ML19330A516

Forwards Ga Co 800620 Memo Re Inside/Out Oxidation of Graphite in Relation to Reactor.Phenomenon Will Not Occur at Facility.Oxidation Was Not Observed in Profiles Generated in Lab Under Representative Reactor Conditions

ML19330A516
Person / Time
Site:	Fort Saint Vrain
Issue date:	07/18/1980
From:	Swart F PUBLIC SERVICE CO. OF COLORADO
To:	Kuzmycz G Office of Nuclear Reactor Regulation
References
P-80223, NUDOCS 8007280493
Download: ML19330A516 (3)

Text

a public service company ce Odonde 12015 East 46th Avenue, Suite 440; Denver, CO 80239 July 18, 1980 Fort St. Vrain Unit No. 1 P-80223 Mr. George Kuzmycz, Project Manager U.S. Nuclear Regulatory Commission Standardization and Special Projects Branch Mail Station 228 Washington, DC 20555 Docket No. 50-267

Subject:

Inside/0ut 0xidation of Graphite

Dear George:

Enclosed, for your information, is a memorandum written by R.D. Burnette of General Atomic Company. The meme addresses the topic of inside/out oxidation of graphite in relation ' a the Fort St. Vrain reactor.

Mr. Burnette reports that, the test conditions that produced this phenomenon in experiments conducted at Battelle Pacific Northwest Laboratories and Oak Ridge National Laboratory were not the same as FSV reactor conditions.

Mr. Burnette concludes that this phenomenon will not occur in the FSV reacter and it has not been observed in oxidation profiles generated in the laboratory under conditions representative of FSV reactor conditions.

If you have any questions concerning this matter, please contact me.

Very truly yours,

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F. E. Swe.rt declueJ Project Manager  :

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R; D. Burnette IN REPLY FRCM REFER TO CCB:480:RDB:25'+

TO S. Brown /T. Gulden /W. Graul DATE 6-20-80 SUBJECT Insidt/Out Oxidation SLM!ARY

, Inside/ou'.: oxidation of graphite has been observed by G. Tingey at BE1 and by Eacherly and Wichner at ORNL. The explanation for inside/out o:<idation is enhanced cetalysis on the inside of large sa=ples due' to a decreased oxygen potential as the oxidants (CO 2 r H2O) diffuse into the sample resulting in chemical reduction of cartain impurity catalysts. Impurities such as iron are highly catalytic in the reduced state but relatively non catalytic in the oxidized state. This could result in chemical reactivity 10 or more times higher on the inside as compared to the cutside.

At FSV the coolant gas is almost always reducing to the catalysts of interest.

Therefore this phenomenon will not occur in the reactor.

DETAILS Scientists at GA, ORNL and 3%1 agree that the most likely techanism for inside/out oxidation is an increase in catalysis inside solid graphite samples. Catalysis would increase on "ha inside if the oxygen potential was lower on the inside as compared to the %cside. This could occur if the oxidants Co., or H,,0 reacted as they diffused in the sample forming the products CO and/or H . ~ ~

3

'.n the experiments at 3E1 the concentrations of CO and CO., were 20 and 80% respectively.

The sample temperature was 825 C. The CO/CO,, ratio was 0.25 on the outside but could easily have been >10 on the inside due to conversion of C07 to CO. Furthermore, the charmodynamic equilibrium for the ratios CO/CO ver Fe/Fe0'is about 2 at the temperature of the BE1 ex,cri=ent. 2 Therefore, the iron i= purities would have been in the oxide form, (Fe0), which is known to be relatively non catalytic, on the outside of the sample and in the reduced , form (Fe), on the inside. Reduced iron, Fe, is known to be highly catalytic in the steam graphite reaction.

In the ORNL experiments the oxidant was water vapor. In their loop system the pro-ducts H,,, CO, and CO were allowed to build up. At least during a part of their test 2

tha catside of the sacoles were exposed to ratios of H,,/H70 << 2 in which case the iron catalysts would be oxidized. (The thermodynamic'ecuilibrium H.,/H,30 ratio for

• tha syste= Fe/Fe0 is also about 2 at the temperature of the ORNL tests ~ 900# C.)

On the inside of the samples the H,,/H,,0' '

could be >> 2 causing a greatly accelerated cataly::ed reaction.

Of V, Ca.

course, catalysts other than iron are prevalent in graphite, including Ni, Ti, These species may occur in clusters and/or in association with anion i=puri-tisc such as oxides, carbides, sulfides, silicates, silicides. Therefore the true thsr=odynamic equilibria are complex and variable depending on the graphite samples and the specific i= purity mix present.

All tests at GA use impurity ratios simulating these in the reactor, i.e., high ratios of H,/H,0 and C0/CO2 - In particular in our o::idation experiments we always work with H3 /H' 0~> 10 which simulates the reactor conditions and and which ensures that all tee tron catalysts are in the reduced state. Over the last 3 or 4 years, ue have determined a number of oxidation profiles on ATJ, SC2020, HLM, PGX, H-451 and ASR-lRG graphite using H 2/H2O > 10. All of the profiles show nor=al behavior, that is. higher oxidation on the outside. In no case was inside/out oxidation observed. Further= ore, ths profiles generated in the laboratory match quite closely with rheoretical profiles calculated using our Standard GOP or OXIDE-3 formulae.

- Our work on oxidation profile is continuing in our High Pressure Test Loop, HPTL.

With this experiment wk will determine rates of oxidation and oxidation profiles under tha influence of real reactor pressure, 750 psia, and turbulent flow conditions. The loop is operating, presently, with annular shaped saeples of PGX graphite (3 cm CD, 1 cm 1D) similar to the surveillance samples in FSV. With some minor modifications larger solid samples up to approx. 6 cm could be used, but I don't see the need for it as long as we use high ratios of H /H 0.

2 2 Tha staff at ORNL will document the conditions and results of their tests where they a found inside/ cut oxidation in some samples. They believe they have enough data to dsteribe an " envelope of conditions" which lead.' to this phenomenon. Their experi--

mtntally deter =ined envelope of conditions will be compared to the theoretical ther=o-dynamic equilibria for several of the important catalysts present.

cc: Jess Lopez G. Engle R. Vollman A. Barsell Bob Wichner - ORNL Carth Tingey - BNWL f i l

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