ML19340B153
| ML19340B153 | |
| Person / Time | |
|---|---|
| Site: | University of Illinois |
| Issue date: | 10/16/1980 |
| From: | Beck G, Milavickas L ILLINOIS, UNIV. OF, URBANA, IL |
| To: | John Miller Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML19340B154 | List: |
| References | |
| NUDOCS 8010210530 | |
| Download: ML19340B153 (2) | |
Text
'
or Nudear Engineering Program l.
214 utear Engiaeering Laborotory Urbano, ifHnois 61801 10-16-80 (217) 333 2295 Jim Miller Standardization 6 Special Projects Branch U..S. Nuclear Regulatory Commission l
Mail Stop-Phillips 228 Washington, D.C.
20555
Dear Mr. Miller:
l University of Illinois Advanced TRIGA Reactor l
Facility License R-115 l
Docket No. 50-151
SUBJECT:
Request for permission to utili:e an alternate start-up channel.
I This request is to use a start-up channel in place of the channel that is described in the Safety Analysis Report, August 1967, and that specified in Section 3.5 of the Technical Specifications. The present channel uses a fission counter with a circuit to operate a 5-decade l
log meter on the console. This system has a bi-stable which prevents the withdrawal of the manually operated control rods if the neutron count rate is less than a set value.
Technical specifications requires a minimum count of 1 per 'second although the set point has been at 4 countes per second.
The replacement would be a BF whose output is fed to a scaler where either a continous count may be obt$ined or it can be set to obtain counts.
for a preset time. The BF tube would be placed near the core where a 3
counting rate of 20-30 counts per second is obtained with all control rods inserted.
For the initial start-up each day, a prescribed procedure would be followed to assure proper detection of the neutron flux as the contol rods are withdrawn. The proposed procedure is attached. However, as a summary the initial step would be'to insert the BF. tube in a designated position and determine the counting rate.
The fast tr$nsient rod would then be withdrawn (air drive) and a second counting rate would be determined to indicate the change of reactivity.
Two of the four manually operated rods -
would then be withdrawn to a position where a critical condition is expected with all four rods at this position.
A third timed count rate would be i
determined at this juncture.
If indications -are satisfactory, the remaining rods would be withdrawn until power increases are noted on the two compensated ion chambers whose output is recorded. After an indicated power level of around 15 watts, the power would be stabilized and the BF tube would be 3
removed from the core region.
All of the above counting rates would be recorded in the daily log book for a comparison on a daily basis.
The request is made due to a malfunction of the start-up channel which has been traced to either the fission chamber or the cable connection at the chamber. The most probable cause 'is a break-'down of the insulation in this To verify thisl the resistance between the signal lead and the ground area.
f connectiogwasmeasuredwithameg-ohmbridgecircuit. A resistance of around 10 ohms was measured compared to an expected value of 109 ohms.
j i
seiong
page 2-The' remainder of the circuit was checked with a pulse generator and found to operate satisfactorily. When the chamber is hooked to the counting circuit, a fluctuating comt rate of 100 to 10,000 counts per second is obtained on the meter with the reactor shutdown. This is attributed to noise from possible arcing at the lower connection.
When this was recogni:ed, inquiries were made for obtaining a fission chamber with the'same basic characteristics. Through normal channels, it would' appear that the minimum time for a replacement would be 3-4 months.
Work is also required to remove a weld from the water tight cover of the fission chamber, to remove and replace the cable in the ektension tube, and then to re-weld the water tight cover. Measurements of the dose rate at the surface of the cover were about 150 millirem / hour. Thus it will be necessary to take precautions to limit the dose to individuals doing the maintenance.
Additional time could help in reducing these doses. Thus, even if a fission chamber is located in a shorter time, it is estimated that the minimum time for a replacement would be 1-2 months.
The shutdown of the reactor would be detrimental to present utilization.
l This includes the education and training of Nuclear Engineering students, numerous tours for outside groups, research on nuclear pumped lasers, and l
irradiation of samples for activation analysis for the Environmental Research l
Institute and the State Geological Survey.
Both of these groups are located on the University of Illinois at Champaign-Urbana Campus. These activities use the reactor approximately 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br /> per week.
l EVALUATION OF, CHANGE The sensitivity of the alternate start-up channel is considerably greater than the present channel. The present counting rate with all control rods inserted is from 4-8 counts per second.
Because of these lower rates and because the output is on a log scale meter,.it is difficult to note l
the change when the first rods are withdrawn.
With the alternate system, l
a distinct change can be noted with the removal of the first control rod.
l (Reference is made to the estimated counting rate increases in the procedure.)
The interlock to prevent contol rod withdrawal would be by-passed.
However,. it is felt that the written procedure that requires specific counting l
rates during initial control rod withdrawal is sufficient to insure that j
fission neutrons are present with the use of an external source. These counts will also verify an increase in the multiplication factor as the control rods are withdrawn. The BF tube would be withdrawn at a low power level 3
to increase its lifetime.
With the present system, the meter reads' full scale at a power level of about -10 watts. Thus it is essentially no longer operable above this power'1evel.
Signed:
AAAN.
Gerald. P. - Beck, Reactor Supervisor ke e37 80 Approved:
'Npelear Reactor Committee Date:
w+
d L. R. Stilavickas, Chairman
.