The SL-1 Accident

SL-1 Recovery Operation, C. L. Storrs (GErNMPO, Idaho) and C. W, Bills (AEC-IDO). 

On January 3, 1961, the SL 1 reactor at the National Reactor Testing Station experienced an excursion that killed the three operators on duty at Uie time. Immediate etforts were devoted to the removal of the victims and to assuring the safety ot the reactor. In May 1961, the General Electric Conq any was called upon to undertake recovery operations with the objectives of gathering evi- dence as to the causes of the accident and of cleaning up the area and restoring.it to useful service. 

The over-all recovery plan started with steps to lower radiation levels, concurrent with the gathering of evidence from the reactor building. Following this, much of the equipment and structure above the reactor pressure vessel was removed, permitting the final step of removing the pressure vessel and transporting. it to the Hot Shop in the north end of the National Reactor Testing Station, where specialized equipment was available to dismantle and examine the core. 

Experience with the SL-1 recovery has demonstrated that a highly contaminated area can te cleaned up, using mostly ordinary manual techniques for the fastest and most economical results. General purpose apparatus which is of valile in such an operation includes devices for remote television, photography, and radiation surveys, and powerful vacuum and steam cleaning equipment. Efficient health physics and radioactive waste disposal provisions are also essential. 

Precise Criticality Determinations In e Solid Homogeneous Assembly, F. Feiner, S. Weinstein, W. C. Oaks, K. V, Cooper (KAPL). 

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Horan, J.R. Gammil, W.P. (1963) The health physics aspects of the SL-1 accident. Health Physics, 9, 177-86. 

SL-1 was a research reactor of the U.S. Army. In the SL-1 accident, a very large fraction of the core was destroyed and most of the primary water was ejected from the primary system. The reactor building filled with steam, which leaked to the environment from gaps in the doors on the operating floor, from open doors in the control room, and from the exhaust on the fan floor. About 10 Ci of noble gas and 80 Ci of iodine were released into the atmosphere. 

A prompt criticality with core disassembly in the far distant future would involve very little radioactivity compared to the present radionuclide inventory in these cores. By the year 2700, nearly all of the current fission product inventory in the cores would have decayed. Also, the amount of fission products produced in a prompt critical excursion is relatively small. For example, the amount of Cs generated in a 10" fission criticality excursion (about the same as the SL-1 accident in the USA) would be 0.044 GBq [31]. 

As indicated in Section 4.3 of Chapter 4, because of the nature of the HCF and its hazardous material inventory, no unmitigated accident scenario will result in radiological exposures at the exclusion area boundary that will approach the off-site EG of 25 rem. Therefore, there are no SSCs required to maintain the consequences of facility operations below the EG (safety-class SSCs). As a result, no TSR Safety Limits (SL) or Limiting Control Settings (LCS) are required for HCF SSCs. Section 4.4 of the chapter addresses those SSCs that perform a significant defense in depth or worker safety function. These safety-significant SSCs are summarized in Table 4.4-1. 

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