ML20086E646

Final Deficiency Rept Re Corrosion Problems W/Control & Orificing Assemblies.Initially Reported on 720811.All 37 Control & Orificing Assemblies Refurbished & Retested

ML20086E646
Person / Time
Site:	Fort Saint Vrain
Issue date:	01/18/1973
From:	Walker R PUBLIC SERVICE CO. OF COLORADO
To:	Kruesi F US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20086E612	List: ML20086E615 ML20086E646
References
10CFR-050.55E, 10CFR-50.55E, NUDOCS 8312070466
Download: ML20086E646 (12)

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' January 18, 1973 Mr. F.E. Kruesi Directorate of Regulatory Operations United States Atomic Energy Commission Washington D.C.

20545

Subject:

Fort St. Vrain Unit No. 1 Deficiency Report 10 CFR 50 Part 50 55 Control and Orificing Assemblies Docket No. 50-267; CDR-31 Ref. :

Interim Report Filed August 11, 1972-

Dear Mr. Kruesi:

Pursuant to the reporting requirements of 10 CFR 50 ve are submitting herewith twenty (20) copies of our final report involving the control and orificing assemblies. Thi.s report is filed to finalize the interim report referenced above, and to report additional findings which were uncovered by-follow-up action initiated by the original deficiency.

All of the 37 control and orificing assemblies necessary for_ normal operation of the reactor have been refurbished and retested per the' attached report, and are presently installed in the reactor vessel. 'Of the seven (7) control and orificing assemblies to be used as spares six (6) are still at'-

Gulf General Atomic 's shop in San Diego for final' rework. It is-felt that the fixes made, to include the procedural changes, are more than adequate to-.

prevent reoccurrence. We vill,'however, check the effectiveness of-the fixes by inspecting one or more of the control and orificing assemblies upon com-pletion.of the' hot flow test and prior to fuel loading. Further' testing vill also be done as-a part of the start-up test program.

If any further problems develop, we vill keep the local Directorate informed. We trust the attached' report vill provide you with sufficient information to evaluate the. deficiency reported, ' and will fulfill:the -

reporting requirements of 10 CFR 50.

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Very truly yours, 9

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.R. F. Walker 8312070466 730228

.Vice President -

PDR-ADOCK 05000267 Engineering and Planning..

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DEFICIEUCY REPORT

-10 CFR 50 PART 50 55 FACILITY: Fort St. Vrain Nuclear Generating Station -

SUBJECT:

Control-Rod Drive and Orificing Assemblies -

REIORT DATE: December 27, 1972-

REFERENCE:

Interim Report, above subject, filed August 11, 1972.

1.

Scope This report -is issued to finalize the interim report referenced above',

and to supplement the above report with additional infomation resulting '

from follow-up action. As a result of the corrosion problems experienced with the seven (7) spare control and orificing assemblies ' additional-.

inspections were performed on the remaining 37 control'andLorificing assemblies that were installed in:the vesse1~ during the hot flow test.

The results of this inspection reycaled'that all=37,of the. control and'~

orificing assemblies had experienced.some type of corrosion in varying degrees. Although the corrosion in general was not great' in ' quantity, corzusion of the shim motor laminations was of concern because. of..the.very :

small clearances between the. rotor and the stator.

All of the control' and orificing (C & 0).. assemblies. have Lbeen sub-sequently reworked. This report.is to serve'as.a final; report concerning the status of all the. C &O assemblies.

2.'

General Description 4

Pursuant to the -corrosion problems of: the :seven' (7) ~ spare lcontroll rod" drive mechanisms reported byl the above treferenced report,(dec'isions were madej iasLa part of.the follow-up' action of the ' original:investigstionL'oiinspecti t

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General Description - (Continued) the 37 control and orificing assemblies. These latter assemblies had been partially checked out and inspected and were installed in their resIective penetrations prior to the hot flow test. The control and orificing assembly checkout and installatiun in the vessel in an air atmosphere began in mid November, 1971. Various checkout tests and preliminary operating tests were conducted on the-assemblies from the time of-initial installation until the PCRV was filled with helium. The last of'the control and orific-ing assemblies was installed in the vessel in February,1972. The PCRV was.

4 evacuated and backfilled with helium in early March,197'2. To the best of our knowledge, all the assemblies were operable at this time.

The hot flow test began June 28,1972, - and continued until August -13, 1972..The PCRV was depressurized and backfilled with air on August 21,'1972.

3 Operating Conditions Prior to the hotflow test the vessel. cavity.therefore, the control--

and orificing assembles were in an. air-atmosphere. The PCRV liner cooling:

system including the refueling penetration cooling system was_ in' operation at approximately 105* F.

Temperature and humidity: in the vessel-cavity <were monitored to insure dev point conditions were ~not experienced.

During the hot flow test the vesse1 was' filled with helium and' operated under the following conditions:

Helium Temperature-J100* - 452' F.-

Helium Pressure

'350 to 450-PSIA-

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Moisture ~

5000 PPMV Maximum Oxygen' (10 PPM The: moisture content given above'was'the result of moisture.b'eing.

driven out of the thermal barrier and-the ~ installed ~ core graphite during the?;,

hot flow test.

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3. -operating Conditions - (Continued): -

' After the hot flow. test vas. terminated,. the helium temperature decayed :

to about 100* F. vith time. The helium was vented and the vessel was-backfilled with air.

4.

Discussions Some two weeks following the termination of the hot flow test,'eight.

(8) of the control and orificing assemblies were randomly selected forTan -

inspection to verify if any corrosion problems existed. Prior-to removal from the PCRV refueling penetrations, attempts were made _to operate all of the eight C & O ascemblies in the shim mode. Three of them failed to_ operate,at'~

normal applied voltage, but did function after manual rotation with the rewind tool. No attempt was made to scram the_ drives so that no conclusive-proof exists as to whether or not the scram function may have been impaired ~

by the corrosion. The eight (8) assemblies were. removed, and the motors -

were disassembled. Rust was observed on each of the rotors and stators of-all eight motors. In addition to 'the rust on the motors and-the' mechanism-housings, there vas a white deposit on the mechanism housings, and in some cases this white : deposit was also found-between the rotor and the Estator.

of the motors.

-0 The remaining 29 C & O assemblies were removed and' disassembled...Allc exhibited some-degree of corrosion as well as the white material deposit'sL All of the'29,C& O assemblies were operated in the shim mode. prior _-to re-moval from the PCRV.. Further. investigation revealed thetithe corzusion ~was.

limited to, or at' letist prevalent on, the; control rod drive; motor assembly.

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The orifice' valves and guide: tubes were virtually; rust free.-.s'"he orifice i

. drive. unit of an assembly, was l disassembled and:showed no! sign of corrosion; i

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Discussions - (Continued)

It was later confizred by certification from the manufacturer that all l

the orifice drive motor assemblies were -treated with a corrosion protective coating. Rust and material deposits were also found on--the refueling penetrations sidevalls and on that portion of the C& O' assembly housin6 within the refueling penetrations.

The corrosion found on the 37 C & O assemblies in the reactor was not E

near as extensive as that found on the seven (7) spare assemblies as reported earlier, 5

Evaluation of Causes Corrosion of the seven (7) spare assemblies is attributed to poor handling and storage conditions as reported earlier. (See incident report filed August 11,1972.)

The formation of corrosion products.on'the 37 C & O assemblies must have occurred as a result of a high moisture and. oxygen atmosphere. The

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helium in the vessel during the hot flov. test contained as much as.5000 4

ppmv vater.. At 400 paia the dev point for helium is 126" F.

With'the penetration cooling tubes:in service the control rod drive mechanisms vere at a temperature somewhere between 105* to 120* F. ' The C& O assemblies and the-refueling penetrations were in'effect a condensing surface forj _.

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i moisture during most of the hot flow test. It is felt that most, if not'-

all of the zust, was. formed when the hot. flow test was terminated.~ iMoist'ure had condensed in the penetrations and on the C &O assemblies. ~ Entry of y

oxy 6en when the-vessel was vented and opened caused the' rust.:LIn' addition,-

some oxygen remained in or could have' entered the vessel!after evacuation and prior to or concurrent-with the initial helium fill.

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Evaluation of Causes_ - (Continued)-

The rust found on.the control rod drive =echanism such as pulleys',

housing, etc. was very light, and certainly the quantity of rust deposits found would not have impaired the performance of t'e drive mechanisms.

h Rust on the inside surfaces of the shim motors was more advanced.-'At.the.

time of the inspection, operation of only three=(3) of'the-shim' motors.was.

impaired.

The white material deposito found were analyzed._ The. results of(the analysis indicates-that the white deposits were formed as 'a result of a residue from a black oxide process applied.to the motors and other_ parts of the assembly mechanism.

Samples of the various deposito were taken for analysis. The results of this analysis are shown'in Table l.

Further analysis.-as to.the possible; cource of the materials Lfound is as followsi SODIUM: Sodium was found as a primary constituent in the white powder.

semples. The helium in the. PCRV during heat-up for the[ hot flow (test had'

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approximately 5000 PPMV water. The dew pointiat400 PSIA is-125* F.! and Lthe -

calculated temperature of.the. control rodidrive. mechanisms' wasfcalculated to be between 105* to 120*J F. thus. acting asDa condensing surface. L This~

environmental condition existed for: approximatEly. two weeks 'over viiich<

time it is felt 'the moisture combined with residue salts leftifrom insuf ;

- ficient' elean'ing during the black oxide process k i The: amount!of' residue; t

remaining' on the. black' oxide; surfaces is related to the) care taken during p

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-the rinsing cycle. This was' notfa'.contzulled' process;and could explain-the random characteristics of the white deposits.;

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TABLE I RESULTS OF CIIEMICAL ANALYSIS Samole Descrintion Spectro Chemical Analvsis_~

Wet Chemistry

>10,000 PPM 710,000 PPM 3

White Powder from Motor of Si, Na, A1,B Fe Na -17%

C&O.Assy No. 23

- B ~1% (10,000 ppm)

Seal Ring, C&O Assy No. 28 Mn, Fe, Ca B, Na

._(B.= 10,000 ppm)

W Fe, Mn B,-Na,.Ca B ~1.4%

Penetration R14

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(B-= 6000 ppm):

Penetration R29 Fe

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.(B-= 10,000 ppm) t Penetratlon R30 Fe,;Ca~

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liigh Ternperature Filter Fe, Ni B, Mn,._ Cr, J Ag,-.

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ALUMINUM, SILICON: Both the cable drum and the rod retract housing of the control rud drive mechanism are fabricated from AMS 4217 Aluminum which is an aluminum alloy containing 7% silicon. The aluminum is amphoteric, that is to say its corrosion rate is at a minimum in neutral water but increases as the water Ph increases or decreases. Due to the presence of salts in the moisture which had been leached from the porous black-oxided parts, the water Ph became basic and resulted in corrosive attack of the aluminum castings.

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CALCIUM:

The calcium was identified to be in the form of calcium sulphate (gypsum, plaster of paris) and it is felt this caterial was residual from initial plant construction.

BOION: There are four possible sources of boron, namely:

The control rods, the reserve shutdown material, the shield located just above the reserve shutdown hoppers and the boronated steel rods in the peripheral core shield-in8 Of these the C & O shield originally is known to have contained on the average O."(% by weight of boron in the fom of boric oxide (B 0 ) as well as 23 the principal shielding material, boronated graphite _(boron carbide in a graphite matrix). The reserve shutdown material and the control rods were limited to less tlian 1/2 percent by weight of B 0. The boronated steel 23 rods contain borun in solution and dispersed as extremely fine carbide particles in a' ferrous matrix. Boric oxide in the presence of water vill form boric acid which is volatile.

The exact source of boron has not as yet been established as three of the four components contained B4C which will oxidize to form B 0 -23 Further investigations are underway to further define the source of boron -

and establish the significance of the findings.

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Evaluation of Causes - (Continued)

SILVER: Silver was found only at the high temperature filter absorber penetration A-1.

Helium by-passing is known to have occurred at this loca-~

tion. The source of silver was'apparently from the plating on the filter absorber seal.

ITON, NICKEL, MANGAHESE: These are all base materials and were anticipated to be found in the samples.

Other analysis to include attempts to obtain a correlation of the.

amount of corrosion with respect to penetration position, penetration purge flows, etc. proved to be inconclusive.

Consequence of Corrosion:

The corrosion of seven (7) spare control and orificing assemblies would..

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have impaired operation of the chim motor And in some cases the corrosion -

was extensive enough to impair or prevent the scram function. l (Note that--

these seven (7) C & O assemblies were exposed to high moisture conditions on the refueling floor outside the PCRV, see CDR-31.)

Operation of three-chim motors was impaired. It is conceivable that if-the corrosion were allowed to pro 6ress unchecked,- that ' operation of the con--

trol rod drives would be impaired. If this problem had not been discovered' at this time, however, the depth Of our testing program is such that the.

7 problem would have been discovered during subsequent ' tests which call f$r.

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Various checksiand exercising of the" drive-mechanism prior:to fuel loading-

and during start-up testing.

The corrosive conditions experiences by the C& O/ assemblies during start-p up will not ' occur during normal reactor' operation.. In-. addition lthe rods will' a

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Consequence of Corrosion - (Continued) be manipulated during~ plant operation and vill be partially strcked once each month per Technical Specification requirements. Any decline in oper-ating characteristics would be noted.

While corrosion of the C& O assemblies has serious Jimplications we feel that our procedures and testing program vere adequate to permit. detection of the problem prior to loading fuel with further depth being provided by the plant start-up test procedures.

Corrective Measures:

The following corrective measures have been taken:

1.

All of the C& O acsemblies have been externally inspected to determine the extent of the rusting. Six of the 37 control rod drive motor mechanism subassemblies (less shielding and guide ' tube subassemblies) were returned to San Diego for. ~ disassembly, detail inspection and: cleaning * -

These six assemblies were selected as-representative of the range ~of the-various degrees of corrosion experienced. The corrosion was not considered-detrimental to the drives, therefore, no further -disassembly of. the - remain- -

1 ing -31 assemblies was required. The' remaining 31 mechanisms have beens externally cleaned (solely for-cosmetic purposes).n

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2.

The shim drive motors have been removed from all 14 C 0 assemblies.

and returned to Varo Incorporated (the manufactureI-) for. application _ of-the protective conting. A procedure has been prepared by Varoiand' approved by Gulf General-Atomic for cleaning of the. motors, including multiple cleane ing cycles for removal of. grease. from between motor laminations..Other-L

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5 Evaluation of Causes - (Continued)

Corrective Measures - (Continued) procedures were prepared by Varo and approved by Gulf General Atomic for the application and quality control of a corrosion protection coating consisting basically of Epoxy Polyamide Primer.

The operation was initially performed on one unit to verify the process. A test was per-frumed to ensure the resulting electrical and torqize characteristics were unaffected. Each motor was tested in accordance with the original test procedure.

3 Certification of material properties of the protective coating -

applied to the motors has been obtained. -Tests of the. protective coating at temperatures up.to 400' F. were.perforced resulting-in no adverse effects on the material.

4.

All but'six (6) of the 44. C &O assemblies have been reassembled and 37 have been reinstalled in the PCRV. 'All CEO assemblies were pre-checked prior. to instellation and:all control. rod drive mechanisms and shim motors have been' tested per the requirements of POT 12-01.. The six.(6)' remaining C& O assemblies are still back in Gulf General-Atomic

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shops in San Diego.

5 The procedures forfshippin6 and storin6 were modified to provide for clean, dry, oxygen free atmosphere.

.6.

The' procedure for reactor start-up and operation ~ vill be ' revised

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a to prevent moisture from condensing on the CRD's.by limiting the' allowable-moisture' concentration at' any1 primary coolant pressure.not to exceed satura-

- tion at a minimum penetration line. temperature of loSLF.iand;to maintain' N

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.the limit on 02 content to 10; ppm...

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Evaluation of Causes - (Continued)

Corrective Measures - (Continued) 7 Additional testing of the C & O assemblies will be done in accordance with start-up test A-4 following core loading and prior to the approach to power.

8.

A random sample of C & O assemblies will be inspected after comple-tion of the hot flow test prior to and/or as a part of fuel loading.

9 The Technical Specification, Section SR 51.1, required a scram once a year and partial stroking once a month.

Test experience indicates that any decline in operating characteristics is gradual, and these monthly tests should give ample warning of deterioration.

10.

Manufacturing and Inspection Procedures for any replacement of black oxided parts will be revised to include an inspection step to verify the removal of residual salts.

11.

C & O assemblies are to be stored in the equipment storage wells and in a protective envircnment of helium.

(This is a standard operating procedure for plant operation.)

12.

That for periods of temporary storage dry, sealed, individual containment packages shall be provided to prevent the entry of moisture from outside sources.

13 One of the assemblies was disassembled to check for corrosion of the orifice stepping motor. No corrosion was evident. Certification of the protective coating applied to the orifice stepping motors has been obtained.

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