CN105185421A - Method for detecting degree of cleanliness of reactor core fuel assembly - Google Patents

Abstract

The invention relates to a method for detecting the degree of cleanliness of a reactor core fuel assembly. The method includes the following steps that first, the total quantity of stains on the surface of the entire fuel assembly and the activity of all nuclides in a cooling agent are obtained through theoretical calculation, and the corresponding relation between the total quantity of the stains and the activity of all the nuclides is found out; then the activity of all the nuclides in the cooling agent is obtained through actual measurement; the activities of all the nuclides, obtained in the above two steps, are compared and analyzed, and accordingly the total quantity of the nuclide stains on the surface of the entire fuel assembly is obtained. By the adoption of the method, the surface contamination condition of the fuel assembly can be determined quickly, no extra measurement or operation to the fuel assembly by a nuclear power plant operating unit is needed, the problem that the surface contamination of a traditional fuel element cannot be determined easily is solved, and a fast and feasible method is provided for detection of the degree of cleanliness of the reactor core fuel assembly. The structure is simple and implementation is convenient.

Description

The detection method of reactor fuel unit clean degree

Technical field

The invention belongs to cleanliness detection field, be specifically related to a kind of detection method of reactor fuel unit clean degree.

Background technology

Nuclear reactor requires to safely and steadily run on the one hand, and claimed staff on the other hand, the public is from excessive radiation irradiation outside the venue, avoids the radioactive contamination of environment.Radiative source term in primary Ioops is operation management in power plant, waste management system designs and the source of radiation protection design.Radioactive nuclide in presurized water reactor primary Ioops cooling medium comprises the activation products etc. that in fission product, actinide, activation corrosion product and primary Ioops, adjuvant or impurity activation produce, and is wherein mainly fission product and activation corrosion product.Fission product does not generally have activation corrosion product important for the contribution of radiation field, but the former (especially clad failure generation) has even more important effect for power plant safety analysis.

At present along with the progress of the technology of fuel element production, the occurrence probability of the breakage of fuel can is more and more lower, and in primary Ioops cooling medium, the source of fission product is mainly from the contribution of fuel element surface contamination.Therefore the cleanliness of reactor fuel element determine the level of activity of the fission product in current primary Ioops cooling medium.For nuclear power plant's operating organization, by the assessment to fuel element surface contamination amount, advantageously in the management that power plant runs.

Summary of the invention

For the defect existed in prior art, the invention provides a kind of detection method of reactor fuel unit clean degree, quick detection fuel is in the fabrication process to the total amount of fuel assembly surface contamination, without the need to unit of operation of nuclear power plant, extra measurement or operation are carried out to fuel assembly, solve traditional fuel assembly surface and pollute the problem determining difficulty; Method is simple, convenient operation.

For reaching above object, the technical solution used in the present invention is: the detection method providing a kind of reactor fuel unit clean degree, comprises the steps:

1) drawn the activity of each nucleic in whole fuel assembly surface contamination total amount and cooling medium by theory calculate, and find out corresponding relation between the two;

2) activity of each nucleic in cooling medium is drawn by actual measurement;

3) by step 2) and step 1) activity that obtains each nucleic compares analysis, draws whole fuel assembly surface contamination total amount.

Further, in step 1) in, described whole fuel assembly surface contamination total amount N, is obtained by following formula $N=S\·N_f\·e\·\frac{A_0}{A}$

Wherein: S is that single fuel rod stain surfaces is amassed; N _ffor total radical of reactor core internal combustion charge bar; E is the enrichment of fuel; A ₀/ A is the actual activity of nucleic and Nuclide measurement activity ratio.

Further, in described cooling medium, the activity of each nucleic is obtained by following formula:

$\begin{array}{c}\frac{{\mathrm{dN}}_{ci}}{dt}=\mathrm{\θ}-\left({\mathrm{\λ}}_i+\frac{Q}{W}\·{\mathrm{\η}}_i+\frac{\left(1-{\mathrm{\η}}_i\right)\·B^{\′}}{\left(B_0-B^{\′}\·t\right)}+\frac{L}{W}+{\mathrm{\σ}}_i\·\mathrm{\φ}\·C_V\right)\·N_{ci}+\\ \underset{j=1}{\overset{n}{\mathrm{\Σ}}}\left(f_{ij}\·{\mathrm{\λ}}_j\right)\·N_{ci}+\underset{k=1}{\overset{n}{\mathrm{\Σ}}}\left({\mathrm{\σ}}_k\·\mathrm{\φ}\·CVR\right)\·N_{ck}\end{array}$

Wherein:

K=supposes that fission product enters the share in cooling medium; The nucleic total atom number that N=fuel element pollutes; Y=fission yield; Σ=macroscopic cross section; Φ=neutron flux; The rate of release of θ=fission product; N _cthe total amount of radioactive nuclide in=reactor coolant; ν=nucleic escape rate coefficient (1/s); N _pthe total amount of radioactive nuclide in=reactor core burst slug rod; The disintegration constant of λ=nucleic; Q=reactor coolant letdown flow; W=reactor coolant quality; η=cvcs is to the removal efficiency of nucleic;

B'=boron concentration slip; B ₀=initial boron concentration; T=working time; L=reactor coolant leakage rate; σ=microcosmic absorption cross section; C _vthe ratio of=Core cooling agent volume and reactor coolant volume; F=decay fraction; The nucleic of the current calculating of i=; The nucleic of j=and i nucleic in same decay chain; K=neutron death generates the nucleic of i nucleic.

Further, in step 2) in, the described method being drawn the activity of each nucleic in cooling medium by actual measurement, in two kinds of situation, for short-life nucleic, measures the time of sample for 16h after sampling; For long-life nucleic, measure the time of sample for 48h after sampling; Then measure respectively after short-life nucleic and long-life nucleic being placed 72h, measurement result is verified with short-life nucleic and long-life Nuclide measurement results contrast respectively.

Further, following formula is utilized to revise short-life nucleic and long-life Nuclide measurement result by above-mentioned, A ₀=Ae ^{λ t}

Wherein: A ₀for the actual activity value of Main Coolant Radionuclide; A is the measurement activity value of Main Coolant Radionuclide; λ is disintegration constant; T is the time interval being sampled to measurement.

Advantageous Effects of the present invention is:

(1) the present invention uses the method that theory calculate combines with the actual measurement of power plant major loop fission product source item, final realization determines fresh fuel fast in the fabrication process to the total amount of the surface contamination uranium of fuel assembly, without the need to nuclear power plant's operating organization, extra measurement or operation are carried out to fuel assembly, solve traditional fuel assembly surface and pollute the problem determining difficulty, the quick detection for reactor fuel unit clean degree provides a kind of feasible method;

(2) method is simple, convenient operation.

Accompanying drawing explanation

Fig. 1 is that in reactor fuel unit clean degree detection method of the present invention, the homologous thread figure between total amount and activity stained by fuel assembly.

In figure:

A-I-131 curve B-X _e-133 curve C-I-133 curves

Embodiment

Below in conjunction with accompanying drawing, the specific embodiment of the present invention is described in further detail.

The detection method of reactor fuel unit clean degree provided by the invention, the method that first the method uses theory calculate to combine with the actual measurement of power plant major loop fission product source item, then compare analysis by the source item of the source item of the major loop calculated and the part nucleic of actual measurement, finally can determine that fresh fuel is in the fabrication process to the total amount of fuel assembly surface contamination fast.

Wherein, the computing method of the surface contamination total amount of reactor fuel assembly, the process of concrete theory calculate is as follows:

First the surface area stain of single fuel rod is calculated by formula (1) and (2); Fuel element pollute total amount by formula (3) calculate, then by formula (4) calculating fission product to the rate of release in cooling medium, finally result is brought into formula (5), the activity of each nucleic in cooling medium can be obtained.

S ₁＝π·d·h(1)

$S_2=\frac{1}{2}\·\mathrm{\π}\·d^2---\left(2\right)$

$N=(S_1+S_2)\·N_f\·e\·\frac{A_0}{A}---\left(3\right)$

$\begin{array}{c}\frac{{\mathrm{dN}}_{ci}}{dt}=\mathrm{\θ}-\left({\mathrm{\λ}}_i+\frac{Q}{W}\·{\mathrm{\η}}_i+\frac{\left(1-{\mathrm{\η}}_i\right)\·B^{\′}}{\left(B_0-B^{\′}\·t\right)}+\frac{L}{W}+{\mathrm{\σ}}_i\·\mathrm{\φ}\·C_V\right)\·N_{ci}+\\ \underset{j=1}{\overset{n}{\mathrm{\Σ}}}\left(f_{ij}\·{\mathrm{\λ}}_j\right)\·N_{ci}+\underset{k=1}{\overset{n}{\mathrm{\Σ}}}\left({\mathrm{\σ}}_k\·\mathrm{\φ}\·CVR\right)\·N_{ck}\end{array}---\left(5\right)$

Wherein:

The external diameter (cm) of d=fuel can;

The length (cm) of h=fuel rod;

N _ftotal radical of=reactor core internal combustion charge bar;

The enrichment of e=fuel;

The atomic weight of A=nucleic;

K=supposes that fission product enters the share in cooling medium;

The nucleic total atom number that N=fuel element pollutes;

Y=fission yield (1/s);

Σ=macroscopic cross section (1/cm);

Φ=neutron flux (n/cm ²s);

The rate of release (1/s) of θ=fission product;

N _cthe total amount of radioactive nuclide in=reactor coolant;

ν=nucleic escape rate coefficient (1/s);

N _pthe total amount of radioactive nuclide in=reactor core burst slug rod;

The disintegration constant (1/s) of λ=nucleic;

Q=reactor coolant letdown flow (g/s);

W=reactor coolant quality (g);

η=cvcs is to the removal efficiency of nucleic;

B'=boron concentration slip (ppm/s);

B ₀=initial boron concentration (ppm);

T=working time (s);

L=reactor coolant leakage rate (g/s);

σ=microcosmic absorption cross section (cm ²);

C _vthe ratio of=Core cooling agent volume and reactor coolant volume;

F=decay fraction (%);

The nucleic of the current calculating of i=;

The nucleic of j=and i nucleic in same decay chain;

K=neutron death generates the nucleic of i nucleic;

For the actual measurement method of power plant's major loop fission product source item, in two kinds of situation, for short-life nucleic, as ¹³³i etc. measure the time of sample for 16h after sampling, carry out first time measure this sample; For longer life nucleic, the impact that can short-lived nuclide avoided the proper extension time to compose γ, as right ¹³¹the Measuring Time of I is 48h after sampling, carries out first time measure this sample; Place and respectively second time is carried out to two kinds of samples after 72h and measure, measurement result and compare with short-life nucleic and long-life Nuclide measurement result and verify respectively.The present invention is the accuracy ensureing measurement result, measurement result is utilized following formula correction, and this correction does not consider that the decay of other parent nucleus produces the situation of daughter nucleus:

A ₀＝A·e ^λ·t(6)

Wherein:

The actual activity value (Bq) of A0=Main Coolant Radionuclide;

The measurement activity value (Bq) of A=Main Coolant Radionuclide;

λ=disintegration constant (1/s);

T=is sampled to the time interval (s) of measurement.

The specific activity of the specific species of the major loop calculated and actual measured value are compared, draws the total amount of fuel assembly surface contamination, specific as follows:

First by calculating the different specific activity staining the fission product of the major loop under total uranium amount correspondence of specific power plant, show by the form of curve; And then according to actual measured value, the existing curve of contrast, can draw the total amount of fuel assembly surface contamination very easily.

As shown in Figure 1, the present invention with ²³⁵u is that example is described, and show that the total amount of fuel assembly surface contamination is about 2.4g.The present invention will consider the releasing mechanism that fission product is different, Xe-133, I-131 and I-133 are compared, can ensure that the measurement activity of nucleic is stain from fuel element outward on the one hand, avoid only there are calculating data on the other hand, do not have the situation of measured value to occur.Especially, when the conclusion of iodine and inert gas exists bigger difference, based on iodine, because the uncertainty of inert gas is larger in primary Ioops cooling medium.

The detection method of reactor fuel unit clean degree of the present invention is not limited to above-mentioned embodiment, and those skilled in the art's technical scheme according to the present invention draws and other embodiment belongs to technological innovation scope of the present invention equally.

Claims (5)

1. a detection method for reactor fuel unit clean degree, comprises the steps:

1) drawn the activity of each nucleic in whole fuel assembly surface contamination total amount and cooling medium by theory calculate, and find out corresponding relation between the two;

2) activity of each nucleic in cooling medium is drawn by actual measurement;

3) by step 2) and step 1) activity that obtains each nucleic compares analysis, draws whole fuel assembly surface contamination total amount.

2. the detection method of reactor fuel unit clean degree as claimed in claim 1, is characterized in that:

In step 1) in, described whole fuel assembly surface contamination total amount N, is obtained by following formula

$N=S\·N_f\·e\·\frac{A_0}{A}$

Wherein: S is that single fuel rod stain surfaces is amassed; N _ffor total radical of reactor core internal combustion charge bar; E is the enrichment of fuel; A ₀/ A is the actual activity of nucleic and Nuclide measurement activity ratio.

3. the detection method of reactor fuel unit clean degree as claimed in claim 2, is characterized in that: in described cooling medium, the activity of each nucleic is obtained by following formula:

$\begin{array}{c}\frac{{\mathrm{dN}}_{ci}}{dt}=\mathrm{\θ}-({\mathrm{\λ}}_i+\frac{Q}{W}\·{\mathrm{\η}}_i+\frac{(1-{\mathrm{\η}}_i)\·B^{\′}}{(B_0-B^{\′}\·t)}+\frac{L}{W}+{\mathrm{\σ}}_i\·\mathrm{\φ}\·C_V)\·N_{ci}+\\ \underset{j=1}{\overset{n}{\mathrm{\Σ}}}(f_{ij}\·{\mathrm{\λ}}_j)\·N_{cj}+\underset{k=1}{\overset{n}{\mathrm{\Σ}}}({\mathrm{\σ}}_k\·\mathrm{\φ}\·CVR)\·N_{ck}\end{array}$

Wherein:

K=supposes that fission product enters the share in cooling medium; The nucleic total atom number that N=fuel element pollutes; Y=fission yield; Σ=macroscopic cross section; Φ=neutron flux; The rate of release of θ=fission product; N _cthe total amount of radioactive nuclide in=reactor coolant; ν=nucleic escape rate coefficient (1/s); N _pthe total amount of radioactive nuclide in=reactor core burst slug rod; The disintegration constant of λ=nucleic; Q=reactor coolant letdown flow; W=reactor coolant quality; η=cvcs is to the removal efficiency of nucleic; B'=boron concentration slip; B ₀=initial boron concentration; T=working time; L=reactor coolant leakage rate; σ=microcosmic absorption cross section; C _vthe ratio of=Core cooling agent volume and reactor coolant volume; F=decay fraction; The nucleic of the current calculating of i=; The nucleic of j=and i nucleic in same decay chain; K=neutron death generates the nucleic of i nucleic.

4. the detection method of reactor fuel unit clean degree as claimed in claim 1, it is characterized in that: in step 2) in, the described method being drawn the activity of each nucleic in cooling medium by actual measurement, in two kinds of situation, for short-life nucleic, measure the time of sample for 16h after sampling; For long-life nucleic, measure the time of sample for 48h after sampling; Then measure respectively after short-life nucleic and long-life nucleic being placed 72h, measurement result is verified with short-life nucleic and long-life Nuclide measurement results contrast respectively.

5. the detection method of reactor fuel unit clean degree as claimed in claim 4, is characterized in that: utilize following formula to revise short-life nucleic and long-life Nuclide measurement result by above-mentioned, A ₀=Ae ^{λ t}

Wherein: A ₀for the actual activity value of Main Coolant Radionuclide; A is the measurement activity value of Main Coolant Radionuclide; λ is disintegration constant; T is the time interval being sampled to measurement.