JPS5810697A - Decay heat estimating device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a decay heat estimating device, and particularly relates to a decay heat estimating device for estimating changes over time in the decay heat of the entire reactor core and each fuel assembly after the reactor is shut down.

Traditionally, decay heat was calculated by off-line computers according to requirements during design or after an accident occurred. in this case,
At the time of design, the planned operation (irradiation) history (function of reactor output and irradiation time) was input, and when an accident occurred, the actual operation history was input, and the decay heat was calculated using K as shown below.

First, consider transuranic elements and fission products (FP) as sources of decay heat. The main transuranium element is I
・U, ”・NP. As a fission product, about 7
There are more than 00 nuclides, of which the major nuclides have different contributions depending on the cooling time, but -・Bb, e・ab,
There are 4 out of 50 nuclides such as ``st-''.Furthermore, by considering the production/decay series for each nuclide and combining the following equation, the production amount Ni of each nuclide is determined.

+J jlh+i e #* ・11(t) ・Nh(
t) one (λ1+g-・-(su・N(ri・am s
ea・-mζ Now, F(t)s Fission reaction rate at time tK rag Fission yield of nucleus 1a2 11*l Production of nuclide 1 per unit decay of nuclide j λ1g Decay constant of nuclide m, halved T for period.

When expressed as
Proportion of absorbing 1llI neutrons into one nuclide to generate nuclide 1 - Electron average neutron absorption cross section of rich nuclide - (Number of nuclide
As a method for finding the solution to the neutron flux equation (1) at time -, Matrlxgx
There are the pon@ntial method and the B@temann method.

The former method solves the atomic number density as a vector quantity, and the solution is expressed in vector representation. The latter is Bet@msn.

The expression is expressed as an algebraic expression. For example, the widely used decay sequence analysis code DCHAIN is Beta
Mann's method is used, but the decay sequence analysis code is 0.
RIQIN uses the above two methods for both short-lived nuclides and long-lived nuclides.

These calculations become enormous when the number of nuclides increases, and when calculating the decay heat for each fuel assembly, it is necessary to calculate the neutron flux spatial distribution and repeat the above calculation for each fuel assembly.
Since the data must be returned, the amount of calculation increases.

On the other hand, for the safety evaluation of the emergency core cooling system of a light water power reactor, the following simple ghure is used.

The formula is used.

P(seng, ts)/pe key At, -...
-(2) ζkok.

p(w, ta) Decay heat at infinite irradiation P6 1 to OMay/fi@5ont,
l Time after the reactor was shut down (cooling m-) A, Hatake 1 Shown in Table 1.

Equation (2) is a very simple equation and can only calculate the decay heat of the entire reactor core, making it inappropriate for making detailed evaluations based on actual VaO changes.

As explained above, currently known decay heat calculation methods include the detailed calculation method and the component calculation method, but the former requires a large amount of calculation capacity and takes a long time to calculate, and the online calculation method It is inappropriate as a
This problem exists in terms of accuracy due to various errors in nuclear data (errors in nuclear fission yield, decay heat nine-branching ratio, neutron capture cross section, etc.). The latter has four drawbacks: it is a simple calculation and has low accuracy, and it is not possible to evaluate each fuel unit.

The present invention has been made in view of the above, and its purpose is to analyze changes over time in the decay heat of the entire reactor core and each fuel assembly using decay heat obtained from actual measurement data such as coolant temperature and flow rate. An object of the present invention is to provide a decay heat estimating device that can accurately estimate decay heat in a short time.

IE1o features of the present invention include an input device that periodically inputs various operations of the nuclear reactor and converts them into signals, and stores operation data from this input device, as well as an influence function, a decay heat estimation model, and an operation history. A storage device that stores information such as output distribution and burnup distribution from the data stored in this storage device.

It consists of a calculation device that calculates changes in decay heat over time, etc.
This calculation device is equipped with an estimation means for estimating decay heat using a function approximation formula, and a correction means for modifying the function approximation formula using decay heat measurement data obtained after the reactor shutdown. . The second feature is that after the point in time when the 11 number approximation error of the function approximation formula corrected by the correction means becomes larger than a predetermined reference value, the calculation device calculates the decay heat determined by the estimation means. Means is provided for estimating the decay heat from the result of multiplying the ratio of the decay heat obtained from the function approximation formula corrected by the correction means at the time and the decay heat obtained by the estimation means at the time. At the point.

Hereinafter, the present invention will be explained by the embodiments shown in FIGS.
This will be explained in detail using figures.

FIG. 1 is a block diagram showing an embodiment of the device of the present invention.
The installation positions of various measuring instruments that output data necessary for calculation are also shown. In Figure 1, 1 is a nuclear reactor, 2
3 is the reactor core, 3 is the primary cooling system, 4.5 is a thermometer that measures the reactor inlet 1 degree of crystallinity and outlet a degree in the primary cooling system 3, respectively, and 6 is 1 that measures the flow rate of the primary system coolant. Next system flow needle,
7 is a primary system main circulation pump, 8 is an intermediate heat exchanger, 9 is a primary auxiliary cooling system, and 10.11 is an at- total,
12 is a primary auxiliary system flow needle that measures the flow rate of the primary auxiliary coolant, 13 is a primary auxiliary system pump, and 14 is a control rod position detector.

Reference numeral 15 denotes a decay heat estimating device according to the present invention, which includes an input device 151 that periodically takes in the operating data that is the output of each needle side means described above, and an input device 151 that stores the operating data that is taken into the human power device 1151 and which will be described later. A storage device 152 that stores a fluence function, a decay heat estimation model, a driving history, etc., and an arithmetic device 153 that calculates an output distribution, a burnup distribution, and a change in decay heat over time from the data stored in the storage device 152. , an output device 154 consisting of a line printer, a cathode ray tube, etc., and a control device 1 that controls these operations.
It consists of 55.

Next, the details of the calculation method in the calculation device 153 will be explained using the flowchart of the decay heat estimation calculation shown in FIG. First, during steady operation, periodically measure the reactor thermal output from the heat balance (step 16).
These heat outputs are approximated as a function of time by a rectangle (see Figure 3), and edited and stored as an operation history (step 17).
). Next, calculate the output distribution by approximate calculation (step 18)
, find the burnup distribution by time integration (step 1
9). Then, as required by the operator (step 21), the change in decay heat over time is estimated using the operation history and combustion 1 distribution (step 20). Here, if the reactor is shut down (step 22), the decay heat is measured from the heat balance (step 23), and this measured value is used to automatically correct the estimation model (step 24). (step 26), the decay heat is estimated (
Step 25).

Next, the main parts of the flowchart shown in FIG. 1 will be explained in more detail. In the steady heat output measurement (step 16), the following 131 to (5) are determined from the heat balance.
Determine the reactor thermal output using the formula.

Pa:PM+PmuQ+)(・・・・・・・・・(3)
PM=FM-CII・ΔT ・・・・・・・・・
(4) Pmu = Fmu・CA・ΔT ・・・・・・・・・
...(5) Here 1 Pa g Reactor heat output P w g Amount of heat removed by the main cooling system PA Amount of heat removed by the auxiliary cooling system Q Pump heat input H; Total amount of heat radiation (heat radiation from the piping surface, etc.) 1F'w, Fm; The coolant flow rate Cw, CA of the main cooling system and the auxiliary cooling system is the coolant specific heat ΔTt of the main cooling system and the auxiliary cooling system. However, 1
When the secondary auxiliary cooling system is activated, decay heat is mainly cooled by this primary auxiliary cooling system.

In the operation history editing (step 17), the average value of the heat output measurement value and the operation time are combined, the sampling time of the heat output measurement is set as ΔT, and the average heat output of the sampled N times is set as PM, the operation time. When is Tw, if the thermal output Poet at the (N+1)th sampling is within a certain reference value (for example, within 5% of Pg), it is calculated using the following formula and stored.

T town, =TH+ΔT, ・・・・・・・・・
...(7) Output distribution estimation (step 18) uses an influence function method suitable for online calculation.

The influence function method will be explained below.

Assume that the three-dimensional power distribution Pp ("*Y*") in Agu control rod lean (reference state 1) becomes P(x, y, z) VC after the gtth control rod operation.

The influence function for the control rod t at that time is −
It is defined as follows.

Toko K.

z, position of the th control rod in the wealth reference state 21 position of the at th control rod after control rod operation In the influence function method,
Output distribution PCX, Y when operating 8 (t=1-N) control rods.

2) is given by the following equation.

(9) Note that the influence function defined by equation (8) is determined in advance by detailed calculations for appropriate changes in the insertion rate of each control rod, and is stored in the storage device 152. I'll keep it.

In the decay heat estimation (step 20), the decay heat change over time during infinite irradiation is determined by detailed conventional calculations that follow the decay series of many nuclides, and this is approximated by a function as follows.

P (te) = J At ”-” ” *
In order to accurately obtain short-term and long-term cooling times, it is necessary to select various values for the decay constant λl. For example, the second part of the decay heat function approximation by PPK in a DEMO class fast reactor
An example of table parameters is shown in Table 2. ＃Subcalculation result and (1
The deviation from the results obtained by 12 is 1ilfiO~10 when cooling.
“Within 3% within seconds.

Decay heat P (T, t) for finite irradiation (irradiation time T) is calculated from the following equation.

P(T,te)=ip(L)−P(L+T)・
...αD Here, t, 1 cooling time 4113 The decay force for an arbitrary irradiation pattern as shown in the figure is calculated as follows by repeatedly using the formula a.

On the other hand, if other operating conditions are the same, the decay heat is proportional to the operating output P, so Equation 4 deviates as follows.

Therefore, if the decay heat during infinite irradiation is approximated by the equation Ql) or the equation 1, the decay heat for any irradiation pattern can be calculated using the aa equation, and furthermore, the decay heat for each fuel assembly can be calculated using the aa equation. It can be calculated by distributing it depending on the magnitude of the output (burnup) of the fuel assembly.

Furthermore, since fuel is replaced during actual operation, fuel groups with different irradiation patterns coexist. Generally, in the case of N patch replacement, the decay heat change over time P+(t,)(1=1~N
). Next, the decay heat change over time p*(t
o) is calculated using the following formula.

Otori-1 Here, nl S The number of fuels in the fuel group having the 1st irradiation pattern This is distributed according to the decay heat of each fuel assembly as shown in the following equation.

P・g(1-Pa ("a)・1"°1"(1°)・
F3hl・(to)・・Mockery Σn+R(L) ΣBA1
s (t,) h j ζ, FAI (t・)1; i Decay of the fuel group belonging to the first fuel group with the same irradiation pattern - Bus (t@) is the burnup of the first fuel assembly belonging to the first fuel group Next, when the decay heat is measured, Decay heat estimation model modification (step 24) will be explained. The above decay heat estimation model is a model to be used when there is no actual measurement data of decay heat, but if actual sub-data is obtained, it can be used!
The estimation model is automatically corrected using the 11 data. At this time, the model is automatically modified based on the following criteria.

'(1) When decay heat is actually measured at 8 points after starting measurement or modifying the model.

(2) After model modification, the difference between the actual measured value and the estimated value exceeds the standard value.

The decay heat estimation model at this ζ is the index l11 shown in a12.
m, and the fitting coefficients Az and λS are determined by the least squares method using past measured values at N points. In this case, since the range a of the cooling time to be treated is narrow, fitting is performed using the superposition of a constant term and an exponential function of about 3 Bi as shown in the following equation ρ.

P Castle (tj=person.+2 people 16'1...
...or-1 The above equation is used to estimate the change in decay heat over time after the present time, but as the cooling time becomes longer, the contribution of the small term of the decay electric current increases and the accuracy deteriorates. Therefore, the error of the fitting near-fault formula shown in ae 2) F is defined by the α9 formula shown below. ] exceeds the standard value, the decay heat is estimated using a corrected formula of the α4 formula.

A・＋Xk−−”” ■−1 ・・・・・・・・・aη Here 1 Δn, 4 people 6. jλt $Aa e At @ Jt fitting error Current cooling time t, ·, Fitting near-image function! If the cooling time when ΔF exceeds a predetermined reference value is t, 1, then t. For ≦t, ≦, the decay heat is estimated using the formula % ``m@ <'e, the decay heat is calculated as Pa(tJ・PM (''*@)/Pa (''
*@ )(Pa (tj is t0 point K (14) formula - t'
Calculated value, PM (Ll) KQ4)
Estimated by the formula *value, RII ("J is t, 1 time point K (value determined by formula 10).

According to the embodiment of the present invention described above, since the calculation is simple, the calculation time is reduced by the above-mentioned collapse sequence analysis code DCHAIN.
The sf is reduced by one order of magnitude compared to the previous model, and the change in decay heat over time for the entire reactor core and for each fuel assembly can be estimated online at high speed. 0%K can also be accurately estimated.

This is especially useful when a nuclear reactor is forced to shut down due to an accident, etc., and is useful when determining the method for removing decay heat, predicting the progress of an accident, and determining when to remove damaged fuel from the reactor. This makes it easier to determine appropriate operating procedures in the event of an accident.

In the flowchart shown in Fig. 2), the output distribution estimation in step 18 is performed using a three-dimensional modified one-group coarse mesh diffusion calculation, the energy mode method, or the synthesis method, and the decay heat estimation in step 25 is performed. The functional form of the 5hureO equation shown in (2) 2 may be used as the fitting equation for the measured data, and the same effect can be obtained.

As explained above, according to the present invention, the temperature of the coolant,
By using the decay heat obtained from actual measurement data such as flow rate, it is possible to estimate light-time changes in the decay heat of the entire reactor core and each fuel mulberry coalescence in a short time and with high precision, especially when the reactor is in an emergency shutdown due to an accident, etc. It has the effect of being effective in determining appropriate operating procedures when

[Brief explanation of the drawing]

1st Lii! 1 is a block diagram showing an embodiment of the decay heat estimating device of the present invention, FIG. 2 is a flowchart showing an embodiment of the decay heat estimation calculation in the calculation device of FIG. 1111, and FIG. 3 is an example of the irradiation history. It is a line diagram. 15... Decay heat estimation device, 151... Input device, 1
52... Recording device, 153... Arithmetic device, 154.
... Output device, 155... Control device. Figure 2 Figure 3 Ginkai

Claims (1)

[Scope of Claims] 1. An input device that periodically inputs various operating data of the nuclear reactor and converts it into a signal, and an influence function that stores the operating data of the input device. It consists of a storage device that stores a decay heat estimation model, driving history, etc., and a calculation device that calculates output distribution, burnup distribution, change in decay heat over time, etc. from the data stored in the storage device. The apparatus is characterized by comprising an estimating means for estimating decay heat using a II number approximation formula, and a corner correction means for correcting the function approximation formula using decay heat measurement data obtained after the reactor shutdown. Heat estimation device. 2. Regularly input various operating data of the reactor 1) An input device that converts signals with a little input into the CJ4, and an influence function that stores operating data from the input device. It consists of a storage device that stores decay heat estimation models, operating history, etc., and a calculation device that calculates output distribution, burnup distribution, decay-1, changes over time, etc. from the data stored in the storage device. The cough calculation device includes an estimation means for estimating decay heat using a function approximation formula, and a correction means for modifying the function approximation formula using decay heat measurement data obtained after the nuclear reactor is shut down.
After the point in time when the function approximation g difference of the function approximation formula corrected by the correction means (by the correction means) becomes larger than the predetermined base value, the function after the correction by the correction means at the point in time is the decay temperature determined by the estimation means. a means for estimating the decay heat (the result of multiplying the ratio of the decay heat obtained by the approximation formula) and the decay heat obtained by the estimating means at the point in time. Estimation device.