ML20210L454
| ML20210L454 | |
| Person / Time | |
|---|---|
| Site: | Byron, Braidwood  |
| Issue date: | 08/08/1997 |
| From: | Lesniak M COMMONWEALTH EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9708210164 | |
| Download: ML20210L454 (6) | |
Text
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a August 8,1997 United States Nuclear Regulatory Commission Washington, D. C. 20555 Attention: Document Control Desk
Subject:
Ilyron Nuclear Power Station, Units 1 and 2 Facility Operating Licenses NPF-37 and NPF-66 NRC Docket Nutnhers: 50-454 and_50-455 liraidwood Nuclear Power Station, Units 1 and 2 Facility Operating Licenses NPF-72 and NPF-77 NBC Docket Numbert 50-456 and 50 457 Clarification to the Primary Containment and Reactor Coolant System Amendment i
Reference:
1, J. Ilosmer (Comed) Letter to USNRC, Primary Containment and Reactor Coolant System Ainendment, dated January 30,1997.
- 2. NRC Request for AdditionalInformation Regarding Primary Containment and Reactor Coolant System, dated February 10,1997.
- 3. J. Ilosmer (Comed) Letter to USNRC, Response to Request for Additional Information Regarding Primary Containment and Reactor i
Coolant System, dated May 23,1997, l
- 4. M. Lesniak(Comed) and Ramin Assa (NRC) telecons of July 3 and 7, 1997.
In Reference 1, Comed submitted a License Amendment Request to the NRC to incorporate the effect of the increased reactor coolant system volume resulting from the planned replacement of the steam generators at Byron, Unit I and Braidwood, Unit 1. In Reference 2, NRC requested additional information regarding the engineering methodologies and analyses. Reference 3 contained the response to Questions 1-3. This letter provides further clarification based on the telecons in Reference 4.
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Please address any questions or comments to this omce Sincerely,
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Marcia T. Lesniak Nuclear Licensing Administrator
_ Attachment cc:
A. B. Beach, Regional Administrator - Rlli G Dick, Byron /Braidwood Project Manager - NRR -
C, Phillips, Senior Resident inspector Braidwood
- S. Burgess, Senior Resident inspector Byron Omcc of Nuclear Safety -IDNS I
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e 10 ADDITIONAL. DEPRESSURIZATION TIME FOR RSGs The time for depressurization of the RSGs was extended to approximately 1.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> (0.5 hour5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> increase) to account for the additional stored energy in the RSG due to increased RSG metal mass and increased secondary side mass. The post-reflood depressurization period occurs after the peak containment pressure, P., is reached. (P.
occurs during the reflood phase at approximately 140 seconds.) Prior to the depressurization period, the heat removal rate from the SGs is primarily determined by the mass flow through the SG tubes and temperature of the secondary side. Therefore, the additional stored energy of the RSGs (metal mass and secondary side mass) does not affect the determination of the peak containment pressure, P., but only impacts the duration of the depressurization period. The increased energy of the RSG associated with higher operating T i value is accounted for by the increase of 3 Btu /lbm (corresponding to an increase in T..i of S.6 *F) during the reflood and depressurization periods and, therefore, is accounted for in the increased P. values proposed.
Bssis for Additional Time Post-reflood depressurization period is defined by Westinghouse as the time when the SGs first equalize with containment pressure to the time when the containment is completely depressurized (14.7 psla). Per B/B UFSAR Table 6.2-33, this period begins at approximately 300 seconds for the limiting LOCA case.
1 The containment analysis model shows that it takes several hours to significantly depressurize (and days to fully depressurize) the containment. Westinghouse conservatively forces SG depressurization to occur 3600 seconds after the SGs equalize with containment pressure.
The M&E releases with the RSGs use the same heat removal rate as the OSGs plus the additional 3 Btu /lbm added to account for the hotter initial temperature of the RSGs.
One hour after reaching equilibrium, the OSGs are depressurized completely per the forced heat removal rate employed by Westinghouse. At this same time, the RSGs are not completely depressurized because they have a greater stored energy than the OSGs due to increased metal mass and increased secondary side water mass.
in order to dissipate the additional stored energy in the RSGs, the depressurization rate for the OSGs (plus the 3 Btu /lbm)is continued for the RSG analysis until the additional RSG stored energy is completely dissipated. (See attached figure.)
Therefore, the OSG post-reflood depressurization period is modeled as 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />, while the RSGs take approximately 1.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> to reach the same condition.
The additional time for the RSG depressurization is still very conservative since the containment analysis shows it takes considerably longer to completely depressurize the containment.
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0 CALCULATION OF ADDITIONAL M&E DURING BLOWDOWN The RSGs have a larger primary side volume:
8 Vaso = 1249.5 A /SG Voso = 936.82 A'/SG A Volume = 312.68 R' Total RSG Volume increase = 4 x 312.68 A' = 1250.72 ft' Assuming a T v. of 588.4 'F plus a control band uncertainty of 9.5 *F and a primary pressure of 2250 psia, the steam tables yield the following:
At 597.9 'F and 2250 psia, Density, p = 43.38 lbm/A' (43.35 lbm/n')
Enthalpy, h = 609.8 Btu /lbm (610.2 Btu /lbm)
Therefore, additional Mass and Energy added during blowdown is:
Amass = AVolume x p = 54,256 lbm (54,;19 lbm)
Ah = 3.3085 x 10' Btu (3.3084 x 10' Btu)
Note: Steam Table values are from validated computer based steam table equations used by FTI. Values in parenthesis differ slightly from FTl values and are based on 1967 ASME Steam Tables. The FI'l values are conservative with respect to the parposes of the P. calculation.
4 1
0-i CALCULATION OF ENERGY DURING REFLOOD The RSGs are designed for an operating prescure of 954 psia (T.nso = 539.1 T) at an RCS average temperature, T.v.aso = $78.3 T.
The OSGs are designed for an operating pressure of 990 psia (Toi.oso== 543.6 T) at a design RCS average temperature, T.v.cso = 588.4 T.
To evaluate tne RSGs at the design T.,. of 588.4 T, the Toi.nso was increased by the difference of the RSO design T... and the OSG design T..
AT = T. oso - T., aso = 588.4 'F - 578.3 T = 10.1 T Toi.aso @ 588.4 7 = Toi.aso + AT = $39.I 7 + 10.1 'F = 549.2 'F The Toi differen::e r.t 588.4 T between the RSG and the OSG is 5.6 'F Because the RSGs operate at a higher Toi than the OSGs at the design T. of 588.4 T, the steam exiting a break (through the steam generator) during reflood could be 5.6 'F hotter.
Therefore, assuming an average containment pressure during reflood of 55 psia, the enthalpy, h, difference between the RSGs and the OSGs is:
haso = 1307.5 ' Btu /lbm @ 549.2 7,55 psia hoso = 1304.8 Btu /lbm @ 543.6 'F,55 psia Ah = haso - hoso = 2.7 Btu /lbm The revised LOCA M&Es conservatively assumed 3.0 Btullbm.
Note: Steam Table values are from' validated computer based steam table equations used by FTI.
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