ML19270G962
| ML19270G962 | |
| Person / Time | |
|---|---|
| Site: | University of Virginia |
| Issue date: | 06/15/1979 |
| From: | Shriver B VIRGINIA, UNIV. OF, CHARLOTTESVILLE, VA |
| To: | Reid R Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 7906220239 | |
| Download: ML19270G962 (3) | |
Text
f f
p..-
/
UNIVERSITY OF VIRGINIA
(
SCHOOL OF ENGINEERING AND APPLIED SCIENCE v
CH AR LOTT ESVILLE. 22908 iV D EP A RTM ENT OF NUCLEAR ENGIN EERING AND ENGINEERING P H YSICS TELEPHONE:
804 924 7136 REACTOR F ACI LITY June 15, 1979 Director, Division of Reactor Licensing U. S. Nuclear Regulatory Commission Washington, D. C. 20546 ATTN:
5fr. Robert W. Reid, Chief Operating Reactor Branch d4 Re:
License No. R-66, Docket No. 50 Reportable Occurrence
Dear 5fr. Reid:
This letter is to inform the NRC of a reportable occurrence at the University of Virginia Reactor Facility as required by Section 6.5 and 6.7 of the UVAR Technical Specifications.
(The Technical Specifications use the obsolete term " abnormal occurrence" instead of the present term " report-able occurrence.")
Specifically, on June 13, 1979 it was determined that one fuel element was releasing small amounts of fission products to the reactor coolant. No re-lease of radioactive caterials to the environment was detected and the health and safety of the public or operating personnel were not affected by this occurrence.
On June 8, 1979 a routine, weekly analysis of the UVAR react e pool water was made. This analysis indicated the presence of fission products in the reactor coolant. A second analysis,,erformed the same day confirmed these results. The level of activity measured at 1:20 P51 for three of the fission product isotopes used to detect leaking fuel elements are listed in the following table:
Specific Activity Isotope fuCi/ mil
-6 I-131
< 1.7x10 I-133 1.9x10- 5%
-5 Xe-135 1.5x10 5%
These measured activities for iodine 131 are below the limits in 10 CFR Part 20 for restricted areas and the activity used to determine that fission products are being released from a fuel element. No increase in the airborne background activity was observed at any time.
Due to the low fission product activity measured it was not clear that it was a result of a leaking fuel O
element. However, these fission products are not normally observed in the Q
reactor coolant and were not observed in the previcus weekly sample, g
2348 295 7906220,2.39
f
- Y The reactor was shut down at 3:37 PM on Friday, June 8, 1979.
Due to the low levels of activity measured in the water and the fact that no increase in airborne activity was detected, no additional measurements were made until
>bnday, June 11, 1979.
At 8:00 AM on hbnday, June 11, 1979 the reactor pool water was again analyzed for the presence of fission products. The results for three c' the isotopes are shown in the following table:
Specific Activity Isotone (UCi/ml)
I-131 4.5x10~
21%
I-133 4.6x10~ 26%
Xe-135
<2.2x10~
The iodine activities were within 20% of the lower detectable limits and xenon was below the detectable limit. Based on these low activities it was concluded that additional reactor operation was necessary to determine whether fission products were being released from a fuel element and, if so, to locate the leaking element.
The reactor was taken to power at 9:02 A31 on June 11, 1979 and operated until 8:49 AM on June 12, 1979.
Samples of the pool water were taken at noon, 5:30 PM and 8:40 PM on June 11, 1979 and at 8:47 AM on June 12, 1979. The highest activities measured during this period are shown in the following table:
Specific Activity (pCi/ml)
Isotope 8:40 PM on 6/11 8:47 AM on 6/12 I-131 1.3x10-6 36%
l'. 6x10-6 s
-6
-6 I-133 7.1x10 9%
9.9x10 7g
-6 Xe-135 4.0x10 11%
1.0x10 5%
~
The observed increase in fission product activity indicated that there was a continuing source of fission products, most likely from a fuel element. Water samples were taken from directly above each of the fuel elements in the core in accordance with the procedure for detecting leaking fuel elements. These sam-ples were counted on June 12, 1979 and the results reviewed on June 13, 1979.
The fission product activity above one of the elements (AN-22) was significantly higher than above the other elements. Based on this data it was concluded that one fuel element (AN-22) was releasing low levels of fission products to the re-actor coolant.
Fuel element AN-22 was removed from the core on June 13, 1979 and moved to the fuel storage rack at the north end of the reactor pool. Nater samples taken directly above fuel element AN-22 and from the bulk pool confirmed that higher fission product levels were associated with element AN-22.
A visual check of 2348 296
n the element did not reveal any obvious signs of fuel element failure.
Fuel element AN-22 was fabricated by Babcock and Nilcox and delivered to the University of Virginia in December 1958. The original fuel loading was 165.1 grams of uranium-235. Approximately eight percent of the uranium-235 had undergone fission when the fission product activity was detected in the reactor pool.
Action has been taken to determine the cause of and correct the source of the fission product activity in the coolant as discussed above. Additional pool water measurements will be taken and analy:ed to confirm that the source of fission products has been removed from the core.
Nater additions to the reactor pool have been less than 75 gallons per day during periods of reactor utilization includine the period when low level fission product activity was detected. These losses are primarily due to evaporation. Since there was no liquid release from the reactor pool and no increase in the radioactivity in the reactor room air was detected it is con-cluded that there was no measurable release of fission products to the en-vironment.
The Nuclear Regn'
,ry Commission Region II Compliance Officer 0Ir. S. A.
Elrod) was informed of the reportable occurrence and corrective actions by telephone on June 13, 1979.
Sincerely, U/\\
Bryk L. Shriver, Director Reactor Facility BLS/ph cc:
Mr. James P. O'Reilly, Director U. S. Nuclear Regulatory Commission Region II, Atlanta, GA 30303 Mr. Steve Ramos Division of Reactor Licensing U. S. Nuclear Regulatory Commission Washington, D. C.
Mr. T. G. Williamson Mr. J. P. Farrar Reactor Safety Committee