Archive for February, 2010

A Conversation with a Phantom

February 16, 2010

Tales from the Nuclear Age:

 Copyright©2010 by Charles Glassmire

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Feb. 15, 2010

A Conversation with a Phantom

          The fuel irradiation program for the NERVA rocket engine was on hold, to the tune of $120,000. Temperature sensing thermocouples were clad in Tantalum to protect against melting, and no one knew of a Tantalum to Stainless Steel braze which would seal the capsules. They had to be sealed because Oxygen in the capsules at 4500 degrees F (white heat) would immediately destroy the contents. Five irradiation capsules now sat unassembled in the downstairs laboratory. Waiting.

          I never had seen a more downcast lead engineer. Dave had forseen the problem and tested it and the first test braze had worked nicely. I had seen the results myself. The test looked beautiful. Now Dave walked around with his hands in his pockets and shuffled down the halls with his eyes firmly fastened on the floor. No one said anything.

          One day I was passing through the High Bay area of the laboratory. The next test engine in the series was NRX-A5 (NERVA Reactor Experiment number A5). The engine was being loaded into its shipping cask, prior to being shipped to the Nevada Test Site. I stopped for a moment to watch the delicate operation. The engine reactor was only six feet long, but the entire engine was Hugh. It was now hanging in the air suspended via a large crane, and was slowly being moved towards the shipping cask which was sitting on a flat bed railroad car. The reactors were shipped out to Jackass Flats Nevada on a train car, and the car was parked inside the high bay on its own railroad track, waiting for it’s cargo engine. I remember musing to myself that we needed the results of our irradiation studies before this test went off a month away.

          Standing next to me, a nondescript engineer had appeared, seemingly from nowhere. I hadn’t seen him come up to stand silently beside me, almost like some apparition from the ceiling shadows of the High Bay. He was wearing a gray business suit and tie (we all wore ties in those days – I wore a suit coat, white shirt and tie every day to work. I owned a dozen and a half white shirts then – the laundry bill was enormous!).  He was rather innocuous in appearance, black horn rimmed glasses, plastic pen holder in his coat picket to protect it from ink damage, and a sheaf of papers clutched in his hand. I had seen this fellow around the lab, but later I couldn’t quite remember where.

           We watched silently, and I was surprised when he struck up a conversation about the test. We exchanged polite comments and he pointedly asked what department I worked in. I told him I was in Materials. Suddenly out of nowhere he asked “How’s the fuel irradiation program going?”  I was surprised; we didn’t broadcast the problems we were having. But for some strange reason, I began blurting out the sad nuclear tale. When I was finished, he didn’t blink an eye.

          “Let’s see,” he mused, “Tantalum to Stainless Steel… I don’t know anything that will do that. But why don’t you call Handy and Harman in New York? If anybody in the world has a braze for those two metals it would be Handy and Harman. They are the best.” From this I surmised he was a metallurgist, but I was rather skeptical about the advice. By this time we were all convinced the problem was unsolvable. He disappeared as silently as he came. I walked back to my desk and put the conversation out of my mind.

          The next morning, the suggestion kept popping up in my conscious. Finally I decided “why not?” I didn’t know it at the time but Handy and "Founders of Handy and Harman"Harman was an old firm with a stellar reputation. Parker Handy founded the firm in 1867, after a career in banking, to deal in bullion and coinage in Manhattan. Later John Harman joined the firm as a director and the name changed. At the turn of the century the firm expanded into metal fabricators, and later into precious metal refining and industrial applications. In 1905 they began to offer line-brazing alloys and high temperature fluxes for joining rare metals. Today they operate seven metal refineries around the world, offer a product line of 45,000 precious metal products, and are a Fortune 500 company.

          Acting only on a hunch, Manhattan information yielded the number, and with extreme doubt I dialed. Asking for sales, I said I needed a braze for Tantalum to 316 Stainless to operate at 4500 degrees F inside a nuclear reactor! The voice on the other end paused, and in the silence I almost hung up the phone, sensing how ridiculous was my request.

          “Oh yes, he said, “That would be Permabraze 130”.

          “What?” I choked out.

          “Permabraze 130 – it does Tantalum to Stainless nicely. It’s a gold alloy wire braze, good up to 5000 degrees F.

           Fighting hard to not drop the phone, I asked whether it contained traces of Copper. Copper was a hugh neutron absorber and poison, and wasn’t allowed anywhere near the GETR reactor.

          “No, he said, not a bit of copper – we have other customers using it for nuclear applications…”

          Finally I asked the price. It wasn’t cheap, being high gold alloy content, but a quantity of the stuff was nowhere near the value of what was at stake. It was a steal at the price.

          I practically ran over to Dave’s cubicle. Quickly I gushed out the story. He didn’t believe it. It was impossible. He raised one objection after another. For a while I thought the whole thing was scrubbed. Finally he asked about Copper. I said they offered to supply a trace element analysis free of charge. Shaking his head he grudgingly said to go ahead and order a small amount and we would “try” it.

          When the small roll of gold wire arrived, I noticed a smile on Dave’s face for the first time in a long while. He grabbed up the reel like a lost baby and ran downstairs to test the braze in the vacuum furnace. It worked like a charm. Then he made me take a sample to a scientist at Mellon Institute, to do a spectrographic analysis verifying there was no trace of Copper. The guy did the test at no charge as a favor, and the results showed no peaks for Copper. We were home free. Several days later the five capsules were sealed, leak checked, and off to GETR Vallecitos for irradiation testing.

  (to be continued…)

GETR

February 1, 2010

Tales from the Nuclear Age:

 Copyright © 2010 Charles Glassmire

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Jan. 31, 2010

 GETR

           Private and government laboratories are often identified by an acronym composed of first letters of the facility name. Thus, Los Alamos Scientific Laboratory becomes “LASL”, Lawrence Radiation Lab “LRL” etc. In the early sixties, the General Electric Company operated a test reactor in California down the coast near a town called Pleasanton. It was located at Vallecitos, about seven miles from Livermore, in the rolling brown hills so

the Vallecitos Reactor Site

the Vallecitos Reactor Site

familiar to all Californians in winter. It was called the General Electric Test Reactor, hence GETR. On the same site was a General Electric boiling water reactor (GEBWR) which supplied electricity to the area up until the middle 1960’s.   

          The GETR had a rather unique capability then. It ran with highly enriched Uranium fuel, an enrichment much too dangerous for ordinary power reactors. This created a very high thermal neutron flux in the reactor core, higher than most any other research reactor in the US at that time. (Neutron flux is a number counting the number of neutrons crossing through an imaginary square centimeter of space inside the reactor core. It sort of tells you how many neutrons are flying around inside the reactor, how many Uranium 235 atoms are fissioning, and thus how much power the reactor is generating. The more flux, the more power and the higher the core temperature.)  It was an experimental testing reactor; consequently it was often used for high power density experimental irradiations requiring unusually high flux. The associated Radioactive Materials Laboratory provided hot cell capabilities to examine radioactively “hot” materials after irradiation. The staff there was a relatively creative bunch, and open minded enough to accept new devices and ideas for testing. This was long before the days when the nuclear industry became introverted and cautious. It was an exciting time.

          So if you were Westinghouse, and were building, say, a very high flux density Nuclear Rocket Engine Vehicle like NERVA, the GETR provided an excellent place to examine the effects of radiation on the nuclear fuel in the NERVA engine. Even if it was General Electric! The fact that GE and Westinghouse were the two major US competitors in the nuclear power reactor-selling business was irrelevant to us engineers. We were going to Mars.

          So it was that I, a very young engineer, was designated to travel from the Astronuclear Laboratory in Pittsburgh to California, along with the lead engineer ( my friend Dave), to irradiate some NERVA fuel and observe the results. I was really chosen because the married guys in our group didn’t want to spend several weeks away from their families, and since I was the single guy, I got elected. I was secretly happy though, since I had never been there, and California seemed a distant and exciting place to visit.

          Now when you irradiate a Uranium based fuel with lots of neutrons, a lot of fissions occur (the Uranium nucleus breaks into several pieces, liberating lots of energy in the process.)  During this energy release nothing gets burned; there is no Carbon emissions involved, so it’s a completely self contained green process. Use the heat to turn a turbine and voila, you are generating clean electricity! We are utilizing the binding energy of the Uranium nucleus, a very strong force which was created billions of years ago in a supernova sun which threw off the planet Earth, and all the Uranium it contains. So, incidentally, all the Uranium on earth is exactly the same age, and has decayed away at exactly the same rate. But back to my story.

          We were to ship small pieces of nuclear fuel to GETR for the test. But these samples got very hot when they were in a high-flux reactor. In fact, the fuel temperature would reach a white hot condition, about 4,100 degrees Fahrenheit. This was around the temperature the NERVA Engine operated, so we had to hold the fuel at that temperature for about 20 minutes for our test. This was quite a challenge. Most ordinary materials melted and vaporized when they got white hot. So we had to contain the stuff in a special capsule. It was the old conundrum about if you had a perfect acid which would dissolve anything in the world, what would you keep it in? Answer: Stainless Steel.  But this would melt at 4000 F, so we used a can inside a can system with circulating cooling water between the two cans. This removed the heat generated, and prevented melting nicely. Or so we calculated.

          Also, there was another complication. We had to know the temperatures inside the inner can. This meant putting in a device called a Thermocouple. This would measure the temperature and send it by wire out of the experiment. The wires had to pass out through the steel can, and thus had to be sealed water and air tight. But, you are asking, why didn’t the thermocouples melt inside that hot can? I had designed the thermocouples to be clad in an exotic metal called Tantalum. It had an extremely high melting point and 4000 F (in a vacuum) didn’t phase this metal. It was expensive though. They were each hand made and fabricated, so the thermocouples cost several thousand dollars each. AND there were six of them. Gasp. But we had to have the data or the test was useless.

          The question was how to seal the devices air tight when they passed through the steel can? Any oxygen left inside would quickly oxidize all the metals and destroy the capsule. Dave had thought about this and earlier had run a test in a vacuum furnace, using silver braze. It had worked beautifully, and afterward Dave had the test piece on his desk when he showed it to me. Around the tantalum was a lovely perfectly smooth meniscus of braze flowing nicely onto the steel. The seal tested air tight. No problem.

          But during the assembly of the test cans it proved impossible to braze the thermocouples to the stainless steel. The technicians destroyed thermocouples, one after another in a futile effort at assembly. After inquiring around, Dave was horrified when the metallurgists told him it was impossible to braze Tantalum to stainless steel!  He desperately tried his furnace test again, and this time the braze wouldn’t seal. It came out in little raggedy beads with holes in the steel can. We now had one hundred thousand dollars (in 1960’s money) of unassembled capsules sitting in the lab with no way to seal them and one very mortified test engineer…

 (to be continued…)