ML20084B275
| ML20084B275 | |
| Person / Time | |
|---|---|
| Site: | Indian Point  |
| Issue date: | 10/11/1972 |
| From: | CONSOLIDATED EDISON CO. OF NEW YORK, INC. |
| To: | |
| Shared Package | |
| ML20084B260 | List: |
| References | |
| NUDOCS 8304060235 | |
| Download: ML20084B275 (4) | |
Text
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Oo o 1 i CONSOLIDATED EDISON COMPANY OF NEW YORK, INC.
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l Indian Point Unit No. 2 f AEC Docket No. 50-247 1
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] Investigation and Consequences of a i
i Steam Generator Nozzle Debris Plug Assembly 1
4 j Being Inadvertently Left In-Place During Operation l . !
j of the Reactor Coolant System ,
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- October 11, 1972 i
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! 8304060235 721110 i PDR ADOCK 05000247 S PDR i
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Introduction .
j Upon removal of the upper internals package, on the evening of Monday, j September 11, 1972, paparatory to defueling the Uhit No. 2 reactor, a
! crtanpled piece of stainless steel was found in the lower flange plate
! of the upper internals package in front of the reactor outlet nozzle
} to No. 22 steam generator. The crumpled piece of stainless steel was i the center piece of a three-piece assembly that had been used to cover l the reactor coolant piping nozzles in the steam Senerators. These as-l semblies had been placed in_the piping nozzles on all four steam ,
j generators of Unit No. 2 during inspections made May through July,1972.
Following the inspections, the Reactor ' Cooling System war closed with j this one plug assembly in the hot leg of Ioop 22. Subsequently, a hydro- ;
j static test of the Reactor Coolant System was perfomed. This test i i required operation of reactor coolant pumps and the resultant flow in l the Reactor Coolant System apparently dislodged the plug. r
- l i Description of Events i
j The three-piece plate assembly was one of four similar assemblies, one j for each of the four steam generators. The plate assembly is made in
! thne sections in order to allow it to be passed into the steam generator j via the small manway. It is assembled in place and put over the n actor -
j coolant piping nozzle, after which it,is taped down to the interior of j the waterbox of the steam generator. The purpose of this plate is to
- prevent foreign objects from falling into the mactor coolant piping
] while work is going on in that waterbox.
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fi NThis plate assembly consists of a quasi-rectangular 16-gauge stainless steel plate, fourteen by thirty-eight inches, and two half moon sections j of 16 gauge stainless steel plate. The three pieces are bolted together j with eight welded cap screws (attached to the half moon sections) and eight wing nuts to fom a circular plate assembly thirty-six inches in diameter. The quasi-rectangular piece was the one found in the upper internals package.
1 j On September 14, 1972 the manway cover of the No. 22 steam generator
! inlet waterbox was removed. An inspection inside the waterbox revealed 1 the other two sections (i.e., the two half moon sections) of the assembly.
i All eight of the welded cap screws had been sheared off. The heads and a
{ part of the cap screws were still welded to the half moon sections.
l During this and subsequent inspections, all but one wing nut and one cap j screw piece (approximately 1/4 inch x 3/4 inch) were found and removed.
Further inspections tre being undertaken to locate these two pieces. The j yellow tape used to tape the three-piece assembly to the reactor outlet i nozzle in the waterbox of the steam generator, has been found in various
! parts of the Reactor Coolant System.
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) The steam generator inlet waterbox tube sheet and tube ends were prelimi-
{ narily inspected and minor scoring of some tube ends was noted. No damage j was found on the tube sheet.
k An inspection of the upper core package revealed no damage.
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An inspection of the primary coolant pipe from the reactor vessel to the waterbox of No. 22 steam generator was conducted by the Operations Engineer for Unit No. 2 on June DO,1972. During that inspection, the plate covering the steam generator inlet nozzle was in place and the ,
Operations Engineer was therefore unable to enter the steam generator.
Two Quality Control Inspectors on July 5, 1972 using a rope ladder ;
attached to a support frame outside the manway entry into the inlet and the outlet waterboxes of No. 22 steam generator, entered the steam generator. They inspected and cleaned the lines and the waterbox up ;
to the reactor vessel from the reactor side of the steam generator, and to the primary coolant pump fmm the steam generator outlet side of the .
I steam generator. Upon ccanpletion of this inspection, a fifty-three pound stainless steel gasket insert plate was installed in the manway opening to the steam generator inlet and outlet boxes and each was held in place with three machine scirews. On July 6, 1972, the Quality Assurance Engineer '
and a Unit No. 2 Watch Foreman performed the final close-out inspection .
on both waterboxes of No. 22 steam generator. Neither man completely l entered either of the waterboxes, but each of them individually put their :
head and shoulders inside the waterbox and made an inspection with the l aid of a light. They reported each waterbox to be clean and completely t clear of all foreign material and authorized re-installation of the manway cover. Prior to re-installing the manway cover, a new flexatallic gasket and the stainless steel insert plate was attached to each manway opening ,
with three machine screws. The insert. plates and new gaskets were ;
personally installed by the Watch Foreman in the presence of the Quality Assurance Engineer immediately following their inspection. The manway covers were installed on No. 22 steam generator on July 6 and 7, 1972. -
N Based upon the above, the most probable cause of leaving the plate '
assembly in the Reactor Coclant System during the hydrostatic. test is as follows:
The inspection of the interior of the steam generator water-boxes and lines using the rope ladder on July 5 and the close- '
out inspection by the Quality Assurance Engineer and Watch l Foreman on July 6 was not actually made on the boiler inlet. '
side of No. 22 steam generator. It is concluded that they inspected the same steam generator and/or waterbox twice.
- Since Nos. 23 and 24 steam generator waterboxes were still open, that is to say, the manway covers were not yet installed on July 5 and 6, it is possible that Nos. 23 or 24 was actuany i the steam generator inspected by one team in one case on July 5, and by the other team in the other case on July 6.
Corrective Action .
In order to assure that a similar occurrence is precluded in the future, .
the following changes were immediate1 r implemented. Each 0,uality Control !
Inspector is now required to keep on als person, while employed as an [
l inspector, a diary in which he will re ard as the inspection process pro- [
l ceeds, details of his observations. Later consolidation of these details i i
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are recorded in the Quality Assurance Engineer's log at the end of his !
2 watch. In addition to existing inventory procedures, each steam generator j waterbox manway access is to be labeled and color coded as to which steam 1
generator, and which waterbox, whether inlet or outlet, it provides access I
to. New and separate entry pemits for each opening and closure into any component are now required. For example, if work inside a component is
) intemittent and the component is temporarily closed, that pemit must be l closed out at that time and a new pemit issued to re-open it to complete the work. Sufficient Quality Assurance manning will be provided to insure i
1 total covera 6e during the time that the component is open. If a Quality Control Inspector is not available at any time, then access to that com-j ponent will be denied. Lock vire and a lead seal shall be used on a i temporary closure at the end of each shift or whenever work is interrupted l'
and/or a Quality Control Inspector is not available at the job site. A mandatory final review of all opening pemits, closing pemits and in-j ventory sheets will be made prior to final closure. Defects in that re-
). view will be noted, and a search made to correct such defects before final closure is authorized. Quality Control in Nuclear Power Generation will
]; establish a Pipe Plug Log for all temporary pipe plugs where the interior of a component has a pipe plug instaned. A tag clearly indicating this j
fact will be attached to the external portion of that component. The Pipe Plug Log will be one of the documents reviewed and satisfied prior to j final closure of the component. The Watch Foreman will make a final j inspection with a Quality Control Inspector as the final closeout in-j spection, as part of the work permit completion.
Safety Implications I
'Had this condition remained undetected prior to operation, it would not j have adversely affected the safety of the plant. Continued Reactor j
Coolant System operation with the plate present in a hot leg of the system j
could eventually have resulted in steam generator leakage. Such leakage would have immediately been detected, and the plant would have been shut down and the condition corrected. The reactor and reactor coolant system
} geometry is such that the plate left in the hot leg could not have caused 1
any core flow blockage. While it is conceivable that a wing nut or cap l
screw piece or a corner of a plate could have caused control rod sticking, this is considered unlikely due to the geometry of the upper internals.
i The plant, however, is designed and operated such that it is capable of being shut down at any time with the most reactive rod stuck fully out.
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Hence, it is concluded that had the assembly been inadvertently left in j
the Reactor Coolant System, and had the reactor been operated, there would not have been a significant safety problem. Nonetheless, the pre-vously described corrective actions are being taken to preclude such an incident occurring again. In addition, it should be noted that Con Edison is engaged, with Westinghouse, in a development program for a loose parts monitoring system. Prior to the discovery of the plate, plans had already i
j been made to take measurements with the developmental system prior to j
initial criticality. Data obtained to date from the developmental system indicate that this system would have detected the presence of the plate.
l It is Con Edison's intent to proceed with the developnent work on a loose i parts detection system. The development work will include in-plant measure-
) ments during plant startup.
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