NRC-87-0073, Forwards GE Transient Performance Evaluation Rept Which Provides Basis for Reduced Feedwater Temp Operation,Per 870511 Meeting.List Operational Constraints Currently Being Imposed to Ensure Addl Thermal Operating Margin

Forwards GE Transient Performance Evaluation Rept Which Provides Basis for Reduced Feedwater Temp Operation,Per 870511 Meeting.List Operational Constraints Currently Being Imposed to Ensure Addl Thermal Operating Margin

ML20214H530
Person / Time
Site:	Fermi
Issue date:	05/19/1987
From:	Agosti F DETROIT EDISON CO.
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
CON-NRC-87-0073, CON-NRC-87-73 TAC-65400, NUDOCS 8705270406
Download: ML20214H530 (10)

Text

__

Detroit r-ni 2

. Edison EE2882 h

W 21 May 19,1987 NBC-87-0073 U. S. thclear Regulatory Constission Attn: Document Control Desk Washington, D. C. 20555

Reference:

Fermi 2 NIC Docket No. 50-341 NIC License No. NPF-43

Subject:

Reduced Feedwater Heatina During a meeting on May 11, 1987, the NIC Staff expressed interest in obtaining additional information from Detroit B51 son with regards to reduced feedwater tenperature operation at Fermi 2. Ehclosure l'to this letter contains the Transient Performance Evaluation Report supplied by General Electric which provides the basis for reduced ,

feedwater tenperature operation. As a result of this report, the i following operational constraints are currently being iW at ,

Fermi 2 to ensure a5ditional thermal operating margin: l

1) Befgre exceeding 25% power, the feedwater tenperature should be 190'F or above.

2) At power levels greater than 25%, the feedwater tenperature should be equal to or greater than the value shown in the attached curve (Enclosure 2),

3) If the assunptions for the General Electric analysis cannot be met, all feedwater heaters should be in service, or the power-should be less than 25%. I If you have any questions, please contact Mr. John Price at (313) l 586-4513.

Sincerely,

<- D 8705270406 870519- i 4 PDR ADOCK 05000341 P PDR Frank E. Agosti-Vice President

~~

!bclear Operations I oct A. B. Davis E. G. Greenman 8 t

W. G. Rogers J. J. . Stefano

/

DCIOSURE 1 l

t f

k

t TRAN$1ENT PERFORMANCE EVALUATION FOR REDUCED FEEDWATER TEMPERATURE OPERATION AT FERMI-2

3.

SUMMARY

Normally, feedwater temperatures increase smoothly from approximately 290'F at 4

25% power to 420*F at 100% power. However, the startup sequence employed at Fermi-2 results in a condition where feedwater temperature is approximately 100*F lower than these nominal conditions for power levels less than 75% as shown in Figure 1. The lower- feedwater temperature has raised a concern regarding impact on transient MCPR for the low power conditions. An analysis has been performed which demonstrates that the reduced temperature has only a minor impact on transient results and that emple margin to the safety limit MCPR

remains. It is concluded that existing MCPR limits are adequate and no changes i to the technical specifications are required.

2. EVALUATION Figure 2 illustrates the typical operating MCPRs (dashed lines in the figare) that result with normal operation over the power flow map. Note that as power is reduced MCPR increases rapidly. Only relatively small reductions in MCPR occur as flow is reduced. This behavior is important from the perspective that the opera' ting MCPR is a minimum near rated power and flow. It is for this reason that design basis transient analyses are performed at the licensed full power condition, i.e., for rated power and flow. Eventhough(aswill.beshown below) some transients may produce larger ACPRs at off-rated conditions, the actual operating MCPR increases much more rapidly so that the full power, full flow operating point is the most limiting state on the power flow map.

Table 1 summarizes the results of the analysis of the feedwater controller failure for both normal and the lower feedwater temperatures. Other transients

l are not adversely impacted. As can be seen, the ICPR values increase only slightly for the reduced feedwater temperature, whereas the OCPR values increase

dramatically. These results are also summarized in Figure 3. The margin to the safety limit MCPR is the difference between the OCPR and the ICPR. Note that the full power operating point is clearly the most limiting and that for the reduced power states very large margins exist.

The analyses described above were performed with power and flow conditions along the nomal startup path. For other unusual conditions, e.g., operation at low power and high flow, ACPR would be larger than for the normal startup conditions. However, the expected OCPR would also increase.

The analyses included credit for the direct scram on stop valve closure which l

has been verified to be set at less than 25% power for Fermi-2. If no credit is taken for direct scram, the delta CPR for the 25% power case would increase by i about 0.60. However, large margins to the safety limit MCPR would still remain.  ;

1 l It should also be noted that other protections exist that serve to minimize the l potential impact of transients at off-rated Conditions. These include the K f

i factor and scram setdown requirements associated with peaking factors in excess of design.

i

3. CONCLUSION l

l These results illustrate that the design basis full power operating point is by .

far the most limiting state on the power flow map. While the transient ACPR values may increase somewhat for off-rated conditions, the increase is very small in coteparison to the increase in actual operating MCPR. In particular the impact of the lower feedwater temperatures is very small and well within the available mergins. Hence, the existing MCPR limits are adequate.

I

. Table 1 Transient Analyses Results for Feedwater Controller Failure with Normal and Reduced Feedwater Temperature Trahsient case CASE 1 S88 1.1 S&EL1 S&RL.i Initial Power 50 50 25 25 (t NBR)

Initial Core Flow 50 50 50 50 (t,NSR)

Feedgater Temp. 350 230 290 180

( F)

Peak Neutron Flux 71 77 42 48

( % NBR ) ,

Peak Heat Flux 113 118 125 133

( % Init. )

^

Peak Dome Pressure 1012 1007 945 944.

( psig )

Peak Vessel Pres. 1026 1012

~

960 960

( psig )

Peak Steamline Pres. 1011 997 946 945

( psig )

Delta CPR* 0.20 0.25 0.32 0.41

s ICPR" 1.26 1.31 1.38 1.47 OCPR " 2.25 2.25 3.46 3.46

~

Margin to SLMCPR+ 0.99 0.94 2.08 1.99 a

ACPR includes option A adjustment factor.

ICPR = ACPR + safety limit CPR (1.06)

OCPR is the expected operating CPR based on statiscal evaluation.

+

SLMCPR is the safety limit MCPR.

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