method flow chart of data processing figure.Rectangle frame among the figure is represented processing procedure, the quadrilateral representative data.The expression that this figure is concise and to the point inverse dynamic rod-drop method data processing and process:

1) time nuclear variable power data (d1) just can obtain reactor core reactivity time dependent data (d3) to ODRM (p1) with falling excellent shutdown according to delayed neutron parameter (d2);

2) after having chosen state point, utilize least square method (p2) to do fitting a straight line, the reactor core reactivity of the rod point that fallen fully.

3) according to reactive balance equation (p3), the reactive data (d4) that provide with the nuclear design report of reactor core with the rod point that falls fully, processing obtain actual measurement fall reactor core reactivity under excellent control rod worth (d5) or the control rod insertion state (or effective multiplication factor, d6).

Fig. 2 is fall rod reactor capability that causes and the changes of reactivity curve that is calculated by ODRM.2A is the reactor capability change curve that rod causes that falls, and 2B is the responsiveness curve that is calculated by ODRM, and 2C is least square fitting straight line and fitting formula, and 2D is the excellent point that begins to fall, and 2E is the excellent point that falls fully.

(5) embodiment:

The excellent shutdown transient data that falls that 4 different burnup points of certain reactor are arranged here, below with burnup at 70MWd/tU, the processing procedure of the excellent shutdown transient data that falls when initial power is 23%FP is an example, introduces data handling procedure and method in detail.

5.1 delayed neutron parameter

Table 2 be burnup at 70MWd/tU, the delayed neutron parameter when initial power is 23%FP.

Table 2 delayed neutron parameter

70MWd/tU
			Group number	Share β i	Disintegration constant λ i/s -1
1	0.000216	0.0125
			2	0.001458	0.0308
3	0.001348	0.1148
			4	0.002813	0.3103
5	0.000958	1.2327
			6	0.000323	3.2875
Total share β	0.007116
			l 0＝25.21×10 -6s		Be worth factor I=0.970

5.2 reactive calculating

The nuclear variable power curve that the fall rod of Fig. 2 " variable power curve (2A) " when being 70MWd/tU burnup point causes, data are obtained by data acquisition system (DAS), and data acquisition time is spaced apart 0.1s.ODRM calculates responsiveness curve (2B) with the delayed neutron parameter of table 2 and the nuclear variable power data of choosing.

Example obtains fitting formula (2C) with least square method:

y＝99.976x-62987 (7)

Wherein y is that (millinile is pcm to reactivity, 1pcm=10 ^-5), x is time (s).According to the description of the 3rd joint, the excellent some time of determining to begin to fall is x=546.7s, and the excellent some time that falls fully is x=548.3s (the excellent test findings that falls shows that single cluster rod drop time is 1.3s), then just can calculate the reactivity that the rod that falls is fully put according to formula (7):

y＝99.976×548.3-62987＝-8170.2pcm

5.3 measure excellent value calculation

The rod point that begins to fall is state point 1, and the rod point that falls fully is state point 2, and status point parameter sees Table 3.The reactivity that introduce the Doppler power loss that need cause variable power according to formula (4), the changes of reactivity (can omit) that the moderator temperature effect is introduced and initial rod position be made correction, just can obtain the value of all control rods when slotting entirely.Revise used data by checking in the nuclear design report.

Table 3 status point parameter (70MWd/tU, initial power 23%FP)

State point	Time/s	The D rod position/step	T ref/℃	T avg/℃	Nuclear power/%FP	Reactivity/pcm
							Rod point 1 begins to fall	546.7	146	299.99	293.93	23.375	0
Rod point 2 fully falls	548.3	0	302.67	293.88	1.185	-8170.2

Table 4 has been listed the measurement result of calculation of 4 different burnup point ARI control rod worths of this calculating and it and theoretical value result relatively, and the absolute value of its relative error is all less than 10%.

The ARI control rod worth measured value of 4 burnup points of table 4, theoretical value are relatively tabulated

Burnup	Initial power level	Rod point reactor core reactivity fully falls	The Doppler effect correction of two state points	The moderator temperature effect correction of two state points	The rod that begins to fall is put the reactivity that introduce the initial rod position	The ARI rod is worth (reactivity that the rod point rod that falls is fully introduced)		Relative error
									Measured value	Theoretical value
						MWd/t U	Pr/％ FP				ρ 2/pcm	Δρ DOP/pcm	Δρ MOT/pcm	ρ RCCA1/pcm	ρ RCCA2/pcm	ρ ARI/pcm	％
70	23.0	-8170.2	266.3	0.5	-260.8			-8697.7	-9314.5	-6.6
						292	48.5				-8286.1	452.3	0.1	-216.9	-8955.4	-9365.1	-4.4
581	97.5	-8008.2	964.5	0.0	-29.0			-9001.7	-9422.8	-4.5
						1683	96.3				-7938.6	857.7	0.0	-78.0	-8874.3	-9261.1	-4.2

Claims (8)

1. reactor reactivity measuring method, it can carry out following measurement safely, fast:

A) pile reactivity measurement (or the effective multiplication factor measurement, d6)

B) reactor control rod is worth and measures (d5)

Described method comprises the following steps:

A) time nuclear variable power data (d1) just can obtain reactor core reactivity time dependent data (d3) to ODRM (p1) with falling excellent shutdown according to delayed neutron parameter (d2);

B) after having chosen state point, utilize least square method (p2) match, the reactor core reactivity of the rod point that fallen fully.With following principle determine to begin to fall the excellent some time with fall the excellent some time fully:

● excellent point (2D) selection principle begins to fall: reactive calculating shows near reactive slightly the vibration 0 or near slightly vibration mean value of nuclear power, be that reactor core is in critical conditions (or reactive calculating show near a reactive slightly vibration constant, promptly reactor core is in subcritical state or supercriticality); Near the excellent point that falls, can judge from reactive or nuclear variable power as far as possible.

● excellent point (2E) selection principle fully falls: constantly begin from the rod that begins to fall, reactive calculating shows that reactive absolute value increases gradually, and reaches or near peak point; And the rod point that falls fully constantly should be greater than beginning the excellent rod drop time (can obtain from the rod test that falls) that constantly adds that falls.

C) according to reactive balance equation (p3), the reactive data (d4) that provide with the nuclear design report of reactor core with the rod point that falls fully, processing obtain actual measurement fall reactor core reactivity under excellent control rod worth (d5) or the control rod insertion state (or effective multiplication factor, d6).

Described method is characterised in that, be by gathering the nuclear variable power data (d1) in the rod motion, find the solution with point-reactor kinetic equation and to obtain reactivity or effective multiplication factor curve (p1 over time, d3), use Least Square in Processing data (p2) then, use reactive balance equation (p3) and nuclear design report data (d4) at last, obtain required pile reactivity (or effective multiplication factor, d6) and reactor control rod be worth (d5).

2. though have the small part reactor that the inverse method is used in combination with rod drop method at present, the method for data processing is still based on the rod drop method disposal route.According to the method for claim 1, it is characterized in that using Least Square in Processing again with the result that the inverse method is handled, can effectively reduce the influence that measuring error is calculated reactivity so on the one hand; The extension of the fitting a straight line reactivity of rod point that just can obtain to fall fully at utmost reduces simultaneously the influence of γ electric current on the other hand.

3. according to claim 1,2 method, it is characterized in that determining beginning to fall the principle of excellent some time and the excellent some time that falls fully, make the extension of fitting a straight line just can obtain to fall the fully reactivity of rod point, farthest reduce the influence of γ electric current, improved computational accuracy.

4. according to claim 1,2,3 method, it is characterized in that with reactive balance equation (p3), can obtain required pile reactivity (or effective multiplication factor, d6) or reactor control rod be worth (d5).

5. according to claim 1,2,3,4 method, it is characterized in that going for various heap types, reactivity measurement speed is fast, precision is high, and operability is good.

6. according to the method for claim 1-4, it is characterized in that going for carrying out on the various initial power level reactivity measurement.But in order to guarantee precision, initial power should be on the level that can ignore neutron source.

7. present commercial nuclear power station mainly adopts transfers boron method (inverse method) to measure the reactor core control rod worth.Because the requirement of commercial nuclear power station technical manual also can't be carried out the measurement of all control rod total values.With transfer the boron method relatively, according to claim 1,2,3,4 method, it is characterized in that measuring all control rod total values.

8. according to claim 1,2,3,4 method, the described method rod point that can be used for beginning for a certain reason to fall is not to be in the excellent situation of falling of critical conditions.The preceding data acquisition of rod point necessary long enough in this case begins to fall, must consider to begin to fall the reactivity of rod point in the reactive balance equation, described method is characterised in that the rod point that begins to fall is not to be in the excellent situation of falling of critical conditions can carry out reactivity measurement yet.

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