ML19348A081
| ML19348A081 | |
| Person / Time | |
|---|---|
| Site: | Oyster Creek |
| Issue date: | 10/16/1981 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19348A053 | List: |
| References | |
| NUDOCS 8111030588 | |
| Download: ML19348A081 (4) | |
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ENCLOSURE SAFETY EVALUATION OYSTER CREEK NUCLEAR POWER STATION una e i DOCKET NO.50 '219 DEGRADED GRID PROTECTION FOR CLASS 1E POWER SYSTEMS INTRODUCTION AND
SUMMARY
Questions, criteria and staff positions regarding degraded grid voltage protection were sent to Jersey Central Power and Light Company (JCP&L) on August 11, 1976 and on June 3,1977. Their responses were dated November 5,19767. April 18, i
1977; September 25, 1979; August 11, 1980; and April 30, 1981. EG&G Islaho un' der contract to NRC perfomed a detailed review and technical evaluation of the submittals. The results of this' review a-contained in EG&G's Technical Evaluation Report (TER) entitled " Degraded Grid hotection for Class lE Power Systems, Oyster Creek Nuclear Power Station Unit 1," dated August 1981 and attached to this report. We have reviewed the TER and, except for two I
conclusions, concur with the findings.
' DISCUSSION The voltage analysis performed by the licensee over the range of normal grid voltages showed that without system modification, voltages below the pick-up rating of certain 460 volt starters and less than the minimum operating
.value of two motors could occur during normal low voltage excursions of the off-site gri.d. Possible system modifications which could alleviate the degraded voltale conditions at the IE bus'es are the following:
(1) adding voltage regulators, (2) raising the second-level trf p setting, (3) raising the voltage to affected equipment by adding new transformers, or (4) replacing em g@
the affected equipment.
oo 08 m0 Option 2 would place the teip setting of the second level voltage protection as relays on the 1E buses within the normal range of grid voltage variations.
of This would violate position 3 of the NRC generic letter dated August' 8,1977.
-m ESn-Theref4re, this option would not be acceptable.
Options 3 and 4 would correct for low grid Voltage conditions, but would not corre:t for overvoltage conditions whict. aay occur on the lE buses during
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lightly-loaded grid conditions. Therefore, these options are less than cptimum solutions.
Option 1 installation of Voltage regulators, was chosen by the licensee and, in the staff's opinion, has the advantage of correcting the " effects of both high and low grid voltage conditions. A minor problem with this arran.gement is that the voltage regulators will only assure acceptable lE bus Voltages d:wn to degraded grid ~ conditions of -20%.
At -22% of normal grid voltage, the second-level undervoltage relays will actuate, causing the on-site generators to start. However, between -20% ond -22% of normal grid Voltage, the Ti bus voltage could be below the operating point of certain motors and starters. This is not considered a serious problem because in this eitremely
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degraded condition, the off-site grid will be unstable and either collapse completely, disintegrate, or cause grid load shedding.
All of these outcomes will affect the voltage of the 1E bus and lead to activation of the onsite generation.
We therefore concur with the licensee that the installation of voltage regulators en the 34.5kv electrical systems provides acceptable voltage levels on the lE
. buses within the cited range of grid -voltages.
This meets our regulatory position il and is acceptable. However, we require that the licensee include limiting conditions of operations in the proposed amendment to the technical specifications to cover situations when the regulators are out of service.
We disagree with EG&G's conclusion in the TER which disallows credit for the valtage regulators because of their limited range. As previously discussed, the voltage regulators will maintain acceptable lE bus Voltages throughout the normal sustainable ranbe of off-site grid, voltages and down to a degraded grid
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. level of -20% of normal.
In the event grid volthges degrdde further, it is the staff's opinion that the off-stte grid would b.e. extremely unstable and would collapse, disintegrate, or initiate grid' load-sh'edding. These
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results would drop the grid voltage further causing the diesel generators to -
start at -22% of normal off-site voltage. The use of voltage regulators provides a means of maintaining acceptable voltages on the 1E buses. The staff concurs and gives credit for their use at this nuclea'r power station.
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EVALUATION CRITERIA
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The criteria used by EG&G in this technical evaluation of the analysis includes 4
GDC 17.(" Electrical Power Systems") of Appendix A to 10CFR50, IEEE Standard 279-1971 (" Criteria for Protection Systems for Nuclear Power Generating Stations"), IEEE Standard 308-1974 (" Class 1E Power Systems for Nuclear Power Generating Stations") ANSI Standard C84.1-1977 " Voltage Ratings for Electrical Power Systems and Equipment (60hz)", and staff positions as detailed in the generic letter sent to the licensee on June 3,1977.
MODIFICATIONS
, -. As a result of the NRC request, JCP&L has installed a second-level undervoltage scheme to protect safety-related equipment from a sustained degraded grid voltage" condition. As previously discussed, the licensee has also' installed
- 34.5 kv voltage regulators to maintain the secondary voltage of the start-up transformers in an acceptable range.
Finally, the licensee has proposed changes to the plant's technical specifications including: relay surveillance rsquirements, setpoints and limits, and limiting conditions for operation.
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CONCLUSIONS 1.
We conclude that acceptable voltage and time setpoints have been selected by the licensee.
2.
Acceptable coincident logic has been employed.
3.
Acceptable time-delays have been selec'.ad.
4.
Disconnection of off-site power on degraded grid condities.: will be automatically initiated.
5.
Voltage monitors meet IEEE standard 27c-1971.
6.
Technical specifications are not complete. The licensee's proposed amendment of technical specifications must include limiting conditions of operations when the. voltage regulators are not in use.
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