LWR type reactor

In a steam generator, a plurality of heat transfer pipes are disposed like helical coils, and the lower portions (end portions on the upstream) of the heat transfer pipes are connected to a feedwater header in the vicinity of the heat transfer pipes. The position of the feedwater header is determined so as to be lower than the lower portion of the steam generator and it is disposed to a reinforcing wall. As a result, the connection pipe connecting the feedwater header and the lower portion of the heat transfer pipe has the end portion thereof on the upstream (the connection portion with the feedwater header) at a lower position and the end portion on the downstream (connection portion with the heat transfer pipe) at a higher position. Accordingly, in the connection pipe, a bent portion having a reduced bending radius is formed in the midway thereof, and the number of bent portions is reduced. The length of the connection pipe is made short. In addition, since the bent portions are disposed only in the vicinity of the feedwater heater and the steam header, a failure sensor can be discharged therein smoothly. (I.N.)