ML14086A386

STP Risk-Informed GSI-191 Aadb RAI 3 Response, Attachment 2

ML14086A386
Person / Time
Site:	South Texas
Issue date:	03/17/2014
From:	Corbitt T, Leavitt J ALION Science & Technology Corp, South Texas
To:	Office of Nuclear Reactor Regulation
Shared Package
ML14086A383	List: ML14086A385 ML14086A386
References
GSI-191, NOC-AE-1 4003082, STI33816627, TAC MF2400, TAC MF2401 ALION-REP-STP-8998-03, Rev 0
Download: ML14086A386 (9)

Text

NOC-AE-1 4003082 Attachment 2 Risk-Informed GSI-191 AADB RAI 3 Response

Risk-Informed GSI-191 AADB RAI 3 Response Authors Janet Leavitt, PhD Alion Science and Technology Thomas S. Corbitt, PhD Alion Science and Technology Reviewers Bruce Letellier, PhD Alion Science and Technology Seyed Reihani, PhD University of Illinois Urbana-Champaign Kerry Howe, PhD University of New Mexico Ernie Kee South Texas Project Nuclear Operating Company

ALION SCIENCE AND TC.CHNOLOGY TECHNICAL DOCUMENT COVER PAGE Document No: ALION-REP-STP-8998-03 I Revision: 0 Page I of 7 Document

Title:

STP Risk-Informed GSI- 191 AADB RAI 3 Response Project No: STP-8898 Project Name: STP Risk-Informed GSI- 191 Support Client: STP Nuclear Operating Company Document Purpose/Summary: Request for additional information 3 (RAI 3) inquired about the potential for pH changes arising from sump acidification through radiolysis of water and plastic sheathing on cabling. This document provides an explanation for variation of calculated pH and experimentally measured pH as well as expected ECCS performance effects. This document is not considered safety-related.

This report includes 8 total pages.

Design Verification Method:

X Design Review Alternative Calculation

___ Qualification Testing Professional Engineer (if required) Approval: Date S Digitalysigned byThomasS.Cobit N:

.......... S. Corb........... S ........ d Teyhnoloy, J4 .. o 1lTSO, Prepared By: Thomas S. Corbitt emall=tcorblt@alionscience.com.,

Dte.: 2014.02.2016:34:5407.00o c=US Printed/Typed Name Signature Date Reviewed By: Janet Leavitt LeavittC3 Printed/Typed Name Signature Date Approved B Megan A.Stachowiak Approved By: Megan Stachowiak 2014.02.21 08:41:47 -06'00' Printed/Typed Name Signature Date Form 3.3.1 Revision 2 Effective Date: 2/28/07

A L 10ON SCIENCE ANDSTECIUIOLOCY REVISION HISTORY LOG Page 2of 7 Document Number: ALION-REP-STP-8998-03 Revision: 0 Document

Title:

STP Risk-Informed GSI- 191 AADB RAI 3 Response REVISION DATE Description 0 02/20/2014 Initial release i

Form 6.1.3 Revision 2 Effective Date: 3/25/13

CSTP Risk-Informed GSI- 191 AADB RAI 3 Response A LIO N Document No: ALION-REP-STP-8998-03 Rev: 0 Page: 3 of 7 Table of Contents Tab le o f C o n te n ts ............................................................................................................................................................................................ 3 Tab le o f Ta b le s ................................................................................................................................................................................................. 3 Ta b le o f Figu re s ................................................................................................................................................................................................ 3 I Risk Informed GSI-191 AADB RAI 3 ................................................................................................................................................. 4 2 R e sp o n se ................................................................................................................................................................................................... 4

2. I Sump Water pH; Calculated vs Measured ............................................................................................................................. 4 2.2 Implications of Experimental Results ........................................................................................................................................ 6 2 .3 Su m m ary .......................................................................................................................................................................................... 6 2 .4 Refe re n ce s ....................................................................................................................................................................................... 7 Table of Tables Table I. Solution characteristics for LB and experimental (CHLE) systems ........................................................... 5 Table of Figures Figure I. 30 day pH trend of LB and experimental (CHLE) systems ............................................................. 5 Figure 2. Acid addition schedule for LB and experimental (CHLE) systems ........................................................... 6

STP Risk-Informed GSI-191 AADB RAI 3 Response AL IO N

,CIO-CE AND TEC-QLOQGý Document No: ALION-REP-STP-8998-03 Rev: 0 Page: 4 of 7 I Risk Informed GSI-191 AADB RAI 3 The LOCA analysis assumes that iodine will be removed from the containment atmosphere by containment spray and natural diffusion to the containment walls. As a result of these removal mechanisms a large fraction of the released activity will be deposited in the containmentsump. The sump water will retain soluble gases and soluble fission products such as iodines and cesium, but not noble gases. The guidance from RG 1.183 specifies that the iodine deposited in the sump water can be assumed to remain in solution as long as the containment sump pH is maintainedat or above 7.

The AST applicationindicates:

"After the first day, the containment sump pH will begin to decrease, reaching 6.8 by the end of the 30-day duration of the radiologicalconsequence analysis for the DBA LOCA, and the impact of that decrease has been reflected in the Control Room and offsite doses."

It is noted that the AST applicationfurther indicates:

"The design inputs for calculatingthe containment sump pool pH were conservatively establishedby the licensee to maximize the acidic contribution to sump pH and minimize the basic contribution."

The GSI-191 applicationindicates the possibility that debris generated during a LOCA could clog the containment sump strainersin pressurized-waterreactors (PWRs) and result in loss of net positive suction head (NPSH) for the ECCS and CSS pumps, impeding the flow of water from the sump.

Discuss the exemption justification as they relate to the effects on sump water pH, radiologicalconsequences, and loss of the containment spray system.

2 Response 2.1 Sump Water pH; Calculated vs. Measured In the following, the pH values resulting from the STP Licensing Basis (LB) alternative source term (AST) calculation [1,2] and the Chemical Head Loss Experiment (CHLE) 30 day tests [3,4] are compared and the differences analyzed. Table 1 summarizes the solution chemistry considered in both the LB calculation and CHLE test [3,4]: concentrations of boric acid; trisodium phosphate (TSP); and radiolysis generated acid. Boric acid and TSP concentrations used to establish initial LB (calculated) sump pH were determined by deterministic analysis. The boric acid and TSP concentrations used for the CHLE experiments were determined from risk-informed analysis of historical plant data [5] and would not be considered conservative in the same sense as the LB AST calculations. Also, unlike the LB calculation, the 30 day CHLE experiments

[3,4] reflect pH trends with the inclusion of corrosion material and fibrous debris. In summary, the observed CHLE pH trend has no effect on potential sump blockage assumed in the LB calculation.

C)STP Risk-Informed GSI- 191 AADB RAI 3 Response A L I ON Document No: ALION-REP-STP-8998-03 Rev: 0 Page: 5 of 7 Table 1: Solution characteristics for both LB [1] and experimental (CHLE [6,7]) systems Chemical Star pH Model CHLE Tests Boron (mM) 283.05 250.50 TSP 1 (mrM) 5.63 8.87 Lithium hydroxide (mM) 0 0.06 30 Day HCI (mM) 0.81 0.81 30 Day HNO3(mM) 0.23 0.23 1

Initial pH 7.0 7.1-7.2 30 day pH 6.8 7.2-7.4 After complete dissolution of TSP After complete TSP dissolution, the two inputs resulted in a difference of approximately 0.1 pH units as summarized in Table 1. The higher initial pH in the CHLE tests reflects the different boric acid and TSP concentrations used to define the systems. There is also a small quantity of lithium hydroxide, 0.06 mM Li, added to the CHLE system. The addition of iodine was not considered in either system. During the 30-day analysis, sump pH in both systems changed. As shown in Figure 1, the LB system predicted a decrease in pH of approximately 0.2 pH units resulting from acid addition over 30 days; however the experimental system produced a slight increase in pH of, on average, 0.18 units over 30 days using the same acid addition schedule used in the LB system (Figure 2).

10

• STARpH [1]

9nCHLE T1 [3]

8 A CHLE T2 [4]

CLIA E

CL 7 6

5 4 5 10 15 20 25 30 0 5 10 15 20 25 30 Time (days)

Figure 1: 30 day pH trend of LB [1] and experimental (CHLE [6,7]) systems.

STP Risk-Informed GSI-191 AADB RAI 3 Response ALI O N Document No: ALION-REP-STP-8998-03 Rev: 0 Page: 6 of 7 QGVR SCIENCE^NO TECHrNO v ag :6o 1.2 1.0 []

E

," 0.8 0

0.6

• StarpH C0.4 ECHLE El M 0.2 0.0 ' I 0 5 10 15 20 25 30 Time (day)

Figure 2: Acid addition schedule for LB [1] and experimental (CHLE [6,7]) systems.

2.2 Implications of Experimental Results The initial pH difference between the LB system and the CHLE test systems [3,4] is expected, primarily due to the difference between the deterministically-assumed boric acid and TSP concentrations and risk-informed (realistic) concentrations. The difference between the LB calculated pH history and the CHLE observed pH history is likely reflective of uncertainty from the LB calculation. The LB calculation is a modeled solution and uncertainties from model development arise from missing reactions, activity corrections and temperature corrected equilibrium data. By neglecting buffering, activity and temperature corrections, the LB system exhibits a greater pH reduction. The additional buffering capacity in the CHLE test system not accounted for in the LB model is a function of the following; 1) greater contribution from TSP, with 8.87 mM TSP versus the 5.63 mM used in the LB system; 2) the presence of fiberglass solids that can contribute to alkalinity by adsorbing H* [8]; 3) addition of a small quantity of lithium hydroxide; and 4) corrosion reactions, specifically aluminum and zinc corrosion.

2.3 Summary The fact that pH in the CHLE system remains above 7.1 despite acid addition for a period greater than 30 days reflects the true buffering capacity of the system. Alkalinity in the CHLE system is augmented by increased initial concentration of TSP and lithium hydroxide, as well as solids such as fiberglass, and by metal corrosion.

The LB system calculations fail to account for these factors. The minor acidic contributions from radiolysis of water and cabling assumed in the LB acid addition schedule would be mitigated by the higher pH as demonstrated in the CHLE experiments. The pH stability observed in the CHLE system indicates that acid additions resulting from radiation exposure will not affect sump blockage and thus are not expected to affect ECCS performance. Furthermore, these experimental results likely represent a lower realistic bound, since the LB case assumes core damage and the effect of strongly basic cesium oxide produced from fuel damage on the basicity of the sump solution [9] is ignored.

2.4 References I. STPNOC UFSAR, Sec. 15.6, Response to RAI 3 in NOC-AE-07002215 and NRC Safety Evaluation.

2. STP, "Post-LOCA containment Sump pH and Maximum Iodine DF for AST Chapter 15 Analysis", NC-651 I, 2006.

3. Leavitt, J.J., Howe, K.J. T I MBLOCA Test Report, University of New Mexico, Albuquerque, NM November 2012, CHLE-0 12.

4. Leavitt, J.J., Howe, K.J. T2 LBLOCA Test Report, University of New Mexico, Albuquerque, NM January 2013, CHLE-014.

5. Leavitt, J.J., Howe, K.J. Determination of the initial pool chemistry for the CHLE test, University of New Mexico, Albuquerque, NM August 2012, CHLE-006.

6. Leavitt, J.J., Howe, K.J. Test I: Medium Break LOCA Tank Test Parameter Summary, University of New Mexico, Albuquerque, NM August 2012, CHLE-0 I.

7. Leavitt, J.J., Howe, K.J. Test 2: Large Break LOCA Tank Test Parameter Summary, University of New Mexico, Albuquerque, NM January 2013, CHLE-0 13.

8. Mitchell, L., Leavitt, J.J., Vogtle GSI- 19 1Water Chemistry Evaluation for Bypass Support, ALION-REP-SNC-8586-12I January 2014,

9. Beahm, E.C., Lorenz, R.A. Weber, C.F. Iodine Evolution and pH control, Oak Ridge National Laboratory, Oak Ridge, TN, December 1992, NUREG/CR-5950, ORNI/TM-12242R3.