Editing SL-1 (section)

==Cause==
One of the required maintenance procedures called for Rod 9 to be manually withdrawn about {{convert|4|in|cm|spell=in}} in order to attach it to the automated control mechanism from which it had been disconnected. Post-accident calculations, as well as examination of scratches on Rod 9, estimate that it had actually been withdrawn about {{convert|20|in|cm|spell=in}}, causing the reactor to go prompt critical and triggering the steam explosion. The most common theories proposed for the withdrawal of the rod are (1) [[sabotage]] or [[suicide]] by one of the operators, (2) a [[murder-suicide]] involving an affair with the wife of one of the other operators, (3) inadvertent withdrawal of the main control rod, or (4) an intentional attempt to "exercise" the rod (to make it travel more smoothly within its sheath).<ref name=tucker /><ref name=McKeown /><ref>{{cite magazine |url=http://www.tinhouse.com/magazine/current-issue.html#justin-nobel |title=ATOMIC CITY |first=Justin |last=Nobel |archive-url=https://web.archive.org/web/20120522203550/http://www.tinhouse.com/magazine/current-issue.html#justin-nobel |archive-date=May 22, 2012 |magazine=Tin House Magazine |issue=51 |date=Spring 2012}}</ref><ref>{{cite magazine |author-link=Maud Newton |url=https://www.nytimes.com/interactive/2012/04/01/magazine/the-one-page-magazine.html |title=A Nuclear Family |first=Maud |last=Newton |magazine=[[The New York Times Magazine]] |date=April 1, 2012}}</ref> The maintenance logs do not address what the technicians were attempting to do, and thus the actual cause of the accident will never be known. However, it seems unlikely that it was a suicide.<ref>{{Citation |title=What Caused America's First Nuclear Meltdown? | date=8 May 2021 |url=https://www.youtube.com/watch?v=uJ8cYheR5xo |language=en |access-date=May 24, 2022}}</ref>{{better source needed|date=November 2022}}

Post-accident experiments were conducted with an identically weighted mock control rod to determine whether it was possible or feasible for one or two men to have withdrawn Rod 9 by 20 inches. Experiments included a simulation of the possibility that the {{convert|48|lb|kg|adj=on}}<ref name=design/> central rod was stuck and one man freed it himself, reproducing the scenario that investigators considered the best explanation: Byrnes broke the control rod loose and withdrew it accidentally, killing all three men.<ref name=tucker/> When testing the theory that Rod 9 was rapidly withdrawn manually, three men took part in timed trials and their efforts were compared to the energy of the nuclear excursion that had occurred.<ref name=ido19300>[https://web.archive.org/web/20160304090610/http://www.id.doe.gov/foia/PDF/IDO-19300a.pdf "SL-1 Reactor Accident on January 3, 1961, Interim Report,"] May 15, 1961, IDO-19300, CEND-128, Combustion Engineering, Inc., Nuclear Division, Windsor, Connecticut.</ref>

{{Blockquote|text=A spare SL-1 control rod actuator assembly was used for mock-up on which the speed of manual rod withdrawal was measured for several subjects. The equipment is the same as that on SL-1 except for the control rod, which is simulated by a weight to give a total movable load of 84 lb, the net weight of the SL-1 movable assembly in water. {{om|br=y}} The test was conducted by instructing the subject to lift the rod as rapidly as possible, while an electric timer, measured the elapsed time from beginning of rod motion to some predetermined distance of withdrawal. Distances up to 30 inches were measured.
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The above reasoning indicates that the required rate of rod withdrawal to produce a period as short as 5.3 milliseconds was well within the limits of human capability.|title=IDO-19300|source=SL-1 Reactor Accident on January 3, 1961, Interim Report, May 15, 1961<ref name=ido19300 />}}

At SL-1, control rods would sometimes get stuck in the control rod channel. Numerous procedures were conducted to evaluate control rods to ensure they were operating properly. There were rod drop tests and scram tests of each rod, in addition to periodic rod exercising and rod withdrawals for normal operation. From February 1959 to November 18, 1960, there were 40 cases of a stuck control rod for scram and rod drop tests and about a 2.5% failure rate. From November 18 to December 23, 1960, there was a dramatic increase in stuck rods, with 23 in that time period and a 13.0% failure rate. Besides these test failures, there were an additional 21 rod-sticking incidents from February 1959 to December 1960; four of these had occurred in the last month of operation during routine rod withdrawal. Rod 9 had the best operational performance record even though it was operated more frequently than any of the other rods.

Rod sticking has been attributed to misalignment, corrosion product build-up, bearing wear, clutch wear, and drive mechanism seal wear. Many of the failure modes that caused a stuck rod during tests (like bearing and clutch wear) would apply only to a movement performed by the control rod drive mechanism. Since the No. 9 rod is centrally located, its alignment may have been better than Nos. 1, 3, 5, and 7, which were more prone to sticking. After the accident, logbooks and former plant operators were consulted to determine if there had been any rods stuck during the reassembly operation that Byrnes was performing. One person had performed this about 300 times, and another 250 times; neither had ever felt a control rod stick when being manually raised during this procedure.<ref name=ido19300 /> Furthermore, no one had ever reported a stuck rod during manual reconnection.

During congressional hearings in June 1961, the SL-1 Project Manager, W. B. Allred, admitted that the lack of supervision by CEI of SL-1 plant operation on an "around-the-clock basis" was because the Atomic Energy Commission (AEC) had rejected the idea "for budget reasons."<ref name=Joint61 /> Allred was also grilled on the matter of increased rod sticking between November 16, 1960, and the final shutdown on December 23. Of the increase, Allred stated, "I was not completely aware of significant increase" and, "I was not aware that this sharp increase had occurred."<ref name=Joint61 /> When asked who was the person responsible for informing him of the sticking problem, Allred said that Paul Duckworth, the SL-1 Operations Supervisor, should have reported this to him but did not. When pressed, Allred said that if he had known of the increased control rod sticking, he "would have shut the plant down for more detailed examination."<ref name=Joint61 />

{{Blockquote|text=The mechanical and material evidence, combined with the nuclear and chemical evidence, forced them to believe that the central control rod had been withdrawn very rapidly. {{omission}} The scientists questioned the [former operators of SL-1]: "Did you know that the reactor would go critical if the central control rod were removed?" Answer: "Of course! We often talked about what we would do if we were at a radar station and the Russians came. We'd yank it out."|author=Susan M. Stacy|source=Proving the Principle, 2000<ref name=ProvePrinciple15/>}}