[en] The modernization of Reactor I and C, consisting of reactor limitation system, reactor control system and rod control system, at Unterweser NPP is the pilot application of the state-of-the-art safety I and C system TELEPERM XS. The Unterweser system has been integrated and tested from December 1996 to May 1997 in the Siemens Erlangen test field and has been installed at site in July 1997. For the period from July 1997 to Jul 1998 the new TELEPERM XS based Reactor I and C system will be operated online-open-loop in parallel to the existing system, in order to get information about the long term stability of the system and conduct intensive personnel training. For one selected function ''Power distribution control'' the operator has the possibility to choose between the old controller and the new TELEPERM XS function. During the 1998 outage the TELEPERM XS system will be connected to the process and the old I and C system will be dismantled. This document describes the experiences gathered during system integration in the test field. (author)