0CAN011301, Revised Alternate Source Term Dose

Revised Alternate Source Term Dose

ML13009A288
Person / Time
Site:	Arkansas Nuclear
Issue date:	01/08/2013
From:	Pyle S Entergy Operations
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
0CAN011301
Download: ML13009A288 (5)

Text

Entergy Operations, Inc.

1448 S.R. 333 Russellville, AR 72802 Tel 479-858-4704 Stephenie L. Pyle Manager, Licensing Arkansas Nuclear One 0CAN011301 January 8, 2013 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555

SUBJECT:

Revised Alternate Source Term Dose Arkansas Nuclear One - Units 1 and 2 Docket Nos. 50-313 and 50-368 License Nos. DPR-51 and NPF-6

REFERENCES:

1. NRC letter dated October 21, 2009, Arkansas Nuclear One, Unit No. 1 -

Issuance of Amendment RE: Use of Alternate Source Term (TAC No. MD7178) (1CNA100901) (ML092740035)

2. NRC letter dated April 26, 2011, Arkansas Nuclear One, Unit No. 2 -

Issuance of Amendment RE: Use of Alternate Source Term (TAC No. ME3678) (2CNA041102) (ML110980197)

Dear Sir or Madam:

The NRC approved modifications to the requirements of the Arkansas Nuclear One, Units 1 and 2 (ANO-1 & 2) Technical Specifications definitions, requirements, and terminology related to the use of an Alternate Source Term (AST) associated with accident offsite and control room dose consequences via References 1 and 2. The computer code Radionuclide Transport, Removal and Dose (RADTRAD) was specifically developed to perform dose analyses using the AST methodology of NRC Regulatory Guide 1.183.

The RADTRAD Users Group was notified by the code developer in December 2011 of an implementation error in the code. The error notification warned about using a particular capability of the code. No actual change to the RADTRAD code itself, or its embedded methodology, has occurred.

A review of the ANO-1 & 2 AST analyses revealed that the error notice applies to the Loss of Coolant Accident (LOCA) for both units. The LOCA analyses for both ANO units have been re-performed using the summing option of RADTRAD. This option is discussed in the attachment. In comparing the dose consequences it was determined that the ANO-1 control dose has increased by more than 10% of the available margin. Thus, correction of the RADTRAD error results in more than a minimal increase in the consequences of an accident and NRC approval is required prior to implementing the new analysis. The remaining results will be addressed via the ANO 10 CFR 50.59 process.

0CAN011301 Page 2 of 2 The purpose of this submittal is to request the NRCs review and approval of the revised LOCA dose calculated for the ANO-1 control room. The results of the analyses are provided in the attachment.

This submittal contains no regulatory commitments.

Should you have any questions, please contact me.

Sincerely, Original signed by Stephenie L. Pyle SLP/rwc

Attachment:

Revised Dose Consequences Based on Alternate Source Term cc: Mr. Elmo E. Collins Regional Administrator U. S. Nuclear Regulatory Commission, Region IV 1600 East Lamar Boulevard Arlington, TX 76011-4511 NRC Senior Resident Inspector Arkansas Nuclear One P. O. Box 310 London, AR 72847 U. S. Nuclear Regulatory Commission Attn: Mr. Kaly Kalyanam MS O-8 B1 One White Flint North 11555 Rockville Pike Rockville, MD 20852 Mr. Bernard R. Bevill Arkansas Department of Health Radiation Control Section 4815 West Markham Street Slot #30 Little Rock, AR 72205

Attachment to 0CAN011301 Revised Dose Consequences Based on Alternate Source Term

Attachment to 0CAN011301 Page 1 of 2 Revised Dose Consequences Based on Alternate Source Term The computer code RADTRAD was specifically developed to perform dose analyses using the alternate source term (AST) methodology of Regulatory Guide 1.183. Both Arkansas Nuclear One, Units 1 and 2 (ANO-1 & 2) have implemented AST using RADTRAD.

The vendor for the RADTRAD computer code notified the RADTRAD Users Group in December 2011 of an implementation error within its RADTRAD code, version 3.0.3.

Specifically, a program error was found to occur if the user selects: (1) a timed release, (2) more than one compartment receives a portion of the released radionuclides, and (3) radionuclide decay. This combination was not correctly implemented in the code; instead the initial fuel inventory is decayed each time a source compartment is entered. The error notice advises users to rerun any problematic cases in multiple runs (i.e., one run for each source term compartment), and then sum the dose results to obtain the correct answer.

Performing, then summing the results of multiple runs has always been available and is typically used in the industry to determine the total dose following an event, (e.g., separate runs for containment leakage, Atmospheric Dump Valve releases, Engineering Safeguard Features (ESF) leakage, containment shine and cloud shine). However, for simplicity and to limit the number of runs, when a release into multiple compartments is simultaneously assumed, the user often combines the release into a single run, since RADTRAD allows this kind of input. The error notice warns against using that capability of the code. No actual change to the RADTRAD code itself, or its embedded methodology, has occurred.

A review of the ANO AST analyses revealed that the error notice applies to the Loss of Coolant Accident (LOCA) analysis for both units. In those analyses, the release into the containment is divided into two compartments, representing the sprayed and unsprayed regions within the structure. Therefore, the LOCA analyses for both ANO units have been rerun, providing separate containment leakage dose contributions from its sprayed and unsprayed regions. Those dose results are then summed with the doses associated with ESF leakage, and for the control room, containment and cloud shine doses, to determine the total doses associated with the accident. All other portions of the analyses have not changed.

The values provided below for the dose consequences in all the tables are in rems. The results of the new LOCA analyses are:

Table 1 - Corrected Doses (Rem - Total Effective Dose Equivalent (TEDE))

Exclusion Area Low Population Unit Boundary (EAB) Zone (LPZ) Control Room 1 11.091 2.738 3.896 2 9.452 0.709 2.094

Attachment to 0CAN011301 Page 2 of 2 The current analyses of record results as reported in the unit specific Safety Analysis Reports are:

Table 2 - Current (Uncorrected) Doses (Rem - TEDE)

Unit EAB LPZ Control Room 1 10.49 2.56 3.77 2 9.084 0.673 2.062 The regulatory acceptance criteria are:

Table 3 - Regulatory Acceptance Criteria (Rem - TEDE)

EAB LPZ Control Room 25.0 25.0 5.0 The difference between the values listed in Tables 2 and 3 is the available margin and are:

Table 4 - Margin to Regulatory Acceptance Criteria (Rem - TEDE)

Unit EAB LPZ Control Room 1 14.51 22.44 1.23 2 15.916 24.327 2.938 The differences between the values listed in Tables 1 and 2 are:

Table 5 - Dose Increases Due to RADTRAD Error (Rem - TEDE)

Unit EAB LPZ Control Room 1 0.601 0.178 0.126 2 0.368 0.036 0.032 When the increased dose consequences due to the reanalysis against the previous dose margins (Table 5) are compared, the results are that the ANO-1 control room dose has increased by more than 10% of the available margin. Therefore, correction of the RADTRAD error results in a more than minimal increase in the consequences of an accident. This requires NRC approval prior to implementation.

The remaining results will be addressed via the Entergy 10 CFR 50.59 process.