NOC-AE-07002186, Response to Request for Additional Information on Proposed Amendment for Alternate Radiological Source Term (AST) Methodology

Response to Request for Additional Information on Proposed Amendment for Alternate Radiological Source Term (AST) Methodology

ML072050341
Person / Time
Site:	South Texas
Issue date:	07/18/2007
From:	Rencurrel D South Texas
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
NOC-AE-07002186, TAC MD4996, TAC MD4997
Download: ML072050341 (6)

Text

Nuclear Operating Company South Tows Pro/cd Electric GencnatingStation P.. Box 289 Wadswrth. Teas 77483 .

July 18, 2007 NOC-AE-07002186 10CFR50.90 U. S. Nuclear Regulatory Commission Attention: Document Control Desk One White Flint North 11555 Rockville Pike Rockville, MD 20852-2738 South Texas-Project Units 1 and 2 Docket Nos. STN 50-498, STN 50-499 Response to Request for Additional Information on Proposed Amendment for Alternate Radiological Source Term (AST) Methodology; TAC Nos. MD 4996 & MD 4997

References:

1. Letter from David W. Rencurrel to NRC Document Control Desk dated March' 22, 2007, "Request for License Amendment Related to Application of the Alternate Source Term" (NOC-AE-07002127)

2. Letter from Charles T. Bowman to NRC Document Control Desk dated April 10, 2007, "STPNOC Alternate Source Term License Amendment Application" (NOC-AE-07002147)

In Reference 1, the STP Nuclear Operating Company (STPNOC) submitted a license amendment request to support application of an alternate source term (AST) methodology. In Reference 2, supplementary information was provided to support the AST application. Reference 2 included the Containment Sump post-LOCA pH calculation. This submittal responds to NRC questions regarding this calculation.

There are no commitments in this submittal. If you have any questions, please call Ken Taplett at 361-972-8416 or me at 361-972-7867.

I declare under penalty of perjury that the foregoing is true and correct.

Executed on 7__/_J__A _

Date a dW.ýRencu -I Vice President, Engineering and Strategic Projects

Attachment:

STPNOC Response to Request for Additional Information ADOt STI:32183919

NOC-AE-07002186 Page 2 cc:

(paper copy) (electronic copy)

Regional Administrator, Region IV A. H. Gutterman, Esquire U. S. Nuclear Regulatory Commission Morgan, Lewis & Bockius LLP 611 Ryan Plaza Drive, Suite 400 Arlington, Texas 76011-8064 Mohan C. Thadani U. S. Nuclear Regulatory Commission Senior Resident Inspector Thad Hill U. S. Nuclear Regulatory Commission Eddy Daniels P. 0. Box 289, Mail Code: MNt 16 Marty Ryan Wadsworth, TX 77483 Harry Holloway Steve Winn, NRG South Texas LP C. M.'Canady Ed Alarcon City of Austin J. J. Nesrsta Electric Utility Department R. K. Temple, 721 Barton Springs Road Kevin Pollo AustinTX 78704 City Public Ser.ice Richard A. Ratliff Jon C. Wood Bureau of Radiation Control Cox Smith Matthews Texas Department of State Health Services 1100 West 49th Street - C. Kirksey Austin, TX 78756-3189 City of Austin Mohan C. Thadani Project Manager U.S. Nuclear Regulatory Commission One White Flint North (MS 7 D1) 11555 Rockville Pike Rockville, MD 20852

Attachment NOC-AE-07002186 Page 1 of 4 STPNOC RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION REQUEST FOR ADDITIONAL INFORMATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION PROPOSED LICENSE AMENDMENT FOR ALTERNATE RADIOLOGICAL SOURCE TERM (AST) METHODOLOGY SOUTH TEXAS PROJECT UNITS 1 AND 2 DOCKET NUMBERS 50-498 AND 50-499 The licensee determined the post-LOCA containment sump water pH using the STARpH computer code. Since the U.S. Nuclear Regulatory Commission staff did not have an opportunity to review this code, the information needed for performing the evaluation of the licensee's program has to be obtained from the description in the submittal, supplemented by the following request for additional information (RAI) prepared by the staff.

NRC RAI #1 In the methodology for determining the post LOCA suppression pool water pH, the licensee employed a two step procedure. In the first step no buffering action of trisodium phosphate (TSP) is assumed. Without the buffer the pH of the suppression pool water will monotonically decrease and eventually will drop below a value of 7. In the second step, the licensee calculated the value of pH at 30 days after a LOCA including buffering action of TSP. When this pH value at 30 days after a LOCA is equal to or higher than 7, because of its monotonic decrease as a function time, all of the pH values for time shorter than 30 days must also be higher than 7.

However, this method does not allow calculation of the actual pH values at different time intervals between zero and 30 days after a LOCA.

Describe how the values of pH listed in Table 4.3-3 were calculated.

Attachment NOC-AE-07002186 Page 2 of 4 STPNOC Response The transient pH was calculated according to the integrated MeV for each of the following time intervals (the end-time for each interval is given):

MeV (gamma) MeV (beia) MeV (total)

End- MeV available for available for available for time for absorbed absorption by absorption by absorption by each by water Hypalon-bearing Hypalon-bearing Hypalon-bearing interval .over material over material over material over (hours) interval interval. interval interval 1 1.72E+23 2.26E+22 2.42E+22 4.68E+22 2 6.50E+22 1.48E+22 1.49E+22 2.97E+22 5 .1.35E+23 3.09E+22 3.03E+22 6.13E+22 12 2.21E+23 4.19E+22 4.37E+22 8.56E+22 24 2.93E+23 4.44E+22 5.28E+22 9.72E+22 72 8.25E+23 1.18E+23 1.50E+23 2.67E+23 240 1.52E+24 2.06E+23 2.98E+23 5.05E+23 480 9.61 E+23 1.02E+23 1.50E+23 2.52E+23 720 6.18E+23 5.38E+22 5.67E+22 1.11E+23 Total 4.81 E+24 6.35E+23 8.21 E+23 1.46E+24 The nitric acid production is on the basis of 0.007 molecules per 100 eV absorbed by the water. Noble gas is not considered to be dissolved in the water; however, 90% of the other radionuclides released from thecore are assumed to be present from t = 0.

The hydrochloric acid production is based on a normalized Rgama = 3.OOE-15 mole-cc/,MeV-lbm and a normalized Rbeta = 1.52E-15 mole-cc/MeV-lbm where the ibm applies to the mass of Hypalon-bearing insulation/jacket material inside containment. A containment free volume of 9.57E+10 cc is used to determine the MeV/cc based on the above values for MeV, and the Hypalon-bearing material mass is 60,132 Ibm. Because

-ofthe penetrating nature of the gamma radiation, only 5.4% of the available radiation energy is absorbed by the Hypalon-bearing material. Because of the limited range of beta radiation in air (and the shielding provided by cable trays and conduit), only 2.7% of the available beta radiation energy is absorbed by the Hypalon-bearing material. These fractions can be determined from the ratio of the product of the normalized values for Rgamma and Rbeta and the mass of Hypalon-bearing material divided by the containment free volume (i.e., 3.00E-15 x 60,132 /9.57E+10 = 1.885E-21 for gamma and 1.52E-15 x 60,132 /9.57E+10 = 9.55E-22 for beta) to the G value for Hypalon (i.e., 3.512E-20 moles/MeV). In other words, if the available gamma and beta radiation were completely, absorbed by the Hypalon-bearing material, the number of moles of HC1 generated would be the product of the available radiation energy (gamma + beta) x 3.512E-20 moles per MeV rather than the product of the available radiation energy times (Rx x 60,132 lbm

/9.57E÷10 cc) where Rx is either the normalized Rgamma or the normalized Rbeta in units of mole-cc/MeV-lbm.

Attachment NOC-AE-07002186 Page 3 of 4 The gamma and beta radiation in the containment atmosphere available for irradiation of cable is assumed to be present at t = 0 and includes the noble gas and 10% of the other radionuclides which are assumed to remain effectively airborne in the containment atmosphere (not added to the sump in spite of the spray operation). Also, 12.5% of the gamma radiation energy generated in the sump water is assumed to escape the sump water and to irradiate cable. This assumption is made in spite of the fact that 100% of that same energy is assumed to produce nitric acid by radiolysis in the sump.

Since the absorbed energy in the sump water and the energy available to irradiate Hypalon-bearing material in the containment atmosphere are both calculated on a time-dependent basis (as presented in the above table), the pH may be calculated at the end of any interval. In this way the time-dependent pH is determined.

NRC RAI #2 Describe how the nitric acid in the post- LOCA containment environment was determined.

STPNOC Response Refer to the response to RAI #1.

NRC RAI #3 The equation on page 108 of Appendix 1 was developed based on the methodology described in NUREG/CR-5950 and was used in the STARpH code for determining the amount of hydrochloric acid (HCl) generated in the sump water during the 30 day period after a LOCA . However, in their review the staff found that the amount of HCI calculated by this equation is insignificantly small and would not provide enough hydrogen ions to produce the values shown in Table 4.3-3. Justify this discrepancy.

STPNOC Response Note that the HCl is assumed to be generated by chlorine released from the irradiation of Hypalon-bearing insulation/jacket material due to the exposure of that material to airborne activity, and an assumed 12.5% of the gamma energy generated in the sump - it is not assumed to be generated in the sump water as the question implies. Nitric acid is assumed to be generated in the sump water.

Attachment NOC-AE-07002 186 Page 4 of 4 As explained in the response to RAI #1, the approach illustrated by the equation identified on page 108 of Appendix 1; i.e.,

R =RH + RPH where R = the total rate of HC1 generation rate (gm-mols/sec)

R-yH = the HC1 generation rate due to Y radiolysis (gm-mols/sec)

ROH the HC1 generation rate due to 43 radiolysis (gm-mols/sec) is used to determine the HCI generation by Hypalon irradiation. However, the actual numerical values given for RYH and RPH on page 108 of Appendix 1 represent the normalized R values (i.e., normalized by EN/V, where E is the available gamma or beta power in MeV/sec, N is the mass of the Hypalon-bearing material in Ibm, and V is the containment free volume in cc), not the absolute R values. Therefore, the numerical values were given in the wrong units. The units should have been mole-cc/MeV-lbm. To obtain the absolute R values in units of mole/sec, the normalized values must be multiplied by a constant (60,132 Ibm of Hypalon-bearing material inside containment divided by the containment free volume of 9.57E+10 cc) and then by the average available gamma and beta radiation power over each time interval (in units of MeV/sec).

This average available gamma and beta radiation power over each time interval may be obtained from the time-integrated (i.e., energy) values given in the table found in the RAI

1. 1 response divided by the duration of each interval in seconds.