ML19336A763
| ML19336A763 | |
| Person / Time | |
|---|---|
| Site: | Fort Saint Vrain  |
| Issue date: | 10/24/1980 |
| From: | Swart F PUBLIC SERVICE CO. OF COLORADO |
| To: | Tedesco R Office of Nuclear Reactor Regulation |
| References | |
| P-80373, NUDOCS 8010310388 | |
| Download: ML19336A763 (6) | |
Text
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October 24, 1980 Fort St. Vrain Unit No.1 P-80373 fir. Robert L. Tedesco Assistant Director for Licensing Division of Licensing U. S. tiuclear Regulatory Commission Washington, D.C.
20555 Docket fio. 50-267
Subject:
Emergency Power Systems
References:
Letters from Tedesco to Warembourg dated 8/25/80 (G-80149 and G-80150)
Dear Mr. Tedesco:
In the referenced correspondence (i.e. G-80150) of August 25, 1980, liRC stated a need to confirm the acceptability of voltage conditions on the Fort St. Vrain Station Electric Distribution System.
Specifically, this was to be in regard to; (1) potential overloading due to transfers of either safety or nonsafety loads, and (2) potential starting transient problems in addition to the concerns expressed in the ilRC's June 2, 1977 correspondence with regard to degraded voltage conditions due to conditions originating on the grid.
The concerns and/or questions have been extracted from the Staff's letter and assigned a number and listed below to insure response to each point:
(1) Based on the experience at ANO, the flRC is requiring all licensees to review the electric power systems at each of their nuclear power plants to determine analytically if, assuming all onsite sources of AC power are not available, the i
offsite power system is of sufficient capacity and capability to automatically start, as well as operate, all required safety loads within their required voltage ratings in the event of (a) an anticipated transient (such as a unit trip) or
^
(b) an accident (such as a LOCA) regardless of other actions the electric power system is designed to autonatically initiate and without the need for manual load shedding of any electric l
loads.
801os,o 3 g g f
a P-80373 October 24, 1980 Page 2 (2)
Protection of safety loads from undervoltage condit.?ons must be designed to provide the required protection without causing voltages in excess of maximum voltage ratings of safety loads and without causing spurious separations of safety buses from offsite power.
(3) IIRC should be infonned of any required sequential loading of any portion of the offsite power system or the onsite distribution system which is needed to assure that power provided to all safety related loads is within the voltage limits for these safety loads.
Guidance on evaluating the perfonaance of electric Power Systems with regard to voltage drops is provided.
(4) The adequacy of the onsite d'.stribution of power from the offsite circuits shall be verified by test to assure that analysis results are valid.
Please provide (a) a description of the method for perforning this verification and (b) the test results of previous tests, verify the results of the analysis, then test results should be submitted and additional tests need not be performed.
(5)
In addition, you are requested to review the electric power systems of your nuclear station to detennine if there are any events or conditions whicr. ecuid result in the simultaneous or
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consequential loss of both required circuits to the offsite network to determine if any potential exists for violation of GDC-17 in this regard.
PSC RESP 0flSE 1 Offsite Power System Five 230Kv transmission lines from widely separated power system grid locations are connected to the Fort St. Vrain switchyard (See Figure 1).
Any one of these lines alone can easily handle the safe shutdown cooling load (less than 1 megawatt) at Fort St. Vrain.
These lines are individually protected through the application of modern protective relaying practices, thus the simultaneous loss of all offsite power is extremely unlikely.
Interface with Onsite Distribution System Offsite power can be supplied to the Fort St. Vrain 4160 volt buses (Note-All 4160v buses are nonsafety related) through either the Reserve Auxiliary Transformers (RAT) or Unit Auxiliary Transfonaer (UAT) from any one of the five transmission lines.
Supply from RAT i
If any of various electrical problems (including undervoltage) are encountered during nonnal operation (i.e. 4160v buses powered from the main turbine generator through the UAT), or a unit trip occurs, automatic transfer to offsite power via the RAT is initiated.
P-80373 October 24, 1980 Page 3 Supply from UAT It is also possible to supply station auxiliaries from offsite power through the main power transformer and the VAT by disconnecting the isolated phase bus links in the main generator leads.
Unit Trips and/or LOFC (Loss of Forced Circulation Cooling)
The Fort St. Vrain Station does not employ a Light Water Reactor.
Therefore, during a unit trip or LOFC situation, there is no rt.q,:irement to immediately start large safety injection pumps or reactor coolant pumps.
These equipment items are not utilized in the FSV High Temperature Gas-Cooled Reactor Design.
The Fort St. Vrain safe shutdown cooling systems utilize nonnally operating plant equipment.
Thus, the equipment requirements for responding to a unit trip or to a LOFC situation are not significantly different.
Likewise, the electrical requirements for responding to a unit trip or LOFC are not significantly different from normal plant operating load.
The safe shutdown cooling load is less than plant operating load.
Protection from undervoltage conditions is provided on the nonsafety related 4kv systems and on the safety related 480v system.
At the staff's request (Letter Tedesco to Warembourg dated 8/25/80, G-80149),
PSC recently reviewed the Fort St. Vrain undervoltage protection in detail.
The types of protection viere found to be adequate and modifications were proposed to provide coincidence logic and to meet the intent of IEEE-279 with the existing undervoltage relaying philosophy.
Technical Specification changes are currently being prepared and will be submitted to the staff on or before December 15,1980 (Refer to Letter from Warembourg to Tedesco dated 10/15/80,P-80364).
System transient analysis studies are available in the Denver Engineering Offices if the NRC desires to review them.
The PSC position on the need for analytical verification is disassed in PSC Response 3.
PSC RESPONSE 2 During normal offsite power vonditions no situations exist at Fort St.
+
Vrain where high voltage conditions, in excess of equipment ratings, l
exist during light load conditions.
As discussed above, the undervoltage protective relaying has recently been reviewed and it was concluded that the setpoints will preclude spurious separations from offsite power.
P_SC RESPONSE 3 No sequential loading of the offsite power system or of the onsite distribution system (when powered from the offsite source) is required at Fort St. Vrain.
I
l P-80373 October 24, 1980 Page 4 i
Autaaatic transfer to the offsite source (via the RAT), following a unit trip, take place in less than two cycles.
Ocsillographs have verified that Sus Voltage changes are hardly noticeltle during this type of trans fer.
The above transfer method is backed up by a second automatic transfer that occurs in 2-3 seconds following 4kv bus undervoltage or a unit 2
trip.
During this method, motor voltage is allowed to decay to a safe level before the transfer is made.
Rotating equipment will still be rotating and current in rush and voltage conditions are within equipment ratings.
If the offsite system (via the RAT), has low voltage, both of the above transfers are blocked.
The 4kv buses are disconnected from 4
the UAT and RAT and large motors are tripped.
Safety related equipment is also load shed from the safety related 480v buses. Therefore, the worst case undervoltage situation in tenns of motor starts is identical to that occurring during normal plant start-up and operation.
No calculations or tests are deemed to be necessary to verify voltage adequacy since it is verified on a regular basis by plant operation.
PSC RESPONSE 4 As previously stated, safe shutdown cooling equipment is normally operating prior to a unit trip or a LOFC situation.
Therefore, the need to start and operate equipment is no different than during normal plant operation.
t Capacity of the RAT and its capability to maintain adequate voltage at the terminals of equipment has been verified by operational experience on a regular basis.
Each time the Fort St. Vrain station goes through start up or shutdown, the safety equipment is operated from the RAT.
There have been no motors or other equipment that nave failed to start because of undervoltage or that have been damaged because of undervoltage conditions.
The UAT is approximately 2 flVA (55 C rise FA ratirg) larger than the RAT Therefore, it also has adequate capacity and capability.
PSC RESPONSE 5 No conditions were found that could result in the simultaneous loss of the required circuits to the offsite network.
Therefore, no potential violations of GDC-17 were identified.
1 If you have any questions regarding these matters, please contact us.
Very truly yours,
~
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/
Frederic E. Swart Nuclear Project Manager i
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