Between October 1 and 15, 2001, Framatome ANP installed two new penetrations in the wall of the fuel pool at Sweden's oldest nuclear power plant - the 445MWe BWR unit Oskarshamn 1. The penetrations, which have a nominal diameter of 8" (DN 200), are needed for connecting the fuel pool to the residual heat removal system that has been redesigned as part of Oskarshamn's ongoing "MOD" modernization program. The purpose of the new connections is to provide the plant with two additional fuel pool cooling trains that can be placed in operation if the system normally used for pool cooling should fail.

Auxiliary bridge with caisson suspended in the fuel pool

Since the entire reactor core will be unloaded to the fuel pool when the unit is shut down in 2002 for the main scope of the modernization work, the two penetrations had to be installed while the plant was still on line. Because the fuel pool cooling system extracts the pool water from the upper region of the pool for cooling, it was not possible to lower the water level in the pool. Hence all activities had to be carried out underwater using a special caisson to provide a dry working area at the pool wall. Thanks to the experience and knowledge gained from a similar project performed in 1997 at the Swiss nuclear power plant Gösgen, the work was able to be completed much faster than expected - in 15 days instead of the 23 days originally planned. According to Anders Ahrenius, sub-project manager for the plant operator, OKG Aktiebolag, the decisive factor here was "the excellent work done by the team from Framatome ANP."

The main goal of the MOD project is to bring Oskarshamn 1 in line with today's safety standards and to enable the unit to continue generating power economically for many years to come. The complete modernization program that spans several years, is scheduled for completion by the fall of this year.

New penetration welded into the fuel pool wall