Information Notice No. 83-66, Supplement 1: Fatality at Argentine Critical Facility

                                                           SSINS No: 6835  
                                                           IN 83-66, Supp 1 

                                UNITED STATES
                            WASHINGTON, DC 20555
                                May 25, 1984

Information Notice No. 83-66, SUPPLEMENT 1:    FATALITY AT ARGENTINE 
                                                  CRITICAL FACILITY 


All nuclear power reactor facilities holding an operating license (OL) or 
construction permit (CP) and nonpower reactor, critical facility, and fuel 
cycle licensees. 


This information notice is a supplement to Information Notice No. 83-66, 
issued on October 7, 1983. It is expected that nonpower reactor, critical 
facility, and fuel cycle licensees will review the information for 
applicability to their facilities. No specific action or response is 

Description of Circumstances: 

The Argentine National Atomic Energy Commission [Comision Nacional de 
Energie Atomica, (CNEA)] provided the NRC Office of International Programs 
with the written report documenting the results of the Commissions 
investigation and evaluation of the September 23, 1983 RA-2 accident near 
Buenos Aries. A translated copy of the CNEA report is attached. 

No response to this information notice is required. If you have any 
questions regarding this matter, please contact the Regional Administrator 
of the appropriate NRC Regional Office or this office. 

                                   Edward L. Jordan Director 
                                   Division of Emergency Preparedness 
                                     and Engineering Response 
                                   Office of Inspection and Enforcement 

Technical Contact:  J. E. Wigginton
                    (301) 492-4967

1.   CNEA Report
2.   Figure 1 Fuel Element 
3.   Figure 2 RA-2 reactor facility
4.   Figure 3B Modified core configuration 
5.   List of Recently Issued IE Information Notices


                                                           Attachment 1    
                                                           IN 83-66, Supp 1 
                                                           May 25, 1984    
                                                           Page 1 of 3     


1.   Description of the Installation 

The RA-2 is a critical assembly reactor operating at 0.1 watt of rated 
power. It has been in operation since 1966 and is used to conduct 
experiments with various core configurations. For experiments, the core 
assembly can be relocated and/or modified. The core consists of MTR-type 
fuel elements and control rods. The fuel elements are MTR-type, 90% enriched 
uranium and consist of 19 fuel plates (see Figure 1). The control rods 
consist of fuel elements in which four of the fuel plates are replaced with 
two cadmium plates. Demineralized water is the moderator; and demineralized 
water and graphite constitute the reflector. 

The installation is shown in Figure 2. 

2.   The Accident 

On Friday afternoon September 23, 1983, a modification of the core 
configuration had been scheduled so that an experiment using the pulsed 
source technique could be conducted. Figure 3A shows the initial core 
configuration and Figure 3B shows the configuration as it was to be 
modified. The operating procedure requires the complete removal of the 
moderator. However, this was only partially done. A short time afterwards, 
when the exchange operations were being carried out, a criticality excursion 

The operator, who was the only person present in the containment, was 
fatally exposed; other persons, who were in the control room and other 
adjacent premises were exposed, but to a much lesser degree. 

3.   Analysis of the Accident 

The President of the Comision Nacional de Energia Atomica (CNEA) (National 
Atomic Energy Commission, Argentine) appointed an ad hoc commission to 
investigate the accident. The conclusions of this commission indicate that 
the basic causes of the accident were as follows: 

(a)  The moderator was not completely removed from the core before the core 
     configuration was modified. 

(b)  Two fuel elements, which should have been removed, were left inside the
     reactor in contact with the graphite reflector. 

                                                            Attachment 1   
                                                            IN 83-66 Supp 1 
                                                            May 25, 1984   
                                                            Page 2 of 3    

(c)  Sequences were performed to change the positions of fuel elements; this
     decreased the subcriticality of the system 

(d)  Two fuel elements of 15 plates were inserted without the corresponding 
     cadmium control plates. The second fuel element was found to be only 
     partially inserted, wherefore it is deemed that its insertion caused 
     the accident. 

(e)  All of the operations were performed without the concurrence or 
     presence of a safety official or the operations supervisor. 

The evolution of the power and the magnitude of the released energy are 
still being investigated. Notwithstanding, it is estimated that the 
excursion was about 10 megajoules, which is equivalent to approximately 3X 
10-17 fissions, which occurred during a few tens of milliseconds. 

Also, the ad hoc commission identified shortcomings in the installation and 
operational procedures, as well as in the way approval was obtained and 
supervision of the experiments was carried out. Because the reactor had been
operating for so many years without incident, an excessive degree of 
confidence had been fostered in regard to minor operations. In addition, 
other more urgent requirements of the nuclear program took precedence. 

4.   Dosimetric and Medical Evaluation 

The dosimetric evaluations were based on (1) measurements of Na-24 to 
determine whole-body dose and of P-32 from samples of hair, (2) the gamma 
spectrometry analysis of the activated metal elements carried by the 
affected persons, and (3) the readings of the radiothermoluminescent and 
criticality dosimeters installed in the building. 

The doses received by the exposed persons are as follows: 

(a)  The operator received a lethal, absorbed dose of about 2000 rads of 
     gamma radiation and 1700 rads of neutrons, which precluded any 
     effective therapeutic measures. The amount of P-32 (resulting from the 
     sulfur activation) found in samples of body hair and the operator's 
     woolen clothing, as well as the clinical manifestations, showed that 
     the exposure had been very nonhomogeneous; the doses received on the 
     upper right side of the body were higher than those elsewhere. 
     Approximately 25 minutes after the accident, the operator showed signs 
     and symptoms (vomiting, migraine headache, and diarrhea) of acute 
     exposure over the entire body. His condition became worse the next day 
     when he suffered gastrointestinal disorders. Then early on September 
     25, neurological and respiratory disorders (radiopneumonitis in the 
     right lung) and edema of the right hand and forearm manifested 
     themselves. Death occurred at 16:45 on the same day. 

                                                            Attachment 1   
                                                            IN 83-66 Supp 1 
                                                            May 25, 1984   
                                                            Page 3 of 3    

(b)  Two persons in the control room at the time of the accident received 
     doses of about 15 rads of neutrons and 20 rads of gamma. At present, 
     they are under medical supervision and have not shown any clinical 

(c)  Five persons received a dose ranging from 4 to 8 rads of neutrons and 
     7 to 10 rads of gamma. They also are under medical supervision. 

(d)  One person received a dose of about rad of neutrons and 0.4 rad of 
     gamma. Nine other persons received doses below 1 rad. 

(e)  The doses received by the affected personnel also are being measured by
     biological dosimetry techniques. 

Page Last Reviewed/Updated Thursday, March 25, 2021