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Library of Congress Subject Headings January, 1956 English LCSH manuscript 24-bit color: 400 dpi January, 1956 Report on the Inspection of the First Raleigh Research Reactor

REPORT ON THE INSPECTION OF THE FIRST RALEIGH RESEARCH REACTOR General

On January 12, 1956, an opportunity arose at Oak Ridge National Laboratory for a meeting of representatives of several groups to discuss the results of the ORNL inspection of certain dis- mantled reactor components, and in particular to hear information and recommendations concerning steps that might be taken to avoid in the future reactor the various corrosion problems of the first reactor. Any appreciable corrosion presents a severe health and safety problem.

 Personnel Present

A meeting was arranged through Dr. K. Z. Morgan who, un- fortunately, was called away by an emergency just before the meeting started. Those present were as follows:

ORNLAECBABCOCK & WILCOXN. C. STATE Ed BohlmanW. H. BehrmanC. C. CardwellF. P. Pike Arnie Olson(for H. M. Roth)William Foley George E. MooreDurand Unidentified

Inspection Procedure

The core was stuck so tightly that the aluminum jacket had to be cut and torn away. The core was then quartered longitudin- ally in such a way as to do the least possible cutting of the coils inside. Six metal pieces were then cut from strategic areas. From each piece a number of metallurgical samples were taken for careful inspection.

 Major Findings

1. While the core had been tightly stuck inside the aluminum thinble, it appeared that this must have been because of the adhesive effect of encrusted uranium salts. By visual examination of the core when freed there was no evidence of any pressure distortion. The top surface, the weak area in regard to internal pressures, was unbowed. None of the welds appeared cracked or distorted. 2. The core wall (1/16") appeared to be in good condition except for a row of 5 families of pin holes. This row was horizontal and about 2 inches long, situated just above a coloration change that apparently represented the solution level. The level of the solution was somewhat indeterminate. Viewed from the inside and at a distance, there seemed to be 5 single pits. Closer examina- tion revealed many pits in each family. From inside to outside, each of the five groups of pits expanded rapidly to areas of l-3 cm2 (my guess) outside. 3. Metallographic techniques of examination of the wall in the pit regions revealed that the wall was spongy because of many internal passageways. This corrosive effect was severe.

4. Careful examination disclosed no evidence of corrosion on the bottom or around the bottom weld. 5. The sample of a cooling coil bend revealed intergranular and transgranular (stress) corrosion inside the coil (water side). My recollection was that the indicated corrosion of one sample was considered to be severe enough to cause failure within not more than one or two years at the most. At least, one metallurgist advanced this opinion and no one disagreed. 6. Except for a few suspicious crystals, of discredited identification, there was no evidence of carbide precipitation. The metallurgists were agreed on this point. 7. On the outside of the core there was a thin (about 1 mil), adhering scale or film of iron, uranium and chromium oxides. 8. No leak could be demonstrated in the coil sections by air pressure. However one section could not be tested (it was destroyed by examination) and the test procedure on the other sections was rather inadequate. It was tentatively judged that the leaks in the tested sections were at most small leaks. 9. The metallographic inspection to date is reported in ORNL 55- 12-70, by C. E. Moore, classified. There will be a subsequent report. 10. Radiation damage to the metals was not evident nor was it to be expected under our conditions. According to Dr. Secoy, radiation damage begins to show in a reasonable period only if the power level is above about 10 KW per liter of solution fuel.

Diagnosis of Core Failure

It was agreed by all that the corrosion was the consequence of the high chloride content (>200 ppm). Pitting is characteristic of chloride attack on stainless steels under comparable conditions (oxidizing media), as is also the location just above the solution level.

It was not characteristic that the corrosion outside should be so much more extensive than inside, particularly since on the outside the solution contact with aluminum should have given protection. The metallurgists were at a loss for a possible ex- planation of this anomalous behavior.

The localization of all pits within a 2 inch streak was also puzzling. However, while no one could say why this occurred, there was no lack of possible explanations. It could readily have derived from some past incident, such a a linear occlusion before or during rolling. Another suggestion was that the welder could have accidentally struck an arc there.

Diagnosis of the Coil Corrosion

It seemed clear that the coils failed because of the corrosive action of the cooling water, probably through the action of chlorides.

 Corrosion Resistance of Alloys

There was no information on corrosion resistance under exactly our conditions. Most of the available information pertained to uranyl sulfate solutions under more severe conditions of temperature and solution velocity. One conclusion was that the net effect of the simultaneous presence of hydrogen, oxygen, and peroxide was that of an oxidizing solution.

By extrapolation of available (classified) data, these deductions were made:

NickelNo good. IncoloyQuite good at high temperature. NionelNo information, but question the high nickel content. Chlorimet 3Much too high in nickel. Carpenter No. 20Probably O.K. Hastalloy CNot bad, almost as good as 347. Stainless 316Poor. Stainless 347Reasonably good, but not very good. TitaniumGood ZirconiumGood

For sulfuric and other acids on Stainless 347, data are available from unclassified sources. We were referred to C. P. Larrabee as a start.

 Recommendations for the Core

1. If the chloride situation could he controlled, use Stainless 347. 2. If the chloride situation could not be controlled, use titanium. 3. By all means, control the chloride situation. For Stainless 347, the extrapolation of available data indicated (at pH = 2.5 ?) no "appreciable" corrosion at 3.5 ppm chloride, but "appreciable" corrosion at the next higher chloride content tested. A limit of 5.0 ppm, or perhaps 3.0 ppm, was suggested if Stainless 347 was used. 4. If a Stainless Steel is used: I. During fabrication, (a) Have a camera record made of the entire welding operation. (b) Take and store samples of the metal. II. After fabrication, (a) Specify treatment with trisodium phosphate, or other alkaline, solution. III. After assembly (or installation) (a) Flush completely with distilled water until certified free of chloride.

IV. During operation, (a) Analyze initial batch of fuel. (b) Monitor fuel for chloride at regular intervals, say once a month.

It is pertinent that the Babcock and Wilcox metallurgist said that it was their experience that chloride was a severe danger for Stainless Steels, and that there were a small but disturbing number of instances where stainless equipment had become accidentally contaminated with chloride between early fabrication and first use. Usually the cause of the contamination remained unknown. To combat this situation, they have frequently adopted a procedure of flushing with trisodium phosphate before items are permitted to leave the plant. A check by the receiver before the use was considered only common sense. In important cases of interest to them, they would insist upon a camera recording of the welding operations, and on the storage of suitable metal samples.

 Recommendation for the Cooling Coil

In some way the cooling water must be made less corrosive. If the cooling water is used once, then discarded, it must be chemi- cally treated, such as in accordance with the suggestions of our Sanitary Engineers. Alternately the cooling water loop could be isolated by a heat exchange unit, and distilled water used as the media. The closed loop was apparently the preferred alternate of those present.

The decision to adopt a closed-loop of distilled water will not be a simple one. The decomposition of water into hydrogen and oxygen will be a hazard that might be aggravated by the purity. The circulating water should be monitored and maintained at a specified specific resistance, which would be about 1/4 million reciprocal ohms if there are no corrosion inhibitors or agents to reduce the radiation damage to the water.