Abstract
Using experimental and simulation method we found a general-purpose simulation software MCNP can be used in our special-configuration calibration of efficiency with the same type fitting curve on the measurement of BWR recirculation pipe build-up with the portable HPGe detector during the outage period. The MCNP simulation deviation can be controled under 10% while ISOCS application here isn’t fitted and only the simple type of sources and shielding can reach 5% deviation yet other complicated ones could be as large as around 60% based on our experiment.