ML19296B226
| ML19296B226 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 01/23/1980 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19296B219 | List: |
| References | |
| NUDOCS 8002200290 | |
| Download: ML19296B226 (3) | |
Text
pa arco UNITED STATES y ' )#q( h NUCLEAR REGULATORY COMMISSION
/.
W ASHINGTON, D. C. 20S55 3,
s j SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATI0fl SUPPORTING AMENDENT NO. 66 TO PROVISIONAL OPERATING LICENSE NO. OPR-21 NORTHEAST NUCLEAR ENERGY COMPANY, ET AL MILLSTONE NUCLEAR POWER STATION, UNIT NO. 1 DOCKET NO. 50-245
1.0 INTRODUCTION
By letter dated Aoril 9,1979, as supplemented September 24, 1979, Northeast fluclear Energy Company (the licensee) requested a Technical Specification Change related to the setpoint adjustment for the Average Power Range Moni-tors (APRM'S) for Millstone Unit No. 1.
That September 24, 1979 submittal also pretosed a Maximum Total Peaking Factor (MTPF) Technical Soecification lirit for the 8X8 retrofit Exxon fuel assemblies inserted into the core during Reload 6.
(Authorized by Amendment No. 61 to Provisional Operating License flo. DPR-21 for the Millstone fluclear Power Station, Unit No. 1, dated May 29, 1979).
This value was t;nintentional-ly omitted from the licensee's reload submittal dated March 5,1979.
Our discussion and evaluation of these proposed Technical Specification changes follow.
2.0 DISCUSSION The staff raised a question about the possibility of causing indications that could confuse the reactor operator.
By letter dated September 24,1979, the licensee proposed additional restrictions to the Millstone 1 Technical Specifi-cation responsive to the Nuclear Regulatory Commission concern.
During normal operation,the actual core peaking factors might exceed the design values. This variance can be accommodated by reducing the APRM setpoints to re-tain the same desired " margin to trip."
The " margin to trip" can be reduced either by lowering the trip setpoint or by increasing the indicated power level.
From the viewpoint of reactor operator performance, causing a power monitor to indicate a level that is different from the true power level introduces an addi-tional source of possible operator confusion.
IEEE Standard 279 Section 4.20 specifies the design principle that indications that could be confusing to the reactor operator should be minimized.
Because the APRM setpoints are flow-biased, recalibration involves re-adjusting several parameters with external test equipment.
Our review of the calibration procedure and discussion with operating personnel indicated that re-calibration requires about one hour for cach of the six APRM channels.
The design does not lend itself to a simple re-calibration procedure.
8002200
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, 3.0 EVALUATION 3.1 APRM The present APRM instrumentation channels have gain adjustments to adjust the channel response toward a more accurate indication with respect to true power as determined by a hea. balance.
Routine use of the gain adjustment to cause the channels to read less accurately is not consistent with the general de-sign principles of IEEE 279.
When full power and temperature equilibrium are attained, setpoint re-adjust-ments are very intrequent.
We have determined that use of the APRM gain ad-justments to maintain an adequate " margin to trip" during full power operation is not a justifiable deviation from the general principles.
During a reactor startup and approach to full power, the APRM setpoints may need to be re-adjusted several times.
To require a lengthy six-hour calibration pro-cedure several times during approach to full power is not reasonable nor in the best interest of safety.
We have determined that, within certain limitations, use of the gain adjustment could be allowed during an approach to full power.
The limitations appropriate for allowing the pin to be used to maintain the APRM " margin to trip" are as follows:
(1) gain edjustment should be used only when the reactor is less than 90% of rated power; (2) the magnitude of such adjustments should be less than 10% of rated power; (3) any intentional inaccuracy of the APRM channels should be made obvious to the reactor operations staff at all times.
Appropriate log entries are to be made for each such gain adjustment.
Each affected APRM in-dicator should be marked in an obvious manner to identify the offset between true power and the power level indicated by the APRM instrumentation.
We have determined that deviation from the prescribed APRM calibration pro-cedures during full. power operations is not consistent with the general prin-ciples of IEEE 279.
However, during reactor startup and approach to full power, the APRM channel gain adjustments may be used, within limitations, to change the " margin to trip." The limitations involved are enumerated above. Accord-ingly, we find, the APRM Technical Specification changes submitted by the licensee's letter dated September 24, 1979 acceptable.
3.2 MTPF On September 13, 1979 the licensee discovered that the Maximum Total Peaking Factor (MTPF) for 8X8 fuel was unintentionally not identified in the Technical Soecifications used to ad.iust the APRM trio and rod block setooint downward when power peaking is high (Licensee Event Report R0-79-25 IT).
A review of operating data verified that the proposed Technical Specification limit had not.
been exceeded thus far in the cycle.
The licensee is presently restricting the MTPF administratively. The licensee informed us by telephone that the soecification on MTPF will be replaced by a specification on a new parameter, Core Maximum Fraction of Linear Power Density (CMFLPD), at the next reload.
CMFLPD is less ambiguous in its definition, and an oversight such as this is not likely te be repeated.
Meanwhile, the licensee's request to change the Technicel Specification to include an MTPF limit for 8X8 fuel is justified.
. The MTPF is a design limit which is dependent on the specific plant and fuel type.
This factor is calculated in conjunction with the design linear heat generation rate limit, the number of fuel bundles for each type, the active fuel length, the rated thermal power and the fraction of heat.
Basically, the MTPF for a given fuel type is the design maximum linear heat generation rate (13.4 Kw/ft for 8X8R fuel) divided by the average linear heat generation rate of that core for that fuel type.
This average linear heat generation rate is calculated as if the entire core were made up of the sub-ject fuel type.
The MTPF is compared to measured total peaking factors, and when the measured value exceeds this design MTPF, the APRM high fl ux scram and rod block set-points are lowered to compensate for this increase <i peaking.
The method-ology by which the MTPF is calculated is identical to that previously ap-proved by tiie staff for 7X7 and 8X8 fuel.
We have reviewed the licensee's submittal and, based on the 8X8R fuel design characteristics, have concluded that the proposed MTPF of 3.00 is acceptable.
4.0 ENVIRONMENTAL CONSIDERATION
S We have determined that the amendment does not authorize a change in effluent types or total amounts nor an increase in power level and will not result in any significant environmental impact.
Having made this determination, we have further concluded that the amendment involves an action which is insianificant from the standpoint of environmental impact, and pursuant to 10 CFR 351.5(d)(4), that an environmental impact statement or negative declaration and environmental impact appraisal need not be prepared in connection with the issuance of this amendment.
- 5. 0 CONCLUSIONS We have concluded, based on the considerations discussed above, that:
(1) because the amendment does not involve a significant increase in the pro-bability or consequences of accidents previously considered and does not in-volve a significant hazards consideration, (2) there is reasonable assurance that the health a safety of the public will not be endangered by operation in the proposed manner, and (3) such activities will be conducted in com-pliance with the Commission's regulations and the issuance of this amendment will not be inimical to the common defense and secur:'y or to the health and safety of the public.
DATE: January 23, 1980