Even though VBWR shutdowns were required for location and removal of five failed fuel assemblies (HPD Program), the increase in fuel exposure was good. Fuel exposures wili pass the values at which cold worked stainless steel cladding was failing under the HPD Program. Failure of the 0.005-inch cold worked stainless steel clad fuel rods in assembly 8L was traced to strain cycling fatigue. A study of tapered fuel rods indicates a potential advantage for us of a variable water/fuel ratio along the flow channel. Natural circulation tests in the hydraulic stability loop were conducted over a range of conditions from stable, to oscillatory with exponential decay, to self-sustaining oscillation of constant amplitude, to unstable oscillations with divergent amplitude. The response to impulses in power input shows the effect of the time delay for transporting steam voids up through the riser. The data permit calculation of oscillation frequency, damping coefficient, time lags, and show the magnitude and character of pressure and velocity changes. The data, which have an experimental scatter of plus or minus 10% maximum, show that burnout heat fiux: decreases with increasing flow up to 2 x 10/sup 8/ lb/hr-ft/sup 2/; has a maximum for hydraulic diameter between 0.25 …

A frequency analysis was made of the VBWR stability test data. Interpretation of the steady-state noise observed in the stability tests involved consideration of several possible sources of excitation. One of these, a theory of water surface waves, is summarized. Visual and destructive examinations were made of selected fuel rods. Fretting corrosion of the Zircaloy-clad fuel rods against stainless steel spacers was observed. Evidence that UO/sub 2/ thermal conductivity increases with time was obtained. Hot gas isotatic pressed fuel rods failed after 316 Mwd/T irradiation and 5 months storage under water. Shakedown operation of a 7-rod test section for measuring burnout heat flux was conducted. A comparison of measured and calculated isotopic composition for uranium and plutonium isotopes after 400 Mwd/T irradiation indicated that the calculations underestimate capture in U/sup 238/ and overestimate capture in Pu/ sup 239/. Flux wire irradiations provided axial and radial flux profiles and the ratio of thermal to fast flux as a function of axial position. (M.C.G.)

Quarterly progress report discussing activities related to the Vallecitos Boiling Water Reactor (VBWR) and related facilities

Quarterly progress report discussing activities related to the Vallecitos Boiling Water Reactor (VBWR) and related facilities

Quarterly progress report discussing activities related to the Vallecitos Boiling Water Reactor (VBWR) and related facilities.

Quarterly progress report discussing activities related to the Vallecitos Boiling Water Reactor (VBWR) and related facilities.

Quarterly progress report discussing activities related to the Vallecitos Boiling Water Reactor (VBWR) and related facilities.