Abstract
Steam generated in a reactor core and water condensed in a pressurizer form a countercurrent flow in a surge line between a hot leg and the pressurizer during reflux cooling. Characteristics of countercurrent flow limitation (CCFL) in a 1/10-scale model of the surge line were measured using air and water at atmospheric pressure and room temperature. The experimental results show that CCFL takes place at three different locations, that is, at the upper junction, in the surge line, and at the lower junction, and its characteristics are governed by the most dominating flow limitation among the three. Effects of inclination angle and elbows of the surge line on CCFL characteristics were also investigated experimentally. The effects of inclination angle on CCFL depend on the flow direction, that is, the effect is large for the nearly horizontal flow and small for the vertical flow at the upper junction. The presence of elbows increases the flow limitation in the surge line, whereas the flow limitations at the upper and lower junctions do not depend on the presence of elbows.
Highlights
The mid-loop operation is to be conducted during plant refueling and maintenance of a PWR (Pressurized Water Reactor)
In addition to this countercurrent flow limitation (CCFL), the steam generated in the reactor core and water condensed in the pressurizer due to heat transfer to the vessel wall may form a countercurrent flow in a surge line which connects the hot leg and the pressurizer
The ROSA-IV/LSTF (Rig-of-Safety-Assessment No 4/Large Scale Test Facility) experiment [3], which simulated the loss of residual heat removal (RHR) systems during mid-loop operation, reported that water accumulated in the pressurizer due to CCFL in the surge line
Summary
The mid-loop operation is to be conducted during plant refueling and maintenance of a PWR (Pressurized Water Reactor). If the loss of cooling systems such as RHR and/or other cooling systems takes place, cooling water in the reactor core may be heated up to boil and the top of the fuel assembly can be exposed to the air In such an event, reflux cooling by the steam generators (SG) is regarded as one of the possible and effective core cooling methods. The authors measured CCFL (Countercurrent Flow Limitation) characteristics in a scale-down model of a hot leg using air and water [1] and reported that CCFL can be accurately evaluated based on a one dimensional momentum balance for air-water two-phase flow [2] In addition to this CCFL, the steam generated in the reactor core and water condensed in the pressurizer due to heat transfer to the vessel wall may form a countercurrent flow in a surge line which connects the hot leg and the pressurizer. Characteristics of CCFL in the surge line must be well understood for safety evaluation of the mid-loop operation
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
