ML102010464

Enclosure 14 - Westinghouse Report, Ses 09-129-NP, (Nonproprietary) Revision 2, Monticello - Steam Dryer Replacement Moisture Carryover Analysis

ML102010464
Person / Time
Site:	Monticello
Issue date:	06/22/2010
From:	Lemoigne Y Westinghouse Electric Sweden AB
To:	Office of Nuclear Reactor Regulation
References
L-MT-10-046, TAC MD9990 SES 09-129-NP, Rev 2
Download: ML102010464 (14)

Text

ENCLOSURE 14 WESTINGHOUSE REPORT, SES 09-129-NP, (NONPROPRIETARY) REVISION 2, MONTICELLO - STEAM DRYER REPLACEMENT MOISTURE CARRYOVER ANALYSIS 13 pages follow

Westinghouse Non-Proprietary Class 3 Westinghouseeport SES 09-129-NP, rev 2 Page 1 of 13 Westinghouse Electric Sweden AB Monticello - Steam Dryer Replacement Moisture Carryover Analysis Author, telephone Dept Yann Le Moigne, +46 21 34 75 01 SES Distribution Order No Xcel Energy ES-09-0224 Abstract This report presents the analyses performed to design the replacement dryer in order to meet the MCO requirement set by Xcel Energy.

The analyses show that the replacement dryer is expected to have the following performances:

• MCO of [

]ax

" pressure drop of [

]axc at a reactor thermal power of 2004 MWt and a core flow of 57.02 Mlb/hr.

The customer requirement of a MCO below 0.030% by weight is therefore met.

The performances of the replacement steam dryer at 102% EPU power (2044 MWt), for a radial power peaking factor of [

]a.c, are also presented in the report.

Review and approval status (Organization, name, initials)

Copy:

SE/A. Andr6n, SES/E. Lillberg, T. Stromgren

Report

• WWestinghouse SES 09-129-NP, rev 2 Page 2 of 13 CONTENTS 1

INTRODUCTION 4

2 REQUIREMENTS 4

3 MOISTURE SEPARATION 4

3.1 Steam Separators 4

3.2 Steam Dryer 5

4 CORE DATA AND INLET MOISTURE TO THE DRYER 5

4.1 Data at EPU Conditions (2004 MWt) 5 4.2 Data at 102% EPU Power (2044 MWt) 6 5

DESIGN OF THE VANE. BANKS 6

5.1 Vane Banks Configuration and Area 7

5.2 Steam Flow through the Vane Banks 7

5.3 MCO Calculations 7

5.4 Pressure Drop 7

6 DESIGN OF THE DRAINAGE SYSTEM 8

6.1 General Description 8

6.2 Design Methodology 9

7 EXPECTED PERFORMANCES 10 7.1 Moisture Carryover 10 7.2 Pressure Drop 10 7.3 Water Level 10 7.4 Carry Under 10 7.5 Performances at 102% EPU power (2044 MWt) 10 8

CONCLUSIONS 11 9

REFERENCES I1I

• Westinghouse Report SES 09-129-NP, rev 2 Page 3 of 13.

ABBREVIATIONS BOC Beginning Of Cycle CFD Computational Fluid Dynamics EOHFP End Of Hot Full Power EPU Extended Power Uprate MCO Moisture Carryover MOC Middle Of Cycle RPV Reactor Pressure Vessel

Westinghouse Repor SES 09-129-NP, rev 2 Page 4 of 13 1

INTRODUCTION A replacement steam dryer will be delivered by Westinghouse to Monticello Nuclear Generating Plant for installation during the outage of 2011. The replacement of the steam dryer is part of the measures taken to perform an EPU from today's thermal power of 1775 MWt to 2004 MWt.

This report documents the analyses of the performance of the steam dryer in terms of moisture carryover and pressure drop. Expected values for the MCO and the pressure drop are given as the results of the analyses.

2 REQUIREMENTS The customer requirement is that the MCO shall be less than 0.030% by weight for a carry-in of 3% by weight at a reactor thermal power of 2004 MWt [1]. In addition, the pressure drop through the steam dryer assembly shall be as low as possible when the MCO requirement is met.

3 MOISTURE SEPARATION In a BWR, the moisture separation is performed in two stages. The two-phase mixture that leaves the core has a quality of around 10-20% when it enters the first separation stage made of the steam separators also called primary separators. The steam separators separate most of the water and the quality of the flow after the separators is around 90-99% (corresponding to a moisture content of 1-10% by weight) depending on the performance of the separators. The remaining water drops are separated in the second stage of separation, the steam dryer. Almost dry steam leaves then the reactor vessel through the steam lines. The moisture content in the steam leaving the reactor vessel is called the MCO.

3.1 STEAM SEPARATORS The steam separators are placed on top of the core shroud and constitute the exit of the core region for the two-phase mixture that is created in the fuel channels. The separators are usually of cylindrical shape. Swirl vanes are placed at their bottom in order to set the mixture flow into rotation. Water and steam are separated by centrifugal force with the water flowing along the inner wall of the cylinder and building a water film there while the steam flows upwards in the center of the barrel. Pick-off rings capture the water film and lead the water between concentric barrels to the water pool that surrounds the separators.

The overall performance of the steam separators depends on the total core flow that passes through them; the quality of that flow; the distribution of the quality between the separators, which is related to the radial peaking factor of the core; the height of the water level in the water pool that surrounds the separators and the number of separators.

Westinghouse Report SES 09-129-NP, rev 2 Page 5 of 13

]a,c The primary separation stage consists of 129 steam separators at Monticello.

3.2 STEAM DRYER The steam dryer is an assembly of vane banks that separate the remaining water droplets from the steam. The vanes are vertical corrugated plates with a saw tooth like profile. The separation is performed by the centrifugal force when the steam flows between these vanes. The heavier water drops impinge on the walls of the vanes while the steam flows around all the corners and exits the vanes almost without any moisture left. The liquid that hits the vanes is then trapped in pockets that lead it by gravity to the bottom of the banks where it is collected and drained.

]a,c The performance of the steam dryer depends on the total steam flow that passes through it and the moisture content of that steam when it enters the dryer. This moisture content is called the carry-in. The size of the water droplets at the inlet of the dryer is also an important parameter since large drops are easier to separate than very small ones that can more easily follow the steam.

4 CORE DATA AND INLET MOISTURE TO THE DRYER 4.1 DATA AT EPU CONDITIONS (2004 MWt)

The inlet moisture content at EPU conditions has been estimated based on core power and flow data provided by the customer, Xcel Energy. The data consist of a general heat balance sheet and core distributions of the active flow for each fuel assembly as well as relative power fraction for each fuel assembly. The data was given at three different points in the burnup cycle: BOC, MOC and EOHFP. For the three points, the core data have been provided at a constant thermal power of 2004 MWt and a constant core flow of 57.02 Mlb/hr.

(7184 kg/s) [I]. All the results presented in this report for a reactor thermal power of 2004 MWt are calculated for this core flow. The radial power peaking factor in the provided power distributions is slightly different for the three points:

]a,c.

• Westinghouse Report SES 09-129-NP, rev 2 Page 6 of 13 The estimated moisture content at the inlet of the steam dryer is:

" BOC:[

]ac

" MOC:[

]a,c

• EOHFP: [

]a,c I

]a,c 4.2 DATA AT 102% EPU POWER (2044 MWt)

]a,c Three different core flow conditions have been analyzed: 46.1 Mlb/hr (80% EPU core flow), 57.6 Mlb/hr (100% EPU core flow) and 60.5 Mlb/hr (105% EPU core flow) [2].

The estimated moisture content at the inlet of the steam dryer is:

0 46.1 Mlb/hr (80% EPU core flow):

57.6 Mlb/hr (100% EPU core flow): [

60.5 Mlb/hr (105% EPU core flow): [

]a,c ac

]a,c The large difference in the moisture content at the inletof the steam dryer compared to the values for 2004 MWt is mainly due to the change in the radial power peaking factor used for the analyses.

5 DESIGN OF THE VANE BANKS The moisture entering the steam dryer is separated from the steam in the vane banks. The steam velocity in the vane banks is crucial to the performance of the steam dryer. [

]a,c

• Westinghouse Report SES 09-129-NP, rev 2 Page 7 of 13 5.1 VANE BANKS CONFIGURATION AND AREA II

]a,c 5.2 STEAM FLOW THROUGH THE VANE BANKS I

Ia,c 5.3 MCO CALCULATIONS L

]a,c 5.4 PRESSURE DROP I

]a,c

• Westinghouse Report SES 09-129-NP, rev 2 Page 8 of 13 6

DESIGN OF THE DRAINAGE SYSTEM The separated water in the vane banks is drained back below the water level of the RPV via a system of drain lines and drain channels. The design of the drainage system is explained in this section.

6.1 GENERAL DESCRIPTION A simplified sketch of the drainage system is shown in Figure 1. The separated water first accumulates in the pockets of the vane banks and flows down to the bottom of the vanes by gravity. [

]a,c

Westinghouse Report SES 09-129-NP, rev 2 Page 9 of 13 a,C Figure 1. Sketch of the drain lines and drain channels 6.2 DESIGN METHODOLOGY

[

oa,c

• Westinghouse Report SES 09-129-NP, rev 2 Page 10 of 13

]a,c 7

EXPECTED PERFORMANCES 7.1 MOISTURE CARRYOVER With the replacement dryer installed, the MCO is estimated to be maximum carry-in of [

]"' at 2004 MWt [3].

]aC for the expected 7.2 PRESSURE DROP The calculated pressure drop for the replacement steam dryer is calculated to be about

[

]a"C for a core flow of 57.02 Mlb/hr and a reactor thermal power of 2004 MWt [3].

7.3 WATER LEVEL The expected pressure drop of [

]a'C corresponds to a water column height of [

,], in the reactor. During normal operation, the water level inside the replacement dryer will be at least [

]ac above the lower edge of the dryer skirt.

At low water SCRAM level, the water level inside the replacement dryer is at least [

]a,c above the lower edge of the dryer skirt maintaining, even in that situation, a water seal between the wet steam below the dryer and the dry steam in the downcomer.

7.4 CARRY UNDER

]a,c 7.5 PERFORMANCES AT 102% EPU POWER (2044 MWt)

The performances (MCO and pressure drop) at a reactor thermal power of 2044 MWt and a radial power peaking factor of [

]

are summarized in Table 1 below for three different core flows [3].

(

Westinghouse Report SES 09-129-NP, rev 2 Page 11 of 13 Table 1. Performances at 102% EPU power (2044 MWt)

K ac The increase in MCO at 2044 MWt compared to the value for a reactor thermal power of 2004 MWt is mainly due to the change in the radial power peaking factor used for the analyses.

[

ac 8

CONCLUSIONS The replacement steam dryer for the Monticello power plant is expected to have the following performances:

MCO of[

pressure drop of[

]a,c

]a,c at a reactor thermal power of 2004 MWt and a core flow of 57.02 Mlb/hr.

The customer requirement of a MCO below 0.030% by weight should therefore be met [

]a,c For a reactor thermal power of 2044 MWt and a radial power peaking factor of [

]ac, the MCO is expected to be []ac.

9 REFERENCES

[P]

]a,c

[2]

Ia,c

• Westinghouse Report SES 09-129-NP, rev 2 Page 12 of 13

[3]

[

]a,c

• Westinghouse Report SES 09-129-NP, rev 2 Page 13 of 13 History Review and approval status (Organization, name) a K

j Revision record a,c