A toroidal thermosyphon consisting of a fluid-filled torus located in a vertical plane was studied analytically and experimentally. Good agreement was obtained between analytical predictions and measurements for large values of the angular displacement of the heated and cooled sections. For smaller angular displacements, the analytical predictions of steady state flow rates were found to exceed the corresponding experimentally observed values. The discrepancies were attributed to a reverse flow phenomenon. Some analytically predicted flows were not physically achievable. In these situations the flow would either reach a steady condition in the opposite direction, or it would oscillate indefinitely.

Preparedas partof Arrangement on ResearchParticipationandTechnicalExchangebetween the FederalMmisterforResearchand Technologyof the FederalRepublicof Germany (BMFT)and the JapanAtomicEnergyResearchInstitute(JAERI) and the UnitedStatesNu-clearRegulatoryCommission (USNRC) in• CoordinatedAnalytical and Experimental Study of the Thermo-h_raulicBehaviorof EmergencyCoreCoolantduring the RefillandReflood Phase of a _.of.Coolant Accidentin a Pressurized WaterReactor(the2D/3D Program).

To address long-term motor operated valve (MOV) performance, the Babcock & Wilcox, Boiling Water Reactor, Combustion Engineering and Westinghouse Groups (B&WOG, BWROG, CEOG and WOG) teamed in 1997 to form the Joint Group (JOG) MOV Periodic Verification (PV) Program. This program is nearing completion, with 98 of the 103 operating U.S. reactor units participating. The goal of the program is to provide a justified approach for periodically testing MOVs, that addresses potential degradation. The program defines an interim approach that specifies periodic tests without flow and differential pressure (DP), at a frequency determined by the MOV’s risk significance and margin. To justify this approach, each participating plant is also DP testing 2 valves per unit. Each valve is tested three times over five years, with at least one year between tests. The data are evaluated jointly to confirm or adjust the initial guidance. The majority of the tests are complete and conclusions are coming into focus. For gate valves, when the valve factor is initially low, increases can occur between one test and a later test. One common way that the valve factor becomes low is disassembling and reassembling the valve. The data show that, following valve disassembly and reassembly, the valve factor tends to be reduced, and it tends to increase in subsequent service. Outside of the valves disassembled and reassembled, some gate valves have low valve factors apparently because the valves are not stroked under DP conditions in service. For butterfly valves, there have been no observations of degradation in bearing friction coefficient. A few valves with bronze bearings in raw (untreated) water service have shown significant variations in friction, but they tend to be a mixture of increases and decreases with no pattern of degradation. Globe valves, both unbalanced and balanced, tend to show a constant valve factor with no indication of degradation.