JPH0961582A - Detecting the surface temperature of cladding of fuel rods - Google Patents

Abstract

(57) 【Abstract】 PROBLEM TO BE SOLVED: To detect and monitor the surface temperature of a cladding tube in a main control room on time. In addition, the calculation load is reduced by using an approximate expression for the cladding tube surface temperature calculation part. SOLUTION: By inputting data of various conceivable situations into a core thermal-hydraulic and fuel temperature analysis code with predetermined parameters, cladding tube surface temperatures under various situations are obtained and obtained in advance. It is possible to detect the real-time cladding tube surface temperature by setting an approximate expression that relates the cladding tube surface temperature to each of the above parameters and inputting real-time data from the NIS panel or the like to each parameter of this approximate expression. Characterize.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting the surface temperature of a cladding of a fuel rod in an operating PWR light water reactor plant.

[0002]

2. Description of the Related Art In determining the soundness of fuel in a light water reactor, since the method of predicting the cladding surface temperature has not been established, the surface of the fuel rod is separated from the nucleate boiling state and the film boiling state where the heat transfer coefficient is low. The standard is the DNB that shifts to. Also, in order to actually predict the surface temperature of the cladding tube,
Since it is necessary to carry out the core thermal-hydraulic analysis and the fuel rod temperature analysis by unsteady handling, both the data capacity and the calculation time become enormous, and it is considered difficult to realize the above prediction method.

However, if the safety margin of the conventional DNB standard is reviewed and a criterion based on the cladding tube surface temperature is adopted, this criterion is naturally used in the operation manual in the event of a reactor failure or accident. Since it is reflected, the merit of detecting and monitoring the surface temperature of the cladding tube in the central control room is great.

[0004]

In view of such a background, the present invention optimizes the operation method in the event of a light water reactor failure or accident by monitoring the surface temperature of the cladding tube from the central control room in real time. The purpose is to deal with this.

[0005]

That is, the method for detecting the surface temperature of a cladding tube according to the present invention, which is adapted to the above-mentioned object, includes a coolant temperature, a core power, a core pressure, a power peaking, a power distribution, and a core / fuel. By inputting data of various conceivable situations for each parameter of shape and size into the core thermal hydraulic and fuel temperature analysis codes, the cladding tube surface temperature under various situations can be obtained in advance, and the obtained cladding can be obtained. Approximate equations that relate the pipe surface temperature and each of the above parameters are set, and the parameters of the coolant temperature, core power, core pressure, power peaking, and power distribution of this approximate equation are set to the current values from the NIS panel, etc. It is characterized in that the surface temperature of the cladding tube at the present time is detected by inputting the data in (1). The NIS here is Nuc.
lear Instrumentation System
em, or nuclear instrumentation system.

[0006]

In the above method of the present invention, the cladding surface temperature, which serves as a criterion for fuel integrity, can be directly monitored on-time, and the cladding surface temperature and the duration of the temperature can be measured. By doing so, the soundness of the cladding material can be determined more specifically.

[0007]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a chart showing a method of detecting the surface temperature of a cladding tube according to the embodiment of the present invention, and FIG. 2 is a chart showing a method of setting an approximate expression in the method of the embodiment.

As described above, the calculation of the surface temperature of the cladding tube requires an enormous amount of calculation time and a large amount of capacity, especially for unsteady handling during transient changes.
The calculation is performed in advance for various input conditions, an approximate expression (RSM) fitted to the calculation result is created, and the approximate expression (RSM) is used as a substitute to shorten the calculation time.

That is, in the present invention, first, as shown in FIG. Coolant temperature, b. Core power, c. Core pressure,
D. Output peaking, e. Output distribution, and f. Core
By inputting data of various conceivable situations for each input parameter of fuel shape and size into the core thermal hydraulic power and fuel temperature analysis code of the computer, the cladding tube surface temperature under various situations can be obtained in advance. , And an approximate expression (RSM) that relates the obtained cladding surface temperature to each of the above parameters is set.

Then, as shown in FIG. 1, the above a. Coolant temperature, b. Core power, c. Core pressure,
D. Output peaking, and e. By continuously inputting the current data from each detector or NIS panel of the main control room to each parameter part of the output distribution,
The current surface temperature of the cladding tube should be continuously detected. It should be noted that the system shown in FIG. 1 also has a function of surveying the fuel rod that is the most thermally severe. This survey function is to identify the hottest rod from the cladding temperature distribution.

As input data to the above approximate expression, the following data are available from the control panel of the main control room on time. I. Coolant temperature (Tin) ··· Core inlet temperature (° C) b. Core power (P) ..... Core power (MW) c. Pressure (W) ・ ・ ・ ・ Core pressure (kg /
cm ² ) In addition, for various steady and unsteady states during design,
The following data are available as data obtained by analytical calculation. D. Output peaking (fz) ・ ・ ・ Axial peaking coefficient e. Power distribution (f (x, y)) ... Power coefficient (radial peaking coefficient) of each fuel rod in the fuel assembly that gives the highest power.

The above-mentioned D and E are also stored in the control panel memory so that they can be pulled out according to the state of the core at that time. Therefore, the approximate expression RSM by the above
Is expressed by the following equation 1.

[0014]

## EQU00001 ## RSM = F (Tin, P, W, fz, f (x, y))

In the method of the present invention, however, it is possible to directly detect and monitor the cladding tube surface temperature, which serves as a criterion for fuel integrity, on-time, and the cladding tube surface temperature and By measuring the duration of the temperature, it is possible to more specifically determine the soundness of the cladding material.

In this case, the soundness of the fuel rod is defined as, for example, "the fuel rod is sound if the duration of the fuel rod surface temperature is about 600 ° C. within 20 seconds". Since it is also considered that an evaluation method based directly on the high temperature strength of various materials will be established, it is preferable that the method of the present invention also represents the limit of the soundness of the cladding by the temperature and its duration. .

[0017]

As described above, the method for detecting the surface temperature of the cladding tube according to the present invention is performed by inputting various situation data that can be assumed in predetermined parameters into the core thermal hydraulic and fuel temperature analysis codes. By setting an approximate expression relating the above-mentioned respective parameters to the cladding surface temperature previously obtained, and detecting the real-time cladding surface temperature by inputting real-time data to the parameters of this approximate expression, It is possible to directly detect and monitor the cladding surface temperature, which is the criterion for fuel integrity, on-time.By measuring the cladding surface temperature and the duration of that temperature, the integrity of the cladding material can be measured. Since it is possible to more concretely judge the characteristics, by directly monitoring these by the operator, the design reference event can be naturally applied to the driving operation at the time of failure or accident. It is possible to also Ruyori specific decisions.

[Brief description of drawings]

FIG. 1 is a chart showing a method for detecting a surface temperature of a cladding tube according to an embodiment of the present invention.

FIG. 2 is a chart showing an approximate expression creating method of the method of the embodiment.

Claims (1)

[Claims] 1. Data on various conceivable situations in the parameters of coolant temperature, core power, core pressure, power peaking, power distribution, and core / fuel shape / dimension are provided as core thermal hydraulic power and fuel. By inputting the temperature analysis code in advance, the cladding surface temperature under various circumstances is obtained, and an approximate expression that relates the obtained cladding surface temperature to each of the above parameters is set, and Coolant temperature, core power, core pressure, power peaking,
And a method for detecting the cladding tube surface temperature of a fuel rod, characterized in that the cladding tube surface temperature at the present time is detected by inputting the current data from the NIS panel or the like to each parameter of the output distribution.