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Roger Rohrbacher’s Interview

Manhattan Project Locations:

Roger Rohrbacher arrived in Hanford in early 1944, where he worked as an instrument engineer at B Reactor. Rohrbacher was tasked with measuring neutron flow and temperature pressure and radiation monitoring. He gives a detailed account of how the reactor functioned and explains specific safety measures in place to prevent a nuclear meltdown. He also discusses many of the early problems that scientists faced during the early days of B Reactor and explains innovations that workers came up with to solve these problems. Rohrbacher explains the secrecy and security that surrounded the project at Hanford and how it affected his work.

Date of Interview:
September 12, 2022
Location of the Interview:


Tell us your name.

Roger Rohrbacher: I’m Roger Rohrbacher. That’s R-O-H-R-B-A-C-H-E-R.

How did you come to Hanford?

Rohrbacher: In 1942 and ’43, I was working for DuPont in an acid plant in Illinois and my buddies were disappearing. They ended up in Richland, so I got the map out and Richland, Pasco weren’t even recorded on the map. I contacted them and I said, “What are you guys doing?”

They said, “We don’t know.”

Another guy interrupted, having only one phone, he said, “Man, it’s sure desolate out here.”

 A couple weeks later, my boss said, “There’s a guy wants to talk to you about a new job.”

 Now, I was young and single and I said, “I’ll take it,” assuming I would end up here in Richland, wherever that was.

 He says, “Report to Dr. So-and-so at the University of Chicago.” Forty miles away, and here I thought I’d see the Great West!

 This was part of the Manhattan Project. I was assigned to an engineering development group. We were dipping samples of aluminum in water, checking for corrosion and film buildup. It wasn’t until years later I found out that somebody had shipped five thousand gallons of Columbia River water to the University of Chicago, and this was what we were doing. These were the process tubes and the jacket material for the fuel.

 I came out here and ended up in Pasco at four AM, or something like that. My buddy was supposed to meet me. He didn’t show up. It turned out, there’s another fellow from DuPont said, “Well, I’ll give you a ride in.” So he did. Then I made the mental note: this guy better have a good excuse. Well, it turned out he was in the hospital. He had an appendicitis attack and surgery that morning. So we let him go.

 I ended up in the Transient Quarters, which was the Corps of Engineers building for a couple of days, and then moved into a dormitory. I presumed I would be doing some chemical work and so forth, but during the interview this fellow said, “We would like to have you in the instrument department.”

 I almost said, “Hey, I play a trumpet; I’ll fit right in.”

 He says, “What do you know about instruments?”

 I said, “Nothing.”

 He said, “You know what an ammeter is?”

 I said, “Yes.”

 “Okay,” he said, “We’re going to give you class training and we’re going to give you hands-on training and so forth, and in about a year you’ll know everything you’ll need to know.” Well, that’s not quite true.

I had helped mostly in B, D, and F [Reactors]. I came out here in April ’44 and worked on instrumentation, mostly flow and temperature and pressure, and then later on radiation monitoring. Matter of fact, that was one of the clues of what was going on. None of us really knew, except maybe a dozen or so scientists.

 Something came up, oh, maybe eight months after start-up, and they had some problems with the chambers monitoring neutrons. And the foreman said, “Move this neutron chamber, you know, a couple of inches one way.”

I said, “Well, I had a whole year of physics. This ain’t no chemical plant,” because that was the story: big chemical plant. What else did DuPont do?

I was in training for a while, worked out of—mostly in the reactor building, concerned with the equipment to measure the neutrons and the pressure and so forth. Each process tube had a flow monitoring device, and then the exit of each process tube had a thermocouple to measure temperature. This is part of DuPont’s program, I might say, its diversity.

 One of the main concerns in the reactor is that you had good cooling—you had all the time—and by monitoring the flow, that gave you a good clue. If that did not respond properly, you had a temperature measurement on the outside. If it got too hot, you knew you were in trouble. That was one of the problems. Everything was fail-safe, like what they call the panellit gauges to measure the flow. They’re all in series, 2004 in series, something like a Christmas tree string. One bulb goes, they all go, and shut down the reactor.

 They call this a SCRAM. This had to do with Enrico Fermi’s first pile in Chicago. Their safety equipment was a rope on a safety rod leading down to a post. There was a man standing down there with an axe. If any trouble came up, he was supposed to chop the rope with the axe. They call it “Safety control rod axe man.” Whether it was ever used or not, I don’t know. Here that term came to use for any unexpected “scram,” and of course there were a lot of reasons for doing that.

 One of the things that came up was, how do you measure a small amount of current? You use a galvanometer, and it was a mirror suspended on a very fine thread. It had little magnets on the side and little coils and a small electric current from the chambers moved this mirror. We’re talking about small: a millionth of a millionth of an ampere. This equipment was pretty World War II stuff: vacuum tubes, a cubic foot of vacuum tube, and maybe fifteen vacuum tubes inside. That detected the small amount of current.

 Anyway, there were a lot of other features in the reactor tube to monitor for what was going on, and if anything failed, they automatically “scrammed” the reactor. The reactor had nine control rods, which were horizontally controlled, and these were electrically driven, at least initially. Later there was another system that provided hydraulic force, and the operator would slowly pull out these rods to start the reactor and then monitor the rate in which the reactor was increasing in power level. The power level was generally measured in a half-life, or how fast it takes to get from one particular power level to another.

 The operator was careful during startup but during operating, when everything was normal, it was quite simple, relatively speaking. Just like a car in cruise control: if you have no traffic in front of you and you don’t need to stop, you just sit there. The operator sat for two hours at a time in the control room, and there’s generally one other operator reading other gauges and so forth.

There’s also a panel that caused an alarm. A red light flashed and a bell rang if something unusual occurred. Then if minor adjustments had to be made, he would move one control rod maybe a half-inch at a time. Of course, when there was a trouble, the reactor scrammed. These nine horizontal control rods would go in the reactor and twenty-nine vertical safety rods would drop in the reactor, and that was automatic.

Little story on the side about these rods: Enrico Fermi came out here at one time when they were testing these rods. He was concerned that they were testing them so much they’d knock the bottom out of the tube in which they were contained, called thimbles. He said, “You ought to put a spring at the bottom to stop the jolt or somehow reduce it.” That information now has been declassified. His code name at Hanford was Eugene Farmer, and the letter says, “Eugene Farmer came out here in so-and-so, and he was reasonably happy with what was going on, but didn’t like our testing program.” I don’t know, it was kind of interesting.

 One other problem with the early days before computers: the panellit gauge—there were 2004, and all the readings had to be taken once a shift. Then, in a similar matter, all the thermocouples that monitored the temperature had to be recorded twice a shift, so a tremendous amount of work. Some of the instrument people came up with a deal to avoid this called the flexowriter.

 They went to a couple typewriter people, and the typewriter people said, “It’s impossible, what you want to do.”

 They said, “Well, send us a typewriter anyway.” And two typewriters came out and their names were removed, the little name tag. They said they didn’t want to have any part in a failed operation. It turned out it worked! This flexowriter could automatically monitor all the process tubes and record their temperatures on a sheet of paper, and that was a real improvement along the way.

 We had some problems with the reactor along the way. One was graphite expansion. Because of the radiation, the graphite expanded to the point where the fuel elements couldn’t pass through the process tube. It would bow it out, like a hump in the middle. The first solution was to make four inch fuel elements instead of eight inches, so they go through easier. Then they’re looking for a permanent solution. They decided that maybe if they could get the graphite hotter, it would reduce this growth. They call this “annealing.” So they mixed the gas. The original gas in the reactor was helium. It was used just to keep the air on the reactor. They mixed that half and half with carbon dioxide, and that caused the reactor graphite to heat up. That heating apparently stopped the growth and maybe even reduced it a little bit, so that was an interesting facet.

 Another problem was fuel ruptures. If there’s not good bonding between the uranium, metallic uranium, of the fuel element and its jacket, you would get a little water inside. The reaction between the water and the uranium would bolt out the fuel element and it would stick. If it got bad enough, you couldn’t even get it out by pushing on it. Sometimes the whole process tube had to be removed. So that was an interesting experience, but the rest of the operation went pretty well.

 One of the problems and concerns was: do we have a problem that needs to be shut down, or do we not? And generally they tended to wait until they knew they had a problem because of the need for production.

 How many times was it scrammed?

 Rohrbacher: In the early days, sometimes a couple times a week. Matter of fact, it got so bad—in the early days, the reactor scrammed quite often, sometimes a couple times a week. Most of the time, it was due to the panellit gauges would just get a little bit off scale, and when one of those things happened, it would scram the reactor. There even was a feeling that, “We can just do away with these panellit gauges and take them out of circuit.” They tried that for a few months and then they said, “Gee, this is not too bright a thing to do.” So they put it back in, and they got a deal to rearrange the system so that it operated better.

 One of the problems, of course: more water flowed through the center of the reactor than the outside. There’s actually three or four zones, and each panellit gauge in each zone had to be almost individually set. In the early days, all this setting had to be done behind the panel, and after a couple of years they decided to move the adjustment knob to the front. That helped a lot, in that regard.

 What made DuPont a good choice for this project?

 Rohrbacher: Well, DuPont was known for construction of plants and for chemical plants and so forth. They were noted for a couple things: one was their safety aspects, and the other thing they called contingency. I never heard of that term used in a plant ‘til I got in this acid plant in Illinois, and our group wanted a storage tank for what you call a sales asset. If it was below sixty-eight percent, you generally sold it. The designer said, “Well, what size tank do you want?”

I said, “About four thousand gallons ought to do it.”

He said, “What’s your contingency?”

“I don’t have any. That’s all we need.”

He said, “Okay, we’ll put in a 4,500 gallon tank.”

I came out here—and this is a story with General Groves and Crawford Greenewalt. The story was that Enrico Fermi said 1,500 tubes was sufficient for the reactor. Crawford Greenewalt went to General Groves and said, “What’s your contingency?”

He says, “Fermi says 1500; it’ll be 1500.”

Greenewalt said, “You know, if something went wrong with this plant, who do you think would get the blame?”

And you know, the Old General was a pretty sharp guy. He says, “How many more tubes do you want?”

He says, “500.” So they put in 500 tubes, and without that the reactor probably wouldn’t even operate. It was a fantastic thing.

Matter of fact, in the early days, B—well, all the reactors were given only a fifty-sixty percent chance of operating, which brings up another question I’m surprised you didn’t ask: how come there’s no A reactor? In the early days at Chicago, the plan was to build eight gas-cooled reactors, and then they had some concern: how do you contain helium and how do you do this and so forth? They changed their view and said, “Well, we’ll build three water-cooled reactors.” That would be the same process.

This is another little sidelight. This is a story I heard, that Fermi was always considered exacting and knew everything and so forth. If he had any questions, he’d whip out a slide rule and come out with the answer. But they said, “Well, if Fermi can build three, and now they have eight sites lined up, A through H, how far apart should these reactors be for safety?”

He said, “Oh, five to ten miles apart.” They were expecting something to the nearest foot, and ended up with a five-mile variation.

 Could you explain the xenon problem?

 Rohrbacher: You know, because this whole project, Manhattan Project, was going full speed and all of the answers were not known—and when the B Reactor was first started up, things went quite smoothly. They started pulling out the control rods and the power level went up, you know, fifty, one hundred megawatts and so forth.

Not all of a sudden, but over a period of time, as they pulled the rods out, the reactor power level kept going down and down. They had all the rods pulled out and the reactor was still non-functioning, or zero power level. At this time, they were concerned with what’s going on.

I’ll have to tell you a little bit about security. This area here was top secret. Most of us had secret, and the big boys and the superintendents had top secret clearance. A room right next to this was a top secret room, and Enrico Fermi and Crawford Greenewalt and John Wheeler were there. They were talking away and Fermi was waving his hands around and so forth. And Bill McCune was there at the time and he talked to his boss. He said, “Go by the door and see what those guys are doing.”

This superintendent comes back all smiles. He said, “You wouldn’t believe it. They’re setting up a pool to guess when the reactor would start on its own, and the winner will get a bottle of wine.” Here was an earthshaking event, you know, will the reactor work or not?

Then they finally decided that during the reaction, one of the fission products was iodine and it’s decayed to xenon. The xenon was a strong neutron absorber. The process went along to where xenon was generated yet absorbed all the neutrons, and they had to shut down.

One of the ways that made it work was, the additional 500 tubes provided more neutrons so that you could start up again. But you could not necessarily start up right away. Normally they’d have to wait for the xenon to decay, and it was a fairly short half-life—maybe, I don’t know, twenty, thirty hours. They usually waited a day and then started up.

Or if they knew right away when the scram occurred, what the problem was, they had a “quickie” start-up. They could start up within twenty minutes. They could go ahead and do that, put the rods in where they were, and hope everything’s okay. Then of course later on—I would guess early ‘50s—enriched fuel was used, which had more uranium-235 and more neutrons were available, so that halfway got rid of the problem on the way.

The extra neutrons would overpower the xenon?

 Rohrbacher: Yes, when you first started, there was no xenon there. As the reactor started to operate, xenon was built up, and as you built up the xenon, the xenon absorbed neutrons. So the neutrons were not hitting more uranium and generating more neutrons, and so forth. By providing additional fuel elements, more uranium, it overcame that. There were still restrictions. That was generally the problem. Then, of course, it was pretty well solved with enriched fuel that had more uranium-235, where the neutrons came from.

 Can you give a good description of this reactor for the layperson?

 Rohrbacher: The core of the reactor is a big cube of graphite. Graphite is like charcoal, carbon. It’s about a thirty-five foot cube, and this graphite reduces the energy of the neutrons. The neutrons come from the uranium. Uranium dug out of the ground is naturally radioactive, and it has two parts: uranium-235, which generates neutrons and is radioactive, and the other uranium, uranium-238, which is not radioactive. In the reactor, the neutrons from the uranium-235 are reduced in energy and hit uranium-238, and that process is what they call transmuting: transmute uranium into plutonium. In this process, this fission process, a lot of other products are also formed. I’d say maybe twelve, fifteen other products; isotopes of cobalt, strontium, cesium and so forth, but the only one of great concern was plutonium.

Another concern with the reactor, after you make plutonium—that took about maybe two and a half days for the process, from uranium-238 to plutonium-239. However, the reaction does not stop then, and the uranium-239, which is the weapons-grade material, converts to plutonium-240, which is not weapons-grade. Well, you could probably use it, but why not use diesel fuel and fertilizer? You know, it’s not that great.

So during the operation, the reactor was shut down every month and the central process tubes were discharged to get the maximum 239. Then the intermediate tubes were probably discharged five or six months, and the peripheral tubes maybe once a year. So that way, they got the maximum plutonium-239, what they want.

Matter of fact, that was about the time computers were coming into being, and one of the manual jobs was how to decide which tube to discharge, or how many discharged in what period of time, based on the neutron flux, how active were the reactor, and so forth, and that was monitored by the temperature rise and the flow. This is a top secret thing. A special man did this every day, and he kept it in the bottom drawer of the safe, top secret, you know. That was used to determine the maximum plutonium-239 coming out.

That was another interesting process, discharging the fuel. The reactor had to be shut down, but they had to keep a small amount of water flowing. They took the caps off the front and the back of the process tubes, and pushed out the charge of metallic uranium that had been irradiated. That dropped into a pool of water and dropped through the air for about twenty, thirty feet and then got into a pool with about twenty feet of water.

To stop the blow, they put in what’s called a mattress pad, which was rubber or plastic or something like that. The fuel elements, they were eight inches long, about an inch and a half in diameter. They didn’t want it to drop on the concrete and break, so this mattress pad stopped it, except the radiation was so terrific that the mattress pad got brittle and the fuel elements would fall through.

Then there had to be strict accounting for all these, and they’re searching all over the basin to find them. The ones behind or underneath the mattress pad, they couldn’t really get to. So they turned off all the lights, and the Cherenkov glow from the irradiated fuel elements showed through, so they could get a tong and could pick them up and put them in there. This was another great concern.

The buckets were loaded. The bottom layer was laid in all horizontal and then the second layer was laid in at right angles, and I think there were sixty-four fuel elements in a bucket. Then, just to confirm that the count was right, they weighed the bucket before they put it in the storage area. One great concern by the Atomic Energy Commission in those days was to account for every fuel element, and that was tough to do, you know—thousands of these things. Well, 64,000 fuel elements in the reactor and they’d discharge a third; that’s going quite a bit. Each shift had to check to make sure everything’s right. However, quite often they would be short or long of fuel elements, so they had a separate hiding place where they kept them. One of the operators said, “One time we were so short, we had to steal from another guy’s secret supply to match it.”

 But yes, what can you do with fuel elements? You pick up a fuel element, you get a lethal dose in fifteen, twenty seconds. Matter of fact, even after the reactor deactivated, I think they found a few along the way.

 Where were they stored?

 Rohrbacher: Hidden away in some corner some place, or maybe a bucket that said, “Do not use. B shift only,” or something like that.

 Of course, another particular problem was occasionally there’d be a mistake, if you might say that. You know, to discharge a process tube, you had to take off the cap front and back and push the fuel out by putting in new fuel. Well, they somehow got the cap off the front of one tube and the cap off the back of the adjacent tube, and the guys were pushing and pushing and they said, “What’s going on here?” And they pushed so hard that part of the thing next to the nozzle in the reactor called the gun barrel—it’s a steel thing about seven, eight feet long—it started to come out of the reactor. So they said, “That’s enough. We’ve got a problem here.”

 Then other problems: the fuel elements would somehow get stuck on the elevator. This was another interesting thing. The operator’s got a fair amount of radiation. They always pick the supervisor or an engineer to take care of the problem things.

 One of the supervisors, Bill McCune, tells the story that they told him. They got an element stuck in the elevator and they gave him an eight foot pole and they said, “You run out there and try to dislodge the fuel, and only try twice. Whether you get it or not, get out of there.” So he got it on the first time. He was running backwards so fast, he ran over the radiation monitor that was monitoring his radiation level in the way. So that’s pretty good.

 Do you have some stories about what people thought was going on out here?

 Rohrbacher: A lot of rumors. Everything was coming in; nothing was going out. Some people said, “Oh, that’s a sandpaper factory. They hold up a glued sheet of paper and the dust coats it.” Another one was FDR’s winter palace. He’s going to convert one of the reactor buildings. Of course, they didn’t know it was a reactor building at that time. And another one: the show and tell at school, the kid says, “I know what they’re making. They’re making toilet paper. My dad brings home two rolls in his lunch bucket every day.”

 Incidentally, one of the persons left the plant with a bunch of copper wire wrapped around his waist, and the patrolman gave him a pat search and said, “Step over here, please.” The rest of us went on. We never saw the guy again. Another story was that they were making horses’ front ends. And the question is, what are you doing with those? “Send them to Washington, DC and connect them up.”

 What were the people like here?

Rohrbacher: I think it’s true that people were dedicated. Of course most of them, in the early days, came from other DuPont plants. Even though they didn’t know what they were doing, they did what they were supposed to. I think there’s a pretty, you know, kind of a comradeship feeling that we’re doing this and so forth.

 The thing that surprised me, of course, after a few security lectures: you never talked about it. You go to a movie and there’d be big letters about a foot and a half high, “Silence Means Security.”

A matter of fact, another interesting story about security meetings: they were supposed to be about a half hour long. They tended to be longer and longer. So we convinced the security people to have the meetings at 11:30. These were the days when there are no cafeterias or anything out here. Twelve o’clock, plus or minus a few seconds, we’d all rattle our tin lunch buckets and the security guy got the message.

 As a matter of fact, the FBI checked us all over ahead of time. I remember my mother called me up and said—this is back in St. Paul, Minnesota—“Roger, what are you doing? They’re asking all about you.” So I came out here. Of course, we did get a bunch of security lectures and we didn’t really get told what we were doing, although we got the impression.

 Bill McCune told a pretty good story. He said one of his operators was hefting one of these fuel elements, and he [the operator] says, “You know, Bill, I used to work in a uranium mine in British Columbia and this feels just as heavy as uranium.”

 Bill says, “Wow, that’s interesting,” and he walked away, and didn’t want to spill the beans. But nothing really was said.

 “What are you doing here?” You have enough of a few pounds of stuff and, you know, we got an inkling. But not until the old Village newspaper came out and said, “It’s the bomb,” that we knew what was going on.

 Matter of fact, a reporter from the TV station in Seattle came here, interviewed a bunch of us, and we were told about security. She said, “Well, that wouldn’t be the same today.” But you know, I think there was a little different attitude, yes. We had bridge clubs and meetings and so forth and volleyball and so forth, and we never talked about it. Of course, volleyball dehydrates a guy. You would have to go to the Gaslight Tavern and drink water, of course, to get your liquids back. But nobody ever said a word that I know of; just a good secret.

 Were there people that didn’t know they were working on a bomb?

 Rohrbacher: Prior to the announcement, most of the people did not know. There was probably a dozen in the early days during startup, and maybe three or four dozen later on. You can’t very well operate the reactor without having a little clue what’s going on. So I would say that’s probably true. Even—well, like myself—that had a pretty good suspicions, we didn’t really know for sure that this was going to end up in an atom bomb. We knew physics was involved and we knew uranium was involved, but that was about it. You just kind of got the stuff by osmosis. Nobody ever said.

 Was it easy to figure out here?

 Rohrbacher: I don’t think any of my acquaintances figured out. I was under the impression that most people did not realize that what they were doing would end up in the atomic bomb. I think they were just kind of guessing and stuff along the way. You got the impression there was something other than a chemical plant and other than anything else, and it concerned something to do with physics. The operators themselves, of course, they were operating the plant based on the neutron production, so they had some clue.

 But people who worked in the hundred areas could not go into the other areas, like the separations area where they separated plutonium from the other stuff. Nor could they go in the laboratory in closer to town where the fuel production was made—only with a good excuse to find out some particular problem related to the reactor. In my case, for example, if there was some instrumentation I wanted to know something about, I could go some other place. But nobody ever talked about what they were doing. It was quite interesting.

 What was your reaction when you found out?

 Rohrbacher: When the official news came out that it’s the bomb, as the local papers said, it’s kind of a surprise and a relief and I halfway said, “Oh, I suspected something like that.” But I think most of us really didn’t, and that’s most surprising. Then of course, got all the little stories about how this—“Didn’t you know what they were doing?” Yes, they’re sticking stuff in the reactor. And of course, piles in, but I don’t think, maybe, ninety, ninety-five percent really knew that it would end up as an atom bomb out of Los Alamos.

 How did the attitudes change the next day you came back on shift?

 Rohrbacher: Well, I don’t remember any particular change in the people after they knew it was an atom bomb and they were making plutonium for that particular reason. Come to think of it, there was some information out prior to the announcement that talked about how much product was being made. “All these ten tons of uranium, and they’re coming out with pounds of this stuff? What’s going on?” But I think the answer is, it probably didn’t change their attitude much.

 Well, the war is still going on, you know, the Cold War getting hotter, and they built more reactors. C Reactor was kind of partly built as an experimental reactor with a slightly different design, and also as a replacement for B. B was shut down for about six months because of the graphite expansion problem, and then there was a replacement for D Reactor, called DR. Well, that’s pretty good; D Replacement sounds pretty good. Then they built a replacement for F Reactor called H.

Then later on, the K reactors, K-East and K-West, were built. Extremely large, maybe twice the size as the original reactors, about four thousand megawatt thermal power generation. Then of course later was an N reactor, which is a dual purpose reactor—made steam for electric generation and plutonium at the same time.

That’s where I ended up, working on N Reactor design, and then in the instrument group concerned with safety aspects. It was a reliability analysis group, and we were to determine what might fail, how often, and what could be done about it. Some interesting results came out. One is, there’s nothing wrong with a simple system.

They were putting in all these complications. “What if this valve doesn’t open?” “We’ll put on a second valve operator.” “What if the second valve operator doesn’t get air to operate it?” “We’ll put on a liquid nitrogen tank to provide that in case.” It got so bad, the best, most reliable thing was have a simple system with a manual override. So if a guy really wanted to open a valve, he could push a button and the valve would open. That was kind of interesting.

Matter of fact, this was the days when the computers were just getting to being. We had this big thing called a fault tree. Everything I could cause as damage to the reactor was put on. We had something like 32,000 inputs which would cause the reactor problems. The computer at that time—this was a Boeing Computer in Seattle—was so skinny compared to today, they had to divide the program into two parts.

This was also the days of Fortran where they had these cards, punch cards, big boxes of cards, shipped into Seattle, and two days later they’d ship the stuff back with the answer. That’s another place we had a lot of women—called them girls, even though one was about sixty-five. They knew as much about the program as we did. We would ask them to do something and one particular thing like in the water treatment plant, we said, “Make up a bunch of cards that have the top part relating to the water treatment plant.”

And the answer would be, “Oh, we knew you would need those. We did those already.” I thought that was pretty good. That was a nice time.

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