ML20196E974

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Revised Flow Dependent Thermal Limits
ML20196E974
Person / Time
Site: Grand Gulf Entergy icon.png
Issue date: 11/07/1988
From: Nir I, Smith F, Temple T
MSU SYSTEMS SERVICES, INC.
To:
Shared Package
ML19295G794 List:
References
NESDQ-83-003, NESDQ-83-003-R00, NESDQ-83-3, NESDQ-83-3-R, NUDOCS 8812120151
Download: ML20196E974 (17)
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Text

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NES0Q 88 003 Revision 0 GRAND GULF NUCLEAR STATION UNIT 1 REVISED FLOW DEPENDENT THERMAL LIMITS Nuclear Engineering Services Department MSU Systems Services, Inc.

November 1988 SS12120151 8S1206 PDR P ADOCK 05000416 PDC +

NE500 88 003 Revision 0 GRAND GULF NUCLEAR STATION UNIT 1 REVISED FLOW OEPENDENT THERMAL LIMITS l

Prepared by:

M e'/1/ W L

1. Ntr Date Lead Nuclear Engineer Plant Systems Analysis Section Reviewed by: > -

- // ed F.~H. Smith' Date Lead Nuclear Engineer Reactor Physics Analysis Section Approved by: .

/' W T. L. Temple / Date Manager Plant Systems Analysis Section 11

TABLE OF CONTENTS i l

Section P.aage 1.0 Introduction.................................................. 1 2.0 Current MCPR f and MAPFAC f

..................................... 1 3.0 Revised MCPR f and MAPFAC f ..................................... 2 4.0 One Loop Flow Runout Core F1ows............................... 4 5.0 References.................................................... 7 1

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4 1

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111 I

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LIST 0F TABLES Tables f.EL'

l. Core Flows for the One Ioop Flow Runout Event................... P,
2. Revi sed Flow Dependent Thermal Limi t s . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

, LIST OF FIGURES 4

5 Figures Page a

1. Revised Flow Dependent MCPR Limit............................... 10
2. Revised Flow Dependent MAPFAC Limit............................. 10
3. Flow Dependent MCPR Limits Comparison........................... 11 l
4. Flow Dependent MAPFAC Limits romparison......................... 11 iv

1.0 Introduction This report documents the rationale for the revit.ed MCPR f and MAPFAC 7

thermal limits for Grand Gulf Nuclear Station Ur.it 1 (GGNS1). These revised limits incorporate:

a. The GGNS-1 specific analysis results calculated by the Advanced Nuclear Fuels (ANF) ,instead of the BWR generic analysis results generated by General Electric (GE),
b. The inhtrent design features of the Loop Manual mode of operation which preclude a two loop flow runout event from being a credible event, and
c. The maximum achievable core flow rate without taking credit for the operator controlled core flow limiter.

The revised MCPR 7 and MAPFAC f thermal limits were derived from GGNS 1 specific analyses performed by ANF for Cycles 2 and 3 (References 1 and 2).

Additional conservatisms were imposed on the revised MCPR f limits as an allowance for future cycles. The probability of future changes in the is low since it was statistically established based or ,

MAPFACf curve varied operating conditions. Therefore, no additional margin of conserva-tism is necessary for the revised MAPFACf limits.

2.0 Current MCPR and 7

MAPFAC 7 The MCPRf and MAPTAC f thermal limits protect the plant from exceeding the MCPR safety limit and the 120% overpower line, respectively, in the event the recirculation flow control valves i advertently open (loop flow runout event). The limiting event for all modes of operation is the  ;

two loop runout event. The current limits are dependent on the operator-1 ,

controlled maximum core flow limiter which is set to either 102.5% or 107%

of rated flow. The MCPR g limits are based on a BWR/6 generic analysis performed by GE for Cycle 1 and confirmed for Cycles 2 and 3 by ANF.

The MAPFAC 7

limits for ANF fuel are based on GGNS 1 specific analy-sis performed by ANF for Cycle 2 and confirmed for Cycle 3.

3.0 Revised MCPR and7 MAPFAC f The revised MCPR7 and MAPFAC7 limit curves are constructed to bound the GGNS 1 specific two loop flow runout analyses results determined by ANF for Cycles 2 and 3. To eliminate the dependence on the operator controlled maximum core flow limiter, the revised curves conservatively assume a maximum core flow of 110*., which bounds the maximum flow achievable for the limiting flow runout event (Reference 3). These curves, labeled 'Non loop Manual" for MCPR g and MAPFAC 7 are shown on Figures 1 and 2, respectively, and are applicable to all flow control modes of operation (the term Non Loop Manual is used to differentiate from the specific Loop Manual mode which is addressed separately below). The revised MCPR g curve incor-porates the margin gain from the GGNS 1 specific analyses over the BWR generic GE analysis.

The Loop Manual mode is an operating mode which provides for independent manual control for each of the two rectreulation flow control valves.

Credit is taken for the fact that a two loop flow runout event is not credible in the Loop Manual mode, in this mode, the flow control valves are controlled independently with no single failure or singin operator action capable of inadvertently opening both valves simultaneously (Reference 4). Thus, in the Loop Manual mode, the limiting credible core 2-

_a

\

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flow increase event is the one loop flow runout event. Table 1 provides the initial and final core flows for the one loop flow runout event. The final core flows are conservatively calculated to bound the maximum achievable core flow rates for the one loop flow runout event (see Section 4.0).

Separate MCPRg and MAPFAC7 limits, applicable only when the plant is in the Loop Manual mode are constructed based on ANF analyses results for Cycles 2 and 3 using the conservative flow rate increases of Table 1 for a one-loop flow runout event. These limits, labeled ' Loop Manual", are shown on Figures 1 and 2 for MCPR7 and MAPFAC g

, respectively.

A numerical tabulation of the Non Loop Manual and the Loop Manual MCPRg and MAPFACf revised limits is provided in Table 2. The current GGNS MCPR operating limit at rated power and flow (1.18) is retained with the revised MCPR g limits.

The revised MCPRg and MAPFAC7 limits are corpared in Figures 3 and 4 to the

, current GGNS 1 i ~its which were used during Cycles 2 and 3. The re-vised MCPR g limit for Non Loop Manual operations is approximately equal or more limiting than the current lu.5 % maximum core flow MCPR 7 limit. 1he revised MAPFAC f limit for Non loop Manual operations is more limiting than both the current 102.5% and 107.% maximum core flow MAPFACf limits. The revised MCPR g and MAPFAC f limits for Loop Manual operations, as ex.

pected, provide for operating flexibility as a result of the inherent design characteristics (i.e., independent control of the flow control valves) of the Loop Manual operating mode.

3-J

--m,

4.0 One-Loon Flow Runout Core Flows During a one. loop flow runout event, a flow increase to maximum loop capacity occurs in one recirculation loop. The flow increase is caused by the inadvertent opening of the recirculation flow control valve (FCV) to the full open position. The position of the FCV in tho other loop remains unchanged. In order to evaluate the effect on the CPR and LHGR during a one loop flow runout event, it is necessary to establish the maximum core flow increase (i.e., final core flow rate minus initial core flow rate) for different initial core flow rates.

The total core flow rate is equal to the sum of the individual loop flow rates (the loop flow is dcfined as the loop . jet pump flow). The loop flow rate is regulated by the recirculation FCV by adjusting the pressure drop across the loop. Under symmetric loop conditions (i.e., same flow rates in both loops) the FCV position can be directly correlated with the core flow rate. For the limiting two loop flow runout event, the maximum open FCV position corresponds to a core flow rate that has been determined to be less than 110% of rated flow (Reference 3). The term "indicated loop flow' rate is cefined as that loop flow rate which would result from a specific FCV position under symetric loop conditions.

For asymetric loop conditions, the FCV position does not uniquely determine the loop flow rate because the loop flow rate is also affected by the flow rate of the other loop. Under asymetric loop conditions the actual loop flow rate may be different from the indicated loop flow rate, and therefore, the actual core flow rate may not equal the sum of the 4 4

Indicated loop flow rates. For the limiting one-loop flow runout event, the affected loop FCV is opened to the maximum open position. This position corresponds to the maximum indicated loop flow rate. The indicated loop flow rate of the other loop is unchanged since the FCV J

position remains the same. >

Under asymetric loop conditions following a one loop runout event, the

loop with the larger flow rate will have an actual flow rate highir than the indicated flow rate. This difference results because of the lower exit pressure exerted by the other loop in the lower plenum. The loop with the smaller flow rate will have an actual flow rate lower than indicated as a result of the higher exit pressure exerted by the other loop. Since the core flow rate is the sum of the actual loop flow rates, a relationship

) between the actual core flow rate (i.e., sum of the actual loop flow rates) to the indicated core flow rate (i.e., sum of the indicated loop flow i

) rates) is required in order to analyze the one loop flow runout event.

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A conservative and simple relationship, applicable to all final core flow I rates, is established by using the indicated core flow rate instead of the actual core flow rate. This relationship is used in evaluating the cos a i flow increase following a one loop runout event. This relationship is conservative (maximizes flow increase) since the indicated final core flow always bounds (i.e., is higher than or equal to) the actual core flow. The t

1 difference between the indicated and actual core flow rates is zero for the symetric loop conditions and increases with an increasing degree of I

asymetry. This relationship has been demonstrated t,y a GGNS plant startup test (one recirculation pump trip, Reference 5). This relationship is also

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l supported by analysis using a computer model which has been validated against GGNS startup test data.

With the above relationship between the indicated loop and actual core flow rates, the change in the core flow rate during a one-loop runout event can be bounded for any set of initial conditions. The following steps are used to establish a conservative flow rate increase for the one loop flow runout event: l l

a. Assume an initial mismatch of i n of rated flow between tie two loops M based on the GGNS Technical Specifications, Section 3.4.1.3 (I M was assumed for all initial core flows even though the lechnical Specifica-tions limit the mismatch to 5% above 73 core flow),
b. Assume that the loop with the lower initial flow rate will be the affecied loop (maximizes flow increase),
c. Assume a maximum indicated loop flow rate of 11% of rated for the affected loop, following the runout event,
d. Establish the final core flow rate as the sum of the individual indicated loop flow rates,
e. Increase the final total core flow rate calculations (a 2.5% conservative bias in flow rate),

f,i' ' Tb individual core channel flow rates are not affected by unequel loop

'y flow rates. This is consistent with the assumption of complete lower

' ~

plenum mixing which was empicyed by GE in their GGNS 1 single loop opration analysis and has been accepted by the NRC (Reference 6). As 6-

lower plenum mixing is governed by vessel design, the validity of this assumption will not be affected by the insertion of ANF fust bundles.

The one-loop runout event final flow rates for various initial flow rates analyzed are presented in Table 1. These flow rates were calculated using the above five steps and represent a conservative upper bound to the actual flow rates expected fa11owing the one loop runout event.

5.0 References

1. ' Grand Gulf Unit 1 Cycle 2 Reload Analysis", XN NF 86 35, Rev. 3, Exxon Nuclear company, Inc., Richland, WA, August 1986.
2. "Grand Gulf Unit Cycle 3 Reload Analysis", ANF 87 67. Rev. 1. Advanced Nuclear Fuels Corporation, Richland, WA, August 1987.
3. Smith. A. R. (GE) to J. G. Cesare (SERI), 'GGNS Maximum Core Flow Capability". SEGE 87/'425,11/87.
4. NEDE 240ll P A 4US, Appendix B.
5. Kingsley, 0.. D. (SERI) to Grace, J. N. (NRC), "Final Sunnary Startup Test Report 12', AECM 8610066, 2/86.

, 6. Kingsley, O. D. (SEr' Denton, H. R. (NRC), PCOL 86/05, AECH 86/0092, 3/86 '' , Single Loop Optration Analysis", GE, 2/86 attached),

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Table 1 Core Flows for the One Loop Flow Runout Event Initial Core Final Core Flow Increase Flow (%) Flow (%) (n of Rated) 100 110 10 90 105 1s 80 100 20 70 95 25 60 90 30 50 85 35 [

40 80 40 30 75 45 , ,

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Table 2 i

Revised Flow Dependent Thensal Limits i

i Non Loop I.oop Non Loop toop Core Manual Manual Manual Manual Flow (%) MCPR MCPR MAPFAC MAPFAC f f f f 105 1.18 1.18 1.0 1.0 91.0 - - 1.0 -

90 - - 0.992 - i 86.3 1.18 - - -

i 1.0 i 84.3 - - -

! 80 1.212 - 0.904 0.977

+

73.4 - 1.18 - -

70 1.271 1.193 0.827 0.928 ,

60 1.345 1.243 0.757 0.880 50 1.441 1.314 0.695 0.837 40 1.566 1.414 0.638 0.794 l i

30 1.727 1.545 0.586 0.752 j i

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, , - - - _. - . _ _ . - . - , _ . _ , , , ~ _ _,,...-e, . - - - - , - ,

FIGURE 1 REVISED FLOW DEPENDENT MCPR LIMIT 1.80 1.70- + NON LOOP WANUAL LOOP WANUAL 1.60-

< 1.50-E1.40-M 1.30-1.20- .

t 1.10-1.00 , , , , , , , , ,

20 30 40 50 60 70 80 90 100 110 120 i COR[ FLOW (!)

i FIGURE 2 REVISED FLOW DEPENDENT MAPTAC LIMIT 1.th 4

1.00- -

ll j 0.00-i

! U

t 0.10-i I

0.70-

- LOOP WANUAL l

I -+- NO N L O O P W AN U A L 0.80-

0.50 , , , , , , , , ,

20 30 40 50 60 70 10 10 100 110 120 CORE FLOW (t) 1 l

I

t FIGURE 3 FLOW DEPENDENT MCPR LIMITS COMPARISON 1.80 l

1.70- -.- NON LOOP WANUAL  !

-+- LOOP W ANU AL 1.50-

  • s'\s N -+- T/5 10 7 1.50- s'N s -+- I/5 10 2. 5

" 1. 4 0 - N'sN'N N s'

M ,. N g'N 1.30-s's 1.20- Y.N . . .-

1.10-1.00 i i i i i i i i i f 20 30 40 50 60 70 10 10 100 110 120 CORE FLOW (1)

FIGURE 4 '

FLOW CEPENDENT MAPFAC LIMITS COMPARISON 1.10 f

1.00- -

i s ,

/,r' O.90- [

,s/s,/

, 1 W - l t 0.80-i

/'/ I l

,r'/s' s ', -+- NON LOOP WANUAL

[

0.70-

1 A' ,',y/ - LOOP WANUAL

+ T/l 107 0.so-  !

-+- I/5 102.5 i 1

0.50 i , , i i i i i i  ;

20 30 40 50 60 70 80 10 100 110 120 CORE FL0t (1) (

l

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