ML20248C608
| ML20248C608 | |
| Person / Time | |
|---|---|
| Site: | General Atomics |
| Issue date: | 08/03/1989 |
| From: | Asmussen K GENERAL ATOMICS (FORMERLY GA TECHNOLOGIES, INC./GENER |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 67-1420, NUDOCS 8908100101 | |
| Download: ML20248C608 (5) | |
Text
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CERERAL ATORNCE l
August 3, 1989 67-1420 Document Control Desk U.S. Nuclear Pegulatory Commission Washington, D.C.
20555 Sabject:
Docket No. 50-163:
Reactor Facility License No.
R-67; Reportable Occurrence Gentlemen:
At approximately 1630 hours0.0189 days <br />0.453 hours <br />0.0027 weeks <br />6.20215e-4 months <br /> on Wednesday, July 26, 1989, General Atomics (GA) notified the Region V office of the Nuclear Regulatory Commission by telephone of an occurrence involving GA's TRIGA Mark F reactor (License R-67) which had occurred earlier that day.
This report was made to Mr.
Greg Yuhas and followed up with detailed reports to Mr.
Mike Cillis the next morning.
The occurrence was report-able not because of any release of radioactivity or person-nel exposure above permissible levels, but rather because of the apparent release (albeit small) of fission products from a fuel element.
This written report is being sub-mitted within 10 days as required by the applicable license, as amended.
The reportable occurrence is described in detail below.
Sequence of Events The GA Mark F reactor is currently in an around-the-clock operating mode to perform in-pile irradiations on direct conversion (thermionic) devices.
On Monday, July 24, 1989, a scheduled shutdown of the reactor was completed.
The purpose of the shutdown had been to perform underwater neutron radiographic examination of the thermionic devices, install a new device, and perform scheduled maintenance and upgrade activities associated with reactor systems.
At 0913 on Wednesday, July 26, a senior reactor operator (SRO) started to take the reactor to full power (1.5 Mw) in order to begin the first of many reactor runs scheduled during the week for neutron radiography of the thermionic devices; typically, ruch runs consist of operating the reactor at full power for up to two hours per run.
Upon reaching full power at 0923, the SRO noticed that readings on the continuous air monitor (CAM), which monitors the air
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i directly above the core region, were rising rapidly, E k 8908100101 890803 i
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. exceeded the alert setpoint (5,000 CPM) quickly, and showed no indication of stabilizing or showing a downward trend.
In addition, the Ar-41 stack monitor was also showing higher than normal count rates.
The SRO initiated two actions immediately; first, he evacuated and sealed off the reactor room, and second, he notified the Deputy Physicist-in-Charge.
Upon noticing the CAM trends, the Deputy Physicist-in-Charge immediately not ified the Physicist-in-Charge.
At 0933, the Physicist-in-Charge ordered the neutron radiography run terminated and the reactor scrammed.
All neutron radiography runs were halted at that time pending an investigation of the higher than normal airborne activity levels.
The Reactor Safety Committee and the Manager of Health Physics were also promptly notified.
Health Physics personnel at this time took the precaution-ary measure of activating the emergency air samplers around the facility to detect any airborne activity outside the reactor building.
The filter paper which collects particulate in the air that is sampled by the CAM was then removed and analyzed by high-resolution gamma-ray spectroscopy.
Fission product activity was detected on the filter with the primary signa-tures being from Rb-89 (t
= 15.1 min.), Cs-138 (t 32.2 min.) and Ba-139 (t
= 82.9 min).
I n a d d i t i o n,2 "
v v2 y
analysis of an activated charcoal filter installed on a second CAM which was undergoing testing at the time showed the presence of I-131, Xe-133 and Xe-135.
Analysis of reactor pool water during subsequent reactor runs to determine the source of the leak showed the presence of varying low-level activities from fission product isotopes, including I-131, Xe-133, Xe-135, Cs-137 and Cs-138, in addition to the activation products normally present in water.
In order to determine the source of these fission products (e.g., damaged clad on fuel element (s) or a recurrence of the tramp uranium problem previously encountered at the facility from 1978-1980), the Physicist-in-Charge instituted a series of reactor runs at or near full power with fuel element substitutions in between each run in order to determine if one or more elements were the source of the observed fission product activity.
The first set of elements that were tested using this process were seven new IEU elements with high weight percent uranium, which were installed in the core following the fuel inspection about i
three weeks earlier.
The instrumented elements (with thermocouple for fuel temperature measurements) were tested next because of the possibility of a pin-hole leak in the water-tight brazed seal inside the thermocouple l
1 l
I i
- leadout tube.
Both tests yielded negative results.
The focus of the tests was then shifted to the FLIP (70%
enriched) fuel elements that were installed in the Mark F reactor in 1973.
When the fission product activity was detected on July 26, 1989, 83 of the 93 fuel elements in the core (including the fuel follower control rods used in the Mark F) were FLIP fuel elements.
The tests with the FLIP fuel elements consisted of substituting elements from storage for a group of about 10 FLIP elements in a region of the core, running the reactor near full power, and observing the trend in activity on the CAM.
Prior to this, an unsuccessful attempt was made to use a " sniffer" techni-que in lieu of the substitution technique.
The " sniffer" technique is an arrangement that makes use of a CAM to
" sniff" the fuel in-core, in small groups of elements, for released gaseous activity to determine the location of a leaking element or group of elements.
1 The substitution tests resulted in the identification of FLIP fuel element number 6368 as the source of the fission product activity.
While the group of 10 elements, which included this element, was out of the core, the observed CAM activity was near normal.
The source of the fission product activity was then determined to be the single element number 6368 by employing the same substitution technique one element at a time.
Element number 6368 was removed from service on July 29, 1989.
Analysist History of FLIP Fuel Element 6368 Fuel element 6368 was manufactured by GA in 1971.
It was first put into service in the GA TRIGA Mark III reactor (R-100) in June 1971.
It was transferred for use in the Mark F reactor (R-67) in November 1973, and has been in use in the Mark F ever since.
It has been installed in the D-ring (location D15) since the inception of around-the-clock operations in January 1985.
This particular element has not been subjected to any unusual operating conditions since its manufacture.
It was used in normal steady-state and pulsing operations performed with the Mark F since 1973.
FLIP fuel has performed exceptionally well in high duty cycle operations at GA and elsewhere, and GA is of the opinion that this failure was an isolated case of a small pin hole which apparently developed after nearly 18 years of use.
Exactly where, when, or whether such failures will occur can never really be predicted.
As required in the applicable technical specifications, GA inspects its fuel annually for mechanical damage, and any
..o
- fuel elements exceeding bending and elongation requirements of tha technical specifications are removed from service, as are elements with known clad defects.
Fuel element 6368 was last inspected-on June 26, 1989, and passed all mechanical damage tests.
Radioactivity Levels and Personnel Exposure While the readings on the continuous air monitor and the stack monitor were both higher than normal for short periods of time, the airborne concentrations of radioac-tivity remained low.
For example, the concentration of the most prevalent radioisotope in the air immediately above the reactor pool, the location of highest concentration, remained less than 2% of its maximum permissible concentra-tion (MPC) for controlled areas.
However, this concentra-tion only persisted for_a short time, i.e.,
about 15 minutes.
The MPC's were established based upon exposures for 40 hours4.62963e-4 days <br />0.0111 hours <br />6.613757e-5 weeks <br />1.522e-5 months <br /> per week for 13 weeks.
Thus, the maximum airborne concentrations experienced e.uring this occurrence wera actually much less than 2% of MPC for controlled areas w'ca the relative duration of the occurrence is taken into consideration.
As a result of dilution, the airborne concentration elsewhere in the reactor room was, of course, much less than that just above the reactor pool.
The stack monitor filter samples showed no detectable contamination, confirming the performance of the High Efficiency Particulate Air (HEPA) filter system.
Similarly, the emergency air samplers near the TRIGA facility showed no detectable radioactivity.
Gaseous fission products released from the TRIGA facility stack included Kr-85, Kr-85m, Xe-1~33, Xe-135, I-131 and I-125.
As mentioned above, their maximum concentrations in the reactor room were much less than 2% of MPC for con-trolled areas.
While the MPCs applicable at our site boundary (i.e., MPCs for uncontrolled areas) are lower than the MPCs for controlled areas by a factor of 33 to 90, depending upon the radioisotope, the corresponding dilution factor is in excess of 90.
Thus, it is concluded that the concentrations of fission gases at our site boundary were also much less than 2% of the applicable MPCs.
This occurrence resulted in no external radiation exposure to the personnel in excess of that received during normal operations, as evidenced by the area monitor readings.
Similarly, the internal radiation exposure of personnel due to this occurrence was negligible, as evidenced by in-vivo total body count results.
These results are as expected
l
,... based upon:
the very low concentrations of airborne ~
i radioactivity, the short half-lives of the airborne radioisotopes,'the immediate evacuation and sealing of the reactor room, and the use of an air hood for the single entry by one persen for limited duration during the investigative phase of this occurrence.
corrective Actions The source of observed fission product activity was found to be fuel element 6368.
This fuel element has been removed from the core and placed in spent fuel storage.
Post-irradiation examination of the element is not planned at this time.
The element has been replaced in the core by.
an LEU element with high weight percent uranium.
with the concurrence of the Safety Committee, normal reactor opera-tions, which were terminated on July 26, were resumed on July 31, 1989.
Both the continuous air monitor and reactor pool water will continue to be monitored for fission product activity on a weekly basis for two weeks after resumption ~of operations.
This will provide further confirmation tho.t the release of fission products has l
ceased following removal of fuel element 6368 from service.
1 We trust you will find the above description of the report-able occurrence and corrective action satisfactory.
If you have any questions concerning this occurrence, please contact me at (619) 455-2823 or Dr. Junaid Razvi at (619) 455-2441.
Very truly yours, Keith E. Asmussen, Manager Licensing, Safety and Nuclear Compliance KEA/JR/mk cc:
Mr. John B. Martin, Administrator, NRC Region V l
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