Editing SL-1 (section)

==Accident and response==
On Tuesday, January 3, 1961, SL-1 was being prepared for restart after a shutdown of 11 days over the holidays. Maintenance procedures required that rods be manually withdrawn a few inches to reconnect each one to its drive mechanism. At 9:01&nbsp;pm [[Mountain Standard Time|MST]], Rod 9 was suddenly withdrawn too far, causing SL-1 to go [[prompt criticality|prompt critical]] instantly. In four milliseconds, the heat generated by the resulting enormous [[power excursion]] caused fuel inside the core to melt and to explosively vaporize. The expanding fuel plates produced an extreme pressure wave that blasted water upward, striking the top of the [[reactor vessel]] with a peak pressure of {{convert|10000|psi}}. The slug of water was propelled at {{convert|160|ft/s}} with average pressure of around {{convert|500|psi}}.<ref name=ido19311 /> This extreme [[water hammer]] propelled the entire reactor vessel upward at {{convert|27|ft/s}}, while the shield plugs were ejected at {{convert|85|ft/s}}.<ref name=ido19311 /> With six holes on the top of the reactor vessel, high-pressure water and steam sprayed the entire room with radioactive debris from the damaged core. A later investigation concluded that the {{convert|26,000|lb|kg|adj=on}} (or thirteen short tons) vessel had jumped {{convert|9|ft|1|in|m}}, parts of it striking the ceiling of the reactor building before settling back into its original location,<ref name=tucker/><ref name=ProvePrinciple15>{{cite book
 |last        = Stacy
 |first       = Susan M.
 |title       = Proving the Principle – A History of The Idaho National Engineering and Environmental Laboratory, 1949–1999
 |publisher   = U.S. Department of Energy, Idaho Operations Office
 |year        = 2000
 |url         = http://www.inl.gov/proving-the-principle/chapter_15.pdf
 |isbn        = 0-16-059185-6
 |url-status     = dead
 |archive-url  = https://web.archive.org/web/20110807212441/http://www.inl.gov/proving-the-principle/chapter_15.pdf
 |archive-date = 2011-08-07
}} Chapter 15.</ref><ref name=ido19311 /> and depositing insulation and gravel on the operating floor.<ref name=ido19311 /> If the vessel's #5 seal housing had not hit the overhead crane, it would have risen about {{convert|10|ft|0|spell=in}}.<ref name=ido19311 /> The excursion, steam explosion, and vessel movement took two to four seconds.<ref name=ido19311 />

The spray of water and steam knocked two operators onto the floor, killing one and severely injuring another.<ref name=autopsy/> The No. 7 shield plug from the top of the reactor vessel impaled the third man through his groin and exited his shoulder, pinning him to the ceiling.<ref name=tucker/> The victims were Army [[Specialist (rank)|Specialists]] Richard Leroy McKinley (age 27) and John A. Byrnes (age 22), and Navy [[Seabee]] [[construction electrician (United States Navy)|Construction Electrician]] [[Petty officer, first class|First Class]] (CE1)<!-- "Construction Electrician" came from Appendix to Proving the Principle, Note 18 of Chapter 15 --> Richard C. Legg (age 26).<ref>{{cite news |title=Nuclear Experts Probe Fatal Reactor Explosion|url=https://news.google.com/newspapers?id=YAAsAAAAIBAJ&pg=4392,459966&dq=idaho+nuclear+accident&hl=en|access-date=July 30, 2010|newspaper=Times Daily|date=January 5, 1961}}</ref><ref>[https://news.google.com/newspapers?id=EaASAAAAIBAJ&sjid=OvcDAAAAIBAJ&pg=4464%2C614495 Spokane Daily Chronicle - Jan 4, 1961]. Byrnes was a [[Specialist_(rank)#Specialist_(1955–present)|Spec]]/5 from [[Utica, New York]], McKinley was a Spec/4 from [[Kenton, Ohio]], and Legg was a [[Seabee]] and "Navy electrician L.C." from [[Roscommon, Michigan]].</ref> It was later established by author Todd Tucker that Byrnes (the reactor operator) had lifted the rod and caused the excursion; Legg (the shift supervisor) was standing on top of the reactor vessel and was impaled and pinned to the ceiling; and McKinley (the trainee) stood nearby. Byrnes died instantly when one of his ribs pierced his heart.<ref name=autopsy/> Only McKinley was found alive by rescuers, bleeding, unconscious and in deep [[shock (circulatory)|shock]].<ref name=tucker/> This was consistent with the analysis of the SL-1 Board of Investigation<ref name=finalreport>[https://catalog.hathitrust.org/Record/000521900 Major Activities in the Atomic Energy Programs, January-December 1962, Appendix 8: Final Report of SL-1 Accident Investigation Board], SL-1 Board of Investigation, Curtis A. Nelson, Atomic Energy Commission, Joint Committee on Atomic Energy, September 5, 1962 (See ''Annual Report to Congress – U.S. Atomic Energy Commission, 1962'', Appendix 8, pp. 518–23)</ref> and with the results of the [[autopsies]], which suggested that Byrnes and Legg died instantly, while McKinley showed signs of diffuse bleeding within his scalp, indicating he survived about two hours before succumbing to his wounds.<ref name=autopsy>[https://inldigitallibrary.inl.gov/PRR/163773.pdf LAMS-2550 SL-1 Reactor Accident Autopsy Procedures and Results], Clarence Lushbaugh, et al., Los Alamos Scientific Laboratory, June 21, 1961.</ref> The autopsy identified each man by name,<ref name=autopsy/> concluded that all three men died of physical trauma,<ref name=tucker/><ref name=autopsy /> and, due to their peculiar injuries, established the most likely locations of each when the reactor exploded.<ref name=autopsy/>

===Reactor principles and events===
Early press reports indicated that the explosion may have been due to a chemical reaction, but that was shortly ruled out. Fast [[neutron activation]] had occurred to various materials in the room, indicating a nuclear power excursion unlike a properly operating reactor.

In a [[thermal-neutron reactor]] such as SL-1, neutrons are [[neutron moderator|moderated]] (slowed down) to control the nuclear fission process and increase the likelihood of fission with [[U-235]] fuel. Without sufficient moderation, cores such as SL-1 would be unable to sustain a nuclear chain reaction. When the moderator is removed from the core, the chain reaction decreases. Water, when used as a moderator, is maintained under high pressure to keep it liquid. Steam formation in the channels around the nuclear fuel suppresses the chain reaction.

Another control is the effect of the [[delayed neutron]]s on the chain reaction in the core. Most neutrons (the {{em|prompt}} neutrons) are produced nearly instantaneously by the fission of U-235. But a few—approximately 0.7 percent in a U-235-fueled reactor operating at steady-state—are produced through the relatively slow radioactive decay of certain fission products. (These fission products are trapped inside the fuel plates in close proximity to the uranium-235 fuel.) The delayed production of a fraction of the neutrons enables reactor power changes to be controlled on a time scale amenable to humans and machinery.<ref name="Introduction to Nuclear Engineering">{{cite book
|last= Lamarsh
|first= John R.
|author2=Baratta, Anthony J.
|title= Introduction to Nuclear Engineering
|publisher= Prentice Hall
|year= 2001
|location= Upper Saddle River, New Jersey
|pages= 783
|isbn= 0-201-82498-1}}</ref>

In the case of an ejected control assembly or poison, it is possible for the reactor to become [[critical mass|critical]] {{em|on the [[prompt neutron]]s alone}} (i.e. [[prompt criticality|prompt critical]]). When the reactor is prompt critical, the time to double the power is of the order of 10 microseconds. The duration necessary for temperature to follow the power level depends on the design of the reactor core. Typically, the coolant temperature lags behind the power by 3 to 5 seconds in a conventional [[LWR]]. In the SL-1 design, it was about 6 milliseconds before steam formation started.<ref name=ido19311 />

SL-1 was built with a main central control rod that could produce a very large excess [[Dollar (reactivity)|reactivity]] if it were completely removed.<ref name=suid /> The extra rod worth was in part due to the decision to load only 40 of the 59 fuel assemblies with nuclear fuel, thus making the prototype reactor core more active in the center. In normal operation control rods are withdrawn only far enough to generate sufficient reactivity for a sustained nuclear reaction and power generation. In this accident, however, the additional reactivity was enough to take the reactor prompt critical within an estimated 4 milliseconds.<ref name=ido19313>''[http://www.id.doe.gov/foia/PDF/IDO-19313.pdf IDO-19313: Additional Analysis of the SL-1 Excursion] {{webarchive|url=https://web.archive.org/web/20110927065809/http://www.id.doe.gov/foia/PDF/IDO-19313.pdf |date=2011-09-27 }} Final Report of Progress July through October 1962'', November 21, 1962, Flight Propulsion Laboratory Department, General Electric Company, Idaho Falls, Idaho, U.S. Atomic Energy Commission, Division of Technical Information.</ref> That was too fast for the heat from the fuel to permeate the aluminum cladding and boil enough water to fully stop the power growth in all parts of the core via negative moderator temperature and void feedback.<ref name=ido19311 /><ref name=ido19313 />

Post-accident analysis concluded that the final control method (i.e., dissipation of the prompt critical state and the end of the sustained nuclear chain reaction) occurred by means of catastrophic core disassembly: destructive melting, vaporization, and consequent conventional explosive expansion of the parts of the reactor core where the greatest amount of heat was being produced most quickly. It was estimated that this core heating and vaporization process happened in about 7.5 milliseconds, before enough steam had been formed to shut down the reaction, beating the steam shutdown by a few milliseconds. A key statistic makes it clear why the core blew apart: the reactor designed for a 3 MW power output operated momentarily at a peak of about 20 GW, a power density over 6,000 times higher than its safe operating limit.<ref name=la13638 /> This [[criticality accident]] is estimated to have produced 4.4&nbsp;×&nbsp;10<sup>18</sup> fissions,<ref name=la13638 /> or about {{convert|133|MJ|kgTNT}} energy.<ref name=ido19313 />

===Events after the power excursion===
[[File:Sl-1-ineel61-9.jpg|thumb|210px|Checking for [[radioactive contamination]] on nearby [[U.S. Route 20 in Idaho|Highway 20]]]]

Heat sensors above the reactor set off an alarm at the NRTS security facility at 9:01&nbsp;pm MST, the time of the accident. False alarms had occurred in the morning and afternoon that same day. The response team of six firemen (Ken Dearden, assistant chief; Mel Hess, lieutenant; Bob Archer; Carl Johnson; Egon Lamprecht; Gerald Stuart; Vern Conlon) arrived nine minutes later, expecting another false alarm.<ref name="berg">{{cite news |last=Berg|first=Sven|title=Nuclear accident still mystery to rescue worker |url=http://www.argusobserver.com/news/nuclear-accident-still-mystery-to-rescue-worker/article_272b80ac-57d0-5dfc-9fe7-440e6e27b6e3.html|access-date=April 6, 2015|newspaper=The Argus Observer|date=December 12, 2009}}</ref> They noticed nothing unusual at first, with only a little steam rising from the building, normal for the cold {{convert|6|F}} night. The firefighters, unable to hail anyone inside the SL-1 facility, had a security guard open the gate for them. They donned their [[Scott Air-Pak SCBA|Scott Air-Paks]], and arrived at the Support Facilities Building to investigate.

The building appeared normal, but was unoccupied. Three mugs of warm coffee were in the break room and three jackets were hanging nearby.<ref name=tucker /> They entered the reactor control room and noticed a radiation warning light. Their handheld radiation detector jumped sharply above its maximum range as they were climbing the stairs to SL-1's reactor operating floor level. This prompted a retreat for a second radiation detector.<ref name=tucker /> The second radiation detector also maxed out at its 200 [[Roentgen (unit)|röntgen]]s per hour (R/hr) scale as they ascended again.<ref name=suid>[https://flibe-energy.com/pdf/ArmyNuclearPowerProgram.pdf The Army's Nuclear Power Program: THE EVOLUTION OF A SUPPORT AGENCY] {{Webarchive|url=https://web.archive.org/web/20211003182412/https://flibe-energy.com/pdf/ArmyNuclearPowerProgram.pdf |date=2021-10-03 }}, 1990, CONTRIBUTIONS IN MILITARY STUDIES, NUMBER 98.</ref> They peered into the reactor room before withdrawing.<ref name="berg" /><!-- It's apparent that the official narrative conflicts heavily with the testimony of the first responders, who describe multiple ascents up to the reactor floor, while the published narrative lists only a few. Referring to the non-governmental sources for the events here will provide much more insight into the happenings prior to the recovery of McKinley. -->

At 9:17&nbsp;pm, a [[health physics|health physicist]] arrived; he and Assistant Chief Moshberger, both wearing air tanks and masks with [[positive pressure]] in the mask to force out any potential contaminants, approached the reactor building stairs.<ref name=tucker /> Their detectors read 25 [[Roentgen (unit)|röntgen]]s per hour (R/hr) as they started up the stairs, and they withdrew.<ref name="IDO-19302">[https://web.archive.org/web/20090118182940/http://www.id.doe.gov/foia/IDO-19302.pdf IDO-19302 IDO Report on the Nuclear Accident at the SL-1 Reactor January 3, 1961 at the National Reactor Testing Station], TID-4500 (16th Ed.), SL-1 Report Task Force, US Atomic Energy Commission, Idaho Operations Office, January 1962.</ref> Finding a higher-scale [[Ionization chamber|ion chamber detector]], the pair reached the top of the stairs to look inside the reactor room for the three missing men.<ref name=McKeown /> Their Jordan Radector AG-500 meter pegged at 500 R/hr on the way up.<ref name=McKeown /><ref name=ProvePrinciple15/> They saw a dim, wet operating floor strewn with rocks and steel punchings, twisted metal, and debris scattered.

[[File:Sl-1-ineel61-667.jpg|thumb|The stretcher rig. Army volunteers from a special Chemical Radiological Unit at [[Dugway Proving Ground]] practiced before a crane inserted the rig into the SL-1 reactor building to collect the body of the man (Legg) pinned to the ceiling directly above the reactor vessel.]] Coming from nearby [[Idaho Falls]], the lead SL-1 health physicist, Ed Vallario, and Paul Duckworth, the SL-1 Operations Supervisor, arrived at SL-1 around 10:30 pm. The two donned air packs and went quickly into the administration building, through the support building, and up the stairs to the reactor floor. Halfway up the stairs, Vallario heard McKinley moaning. Finding him and a second operator on the floor who appeared to be dead, the two decided to return to the checkpoint and get help for the bleeding McKinley.<ref name=McKeown />

The two were joined by three health physicists who donned air packs and went with them back to the reactor floor. The masks on their air packs were fogging up, limiting visibility. McKinley was moving slightly, but his body was partially covered with metal debris, which the rescuers had to remove in order to carry him with a stretcher. Vallario also moved debris in his attempt to find the missing crewman. Byrnes was partially covered with steel pellets and blood.<ref name="impulse" /> Another man checked for Byrnes' pulse and announced that he was dead.<ref name=impulse />

Three men attempted to remove McKinley via the outside stairs, sending one man outside to meet them with a truck.<ref name=impulse /> But after carrying McKinley across the operating floor to the exit, they discovered equipment blocking the emergency exit door. This forced the rescuers to reverse course and use the main stairs.<ref name=impulse>[https://www.carnegiehero.org/wp-content/uploads/2021/02/64.winter.2021_web.pdf Impulse Issue 64, Winter 2021], Carnegie Hero Fund Commission</ref>

During the movement of McKinley, two men had their Scott Air-Paks freeze up and cease to work. Duckworth evacuated due to the malfunction, while Vallario removed his mask and breathed contaminated air to complete the evacuation of McKinley.<ref name=hero>{{Cite web |url=https://mychfc.org/hero.aspx?hero=45570 |title=Carnegie Hero Fund Commission, Vallario award |access-date=2020-11-09 |archive-date=2020-11-09 |archive-url=https://web.archive.org/web/20201109081454/https://mychfc.org/hero.aspx?hero=45570 |url-status=dead }}</ref><ref name=McKeown/> The rescue took about three minutes.<ref name=impulse />

The evacuation of McKinley turned quickly into a major radiological problem. McKinley was first shuttled into a panel truck and then into the back of an ambulance.<ref name=ido19300 /><ref name=McKeown/> The on-call nurse, Helen Leisen, tending to the patient in the back of the ambulance, heard at least a faint breath, perhaps his last. But before the vehicle made it to nearby Highway 20, the AEC doctor had the nurse evacuate and, entering the ambulance, found no pulse. He pronounced the man dead at 11:14 pm. The contaminated ambulance, with the body of McKinley, was driven out into the desert and abandoned for several hours.<ref name=McKeown/>

Four men had entered into the reactor building at 10:38 pm and found the third man.<ref name=ido19300 />{{rp|105}} Legg was discovered last because he was pinned to the ceiling above the reactor by a shield plug and not easily recognizable.<ref name=tucker/>

Extensive decontamination was conducted that night. About 30 of the first responders took showers, scrubbed their hands with [[potassium permanganate]], and changed their clothes.<ref name=ido19300/><ref name=McKeown/> The body in the ambulance was later disrobed and returned to the ambulance, which took it to a nearby facility for storage and autopsy.<ref name=ido19300 />

On the night of January 4, a team of six volunteers worked in pairs to recover Byrnes' body from the SL-1 operating floor. It was taken, also by ambulance, to the same facility.<ref name=ido19300 />

After four days of planning, the third body, by far the most contaminated, was retrieved. Modifications to the reactor room had to be performed by a welder inside a lead shielded box attached to a crane.<ref name="IDO-19302" /> On January 9, in relays of two at a time, a team of ten men, allowed no more than 65 seconds exposure each, used sharp hooks on the end of long poles to pull Legg's body free of the No. 7 shield plug, dropping it onto a {{convert|5|by|20|ft|adj=on}} stretcher attached to a crane outside the building.<ref name=tucker/><ref name=ProvePrinciple15 /><ref name="IDO-19302" />

Radioactive copper [[copper-64|<sup>64</sup>Cu]] from a cigarette lighter screw on McKinley and a brass watch band buckle from Byrnes both proved that the reactor had indeed gone prompt critical.<ref name=ido19300 /> This was confirmed with several other readings, including gold [[Gold-198|<sup>198</sup>Au]] from Legg's wedding ring. Nuclear accident dosimeters inside the reactor plant and particles of uranium from the victim's clothes also provided evidence of the excursion. In an unusual finding for an autopsy, hair samples taken from the head and pubis of the victims were analyzed to suggest their relative positions during the reactor excursion and to estimate the number of fissions using [[Phosphorus-32]] activity.<ref name=autopsy /> Before these discoveries of [[neutron activation|neutron-activated elements]] in the men's belongings and in their hair, scientists had doubted that a nuclear excursion had occurred, believing the reactor was inherently safe. [[Strontium-91]], a major fission product, was also found with the uranium particles.<ref name=ido19300 /> Air sampling downstream of the reactor discovered fission products, as well.<ref name=Joint61 /> All of these findings ruled out early speculation that a chemical explosion caused the accident and helped establish the energy released by the excursion.<ref name=ProvePrinciple15/>

Some sources and eyewitness accounts confuse the names and positions of each victim.<ref name=tucker/> In ''Idaho Falls: The Untold Story of America's First Nuclear Accident'',<ref name="McKeown">{{cite book |last=McKeown |first=William |title=Idaho Falls: The Untold Story of America's First Nuclear Accident |publisher=ECW Press |year=2003 |isbn=978-1-55022-562-4 |location=Toronto}}, [https://books.google.com/books?id=ATkLIZ06YJQC&pg=PA2]</ref> the author indicates that the rescue teams identified Byrnes as the man found still alive, believing that Legg's body was the one found next to the reactor shield and recovered the night after the accident, and that McKinley was impaled by the control rod to the ceiling directly above the reactor. The misidentification, caused by the severe blast injuries to the victims, was rectified during the autopsies conducted by [[Clarence Lushbaugh]], but this caused confusion for some time as the autopsy was classified until the 1990s.<ref name=McKeown /><ref name="Lushbaugh_Interview">{{Cite book|url=https://digital.library.unt.edu/ark:/67531/metadc672291/|title=Human radiation studies: Remembering the early years: Oral history of pathologist Clarence Lushbaugh, M.D., conducted October 5, 1994|publisher=[[United States Department of Energy]]|year=1995}}</ref>

The seven rescuers who carried McKinley and received Carnegie Hero awards from the [[Carnegie Hero Fund]] in 1962 were: Edward Vallario, SL-1 Health Physicist; Paul Duckworth, the SL-1 Operations Supervisor; Sidney Cohen, the SL-1 Test supervisor; William Rausch, SL-1 Assistant Operations Supervisor; William Gammill, the on-duty AEC Site Survey Chief; Lovell Callister, health physicist, and Delos Richards, health physics technician.<ref name=Carnegie2>[https://www.carnegiehero.org/hero-search/edward-j-vallario/ Edward J. Vallario Award] and [https://www.carnegiehero.org/from-the-archives-explosion-in-the-nuclear-reactor-room/ From the Archives: Explosion in the Nuclear Reactor Room]</ref><ref name=Carnegie>Carnegie Hero Fund Commission heroes:
[https://mychfc.org/hero.aspx?hero=45880 Duckworth award] {{Webarchive|url=https://web.archive.org/web/20201114161202/https://mychfc.org/hero.aspx?hero=45880 |date=2020-11-14 }},
[https://mychfc.org/hero.aspx?hero=45881 Cohen award] {{Webarchive|url=https://web.archive.org/web/20201116214321/https://mychfc.org/hero.aspx?hero=45881 |date=2020-11-16 }},
[https://mychfc.org/hero.aspx?hero=45882 Rausch award] {{Webarchive|url=https://web.archive.org/web/20201116043906/https://mychfc.org/hero.aspx?hero=45882 |date=2020-11-16 }},
[https://mychfc.org/hero.aspx?hero=45570 Vallario award (with details of the event)] {{Webarchive|url=https://web.archive.org/web/20201109081454/https://mychfc.org/hero.aspx?hero=45570 |date=2020-11-09 }},
[https://mychfc.org/hero.aspx?hero=45883 Gammill award (some details)] {{Webarchive|url=https://web.archive.org/web/20201109090945/https://mychfc.org/hero.aspx?hero=45883 |date=2020-11-09 }},
[https://mychfc.org/hero.aspx?hero=45944 Callister award] {{Webarchive|url=https://web.archive.org/web/20201109112533/https://mychfc.org/hero.aspx?hero=45944 |date=2020-11-09 }},
[https://mychfc.org/hero.aspx?hero=45943 Richards award] {{Webarchive|url=https://web.archive.org/web/20201116105502/https://mychfc.org/hero.aspx?hero=45943 |date=2020-11-16 }}.</ref>