PWR integrated leak rate test, a review of experiences and results

This paper reviews the Integrated Leak Rate Test as carried out in the USA and as reported in papers for European countries. The methods of analysis of test results are discussed and it is recommended that only the mass point method be permitted. The reliability of the instruments used in a test are described and the care needed during a test is identified. The use of a preliminary zero pressure test is recommended as a necessary part of the test to counter any instrument inaccuracies, to identify any unwanted temperature gradients, and to ensure that no ingress of water or air is taking place at the start of a test. Valves are identified as the major leak source during tests with about 40% of tests being adversely affected by their performance. Recommendations are given to improve the reported integrity of the valves. The use of the part pressure test is discussed and for various reasons it is recommended that only full pressure tests (at design accident pressure) be permitted. The lack of correlation between full and part pressure tests is considered to be due to gas absorption/release of internal concrete and the behaviour of steam generator equipment giving greater leaks at higher pressures. Secondary effects of diurnal influences and the use of the ideal gas laws in place of more accurate Van de Waals state equation are discussed