Masters Theses

Date of Award

5-1993

Degree Type

Thesis

Degree Name

Master of Science

Major

Nuclear Engineering

Major Professor

Belle R. Upadhyaya

Committee Members

Laurence F. Miller, Rafael B. Perez

Abstract

The purpose of the present research is to study the dynamic behavior of coolant pressure in the primary loop of a pressurized water reactor (PWR). One of the objectives is to determine the important parameters that influence the standing wave behavior of the pressure noise process. As a consequence of this analysis, certain frequency range of the pressure noise spectrum may be related to coolant temperature in a PWR. Previous studies of pressure noise behavior were able to identify the standing wave frequency for a given operating condition. This frequency varies in the range 6 - 8 Hz, depending on the system dimensions and operating characteristics. This frequency shifts with changes in coolant temperature. The present research is motivated by these experimental observations. One of the objectives is to perform a detailed theoretical analysis of the relationship between pressure noise signature and primary coolant temperature in a PWR. As a consequence of this, it is possible to develop a technique for estimating average hot leg temperature. This approach, when properly implemented, could be used as an alternative estimator of average hot leg temperature. Because pressure noise dynamics, driven by the compressibility behavior of water, is proportional to sound velocity in water, the pressure noise characteristics can be studied through an acoustical phenomenon in water. It is hypothesized that if the temperature of water is greater than 300 °F (150 °C), sound velocity in the water decreases, with increasing temperature. As a result, the frequency of the pressure noise standing wave would also decrease. Therefore, the changes in pressure noise spectra may be related to changes in hot leg temperature. The analytical calculations are applied to operating PWRs and compared with measured pressure noise data. The limited availability of the data is a drawback in performing detailed comparison of analytical and experimental results. Typical four-loop Westinghouse PWRs have wide-range pressure transmitters in their hot leg piping. The actual implementation of the technique for estimating hot leg temperature can be enhanced by the use of narrow-range pressure transmitters. Detailed modeling of pressure fluctuations in the primary coolant systems of a two-loop (470 MWe) PWR and a four-loop (1140 MWe) PWR clearly showed the standing wave frequencies in the range 6 - 8 Hz at full power conditions. These frequencies were also seen in the power spectral densities of pressure noise signals. It was observed that the standing wave frequency changes as a function of average hot leg temperature, decreasing with increasing temperature. Eventhough the magnitude of the frequency is influenced by temperatures in the components of the primary coolant system, the dominant effect is due to the compressibility changes in the vessel upper plenum and temperature in the hot leg. For a typical four-loop Westinghouse PWR, the measured pressure noise frequency was 7.27 Hz at an average hot leg temperature of 618.3 °F (325.7 °C). The theoretical (model-based) natural frequency for this condition was 7.34 Hz. This result establishes the direct relationship between coolant temperature and pressure noise frequency. When primary coolant temperature and pressure are measured accurately in a PWR, a calibration-type curve may be generated and used for estimation of hot leg temperature. Further study is necessary to prove that the frequencies in the range 6-8 Hz are affected dominantly by the hot leg temperature.

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