January 3, 2020
Day 3 of 366

 

January 3rd is the third day of the year. It is the tenth of the Twelve Days of Christmas.

In the United States, it is “celebrated” as National Chocolate Covered Cherry Day, National Drinking Straw Day, and National Fruitcake Toss Day.

 

Historical items of note:

• In 1870, construction began on the Brooklyn Bridge.
• In 1892, English writer, poet, and philologist J.R.R. Tolkien was born.
• In 1933, Minnie D. Craig was elected as Speaker of the North Dakota House of Representatives. She was the first woman to hold a Speakership in the United States.
• In 1937, American director, producer, and screenwriter Glen A. Larson was born. He would create or work on several Generation X television classics, including Battlestar Galactica.
• In 1938, The March of Dimes was established by President Franklin D. Roosevelt as a foundation to fight polio.
• In 1953, Dragnet starring Jack Webb premiered on NBC.
• In 1959, Alaska was admitted as the 49th state in the United States.
• In 1975, actress, writer, and mathematician Danica McKellar was born.
• In 1977, Apple Computers was incorporated.
• In 1993, Star Trek: Deep Space Nine premiered.
• In 2000, the final daily edition of Peanuts was published.

 

In 1961, the Stationary Low-Power Reactor Number One (SL-1) nuclear accident occurred. The boiling water reactor was part of the Army Nuclear Power Program located at the Nuclear Reactor Testing Station near Idaho Falls, Idaho. The project was designed to create small nuclear power sources to provide electrical power and heat for remote facilities in the arctic.

The reactor was shutdown on December 21, 1960 for routine maintenance. Part of this maintenance was the installation of 44 wires to monitor neutron flux in the core. In preparation for a reactor restart on January 3, 1961, the main central control rod was to be manually withdrawn by a few inches to reconnect it to its drive mechanism. At 9:01pm, the rod was suddenly withdrawn too far.

Both boiling water and pressurized water reactors rely on the fission of nuclear fuel to produce neutrons. Those created directly after a fission event are called prompt (or fast) neutrons. Those created after the further decay of fission products are called delayed neutrons. Each of these neutrons can interact with the fuel to create more reactions, and each fission event generates heat with (eventually) generates power.

If enough fission events occur to make a reaction steady and self-sustaining, the reactor is called critical. Unlike what nearly every science-fiction property tells us, a critical reactor is a happy reactor. If the rate of fission events decreases, the reactor becomes subcritical. The reverse, an increase in fission events, causes the reactor to become supercritical.

These deviations from a critical state are controlled by reactivity. A positive reactivity event leads to supercriticality and a negative reactivity event pushes toward subcriticality. The withdrawal of a control rod, for example, increases the ability for neutrons to interact with fuel and is an insertion of positive reactivity.

If a significant number of prompt neutrons are created, the reactor becomes prompt critical and uncontrollable. It generates neutrons and power output at an exponential rate. This is what happened at SL-1.

The operators inadvertently pulled the control rod too far, and the rapid withdrawal inserted enough positive reactivity to make the reactor prompt critical. The reactor was rated for 3 megawatts, but in four milliseconds it generated 20 gigawatts of power. The fuel inside the core melted and vaporized, causing a slug of water to explosively propel the entire reactor vessel upward. The shield plugs were ejected from the top of the core, opening holes that sprayed radioactive water, fuel, and debris all over the room. The water knocked two of the operators to the floor, killing one on impact. One of the plugs struck the third operator in the groin and pinned him to the ceiling.

The entire event took approximately four seconds.

The operator that survived the event later succumbed to his wounds, however the radiation exposure from the accident would have killed all three even if they hadn’t suffered any physical trauma.

The event forced the Army to abandon the design. It also helped solidify the “one stuck rod” criterion in future designs to ensure that no single control rod withdrawal could lead to a similar accident. Essentially, a nuclear reactor must be able to maintain a shutdown state with the most reactive rod stuck at its maximum position.

Just like other major nuclear accidents, the event is used to train operators and engineers to this day.

 

The Thing About Today is an effort to look at each day of 2020 with respect to its historical context.

For more creativity with a critical eye, visit Creative Criticality.