Experimental Study on Transient Boiling Heat Transfer in an Annulus with a Narrow Gap

Abstract

The importance of heat transfer in a narrow gap has been pointed out in relation to the in-vessel retention of molten core under a severe accident condition of a light water reactor. In this study, heat transfer experiment has been carried out using internally heated annuli with a narrow gap and closed bottom. Effects of gap clearances (1.0, 2.0, 4.0 mm) on the cooling process were examined. The inner wall initially heated up to 800 C was cooled down by water supplied to the upper plenum, the transient rod temperature being measured. From the temperature history, transient boiling curves were obtained, which were compared with predictions by existing heat transfer correlations for nucleate boiling critical heat flux (CHF) and film boiling. In narrow gap channels water penetration to the gap was restricted by counterflowing vapor, which lead to a decrease of heat transfer coefficients.

Modeling and Validation of In-Vessel Debris Cooling during LWR Severe Accident

“…Henry and Hammersley 10) measured temperature trends under CCFL conditions at high superheat in quenching tests. [18][19][20] In this study, using the recent quenching test results, [16][17][18][19][20] we validated the correlations 11,12) for the average CHF and local boiling heat fluxes. Therefore, using the data, the authors derived correlations for the average CHF restricted by countercurrent flow limitation (CCFL) and local boiling heat fluxes.…”

“…Equations (16) and (19) give the weaker dependence on superheats than data. (16) and (17) give a good agreement of the superheat dependence with data but give the larger heat fluxes than data. (16) and (17) give a good agreement of the superheat dependence with data but give the larger heat fluxes than data.…”

“…In order to evaluate the effect of the pressure on the nucleate boiling heat fluxes, we calculated temperatures and heat fluxes on the vessel inner surface using a one-dimensional heat conduction equation and the temperatures measured on the vessel outer surface in the ALPHA/IDC001 experiment 15) at the pressure of 1.3 MPa. Equations (16) and (18) overestimates heat fluxes due to the unsuitable pressure term, which is obtained from the quasi-steady state CHF tests at low superheats. Equations (16) and (18) overestimates heat fluxes due to the unsuitable pressure term, which is obtained from the quasi-steady state CHF tests at low superheats.…”

“…Figure 6 compares the boiling curve in the heated inner wall by Tanaka et al 16) with correlations for the nucleate boiling heat fluxes. Equations (16) and (19) give the weaker dependence on superheats than data. On the other hand, Eqs.…”

“…However, these experiments were performed under the quasi-steady state and low superheat conditions. Therefore, we performed quenching experiments in cooperation with Kyoto University 16,17) and Kogakuin University. In their study, however, local heat transfer and CHF correlations were not derived.…”