Tank represents closed loop circulating gas system for leak detection by dew point monitoring in nuclear reactors. A nitrogen cylinder at 150 kgsc through single stage PRV set at delivery pressure of 0.5 kgsc is riding on to system of volume 10 m3 for make up of leakages.
I need to know the time required for initial filling of system, is it possible to calculate using flow characteristics of PRV, please provide guidance.

Rsk:

Your description is hard to understand. It would have been so much easier if you simply generate a simple, engineering sketch and diagram with call-outs. This is what always happens when students simply copy the homework problem they are given and pass it on to someone else for resolving.

I think what you are asking is: If you have a gas system comprised of a tank and other equipment, can you calculate the time required to initially fill the entire system (10 m3) with nitrogen to a fill pressure of 0.5 kg/cm2 (assuming the system is initially at a very low vacuum) by using your pressure regulator's flow characteristics.

I don't think you can because what you basically have is a batch filling process that is differentially decreasing in driving force as the system fills up to the target pressure. However, I think you can estimate it.