L-2012-168, Response to NRC Nuclear Performance and Code Review Branch Request for Additional Information Regarding Extended Power Uprate License Amendment Request

Response to NRC Nuclear Performance and Code Review Branch Request for Additional Information Regarding Extended Power Uprate License Amendment Request

ML12115A180
Person / Time
Site:	Saint Lucie
Issue date:	04/19/2012
From:	Richard Anderson Florida Power & Light Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
L-2012-168
Download: ML12115A180 (4)

Text

0 Florida Power & Light Company, 6501 South Ocean Drive, Jensen Beach, FL 34957 FPL.

April 19, 2012 L-2012-168 10 CFR 50.90 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555 Re: St. Lucie Plant Unit 2 Docket No. 50-389 Renewed Facility Operating License No. NPF-16 Response to NRC Nuclear Performance and Code Review Branch Request for Additional Information Regarding Extended Power Uprate License Amendment Request

References:

(1) R. L. Anderson (FPL) to U.S. Nuclear Regulatory Commission (L-2011-021), "License Amendment Request for Extended Power Uprate," February 25, 2011, Accession No. ML110730116.

(2) R. L. Anderson (FPL) to U.S. Nuclear Regulatory Commission (L-2012-147), "Response to NRC Nuclear Performance and Code Review Branch Request for Additional Information Regarding Extended Power Uprate License Amendment Request," April 5, 2012.

By letter L-2011-021 dated February 25, 2011 [Reference 1], Florida Power & Light Company (FPL) requested to amend Renewed Facility Operating License No. NPF-16 and revise the St.

Lucie Unit 2 Technical Specifications (TS). The proposed amendment will increase the unit's licensed core thermal power level from 2700 megawatts thermal (MWt) to 3020 MWt and revise the Renewed Facility Operating License and TS to support operation at this increased core thermal power level. This represents an approximate increase of 11.85% and is therefore considered an Extended Power Uprate (EPU).

During a phone call on March 22, 2012 the NRC staff requested additional information related to the analysis of post-LOCA boric acid precipitation in support of their review of the St. Lucie Unit 2 EPU License Amendment Request (LAR). The attachment to this letter transmits the requested information. The question and response are similar to the St. Lucie Unit 1 response provided by FPL in the Reference 2 letter.

This submittal contains no new commitments and no revisions to existing commitments.

Da an FPL Group company

L-2012-168 Page 2 of 2 This submittal does not alter the significant hazards consideration or environmental assessment previously submitted by FPL letter L-2011-021 [Reference 1].

In accordance with 10 CFR 50.91(b)(1), a copy of this letter is being forwarded to the designated State of Florida official.

Should you have any questions regarding this submittal, please contact Mr. Christopher Wasik, St. Lucie Extended Power Uprate LAR Project Manager, at 772-467-7138.

I declare under penalty of perjury that the foregoing is true and correct to the best of my knowledge.

Executed on I cl -r; - 1A.1 Very truly yours, Richard L.Anderso Site Vice President St. Lucie Plant Attachment cc: Mr. William Passetti, Florida Department of Health

L-2012-168 Attachment Page 1 of 2 Response to NRC Nuclear Performance & Code Review Branch Request for Additional Information The following information is provided by Florida Power & Light (FPL) in response to the U. S.

Nuclear Regulatory Commission's (NRC) request for additional information. This information was requested to support Extended Power Uprate (EPU) License Amendment Request (LAR) for St. Lucie Unit 2 that was submitted to the NRC by FPL via letter L-2011-021 dated February 25, 2011, Accession Number ML110730116.

During a phone call on March 22, 2012 the NRC staff requested additional information related to the analysis of post-LOCA boric acid precipitation in support of their review of the St. Lucie Unit 1 EPU LAR. One question was identified during the phone call as also being applicable to St.

Lucie Unit 2; this question has been paraphrased by FPL. The question and response for St.

Lucie Unit 2 are provided below.

Question I Provide clarification of the lower plenum temperature prior to sump recirculation, and how that temperature would affect boric acid precipitation. Specifically, the NRC Staff noted the following from their own confirmatory analysis [of the St. Lucie Unit I EPU submittal]:

Note the concentration spike at about 45 min. is about 12.5 wt%, which marks the beginning of lower plenum mixing at a lower plenum temperature of about 140 OF (Note, the precipitation limit at 140 OF is 12.97 wt%). One needs to show that the concentration in the core, when safety injection flow begins to enter and mix with the lower plenum, is below the precipitation limit at the min lower plenum temperature.

Response

The boric acid analysis does not explicitly calculate the temperature in the lower plenum. The analysis assumes saturation at atmospheric conditions, which is conservative, as it maximizes core boil-off.

Following a large break loss-of-coolant accident (LBLOCA), safety injection (SI) comes from the refueling water tank (RWT) prior to sump recirculation. This is the timeframe being examined for this response, so all SI will come from the RWT. RWT minimum liquid temperature is 51 OF.

This time in the LOCA long term cooling transient is also before simultaneous hot and cold leg injection, so all SI is being injected into the cold legs, and travels down the downcomer to the lower plenum. The core region is at much hotter, saturation conditions (i.e., 212 OF) due to decay heat.

The liquid temperature distribution in the reactor vessel during long term cooling would be expected to be subcooled single phase liquid in the lower plenum, subcooled to saturated liquid in the lower core region, and saturated two-phase liquid-vapor in the remainder of the core region and outlet plenum region. This represents a hydrodynamically stable condition, i.e., the

L-2012-168 Attachment Page 2 of 2 layers (less dense atop more dense) will remain heterogeneous unless a destabilizing force is applied. Up to the point of the transfer to sump recirculation, the coolant is an aqueous boric acid solution. Boric acid is only mildly miscible in the vapor phase so it accumulates in the liquid phase as boiling occurs in the core region. The accumulation of solute can provide the destabilizing force needed to produce convection (heat and mass transport) between the layers.

Therefore, the lower plenum region would be at a temperature between 51'F and 212 OF during the time following a LBLOCA prior to sump recirculation. The LBLOCA emergency core cooling system (ECCS) performance analysis calculates downcomer liquid temperature during reflood, which can be used to approximate lower plenum temperature during this time.

Per the LBLOCA ECCS performance analysis, the downcomer liquid temperature is 130 OF during the refill/reflood timeframe.

Note that in support of a separate NRC RAI (SRXB-1 13; see Reference a.), a figure was generated that only calculates the downcomer liquid temperature out to 500 seconds post-LOCA (approximately 8 minutes). However, the limiting LBLOCA case that this figure is based on was run out to 900 seconds post-LOCA (i.e., 15 minutes) and shows a downcomer liquid temperature of 130 OF at that time as well. Due to the steady-state nature of the downcomer liquid temperature seen in the figure, it is judged to be appropriate to use this value for the entire period post-LOCA prior to sump recirculation.

The LBLOCA analysis assumes no condensation of steam in the cold legs after the safety injection tanks (SITs) have emptied. Including this condensation would increase the temperature of the SI liquid from the RWT before it reaches the downcomer. The current analysis models no condensation to calculate liquid temperatures, which results in the SI liquid entering the downcomer at the RWT temperature (i.e., 51 OF). In support of a separate NRC RAI (SRXB-1 12; see Reference a.), Westinghouse evaluated the effect of accounting for both partial condensation and full condensation in the cold legs. This evaluation concluded that accounting for even partial condensation in the cold legs results in a significant increase in fluid enthalpy in the downcomer. By 500 seconds post-LOCA, the downcomer is approaching saturation conditions. Based on Figure 1c from the response to RAI SRXB-1 12 (Reference a.),

the liquid enthalpy can be conservatively estimated to be 190 BTU/Ibm. At a pressure of 14.7 psia and enthalpy of 190 BTU/Ibm, the temperature of liquid in the downcomer would be 212 OF.

Taking credit for condensation of steam in the cold legs and considering the mixing of lower plenum fluid with the borated hot fluid from the core, the lower plenum temperature would be 212 OF. A temperature of 212 OF corresponds to a boric acid solubility limit in the lower plenum of 27.53 wt%.

References

a. R. L. Anderson (FPL) to U.S. Nuclear Regulatory Commission (L-2012-131), "Response to NRC Reactor Systems Branch Request for Additional Information Regarding Extended Power Uprate License Amendment Request," April 5, 2012.