DD269933A1 - METHOD FOR DETERMINING REACTIVITY COEFFICIENT IN NORMAL OPERATION - Google Patents

Abstract

The invention relates to a method for determining reactivity coefficients of pressurized water reactors during normal operation of the reactor plant. The aim and the object are to provide a method for determining reactivity coefficients of pressurized water reactors in the normal operation of the reactor plant in order to be able to demonstrate the guarantee of the nuclear safety of the reactor plant and thus ultimately increase the profitability of the nuclear power plant. This is achieved by using the normal fluctuations in the frequency of the electric energy network as the disturbance of the reactor state necessary for the determination of reactivity coefficients.

Description

2 ^ 9933

Ancestors for determining reactivity coefficients in normal operation

Field of application of the invention

The invention relates to a method for determining reactivity coefficients of pressurized water reactors during normal operation of the reactor plant.

Characteristic of the known technical solutions

The determination of reactivity coefficients, especially at full power of the reactor system, is an important prerequisite for safe reactor operation, since the reactivity coefficients quantitatively describe the effect of the inherent safety of a nuclear reactor, for example, by increasing the temperature of the chain reaction by merely utilizing physical laws ,

Usually, reactivity coefficients are determined during start-up of the reactor with minimally controllable Leiatiirig. For this purpose, the effectiveness of the control rods are first measured at two temperature levels, and the reactivity coefficient of the moderator temperature is subsequently determined from the compensation of the moderator temperature effect resulting from the warm-up of the moderator by the method of the control rods required for this purpose.

A disadvantage of this method is that it can only be used with minimally controllable power of the reactor, ie not in normal operation.

26 99 3

Can during normal operation applicable method to?. '. Determination of reactivity coefficients is proposed in DE-OS 32 38 522 "Method and apparatus for monitoring the reactivity balance of the core of a nuclear reactor for the diagnosis of reactivity disturbances" in which except direct and indirect measured values according to a recursive rarameter estimation method used to monitor the reactance balance , A disadvantage of the described method is that no statements are made about the type of reactivity disturbances necessary for the measurement of the reactivity coefficients. It must therefore be assumed that it must be changed from the outside operating parameters or must be maintained until the original reactivity balance was disturbed by a noticeable increase in burnup. This must be intervened either in the normal operation of the reactor or it must take so long time to a noticeable burn occurred.

Object of the invention

The aim of the invention is to increase the level of nuclear safety and economy of pressurized water reactors by determining reactivity coefficients in normal operation, i.e. "without interfering with reactor operation.

Explanation of the essence of the invention

The invention has for its object to provide a method for determining reactivity coefficients of pressurized water reactors in normal operation of the reactor plant without having to make special experiments to dan proof of ensuring the nuclear safety of the reactor system can lead and thus ultimately the cost of the nuclear power plant especially to diagnose reactivity disorders.

For the 3rmit ⁺ development of reactivity disturbance of the state of the reactor core is always required. According to the invention - in contrast to the usual deliberate change of this condition - the effects of the ever-present otherwise

actually used disturbing fluctuations in the grid frequency of the electrical energy supply network.

For this purpose, the mains frequency is registered periodically in parallel to the relevant parameters: average moderator temperature, cooling fluid heating in the gap zone, pressure in the primary circuit, control rod position and neutron flow level in the gap zone. According to the invention is used that a random change in Netzfrequonz due to the net zfrequem dependency of the speed of the main circulation pumps a similar change ». > r causes coolant to flow through the nip zone of the nuclear reactor. This change dxsv coolant delivery is the presumed failure of the split zone state. By its own control behavior or by the reaction of Reaktorsteuerxmg on this disorder, the reactor goes back to a stable state. In this case, a change of at least two of the operating parameters: mean moderator temperature, coolant heating in the nip zone, pressure in the primary circuit, control rod position or Neutronenflußniveau in the nip zone has taken place, since the reactivity is zero in the steady state, so that coupled with the genarjiten operating parameters reactivity effects caused by the disturbance, compensate each other.

According to the invention, the periodically recorded measured values are accordingly observed and, after occurrence of measurable mains frequency changes, the operating parameter changes made therefor are determined. From the knowledge of the mutually compensating reactivity effects, the resulting ratios of the reactivity coefficients with respect to the measured operating parameters are then determined from the ratios of the operating parameter changes. From the knowledge of a reactivity coefficient, the others are then determined from these ratios.

To improve the accuracy of the parameters, it is expedient to carry out the method steps described several times in succession and to subject the reactivity coefficients to statistical averaging.

Au & führungsbeiBpiel

The invention will be explained in more detail below with reference to an exemplary embodiment.

In the example, without limiting the generality, the case is considered that the line frequency change is not accompanied by a change in the Regelatabposition or the pressure in Primärkreislcat'f, so that only reactivity effects with respect to moderator temperature and reactor performance are effective. It generally applies to a reactivity change a Q ^Δ ? - ^Γ Τ _Μ * ^T M ^{+ r} Q * ^{Q + Γ} ρ ^{ΔΡ + r} h ^Ah

with Γ _Μ as moderator temperature, Q as reactor power, ρ as pressure in the primary circuit and h as height position of the control elements and Δ as a sign for the change of the operating parameter and Γ *. as reactivity coefficient with respect to change in quantity i (i stands for T _M , Q, p, h)

 In this particular example, Δρ = 0 and Ah = 0, so that

to use.

If the measured line frequency f changes to the value oc * f (oc - dimensionless parameter, ot «l), the coolant throughput through the nip zone m changes in oc m as a result of the mains frequency dependency of the speed of the main circulation pumps. At the same time, the coolant heating up in the gap zone t ₁ or t ₂ and the mean modulator temperature T _M1 or T _M2 are to be measured before or after the line frequency change

 Thus one determines after

(« - c · mt with c as the specific heat capacity of the coolant from Q ^ = cmt ^, and

Q ₂ = cmt ₂ · oc

the reactor power before and after mains frequency change.

Since the reactor is critical both before and after the mains frequency change, ie Δ§ » O, one obtains with

AT _M = T _M2 - T _M1 and AQ = Q ₂ - Q ₁ for the reactivity coefficients

⁰ = · ^Γ Τ _Μ ^(Τ _Μ 2 -

and further

or.

T - -! T, m - or f. «- β- ^ k-

Q ¹ M ₂ ¹ Ml ¹ M ¹ M ^ ¹ Ml

ui> d can thus exiniteln the reactivity coefficient of Moderatortemperaxux ¹ .

If the pressure in the primary circuit and the height position of the control rods also change, then at least two or three network frequency changes are to be detected before the reactivity, coefficient coefficients are determined, whereby the algorithm must be used in an analogous manner with the aid of the algorithm for solving linear systems of equations.

Claims (2)

claim 1. A method for determining reactivity coefficients of pressurized water reactors in normal operation, characterized in that are used as the necessary for the determination of reactivity coefficient disorder of the reactor state, the normal fluctuations in the frequency of the Slektroenergienetzes by periodically the mains frequency together with the Betriebsparrmeters: moderate moderator temperature, pressure ir . primary circuit Kühlmittelaufwärmung in the reactor core, control element positions and Nevtronenflußniveau be measured in the gap zone, wherein the measured values of the Netzfrequomz be compared as long as with the first measurement value to a measurable change of the network frequency is detected, and then from the said first measured value and Measured value of detected change in the network frequency together registered operating parameters, the respective operating parameter change is determined, so daü therefrom the ratios of the reactivity coefficients of mutual ig in the normal operation of the reactor compensating caused by the mains frequency change reactivity effects to be ermi telt « 2. A method for determining reactivity coefficients of pressurized water reactors in the Noranlbetrieb according to item 1, characterized in that the method described in point 1 / jur reactivity coefficient determination is applied several times in succession and the resulting reactivity coefficients of a statistical averaging are used to determine mean reactivity coefficients mean reactivity coefficients to be determined.