Induced nuclear reactions: processes – systems – and elements – Reactor structures – Orifice or fluid control at inlet or outlet of coolant channels
Reexamination Certificate
1998-10-22
2001-03-13
Behrend, Harvey E. (Department: 3641)
Induced nuclear reactions: processes, systems, and elements
Reactor structures
Orifice or fluid control at inlet or outlet of coolant channels
C376S204000, C376S282000, C376S292000, C138S089000, C138S097000
Reexamination Certificate
active
06201847
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to nuclear reactors and more particularly, to assemblies and methods for coupling core spray line assemblies within such reactors.
A reactor pressure vessel (RPV) of a boiling water reactor (BWR) typically has a generally cylindrical shape and is closed at both ends, e.g., by a bottom head and a removable top head. A core shroud, or shroud, typically surrounds the core and is supported by a shroud support structure.
Boiling water reactors have numerous piping systems, and such piping systems are utilized, for example, to transport water throughout the RPV. For example, core spray piping is used to deliver water from outside the RPV to core spargers inside the RPV and to cool the core. Typically, the core spray piping is coupled to a thermal sleeve which is welded to a RPV nozzle, or safe end.
Stress corrosion cracking (SCC) is a known phenomenon occurring in reactor components, such as structural members, piping, fasteners, and welds, exposed to high temperature water. The reactor components are subject to a variety of stresses associated with, for example, differences in thermal expansion, the operating pressure needed for the containment of the reactor cooling water, and other sources such as residual stresses from welding, cold working and other inhomogeneous metal treatments. In addition, water chemistry, welding, heat treatment and radiation can increase the susceptibility of metal in a component to SCC.
Reactor internal piping, such as thermal sleeves and core spray lines, occasionally requires replacement as a result of SCC. Replacing the core spray piping often requires removing the core spray line from the RPV safe end. Because the spray line is welded to the safe end, removing the spray line from the safe end often damages, or breaks, the safe end. To replace the safe end, the reactor must be drained to an elevation below that of the safe end. The safe end is then cut off and a replacement is welded to the RPV. Thereafter, the replacement core spray line is welded to the replacement safe end. Replacing a safe end is time consuming and tedious.
It would be desirable to provide an assembly which facilitates replacing core spray lines without removing the reactor pressure vessel safe end. It also would be desirable to provide such an assembly which is easily removed and installed without the necessity of welding.
BRIEF SUMMARY OF THE INVENTION
These and other objects may be attained by a T-box assembly which facilitates attaching a core spray line to a reactor core spray nozzle safe end without welding. In one embodiment, the T-box assembly includes a T-box housing, a cruciform wedge, and a draw bolt. The T-box housing includes three ends, and is configured to be positioned so that a first end is located inside a core spray nozzle and engages the core spray nozzle safe end. The other two ends are configured to be in substantial alignment with each other and couple to core spray line header pipes. The T-box housing also includes a cover opening that is in substantial alignment with the first end, and receives a T-box cover plate. The T-box cover plate includes a draw bolt opening for receiving the draw bolt. The first end of the T-box also includes a plurality of positioning lugs configured to engage the core spray nozzle to center the T-box housing in the nozzle bore.
The cruciform wedge includes a central member having a bore extending therethrough. Four web members extend from the central member. The web members are configured so as to form an X shaped configuration. Two support members extend between the ends of adjacent web members with a first support member extending between the first and second web members, and a second support member extending between the third and fourth web members. The support members engage the bore of the core spray nozzle safe end.
The draw bolt extends through the bore of the central member of the cruciform wedge. The draw bolt includes a cap portion located at one end configured to be larger than the diameter of the bore through the central member of the cruciform wedge. The opposite end of the draw bolt extends through the draw bolt opening in the T-box cover plate and threadedly engages a draw bolt nut. The draw bolt and cruciform wedge may have spherical mating surfaces to preclude bending of the draw bolt.
The T-box assembly is used to connect a core spray line to the safe end of a core spray nozzle by coupling the first end of the T-box housing to an end of the safe end and coupling the other two ends of the housing to core spray distribution header pipes. Particularly, to couple the first end of the T-box housing to the safe end, the cruciform wedge and draw bolt are inserted into the safe end bore. The cruciform wedge is configured with the webs in an X-shaped configuration and only two support member connecting web members to permit the wedge to be inserted into the safe end bore. The wedge is inserted in an orientation that positions the axis of the bore of the cental member of the wedge perpendicular to the bore of the nozzle safe end. The wedge is then tilted so as to move the central member bore into co-axial alignment with the safe end bore with the support members engaging the inside surface of the safe end bore. The draw bolt is then inserted through the bore of the wedge central member with the threaded end of the draw bolt extending away from the safe end and towards the T-box housing.
The T-box housing is then positioned with the alignment lugs engaging the inside surface of the core spray nozzle and the first end of the housing engaging the end of the safe end. The T-box cover plate is positioned over the cover opening with the threaded end of the draw bolt extending through the draw bolt opening in the cover plate. The draw bolt nut is then threaded onto the bolt and tightened to a predetermined torque. The core spray header pipes are coupled to the other two ends of the T-box housing to complete the installation.
The above described T-box assembly facilitates replacing the core spray line without removing the core spray nozzle safe end or draining the reactor. In addition, the T-box assembly facilitates attaching the core spray line to the safe end without welding.
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Drendel David B.
Jensen Grant Clark
Armstrong Teasale LLP
Behrend Harvey E.
General Electric Company
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