ML19263D376
| ML19263D376 | |
| Person / Time | |
|---|---|
| Site: | University of Illinois |
| Issue date: | 03/22/1979 |
| From: | Beck G, Wehring B ILLINOIS, UNIV. OF, URBANA, IL |
| To: | NRC OFFICE OF INSPECTION & ENFORCEMENT (IE) |
| References | |
| NUDOCS 7903290114 | |
| Download: ML19263D376 (2) | |
Text
'lJniversity o" llinois at Uraana-Clampaign Nudear Engineering Program 214 Nnlear Engineering laborof ory u, bono, noen mo' March 22, 1979 (217) 333 2295 Director Division of Reactor Licensing U. S. Nuclear Regulatory Commission Washington, D. C.
20555
SUBJECT:
Abnormal occurrence at the University of Illinois Advanced TRIGA Reactor, License No. R-115.
EVENT On March 21, 1979 the reactor was operated for 6 minutes at 50 kW and for slight iy over 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> between 8 and 250 watts in violation of the Limiting Ladition for Operation with respect to the shutdown margin as given in the Technical Specifications, Section 3.1.h.
The condition was noted at the completion of a control rod calibration and the reactor was shutdown.
Changes were then made to bring the system in compliance with the specification.
DISCUSSION on the previous day, difficulties were experienced with the fast transient rod when it appeared that the control portion was not moving with the drive assembly part of the time. The air was applied and released several times.
A check was then made on the critical rod positions and it became obvious that the rod had remained in the core, indicating a broken connection.
Before removing the rod a check was made on the shutdown margin with this rod and the most reactive remaining control rod completely removed from the core region.
Control rod curves gave a shutdown margin of 654 compared to the limit of 50c for this condition.
Work then progress on the removal of the fast transient rod. At this time it was found that a connection just above the poison section had been broken. The break was in the same place as one that had occurred on September 2,1969 (Report to Director, Division of Reactor Licensing on September 10, 1969).
Although the present rod was designed with a greater cladding thickness in the region where the break occurred with the first rod, it is assumed that fatigue was the cause of the present malfunction.
It is estimated that air has been applied to this rod approximately 20,000 times with an equivalent number of drops back into the core.
A report was made to the members of the Nuclear Reactor Committee and by concensus it was decided to continue normal steady-state operations with the fast transient rod removed.
This was also done in 1969 for about 2 months until a replacement rod was obtained.
Normal checks on critical rod positions were done on the morning of March 21.
This included the operaticn at 50 kW to assure correct fuel temperature readings.
Following this operation measurements were started on the reactivity worths of the remaining control rods. This was to be completed to assure that the shutdown margin was sufficient.
These measurements are made by a series of positive periods obtained by moving the rod to be calibrated in steps from the DN to the UP position.
During this time the remaining rods are kept at the same level so that consistent results can be obtained.
With the rod at its full UP position, the 1
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Page 2 operator in charge notel that the remaining rods were at a position where the shutdown margin could be inadequate.
The reactor was shutdown to recheck the values.
Individual control rod curves for the remaining control rods showed that the shutdown margin was about 304 with the rod being calibrated in the UP position. At this time the initial rod positions at the start of operations were checked and they indicated a shutdown margin of 424 At this juncture, two fuel elements were removed from the G-hexagonal and replaced by graphite dummy elements. The control rod curves indicated that this removed 324 of reactivity and hence increase the margin by the same amount.
Checks were then made with level rod positions and also with the two most reactive rods in the full up position.
The shutdown margin found to be 744 using a 4-rod curi-and 71c using individual contro wcs rod curves with the rod that is assumed to have the greatest reactivity at the UP position.
Checks made the followlag day indicated that this had decreased to about 694 and 614 respectively.
The reactivity worth of all control rods will be measured and a power calibration will be completed before resuning normal operations.
CORRECTIVE ACTION As noted in the discussion, action has already been completed to co rre ct the infraction.
In the future, greater care will be exercised to assure that the limits are not exceeded.
h'ith the present situation, a lower limit for the initial rod positions (cold critical) will be utilized.
This will be checked at the start of each day of operation to assure compliance.
Signed:
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() _ _ s Q d C '
. CIJ'A b t
Gerald P-Beck, Reactor Supervisor 61 tut
[d Ldc UM Bernard W. h'ehring, Act. Chtirman Nuclear Reactor Committee CC:
Region III, Office of Inspection and Enforcement