ML17252A871
| ML17252A871 | |
| Person / Time | |
|---|---|
| Site: | Indian Point  |
| Issue date: | 10/11/1972 |
| From: | Zarakas P Consolidated Edison Co of New York |
| To: | Kreusi F US Atomic Energy Commission (AEC) |
| References | |
| Download: ML17252A871 (5) | |
Text
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William E. Cald..
w~l.I, Jr.
Vice President
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Consolidated Edison Company of New York. Inc.
4 Irving Place. New York. N Y 10003 Telephone (212) 460-5181.
Mr. Frank E. Kreusi, Director Dire*ctorate of *Regtilatory *operations u.s. Atomic Energy Commission Washington, D. C..
20545
- Dear M..r. Kreusi October 11, 1972.
Re Indian Point Unit No. 2 AEC Docket No. 50-247 On September 12, 1972 Consolidated Edison notified the Commission bytelephon1= that a Steam Generator nozzle debris plug assembly had been.inadvertently lef't in place during a hydrostatic test of' the Reactor Coolant Sy-stem.
Enclos~d herewithis a report entitled "Investigation and Con-sequences of a Steam_ Generator Nozzle Debris Plug Assembly Being Inadvertently Left In-Place During Operation of tne Reactor :coolant System" dated October 11, 1972 for the above-referenced.plant.
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cw Very truly yours Copy to James P. 0-, Reilly, Director Regulatory Operations Region 1.
- U. S. Atomic Energy Commission 970 Broad Str!=et.
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CONSOLIDATED EDISON COMPANY OF NEW YORK, INC.
Indian Point Unit No. 2 AEC Docket No. 50-247 Investigation and Consequences.of a Steain Gene~ator Nozzle Debris Plug Assembly Being Inadvertently Le~ In-Place During Operation
- of.the Reactor Coolant System October 11, 1972
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Introduction Upon removal of the upper internals package, on the evening of Monday,.
September ll, 1972, preparatory to defueling the Unit No. 2 reactor, a crumpled 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*
the center piece* of a three-piece assembly that had been used to cover the reactor coolant pipins nozzles in the steam generators.
These as~
semblies had be.en placed in_ the piping nozzles o_n all four steam generators of Unit No *. 2 during inspections made May through July, 1972.
Following the ins:Pections, the Reactor *cooling System was closed with this one plug assembly in the hot leg of Loop 22.
Subsequently., a hydro- *
- static test *of the Reactor Coolant *System was performed.
This test
- required operation of reactor coolant* pumps and the resultant flow in
-the Reactor Coolant System apparently dislodged the plug.
Description of Events The three-piece plate*assembly was one of four similar assemblies, one fo.r each of the. ~our steam* generators.
- The plate assembly is made in three sections.in order to allow it to be passed into.the steam generator via the small manway.
It is assembled* in place and put over the reactor coolant piping nozzle, after which it _is taped down to the interior of the waterbox of the steam generator.
The purpose of this plate is to prevent foreign.objects from falling into the reactor coolarit piping while work is going on in that waterbox~
"~is plate assembly co~sists of a quasi~rectangular.16-gauge stairiless steel plate, fourteen by thirty-eight inches, and two *half moon sec:tions of 16 gauge stainless steel plate.
The three pieces are bolted together.
with eight welded cap screws (attached to the half moon sections) arid eight wing nuts to form a circular plate assembly thirty-six inches in diruneter.
The quasi-rectangular piece was.the one found in the upper..
internals package~-
On September 14, i972 the manway cover of the No. 22 steam generator inlet waterbox was removed.
An inspection inside the waterbox revealed the other two sections (i.e., the two half moon sections) of the ass~mbly.
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.
During this and subsequent inspections, all but one wing nut and one. cap screw piece (approximately 1/4 inch x 3/4 inch) were found and removed.
F\\lrther inspections* are being undertaken to locate these two pieces.
The -
yellow tape used to tape the three':" piece assembly to the** reactor outlet nozzle in the waterbox of the steam generator, has been. found in various. *.
parts of the Reactor Coolant System.
The steam generator inlet waterbox tube sheet and tube ends were prelimi-narily inspected and minor scoring of some. tµbe ends was noted.
No damage
.was found on the tube sheet.
An inspection of the u];>per 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 2o, 1972.
Durine; 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 manwayentry 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 t*o the reac:tor vessel from the reactor side of the steam generator,. and
. to the primary coolant pump from the steam generator outlet side of the steam generator.
Upon completion of this inspection, a fi:f'ty-three pound
. stairiless steel easket 'insert plate was installed in the manway. opening to the steam generato'r inlet and outlet boxes and each was held in place with three machine screws.
On July 6, 1972, the Quality Assurance Engineer*
and a Unit No. 2 Watch Foreman performed the. f'inal close-out inspection on both waterboxes of No. 22 steam generator~ Neither man completeiy entered either of the waterboxes, but each of them individually put their.
head and shoulders inside the waterbox and made an inspection. with the
- a,.id of a light. They reported each waterbox to he clean arid completely clear of all foreign material and authorized re-installation of the manway cover.
Prior to re-installing the manwa..v cover, a new nexatallic gasket and the stainless stee.l 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 Ass~ance.Engineer inn:n.ediately following their inspection~ The manway covers were instaLled on No. 22 steam generator on July 6 and 7, 1972.
-Based upon the above, the most probable cause of leaving the plate
. assembly in the Reactor.Coolant 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 Assi.lrance Engineer and Watch* * *
- Foreman on July 6 was not actually made ori 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 actually.
the steam generator inspected by one team in one case on July 5, and by the other t~aro in the other case on July 6.
I' Corrective.. Action In order.to assure that a similar occurrence is precluded in the future, the following. changes were immediately implemented.
Each Qualit~r Control*
Inspector is now required to keep on his person, while employed as an inspector' a diaI"'J in which he will record as the inspecticm process pro-ce~ds,. details of his observations.
- Later consolidation of these detRils
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. are re~orded in the Quality Assurance Engineer's,loe at the end of his
.* watch.
In addi tioti to existing inventory procedures,* each steam generator.
waterbox manway access is to be _labeled and color coded as to which steam genera.tor, and which waterbox, whether inlet or outlet, it provides access to. New and separate. entry penni ts for each opening and closure into any
- component are now required..For exa.rr.ple, if work inside a component is intermittent and the component is temporarily.closed, that permit must be closed out at that time and a new permit issued to re-open it to complete the work.
Suf'ficient Quality Assurance manning will be provided to insure
- total coverage during the time that the component is.open.
If a Quality Control Inspector is not.available at a,ny time, then access* to that com-.
ponent *will* be denied.
- temporary closure at the end of each shi~ or whenever work is interrupted
- -*a:nd/0-r***a *Quality 'Control Inspe*ctor "i*s.. not a:va:ilable at the job.site. A
- mandatory final review of all opening permits, closing permits and in-ventory *sheets will be made prior to final closure.
Defects in that re-view will be: noted, and.a search inade 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 piug installed.
A tag clearly indicating this
- .. fact will be atta!=!he.d to the. external portion of that component.
- The Pipe Plug Log will be one of the documents reviewed and satisfied prior to final closure of the component~.The Watch Foreman will ma.lee a final inspection with. a Quality Control Ins~ctor as the final closeout in- *
- spection, as part of the work permit completion.
- Safe~ Implications
"---Had this condition remained undetected prior to operation, it would not have adversely affected the safety of the plant.
Continued Reactor
.Coolant System operation with the plate present in a hot leg of' the system.
could eventually have resulted in steam generat:or le~ge. 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 any core flow blockage~ While it is conceivable that a wing nut or cap screw piece or a corner of a plate could have caused control rod sticking, this is considered tmlikely due. t.o the geometry of the upper internals.
The plant, however, i~ designed and operated such. that it :i_s capable of
- being shut down at any time with the most reactive rod stuck fully out.
Hence, it is concluded that had the assembly been inadvertently iert in the Reactor Coolant System, and had the reactor been operated, there would not have been a significant safety problem.
Nonetheless, the pre-vously descr_ibed corrective actions are being taken to preclude such an incident occurring a~ain~ 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 discover;: _of the plate, plans had already
- been made to take measurements with the developmental system prior to initial critic8.lity.
Data obtained to date from the developmental. system indicate that this system would have detected the presence* o.f the plate: _ *
.It is Con Edison's intent to proceed with the development work on a loose
- parts detection system.
The development work will include in-plant measure-*
ments during plant startup.
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