Basic test on sodium fire protection systems (4); Water simulation test of a leak from IHTS pipe

Himeno, Yoshiaki; *; *

PNC TN9410 86-088, 37 Pages, 1986/08

PNC-TN9410-86-088.pdf:3.3MB

In the safety evaluation of the Monju design basis sodium leak accident, a large leak from an IHTS pipe whose leak hole is equivalent to (1/4)Dt (where, D is the pipe diameter and t is the pipe wall thickness) is postulated. To investigate the possible occurrence of a spray fire in the event of a sodium leak, a water simulation test has been conducted. Three test sections (straight, elbow, and T pipes) of the full-mockup Monju ITHS pipes with thermal insulation jackets (the jackets consisted of an inner and an outer jackets) were manufactured for this purpose. The test was divided into two parts. One was with the test sections equipped with their inner jacket only and the other with the test sections equipped with both inner and outer jackets. Subjects investigated in the test were (a) leakage flow pattern, (b) fraction of spray flow among a total leak flow, (c) droplet diameters of a spray flow, and (d) pressure drop coefficient across a leak hole and the thermal insulation jackets. From the test results, the following conclusions were drawn. (1)Test sections with the inner jackets only. More than 50% of a leak flow is in the form of a spray. Number mean diameter of the spray droplets determined is several millimeters. (2)Test sections equipped with both inner and outer jackets. A spray formation is almost perfectly suppressed. Since an integrity of the thermal insulation jackets during a leak has already been confirmed, the results indicates that a spray fire does not occur in the event of an real sodium leak. (3)Pressure drop coefficient across a leak hole and thermal insulation jackets Pressure drop coefficient determined is 2.3-2.8. While, the pressure drop coefficient used in the safety evaluation of the Monju sodium leak accident is 1.0. Comparison of these two numbers indicates that the safety margin of the Monju safety evaluation in regard to a sodium leak flow is about 50%. It is also Confirmed that the most part of the pressure ...