ML20213E171
| ML20213E171 | |
| Person / Time | |
|---|---|
| Site: | Columbia  |
| Issue date: | 05/07/1982 |
| From: | Rubenstein L Office of Nuclear Reactor Regulation |
| To: | Tedesco R Office of Nuclear Reactor Regulation |
| References | |
| CON-WNP-0511, CON-WNP-511 NUDOCS 8206100080 | |
| Download: ML20213E171 (8) | |
Text
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Docket No:
50-397 MEMORANDUM FOR: Robert L. Tedesco, Assistant Director for Licensing DL FROM:
L. S. Rubenstein, Assistant Director for Core and Plant Systems, DSI
SUBJECT:
SUPPLEMEtiT TO CHAPTER 8, SAFETY EVALUATI0tl REPORT - WPPSS NUCLEAR PROJECT NO. 2 g c;- /
Plant Name: WPPSS Nuclear Project No. 2 p
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Licensee: Washington Public Power Supply System C,
Docket No:
50-397 e n._.y,_,,,,f,,,g s jr J U'!;^. d g Licensing Stage:
CL t7 Project Manager:
R. Auluck R.'_.in!.2.,[,'(.
Systems Integration Branch: Power Systems (y
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j PSB Reviewers :
S. Rhow/R. Giardina s i Review Status: Complete The enclosed Supplement No.1 to the Safety Evaluation for the WNP No. 2 covers degraded grid voltage protection. We have found the applicant's design acceptable.
The review of the verification test results for this item is to be performed by the Office of Inspection and Enforcement (0IE).
It is thus recommended that OIE be formally requested to perform the subject verification.
We, therefore, consider the open item of the Chapter 8 in our February 16, 1982 memorandum closed.
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- A M fc 7 L. S. Hubenste14 j L. S. Rubenstein, Assistant Director for Core and Plant Systems Division of Systems Integration so a.
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ENCL JURE SUPPLEMENT TO CHAPTER 8 SAFETY EVALUATION REPORT WPPSS NUCLEAR PROJECT No. 2 B.2.6 Adecuacy of Station Elect ric Distribution System Voltaaes The fotLowing items (by number) address our evaluation of the WNP No. 2 design for conformance with the corresponding position numbers of Branch Technical Position PSB-1 in SRP.
1.
There are three redundant and independent emergency buses.
Each bus has two Levels of undervoltage protection:
(1)
Primary (Loss of power), and (2) second level (degraded grid voltage).
The loss of power protection at the 4.16 kv emergency buses consists of a single phase instantaneous undervoltage relay with a setpoint at 69 percent of the bus nominal voltage and a timer of 2 seconds delay.
The degraded grid voltage protection at the 4.16 kv emergency buses consists of three single phase instantaneoes undervoltage relays with a trip point of 87.3 percent of the bus nominal voltage.
The relays are arranged in a two-out-of-three Logic with a time delay of 8 seconds.
l
. Upon loss of both normal and startup sourcess the tie breakers between the 4.16 kv Class 1E and the 4.16 kv non-Class 1E switchgear buses are automatically opened, thereby shedding alL Loads supplied via the 4.16 kv non-Class 1E buses.
The 4.16 kv Class 1E bus undervoltage signals (Loss of power) cause trip of att 4.16 kv feedbreakers except the permanently connected Loads.
The Division 1 and 2 4.16 kv Class 1E buses are then automatically transferred to the backup startup sources (115/4.16 kv backup auxiliary power transformer).
In the event this source is also unavailable these buses would be automatically transferred to the onsite standby sources (diesel gen e rat o r).
The loading sequence for Division 1 and 2 is accomplished through the use of electromechanical time delay relays.
Upon loss of both normal and startup sourcess the Division 3 (HPCS) 4.16 kv bus is automatically transferred to the Division 3 onsite standby source (diesel generator).
Load shedding and load sequencing are not required in this division.
l The primary undervoltage sensing scheme for the 4.16 kv Class 1E distribution system utilizes instantaneous undervoltage relays to start the Division 1r 2 and 3 standby diesel generators immediately upon loss of l
voltage at this associated buses.
In the event that voltage loss is maintained for two seconds, the Division
1 and/or 2 timers. trip the incoming breakers, institute Load shedding and energize additional two-second and five-second timers.
The second two-second timers utilized to attempt closing the backup source breakers; backup source undervoltage relays wilL inhibit breaker closure in the event of backup source undervoltage.
The five second timers are used to inhibit closure of the diesel generator breakers until the system has h ad time to attempt reestablishment of supply from the backup source.
The Division 3 single three-second timers which is energized by the primary undervoltage relaying, provides the permissive for closing its diesel generator breaker.
A second Level of undervoltage protection is provided to protect against the effect of sustained degraded grid voltage.
In the event of sustained bus undervoltage (87.3% of nominal bus) Lasting more than 8 seconds, the second level of undervoltage protection automatically t rips the f eeder breaker connecting the normal /startup sources to their respective 4.16 kv Class 1E buses.
This action results in loss of bus voltager and primary undervoltage relays are initiated as discussed above.
The trip setpoint of each secondary relay is 3631 volts, 87.3% of nominal bus voltage and 90.8% of nominal motor voltage.
Trip setpoint is above minimum operating voltages f
~
. 90% of motor nominal voltage at the terminal.
Eight seconds of time delay is provided to permit override of motor starting voltage drop.
The duration of motor starting voltage drop is 2~5 seconds.
The arrangement utilizes a two-out of-three coincidence logic to preclude the possibility of spurious degraded voltage signal and facilitate testing.
The applicant has demonstrated that Class 1E equipment is able to start and permit its required function for 8 seconds when the voltage on the 4.16 kv Class 1E bus degrades below 90.8% (setpoint) up to 80% of motor nominal voltage.
For voltage less than 80%e the motor torque could be less than the load torquer thus resulting in l
decelerating and eventual stalling.
The motors are protected against locked rotor conditions by a relay which trips and locks out in 10 seconds.
Since the second l
Level of undervoltage relaying is set t o t rip. the offsite power source breaker 8 seconds after the undervoltage condition develops, the load shedding trips motors without locking them out.
The design complies with our position and is, therefore, acceptable.
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. 2.
The load shedding and sequencing features are retained after the diesel generators are connected to their respective buses.
In the WNP No. 2 design, the load shedding would be instituted only if bus voltage were to dip below 69% of the nominal bus voltage.
The applicant's analysis shows that the voltage drop for the largest loads is not below 69% unless a major p r ob l e m is to occur to the onsite power source.
3.
The appli cant has stated that the transformer tap will be set to obtain optimum voltage levels.from no-load to fully loaded conditions under anticipated voltage variation of the offsite power system.
The staff finds this to be consistent with its requirement and, therefores acceptable.
4.
Verification testing is required to be performed prior to initial full power operation on all sources of offsite power.
The applicant has committed to perform preoperational tests to verify the actual voltage profiles of the onsite power distribution system in accordance with our position.
The staff concludes this commitment is acceptable subject to verification by 1E that testing is done in accordance with guidelines of BTP PSB-1.
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On the basis of our review and evaluations we have concluded that the degraded grid voltage protection f or WNP No. 2 satisfies our positions and is, therefore, acceptable.
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