Information Notice No. 83-66, Supplement 1: Fatality at Argentine Critical Facility
SSINS No: 6835
IN 83-66, Supp 1
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, DC 20555
May 25, 1984
Information Notice No. 83-66, SUPPLEMENT 1: FATALITY AT ARGENTINE
All nuclear power reactor facilities holding an operating license (OL) or
construction permit (CP) and nonpower reactor, critical facility, and fuel
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
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
IN 83-66, Supp 1
May 25, 1984
Page 1 of 3
REPORT OF THE ACCIDENT THAT OCCURRED TO THE
CRITICAL ASSEMBLY RA-2 REACTOR ON SEPTEMBER 23, 1984
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.
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
(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.
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