Patent Number: 
Section: claims

1. A reactor pressure vessel, comprising: a reactor pressure body having a chamber formed therein and a cross-section;  upper connecting branches connected to said reactor pressure body;  an upper support plate disposed in said reactor pressure body above said upper connecting branches and expanding over said cross-section of said reactor pressure body, said upper support plate dividing said chamber of said reactor pressure body into an upper dome chamber and a lower chamber, said upper support plate having openings formed therein for accommodating control rods and at least one equalization opening formed therein, said equalization opening having a cross section; and  a device fitted in said equalization opening for varying said cross section as an inverse function of a temperature in said lower chamber. 2. The reactor pressure vessel according to  claim 1 , including core installations disposed in said reactor pressure body, said reactor pressure body having a pressure vessel wall, a space between said pressure vessel wall and said core installations defines an equalization chamber leading to said equalization opening formed in said support plate body, said equalization opening and said equalization chamber forms a bypass between said lower chamber and said upper dome chamber. claim 1 3. The reactor pressure vessel according to  claim 1 , wherein said cross section of said equalization opening is passively temperature-controlled. claim 1 4. The reactor pressure vessel according to  claim 1 , wherein: said device in an event of a temperature drop enlarges said cross section of said equalization opening by utilizing a thermal contraction of a material of said device, and in an event of a temperature rise said device reduces said cross section of said equalization opening by utilizing a thermal expansion of said material of said device. claim 1 5. The reactor pressure vessel according to  claim 4 , wherein said device has an expansion sleeve. claim 4 6. The reactor pressure vessel according to  claim 5 , wherein said device has a cylinder and a hollow piston guided in said cylinder, said device further having an expansion sleeve connected to said hollow piston, said hollow piston having end openings and an interior formed therein and said cylinder having cooling openings formed therein, said interior of said hollow piston connected by way of said end openings of said hollow piston to both said lower chamber below said support plate and to said upper dome chamber disposed above said support plate, and said hollow piston has additional lateral openings formed therein which when said expansion sleeve contracts aligns with said cooling openings of said cylinder. claim 5 7. A process for temperature equalization between an upper dome chamber disposed above a lower chamber in a reactor pressure vessel, a support plate occupying a cross section of the reactor pressure vessel above upper connecting branches of the reactor pressure vessel and the supporting plate separating the upper dome chamber from the lower chamber, which comprises the steps of: supplying a flow of a medium between the upper dome chamber and the lower chamber through an equalization opening in the support plate; and  using a device fitted in the equalization opening for varying the flow of the medium as an inverse function of a temperature in the lower chamber by varying a cross section of the equalization opening. 8. The process according to  claim 7 , which comprises supplying a bypass flow of the medium from the lower chamber, which is a reactor annulus defined by a pressure vessel wall and core installations, into the upper dome chamber through the equalization opening. claim 7 9. The process according to  claim 7 , which comprises using a passively temperature-control method for controlling the flow of the medium. claim 7 10. The process according to  claim 7 , wherein the flow of the medium is increased owing to a temperature drop when shutting down the reactor pressure vessel. claim 7