ML20024D189
| ML20024D189 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 07/26/1983 |
| From: | Reinaldo Rodriguez SACRAMENTO MUNICIPAL UTILITY DISTRICT |
| To: | Eisenhut D Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML20024D190 | List: |
| References | |
| RJR-83-579, TAC-52047, NUDOCS 8308030283 | |
| Download: ML20024D189 (10) | |
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$SMUD SACRAMENTO MUNICIPAL UTILITY DISTRICT O 6201 S Street, Box 15830, Sacramento, Califomia 95813; (916) 452-3211 RJR 83-579 July 26, 1983 DIRECTOR OF NUCLEAR REACTOR REGULATION ATTN: DARRELL G EISENHUT, DIRECTOR DIVISION OF LICENSING U S NUCLEAR REGULATORY COMMISSION WASHINGTON DC 20555 DOCKET NO. 50-312 LICENSE NO. DPR-54 PROPOSED AMENDMENT N0. 98 In accordance with 10 CFR 50.59, the Sacramento Municipal Utility District hereby proposes to amend its Operating License DPR-54 for Rancho Seco Nuclear Generating Station, Unit No.1; enclosed are forty (40) copies of this proposal entitled Proposed Amendment Number 98.
This Proposed Amendment Number 98 modifies the License Change No. 46 approved by the NRC on March 21, 1983. The reason for this change results in the differ-ence between proposed and "as built" delay times in Table 3.7-1 of the Technical Specifications.
Details of the analysis is documented in the affected "No Significant Hazards Consideration Evaluation."
The Technical Specifications Section 3.7.1 requires "All nuclear service buses, nuclear service switchgear, and nuclear service load shedding systems are oper-able." This change is required to make the load shedding system operable and therefore Rancho Seco cannot be' brought critical until the NRC approves this Proposed Amendment.
The unit will remain at hot shutdown until Proposed Amendments Nos. 83 and 88 are approved. These latter amendments involve TMI Modifications and Cycle 6 operating limits respectively.
We would appreciate your prompt attention to this proposal.
If you have any questions concerning this proposal, please contact Mr. Ron Colombo, at the Rancho Seco Nuclear Generating Station.
8308030283 830726 PDR ADOCK 05000312
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9 SACRAMENTO MUNICIPAL UTILITY DISTRICT Rancho Seco Nuclear Power Station Attachment Proposed Amendment No. 98 No Significant Hazards Consideration Evaluation
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Osuun SACRAMENTO MUNICIPAL UTILITY DISTRICT O 6201 S Street, Box 15830, Sacramento, California 95813; (916) 452-3211 Dr. Gerald Wong Radiological Health Branch State Department Health Services 714~"P" Street Office Building #8 Sacramento, CA 95814 l
l AN. ELECTRIC SYSTEM SERVING MORE THAN 600,000 IN THE HEART OF C AllF O R NI A
10 CFR %50.91 requires that requests for amendment must be accompanied by an evaluation of the hazards considerations involved. Such evaluation is to focus on the three standards set forth in 10 CFR 50.91(b) as quoted below:
The Commission may make a final determination pursuant to the procedures in s50.91 that a proposed amendment to an operating license for a facility licensed under 50.21(b) or 50.22 or for a testing facility involves no significant hazards consideration, unless it finds that operation of the facility in accordance with the proposed amendment would:
(1)
Involve a significant increase in the probability or consequences of an accident previously evaluated; or (2) Create the possibility of a new or different kind of accident from any accident previously evaluated; or (3)
Involve a significant reduction in a margin of safety.
As set forth more fully below, Sacramento Municipal Utility District submits that the activities associated with this amendment request are outside the standards set forth in 10 CFR 50.91(b) and, accordingly, a no significant hazards consideration finding is warranted. To put the matter in perspective, necessary background is first provided; thereafter, a discussion of the Significant Safety Hazard Considerations is provided.
By application dated February 2, 1981, as revised July 16, 1982, the Sacramento Municipal Utility District requested changes to the Technical Specifications appended to Facility Operating License No. DPR-54 for the Rancho Seco Nuclear Generating Station. The proposed changes added TS requirements for the degraded voltage protection system for Class lE equipment that were installed during the cycle 6 refueling outage.
In response to NRC's generic letter of June 3, 1977, pertaining to degraded grid voltage protection, SMUD proposed certain design modifications and draft changes to the TSs. The NRC Safety Evaluation (SE) dated February 11, 1981, concluded that the design modifications were acceptable and that the draft TSs, once implemented would be satisfactory. SMUD formally submitted the Tss by application dated February 2, 1981.
NRC review of the application and the proposed T5s confirmed the findings of the February 11, 1981 SE.
As-agreed to in a conversation with SMUD staff, and as confirmed in SMUD's July 16, 1982 letter, the switchyard voltage necessary for startup specified in TS 3.7.1.I has been changed to 214 KV.
The NRC found that the proposed TSs met the criteria for periodic testing of protection systems and equip-ment, and were therefore acceptable.
The District has completed modifications to satisfy the following criteria as provided in the June 3, 1977 letter.
A.
The selection of voltage and time set points shall be determined from an analysis of the voltage requirements of the safety-related loads at all onsite system distribution levels.
B.
The voltage protection shall include coincidence logic to preclude spurious trips of the offsite power source.
C.
The time delay selected shall be based on the following conditions:
- 1) The allowable time delay, including margin, shall not exceed the maximum time delay that is assumed in the FSAR accident analysis.
- 2) The time delay shall minimize the effect of short duration disturbances from reducing the availability of the offsite power source (s).
- 3) The al'lowable time duration of a degraded voltage condition at all distribution system levels shall not result in failure of safety systems or components.
D.
The voltage monitors shall automatically initiate the disconnection of offsite power sources whenever the voltage setpoints and time delay limits have been exceeded.
E.
The voltage monitors shall be designed to satisfy the requirements of IEEE Standard 279-1971, " Criteria for Protection Systems for Nuclear Power Generating Stations".
F.
The Technical Specifications shall include limiting conditions for operation, surveillance requirements, trip setpoints with minimum and maximum limits, and allowable values for the second level voltage protection monitors.
G.
As proposed in the District's response to NRC dated July 19, 1977 the District will install an overvoltage alarm on the 4160 volt bus to alarm in the control room.
This modification installed three potential transformers each on the nuclear safety buses 54A and S48. Each PT monitors a different line to line voltage and drives an undervoltage relay and overvoltage relay. The protective relays control auxiliary relays which are connected in a 2 out of 3 coincident logic sequence. The coincident logic precludes spurious trips and satisfies the requirements of IEEE 279. The setpoint for the relays was determined from the over/undervoltage study. The minimum trip setpoint for an undervoltage condition is equal to the minimum voltage the equipment is qualified to operate at. The setpoint will not cause spurious inadvertant operation since the maximum trip setpoint.is below the normal operation voltage range of 221 kv to 239 kv. The following table depicts 4
this:
4160 Volt Bus Switchyard Voltage Voltage Max. Trip Setpoint:
3809 volts 218 KV l
Trip Setpoint:
3771 volts 216 KV Min. Trip Setpoint:
3733 volts 214 KV The maximum trip set point for an overvoltage condition is equal to the maximum voltage the equipment is qualified to operate ct.
The set point will not cause spurious inadvertant operation since the minimum trip set j
point is above the normal operating range of 221 KV to 239 KV.
The following table depicts this:
4160 Volt Bus Switchyard Voltage Voltage j
l Max. Trip Setpoint:
4626 volts 244 KV Trip Setpoint:
4580 volts 242 KV Min. Trip Setpoint:
4543 volts 240 KV
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The manimum time delay including margin for a complete loss of voltage is 2.5 seconds. An inverse time delay relay was selected so that short-duration disturbances would not cause inadvertant disconnections from the offsite power sources.
The requirement for this Technical Specification change (Proposed Amendment No. 98) resulted-from field tests performed on the installed two-out-of-three coincident logic committed to the referenced response.
The time delay listed for the undervoltage dropout was not testable since an inverse time delay relay can only be relied on to operate when the voltage is less than the trip set point minus its tolerance. For Rancho Seco, the trip set point minus the tolerance is 3733 volts at the 4160 volt bus, which was shown acceptable in the reference and equates to 214KV at the switchyard. The proposed Technical Specification change does not change the voltage trip set point as determined from the referenced analysis.
Field experience and testing has identified a requirement to clarify the time delay setting on the E-10lls for the instantaneous overcurrent element (ITH) for the 4160 volt motors.
The new value will be shown as "7.5 CY TOT i 1 CY" rather than "6 cycles offset".
This value has been proven to avoid spurious motor breaker trips and is within the capabilities of the overcurrent element.
The following 4160 volt motor overcurrent relays require an adjustment (increase) to assure the undervoltage trip relay will operate prior to the overcurrent relay under the worst case degraded voltage condition.
Switchgear Position Relays (3 ea)
Motor
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4A02 Com-5 Reactor Make-up Pump P236 (Alt feed) 4A04 Com-5 High Pressure Injection Pump P238A 4A05 Com-5 Decay Heat Removal Pump P261A 4A07 Com-5 Nuclear Service Raw Water Pump P472A 4806 Com-5 Nuclear Service Raw Water Pump P472B 4B07 Com-5 High Pressure Injection Pump P238B 4B08 Com-5 Reactor Make-up Pump P236
. 4B09 Com-5 Decay Heat Removal Pump P261B' In a Mattimoe to Stolz le'tter dated April 21, 1982 the District committed to. replace any MCC overload heaters that could trip during a degraded grid condition. The following MCC starters require new overload heaters to withstand at least 1.15 times full load amperes which could occur under a sustained undervoltage condition.
MCC Starter S2Al 101 102 104 105 113 114 116 118 124 S281 104 105 114 117 119 123.
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Evaluation The following evaluation is an extension of the District's response to Guideline #10 in Enclosure I Part B of the referenced letter. The analysis below assures that the relay operating range provided in the table will prevent equipment failures due to undervoltage. We have assumed that the bus voltage falls to just below 75% of the rated motor voltage, and that the motors stall and draw 75% of rated locked rotor current.
It is extremely unlikely that this condition could occur, since it implies a corresponding switchyard voltage of 172Kv persisting for several seconds.
- In spite of these extremely conservative assumptions, the District has confirmed that, in every case, the bus supply breakers will trip on undervoltage before motor loads trip on overcurrent, and that the undervoltage conditions will not lead to dcmage of the motors.
The District has also determined that a drop in the supply voltage into the 75 to 90 percent range would in every case lead to tripping on undervoltage prior to tripping on overcurrent, and prior to motor damage. Undervoltages in this range are not the worst case, since motors will not stall above 75%
voltage, and thus, will not encounter sustained high currents.
Non-motor loads have also been considered, and a worst-case analysis of undervoltage conditions has shown that tripping on undervoltage will occur prior to overcurrent tripping, and that no equipment damage will occur.
The 4160 volt motor overcurrent relays were reviewed and the District confirms that the undervoltage relays will operate prior to operation of the motor overcurrent relays. The feeder breakers to and from the station service transformers are set for a larger overcurrent condition than could possibly result from a degraded voltage condition making it highly unlikely that the breakers would trip from an undervoltage condition. Even so, the time delay is longer than that required for the undervoltage trip relay to function.
The District looked at the direct acting overcurrent trip elements on the 480V switchgear protecting the large 480V motors. The District confirms that the undervoltage trip relays will operate before the overcurrent trip elements. The feeder breakers to the 480 volt motor control centers (MCC) also have direct acting overcurrent trip elements.
These have also been confirmed to operate at a longer time delay than the undervoltage trip relays.
The breakers for the 480 volt motors at the MCCs are sized for short circuit protection resulting in locked rotor tripping times of 30 to 60 seconds. This is well beyond the time delay of the undervoltage trip relays. The breakers for the non-motor loads at the MCCs are sized above their normal full load current. Since the current to the non-motor loads can only decrease under low voltage conditions, there will be no problems with the breakers tripping under a degraded voltage condition.
The District has reviewed and confirms that the MCC 480 volt motor overload relay heaters are sized to allow operation at a 115% of full load current which would occur at the degraded voltage limit. Additionally, the delay times for these heaters are longer than that required for the undervoltage trip relays to function. The motor operated valves (MOV) do not have overload relay heaters installed and, therefore, do not have a problem with any time delay associated with a degraded voltage condition. 1
All the control circuits for loads above the 480 volt MCC level are DC circuits fed from battery-backed sources and are not affected by a degraded voltage condition.
The control circ uits for the loads fed from the 480 volt MCCs are AC and fused to protect for short circuits. The District has performed a review and confirms that fuse sizing will allow operation under a degraded voltage condition beyond the time required for the undervoltage trip relays to operate.
The District has also identified a need to increase the time delay for the overvoltage relays to prevent spurious trips. The increase in time delay from 3 seconds to a maximum of 8 seconds is considered insignificant because overvoltage occurrences experienced and anticipated are rare and limited in peak value and our loads are essentially insensitive to overvoltage operation for this short time.
The voltage monitors automatically initiate the disconnection of offsite power sources, initiate start of the diesel generator and alarm in the control room whenever the voltage setpoint and time delay limits have been exceeded and two out of three relays have operated.
The addition of the new equipment will not overload the potential transformers.
The addition of the new equipment will have-an insignificant effect on the performance of the existing batteries.
All new equipment is purchased from the switchgear manufacturer, Brown Boveri Electric, Inc. (ITE), qualified to IEEE 323, 1974 or taken from the District's stock of spare parts for the switchgear (same component installed in existing equipment).
Brown Boveri Electric, Inc. will provide documenta-tion that field additions will not invalidate the original equipment seismic certifications.
The new overload relay heaters installed in the 480 volt motor starters are purchased as commercial grade spare parts.
The annunciator circuit was modified to consolidate the alarms.
An alarm will occur if the bus has an under/overvoltage condition. This is sensed two ways - by each under or overvoltage sensing circuit and by an undervoltage or overvoltage alarm relay. The bus feeders from the startup transformers are also individually monitored. The same alarm is also activated by bus unloading via the 4ATA4 relay. The IAV target relays are separated from the annunciator parallel contacts and assured adequate current for target acti-vation by addition of a fast acting relay. The. existing undervoltage alarm relay on the 480 volt bus is replaced with a new qualified solid state relay to eliminate the IAV target activation problems.
Loss of DC voltage to the under/overvoltage cirsuit will cause an alarm by de-energizing the 4A(B)ULI thru 3 relays.
The time delay required for circuit initiation if accomplished by relay 62A which eliminated the need for relay 628.
A single failure of any of the following new equipment listed below to be installed per this modification will not prevent the scheme from operating properly or cause it to operate when it is not required. L
Potential Transformers Voltmeters Overvoltage Relays 459A(B)1 thru 3 Undervoltage Relays'427A(B) I thru 3 Fuses Control Relays 4A(B)ULI thru 3 The two out of three logic used in the design allows a single failure of the above equipment without any effects on the operation of the system.
However, their failure would impact one diesel, and is no different than other relays in the existing scheme where one failure can prevent one diesel from starting.
.Thus, the margin of safety is not significantly reduced by the proposed i
over/undervoltage time delay trip values.
Thus, it has been shown that the proposed Rancho Seco Unit 1 Emergency 7
Power System modification does not:
1)
Involve a significant increase in the probability or consequences of an accident previously evaluated; or f.
- 2) Create the possibility of a new or different kind of accident from any accident previously evaluated; or j
i 3)
Involve a significant reduction in a margin of safety.
As such, SMUD has determined and submits that the proposed over/undervoltage time delay' trip values' described herein do not involve a significant safety hazard.
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