Advanced two-phase instrumentation program. Quarterly progress report, July-September 1981. [PWR]

The performance of the Westinghouse Reactor Vessel Level Indicating System (RVLIS) in the S-UT-3 test (a communicative break in the cold leg of Semiscale) was analyzed. The Westinghouse RVLIS gave similar indications to Semiscale Test Facility instrumentation measuring the same phenomena (differential pressure (dP)) over equal spans. The Westinghouse measurement is apparently conservative when compared with the two-phase froth level. These dP measurements appear to be nonconservative estimates of level, however, when the measurement system spans the upper core support plate. Level measurement errors of up to 150 cm (60 in.) were observed during S-UT-3. Westinghouse claims that these differences are caused by differences between Semiscale and Westinghouse Reactors. A recommendation for resolving these differences is made.