ML20052C196

Nonproprietary Response to NRC Questions of FATES3 & Calvert Cliffs 1 Cycle 6 Reload.

ML20052C196
Person / Time
Site:	Calvert Cliffs
Issue date:	04/23/1982
From:	ABB COMBUSTION ENGINEERING NUCLEAR FUEL (FORMERLY
To:
Shared Package
ML19268D320	List: ML20052C191 ML20052C196
References
CEN-205(B)-NP, NUDOCS 8205040487
Download: ML20052C196 (12)

Text

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. . . e l CEN-205(B)-NP RESPONSE TO NRC QUESTIONS ON FATES 3 AND THE CALVERT CLIFFS 1 CYCLE 6 RELOAD April 23,1982 COMBUSTION ENGINEERING, INC.

O 1 8205040487 820427 PDR ADOCK 05000317 P PDR

LEGAL NOTICE This report was prepared as an account of work sponsored by Combustion Engineering, Inc. Neither Combustion Engineering nor any person acting on its behalf:

A. Makes any warranty or representation, express or implied including the warranties of fitness for a particular purpose or merchantability, with respect to accuracy, completeness, or usefulness of the information contained in this report, or that the use of any information, apparatus, method, or process disclosed in this report may not infringe privately owned rights; or B. Assumes any liabilities with respect to the use of, or for damages resulting from the use of, any information, apparatus, method or process disclosed in this report.

l Question 1 Has the Combustion Engineering ECCS evaluation model (STRIKIN) been modified to account for revisions in the FATES 3 code in areas such as gap conductance?

Response 1 The Combustion Engineering ECCS evaluation model did not require modification to account for revisions in the FATES 3 code. The ECCS model and conputer codes, including the hot rod heatup code STRIKIN-II, remain unchanged from those approved by NRC for compliance with 10CFR50, Appendix K. STRIKIN-II utilizes the FATES 3 burnup dependent characterization of fuel rod conditions (fuel density, pin pressure, fission gas content, plus cold clad and fuel dimensions)asinput. STRIKIN-II then initializes itself based on th,is FATES 3 input and the ECCS analysis assumpti6ns of peak kw/ft and limiting axial power distribution.

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'Oucstion.2 .

Qo the pellet volume averaged temperatures and hot rod internal pressures calculated by the FATES 3 code continue to be bounded by those values calculated with STRIKIH if the FATES 3 code is ramped to the some LOCA initial power conditions used by STRIKIN? What are the power distributions used in STRIKIN? What are the fuel (centerline and surface) and cladding (inside and outside) tenperatures corresponding to those results given in Section 8.3 of the Calvert Cliffs Unit 1, Cycle 6 Reload Report? Is this conclusion changed by the instantaneous fission gas release model in FATES 3 or the burnup assumed for the calculation?

Response 2 Pellet volume averaged temperatures and hot rod internal pressures of FATES 3 continue to be bounded with STRIKIN.

STRIKIN-II and FATES 3 were used to calculate fuel temperatures and hot rod internal gas pressures for the same assucptien of burnup, initial pcwer letel, and power distribution for verification. Table 2-1 lists the FATES 3 and STRIKIN-II fuel temperatures and pin pressures predicted at two rod average bu rnups. In each case the same peak power and axial and radial power distributions were assumed. The data shown is not for CC-1, Cycle 6 but for identical fuel with a trapazoid axial power shape set at a peak of 10.46 ku/ft and an axial average of 9.39 kw/ft. The 4500 MWD /MTU data is typical of early in life fuel conditions. This corresponds to fully densified fuel, maximum fuel-clad, gap size and hence the time of maximum stored energy in the fuel.

The 25,500 MWD /MTU data is typical of end of cycle fuel conditions with high pin pressures, fuel-clad contact and relatively low stored energy in the fuel.

For both conditions, a close correspondence between fuel centerline, fuel ,

surface and volume average fuel temperatures is shown. The STRIKIN-II volume I averaged tenperatures are shown to be slightly higher than FATES 3. The pin pressure is transferred directly from FATES 3 to STRIKIN-II. Therefore, there is an exact correspondence of this parameter.

2-1

- The powet dist,ributions used in STRIKIN-Il for E' CS C performance. calculations have four basic components. First, a g:neric normalized axial powir s-distribution is used for all C-E ECCS . calculations having a 1.68 peaking factor at 65% of the core height. This generic axial shape was developed from sensitivity studies documented in CENPD-132-P and reviewed and approved by NRC for conservative application in C-E ECCS performance analyses., Second, the normalized radial distribution of heat generation rate in the fuel pelle: is transferred as input directly from FATES 3. Third, the absolute power generation in STRIKIN-II is defined by selecting a target peak linear heat rate (kw/f t) input specification for the peak power node. Fourth, fractions of total rod power generated in the pellet, clad and coolant are specified. Thes e ,

four components together yiele a complete definition of the hot rod poder distribution.

Table 2-2 lists the actual initial fuel and clad temperatures predicted by STRIKIN-II at 15.5 kw/ft at the two burnups discussed in Section B.3 of the:

Cycle 6 reload report.

STRIKIN-II remains consistent with the fuel parameter predictions of FATES 3 at all burnups and this conclusion is not changed by the instantanacus fisalon gas release model in FATES 3. --

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2-2

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.. s TABLE'2-1

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- Comparison of FATES 3 and STRIKIN-II Fuel Parameter Predictions s.

Comparison 0 4500 mwd /mtu (Rod Average Burnup):

Code Fuel Centerline Fuel Surface Volume Avg. Pin Pressure Temp (F) Temp (F) Fuel Temp (F) (psia)

FATES 3 2625 1058 1782 1178 STRIKIN-II 2624 - 1071 1793 1178 Comparison 0 25,500 mwd /mtu (Rod Average Burnup):

FATES 3 2275 839 1495 1646

( STRIKIN-II 2280 853 1508 1646 d

2-3

TABLE 2-2 STRIKIN-II Fuel Parameter For Calvert Cliffs Unit I Cycle 6 Burnup_ Fuel Temperature (*F) Clad Temp (F) Pin Pressure Center .

Line Surface Vol Avg. ID OD (osia) 3000 mwd /mtu 3C34 1044 2213 767 663 1251 34000 mwd /mtu 3551 992 2127 766 663 2191 I

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Question 3 Please supplement Section 2.4, " Application of fission gas release model to a variable fuel temperature history" in sufficient detail to permit programming of the model in an NRC fuel performance audit code.

Response 3 Combustion Engineering has developed a fission gas release model which uniquely accounts for variable power and temperature history. The new model accounts for gas release from individual regions of a fuel pellet (radial rings) and more properly calculates fission gas release rate based on the current unreleased fission gas inventory in each region. In addition, the mechanism of grain boundary sweeping which accompanies grain growth is recognized and the associated fission gas release modeled. C-E believes thisfeature to be particularly important in modeling fission gas release after a significant power increase. A description of the method by which C-E models the fission gas release equations described in CEN 161(B) is given below and is followed by a detailed example. .

T Q . . . . . .. .. : . _::=. ^ : .. -- - T.::._; ; - --- .__ T3- _ L ; ; ;_-

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These empirically derived curves are described by

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. whsre (3-la)

(3-lb)

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l Terms are the same as defined in Section 2.2 of CEN 161(B).

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- = . .. .:.._..--_..----- - ._ - - ,_. - - - - - - - - - - - - - - . - - - . - . -

Ignoring grain growth for the moment, the fission gas inventory is computed

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from Equation 3-1 using specific rules _.. _ . .. . _. __ _ _ . . . . _ . _ __. . _ . . . _ . .

and then computing the release fraction from 1

(3-2) 1 The rules necessary for application to a variable temperature history are:

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M emu W.

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kf tempar'atures are sufficiently high for a period of tima, grain growth occurs as described by Section 2.2 of CEN-161(B). If grain growth is predicted to

. occur during an increment of history, then an additional decrease in inventory

. (or gas release) is computed __ _ , _ _ _ _ _ _ _ _

as described above. This decrease in inventory is given by (3-3)

Terms are the same as defined by CEN-161(B). Rules applied when grain growth occurs are:

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- - . .a An example of cycling between two temperature leve,ls Tj and T2 is given in

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The additional increments shown in the figure follow the same pattern.

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Figure 3-1 i

FATES 3 MODELING OF TEMPERATURE CYCLING BELOW TEMPERATURE

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