[en] Flow-induced vibrations in the fuel element assembly of a research reactor were monitored and it was established that long-term monitoring of liner plug vibration can be used to indicate the mechanical integrity of a fuel element if a sufficient case history is established. The vibrational behaviour of a number of fuel elements with different integral modifications were examined but only a relatively small change in vibration levels was obtained. The overall vibration levels were most effectively decreased by installing flow straighteners in the exit nozzles of the plenum chamber. (author)

No abstract available

No abstract available

[en] A six rod cluster rig was built to study the structure of turbulent velocity and pressure fluctuations in a closely spaced square-pitched array of rods. The test section contains six 14 cm diameter rods arranged in two four rod subchannels, which are interconnected across one rod gap; spaced at a pitch to diameter ratio of 1.193, and having a total length of 9.14 metre. Walls were inserted in all other rod gap areas, and the effect of these walls on the average velocity distribution in the interconnected gap region was compared numerically to the distribution for an infinite array, and this showed that the effect of the walls was negligible for the chosen pitch to diameter ratio. This fact was confirmed experimentally by Preston tube measurement of the wall shear stress distribution for the top and bottom centre rods, showing that the effect of the wall extended approximately 30⁰ around the rod. An investigation was made of the spectra of the dynamic pressure and the structure vibration for the 45 kW centrifugal air blower; calming entry drum to the rig; and test section, as a function of Reynolds number, for the range of 10⁴ to 2.4x10⁵. The spectra showed that some of the lower frequency pressure components of the blower were propagating through 15 metre of 20 cm diameter ducting to the drum and test section, and exciting mechanical vibration of the test section. Approximate calculations of the possible flexural mechanical resonances of the system indicated that the frequencies contained in the pressure field were near some of the resonances, which would enhance the flow induced vibration. This far field pressure effect was most evident at the lower R

No abstract available

No abstract available

[en] A six rod rig was built to study the structure of turbulent velocity and pressure fluctuations in a closely spaced square-pitched array of rods. An investigation was made of the spectra of the dynamic pressure and the structure vibration for the 45 kW centrifugal air blower; calming entry drum to the rig; and test section, as a function of Reybolds number, for the range of 10⁴ to 2.4x10⁵. The spectra showed that some of the lower frequency pressure components of the blower were propagating through 15 metre of 20 cm diameter ducting to the drum and test section, and exciting mechanical vibration of the test section. Approximate calculations of the possible flexural mechanical resonances of the system indicated that the frequencies contained in the pressure field were near some of the resonances, which would enhance the flow induced vibration. This far field pressure effect was most evident at the lower Reynolds numbers. As the Reynolds number was increased above 1.1x10⁵, a large low frequency peak developed on the pressure spectra of the test section. (Auth.)

No abstract available

[en] Acoustic emission occurs in a metal when an applied stress causes movement of flaws. The magnitude and frequency content of each emission 'burst' generated depend on the nature of some source mechanism, and proveded the characteristics of the propagation path between the source and a detecting transducer are definable and substantially constant an analysis of individual bursts should allow the various source mechanisms to be identified. The analysis procedure chosen was to obtain the amplitude spectral density for each burst and to characterisc this by computing a single parameter, the median frequency, i.e. the frequency which divides the spectrum into two equal areas. A series of experiments was carried out using zirconium specimens, and the experimental results indicated that three separate metallurgical mechanisms produced acoustic emissions. The results also indicated that one of these mechanisms was dominant. A concurrent metallurgical examination showed that a large amount of twin initiation took place and that there were smaller amounts of twin broadening and slip. (orig.)

[en] It has been suggested that the low-red shift quasar 1928 + 738 be utilized in the establishment of an extragalactic reference frame. We have observed the quasar in blue light during an interval of 137 days and found it essentially constant, varying by no more than about I 0.15 magnitude from its average value. Slowly varying long-term changes are not ruled out and others are encouraged to monitor this source in the future. (author)