ML20217B913

Derivation of Safety Valve Parameters,To Simulate Inlet Pressure Drop,For Input to Cesec Code for Chapter 14.9 & 14.10 Transient Analyses

ML20217B913
Person / Time
Site:	Fort Calhoun
Issue date:	01/23/1997
From:	Robert Lewis OMAHA PUBLIC POWER DISTRICT
To:
Shared Package
ML20217B907	List: LIC-98-0038, Forwards Response to Request for Addl Info on Mssvs.Revised Values for Table 1 Do Not Change Overall Conclusion of Analysis & Noted as Corrections in Attachment 1 to Ltr ML20217B913
References
EA-FC-97-004, EA-FC-97-004-R00, EA-FC-97-4, EA-FC-97-4-R, NUDOCS 9803260211
Download: ML20217B913 (4)

Text

I E. .*.- EA-FC-97-004 REV. 0 1 PAGE 00308(

Authors, R. E. Lewis, PE Date: Jan. 23, 1997 T1 Nile . Derivation of safety valve parameters,-to simulate inlet pressure drop, for input to CESEC code ~for Chapter-14.9 and 14.10 transient analyses. , , {

'The CESEC code used for _ the Chapter 14.9 and 14.10 transient analyses.does not account for . line pressure losses between the Steam Generator (SG),and the Main Steam Safety valves (MSSV).

To simulate the'effect of line pressure losses the available input parameters must be adjusted, based on equating CESEC derived flows to expected flows for the same SG pressure. .The code input parameters which represent the MSSVs are area, fraction of area at initial opening, setpoint, accumulation and blowdown.

.For pressures less than 1600 psia, saturated steam flow thru a

' safety valve can be predicted from Napier's formula ass j W(.Zb/br] = 51. 4 5 *A [in 2] *K* (R*P,,e [psig) +14. 4 ) ,

where ' A' ' is' the limiting valve opening area, 'K' is a flow I coefficient typirally considered to be 0.975, 'R' is a multiplier on setpressure which is equal to 1.0 at an initial valve opening of 70% and is equal to 1.03 at an accumulation pressure of 3% when the 3 valve is 100% open and ' P,,i '

is the valve setpoint and 14.4 I represents atmospheric pressure at 1007' above sea level.

Effective Area The valve inlet pressure is treated by CESEC as being equal to the SG pressure (i.e. no intervening pressure drop) . In the actual system, the SG pressure will be greater than the valve inlet pressure when there is flow thru the valve and/or process line. For the actual system, operating at a given SG pressure, there will be less flow thru an open valve (due to the reduced pressure head available across the valve) than will be predicted by CESEC if the actual valve area is input. If a smaller " effective area" is input, the code can be forced to calculate a SG pressure, required to produce.the same flow as the actual system, which is equal to the SG pressure of the actual system. When the valve is full open, at an accumulation of 3% (R=1.03), the SG pressure in the actual system will be equal to 1.03*setpoint plus the line pressure drop i associated with 100% of full flow. However, the driving pressure for flow thru 'the valve will be 1.03*setpressure. For the CESEC derived i flow' (based on ' a driving pressure of '1.03*setpoint+11ne losses) to equal the' actual flow, the two systems can be related thru Napier's equation as:

[1.03*P,,e+APw ,+14.4)*A,ff = (1. 0 3

• P,,e+14 . 4 ]

• A "9903260211'990318 '

PDR ADOCK 05000295 P PDR ,,

• - EA-FC-97-004 REV. C PAGE 00000 where the pressure loss is the sum of- run + branch for a system and valve f}owing at-100% of capacity:

A P2 ,,, = A P,un+ A Phruch l

for which An can be derived as:

[1. 03 *P,,e+14 . 4 ]

[1. 0 3

• P,,,+ A P2c,,+14 . 4 ]

At the setpoint of the valve (R=1), for which the opening area will be 70% of full open, the SG pressure in the actual system will be equal to the setpoint plus the line pressure drop associated with, 70% of full flow. However, the driving pressure for flow thru the valve will be the setpressure. Therefore:

A*fp7 0% = 0 . 7 +A*

[ P,,,+ A P 2,,,97 0 % +14 . 4 ] .

where the pressure loss is based on a valve flowing at 70% of full flow, which can be conservatively estimated from:

A P2 ,,,@7 0 % = A P,,,+ A Pbrach * ( 0 . 7 ) 2 which assumes the run and branch pressure loss terms are derived at 100% flow and that run losses are not significantly affected by the reduced flow of one valve.

Effective 70%'Openina Area Ratio From the previous derivations of effective areas, the effective opening area fraction for 70% flow will be y*" , ArS70%e A,a I

'.. - ~ EA-FC-97-004 REV. C -

PAGE 0300G; Eff'ecti e'Setooint For. conditions' representing flow thru the run pipe, an adjustment-is needed to account for the pressure diop in the run pipe (aihead of the -MSSV branch) prior to 'a particular valve opening. This adjustment can be accomplished by artificially increasing the input valve setpoint by the amount equal to the run pipe pressure' drop.

For the lowest setpressure MSSV this adjustment would be zero since no flow - exists immeadiately following the transient. For each

' higher setpressure valve, only the drop associated with the flow-

' thru the lower-setpressure valves need be accounted for in this adjustment. The prescure drop in the run pipe is proportional to the flow , and for each. valve can be derived from the maximum drop s

at full SG flow by:

W 2 A P,,, = ( A P,,,) m* ( 3 . 3E6 where 'W' is the flow in the run pipe at the time the valve in question would be expected to open.

The effective setpoint is thens (Psee) ett = P,,e+ A P,,,

Effective Accumulation At a' valve inlet accumulation pressure'of 3% (R=1.03) in the actual system, which represents a full open valve, the flow can be related  ;

(with Napier's formula) to that of the CESEC model by an " effective accumulation", which produces the same flow thru the effective area at the' effective setpressure:

[R,ff * (P,,e) ,ff +14 . 4 ) *A,ff = [1. 03 *P,,e+14. 4) *A rearranging for Rg results in:

• A 1#*4 A R,ff = 1. 03 * (P,,e) ,gg A,gg+ ( P ,,e) ,gg * ( A,gg-1) 1

)

E

i'

• 2 '

• EA-FC-97-004 REV. 0 PAGE 00:033-Effactiv'e Blowdown L An ef fective blowdown can be derived in an analogous nenner to the accumulation as follows: , ,.

• A + 14*4 A

-1)

E,ff = 0 . 9 6 * -- (P,,e) ,gg - A,gg ( P,,e) ,gg* ( A,gg where 0.96 is based on a blowdown of 4%..

-Adjustments to the blowdown parameter, will have no effect on the peak secondary pressures since they occur during the opening cycle of the MSSVs, for the transients of concern.

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