U.S. patent application number 09/973323 was filed with the patent office on 2002-02-07 for banded ecp sensor.
Invention is credited to Hale, Donald Allan, Kim, Young Jin, Moran, Eric.
Application Number | 20020015463 09/973323 |
Document ID | / |
Family ID | 23572876 |
Filed Date | 2002-02-07 |
United States Patent
Application |
20020015463 |
Kind Code |
A1 |
Kim, Young Jin ; et
al. |
February 7, 2002 |
Banded ECP sensor
Abstract
An ECP sensor includes a tubular ceramic probe having a closed
tip at one end packed with a metal and metal oxide powder. A metal
support tube receives an opposite end of the probe, and is joined
thereto by a braze joint therewith. An electrical conductor extends
through the support tube and probe, and has an end buried in the
powder for electrical contact therewith. A ceramic band bridges the
probe and tube at the joint for sealing thereof.
Inventors: |
Kim, Young Jin; (Clifton
Park, NY) ; Moran, Eric; (Schenectady, NY) ;
Hale, Donald Allan; (San Jose, CA) |
Correspondence
Address: |
GENERAL ELECTRIC COMPANY
CRD PATENT DOCKET ROOM 4A59
P O BOX 8
BUILDING K 1 SALAMONE
SCHENECTADY
NY
12301
US
|
Family ID: |
23572876 |
Appl. No.: |
09/973323 |
Filed: |
October 9, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09973323 |
Oct 9, 2001 |
|
|
|
09397840 |
Sep 17, 1999 |
|
|
|
Current U.S.
Class: |
376/305 |
Current CPC
Class: |
G01N 17/02 20130101;
G21C 17/00 20130101; Y02E 30/30 20130101 |
Class at
Publication: |
376/305 |
International
Class: |
G21C 009/00 |
Claims
What is claimed is
1. A sensor for measuring electrochemical corrosion potential in a
nuclear reactor comprising: a tubular ceramic probe having a closed
tip at one end packed with a metal and metal oxide powder; a metal
support tube having one end receiving an opposite end of said
probe, and joined thereto by a braze joint therewith; an electrical
conductor extending through said support tube and probe, and having
an end buried in said powder for electrical contact therewith; and
a ceramic band bridging said probe and tube at said joint for
sealing thereof.
2. A sensor according to claim 1 wherein said band locally coats
said probe and tube at said braze joint, and is spaced from said
probe tip.
3. A sensor according to claim 2 wherein both said probe and band
comprise zirconia.
4. A sensor according to claim 3 wherein said powder comprises iron
and iron oxide.
5. A sensor according to claim 3 wherein said powder comprises
copper and copper oxide.
6. A sensor according to claim 3 wherein said powder comprises
nickel and nickel oxide.
7. A sensor according to claim 3 wherein said band comprises
yttria-stabilized-zirconia or magnesia-stabilized-zirconia.
8. A sensor according to claim 3 wherein said band is directly
bonded to said probe and tube at said braze joint.
9. A sensor according to claim 3 further comprising a bond coating
underlaying said band and bonded to said probe and tube at said
braze joint.
10. A sensor according to claim 3 wherein said probe comprises
magnesia-stabilized-zirconia.
11. A sensor for measuring electrochemical corrosion potential in a
nuclear reactor comprising: a tubular ceramic probe having a closed
tip at one end packed with a metal and metal oxide powder; a metal
support tube having one end receiving an opposite end of said
probe, and joined thereto by a braze joint therewith; an electrical
conductor extending through said support tube and probe, and having
an end buried in said powder for electrical contact therewith; and
a ceramic band locally coating said probe and tube at said braze
joint for sealing thereof, and spaced from said probe tip.
12. A sensor according to claim 11 wherein both said probe and band
comprise zirconia.
13. A sensor according to claim 12 wherein said probe comprises
magnesia-stabilized-zirconia, and said band comprises
yttria-stabilized-zirconia.
14. A sensor according to claim 13 wherein said powder comprises
iron and iron oxide.
15. A sensor according to claim 14 further comprising a bond
coating underlaying said band, and bonded to said probe and tube at
said braze joint.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates generally to nuclear reactors,
and, more specifically, to electrochemical corrosion potential
(ECP) sensors therein.
[0002] In a boiling water nuclear reactor, water and steam are
channeled through various conduits formed of stainless steel.
Normal water chemistry conditions include high oxidizing species,
such as oxygen and hydrogen peroxide which may lead to
intergranular stress corrosion cracking (IGSCC) of the stainless
steel.
[0003] IGSCC can be mitigated by lowering the concentrations of
ionic impurities and oxidizing species in the reactor water. This
may be effected using hydrogen water chemistry (HWC) in which
hydrogen is added to the feed water of the reactor. The primary
purpose of the added hydrogen is to reduce the dissolved oxidant
concentrations and thereby lower the ECP below a critical value at
which IGSCC susceptibility is significantly reduced.
[0004] Various forms of ECP sensors are used for measuring ECPs in
the reactor. The sensors have different configurations for
measuring ECPs, and are subject to different problems which affect
their useful lives. The useful life should cover the duration of at
least a single fuel cycle which is about eighteen months in the
United States. However, experience in actual nuclear reactors has
demonstrated sensor failure in a shorter duration due to various
causes.
[0005] U.S. Pat. Nos. 5,848,113 and 5,896,432, commonly owned by
the present assignee, disclose and claim two different types of ECP
sensors specifically configured for solving corresponding failure
problems during operation.
[0006] A different type of ECP sensor includes a ceramic probe in
which is packed a mixture of metal and metal oxide powder for
providing a corresponding reference ECP. This mixture may include
iron and iron oxide (Fe/Fe.sub.3O.sub.4), or copper and copper
oxide (Cu/Cu.sub.2O), or nickel and nickel oxide (Ni/NiO).
[0007] In this type of sensor, the probe is typically in the form
of a zirconia tube brazed to a support tube made of a suitable
metal such as Invar or "alloy 42", which in turn is welded to a
stainless steel tube. An electrical conductor extends through the
tubes into the probe and is buried in the operative mixture.
[0008] In one example, the ceramic probe is formed of
magnesia-stabilized-zirconia (MSZ) brazed to an alloy 42 support
tube. Since the ceramic probe and metal tube have different
coefficients of thermal expansion, they are subject to thermal
shock during high temperature operation inside the nuclear reactor
which can lead to cracking of the braze joint. The braze material
is also subject to corrosion during operation. Both problems limit
the useful life of the sensor, since failure of the braze joint
causes water leakage inside the sensor and failure thereof.
[0009] Accordingly, it is desired to provide an improved ECP sensor
addressing these problems.
BRIEF SUMMARY OF THE INVENTION
[0010] An ECP sensor includes a tubular ceramic probe having a
closed tip at one end packed with a metal and metal oxide powder. A
metal support tube receives an opposite end of the probe, and is
joined thereto by a braze joint therewith. An electrical conductor
extends through the support tube and probe, and has an end buried
in the powder for electrical contact therewith. A ceramic band
bridges the probe and tube at the joint for sealing thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The invention, in accordance with preferred and exemplary
embodiments, together with further objects and advantages thereof,
is more particularly described in the following detailed
description taken in conjunction with the accompanying drawings in
which:
[0012] FIG. 1 is a schematic representation of an ECP sensor shown
in relevant portion of a nuclear reactor in accordance with an
exemplary embodiment of the present invention.
[0013] FIG. 2 is an enlarged, sectional view of a portion of the
sensor illustrated in FIG. 1 in accordance with an alternate
embodiment.
DETAILED DESCRIPTION OF THE INVENTION
[0014] Illustrated schematically in FIG. 1 is an ECP sensor 10
configured for measuring electrochemical corrosion potential of
reactor surfaces in circulating water 12 inside the pressure vessel
of a conventional boiling water nuclear reactor 14, shown in
relevant part.
[0015] The sensor includes a tubular ceramic probe 16 having a
closed tip 16a in the form of a cup at a distal end of the probe
packed with a dry metal and metal oxide mixture or powder 18.
[0016] A metal support tube 20 has a distal end receiving an
opposite, proximal end of the probe for support thereof, and is
joined thereto by a braze joint 22 therewith. The support tube 20
may be formed of conventional alloy 42 or Invar, for example. The
braze joint may be a conventional alloy, such as silver, copper,
and titanium alloy. The support tube 20 is typically welded
coaxially with a secondary support tube 20b typically formed of
stainless steel.
[0017] An electrical conductor 24 extends coaxially through the
support tubes 20, 20b and the probe 16, and has a distal end buried
in the powder 18 for electrical contact therewith. A coaxially
electrical cable 26 extends through a suitable sealing collar 28 at
the proximal of the secondary tube 20b and is suitably joined to
the electrical conductor 24 inside the sensor. The cable 26 is
suitably routed to a conventional digital volt meter 30 for
measuring electrochemical corrosion potential.
[0018] The sensor 10 as above described is conventional in
configuration and operation in the reactor. In one embodiment, the
powder 18 is a mixture of iron and iron oxide (Fe/Fe.sub.3O.sub.4)
for providing a constant reference potential of -820 mV vs standard
hydrogen electrode (SHE) at 288.degree. C. in high purity
water.
[0019] As indicated above, this type of sensor is subject to
thermal shock and corrosion at the braze joint 22 during operation,
but for the improvement in accordance with the present invention.
In a preferred embodiment, a ceramic band 32 is selectively applied
around the perimeter of the sensor for bridging the probe and
support tube at the braze joint for covering and sealing
thereof.
[0020] The band 32 preferably locally coats the probe and support
tube at the braze joint and is spaced from the remainder of the
probe including its tip 16a.
[0021] The ceramic probe 16 may be formed of
magnesia-stabilized-zirconia (MSZ) or yttria-stabilized-zirconia
(YSZ) which have different coefficients of thermal expansion than
that of the metal support tube 20, and that of the braze joint
22.
[0022] The ceramic band 32 is preferably also zirconia, such as MSZ
or YSZ, for matching the coefficient of thermal expansion of the
ceramic probe. Since the band 32, like the probe 16, has a
different coefficient of thermal expansion than that of the support
tube 20 and braze joint 22, it is preferably applied locally or
selectively solely at the exposed end of the braze joint 22 between
the probe and support tube.
[0023] In one embodiment, the ceramic band 32 is directly bonded to
the probe and tube at the braze joint in a coating effected using
conventional plasma spraying equipment. The band 32 thusly provides
an intimate bond with the probe and support tube for providing an
effective seal at the juncture therebetween in which is found the
braze joint 22.
[0024] A relatively thin coating of the ceramic band 32 of about
5-10 mils thick (0.13-0.25 mm) provides thermal shock and corrosion
protection of the braze joint for extending the useful life of the
sensor. The coating band may be applied using plasma spraying in
vacuum or in air to produce a relatively high density coating of up
to about 97% density. The thin and narrow band of ceramic coating
accommodates differential thermal expansion and contraction between
the probe and the support tube for reducing the likelihood of
cracking thereat.
[0025] FIG. 2 illustrates an alternate embodiment of the sensor
illustrated in FIG. 1 in which a bond coating 34 is firstly applied
at the junction of the probe and support tube for enhancing the
adherence of the ceramic band 32 atop the metal support tube 20. In
either embodiment illustrated in FIGS. 1 and 2, the surfaces of the
probe and support tube are prepared using conventional grit
blasting, followed in turn by the bond coating 34, if used, and the
ceramic band 32.
[0026] The bond coating 34 may be about the same thickness as that
of the ceramic band 32 and is also locally applied in the immediate
region of the junction between the probe and the support tube. The
bond coating may be conventionally applied, such as by plasma
spraying. And any suitable bond coating may be used, such as Nickel
210, which is a nickel-chrome-iron-aluminum alloy, or MCrAlY alloy,
where M is nickel-cobalt-iron or nickel-cobalt alloy. The bond
coating 34 underlays in most part the ceramic band for improving
its adherence to at least the metal support tube.
[0027] In a preferred embodiment, the powder 18 is a mixture of
iron and iron oxide trapped within a MSZ ceramic probe 16 brazed to
an alloy 42 support tube 20. The ceramic band 32 is preferably
YSZ.
[0028] In alternate embodiments, the powder 18 may be a mixture of
copper and copper oxide (Cu/Cu.sub.2O), or a mixture of nickel and
nickel oxide (Ni NiO), both in corresponding MSZ probes 16.
[0029] The ceramic band 32 thusly provides a hermetic water seal at
the braze joint, and a thermal barrier providing thermal
insulation. YSZ is the preferred material for the band 32 as having
had proven resistance to high temperature and high flow water under
high radiation environments in nuclear reactors.
[0030] The YSZ ceramic band 32 additionally provides electrical
insulation for preventing the formation of a corrosion cell, even
after long term exposure to high temperature water under various
water chemistry conditions possible in a nuclear reactor
environment. The YSZ ceramic coating therefore has proven stability
for this hostile environment.
[0031] While there have been described herein what are considered
to be preferred and exemplary embodiments of the present invention,
other modifications of the invention shall be apparent to those
skilled in the art from the teachings herein, and it is, therefore,
desired to be secured in the appended claims all such modifications
as fall within the true spirit and scope of the invention.
[0032] Accordingly, what is desired to be secured by Letters Patent
of the United States is the invention as defined and differentiated
in the following claims in which we claim:
* * * * *