JPS6021359B2 - How to quickly and accurately generate core power in a nuclear reactor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention rapidly increases core power in a nuclear reactor by combining a time-delayed but accurate signal from the thermal balance with a less accurate but rapidly measured signal from an ex-core neutron detector. and relates to a method for accurately determining it.

Making quick and accurate measurements of reactor power is
It is of great importance for control, power limiting and safety systems in nuclear reactors, especially those used in power plants.

It is well known that an ex-core neutron detector is used to determine the reactor generated energy, ie, the power output, in a nuclear reactor.

These measure neutrons outside the reactor core over, for example, idle levels up to 125% of full power and provide signals to operators, reactor maintenance systems, and reactor control equipment. The ex-core neutron detector of a typical system is located in a vertical wall just outside the reactor vessel and inside the primary shield.
The signal detected by the ex-core neutron detector ranges from approximately 1 neutron/second during reactor shutdown to 10 to 1 and 3 neutrons/second during reactor overpower trip (typically 125% of full power). This is the neutron east information in the range of . Although these neutron east fixed value signals are measured almost instantaneously, they are not necessarily proportional to the reactor power in a large-scale reactor core, and especially not proportional to the reactor power during the load transition period. As a result, the measurement signal of the ex-core neutron detector is determined by the reactor power value determined from the temperature rise range of the coolant in the primary loop or the reactor power value determined from the heat balance between the primary and secondary sides, as described below. must be corrected. In pressurized water reactors, the reactor is cooled by high pressure water as the primary coolant so that the average enthalpy of water leaving the reactor is less than the enthalpy at saturation temperature.

The high pressure primary coolant is directed to a steam generator and steam is generated on the secondary side. Automatic correction of the neutron east constant signal with the help of the reactor power value determined from the heating range of the coolant in the primary loop was usually brought about by a closed-loop control system.

The disadvantage of this is that the correction cannot follow the reactor power quickly enough if rapid power changes occur. This ultimately means that an automatic compensation system is useless if rapid load changes occur since it may not result in a safe output value. Determination of reactor power from the heat balance on the primary or secondary side is much more accurate than measurements by ex-core neutron detectors due to physical reasons, but on the other hand compared to the quick indication of ex-core neutron detectors. The response is slow and the signal output is delayed under transient conditions due to the presence of the coolant transit time between the temperature measurement points at the entrance to the core and the exit therefrom.

Various strategies have been proposed to take advantage of the advantages while avoiding the disadvantages of power measurements dependent on neutron and thermal parameters. For example, U.S. Patent No. 3,752,73
No. 5 teaches the use of the difference between the neutron east power signal and the thermal power signal to adjust the neutron east power signal. US Pat. No. 3,356,577 also discloses a similar technique. According to the method of the invention, a signal is generated by time-delayed but more accurate measurements from the thermal balance. This thermal power signal is adjusted to quickly and accurately generate a power signal corresponding to the power of the reactor core by modifying it to correspond to a predetermined relationship between the ex-core neutron detector signals. Ru. The adjusted thermal power signal is formed as a function of the product of the thermal power signal and the quotient of the ex-core neutron detector signals at two different times. The present invention will be explained in detail below. According to the invention, the thermal reactor power is measured from a time-delayed fixed value of the heat balance on the primary or secondary side, and the changes in the ex-core neutron detector readings that occur during this time delay are as described above. It is added as a speed factor component to the value of the thermal furnace power measured from the heat balance.

This configuration provides a rapid and accurate signal that is useful for reactor control, power limiting, or reactor safety, and that can be reliably applied to the occurrence of rapid transient events. Additionally, time-delayed measurements may be formed from coolant enthalpy differences or from coolant warm-up ranges.

The rapidity factor component is formed as the quotient of the ex-core neutron detector reading at a first point in time and that at a subsequent point in time.

In this case, the furnace power signal is formed as the product of the thermal furnace power and the rapidity factor component. The method according to the invention and its operating principle will be explained with reference to a practical application. The thermal power signal of a nuclear reactor is formed, for example, from a thermal balance in the reactor coolant system, for example on the primary coolant side.

Measuring this value takes a relatively long time compared to the quick determination of measurements by ex-core neutron detectors. The time difference is a few seconds and is displayed as to. The change in the measured value of the rapid-indicating ex-core neutron detector that occurs during this time delay is the rapid factor component that causes the primary coolant temperature to rise (warm-up).
Added to above measurements of range. This rapidity factor is determined as the quotient of the ex-core neutron detector indication at time t and time t-1. The catastrophic thermal power signal of a nuclear reactor is formed as a function of the product of the thermal power signal and a rapidity factor. This is compatible with digital systems. The value of the reactor power Q thus determined is suitable for use in the reactor control system, in the power limitation system and in the reactor safety system for the occurrence of rapid transient events.

FIG. 1 is an explanatory diagram showing the principle of the present invention.

Typically, the thermal power signal is derived from the enthalpy difference of the primary coolant entering and leaving the reactor core or from the enthalpy difference of the secondary coolant entering and leaving the steam generator. It will be done. Enthalpy values are determined by measuring process parameters available through instrumentation and calculating enthalpy in a manner well known. A neutron east signal is also generated at the same time, typically by a neutron east signal sensor, such as an ex-core neutron detector. The neutron output signal serves to modify the thermal output signal. In the division unit 5 a normalized signal is generated which is proportional to the quotient between the neutron east signal and the delayed neutron east signal. The standardized signal is multiplied by the thermal power signal in a multiplication unit 4 to determine the instantaneous core power currently being sensed by the heat detector (which cannot be measured immediately due to the time delay of the thermal response). get a value equal to . Under steady-state conditions, there is no change in the value of the neutron east signal and therefore the normalized signal is zero, so no adjustment is made to the thermal output signal. The normalized signal is adjusted by a delay unit 6 with a time factor K so that the delayed neutron output signal has the same time response as the thermal output signal.
Figure 2 shows the thermal output signal [Q
th] and the corresponding neutron output signal [Qp] from the ex-core neutron detector are displayed as a graph as a function of time.

At a given time [t:n], the thermal power sensed by the thermal sensor is adjusted by digital means such that the output signal of the system is defined by the following function: [output signal]n =Qthn The measurement time difference [ΔT] must be chosen to be approximately equal to the time constant of the Q-ratio response.

Therefore, the second time point n
The thermal output signal [[Qthn] at is adjusted. The present invention thus determines a thermal output signal that is accurate under steady-state conditions but exhibits a slow response to transition conditions, and combines it with a fast neutron signal that is fast-responsive but has an error even in steady-state conditions. It is intended to be a method for quickly and accurately quantifying the core power of a nuclear reactor by coarsely merging it with the East signal in a novel manner.

[Brief explanation of the drawing]

FIG. 1 is a schematic logic diagram of a system embodying the principles of the invention, and FIG. 2 is a graph illustrating thermal and neutron output signals as a function of time. 4... Multiplier, 5... Division unit,
6...Delay unit. Figure 1 Figure 2

Claims (1)

Claims: 1. A method for accurately and rapidly generating an output signal corresponding to the core power of a nuclear reactor comprising a reactor core and through which a heat-receiving fluid flows in heat transfer relationship with the reactor core, comprising:
generating a first neutron flux signal (Qpn-1) corresponding to the reactor power at a first time point (n-1);
generating a second neutron flux signal (Qpn) corresponding to the reactor power at a time (n), a thermal power signal (Qthn) resulting from the temperature difference of said fluid cooling the reactor at said second time (n); and the second point in time (n).
A method of rapidly and accurately generating core power in a nuclear reactor comprising: generating a power signal proportional to the product of the quotient of the first and second neutron flux signals and the thermal power signal. 2. The method of claim 1, wherein the first neutron flux signal is a divisor of the quotient of the neutron flux signals.