ML20034H004
| ML20034H004 | |
| Person / Time | |
|---|---|
| Site: | University of Michigan |
| Issue date: | 03/05/1993 |
| From: | Burn R MICHIGAN, UNIV. OF, ANN ARBOR, MI |
| To: | Vick L NRC |
| References | |
| NUDOCS 9303150052 | |
| Download: ML20034H004 (3) | |
Text
NUCLEAR REACTOR LABORATORY THE UNIVERSITY OF MICHIGAN phoenix Memorial Laboratory i
Ford Nuclear Reactor Ann Arbor, Michigan 48109-2100 (313) 764-6223 March 5, 1993 U.S.
Nuclear Regulatory Commission Larry Vick Operator Licensing Mail Stop 10D18 Washington, D.C.
20555 Re: Ford Nuclear Reactor Operator Examinations, f
December 15 - 16, 1992 8
i
Dear Mr. Vick:
In your examination report related to the referenced operator examinations, you stated that:
"A generic weakness was identified during the operating exam concerning the difficulty that each of the candidates exhibited when asked to explain the relationship between reactor power instrument readings and actual reactor power."
We are concerned about this statement, because the specific weakness was not identified to us, and we cannot determine what it is from the statement in the examination report.
We have discussed the your comment with our staff and came up with ideas such as the following, but we are not truly sure what you meant:
1.
You did not feel that performance of the calorimeter at one megawatt to determine thermal power was applicable to two megawatt thermal power., and 2.
You felt that some instrument'in the control room should read exactly 2.0 megawatts at all times Enclosed is a memorandum that we distributed to the operations staff related to thermal and instrument power.
We feel that each operator was aware of the content of the memorandum before the examination, though individually they may not have been able to express their knowledge as clearly and concisely.
Would you please clarify the meaning of your statement?
Sincerely, D.
((
B R
9 Reed R.
Burn 0
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NUCLEAR REACTOR LABORATORY THE UNIVERSITY OF MICHIGAN
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2301 Bonisteel Boulevard Ann Arbor, Michigan 48109-2100 (313) 764-6223 Memorandum To:
Reactor Operations Staff From:
Bob Burn Date:
February 15, 1993
Subject:
Relationship Between Reactor Power Instrument Readings and Actual-Reactor Power.
During the operator licensing examinations, December 15 - 16, 1993, the NRC examiners identified a " generic weakness" as follows:
"A generic weakness was identified during the operating exam concerning the difficulty that each of the candidates exhibited when asked to explain the relationship between the reactor instrument readings (in % power) and the actual reactor power (in megawatts thermal)."
We received no clarification of what the eraminers meant by this weakness.
It may have been a misunderstanding between1the examiners and the candidates as.to exactly what they expected for an answer.
For startups following reactor shutdowns in excess of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />,.
reactor power is raised to an. indicated power level of'one megawatt.
and a calorimeter is performed in accordance with Operating Procedure 106 to determine absolute thermal power.
The calorimeter is conducted by securing secondary cooling and allowing the energy of the reactor to heat up the fixed. volume of pool water.
Reactor power is the product of the-pool mass (approximately 50,000 gallons which must be converted to pounds mass), the specific heat of water (approximately 1.0 Btu /lbm a F for water between freezing and boiling), and'the heat-up-rate of the pool water in aF/hr).
This product is Btu /hr which is converted to megawatts by the factor 3.-41x106 Btu /hr-Mw.
While this is what we do in theory to calculate thermal power, we actually use precalculated tables'of power to heat-up-rate and multiply the measured heat-up-rate by a conversion factor, for example 1 Mw/8.65 aF/hr for a full pool, to determine power.
Based on this measured power level, we adjust the linear 11evel setpoint up or down so that actual power is one megawatt.
For example, if the measured power were determined to'be 1.05 Mw with-the' linear level setpoint at 100 %,
the setpoint would be_ adjusted down to 95.2 % so that actual power would be one.Mw.
1
Relationship Between Reactor power Instrument Readings and Actual Reactor power l
February 15, 1993 i
At this point, power is raised to two megawatts and the log N and j
power ranges A and B can be adjusted using Operating Procedure 107 to read 100 % and 2.00 respectively.
As xenon builds up in the core, the shim-safety rods are withdrawn and flux tends to shift upward.
The ion chambers are located above the top of the core. They will tend to see an increasing flux and provide an increasing indication as xenon builds up.
They wi)) "think" that power is increasing.
The automatic control system will "think" that power is increasing and will insert the control l
rod to bring power back down to the setpoint.
Actual power will j
decrease.
We recognize this because core differential temperature, T2 -Ts, will decrease.
When core differential temperature reaches the lower operational limit, typically 13.4 aF, the linear level 4
setpoint must be increased to increase actual power and maintain core differential temperature in range, typically 13.4 - 13.8 *F.
As xenon builds up, the linear level setpoint will be adjusted higher and higher.
We have limits of 95 - 105 % on the setpoint so at some time, the chamber must be moved away from the core to reduce i
indicated power from 105 % to 95 % without changing actual power.
t k
In Operating procedure 101, we also have set range limits on the.
other ion chamber channels.
As the xenon-induced flux shift is occurring, they may need to be adjusted to be kept in operational i
range:
Log N 80 - 200 %
Safety A and B 1.90 - 2.10 In summary, once thermal power has been determined by the l
calorimeter, we keep track of thermal power by observing core differential temperature.
If core differential temperature is low.
- [
z the linear level setpoint must be increased (i.e.,
indicated power must be increased).
If core differential temperature is too high, j
linear level setpoint must be decreased.
If core differential e
temperature is within its acceptable operating range, the ion
]
chambers need not be adjusted if they are within their acceptable j
operating ranges.
i
)
We are almost never at exactly two megawatts thermal power.
It would not be reasonable to continually adjust power to provide an exact value of core differential temperature.
Because of tihe lag time between power adjustment and water temperature response, fine ~
l tuning and maintaining a fixed value would be impossible.
i t
Reactor power, once the cooling system is in operation, is the j
product of mass flow rate (1bm/hr), specific heat, and core differential temperature (oF) with conversion from Btu /hr to Mw.
J r
i It could be that the NRC examiners were looking for the relationship j
i between core different.
,1 temperature and power during operation and the need to adjust indication to produce the proper value of core differential temperature.
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