Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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MOVEABLE ISOLATED ROD COUPLINGS FOR USE IN A NUCLEAR REACTOR
CONTROL ROD DRIVE
[0001] This application is a division of application number CA 3,029,845,
filed July 13,
2017.
BRIEF DESCRIPTIONS OF THE DRAWINGS
[0002] Example embodiments may become more apparent by describing, in
detail, the
attached drawings, wherein like elements are represented by like reference
numerals, which are
given by way of illustration only and thus do not limit the terms which they
depict.
[0003] FIG. 1 is an illustration of a drive rod connection to a control
rod assembly useable in
example embodiments.
[0004] FIG. 2 is a plan illustration of an example embodiment control rod
drive mechanism
using extended lift coils.
[0005] FIG. 3 is a profile illustration of the example embodiment control
rod drive
mechanism using extended lift coils.
[0006] FIG. 4 is another profile illustration of the example embodiment
control rod drive
mechanism using extended lift coils.
BACKGROUND
[0007] FIG. 1 is an illustration of a drive rod¨control rod assembly
(CRA) connection 10
useable with example embodiment control drives. In most conventional PWR
control rod
assemblies, drive rod 11 and actuating rod 12 extend in lateral support tube
16 from above a
reactor pressure vessel 1 down to a lockable spud or bayonet 13 that joins to
CRA 15 via locking
plug 14. CRA 15 contains neutron absorbent materials what can be used to
control a nuclear
chain reaction based on an amount of vertical insertion. Control rods are
driven from above by
vertical movement of actuating rod 12 and drive rod 11, under force from the
control rod drive
mechanism.
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[0008] The following documents describe control rod drive mechanisms used
in nuclear
reactors: US Pat Pub 2015/0255178 to Tsuchiya et al; US Pat 4423002 to Wiart
et al.; US Pat
4369161 to Martin; US Pat 4338159 to Martin et al.; US Pat 4044622 to
Matthews; US Pat
9305669 to Hyde et al.; US Pat 3933581 to McKeehan et al.; US Pat 4048010 to
Eschenfelder et
al.; US Pat 4092213 to Nishimura; US Pat 4147589 to Roman et al.; US Pat
4288898 to Adcock;
US Pat 4484093 to Smith; US Pat 5276719 to Batheja; US Pat 8915161 to Akatsuka
et al.; US
Pat 4518559 to Fischer et al.; US Pat 5517536 to Goldberg et al.; US Pat
5428873 to Hitchcock
et al.; US Pat 8571162 to Maruyama et al.; US Pat 8757065 to Fjerstad et al.;
US Pat 5778034 to
Tani; US Pat 9336910 to Shargots et al.; US Pat 3941653 to Thorp, II; US Pat
3992255 to
DeWesse; US Pat 8811562 to DeSantis; and "In-vessel Type Control Rod Drive
Mechanism
Using Magnetic Force Latching for a Very Small Reactor" Yoritsune et al., J.
Nuc. Sci. & Tech.,
Vol. 39, No. 8, p. 913-922 (Aug. 2002).
SUMMARY
[0009] Example embodiments include control rod drives including linearly-
moveable control
elements to control neutronics in a nuclear reactor. Example control rod
drives may include an
isolation barrier impermeably separating pressurized reactor internals from
external spaces like
containment. One or more induction coils are linearly moveable outside of the
isolation barrier,
while the control element is inside the isolation barrier in the reactor.
Example control rod drives
may move the control element via a magnet immovably connected to the same by
linearly
moving the induction coils to linearly drive the magnets. The induction coils
may be mounted on
a vertical travelling nut and linear screw to fully move across a whole
distance equivalent to
complete insert and withdrawal of the control element from the reactor. A
closed coolant loop
may cool the induction coils, which may otherwise be maintained in a vacuum or
other
environment distinct from reactor internals in a housing about an end of the
reactor. Example
embodiment control rod drives may include a control rod assembly housing the
magnet that
directly joins to the control element. The control rod assembly may lock with
magnetic
overtravel latches inside the isolation barrier to maintain an overtravel
position. Overtravel
release coils outside the isolation barrier can release or otherwise move the
latches, which may
be spring-biased, to adjust the connection between the latches and assembly.
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[00101 Example methods include linearly moving the induction coil to
drive the control
element via the magnetic material secured to the same. In this way, the
control element may be
inserted and withdrawn with no mechanical linkage permeating the isolation
barrier. By
mounting the induction coil on a vertical travelling nut that moves linearly
with rotation of a
linear screw, the magnetic material may be driven with the moving induction
coil, thus driving
the control element. A motor can rotate the linear screw outside the isolation
barrier to achieve
this motion. When the coil is de-energized, the control element may be driven
by gravity into a
reactor, achieving a scram. Example methods may drive the control rod to an
overtravel position,
where overtravel latches hold the same, for removal, attachment, and/or other
maintenance of the
control element from/to/on the control rod assembly. Following desired
overtravel actions, the
overtravel coils may be energized to release the latches through magnetic
materials in the latch
biasing them to an open position.
DETAILED DESCRIPTION
[00111 Because this is a patent document, general broad rules of
construction should be
applied when reading it. Everything described and shown in this document is an
example of
subject matter falling within the scope of the claims, appended below. Any
specific structural
and functional details disclosed herein are merely for purposes of describing
how to make and
use examples. Several different embodiments and methods not specifically
disclosed herein may
fall within the claim scope; as such, the claims may be embodied in many
alternate forms and
should not be construed as limited to only examples set forth herein.
[0012] It may be understood that, although the terms first, second, etc.
may be used herein to
describe various elements, these elements should not be limited to any order
by these terms.
These terms are used only to distinguish one element from another; where there
are "second" or
higher ordinals, there merely must be that many number of elements, without
necessarily any
difference or other relationship. For example, a first element could be termed
a second element,
and, similarly, a second element could be termed a first element, without
departing from the
scope of example embodiments or methods. As used herein, the term "and/or"
includes all
combinations of one or more of the associated listed items. The use of "etc."
is defined as "et
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cetera" and indicates the inclusion of all other elements belonging to the
same group of the
preceding items, in any "and/or" combination(s).
[0013] It may be understood that when an element is referred to as being
"connected,"
"coupled," "mated," "attached," "fixed," etc. to another element, it can be
directly connected to
the other element, or intervening elements may be present. In contrast, when
an element is
referred to as being "directly connected," "directly coupled," etc. to another
element, there are no
intervening elements present. Other words used to describe the relationship
between elements
should be interpreted in a like fashion (e.g., "between" versus "directly
between," "adjacent"
versus "directly adjacent," etc.). Similarly, a term such as "communicatively
connected" includes
all variations of information exchange and routing between two electronic
devices, including
intermediary devices, networks, etc., connected wirelessly or not.
[0014] As used herein, the singular forms "a," "an," and "the" are
intended to include both
the singular and plural forms, unless the language explicitly indicates
otherwise. It may be
further understood that the terms "comprises," "comprising," "includes,"
and/or "including,"
when used herein, specify the presence of stated features, characteristics,
steps, operations,
elements, and/or components, but do not themselves preclude the presence or
addition of one or
more other features, characteristics, steps, operations, elements, components,
and/or groups
thereof
[0015] The structures and operations discussed below may occur out of the
order described
and/or noted in the figures. For example, two operations and/or figures shown
in succession may
in fact be executed concurrently or may sometimes be executed in the reverse
order, depending
upon the functionality/acts involved. Similarly, individual operations within
example methods
described below may be executed repetitively, individually or sequentially, to
provide looping or
other series of operations aside from single operations described below. It
should be presumed
that any embodiment or method having features and functionality described
below, in any
workable combination, falls within the scope of example embodiments.
[0016] The Inventors have newly recognized that control rod drives in
nuclear reactors are
typically mechanical drives using direct contact points that must pass through
or be inside a
reactor CRDM pressure boundary 150. Such direct contact and positioning
creates a challenging
environment for the mechanical drives that typically must operate to move
control rods over a
period of several months or years without maintenance. For example, reactor
temperatures,
leaked coolant, and noncondensible gasses found inside example embodiment CRDM
200
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pressure boundary 150 can cause corrosion and associated stress corrosion
cracking, hydriding,
and hydrogen deflagration problems with mechanical drive parts. The cooling
mechanisms and
heat from direct contact with the drives interact with example embodiment CRDM
200 pressure
boundary 150 to also cause thermal cycling problems during actuation of
mechanical drives over
the course of operation. Penetrations in a control rod drive required for
mechanical connection
also represent an avenue for leakage of reactor coolant. The Inventors have
newly recognized a
need for a control rod drive that has less engagement with example embodiment
CRDM 200
pressure boundary 150 as well as mechanical contacts that represent high-
failure points.
Example embodiments described below uniquely enable solutions to these and
other problems
discovered by the Inventors.
Positioning and Scramming the CRDM
[0017] FIG. 2 is a plan view illustration of an example embodiment
control rod drive
mechanism 200. FIGS. 3 and 4 are profile views of the same example embodiment
control rod
drive mechanism 200 of FIG. 2, with FIG. 3 showing assembly 210 in a seated
position and FIG.
4 showing assembly 210 in an overtravel position. Descriptions of actuating
rod 103, position
indication magnet 115, lift rod actuating magnet 104, key features 118, are
given in the co-
owned U.S. patent application 15/640,428 (publication number US 20180019026)
filed June 30,
2017 to Morgan et al. for "STATIONARY ISOLATED ROD COUPLINGS FOR USE IN A
NUCLEAR REACTOR CONTROL ROD DRIVE".
[0018] As seen in FIG. 4, following coupling of lift rod 112 and drive
rod 111 to CRA 210,
CRA 210 is positioned by outer linear screw 123 and scram lift coils.
Levitating and scram
coils 124 are mounted on outer vertical travel nut 125 and are energized to
magnetically couple
lift rod 112 via lift magnet 114 or other materials within example embodiment
CRDM 200
pressure boundary 150. CRDM Motor 126 rotates outer linear screw 123 within
CRDM
structural housing 106. Rotation of outer linear screw 123 causes vertical
movement of outer
vertical travel nut 125 and levitating and scram coils 124 that are keyed to
prevent rotation by
position indication probe housing 135. Outer vertical travel nut 125 and
energized levitating and
scram coils 124 are moved vertically on outer linear screw 123 within the
drive range. Levitated
lift rod 112, drive rod 111, and CRA 210 follow the magnetic field. Feedback
from position
sensors and position indication probes 105 control outer linear screw 123
rotation and move
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CRA 210 in CRDM 200 to its desired position for reactor control. Outer linear
screw 123
provides fine motion control of internal lift rod 112, drive rod 111 and CRA
210.
[0019] There is a vacuum 121 between example embodiment CRDM 200 pressure
boundary
150 and outer linear screw 123 and between levitating and scram coils 124 and
outer linear
screw 123 to limit heat transfer between coils 124 and CRDM pressure boundary
150. Vacuum
121 may provide a more uniform temperature gradient on example embodiment CRDM
200
pressure boundary 150 that minimizes thermal cycling.
[0020] Simplification of example embodiment CRDM 200 pressure boundary
150 and lift
rod internals may allow the size of CRDM pressure boundary 150 to be reduced
such that
example embodiment CRDM 200 pressure boundary 150 wall thickness can be
enhanced to
minimize effects of corrosion, hydriding, and hydrogen deflagration problems.
[00211 Reactor safety features requiring a scram provide inputs to the
control system for
levitating and scram coils 124 (in their energized state). If reactor
conditions warrant a scram,
the control system de-energizes levitating and scram coils 124. This drops the
magnetic field
levitating lift rod 112, drive rod 111, and CRA 210, and gravity quickly acts
on the unsupported
weight to scram the reactor. Any CRDM failure causing a loss of scram coil
current may also
lead to a conservative control rod scram.
[0022] Levitating and scram coils 124 are continuously energized during
CRDM operation
and may use a cooling flow through their travel range. Flexible coolant
inlet/outlet lines 107
(FIG. 5) are oriented from the top of CRDM 200 and reach levitating and scram
coils 124
through slotted openings of CRDM structural housing 106. Coolant inlet/outlet
lines 107 along
with the control circuits for levitating and scram coil 124 can have counter
weights or spring reel
feeds to keep them under slight tension during drive operation.
CRDM preparation for Refueling Process
[0023] Drive rod 111 may be decoupled from CRA 210 as described in the
above-
mentioned co-owned U.S. patent application (publication number US
20180019026). Outer
linear screw 123, vertical travelling nut 125, and energized levitating and
scram coils 124 are
then used to maneuver lift rod 112 and drive rod 111 to an overtravel position
as shown in
FIG. 3. In the overtravel position, two spring-actuated overtravel latches 116
engage a
shoulder or window in example embodiment CRDM 200 pressure boundary 150 to
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lock CRA 210 at the overtravel height. Power can then be secured to or
disconnected from motor
126 (FIG. 2) and levitating and scram coils 124 (FIGS. 2 & 4) for duration of
the refueling
process. The lower end of drive rod 111 is carried to an elevation that is
clear of the upper to
lower vessel disassembly process.
[0024] When refueling is completed, motor 126, outer linear screw 123,
and levitating and
scram coil 124 are energized to carry the weight of lift rod 112 and drive rod
111 in the
overtravel position. Overtravel release coils 108 are then energized to
compress spring actuated
structural support 117 resting on example embodiment CRDM 200 pressure
boundary 150
structural support. Magnetic material 119 drawn outward on overtravel latches
116 causes the
spring actuated structural support 117 to clear example embodiment CRDM 200
pressure
boundary 150 structural support and the drive can be positioned to recouple to
CRA 210 for
operation.
CRDM support Structure
[0025] As shown in FIG. 2, CRDM pressure boundary 150 is supported
vertically off of the
CRDM nozzle pressure boundary flange 120 in CRDM structural housing 106 of the
RPV
flange. Lateral support to upper portions of CRDM pressure boundary 150 is not
provided other
than the close proximity of linear screw 123 across vacuum gap 121.
[0026] CRDM structural housing 106 is also fixed to CRDM nozzle pressure
boundary
flange 120. Insulating washers and other items can be utilized to reduce the
thermal heat transfer
from the RPV head to components in CRDM 200. The internal bearings/bushings of
rotating
linear screw 123 are supported from CRDM structural housing 106 and not
pressure boundary
150 to avoid heat conduction. PIP probes 105 are inserted vertically through
the upper flange of
CRDM structural housing 106 and are laterally supported at a minimum of the
upper and lower
ends of CRDM structural housing 106. Motor 126, brake, and position sensors
may be mounted
on the top end of CRDM structural housing 106 and engage outer linear screw
123 through a
geared coupling. Cooling lines 107 are run to motor 126 which is located as
remote as possible
from the reactors thermal and radiation output. Motor 126 may also be isolated
by a vacuum 121
from CRDM pressure boundary 150.
[0027] Example embodiments and methods thus being described, it may be
appreciated by
one skilled in the art that example embodiments may be varied and substituted
through routine
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experimentation while still falling within the scope of the following claims.
For example, a
generally vertical orientation with control rod drives above a pressure vessel
is shown in
connection with some examples; however, other configurations and locations of
control rods and
control rod drives, are compatible with example embodiments and methods simply
through
proper dimensioning and placement - and fall within the scope of the claims.
Such variations are
not to be regarded as departure from the scope of these claims.
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