The leak before break(LBB) concept is difficult to apply to a structure wit
h a thin tube that is immersed in a water environment. A heat exchanger in
a nuclear power plant is such a structure. The present paper addresses an a
pplication of the LBB concept to a heat exchanger in a nuclear power plant.
The minimum leaked coolant amount( approximately 37.9 liters) containing t
he radioactive material which can activate the radiation detector device in
stalled in near the heat exchanger is assumed. A postulated initial flaw si
ze that can not grow to a critical flaw size within the time period to acti
vate the radiation detector is justified. In this case, the radiation detec
tor can activate the warning signal caused by coolant leakage from initiall
y postulated flaws of the heat exchanger. The nuclear plant can safely shut
down when this occurs. Since the postulated initial flaw size can not grow
to the critical flaw size, the structural integrity of the heat exchanger i
s not impeded. Particularly the informational scenario presented in this pa
per discusses an actual nuclear plant.