jan 3, 1961 - Work on the Reactor Core is Completed, and the Accident Occurs


Work planned for the reactor core was the insertion of 44 cobalt flux measuring assemblies into coolant channels between plates of the fuel elements throughout the core. Access to the core, to install these assemblies, through nozzles in the head of the
reactor vessel required removal of the control-rod drive assemblies. This portion of the work was begun during the early morning hours
of January 3, 1961. When the day crew (including personnel from the military and from Combustion Engineering) arrived at the SL-1 on January 3, disassembly had been completed. Installation of the flux measuring assemblies was accomplished during the day shift under the supervision of Combustion Engineering personnel.

The crew of the next shift (4:00 p.m. to midnight, January 3) consisted of three military personnel: the shift supervisor (a qualified chief operator), his operator-mechanic assistant (a qualified operator), and a trainee. This crew and the following one were assigned the task of reassembling the control rod drives and preparing the reactor for startup.

First indication of trouble at the SL-l reactor was an automatic alarm received at Atomic Energy Commission Fire Stations and Security
Headquarters at 9s01 p.m. (MST) January 3, 1961. The alarm was immediately broadcast over all NETS radio networks. At the same
time, the personnel radiation monitor at the Gas Cooled Reactor Experiment gate house, about one mile distant, alarmed and remained
erratic for several minutes.

Upon the receipt of the alarm, which could have resulted from excessive temperature, high radiation, by being struck by a
missile, or a pressure surge in the region above the reactor floor, the Central Facilities AEC Fire Department at the NRTS and AEC
Security Forces responded. A health physicist from the Materials Testing Reactor (operated for the AEC by the Phillips Petroleum Company) was called at this time.

Upon entering the SL-l fenced area, the. fire department personnel were unable to arouse the SL-l crew. Access to the reactor support building was gained through use of the security patrolman's keys. The assistant fire department chief sntered the reactor support building and immediately detected radiation levels up to 25 roentgens per hour (r/hr). He could observe none of the SL-l crew in the reactor support building. The health physicist from the Materials Testing Reactor arrived and entered the reactor support building. He observed increasing radiation levels as he proceeded toward the reactor building; he detected levels of 200 r/hr at the stairway to the reactor.

The decision to enter into the reactor building to attempt to locate the operating personnel was made after the arrival of the CEI plant health physicist. Entry by him, and others, located two of the crew on the floor near the reactor in a radiation field of approximately 1000 r/hr. One of the two crewmen was
still living; the other, dead. Removal of the living man was accomplished by approximately 11:00 p.m. Shortly thereafter, he was pronounced dead by one of the AEC physicians who responded to the emergency call.

Added to timeline:

9 days ago
SL-1 Reactor Accident Timeline


jan 3, 1961
~ 57 years ago
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