U-603171, Forwards Response to NRC List of Questions Re LAR Re Overall Effort to Resolve Degraded Voltage Concerns at CPS
| ML20207B064 | |
| Person / Time | |
|---|---|
| Site: | Clinton  |
| Issue date: | 02/25/1999 |
| From: | Sipek J ILLINOIS POWER CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| U-603171, NUDOCS 9903050402 | |
| Download: ML20207B064 (4) | |
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llhnois Power Company Clinton Power Station P O. Box 678 Chnton. IL 61727 Tel 217 935-8881 Joseph V. Sipek PGMR o'<ector - ceme'"9
-~c" U-603171 8E.100a February 25, 1999 Docket No. 50-461 10CFR50.90 Document Control Desk Nuclear Regulatory Commission Washington, D.C. 20555
Subject:
Clinton Power Station AdditionalInformation Regarding Proposed Amendment ofFacility Operatina License No. NPF-62 (LS-98-012)
Dear Madam or Sir:
By Illinois Power (IP) letter U-603146, dated January 20,1999, (and as supplemented by IP letters U-603153 and U-603158, dated Febmary 4,1999, and Febmary 8,1999, respectively) IP requested amendment of the Clinton Power Station (CPS) Operating License (License No. NPF-62) pursuant to 10CFR50.90. The requested changes are part of an overall effort to resolve degraded voltage concerns at CPS.
4 Subsequent to the previously mentioned correspondence, a list of additional questions was provided to IP for which written responses were also requested. The purpose of this letter, therefore, is to submit documented responses to these questions.
IP's application for amendment is currently undergoing NRC review, and the attached information is intended to support that review.
I Sincerely yours, n
Josep V. ip k Director-Licensing h0 0l JFK/krk 9903050402 990225 l
PDR ADOCK 05000461 P
U-603171 Page 2 f
Attaciunent-cc:
NRC Clinton Licensing Project Manager NRC Resident OfHee, V-690 Regional Administrator, Region III, USNRC Illinois Department ofNuclear Safety i
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6 to U-603171 Page 1 of 2
, Responses to NRC Questions identified During the Review of the License Amendment Application Regarding Degraded Voltage Modifications 1.a Figure 2 ofIP letter dated January 20,1999, shows that with the RAT tap at position 3 the SVC will be at its limit of correction when the 345-kV grid is at its lowest limit of 0.94 per unit. Page 11 la attachment 2 ofIP letter dated February 4,1999, shows that for the ERAT the SVC is at its limit of correction at a point just above the lower operating limit of the 138-kV grid. These figures indicate that, with the additional reactive current larush associated with motor starting following an event, the 4-kV bus voltage will likely dip below the dropout point of the DGR relays. Have the calculations associated with the new analytical values established that safety equipment will operate properly over the transient and that motors will start property? Have they verified that the voltage will recover above the DGR reset point of the relays before the timers associated with the relays time out?
Response
The referenced figures illustrate the relative operating parameters for the RAT SVC and
. ERAT SVC (following approval of the requested amendment and subsequent re-calibration of the DGR relays) for steady-state LOCA-loaded conditions and as such they do not reflect the transient behavior of the system during a LOCA block start of the safety related loads.
The calculations associated with the new analytical values are similar to those provided during the review process leading up to approval of Amendment 110 to the CPS Operating License. The current calculations model the transient behavior for a LOCA block start and its impact on the starting ofloads (similar to the calculations performed for Amendment 110) and they continue to support satisfactory starting ofloads during the LOCA block start. Furthermore, although the voltage at the 4.16-kV bus will dip below the relay trip point during the load starting phase of the event, the voltage will recover to a level above the relay reset point before the relay timer causes the 4.16-kV bus to separate from the offsite source and energize the bus from the associated emergency diesel generator.
1.b Please provide a copy of the text portion of calculation 19-AQ-02 for our review.
Response
A copy of the text portion of 19-AQ-02 will be provided on or before March 5,1999.
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b Attachment t to U-603171 Page 2 of 2 2.a The response to question 4.s la the February 4,1999 letter indicates that when CPS is producing power it provides a good deal of the voltage support to the 345 kV grid la the vicinity of Clintos. Fotowing as accident, what will trip the mala turbine and when will this occur?
Response
i The main turbine is tripped on an MSIV closure caused by a LOCA.
1 2.b What wiu separate the main generator from the 345-kV grid and when will l
this occar?
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Response
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The primary signal that separates the generator from the grid is reverse power. It can take several minutes for the main turbine-generator to coast down such thtt the reverse power i
relay will cause the 345-kV breakers to open.
1 2.c
' When the 4-kV BOP buses are fed from the UAT, what signal transfers them to the RAT following an accident?
Response
l Assuming no manual operator action following an accident, and the subsequent trip and coast down of the main turbine-generator unit, a signal from the reverse power relay will cause the main power transformer output breakers to open. The trip signal for the 4.16-kV BOP bus transfer is initiated when the main power transformer output breakers open.
1 2.d What is the approximate elapsed time from initiation of the accident signal to transfer of the BOP loads to the RAT and separation of the main generator from the 345-kV system?
EME2GM The BOP loads at CPS have always been modeled as transferring to the RAT immediately upon a LOCA signal. However, as evidenced by past experience with plant trips (similar to the response expected following a LOCA), several minutes elapse between the turbine trip and separation of the generator from the 345-kV system. This is due, in part, to the large rotational momentum of the main turbine-generator unit. Modeling the BOP load transfer as occurring immediately is thus considered to be conservative. On this basis, changing the normal electrical system lineup to supply the BOP loads from the RAT during periods with a potential for creating an overvoltage condition on the 4.16-kV buses does not change the loaamg model or any of the assumptions regarding RAT loading or the power source for BOP loads dering a LOCA as previously analyzed.
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