History can be sweetly written

As with genre fiction, mainstream (i.e. non-academic) history need only possess clear prose. The point is the history, the story, the organization, the data. Virtuosic stylistics, if they arise, are a bonus. So when you find a historian whose writing is a pleasure to read, savor her, my friends, savor her.

James Mahaffey Atomic Awakening

My go-to paragon of evocative history style is Richard Rhodes but another author I’ve probably mentioned before in this blog is James Mahaffey. Mahaffey is far less renowned than Rhodes but man, can he write! Here he is in full flight, describing the reactor design choices made by the father of the modern PWR, Admiral Hyman Rickover:

He found himself in a technical area schizophrenically divided between fanciful, anything-goes designs and an immovable bedrock. Conventional wisdom in the late ’40s was to build a uranium-fueled reactor out of graphite, such as the big power reactors at Hanford. It was true that nobody had been killed at Hanford, but there was nothing inherently safe about a graphite pile. You could not get anywhere near it when it was running, and the failure of a pump or valve would lead to a chain of damages. Lose water coolant through leakage or boil-off, and the reactivity of the pile would be improved, sending the machine into an exponential power excursion, as the graphite alone was a more advantageous moderator than graphite with water in it. Graphite reactors also had to be semi-continuously refueled, as the slight percentage of U-235 in natural uranium would burn down to a sub-critical concentration quickly.

Rickover had correctly assumed years ago that plenty of uranium would be available, and now it was, thanks to the discovery in Utah, and so he designed the submarine reactor to use 50 percent enriched U-235. Using a high U-235 content meant that his boat could cruise the world at full speed for many years without refueling. This eliminated the dangerous step of having to swap out burned fuel in the middle of operations. It also meant that there was no need for a high-performance moderator, such as graphite or heavy water. He could use the hydrogen in common tap water to slow the neutrons, and so he could afford to waste a few neutrons. In fact, it would take as few as one bounce off a hydrogen nucleus to slow a neutron down to fissioning speed, so the slowing-down distance would be minimal. The reactor core could thus be quite small, about the size of a garbage can.

Having ordinary water as both coolant and moderator was a safety feature, because if you lost coolant you lost moderator, and the reactor would shut down automatically, instead of increasing power. So that the reactor would fit in the 28-foot form factor of the German submarine hull, Rickover worked on a pressurized water design. The coolant would be kept at high pressure, so it would not boil, and this allowed a minimum reactor size, with no need for a steam separator at the top. The cooling water was kept in a closed loop and circulated with an electric pump. By keeping this primary cooling loop sealed, any radioactivity leak from a fuel breakdown was confined to the reactor vessel and a minimum amount of plumbing. Heat captured by the primary loop was then transferred to a secondary loop, also running on fresh water, by one or more water-to-water heat exchangers, acting as boilers. Nothing in the outer loop could become contaminated with radioactivity, and it would always be safe to do maintenance work involving the secondary plumbing.

Water boiled in the “steam generators” by proximity to the super-heated liquid from the primary loop then ran a multi-stage steam turbine. The steam was then condensed and piped back to the steam generator, in a secondary, closed loop. By artful positioning of the maze of pipes, pumps, condensers, and steam generators, the entire power plant, generating 50 megawatts of power at the propeller shaft, could be fitted in a conventional submarine hull, with plenty of room left over. There was no need to store thousands of gallons of diesel fuel or tonnes of lead-acid batteries in this new type of undersea vessel. Rickover’s design looked safe and forgiving, practical, and even implementable.

Mahaffey, James. 2009. Atomic Awakening: A New Look at the History and Future of Nuclear Power. Pegasus, New York, pp. 213-215