Another item related to the TMI CONTRIBUTING causes is that all operating B&W plants except Davis-Besse had similar Dresser PORVs. Davis-Besse had a Crosby PORV, but the operating concept of the valve was the same as the Dresser PORV. This information is from an NRC NUREG published in September 1990. I also saw the Davis-Besse PORV disassembled and inspected in 1985.