CA1220574A - Safety grade pressurizer heater power supply connector assembly - Google Patents

Abstract

ABSTRACT

An integral safety-grade pressurizer heater power supply connector assembly which can withstand severe environmen-tal conditions such as a loss of coolant accident and main steam-line break while providing uninterrupted power to a pressurizer heater in a pressurized water nuclear reactor system is provided. The assembly has a pin-socket type connector, flexible sealed conduit, internal high temperature cable, and a shop splice assembly which attaches the connector assembly to power cabling in an area where the adverse environmental conditions have been substantially moderated.

Description

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The invention relates to a power supply connector assembly for the heater of a pressurized water nuclear reactor pressurizer.

In a typical pressurized water nuclear reactD~,a nuclear core of fissionable material is cooled by primary coolant which during operation flows past the core and picks up heat therefrom. This reactor coolant is under a consider-able pressure during operation such that the heated water remains in a subcooled state.

This pressure is maintained within certain limits by means of a pressurizer, essentially an external upright pressure vessel equipped with a spray nozzle and electric heaters.

The pressurizer contains water and steam. To increase prim-ary coolant pressure, for example during heat losses, reac-tor startup, and load changes causing a pressure drop, theelectric heaters heat the water within the pressurizer, thereby creating more steam and displacing water to a surge line connected to the primary coolant system.

The electric heaters used to increase steam pressure are typically found within the lower section of the pressurizer.
These heaters are o~ the direct-immersion type, sheathed in stainless steel or Inconel (trade mark) alloy, and shop assembled in bundles. Each of the two or three bundles is field installed through penetrations in the vessel wall, 2S and sealed by means of a gasketed closure. ~n ele¢trical connection is then made to the end of each heater using a special fitting which provides insulation from the steam and water.

The use of special connectors or cable assemblies to provide electrical power to ~le pressurizer heaters in a nuclear steam yenerating electricl supply system is well known i~
the art. However, in the past, these connectors with - ~LZZ~574 attached power supply cabling have not been designed as an integral unit capable of opera-ting during and after a severe environmental transient, for example a loss-of coolant acci-dent (~OCA) or a main steam-line break (MSLB).

Instead, these connectors have commonly been comprised of simply a standard, pin-socket type connector tied to a braided cable. As a result, there have been several inci-dents where pressurizer heaters were rendered temporarily inoperative due to severe adverse environmental effects.
These unanticipated periods of inoperability are extremely undesirable as they may hamper control and operation of the pressurizer, and thereby the primary coolant system.

It is therefore desirable, as a solution to this recurrent problem, to design an integrated pressurizer heater power supply connector which would have the ability to resist ex-treme environmental conditions.

According to the invention, there is provided a pin-socket type connector assembly attached to a power cable used to supply electrical power to an electric heater within a pressurizer of a pressurized water nuclear reactor compris-ing a flexible sealed conduit, an internal braided cable, the flexible sealed conduit surrounding a central portion o~ the internal braided cable, and means for attachiny the conneckor assembly to the power cable in an area where adverse environmental conditions are substantially moderated.

The problems associated with the prior art are solved to a substantial extent through the prac-tice of this invention, since pressurizer heater power supply connector assembly can comprise a pin-socket type connector, flexible sealed conduit, internal high temperature cable, and a shop splice assembly which attaches the connector assembly to power cabling in an area where the adverse environmental conditions have ,,0 .. . -.
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been substantially moderated. Thus, a power supply connec-tor assembly according to the present invention is able to withstand extreme environmental conditions.

Further features of the invention will be apparent from the following description with reference to the accompanying drawings, in which reference numerals shown in the drawings designate like or corresponding parts throughout the same.

In the drawings:

~Z;~0574 Fig. 1 is a side view, partially schematic and partially in perspective, of a pressurized water reactor pressurizer with electric heater bundles in the --lower section thereof; ::

Fig. 2 is a cross-sectional view of an electric heater bundle located within the pressurizer, with integral heater receptacles located outside the wall -of the pressurizer;

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Fig. 3 is a side view of a heater bundle viewed from outside the pressurizer;
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Fig. 4 is a detailed side view, partly in section, of an integral heater receptacle;

Fig. 5 is a safety grade pressurizer heater power supply connector assembly in accordance with the present invention;

Fig. 6 is a detailed sectional view, longitudinally, of a shop splice assembly in accordance with the present invention.

DETAI~ED DESCRIPI~ON OF THE ~?REFERRED EMBt)D~MENT
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Referring to Fig. 1, a pressurized water reactor pressurizer 10 has an electric heater bundle 12 located in the lower section thereof. Typically two or three such electric heater bundles 12 will be present. E~ach electric heater bundle 12includes a group of electric heater elements 14..

Each electric heater bundle 12 is oriented in a horizontal plane within the lower portion of the pressurizer 10. The extremities of each electric heater element 14 of an electric heater bundle 12 project through a cover plate 18. Studs 20 hold the cover plate 18 to the wall 16 of the pressurizer. These features are best seen in Fig. 2. The portion of each electric heater element 14 projecting beyond, i.e., outside the cover plate 18, ends in an integral heater receptacle 22. Fig. 3 shows an end view of an electric heater bundle 12 3 :

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including the cover plate 18, lifting lugs 24, a plurality of studs 20 arranged along the circumference of cover plate 18, and a plurality of integral heater receptacles 22 arranged within the central portion of cover plate 18.

Fig. 4 shows an integral heater receptacle 22. A pair of pins 26 interconnects with corresponding contact sockets 44 (see Fig. 5) of the safety grade pressurizer heater power supply connector assembly. Threaded element 28 interconnects with couplin~ nut 36 (see Fig. 5) of the safety grade pressurizer heater power supply connector assembly.

The pressurizer heater, electric heater bundles with electric heater elements 14, cover plate 18 and related hardware, and integral heater receptacle 22 are essentially standardized parts with minor modifications.
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Fig. 5 shows a safety grade pressurizer heater power supply connector assembly in accordance with the present invention. A pin-socket type connector 30, as indicated above, connects to a pair of pins 26 of integral heater receptacle 22 best shown in Fig. 4. A connector assembly also includes a shell 32 surrounding an insert 34. This insert is preferably made of a ceramic material. As also indicated above, coupling nut 36 connects to ~hreaded element 28 of ~he integral heater receptable 22. The connector assembly also includes a rear insert 3g and a back shell 40 encompassing an internal braided cable 4~. This internal cable is typically a high temperature glass braid cable, and a potting compound 46 fills the interstices between the cable 48 and the back shell 40. A
hose adapter 49 circumf eren~ially surrounds the internal braided cable 48, potting compound 46, back shell 40, and rear insert 38. The end of the connector assembly closest to the pressurizer wall, as just described~ is also with sorne modifications a standard part well known in the art.

A flexible corrugated hose 42 surrounds the central portion of internal braided cable 48, typically for a distance of about 9 feet although greater or lesser lengths of cable 48 and corresponding lengths of flexible corrugated hose 42 may be employed.

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A gasket 50 is typically used to ensure a sealing relationship between the pin-socket type connector 30 of the safety grade pressurizer heater power supply connec~or assembly and each integral heater receptacle 22 of electric heater element 14 of electric heater bundle 12.

A shop splice assembly 52 ties the internal braided cable, already described, toan external power source. Fig. 6 shows details of the shop splice assembly 52 including a cable clamp 54, header adapter 56, transition sleeve S8, and pottingboot 62. Cable clamp 54 is welded to header adapter 56, which is in turn welded ~o transition sleeve 58. Cable clamp 54 acts as a pressure seal.
Transition sleeve 5~ in turn overlaps and is welded to potting boot 62. A plate 60 is welded to and bounded by a radially interior edge of transition sleeve 5~ as well as one end of potting boot 62. A standard penetration device 64 is housed within potting boot 62. Butt splices 68 connect internal braided cable 48 on oneside of a standard header assembly 70. A power cable 72 leading to a power source extends from butt splice 68 on the opposite side of standard header assembly 70 through the standard penetration device 64 within a flexible sleeve 7~. The volumetric space between butt splices 68 and ca~le clamp 54 and transition sleeve 58 respectively are filled with potting 66 to ensure resistance to shock and vibration, and to provide additional dialectric material. Potting ~6 is also present in the space between standard penetration device 64 and potting boot 62.

Practice of this invention provides extremely good resistance to mechanical damage to what would otherwise be fully exposed electrical power cable.

This apparatus also provldes resistance to the detrimental effects of fire sinceall materials used are non-combustible and maintain structural integrity at hightemperatures. During accident simulations, full size units withstood a temperature range of about 40 to about 500F., and a temperature increase of about 380F. (from a starting temperature of 120F. to a final temperature of 500F.) in less than 10 seconds coincident with pressures of up to 80 psig.

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The electrical components are mechanically separated by a non-conductive mechanical protective boundary fro~n other non-protected electrical components. Ampacity is rated~)52.6 amps at rated 460 VAC, 60 Hz, single phase.

~his apparatus has shown resistance to a chemical spray of Hydrazine (N2H4) and boric acid with a spray rate of 0.25 ~allons per minute per square foot. It is also resistant to seismic forces of up to six g's horizontal, two ~'s vertical (simultaneously applied); and to water, steam, and substantial doses of both 8amma and beta radiation.

Thus, this connector assembly provides an improved method of supplying uninterrupted electrical power for the operation of pressurizer heaters in a pressurized water reactor system during and after the occurrence of an event which produces an extreme environment in the connector area.

- While in accordance with the provisions of the statutes, there is illustrated and described herein a specific embodirnent of the invention, those skilled in the art will understand that chan~es may be made in the form of the invention covered by the claims and that certain features of the invention may be used to advantage wlthout the corresponding use of the other features.
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Claims (2)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A pin-socket type connector assembly attached to a power cable used to supply electrical power to an electric heater within a pressurizer of a pressurized water nuclear reactor comprising a flexible sealed conduit, an internal braided cable, the flexible sealed conduit surrounding a central portion of the internal braided cable, and means for attaching the connector assembly to the power cable in an area where adverse environmental conditions are substantially moderated.

2. The combination according to Claim 1 wherein the means for attaching the connector assembly to the power cable comprises a cable clamp, a header adapter overlapping and connected to the cable clamp, a transition sleeve overlapping and connected to the header adapter, a potting boot overlapped by and connected to the transition sleeve, a braid bounded by the transition sleeve and the potting boot, a penetration device housed within the potting boot, a pair of butt splices, a standard header assembly, the butt splices connecting the internal braided cable to the standard header assembly, the butt splices being spaced from the cable clamp and the transition sleeve, and potting disposed within the space between the butt splices, the cable clamp, and said transition sleeve.