JPH01248097A - Feed water control system for boiling water nuclear reactor - Google Patents

Abstract

PURPOSE:To diminish occasions of scrams, by providing a first function which supposes a mass flow rate of a two phases flow pouring into a nuclear reactor dome from an upper plenum of the nuclear reactor and by providing the second function which supposes a steam quality of the two phases flow. CONSTITUTION:An overall flow rate WLP is expressed by an equation I. As a portion theta (usually around 10%) of WLP becomes a leak flow, a channel flow rate WC and the leak flow rate WB are expressed as equations II and III, respectively. Subsequently, with receiving heat from a thermal nuclear reaction at a reactor core, WC and WB turn into a two phases flow with an average quality XUP, a void ratio alphaUP and a pressure PCORE, at an upper plenum. The quality X is determined by the equation IV and the void ratio alpha is determined by the equation V. Therefore, a steam flow rate is expressed as (quality) X total flow, and the remains are given as a saturated water flow rate. In this way, through supposing the physical quantities of state (a separator inlet flow rate WUP and the quality XUP), occasions of scrams caused by a reactor water level 'high' or 'low', can be diminished.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a water supply control device for a boiling water nuclear reactor, and in particular, to stably control the water level in the reactor and avoid scrams due to fluctuations in the water level. This invention relates to a multivariable control system suitable for.

[Conventional technology]

In boiling water reactors (hereinafter abbreviated as BWR), the water level of the reactor is also an important monitoring indicator, as is safety lifting, and the reactor core is designed so that it will not be exposed even in various hypothetical accidents. There is. Even during normal operation, a control method for the safety tube 1 is adopted to suppress fluctuations in the water level as much as possible, and to deal with fluctuations in the water level as quickly as possible with sufficient margin. In other words, in response to water level fluctuations, multiple set points are set on the increasing and decreasing sides, and an alarm or scram command is issued to urgently insert a control rod into the reactor. Although the reactor water level (indicating the water level outside the shroud, hereinafter simply referred to as reactor water level) changes depending on various plant conditions, the main control means is the feed water flow rate. Conventionally, the reactor water level setting signal was used to operate the valve that controlled the feed water flow rate.

The basic three-element control system uses the main steam flow rate signal and the feed water flow rate signal. Also, at startup, due to control safety,
They had switched to single-element control that uses only the reactor water level measurement signal.

However, with three-element control, when some events occur, the water level drops too much (or rises too much) and scrams occur even though there is no need to scram, which lowers the operating rate. Ta. Alternatively, it was desired to improve the water level control ability so that the water level does not fluctuate significantly and scram due to disturbances such as lightning strikes in the power system.

Conventionally, various improvement measures have been considered based on simulation tests and observations of actual machine phenomena, assuming these various situations. Conventional improvement plans are shown in References 1) to 10). In the following explanation of the present invention, the differences from conventional designs will be touched upon from time to time, but here, the features and differences of each of the conventional designs will be summarized.

Reference 1) changes the set point of the water level control system according to the recirculation flow rate so as to correct the core flow rate dependent error of the water level gauge for the safety protection system.

Reference 2) adds the output of the set pressure regulator or the speed control error signal of the recirculation system to the control error signal of the water supply control system, respectively, with a negative sign and a positive sign.

Reference 3) changes the gain of a three-element water level control system depending on the rate of change in furnace pressure.

Reference 4) calculates the differential value of the recirculation flow rate signal and adds this to the control error signal of the three-element water level control system with a negative sign.

Reference 5) calculates the differential value of the recirculation flow rate signal and adds this to the water level set value of the three-element water level control system.

Reference 6) adds a reactor water level error signal as a pressure control system set point change request signal when a pump trip signal is generated.

Reference 7) temporarily raises the water level set point when the water level suddenly decreases.

Reference 8) incorporates main steam pipe pressure, feed water temperature, and reactor dome pressure as signals for three-element signal calculation correction of main steam flow rate, feed water flow rate, and reactor water level signal.

Reference 9) introduces the signal obtained by passing the reactor pressure signal and recirculation flow rate signal through a specific filter into the water level error signal of the feedwater control system in the form of multiplication, or alternatively, the water level error signal is multiplied by the water level error signal of the pressure control system. The filtered signal is used in multiplication to vary the gain of the signal path added to the control error signal.

Reference 10) takes into account the opening degree of the valve of the return piping on the discharge side of the feedwater pump, and reduces the core flow rate when there is an excessive feedwater flow rate request.

[Problem to be solved by the invention]

Conventional methods are considered to be effective to a certain extent in each situation, but their background is based on inferences based on qualitative trends, parameter surveys using simulations, R observations of actual machine phenomena, etc. Regarding the internal state of the reactor, the results were obtained based on the following points: ``The core flow rate increases (or decreases), and voids increase (or decreases)...'' It is a measure.

Therefore, it is difficult to expect that the system will be effective in all operating situations such as startup, low output, high output, abnormality, and accident.

Therefore, an object of the present invention is to provide a control device centered on a water supply control system that suppresses fluctuations in reactor water level as much as possible under a wide range of operating conditions, improves operating efficiency, and expands safety margins. It is to be.

[Means to solve the problem]

Unlike conventional methods, the above objective is achieved by quantitatively understanding and grasping the physical mechanism of reactor water level formation, and by utilizing control means as much as possible according to the operating conditions.

The physical mechanism of reactor water level formation will be explained below, but the specific configuration of the control system depends on the type and number of measurable sensors and the type of actuator (operating end) (which differs depending on the type of BWR). This will be explained in detail later.

[Effect]

To explain the physical mechanism of reactor water level formation, Figure 1 shows the basic structure of a BWR. However, Figure 1 shows the internal structure of the pressure vessel 1 of a BWR that has recirculation pipes 21, 23, 24 outside and a jet pump 2o inside (however, numbers in the 100s are physical quantities. ).

In particular, the shroud 8 is a region that concentrically divides the reactor. In addition, the bulk water capital 16 is a part relatively close to the water surface, and usually refers to a part where saturated water or voids exist, and the downcomer part 17 refers to the recirculation piping 2 below from the bulk water capital.
This refers to the area up to the vicinity of exit 6. A core flow 102 discharged from the jet pump 25 is divided into a channel flow 103 passing through the core channel section 2 and a leakage flow 104 flowing through the core bypass channel section. The channel flow 103 entering the fuel rod assembly supported by the inlet grid plate 7 and the upper grid plate 18 becomes a two-phase flow of steam and water and flows into the upper plenum section 9.
Go out. Leakage flow 104, typically within 10%, also escapes into the upper plenum 7. On the other hand, the jet pump 25 is connected to the downcomer 17 via piping 26.
Suctioned sub-cooled water (water supply flow 110 and bulk water flow 1 supplied from the water supply sparger 10 via the water supply pipe 11)
09 forms mixed sub-cooled water) through pump 31
The pressure is increased through the discharge pipe 27, and the communication pipe 28
o Branched into several jet pump drive water pipes 29,
A driving stream 119 is ejected from the jet pump nozzle 30, and a part of the subcooled water 111 is sucked into the downcomer, and the jet pump generates the core stream 102. One of the purposes of the jet pump 25 is to generate a large amount of suction flow with a small driving flow 119, and one of its performance is defined as the M ratio of the following equation.

Usually, an external recirculation system as shown in this figure is composed of two independent systems, A system and B system.

Furthermore, the two-phase flow in the plenum 9 is caused by the standpipe 2
2, it enters a steam/water separator (hereinafter abbreviated as separator). In FIG. 1, the liquid phase is shown by a solid line, and the gas phase is shown by a broken line. The two-phase flow is swirled in the separator and centrifuged, and most of the flow is directed to the dryer 20 as a gas-phase flow (steam flow) 116, and as a liquid-phase flow (saturated water flow) 112.
One part of the gas phase is directed into the bulk water as a vapor stream 113 (this flow is called a carry-under flow), and one part of the liquid phase is discharged into the bulk water as saturated water streams 114 and 115. , is discharged from the top of the separator (this is called a carryover flow). A portion of the carryover flow is a flow 114 that directly falls to the water surface 100 and a portion that falls to the drain duct pipe 21 via the dryer 116. Strictly speaking, the corrugated plate-shaped dryer 116 removes the steam flow 116 and the slightly saturated water it contains, and high quality steam is sent as the main steam flow 101 from the main steam pipe 16 to the turbine.

Even when the relief safety valve is activated and steam flows out from the pressure vessel, the steam flow is also included and represented by 110.

Additionally, a cleanup stream 118 that purifies the reactor water is taken from a branch pipe 32 from the recirculation system piping 26 and returned to the water supply piping 11. Also, for the purpose of cooling the control rods, a small flow of coolant 120 is injected from the lower part 19 and passes through the control rod guide tubes to join the leakage flow.

Next, a device (sensor) for measuring the state inside the nuclear reactor will be described, but as mentioned above, it differs depending on the reactor type. Normally,
In order to measure the water level outside the reactor shroud, a differential pressure type water level gauge can be used to divide the measurement range, and can be used for multiple purposes.
Multiple units are installed for multiplexing. Upper tap piping 12
is connected to the liquid level standard 15, and converts the difference between the water head between the lower tap piping 13 and the liquid level and the fixed water column formed by the piping 14 and the liquid level standard 15 into electricity using a differential pressure gauge. .

Used as reactor water level signal Lw*.

Inside the reactor core (channels 2 and 3 will be collectively referred to as this), neutron flux detectors 5 (LPRM) are installed as strings 6 at four points in the axial direction and several dozen pieces in the horizontal direction.
arranged in three dimensions.

An APRM is also installed that indicates the average furnace output φ that is averaged over the entire furnace.

The flowmeter measures the jet pump total flow rate WJp, the leakage flow differential pressure between the core grid plates Wc111. Water supply flow rate WFW skewer.

The main steam flow rate WMs and even the flow rate W PLR of the recirculation pipe 27 may be measured as a differential pressure across a venturi pipe or pipe elbow.

The pressure gauge measures the pressure of the steam dome of pressure vessel 1 P DOME
, as the pressure downstream of the main steam pipe, the pressure immediately after the main blocking valve 121 is PH8! It is installed for the purpose of measuring V, turbine inlet side pressure PT, etc. Normally the upper plenum pressure P
The pressure inside the shroud 8, such as the core, is often not measured.

The thermometer measures the feed water temperature TFW and the temperature TLP on the intake side of the reactor water purification system.

These sensors may be of the same type used in parallel, or a plurality of wide-range, narrow-range, etc. sensors may be installed depending on the expansion of the measurement range or the different purposes of use. Furthermore, at present, there are many cases where information is limited to on-site instructions and displays, and is not imported into central control room instruments or computers.

As described below, which signals from these sensors are used to
Each control system has its own characteristics depending on how it is configured.

FIG. 2 summarizes the flow conditions in the reactor, focusing on the formation of the reactor water level 100. A region 200 is located inside the pressure vessel 1 from the upper free water surface to the suction pipe 26 of the recirculation system of the downcomer.
until the exit. Consider the balance of fluid flowing in and out of this area.

The inflowing mass flow rate W, n is expressed by equation (2).

'1Ln=WsEp+z+WsEpycu+WrAi,
L+z+Worv+z+WcoN, z+WFw+Wcu
w - (2) where, WsEpyl: saturated water flow rate separated by the separator WSEP, Cυ: separator carrier vapor flow rate WrAL+z: separator carryover water free fall flow rate Wous, z: separated water in the dryer, condensed water Flow rate WFII eTotal water supply flow rate (sum of both systems A and B) Wcon,t: Condensed water amount at free liquid level On the other hand, area 2
The flow rate flowing out from 00 is expressed by the formula (3) % W Jp^, s: Total flow rate of the suction flow of the jet pump belonging to the recirculation system of the A system.

(However, natural circulation components are excluded) WJPA, o: Total flow rate of driving water flow of jet pumps belonging to A system.

(However, natural circulation components are excluded) Wcuw: Purification system flow rate extracted from the recirculation piping or lower plenum and returned to the water supply piping WNAT: Flow rate flowing out from area 200 due to natural circulation force WEV^2g: Due to reduced pressure boiling, etc. , the flow rate of vapor evaporating from the free liquid surface to the dome WJPB,S; W, +pa+o: Wcua is
respectively W JP P^, s; WJPA, D; W
Flow rate of B system of recirculation system compatible with CUA.

The total flow rate 102 (WLP) reaching the core inlet is expressed by equation (4).

WLP = WNAT + WJPAIs + W, +
pa, s+WJP^, D+WJPBID
(4) Since a proportion θ (usually about 10%) of Wt and p becomes a leakage flow, the channel flow Wc and the leakage flow Wa are expressed by equations (4) and (5).

Wc=(-1-〇) ・WLP
-(5) Wa=θ ・WLP
...(6) Next, the amount of heat W is generated by nuclear thermal reaction in the reactor core. After ore, Wc,
Wa is the average quality Xu in the upper plenum
It becomes a two-phase flow with p, void ratio αUP, and pressure P core. Quality or, in equation (6), void rate α is (7)
The amount determined by the formula.

(7) Volume occupied by (steam + saturated water) (8) Therefore, steam flow rate = (quality) x (total flow rate), and the remainder is given as the saturated water flow rate.

This two-phase flow passes through the standpipe 22 and rushes into the separator 23. Separators have very complex characteristics, and the characteristics have been evaluated experimentally (see Reference 11).

Generally, the following characteristics of a separator are arranged as a function of the quality of the inlet two-phase flow Xup, the inlet flow rate Wup, and the water level Lss from the lower end of the separator skirt (assuming no movement of fluid between the two phases).

WsEp+7= (1-Xup) NWup -WSE
PICO°-(11)WMs2Xup NWup -W
SEP, CU - (12) where βCU is the carry-under and is the proportion of steam mixed into the total flow rate leaving the separator skirt.

βCO is carryover, which is the proportion of saturated water mixed into the total flow rate flowing out from the top of the separator.

According to the experiment, βcu= g (Xcu, Wup, Lss)
−(13) βco= f (Xcu, Wup+
Lss) ... (14), and are quality values whose typical examples are shown in FIGS. 3 and 4, respectively.

On the other hand, the natural circulation flow rate WNAT in equation (3) generates the driving force (water head difference) ΔW N A t in equation (15) based on the density difference inside and outside the shroud.

ΔWNAT=(DingBLK'Q BLKjudowN-Q
DWN) (p core-Q core)
-(15) Here, QBLK: Height difference Q from the free liquid level to the lower end of the bulk water region, DWN: Height difference from the lower end of the bulk water region to the core inlet height ncOre: To the effective length BL of the core: Bulk Water average density DIIN: Downcomer average density J' Core
: Determined by the two-phase flow rate homogeneity of the core, corresponding to the average void rate acore.

As will be described later, the measured value of the core flow rate includes the natural circulation flow rate, so there is no need to specifically evaluate equation (15). However, when the pump stops and the accuracy of the flowmeter is poor due to extremely low flow rate, W
Evaluate NAT.

Furthermore, the flow rate Wu of the two-phase flow flowing through the stand pipe 22
p is the pressure difference between the upper plenum pressure P core and the dome pressure P DOMH, and the flow resistance of the separator K s
This is an amount determined by ep and water head ΔH8EP.

The same is true for other channels, but the pressure loss due to flow is 2
It is proportional to the square of the total flow rate of the phase flow, and as its coefficient, K SE
P is given.

In the above explanations of equations (2) 2 to (15), we have shown static relationships, but in an actual nuclear reactor, the balance equation for flow in equation (16) dynamically relates each part. This describes the moment-to-moment changes in water level.

...(16) Here, i: channel number, length AI of the second channel (i) cross-sectional area of the second channel (i) WI: flow rate Ki of the channel (i): flow channel (i) Flow pressure loss coefficient Δ-PI Differential pressure ΔH1 between the front and back of the two flow paths (i): flow path (
Head differential pressure ΔA12 of i): Effect when the cross section suddenly changes in flow path (i) Kl': Contraction/expansion flow pressure loss coefficient of flow path (i) Finally, all these dynamic characteristic equations are combined simultaneously. If you solve this, you can see the changes in each flow rate.

In particular, the change in water level in the area of interest is expressed by the following equation:

Lw '□=(WIn-Wout)/(AIF"411)
・06)t Here, Lw: Water level AW based on the bottom of the downcomer = Effective cross-sectional area outside the shroud near the current water level ρW: Average density of water outside the shroud The actual effective cross-sectional area AW outside the shroud is , as shown in FIG. 5, changes due to the influence of the structure.

The present invention aims to reduce changes in the reactor water level under all conditions of the reactor, in other words, (17)
The goal is to make the formula dLw/dt (time rate of change in reactor water level) small.

For this purpose, in principle, on the right side of equation (16), W I
The water supply flow rate Wr so that n = W out
Just adjust w.

For the condition of W 1n = W out, (1)
When expanded using the relationships in equations (15) to (15), equation (17) is obtained.

WFW: (WJPA Is +WJPB +s+ W
JPA r o +WJPB ID+WNAT +WE
VA , d(WSEP , t + WSEP, cυ + WF
Au,,z+WoRs+z+Wcos,z)=((1
+ M) WJPA, D+ (1+M) WJPBID+W
NAT + WEVA, g) - WFALL + t +
WDRNsu1 +Wcos I1・βcoβcu+[
Xupβco/(1-βco) (1-Xup))・(
1-βcu) (1-βco)) ・=
(17) Note) Carrier conductor βCυ, carryover βco
Instead of (interconvertible), λcu = WSEPICU/ (Xup畢Wup)
−(17A)λco=WsEp, co/((1
-Xup)Wup)) -(17B) If we use (1
7) Equation can also be expressed in a simpler form as follows.

WFw=:Wp+Wt=v^+g-WFALLll-
WDRNll-WcoN,t Wup((1-λco
) (1-Xup)+λcu-Xup)
-(17C) In the conventional BWR water supply control system,
The basic principles are (1) matching the reactor water level to a set value, and (2) matching the feed water flow rate to the main steam flow rate, and various modifications have been made. In the state determined by equation (17), the value is equal to the main steam flow rate VMS, but in a transient state, the value is considerably different.

However, although not all the physical variables in equation (17) are measured, if two physical quantities can be estimated: the vapor quality Xup of the two-phase flow flowing into the separator and the total flow rate Wup of the two-phase flow, , Equation (17) can be used with good accuracy and can be applied to a wide range of water level control. In practice, the flow rate of the liquid phase components separated by the separator (1-X
up) Wup is the main physical quantity.

Here, among the constants and variables in equation (17), the one whose measured value can be used directly is W J P^IDI
WJPB, D. For the remaining variables, we will use the following estimations and approximations.

(1) The M ratio of the M nitrogen jet pump has been subjected to various individual tests and theoretical analysis, and can be expressed as a dependence on the flow rate in the form shown in Figure 6.

(2) WNAT: The natural circulation flow rate is calculated by taking into account the head change in equation (15) and the flow delay inherent in the reactor (18
).

...(18) Here, KNAT: Pressure loss coefficient a NAT, b NAT: Constant determining delay S Nira plus operator Below, Laplace (G(s)y x(t)) is the time domain signal x(t) The time response obtained by processing using the Laplace-transformed transfer characteristic G(s) is shown.

The p core included in AHNAT in equation (17) is actually a function of the void ratio CL CORE obtained by averaging the voids distributed three-dimensionally in the nuclear reactor.

(3) WEV^, t: Evaporation from the free water surface (particularly appears during depressurization t. In particular, since the bulk water city is close to saturation, bubbles are generated directly inside, and at a velocity v6 1 + Tg-5 = O -P DOME> 0...(19) Here, Kg: Evaporation gain, Tg: Delay time constant corresponding to Vg (4) WF^shiri, CO: Carry-over water falls directly to the water surface The amount is the δF ratio of the total carryover flow rate.

WF^shishi, co= δF 1 WSEPICO-(
20) δF is given as a function of WSEP and Co as shown in FIG.

(5) wDR), , : carryover, and
The water droplets inside the main steam are removed by a dryer, and the resulting water is collected in a drain and falls.

...(21) Here, KDRN Nigain TDRN: Dryer drain holding time constant (6)' WCON, x: Represents the liquid level and the condensation of steam on the dome structure, and the dome pressure P DO
This occurs when ME increases rapidly. This characteristic is approximated by the following equation.

WcoN, t = KCON ′P DOME (
P DOME > O) = O, O (PDOME < O) ... (22) Here, KCON: Condensation gain (7) X'up: Upper plenum quality Xup
is a quantity determined by flow rate WLP, reactor pressure PCore, core inlet enthalpy hLP, and core thermal output QCORH.

Wup+g+Wup, z Qco+tE-WLp(h x -h LP) -Dc
PcouE(hg hg)・WLP...(23) Here, Wup+g, Wup+1: Gas phase and liquid phase flow rate in the upper plenum hay hz: Pressure P C0RE L Therefore, enthalpy of saturated steam and saturated water Dc: Reactor core and A function of the mass of each fluid phase in the upper plenum and the physical properties of steam and saturated water QCORE: The heat generated by nuclear fission in the core thermal output is
It is possible to easily and accurately obtain the estimated value of the amount Xup transmitted to the cooling water with a certain delay time.
This is one requirement in this patent. Equation (23) shows an example of how to calculate it, but various models can be used, such as introducing the bypass flow rate shown in Equations (5) and (6), and treating the reactor core and upper plenum separately. This is permissible to the extent that real-time online processing is possible.

(8) Wup: The flow rate WυP of the two-phase flow flowing into the separator is the most important state quantity in this patent.

Even if Xup is not calculated, in equation (17), ignoring other secondary effects, WFW = Wt, p - Wup + WMS
Even if approximated by °°° (24), the water supply control system is sufficiently improved. During steady state, W up =
Since it is WLP, it is all about accurately finding the change in Wup during the transient period in response to the change in the reactor core and upper plenum.

That is, the flow rate Wup of the two-phase flow is given by the following model.

Wup=WLP-Mc+up
...(25) Here, Mc+UP is the subcooled water mass (Msc) in the core and upper plenum and the two-phase flow mass (
Mice), which varies greatly depending on the reactor core situation. The model is derived from mass balance, energy balance, etc., and takes the form of the following equation (see reference 12 for details)
.

Me+υp= f (Mc+upνMg, ct Mt*
up+ Msc*Mx, c, Mx, up, (ICO
RE, PcoREe etc)...(26) where, Mi, c, Ml, c: Steam in the reactor core, saturated water mass M t , υp, Mz, υP Steam in the second upper plenum, saturated water mass Msc: Reactor Inner subcool water mass αC0RE: Void ratio in the reactor PCORE: Average pressure in the reactor and upper plenum For example, when a control rod is inserted, αC0RE decreases,
MgecHMtgup also decreased, Mzlup+ Mic
e and Msc increase, and as a result, MC+UP changes as shown in FIG.

From the standpoint of water level control, the model that requires Mc+UP is:
The accuracy may be relatively low, and the effect of minute changes in pressure over a short period of time may be ignored.

Rather, it is desirable to have something that suppresses changes caused by heat transfer (a relatively slow phenomenon).

One method is the first-order method, which reflects simulations and actual machine tests.

It can be approximated by the following equation as a linear combination of PcouEt WLP.

...(27) Here, it is assumed that .P CORE is proportional to P DOME.

・Ct, Cz, Ca are appropriate coefficients ・τ is a constant when considering flow delay In the conventional three-element control system, this corresponds to the assumption that Me+υp=o, and its validity is Wup = WLP +W
MS: It is only guaranteed by the relationship WsEp, g = WFII. In other words, changes in the amount of steam and saturated water in the reactor, changes in the quality of the outlet, and changes in the outflow flow rate based on the void ratio of the reactor and upper plenum, changes in the inlet subcool, etc. were ignored.

Naturally, various methods for determining the two-phase flow rate Wup can be considered depending on the precision or coarseness of the model used, but this patent does not provide any regulations regarding the Wup or Xup models. Another way to obtain WUP will be shown.

Equation (25) attempts to calculate Wup from the conditions inside the shroud, but here we try to estimate Wup from the conditions outside the shroud, that is, the dome pressure, main steam flow rate, and reactor water level signals. do.

Divide the area outside the shroud and the dome into the free liquid surface and the border,
If the respective volumes are Vυ and v, the total area V2=V
A relationship in which the time change of υ+vL is always zero, a balance formula for mass flowing into each region, a balance formula for energy, and.

The following equation can be determined from the relationship between v and the reactor water level Qw determined from the shroud cross-sectional area AW.

PDOME: f function(Wspp+g+
Was, WEv^, g.

WcoN, t, flw, etc) ・・−
(28) QW: function (WLp+
WUPI WPW, AwtWoRs, z+W
rAu, +z, V/coN, c, etc)...(
29) From now on, Wup= f function (Q 11. W+s+
WFw, WLPIAll PDOME, etc) ... (30) That is, measurable quantity Qw, PooMe+ WLP
.

It is possible to approximately obtain the value of Wup from WFI ate under appropriate assumptions.

However, like the equation (25), the equation (30) also holds that WLIP=WLP during steady operation, so it is only necessary to focus on the fluctuation during a transient period.

In fact, when determining the values of Wup and Xup, it may be necessary to perform iterative convergence calculations to avoid logical contradictions between output and input.

In short, this patent uses actual measurements obtained from as many sensors as possible and a dynamic model to estimate the quality and flow rate of the two-phase flow flowing into the steam separator, thereby contributing to the formation of the reactor water level. The main idea is to find the flow path and each flow rate, and then give the feed water flow rate derived from the condition that the rate of change of the reactor water level is zero as the target value for the feed water flow rate of the water supply control system.

Of course, it is possible to install means of directly measuring WUP rather than estimating it (current BW
(Not measured in R).

As a first means, venturi type flowmeters are installed in several of the standpipes, and this signal is equivalently converted into Wup flowing through all the standpipes.

A second method is to measure the pressure in the upper plenum in addition to the current dome pressure measurement, and calculate the flow rate from the differential pressure between the two.

etc. are possible.

Furthermore, since it is difficult (but not impossible) to directly measure the amount of Xup, the void ratio of the upper plenum is measured with a void meter, and the relational formula (Reference 12) that provides the correlation between voids and quality is used. p206-P211 of
It is also a good idea to calculate the quality backwards using

(9) Core flow rate (W t, p ) As can be seen in these formulations, the core flow rate WLP is
It is a key parameter in determining various flow characteristics, and uses signals based on actually measured values. Measured values include natural circulation flow. Therefore, the core inlet flow rate is WLP = (M + 1) (W, +
pA, o+ WJps+a) + WNAT...(3
1) It is also expressed as

Generally, Tg in equation (19) and the delay time from the recirculation loop flow rate to the core inlet, which will be described later, are delay times related to the flow velocity. Therefore, after adjusting the delay time along the flow of the core flow, it is preferable to approximate the delay time with a function that becomes slower as the core flow rate decreases, as shown in FIG. 9.

Although there are various errors based on this, there is no need to worry as these errors are canceled out by the function of the water supply control system to match the water level to the target setting. Therefore, when the state of the reactor changes, the target water supply flow rate to be operated can be quickly taught to the water supply control system so that the change does not appear in the water level.

In the present invention, by sending a target value of water supply flow rate that reduces water level fluctuations to the control system in accordance with a physical model of water level formation, water level control that has a rapid and stable water supply function in a wide range of operating conditions is achieved. A system can be constructed.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. B
WR connects the external recirculation system 1000 with a pump motor 222 and a generator 27. Fluid coupling 28. Drive motor 29. Speed controller 3
0. It is composed of a main controller 31.

The water supply and condensate system 500o is connected from the condenser 32 to the condensate pump 3.
3. The main system is a water supply pump 35 driven by a turbine 34,
A water supply pump 37 driven by a motor 38 is used as a backup system, and the water supply flow rate WFW is controlled by control valves 39 and 36.

The turbine system 3000 includes a generator 4o and a low pressure turbine 41
．． High pressure turbine 42. Adjustment valve 43. Stop valve 44. For the system consisting of the bypass valve 45, there is a function to adjust the turbine inlet pressure P by a pressure sensor 46, and a control valve.
It consists of a control system 48 that uses changes in the signal from the rotation speed meter 47 of the generator 40 to switch the function of making the output of the generator 40 follow the set point Lo or a request from the system. The output of the generator 4o is ultimately regulated in the recirculation system 1000 by means of a signal line 49.

The control rod drive system 4000 is manual, and the structure of the reactor is the same as that in FIG.

A water supply control system according to this embodiment is constructed using the following signals for a BWR of the form shown in FIG. 10 (type A).

Hereinafter, all actual measured values obtained by the sensor are shown with an umbrella mark on the right shoulder (Example W Umbrella, +p^to).

Example (Type A case, 1) - Assume that the following can be used as measurement signals.

(a) Reactor water level gauge signal Llw (b) Feed water flow meter signal W fist FW (c) Main steam flow meter signal WaMs (d) Reactor dome pressure gauge signal p too to E (e) Reactor core inlet grid plate (f) Reactor water purification system intake water temperature gauge signal T*t,p(
g) Core average neutron flux measurement system signals φfist^PRM These measurement signals are smooth signals through appropriate smoothing processing, and their rate of change over time can be approximately determined. do.

The time rate of change X of the signal X is given by the following equation using a pseudo-differential effect.

Here, T is set such that T<1.

The configuration of the water supply control system 2000 according to this embodiment will be described below. In element 2800, the specific volume (
V), enthalpy (h), temperature pull, or a function Table (·) obtained by a fitting formula.

In the quality estimation unit 21oO of FIG.
The quality Xup is estimated based on equation (23).

For this reason, the following quantities are determined from actual measurements.

...(33) Here, TruEL: Fuel rod heat transfer time constant (about 6 seconds) KAPRM: Conversion coefficient to heat hLp=Table (T*Lp+ P umbrella DOMIm+
ΔHEAD)...(34) ΔI(EAD: Dome-lower plenum head constant h
gL:Table(P *DOME+ KcoRE6
(W * Lp) 21゛ straight 35) KCORE: Core separator pressure loss coefficient h t '=Table (P * DOME + KcoR
E(W*Lp)21 (36) Dc# is originally a variable, but is approximated by a constant based on simulation.

It was calculated using equation (23). Adding the error term εxup (constant) between the quality Xup and the upper plenum quality obtained using a detailed model in online performance calculation, X up = X up + εxup
-(37), further accuracy is guaranteed.

Next, the separator flow rate estimation unit 2200 estimates the flow rate Wup of the two-phase flow at the separator inlet based on equation (30).

One specific example of equation (30) is the following equation.

1 dv* Vg dp ...(38) At this time.

Aw=Table(Low) ip p w=Table(P umbrella ooop, T umbrella LP,
Low) Mo, g: (Mo+g=Wup
j Find it as a solution of Xup-WIMS. or a constant) or Wup using equation (25) instead of equation (30)
It is also possible to use (27) Coefficients C1, C in formula
At 2°C3, a preliminary evaluation is performed in advance by simulation under various operating conditions, and an appropriate value is selected.

What should be noted is that the measured value (e) measures the total core inlet flow rate including the natural circulation flow rate.

Therefore, the calculation of equation (18) is essentially unnecessary.

Remaining WFALL+t, WortN+z+ βCo,
βcu or λco, λcu are all water level W, flow rate W
The auxiliary flow rate estimator 2300 calculates the quality Xup by table extrapolation. Therefore, the water supply flow rate becomes
It can be found as 0.

-WcoN,z -Wup((1-λco)(1-Xu
p) + λco X up ) −(
39) For reference, in conventional three-element control, βcu=βC
O=O, WFAL, z=WoRN, z=W
EvA+g=WcoN, t=The target value is simply equal to the main steam flow rate. In addition, in any other conventional example, the core inlet flow rate WLP passes through the reactor core and upper plenum, which take various states, and reaches the separator with a flow delay and a change in quality. Does not involve physical processes. Furthermore, as can be seen from the characteristics of the separator shown in FIG. 4, the conventional method cannot handle the effect that carryover increases due to quality XuP and falls to the free liquid surface with a delay time. Also, as seen in other conventional examples.

Based on the three-element control system, instead of changing the water level setting point or temporarily adding, subtracting, or multiplying the control error signal, the target value of the water supply flow rate can be determined as shown in equation (39). The feature is that the water supply control system is configured in the original form of specification.

Elements 2100, 2200° 230 in FIG. 10 of the water supply control system for (Type A case (1)) of this embodiment
For the 0.2400 part, a more detailed example is shown in the first
Shown in Figure 1.

The following can be considered as a further simplified version of the configuration shown in FIG.

(Case 2): It is also practical to use equations (25) and (27) instead of the output Wup of the addition element 2009.

(Case 2): When output quality Xup is not used as information at all, 2012
．． 2013. ..., 2027 is deleted.

Xup=1. 'O, λcoco, λcu=o. At this time, as Wup (25), (27)
A formula may also be used, and in this case, the simplest configuration is obtained.

(Case 3): When PPM is not used for the signal φ umbrella of the nuclear instrumentation system, the reactor thermal output QCORE is well expressed by a linear equation unless the control rods are operated.

QCORE: KQ ′ WLP
-(40) Here, KQ: Output/Core Flow Gain At the time of an event such as a scram, the scram signal generation time t SCRM can be expressed as follows.

QCORE=KQ-WLC・φa(t, tS
CRM) - (49) Here, φG is a table where the time change of neutron flux, which decreases almost exponentially, is multiplied by the heat transfer time constant delay of the fuel rod.

(Case 4) Two cases, 1 The core flow rate is not the differential pressure between the grid plates, but the sum of the jet pump flow rates W I J P
When given by. At this time, signal processing for smoothing is performed, so there is a large delay.

Therefore, in the next processing, the signal with reduced delay is
Used as P.

...(50) Here, Tl: Delay time T2<1 (Case, 5): In Case 1 or 4, as the core flow rate,
Alternatively, when using recirculation drive water flow rate W+IPLR.

For both A system and B system, from the M ratio curve shown in Figure 6, WLP = (M + 1)・WIPLR... (5
For 1), use the obtained value.

(Case 6) Instead of calculating the inlet enthalpy hLP from the core inlet temperature in Case 2 and 1, a table value given as a function of core flow rate and thermal output is used instead.

(Case, 7) Reactor pressure measurement value P in two cases, 1
``If DOME is not used, in the estimation calculation of Wup and Xup, the P ratio is set to ooMp2O, and all physical property values are approximated by the rated pressure. Therefore, in the example of Fig. 12, elements 2011, 2027, 2017. 201520
Delete 16.

(Case 8): Elements 2012 to 2014, 2019, and 2020 are omitted when carryover is not considered.

(Case 9) In Case 2, Cases 1 to 8,
The trend was to estimate Xup and Wup using a model that had as much physical meaning as possible. In this case, on the contrary, a numerical simulation is performed for Xup and Wup based on a detailed physical model, and a transfer function is determined by fitting the obtained numerical simulation results. The method of fitting is
A multivariate autoregressive model (AR model) is practical. In this method, Wup=Loplace(G1(s), WLp)+L
oplace(Gz(s)+φAPRM)+Lop
lace(Ga(s), PooME)+Loplac
e(Ga(s), WMS)...(51a) (Similarly for Xup).

Here, each G+(s) is (n>m)s”+b in the AR model
ts"-'+...-+b.

The coefficient is determined in the form. In this case, the structure of how to obtain Wup and Xup in FIG. 11 is also the above equation (51a),
(51b) changes corresponding to equation (51b). It is simple and effective if the scope of application is limited according to the scope of the simulation.

It is of course possible to further combine the above cases depending on the usage range of the actual measurement value signal and the type of event for which water level control is to be improved, and this will produce a certain limited effect.

The configuration of elements 2002, 2004, and 2031 of the water supply control unit 2600 in the embodiment shown in FIG.
W (element 2001 is a flow rate sensor) and the reactor water level error signal E1. which is the output of element 2031. are considered to be completely equivalent, and are added in element 2003, sent to a proportional-integral controller 2004, and an operation command is sent to the valve actuator 2005.

Various configurations of this part are possible as shown below, but the method of instructing the set point of the water supply flow rate of this embodiment is equally effective for any of these configurations of the water supply controller.

Configuration example of water supply controller (1) Proportional-integral controller PI (εL
) and PI (ε豐) are provided, and the actuator 2005 is operated by the sum of each output.

Configuration example of water supply control system (2) In the above example (1), the sum of the output of PI (εL) and the output of εW is provided as the input of P I Ci w), and the output of PI (tw) is used as the input of actuator 2o05. It can be applied to a two-loop control system that operates

Configuration example of water supply control system (3) In reality, pipes each having a plurality of valves and a motor that changes the rotation speed of the pump are arranged in parallel, and the water supply flow rate is determined as the total flow rate. Control the flow rate through individual pipes.

In particular, in order to prevent an increase in the rotational speed (runout) of the pump, the set value of the water supply flow rate is divided and given as a target value of the flow rate of each pipe.

Also in this method, the set value of the water supply flow rate according to this embodiment is divided and given as the target value of each pipe flow rate. The innermost loop controls the flow rate of each individual pipe with the controller PI (sW/N), and in order to further define the total flow rate,
PI (εL), which has the same two-loop configuration as the above example (2),
The output of PI (εW) of PI (εW) is set to the innermost controller P.
It can also be applied to a 3-loop control system that divides and distributes to the set points of I ([in/N).

In this embodiment, the function of the water level setter 2500 shown in FIG. 10 is not particularly concerned. Although there are methods for changing the water level setting point in the event of an abnormality or accident, this embodiment can be used in common with both methods.

Next, the operational functions of the water supply control system according to this embodiment at the time of an abnormal accident in the plant will be explained.

However, in the event of an abnormality in the water supply system itself, operations such as switching to and starting up the standby unit (37 and 38 in Figure 10) will be performed using various conventional methods and will be integrated with this system.

The protective operation function section 2700 in FIG. 1o receives trigger signals and trip signals indicating various abnormalities and accidents. The following judgments are made based on this information and information on the water supply control system itself.

given by element 2400.

For example, suppose you are faced with a situation in which a command to insert 5 selection control rods is issued for some reason and the reactor output is reduced to continue operation.

In this case, in the conventional example, there is a tendency for the water level to change significantly, and it is possible that the water level will reach the lower limit in a short period of time and cause a scram, or that the water level will reach the upper limit after a relatively long period of time and cause a scram. There is sex.

With the water supply control of this embodiment, the water level control characteristics are greatly improved, so there is little possibility that the margin value will increase and scram will occur.However, due to the addition of other factors, etc. 0 or more. (If it exceeds a small amount, it may return to within the range after one hour, so it should be left alone.) The water supply capacity excess amount EFW is defined by the following equation.

...(52) When this EFW remains at TEF11 or more for a certain period of time, the situation exceeds the ability to adjust the water level by water supply control, and in the early morning when WFW>O, the water level becomes "low". There is a concern that scrums or problems may occur due to this.

Therefore, as one measure at this time, when WFII ) is 0, a signal l EWL that decreases the core flow rate WRC according to the value of Epw is used. Add to the speed setting signal of 1000.

As the core flow rate WLP decreases, the rate of decrease in the water level decreases. The result is reflected in the signal EFIF, and once it enters the adjustable range of the feed water control system, the core flow rate stops decreasing.6 Conversely, when Wpw < O, EEIL becomes a positive value and the core flow rate increases (upper limit ) to prevent a sudden rise in water level. In this way, it is possible to continue driving while avoiding a scram. The signal line 27o1 in FIG. 10 is a group of plant abnormality occurrence signals, which not only meets the condition of equation (54) but also matches the abnormal signal, and after confirmation, the above function is activated, and a signal is sent to the recirculation system via the signal line 2702. εEWL (usually zero) is sent.

Furthermore, depending on the type of abnormality or accident, steam may be dumped via the bypass valve 45 while the turbine system 3000 in FIG. A situation occurs. At such times, the reactor pressure P DOME can vary considerably.

(However, pressure changes are allowed even when generating electricity but not in load-following operation.) Alternatively, in situations where the reactor has already scrammed, the pressure can change significantly. In such a situation, the pressure should be adjusted so that water level fluctuations do not cause a transition to a higher grade treatment (e.g., closing the main blocking valve at the reactor outlet).
Decrease in water level.

It is also possible to increase the number.

Using the same signal as (52) to (53), tEwL=Kpd ・EFw −Sig corresponding to equation (55)
n(WrW) − (56) where KPT:
The positive coefficient is determined by the pressure setting turbine inlet pressure PT of the turbine control system 3000 in FIG.
decreases and the water level tends to rise.

εEj? L is sent out via signal line 3001.

The above is an example of the structure of this patent for a type A BWR.

As a type B BWR, instead of changing the core flow rate by changing the rotation speed of the motor of the type A recirculation system shown in Figure 10, there is a type that adjusts the opening degree of the discharge valve of the pump with a constant rotation. be. The change is such that the signal 412702 is added to the set point of the valve opening control system.

Some type C BWRs do not include the jet pump of the recirculation system shown in FIG. 1o, and use the discharge flow rate of the pump 22 as the core flow rate. This can be replaced with M ratio=0 in the discussion regarding type A.

As a type D BWR, there is an internal pump type in which a pump equivalent to the pump 22 is placed in the furnace instead of the jet pump in the recirculation system shown in FIG. The rotation speed of the pump is frequency controlled by a thyristor. Therefore, the 5 signal vA2702 is added to the change point of the set frequency. The method for measuring the core flow rate is to obtain the core flow rate from the differential pressure between the grid plates at the core inlet as well as the differential pressure signal between the upstream and downstream sides of the impeller of the internal pump. Core flow rate W
*Use these signals as LP.

Type E BWR includes a natural circulation type.

In this case, the core flow rate is measured by the pressure differential between the inlet grid plates.

The core flow rate is given as WNAT in the form shown in equation (18). Therefore, from the relationship of equation (15), I C0RE
Count backwards, and in turn, CEC0RE and quality Xup.
It is possible to estimate There is also a natural circulation type that does not have a supply separator to provide this quality, but the carryover and carryunder characteristics in this case are quite different from those shown in FIGS. 3 and 4, but the corresponding actual measurement values are used.

References (1) JP-A-51-42894 (2) JP-A-51-111595 (3) JP-A-Sho 5
Publication No. 2-33117 (4) Japanese Patent Application Laid-Open No. 1983-109998 (5) Japanese Patent Application Laid-Open No. 1983
Publication No. 5-149099 (6) Special Publication No. 62-40602
Publication No. (7) JP-A-56-163498 (8) JP-A-Sho 5
7-22594 (9) JP-A-58-18199 (10) JP-A-58-201097 (11) Varnish Wosk; R.H. Moenasme 73-
WA/P, -4, 1973 [S, Wolf: R, H,
Moen ASME 73-WA/P, -41973
[R,T.

Lahey, F. J., Moody, The Therm.
al Hydraulics ofa Boiling
Water Nuclear Reacfor Am
erican Nuclear 5ociety, 197
7] [Effects of the Invention] According to the present invention, it is possible to do this by estimating the physical quantities related to the formation of the water level in the reactor (particularly the separator inlet flow rate Wup and its quality Xup). By applying this to the water supply control system, the water supply control system with very little water level fluctuation can be made to operate in a manner that can be provided from start-up to output changes, resulting in scrams caused by high or low reactor water levels. This has the effect of reducing the amount of

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of the flow situation in the reactor of a boiling water reactor, Figure 2
The figure is a diagram explaining the mechanism of reactor water level formation, Figure 3 is a diagram of separator carry-under characteristics, Figure 4 is a diagram of separator carry-over characteristics, and Figure 5 is a diagram of changes in the effective cross-sectional area outside the shroud in the longitudinal direction. Fig. 6 is a characteristic diagram of jet pump M ratio dependence on core flow rate, Fig. 7 is a characteristic diagram of fall of carryover water, and Fig. 8 is a characteristic diagram showing temporal changes in fluid mass held in the reactor and upper pronum. Figure 9 is a characteristic diagram of the core flow rate dependence of the in-reactor flow delay time constant, Figure 10 is a configuration diagram of a BWR equipped with a feed water control system that is an embodiment of the present invention, and Figure 11 is the feed water control system of Figure 10. Detailed view of a part of. 2000...Water supply control system, 210o...Xu
p's abnormality/accident response department, 2800...Table interpolation unit for physical property values, etc. 10th exposure λω cram school 3 mouth 4th plan 4 lity

Claims (1)

[Claims] 1. In a boiling water reactor, reactor dome pressure, reactor water level, reactor feed water flow rate, main steam flow rate, core inlet flow rate,
The first function estimates the mass flow rate of the two-phase flow discharged from the reactor upper plenum to the reactor dome using all or part of the six types of measurement signals and signal change rates of the average in-reactor neutron flux. and a second function of estimating the steam quality of the two-phase flow using all or part of the six types of measurement signals and signal change rates; and the mass flow rate and steam quality of the two-phase flow. and the above 6
A third function that calculates the target setting value of the feed water flow rate from the balance relationship between the inflow and outflow of the mass flow rate in the area that forms the reactor water level, using all or part of the various measurement signals and signal change rates. and a fourth function of adjusting the water supply flow rate so that the error between the reactor water level set value and the measured value of the reactor water level, and the error between the target set value of the water supply flow rate and the measured water supply flow rate approach zero. And, under the occurrence of plant abnormalities and accidents, for the target set value of the water supply flow rate that exceeds the limit of water supply capacity,
Boiling characterized in that it consists of all or part of the fifth function of applying an amount exceeding the limit of the water supply capacity to the flow set point of the recirculation flow control system or to the pressure set point of the turbine control system. Water reactor water supply control system. 2. In a boiling water reactor, reactor dome pressure, reactor water level, reactor feed water flow rate, main steam flow rate, core inlet flow rate,
The first step is to estimate the mass flow rate of the two-phase flow discharged from the reactor upper plenum to the reactor dome using all or part of the six types of measurement signals of the in-reactor neutron flux and the signal conversion ratio.
and a second function of measuring the void fraction of the two-phase flow and converting it to steam quality, or a third function of measuring the mass flow rate of the two-phase flow and one of the six types described above. a fifth function consisting of a fourth function of estimating the vapor quality of the two-phase flow from a measurement signal and a rate of change of the signal, or a fifth function consisting of the second function and the third function;
The mass flow rate of the above two-phase flow, the steam quality and the above 6
A sixth function calculates a target setting value of the feed water flow rate from the balance relationship between the inflow and outflow of the mass flow rate in the area forming the reactor water level, using all or part of the various measurement signals and signal change rates; , a seventh function of adjusting the water supply flow rate so that the error between the reactor water level set value and the reactor water level set value and the error between the target set value of the water supply flow rate and the measured water supply flow rate approach zero; In the event of a plant abnormality or accident, the amount exceeding the water supply capacity limit is set at the flow rate set point of the recirculation flow control system, or the turbine control The eighth pressure applied to the system pressure set point
A boiling water reactor water supply control system characterized by comprising all or a part of the functions of.