ML16279A343

From kanterella
Jump to navigation Jump to search

Audit Report for 8/3-4/16, Nrr/Dra/Arcb Regulatory Audit at Westinghouse Facility in Rockville, MD, to Support Review of License Amendment Request for Adoption of Alternative Source Term
ML16279A343
Person / Time
Site: Diablo Canyon  Pacific Gas & Electric icon.png
Issue date: 10/27/2016
From: Balwant Singal
Plant Licensing Branch IV
To: Halpin E
Pacific Gas & Electric Co
Singal B
References
CAC MF6399, CAC MF6400
Download: ML16279A343 (39)
v • d • e


Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 October 27, 2016 Mr. Edward D. Halpin Senior Vice President, Generation and Chief Nuclear Officer Pacific Gas and Electric Company Diablo Canyon Power Plant P.O. Box 56, Mail Code 104/6 Avila Beach, CA 93424

SUBJECT:

DIABLO CANYON POWER PLANT, UNITS 1 AND 2 - REGULATORY AUDIT REPORT FOR THE AUGUST 3-4, 2016, AUDIT AT THE WESTINGHOUSE FACILITY IN RO.CKVILLE, MARYLAND, IN SUPPORT OF ALTERNATE SOURCE TERM LICENSE AMENDMENT REQUEST (CAC NOS. MF6399 AND MF6400)

Dear Mr. Halpin:

By letter dated June 17, 2015 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML15176A539), as supplemented by letters dated August 31, October 22, November 2, November 6, and December 17, 2015; and February 1, February 10, April 21, and June 9, 2016 (ADAMS Accession Nos. ML15243A363, ML15295A470, ML15321A235, ML15310A522, ML16004A363, ML16032A603, ML16041A533, ML16120A026, and ML16169A264, respectively), Pacific Gas and Electric (PG&E, the licensee), submitted a license amendment request to revise the licensing bases to adopt the alternative source term as allowed by Title 10 of the Code of Federal Regulations (10 CFR), Part 50, Section 50.67, "Accident source term," for Diablo Canyon Power Plant, Units 1 and 2.

The U.S. Nuclear Regulatory Commission (NRC) staff conducted a regulatory audit at the Westinghouse facility in Rockville, Maryland, on August 3 and 4, 2016, to allow the NRC staff to review technical information related to the atmospheric dispersion modeling analyses submitted by PG&E in support of its LAR submittal. Attached is the audit report, which was completed in accordance with the guidance set forth in NRC Office of Nuclear Reactor Regulation, Office Instruction LIC-111, "Regulatory Audits," dated December 29, 2008 (ADAMS Accession No. ML082900195).

E. Halpin If you have any questions, please contact me at 301-415-3016 or via e-mail at Balwant.Singal@nrc.gov.

Sincerely,

£~~,~µ Balwant K. Singal, Senior Project Manager Plant Licensing Branch IV-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-275 and 50-323

Enclosure:

Audit Report cc w/encl: Distribution via Listserv

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 REGULATORY AUDIT REPORT PERFORMED AT WESTINGHOUSE FACILITY FROM AUGUST 3 AND 4. 2016. IN SUPPORT OF THE LICENSE AMENDMENT REQUEST TO REVISE THE CURRENT LICENSING BASES TO ADOPT THE ALTERNATIVE SOURCE TERM PACIFIC GAS AND ELECTRIC COMPANY DIABLO CANYON POWER PLANT. UNITS 1 AND 2 DOCKET NOS. 50-275 AND 50-323

1.0 BACKGROUND

By letter dated June 17, 2015 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML15176A539), as supplemented by letters dated August 31, October 22, November 2, November 6, and December 17, 2015; and February 1, February 10, April 21, and June 9, 2016 (ADAMS Accession Nos. ML15243A363, ML15295A470, ML15321A235, ML15310A522, ML16004A363, ML16032A603, ML16041A533, ML16120A026, and ML16169A264, respectively), Pacific Gas and Electric Company (PG&E, the licensee),

submitted a license amendment request (LAR) to revise the licensing bases to adopt the alternative source term (AST) as allowed by Title 10 of the Code of Federal Regulations (10 CFR), Part 50, Section 50.67, "Accident source term," for Diablo Canyon Power Plant (DCPP), Units 1 and 2.

The U.S. Nuclear Regulatory Commission (NRC) staff issued an initial set of requests for additional information (RAls) on October 1, 2015 (ADAMS Accession No. ML15278A049).

These RAls primarily focused on acquiring: (1) meteorological (Met) data; (2) input and output files for the ARCON96 dispersion modeling runs, including Met data formatted for input to that model; (3) input files for the proprietary EN-113 dispersion model and a description of the EN-113 model input file structure; and (4) plant drawings used to determine certain model input parameters. The licensee provided its response to the NRC staff request on November 2, 2015.

The NRC staff reviewed the licensee's RAI responses and identified a discrepancy between the sequential hourly Met data formatted per NRC Regulatory Guide (RG) 1.23, "Meteorological Monitoring Programs for Nuclear Power Plants," Revision 1, March 2007 (ADAMS Accession No. ML070350028), and the Met data formatted for input to the ARCON96 (and presumably EN-113) dispersion model(s), along with other characteristics based on that data. The NRC staff was unable to determine, among other items, whether the appropriate Met data were input to the modeling runs. Priority was given to resolution of these discrepancies over initiating Enclosure

review of the ARCON96 modeling analysis because of its potential impact on previously submitted relative concentration (X/Q) values and subsequent radiological dose calculations.

The NRC staff's second set of RAls related to the Met data used to execute the dispersion models was provided to the licensee on February 17, 2016 (ADAMS Accession No. ML16048A232). The licensee evaluated the issues, confirmed the NRC staff-identified discrepancy between the Met data formatted per RG 1.23 and the Met data used as input to the dispersion models, and after correction, determined the effects on the subsequent dose calculations. The licensee provided its responses to those RAls by letter dated April 21, 2016.

The NRC staffs review of the ARCON96 and EN-113 dispersion modeling analyses continued after receiving the second set of RAI responses. A decision was made to subsequently conduct an audit of the licensee to allow the NRC staff to review calculations performed in support of the analyses during the audit.

The NRC staff conducted the regulatory audit on August 3 and 4, 2016. This audit report is completed in accordance with the guidance set forth in NRC Office of Nuclear Reactor Regulation, Office Instruction LIC-111, and "Regulatory Audits," dated December 29, 2008 (ADAMS Accession No. ML082900195).

2.0 REGULATORY AUDIT BASIS The focus of this audit was to review the analyses submitted by the licensee referenced in the Background section; in particular the atmospheric dispersion modeling analyses of onsite and offsite impacts due to hypothetical design-basis accident releases which provide direct input to subsequent dose calculations. The following regulations and regulatory guidance served as the basis for this audit.

Criterion 19, "Control room."

  • NUREG-0800, "Standard Review Plan for the Review of Nuclear Power Plants:

LWR Edition" (SRP) Section 2.3.4, "Short-Term Atmospheric Dispersion Estimates for Accident Releases," Revision 3, March 2007,Section II, "Acceptance Criteria" (ADAMS Accession No. ML070730398).

Among other items, SRP Section 2.3.4 states that the atmospheric dispersion models used to calculate X/Q values from accident releases at offsite and onsite locations should be documented in detail and substantiated so that the NRC staff can evaluate the appropriateness of their use with regards to release characteristics, plant configuration, plume density, meteorological conditions, and site topography.

  • RG 1.145, "Atmospheric Dispersion Models for Potential Accident Consequence Assessments at Nuclear Power Plants," Revision 1, November 1982, Reissued February 1983 (ADAMS Accession No. ML003740205).
  • NUREG/CR-2858 (PNL-4413), "PAVAN: An Atmospheric-Dispersion Program for Evaluating Design-Basis Accidental Releases of Radioactive Materials from Nuclear Power Stations," November 1982 (ADAMS Accession No. ML12045A149).

'Atmospheric Dispersion Models for Potential Accident Consequence Assessments at Nuclear Power Plants,"' October 1981 (ADAMS Accession No. ML12045A197).

  • RG 1.194, "Atmospheric Relative Concentrations for Control Room Radiological Habitability Assessments at Nuclear Power Plants," June 2003 (ADAMS Accession No. ML031530505).
  • NUREG/CR-6331 (PNNL-10521), "Atmospheric Relative Concentrations in Building Wakes," Revision 1, May 1997.
  • RG 1.183, "Alternative Radiological Source Terms for Evaluating Design Basis Accidents at Nuclear Power Reactors," July 2000 (ADAMS Accession No. ML003716792).
  • NUREG-0737, "Clarification of TMI [Three Mile Island] Action Plan Requirements: Requirements for Emergency Response Capability," Supplement No. 1, Reprinted February 1989 (ADAMS Accession No. ML102560009).
  • RG 1.23, "Meteorological Monitoring Programs for Nuclear Power Plants,"

Revision 1, March 2007 (ADAMS Accession No. ML070350028).

3.0 REGULA TORY AUDIT SCOPE The scope of the audit was to examine and evaluate technical and process information (e.g.,

functions, inputs, and assumptions) related to (1) the proprietary EN-113 dispersion model used to estimate offsite X/Q values at the exclusion area boundary (EAB) and the outer low population zone (LPZ) boundary, and (2) the NRG-accepted ARCON96 dispersion model used to estimate onsite X/Q values at the various air intakes and ingress I egress locations to the Control Room (CR) and Technical Support Center (TSC).

  • Purpose - The intent of reviewing this information was to (1) evaluate those accident-related atmospheric dispersion analyses for conformance to applicable regulatory requirements and guidance, and (2) determine the reasonability of the

dispersion modeling results presented in the documentation that supports the AST LAR. With respect to the proprietary EN-113 dispersion model, the intent was not to endorse the model but rather to determine its acceptability for the AST submittal.

  • Goals and Objectives - The information contained in this audit report that is expected to be referenced, as appropriate, by the safety evaluation prepared for the subject LAR submittal. This is especially important for the EN-113 modeling analysis, which uses a proprietary computer code.

The audit was also meant to identify the information needs to be submitted on the docket for completing the review as additional RAls after completion of the audit. The responses to any such RAls may require Revision to dispersion model input and output files (in the case of ARCON96 model runs), revised dispersion model input files and summaries of all applicable output results (in the case of EN-113 model runs) and, if necessary, revised Met data formatted for input to the respective models. The Revision or correction of any related figures or drawings, and summary tables of dispersion or dose calculation results will be expected to be provided as part of the RAI response(s).

4.0 AUDIT LOCATION AND DATES The audit was conducted at the Westinghouse facility in Rockville, Maryland, on August 3 and 4, 2016. A closeout meeting was held at the conclusion of the audit on August 4, 2016.

5.0 AUDIT TEAM Title I Organization Team Member Team Leader, NRO/DSEA/RHM1/RMOT Brad Harvey Audit Leader, NRO/DSEA/RHM1/RMOT Michael Mazaika Technical Support, NRO/DSEA/RHM1/RMOT Jason White Senior Project Manager, NRR/DORL/LPL4-1 Balwant Singal Branch Chief, NRO/DSEA/RHM1 Christopher Cook A list of audit participants and their affiliation is presented as Attachment 1 to this report.

6.0 DOCUMENTS AUDITED The information reviewed during the audit was based on review of the information already submitted, including responses to RAls.

The purpose of the audit was not to endorse the proprietary EN-113 dispersion model. Hence, no review of the code itself or any related quality assurance documentation was made. Only the input files and information on the input file structure was reviewed during the audit.

Attachment 2 to this report contains a list of documents that were reviewed by the NRC staff during the audit, in part or in whole, to review specific aspects of certain technical aspect (e.g.,

development of a model input value). These documents were made available to the NRC staff in hard copy form during the audit and may not be submitted on docket.

7.0 AUDIT ACTIVITIES AND TECHNICAL DISCUSSIONS An audit plan and agenda were transmitted to the license by letter dated July 12, 2016, prior to the audit (ADAMS Accession No. ML16193A332). The audit entrance meeting summarized the background information presented earlier in this report and reiterated the purpose and statement of the audit's goals and objectives.

Tables 1 and 2 present the technical information and supporting analysis reviewed and discussed during the audit and results of the review and are provided in Attachments 3 and 4, respectively, to this audit report. Table 1 identifies technical areas of interest to the NRC staff regarding the EN-113 dispersion modeling analysis of offsite impacts at the EAB and outer LPZ boundary. Table 2 identifies technical areas of interest to the NRC staff regarding the ARCON96 dispersion modeling analysis of onsite impacts at the various air intakes and ingress/egress locations to the CR and TSC. Tables 1 and 2 also show the results of the NRC staff review for each technical area of interest based on the information made available to the NRC staff during the audit. Tables 1 and 2 also indicate the areas requiring the licensee to submit certain information on docket and will be the subject of future RAls.

8.0 EXIT BRIEFING On August 4, 2016, the NRC staff closed out the regulatory audit with an exit briefing on the results of the review of technical information made available during the audit. The license was briefed on the potential topics of interest where the NRC staff is likely to request additional information.

Date:

Attachments:

1. Audit Participants
2. Documents Reviewed
3. Table 1 - EN-113 Dispersion Modeling Analysis
4. Table 2 - ARCON96 Dispersion Modeling Analysis

ATTACHMENT 1 AUDIT PARTICIPANTS NAME TITLE ORGANIZATION Balwant Singal Senior Project Manager N RC/NRR/DORL/LPL4-1 Hossein Hamzehee Manager, Regulatory Services PG&E Mike Wright Manager, LBVP PG&E Stephen Vigeant Senior Scientist CB&I Federal Services*

Sreela Ferguson Supervisor - Rad & TH Group Westinghouse I WECTEC*

Keith Ferguson Radiological Specialist Westinghouse I WECTEC*

Christopher Cook Branch Chief NRC/NRO/DSEA/RHM1 Brad Harvey Acting Team Leader NRC/NRO/DSEA/RHM1/RMOT Jason White Physical Scientist-Meteorologist N RC/NRO/DSEA/RHM 1/RMOT Michael D. Mazaika Physical Scientist-Meteorologist NRC/NRO/DSEA/RHM1/RMOT Kristy Bucholtz Reactor Engineer NRC/NRR/DRA/ARCB

  • Contract staff representing PG&E NRC = U.S. Nuclear Regulatory Commission NRR =Office of Nuclear Reactor Regulation NRO =Office of New Reactors DORL/LPL4-1 = Division of Operating Reactor Licensing, Plant Licensing Branch IV-1 DSEA/RHM1/RMOT =Division of Site Safety and Environmental Analysis, Hydrology and Meteorology Branch 1, Meteorology and Oceanography Team DRA/ARCB =Division of Risk Assessment, Radiation Protection and Consequence Branch PG&E/DCPP = Pacific Gas and Electric Company

ATTACHMENT 2 LIST OF DOCUMENTS REVIEWED Diablo Canyon Alternative Source Term Radiological Calculations A. Calculation Number (Cale. No.) 14078104-C-M-0001, Revision 1, Atmospheric Dispersion Factors (X/Qs) at Control Room Receptors for Post-Accident LOCA Radiological Releases Using the ARCON96 Program.

B. Cale. No. 14078104-C-M-0002, Revision 0, Atmospheric Dispersion Factors (X/Qs) at the Exclusion Area Boundary and Low Population Zone for Radiological Releases from Unit 1 and Unit 2 Using Regulatory Guide 1.145 Methodology.

C. Cale. No. 14078104-C-M-0003, Revision 1, Atmospheric Dispersion Factors (X/Qs) at Control Room Receptors for Fuel Handling Accident Radiological Releases Using the ARCON96 Program.

D. Cale. No. 14078104-C-M-0004, Revision 1, Atmospheric Dispersion Factors (X/Qs) at Control Room Receptors for Radiological Releases from MSSVs/ADVs Using the ARCON96 Program.

F. Cale. No. 14078104-C-M-0006, Revision 0, Atmospheric Dispersion Factors (X/Qs) at TSC Receptors for LOCA Radiological Releases Using the ARCON96 Program.

G. Cale. No. 14078104-C-M-00028, Revision 0, Effect of Using the Stability Classes based on Regulatory Guide 1.23 Methodology on Accident Atmospheric Dispersion Factors (X/Qs) and Associated Dose Consequences at On-Site and Off-Site Receptors.

ATTACHMENT 3 Table 1 Technical Areas of Interest & Resolution Status Regarding EN-113 Dispersion Modeling Analysis of Offsite (EAB and LPZ) Impacts Need ITEM TECHNICAL ISSUE RESOLUTION for RAI 1 Issues Related to Input Card 3 of Proprietary EN-113 Model 1(a) The period of record (POR) of meteorological (Met) data used for The licensee confirmed that the input files and file description No the EN-113 atmospheric dispersion modeling analysis of offsite provided with the November 2, 2015, RAI response represent the impacts in support of the LAR 15-03 submittal has been stated to EN-113 runs that support LAR 15-03.

be 2007 thru 2011. However, the variables "!START" and "!STOP" on Card 3 for each of the three EN-113 model input files, provided The licensee reported that the EN-113 model input files with the November 2, 2015, RAI response, are shown as "87001" represented the 2007-2011 POR. The variables "!START" and and "91365," respectively. "!STOP" on Card 3 for each of the EN-113 input files are designated as "87001" and "91365," respectively, as a The licensee should confirm whether the three EN-113 model work-around for a Y2K year and date time stamping issue.

input files represent the offsite dispersion modeling performed for EN-113 was developed in the 1970s and has not been updated to LAR 15-03 and, more importantly, verify whether or not the X/Q address this dating issue. The NRC staff is familiar with this issue values and subsequent dose calculations are based on Met data and work-around and determined this this approach to be for the 1987 through 1991 5-year POR or the 2007 thru 2011 reasonable.

POR.

The Met data input to the EN-113 model runs (corrected for If the 1987-1991 POR of Met data was used, the licensee should classification of stability class consistent with RG 1.23) was revise the X/Q estimates for the U1 (EAB), U2 (EAB), and U1/U2 provided with the April 21, 2016, RAI response.

(LPZ) EN-113 model runs, subsequent dose calculations, and other related discussions and summary tables in the Updated Final The NRC staff determined that the information provided by the Safety Analysis Report (UFSAR) and elsewhere in the LAR licensee was sufficient to address the technical issue and no submittal. further action is warranted.

If the 2007-2011 POR of Met data was used, the licensee should provide the EN-113 model input files that correspond to the LAR 15-03 dispersion modeling analyses along with the sequential hourly Met data formatted for input to the EN-113 model.

If necessary, the licensee should revise the discussions in the UFSAR accordingly.

Table 1 Technical Areas of Interest & Resolution Status Regarding EN-113 Dispersion Modeling Analysis of Offsite (EAB and LPZ) Impacts Need ITEM TECHNICAL ISSUE RESOLUTION for RAI 1(b) The licensee should explain how the variable "DHT," which is set The licensee stated that EN-113 classifies stability using variable No to a value of" 100" for the U 1 (EAB), U2 (EAB), and U 1/U2 (LPZ) "DHT" based on how input delta-T (stability) data are provided. If model input files, relates to the actual vertical distance of delta-T values in input Met file represented literal vertical distance separation for the delta-T measurement system, to the Met data between two measurement levels, that would trigger conversion to input to the EN-113 dispersion model, and to the units of measure °C/100 m to classify stability before use in X/Q calculations. In this specified in Table 1 of Regulatory Position C.2.2 and Appendix A case, input data already represented °C/100 m so the variable in RG 1.23, Revision 1 for defining Pasquill stability class as a "DHT" was set to "100."

function of delta-T (i.e., degrees Celsius (0 C) per 100 meters (m)).

The NRC staff determined that the information provided by the licensee was sufficient to address the technical issue and no further action is warranted.

1(c1) The licensee should explain why different calm threshold wind Variable "IREDIS" is a calm redistribution function assigning hours No speed values, and possibly units of measure for wind speed, were with calm wind conditions to non-calm wind directions similar to specified by the variable "IREDIS" for the U1 (EAB) and U2 (EAB) PAVAN. The licensee indicated that these threshold values are EN-113 model input files (i.e., set to a value of "2" indicating a not used to calculate X/Q values. The licensee acknowledged calm speed of 1.5 meters per second (m/sec) or 3.3557 miles per incorrect use of different threshold values and units of measure for hour (mph)) compared to the U1/U2 (LPZ) EN-113 model input file U1 (EAB) and U2 (EAB) runs versus U1/U2 (LPZ) run. However, (i.e., the variable "IREDIS" set to a value of "1" indicating a calm the licensee does not plan to re-run EN-113 model for the speed of 1.5 mph). LAR 15-03 submittal having looked at the effect of consistent "IREDIS" settings prior to the audit and found no significant difference in controlling X/Qs because of infrequent occurrence of calm winds at DCPP site.

The NRC staff determined that the information provided by the licensee was sufficient to address the technical issue and no further action is warranted.

Table 1 Technical Areas of Interest & Resolution Status Regarding EN-113 Dispersion Modeling Analysis of Offsite (EAB and LPZ) Impacts Need ITEM TECHNICAL ISSUE RESOLUTION for RAI 1(c2) The licensee should confirm the starting threshold wind speeds for The licensee was not sure of starting threshold wind speeds for No both the anemometer and wind vane on the primary and back-up anemometers and wind vanes on primary or back-up Met towers, Met towers during the modeled 5-year POR. As necessary, the although it was thought to be 0.5 m/sec for the anemometer. The licensee should reconcile, consistent with the definition for "calm" licensee's wind speeds used for X/Q calculations under calm in Regulatory Position C.1 of RG 1.23, any differences between conditions were assumed to be 0.5 mph (accident releases) and the highest of the starting speeds for the anemometer and wind 0.3 mph (annual average calculations) (see variables "CALMAC" vane on each tower, against the appropriate threshold value for and "CALMAN" on Card 8 as opposed to values entered on Card 3 calm wind conditions presumably specified by the variable for variable "IREDIS").

"IREDIS."

The NRC staff determined that these values represent acceptably conservative assumptions for calculation purposes and that the licensee's approach was reasonable because the infrequent occurrence of light wind conditions at the DCPP site should not affect the resulting X/Q values. As such, the staff determined that the information provided by the licensee was sufficient to address the technical issue and no further action is warranted.

1(c3) Given that the variable "ISPUNT" on Card 4 is set to "O" for each of The licensee indicated that there is no relationship between the No the EN-113 input files indicating that the unit of measure for wind variable "ISPUNT" on Card 4 and the variable "IREDIS" on Card 3.

speed is mph, the licensee should confirm that there are no See the resolution status for Item 1(c1) regarding the function of discrepancies between the units of measure that appear to be the variable "IREDIS." The variable "ISPUNT" designates the units associated with the variable "IREDIS" for the U1 (EAB) and U2 of measure for the wind speed data input to EN-113. The setting (EAB) model runs and the hourly Met data input to EN-113 or the of "O" corresponds to "mph." Wind speed values are in units units of measure that appear to be associated with the variable of mph in the EN-113 input Met data file. Spot checks made by "IREDIS" for the U1/U2 (LPZ) model run and the hourly Met data staff on conversion of wind speed (as input to EN-113) versus input to EN-113. units of measure in RG 1.23 (i.e., m/sec) data file were determined to be acceptable.

The NRC staff determined that the information provided by the licensee was sufficient to address the technical issue and no further action is warranted.

Table 1 Technical Areas of Interest & Resolution Status Regarding EN-113 Dispersion Modeling Analysis of Offsite (EAB and LPZ) Impacts Need ITEM TECHNICAL ISSUE RESOLUTION for RAI 2 Issues Related to Input Card 4 of Proprietary EN-113 Model 2(a1) The EN-113 input file description for Card 4 indicates that the first The licensee indicated only three of the six 24-hour records for No nine entries on that card specify three-character Met data each day of the input Met data file are used by EN-113 and parameter IDs. Of those, three IDs are given - "Speed" (131 }, "Dir" correspond to the non-zero IDs (i.e., 131, 132, and 136) entered (132), and "Delta T" (136). All other IDs are entered as "O." on Card 4. Numerical values assigned to the three other 24-hour However, the sequential hourly, ASCII-character Met data file input daily records are "dummy" values produced by a Fortran program to the EN-113 model includes six parameters (lines of data) per used to prepare the Met data file. The Fortran program was Julian Day (i.e., IDs= 131, 132, 134, 135, 136, and 137). The originally set up to provide input to other codes that utilize Met licensee should identify the Met parameters or data corresponding data (not applicable to this LAR analysis). The NRC staff made to parameter IDs 134, 135, and 137 along with the respective units spot checks on conversion of wind speed (input to EN-113 of measure. as mph) versus units of measure in RG 1.23 (i.e., m/sec) data file and consistency of time/date stamping between both files. Spot checks OK.

The NRC staff determined that the information provided by the licensee was sufficient to address the NRC staff concerns and no further action is warranted.

2(a2) The licensee should confirm whether the Met parameters or data This concern covered the possibility that data associated with Met No corresponding to parameter IDs 134, 135, and 137 were parameter IDs 134, 135, and 137 were input to the EN-113 accounted for in the EN-113 modeling runs for the LAR and, if so, modeling analysis. The licensee confirmed that this is not the how those values are used in the dispersion calculations. case. See resolution status for Item 2( a 1).

The NRC staff determined that the information provided by the licensee was sufficient to address the NRC staff concern and no further action is warranted.

Table 1 Technical Areas of Interest & Resolution Status Regarding EN-113 Dispersion Modeling Analysis of Offsite (EAB and LPZ) Impacts Need ITEM TECHNICAL ISSUE RESOLUTION for RAI 3 Issues Related to Input Card 6 of Proprietary EN-113 Model 3(a1) The variable "ISTRLN" on Card 6 appears to relate to the The licensee indicated that although EN-113 operates using hourly No calculation (interpolation) of XIQ values between (presumably) a Met data as input (as opposed to PAVAN which uses joint 1-hour average value and some endpoint in time. There appears frequency distributions of wind speed, wind direction, and to be two numerical entries associated with this variable (i.e., "O" atmospheric stability class as input), EN-113 can calculate X/Q and "2") for the U1 (EAB), U2 (EAB), and U1/U2 (LPZ) EN-113 values for intermediate time periods beyond the 0-2 hour interval, model input files. The "O" entry suggests that "no calculation" is such as for the LPZ, by logarithmic interpolation. The variable made. The licensee should explain how each of the two numerical "ISTRLN" on Card 6 controls this function. The first of the two entries for this variable relate to the calculation of the 0- to 2-hour entries for this variable instructs the code to use logarithmic XIQ values reported for the EAB distance relative to U1 and U2 interpolation rather than hourly X/Q values to calculate X/Q values and to the calculation (and/or interpolation) of the 0- to 2-hour, for the intermediate time periods. The second of the two entries 2- to 8-hour, 8- to 24-hour, 1- to 4-day, and 4- to 30-day X/Q for "ISTRLN" sets the shorter-term endpoint for the interpolation.

values estimated for the outer LPZ boundary distance. In this case, the value "2" assumes the appropriate 1-hour X/Q value represents a 2-hour average on the interpolation curve. The annual average X/Q value, representing the other end point for the interpolation, is determined elsewhere by EN-113.

The NRC staff determined that the information provided by the licensee was sufficient to address the NRC staff concern and no further action is warranted.

3(a2) The licensee should discuss the consistency of this apparent The licensee stated its method is consistent with approach used No methodology with the guidance in RG 1.145, Revision 1, by PAVAN model which implements RG 1.145.

Re-issued February 1983 and NUREG/CR-2858 (PNL-4413),

dated November 1982. The NRC staff determined that the information provided by the licensee was sufficient to address the technical issue and no further action is warranted.

Table 1 Technical Areas of Interest & Resolution Status Regarding EN-113 Dispersion Modeling Analysis of Offsite (EAB and LPZ) Impacts Need ITEM TECHNICAL ISSUE RESOLUTION for RAI 3(b) In light of the apparent discrepancy between the calm threshold The licensee indicated that the variable "ICALM" on Card 6 has a No wind speed specified for the U1 (EAB) and U2 (EAB) model input different function than the settings for "IREDIS" on Card 3 (i.e.,

files (i.e., 1.5 m/sec) and that specified for the U1/U2 (LPZ) model which distributes hours with calm winds to non-calm wind run (i.e., 1.5 mph) on Card 3, the licensee should confirm the directions). "ICALM" is related to the variables "CALMAC" and validity of setting the variable "ICALM" on Card 6 to a value of "O" "CALMAN" on Card 8; that is, the wind speed value to be used to for the U1 (EAB), U2 (EAB), and U1/U2 (LPZ) EN-113 model input calculate an hourly X/Q value under conditions when the wind files which appears to implement the default re-setting of the wind speed for that hour is considered to be calm (i.e., "CALMAC") and speed to the (presumably threshold) calm speed value if the the wind speed value to be used to calculate an annual average (hourly) "wind speed falls below the calm speed." X/Q value for those hours during the POR that are considered to be calm (i.e., "CALMAN").

The NRC staff determined that the information provided by the licensee was sufficient to address the technical issue and no further action is warranted.

3(c) The variables "UCU" and "UCS" on Card 6 appear to relate to The licensee indicated that despite setting the variables "UCU" No correction factors to be applied, respectively, to the wind speed and "UCS" on Card 6 to "0.00" for the EAB and LPZ EN-113 during unstable I neutral stability conditions and during stable modeling runs instead of the default value of "1.0," there was no conditions if (presumably) the wind speed measurement height adjustment to the wind speed for any difference between the wind and release height are different. The variables "UCU" and "UCS" speed measurement height and the release height. For these are set to "0.00" for the U1 (EAB), U2 (EAB), and U1/U2 (LPZ) model runs, accident releases are assumed to be ground-level EN-113 model input files. However, the input file description (default release height of 10 m) which is the same as the wind indicates that the default setting for these variables is "1.0." speed measurement height. Therefore, no adjustment is made to the wind speed used in the X/Q calculations. This is consistent The regulatory guidance in NUREG/CR-2858 (PNL-4413), dated with the relationship between the variables "TOWERH" and November 1982, indicates that for a ground-level release, the "IRETYPE" in the PAVAN user's guide (NUREG/CR-2858).

release height is set to 10 m. This height is the same as the lower wind measurement height on the DCPP, Units 1 and 2, Met tower The NRC staff determined that the information provided by the such that no height adjustment for wind speed appears to be licensee was sufficient to address the technical issue and no necessary for the dispersion calculations. Given that the variable further action is warranted.

"MESHT" on Card 7 is set to "O," indicating "[s]peed modification with height not made" and that the setting for the variable "I RETYPE" on Card 5 corresponds to a ground-level release, the licensee should confirm that the non-default settings for variables "UCU" and "UCS" are consistent with the regulatory guidance in NUREG/CR-2858.

Table 1 Technical Areas of Interest & Resolution Status Regarding EN-113 Dispersion Modeling Analysis of Offsite (EAB and LPZ) Impacts Need ITEM TECHNICAL ISSUE RESOLUTION for RAI 4 Issues Related to Input Card 7 of Proprietary EN-113 Model 4(a) The variable "ISECVG" on Card 7 appears to relate to sector The licensee indicated that the variable "ISECVG" (i.e., sector No averaging and is set to a value of "1" for the U1 (EAB), U2 (EAB), averaging) only applies to the calculation of annual average X/Q and U 1/U2 (LPZ) EN-113 model input files suggesting that sector values, but not to the calculation of hourly X/Qs. The licensee also averaging is performed in calculating the X/Q values at each stated that the statement in the fourth bulleted item under Section boundary location. Further, the option selected indicates that 5.1 (Paragraph 8) of the Technical Assessment (i.e., "[t]he plume sector averaging is made "without correction." centerline from each release is transported directly over the receptor") applies only to the calculation of hourly X/Q values.

The licensee should confirm whether this variable affects only the estimate of annual average X/Q values used to interpolate The NRC staff determined that the information provided by the intermediate, short-term accident-related X/Q values (i.e., 2-8 licensee was sufficient to address the NRC staff concerns and no hours, 8-24 hours, 1-4 days, and 4-30 days) at the outer LPZ further action is warranted.

boundary or calculations of the 0-2 hour X/Q values at the EAB receptor distances (only) and the 0-2 hour X/Q values at the LPZ.

If the latter, the licensee should reconcile and/or clarify the text in the fourth bulleted item under Section 5.1 (Paragraph 8) of the "Diablo Canyon Power Plant Technical Assessment, Revision 2,"

which states that "[t]he plume centerline from each release is transported directly over the receptor."

4(b) The variable "IBWEFF" on Card 7 is set to a value of "5" for the U1 The licensee stated that the "Rancho Seco ('77) building wake (EAB), U2 (EAB), and U1/U2 (LPZ) EN-113 model input files. This meander" option selected with the variable "IBWEFF" on Card 7 entry indicates that building wake effects on short-term dispersion implements the methodology in RG 1.145. The licensee also calculations are accounted for and based on "Rancho Seco ('77) acknowledged that the terminology used to describe this option is building wake meander." Horizontal plume dispersion (sigma-Y) not as clear as it could, reiterating that the code and descriptions values, based on the results from the Rancho Seco and were developed many years ago. The NRC staff indicated that Experimental Organic Cooled Reactor field tests to characterize these factors and the cited regulatory guidance were the bases for plume meander effects, are shown on Figures 11-2 through 11-5 for the NRC staff concerns raised in the questions that follow.

atmospheric stability classes D through G, respectively, as documented in the technical basis for RG 1.145 (i.e., The audit scope did not include inspection of the EN-113 code NUREG/CR-2260 (NUS-3854), October 1981). itself.

In particular, for a downwind distance of 800 m, similar to many of the EAB distances entered for the variable "DISITE" on Card 11 of the U 1 (EAB) and U2 (EAB) EN-113 model input files, the plotted sigma-Y values range from approximately 0.25 to 3.0 times higher, depending on stability class, than the plume meander adjustment factors incorporated into RG 1.145. Consequently:

Table 1 Technical Areas of Interest & Resolution Status Regarding EN-113 Dispersion Modeling Analysis of Offsite (EAB and LPZ) Impacts Need ITEM I TECHNICAL ISSUE RESOLUTION I for RAI 4(b1) IThe EN-113 input file description suggests that there is a building The licensee indicated that EN-113 implements RG 1.145 No wake I meander component associated with the "IBWEFF" Regulatory Position C.1.3.1 (a) for plume meander when the wind variable. If so, the licensee should confirm the wind speed speed is less than 6 m/sec under D, E, F, and G stability threshold(s) and specify the atmospheric stability conditions that conditions based on Figure 3 of RG 1.145. Plume meander is not implement the adjustments for plume meander in the dispersion implemented for other Met conditions consistent with RG 1.145 model calculations. Regulatory Position C.1.3.1 (b).

The NRC staff determined that the information provided by the licensee was sufficient to address the NRC staff concerns and no further action is warranted.

1------------------------------------------------------------------------------ -----------------------------------------------------------------------------1-----------

4(b2) The licensee should discuss the consistency of the methodology The licensee stated that the "Rancho Seco ('77) building wake I No invoked by setting the variable "IBEWFF" on Card 7 to "5" with the meander" option selected with the variable "IBWEFF" on Card 7 guidance in RG 1.145, NUREG/CR-2858, and NUREG/CR-2260, implements the methodology in RG 1.145 without modification.

which implements or is the basis for the regulatory positions in RG 1.145. IThe NRC staff determined that the information provided by the licensee was sufficient to address the NRC staff concerns and no further action is warranted.

1------------------------------------------------------------------------------ -----------------------------------------------------------------------------1-----------

4(b3) The licensee should confirm whether any adjustment is made to The licensee indicated that EN-113 makes no modification to the I No the vertical plume dispersion parameter (i.e., sigma-Z) in sigma-Z (or the sigma-Y) dispersion curves in RG 1.145. Staff estimating X/Q values with the EN-113 model when the "Rancho noted that no sigma-Z measurements were made during the Seco ('77) building wake meander" methodology is invoked by Rancho Seco field tests or as documented in NUREG/CR-2260 setting the variable "IBEWFF" on Card 7 to "5." If so, explain and (NUS-3854), the technical basis for RG 1.145.

provide technical justification for that approach.

The NRC staff determined that the information provided by the licensee was sufficient to address the NRC staff concerns and no further action is warranted.

4(b4) If any other differences exist between the cited regulatory The licensee stated that no other differences exist between No guidance and the "building wake meander" methodology controlled RG 1.145 and the building wake methodology implemented by the by setting the variable "IBWEFF" to "5" in the U1 (EAB), U2 (EAB), EN-113 model for this LAR submittal.

and U 1/U2 (LPZ) EN-113 model runs, the licensee should provide technical justification for those approaches, especially if the X/Q The NRC staff determined that the information provided by the calculation results are less conservative, had the guidance in licensee was sufficient to address the NRC staff concerns and no RG 1.145 been followed. further action is warranted.

Table 1 Technical Areas of Interest & Resolution Status Regarding EN-113 Dispersion Modeling Analysis of Offsite (EAB and LPZ) Impacts Need ITEM TECHNICAL ISSUE RESOLUTION for RAI 4(c) The variable "ITERIN" on Card 7 appears to allow for the model The licensee confirmed that default open terrain adjustment calculations to be adjusted for the effects of nearby terrain on factors (TAFs) were input to the EN-113 model runs for the EAB dispersion and is set to a value of "1" for the U1 (EAB), U2 (EAB), and LPZ to account for terrain recirculation effects at the DCPP and U 1/U2 (LPZ) EN-113 model input files. The U 1 (EAB) and U2 site based on the option selected for the variable "ITERIN" on (EAB) input files specify 16 identical terrain adjustment factors Card 7 and that these factors were based on Figure 4.2 of (TAFs) set to a value of "4.0" (presumably one for each of the 16 NUREG/CR-2858. Factors are as listed for each of the 16 standard direction sectors). However, the U1/U2 (LPZ) input file direction sectors which were included as part of the echo of model specifies 16 TAFs with each set to a value of "1.25." inputs in the output files for each model run. This model input information was provided to the NRC staff, along with descriptions The fifth bulleted item under Section 5.1 (Paragraph 8) of the of the input file structure and available input options, as part of the "Diablo Canyon Power Plant Technical Assessment, Revision 2," November 2, 2015, RAI response.

states that "[a] terrain recirculation factor of 4 is used in the calculation of the annual average X/Q values." Given the distances to the respective EAB and outer LPZ boundaries specified on Card 11 of the EN-113 input files, the TAFs are consistent with the default TAFs from Figure 4.2 in NUREG/CR-2858 for the NRG-approved PAVAN dispersion model. Therefore:

4(c1) The licensee need to reconcile and/or clarify the fifth bulleted item The licensee acknowledged that the referenced bulleted item in Yes under Section 5.1 (Paragraph 8) of the referenced Technical Section 5.1 of the Technical Assessment and the parallel text in Assessment, as well as the parallel text in Subsection 2.3.5.2.1 of Subsection 2.3.5.2.1 of the UFSAR only represents the TAF the UFSAR, Revision 21, as proposed to be revised on applied to the U1 (EAB) and U2 (EAB) model runs.

December 17, 2015 (ADAMS Accession No. ML16004A363), and elsewhere as appropriate, as to the numerical value of the "terrain The NRC staff determined that the information provided by the recirculation factor" actually input to the U1 (EAB), U2 (EAB), and licensee was sufficient to address the technical issue. An RAI will U1/U2 (LPZ) EN-113 model runs. be issued requesting that the licensee update the Technical Assessment and UFSAR to include the TAF applied to the U1/U2 (LPZ) model run.

Table 1 Technical Areas of Interest & Resolution Status Regarding EN-113 Dispersion Modeling Analysis of Offsite (EAB and LPZ) Impacts Need ITEM TECHNICAL ISSUE RESOLUTION for RAI 4(c2) Given the location of the DCPP site, the licensee should explain The licensee indicated that the "ITERIN" option on Card 7 for TAFs No the rationale for not setting the variable "ITERIN" to "6" which associated with a coastal setting was not selected because the appears to correspond to TAFs associated with a coastal setting. licensee is not familiar with where and how the measurements resulting in those factors were made, or how the TAFs were determined. The licensee was also not sure if earlier field studies conducted at and around the DCPP site (as discussed in UFSAR),

to evaluate stability classification approaches based on measurements of horizontal and vertical wind direction fluctuation and delta-T, also included development of site-specific TAFs.

Because of these uncertainties, the licensee considered the default open terrain adjustment factors from NUREG/CR-2858 for the NRG-approved PAVAN dispersion model to be conservative.

The NRC staff determined that the licensee's approach was reasonable and that the information provided by the licensee was sufficient to address the NRC staff concerns and no further action is warranted. The staff notes that the UFSAR discussions of these site-specific field studies and wind conditions at the site suggest that dispersion conditions are generally good and so assumption still considered to be reasonable.

Table 1 Technical Areas of Interest & Resolution Status Regarding EN-113 Dispersion Modeling Analysis of Offsite (EAB and LPZ) Impacts Need ITEM TECHNICAL ISSUE RESOLUTION for RAI 5 Issues Related to Input Card 8 of Proprietary EN-113 Model 5(a1) The variables "CALMAC" and "CALMAN" on Card 8 appear to The licensee pointed out that difference between wind speeds No specify default wind speeds that are assigned to (presumably used for X/Q calculations under calm conditions (i.e., "CALMAC" =

hourly) calm wind observations in calculating accident and annual 0.5 mph for accident releases and "CALMAN" = 0.3 mph for average X/Q values and are set to "0.5" and "0.3" mph, annual average calculations) on Card 8 is based on difference respectively. The settings are the same for these variables for the between RG 1.145 and RG 1.111. The NRC staff acknowledges U1 (EAB), U2 (EAB), and U1/U2 (LPZ) EN-113 model runs. The this difference (see Regulatory Position C.1.1 (Paragraph 4) in licensee should explain the rationale for assigning different default RG 1.145 which calls for higher of starting speed of anemometer calm wind speeds to the accident and annual average X/Q or wind vane and Regulatory Position C.4 (Paragraph 4) in calculations. RG 1.111 which calls for one-half of higher of starting speeds for those instruments).

Although licensee was not sure of starting threshold wind speeds for anemometers and wind vanes on primary or back-up Met towers, the NRC staff believes that these values represent acceptably conservative assumptions for X/Q calculation purposes and that the licensee's approach was reasonable because the infrequent occurrence of light wind conditions at the DCPP site should not affect the resulting X/Q values. As such, the NRC staff determined that the information provided by the licensee was sufficient to address the NRC staff concerns and no further action is warranted.

Table 1 Technical Areas of Interest & Resolution Status Regarding EN-113 Dispersion Modeling Analysis of Offsite (EAB and LPZ) Impacts Need ITEM TECHNICAL ISSUE RESOLUTION for RAI 5(a2) The licensee should explain the relationship between the default The licensee indicated that the variable "IREDIS" on Card 3 which No calm wind speeds specified by the variables "CALMAC" and distributes hours with calm winds to non-calm wind directions has "CALMAN" on Card 8 and the calm threshold wind speed for the a different function than the settings for the variables "CALMAC" U1 (EAB) and U2 (EAB) model input files (i.e., 1.5 m/sec) and for and "CALMAN" on Card 8; that is, the wind speed value to be used the U1/U2 (LPZ) model run (i.e., 1.5 mph) (refer to Items 1(c1 ), to calculate an hourly X/Q value under accident conditions when 1(c2}, and 1(c3) pertaining to Card 3 for these latter values). The the wind speed for that hour is considered to be calm (i.e.,

licensee should also confirm the validity of these settings in light of "CALMAC") and the wind speed value to be used to calculate an the apparent discrepancy between the calm threshold wind speeds annual average X/Q value for those hours during the POR that are and, if necessary, reconcile with the settings for the variables considered to be calm (i.e., "CALMAN").

"CALMAC" and "CALMAN" on Card 8.

The NRC staff determined that the licensee's approach was reasonable because the values for "CALMAC" AND "CALMAN" represent acceptably conservative assumptions for X/Q calculation purposes and because the infrequent occurrence of light wind conditions at the DCPP site should not affect the resulting X/Q values. As such, the staff determined that the information provided by the licensee was sufficient to address the NRC staff concerns and no further action is warranted.

Table 1 Technical Areas of Interest & Resolution Status Regarding EN-113 Dispersion Modeling Analysis of Offsite (EAB and LPZ) Impacts Need ITEM TECHNICAL ISSUE RESOLUTION for RAI 5(b) The variable "BHT" on Card 8 appears to identify a representative The licensee indicated that the building cross-sectional area was Yes building height which is presumably considered in the calculation based on the projected height and width of the cylindrical portion of annual average X/Q values to account for structural wake of the containment building plus the domed portion on top of the effects on dispersion and is set to a value of "66.5" (presumably in containment. The licensee suggested that the cross-sectional meters) for the U1 (EAB), U2 (EAB), and U1/U2 (LPZ) EN-113 area of the domed portion was estimated based on a triangular model runs. Further, 16 values are entered on Card 10 for the representation minus a small portion of the dome on each side.

variable "A" in each of the three EN-113 input files representing the "[b]uilding wake effect area"; each is set to a value of "2745" Based on a calculation review during the audit, the NRG staff (units of measure are not specified). Based on the drawings determined that the area of the domed portion of the containment referenced in the RAI responses of November 2, 2015, the building was accounted for by treating it as a hemisphere rather variables "BHT" and "A" appear to correspond to the containment than a triangular shape. However, the staff does not consider this structure. to be an issue. Using the cross-sectional area of the containment building to account for wake effects is conservative (i.e., smaller The licensee should explain how the building cross-sectional area area) compared to the larger cross-sectional area of all the other was determined (including the domed-portion of the containment structures directly adjacent to the containment building.

structure, if applicable). See also Items 6(a1) and 6(a2) pertaining to Card 10 regarding a potential discrepancy with the specified The NRG staff determined that the information provided by the building cross-sectional area. licensee was sufficient to address the NRG staff concerns. An RAI will be issued requesting that the licensee update the UFSAR and Technical Assessment to explain how the building cross-sectional area was determined (including the domed-portion of the containment structure).

Table 1 Technical Areas of Interest & Resolution Status Regarding EN-113 Dispersion Modeling Analysis of Offsite (EAB and LPZ) Impacts Need ITEM TECHNICAL ISSUE RESOLUTION for RAI 6 Issues Related to Input Card 10 of Proprietary EN-113 Model 6(a1) The minimum cross-sectional area of the reactor building identified The licensee confirmed that a value 27 45 sq-m was used to Yes in Subsection 2.3.4.7 (Paragraph 4) and Subsection 2.3.5.2 account for building wake effects in the EN-113 modeling analysis (Paragraph 1) of the UFSAR (Revision 22) is 1600 square meters of offsite X/Q values at the EAB and LPZ receptors. The licensee (sq-m) and is designated as the variable "A." However, the 16 also indicated that value of 1600 sq-m for the minimum values entered on Card 10 for the variable "A" for each of the U 1 cross-sectional area of the containment buildings is a value (EAB), U2 (EAB), and U1/U2 (LPZ) model runs is 2745 (units of entered in the plant meteorological computer for its X/Q measure not specified). calculations (possibly for emergency response purposes, although licensee was unsure of its purpose and history) but was not the Further, Section 5.1 (in Paragraph 3, for the variable "A," and in value used for design basis X/Q calculations. The licensee also Paragraph 7) of the "Diablo Canyon Power Plant Technical Report, stated that the use of a containment building cross-sectional area Revision 1" and the later "Diablo Canyon Power Plant Technical of 2745 sq-mis conservative (i.e., smaller area) compared to the Assessment, Revision 2" does not specify the building actual larger cross-sectional area of all the other structures directly cross-sectional area used for the offsite impact modeling analysis. adjacent to each containment building.

In addition, Subsection 2.3.5.2.1 (Paragraph 3) of the UFSAR, Revision 21, as proposed to be revised on December 17, 2015 The NRC staff determined that the information provided by the (ADAMS Accession No. ML16004A363), no longer specifies the licensee was sufficient to address NRC staff concerns. An RAI will building cross-sectional area used for this offsite impact analysis. be issued requesting that the licensee update the UFSAR and Technical Assessment to identify the cross-sectional area of the Consequently, the licensee should explain the rationale for and containment building used as input to the EN-113 dispersion impact of the potentially non-conservative change to the licensing modeling analysis for the EAB and LPZ receptors, and to the basis by assuming a building cross-sectional area of 2745 ARCON96 modeling analysis for the CR and TSC receptors. The (presumably in sq-m) compared to the value of 1600 sq-min the RAI will request the licensee to confirm whether the value of 2745 referenced UFSAR subsections. sq-m rather than 1600 sq-m represents a change to the current licensing basis for the offsite and onsite dispersion modeling analyses.

6(a2) If necessary, the licensee should reconcile any discrepancies with The licensee stated that both the EN-113 and ARCON96 models No the ARCON96 onsite dispersion modeling analyses which accounted for wake effects due to the containment buildings using incorporate a similar building cross-sectional area of 2744.5 sq-m. a building cross-sectional area of approximately 2745 sq-m.

The NRC staff determined that the information provided by the licensee was sufficient to address the NRC staff concerns and no further action is warranted.

Table 1 Technical Areas of Interest & Resolution Status Regarding EN-113 Dispersion Modeling Analysis of Offsite (EAB and LPZ) Impacts Need ITEM TECHNICAL ISSUE RESOLUTION for RAI 7 Issues Related to Input Card 11 of Proprietary EN-113 Model 7(a1) The variable "DISITE" on Card 11 appears to specify distances to The licensee indicated that DCPP, Units 1 and 2, Site Boundary Yes the "site boundary" for each of 16 direction sectors from a given and EAB were not collocated in all direction sectors, including release point beginning with the distance to the receptor to the those sectors along the shoreline adjacent to the plant (i.e., a south (i.e., wind from the north) and continuing in a clockwise portion of the southeast clockwise through a portion of the direction. The discussion in Section 5.1 (Paragraph 5) of the northwest sector). The licensee recognized that UFSAR Figure "Diablo Canyon Power Plant Technical Assessment, Revision 2" 2.1-2 better represented the relationship between those indicates that these distances correspond to the EAB. Figure boundaries than Figure 5.1-1 as cited in the Technical 5.1-1, referenced from Section 5.1, does not appear to specifically Assessment. However, the licensee also understood that UFSAR identify the EAB when compared to Figure 2.1-2 of the UFSAR. Figure 2.1-2 and other discussions in the UFSAR and Technical Assessment do not provide sufficient information to either confirm The EAB and Site Boundary appear to be collocated in portions of that Site Boundary and EAB are not collocated in the direction the northwest clockwise through the northeast direction sectors sectors along the shoreline, to verify the distances to the EAB and to be two distinct boundaries in portions of the northeast assigned to those sectors on Card 11 of the U1 (EAB) and U2 clockwise through the southeast direction sectors relative to True (EAB) EN-113 model runs, or to confirm that the guidance in North. Further, some of these sectors extend beyond the coastline Regulatory Position C.1.2 of RG 1.145 for selecting those into the Pacific Ocean adjacent to the DCPP, Units 1 and 2, plant distances is met.

site, including a portion of the southeast clockwise through a portion of the northwest direction sectors. Except for portions of The NRC staff determined the information discussed by the the southeast and northwest sectors, Figure 2.1-2 of the UFSAR licensee during the audit to be sufficient to address the NRC staff gives no clear indication of the actual EAB location within this concerns. The NRC staff plans to issue an RAI requesting that the sector range; only the site boundary is designated. licensee update the UFSAR and Technical Assessment with additional information that describes the basis and location of the Distances for the variable "DISITE" (or EAB) are specified for each offshore EAB receptors.

of the 16 direction sectors for the U1 (EAB) and U2 (EAB) EN-113 model input files. The discussion in Subsection 2.3.5.2.1 (Paragraph 5) of the UFSAR, Revision 21, as proposed to be revised on December 17, 2015 (ADAMS Accession No. ML16004A363), indicates that the EAB distances are derived from Figure 2.1-2 in accordance with Regulatory Position C.1.2 of RG 1.145.

The licensee should confirm whether the EAB and the Site Boundary are collocated in the southeast clockwise through the northwest direction sectors. If not, the licensee should explain, for both Units 1 and 2, the basis for any modeled EAB receptor distances located offshore.

Table 1 Technical Areas of Interest & Resolution Status Regarding EN-113 Dispersion Modeling Analysis of Offsite (EAB and LPZ) Impacts Need ITEM TECHNICAL ISSUE RESOLUTION for RAI 7(a2) The licensee should update UFSAR Figure 2.1-2 to clearly As an alternative to revising UFSAR Figure 2.1-2 to show the Yes illustrate the location of the continuous EAB in the southeast location of the continuous EAB in the southeast clockwise through clockwise through the northwest direction sectors. In addition, the the northwest direction sectors, the licensee proposed to update licensee should provide a tabular list, on that figure or elsewhere, related sections of the UFSAR and Technical Assessment with which identifies the modeled distances to the EAB from the additional information that describes the basis and location of the nearest edge of the respective containment buildings for both offshore EAB receptors. Updates to include a table(s) that lists, by Units 1 and 2 for all direction sectors consistent with the guidance direction sector and unit, the distances to the EAB receptors from in Regulatory Position C.1.2 of RG 1.145. the nearest edge of the Unit 1 and Unit 2 containment buildings for all direction sectors. The NRC determined that the proposed approach should resolve NRC staff concerns.

The NRC staff plans to issue an RAI requesting that the licensee update the UFSAR and Technical Assessment with a table or tables that list the modeled distances to the EAB from the nearest edge of the respective containment buildings for DCPP, Units 1 and 2, and for all 16 direction sectors consistent with the cited guidance in Regulatory Position C.1.2 of RG 1.145, Revision 1.

Table 1 Technical Areas of Interest & Resolution Status Regarding EN-113 Dispersion Modeling Analysis of Offsite (EAB and LPZ) Impacts Need ITEM TECHNICAL ISSUE RESOLUTION for RAI 7(b) In verifying the distances to the EAB specified for the variable The NRC staff reviewed UFSAR Figure 2.1-2 during audit. Based No "DISITE" on Card 11 in the U1 (EAB) and U2 (EAB) EN-113 model on the review, the NRC staff determined that for the east-northeast input files, the exclusion area boundary, as shown on UFSAR sector, the staff misinterpreted the markings of various boundaries Figure 2.1-2, follows a zig-zag pattern within the east-northeast included on Figure 2.1-2 and within radial area extending 22.5 clockwise through a portion of the southeast direction sectors with degrees either side of the ENE direction radial (in accordance with that boundary approaching closer and extending farther away from the cited regulatory position). Based on the review and the containment buildings for the two units. For the east-northeast discussions with the licensee, the NRC staff determined that for and perhaps the southeast direction sectors for both the U1 (EAB) the southeast sector, portion of the DCPP, Units 1 and 2, site and U2 (EAB) input files, the "DISITE" values do not appear to boundary along the shoreline was not collocated with the EAB for agree, within reason, with the location of the EAB as illustrated in receptors located offshore. Subsequently, the staff was able to UFSAR Figure 2.1-2 and using the guidance in Regulatory confirm the distances to the EAB for the east-northeast and Position C.1.2 of RG 1.145 as cited by the licensee. southeast direction sectors.

The licensee should confirm the distances to the EAB specified for The NRC staff determined that the information provided by the the variable "DISITE" on Card 11 in the U1 (EAB) and U2 (EAB) licensee was sufficient to address the NRC staff concerns and no EN-113 model input files for the east-northeast and southeast further action is warranted.

direction sectors. If any of the modeled EAB receptor distances should be located closer to the nearest edge of the respective containment buildings, then the licensee should discuss the basis for assigning the distance(s) to the EAB receptor(s) in question and if changed make the necessary revisions.

8 Other Potential EN-113 Dispersion Modeling Analysis Issues 8(a1) The licensee should confirm that the X/Q values for the EAB and The licensee stated that the maximum offsite 0.5% No outer LPZ boundary summarized in Table 5.1-1 of the "Diablo sector-dependent X/Q values listed in Table 5.1-1 of the Technical Canyon Power Plant Technical Assessment, Revision 2," were, in Assessment were selected from among fill 16 direction sectors, fact, selected from among fill 16 direction sectors whether located whether located over land or over water, from the respective U 1 over land or over water. If not the case, then the licensee should (EAB}, U2 (EAB}, and U1/U2 (LPZ) EN-113 model runs.

clarify the text in Section 5.1 and Note 2 to Table 5.1-1 of the Technical Assessment as well as the text in Subsection 2.3.5.2.1 The NRC staff determined that the clarifications provided by the (last paragraph) of the UFSAR, Revision 21, as proposed to be licensee during the audit were sufficient to address the NRC staff revised on December 17, 2015 (ADAMS Accession concerns.

No. ML16004A363}, by explaining the basis for following that approach which is inconsistent with the guidance in RG 1.145.

Table 1 Technical Areas of Interest & Resolution Status Regarding EN-113 Dispersion Modeling Analysis of Offsite (EAB and LPZ) Impacts Need ITEM TECHNICAL ISSUE RESOLUTION for RAI 8(a2) Since the N-113 dispersion model is a proprietary code, the NRC The NRC staff plans to issue an RAI requesting that the licensee Yes*

staff requested for only the input files and a description of their include the sector-specific 0.5% XJQ values and sector-specific structure in a previously issued RAI. However, Table 5.1-1 of receptor distances for the U1 (EAB), U2 (EAB), and U1/U2 (LPZ)

Revision 2 to the referenced Technical Assessment only lists the model runs in the Technical Assessment table(s).

highest accident-related X/Q values at the EAB and outer LPZ boundary. Therefore, consistent with Regulatory Position C.4 in RG 1.145, the licensee should provide a summary of all direction-dependent sector X/Q values for the U 1 (EAB), U2 (EAB), and U1/U2 (LPZ) EN-113 model runs equivalent to the output of the NRG-accepted PAVAN dispersion model.

8(a3) The licensee should update UFSAR Figure 2.1-2 to clearly As an alternative to revising UFSAR Figure 2.1-2 to show the Yes illustrate the location of the defined 2,000-yard radius offshore location of the defined 2,000-yard radius offshore Security Zone, Security Zone, referenced in the last paragraph of UFSAR the licensee proposed to update Section 2.1 of UFSAR with Subsection 2.1.2.1.3, and its relationship to the distances entered additional information that describes the location of the Security for the variable "DISITE" on Card 11 in the U1 (EAB) and U2 Zone in relation to the EAB receptors also located offshore as (EAB) EN-113 model input files for at least the south-southeast input to the U1 (EAB) and U2 (EAB) EN-113 model runs. The clockwise through the west-northwest direction sectors. If the NRC staff considered the proposed alternative to be a reasonable boundary that represents the defined Safety Zone differs from the approach.

modeled distances to the EAB, the licensee should explain and/or reconcile the basis for those differences. The NRC staff plans to issue an RAI requesting the licensee to update Section 2.1 of the UFSAR, where appropriate, with additional information that describes the location of the 2000-yard radius offshore Security Zone in relation to the EAB receptors, also located offshore in at least the south-southeast clockwise through the west-northwest direction sectors.

8(b) Neither Section 5.1 nor Table 5.1-1 of the "Diablo Canyon Power Refer to the following items.

Plant Technical Assessment, Revision 2," appears to address the estimation of 5-percent overall site X/Q values for the U1 (EAB),

U2 (EAB), and U1/U2 (LPZ) EN-113 model runs. The NRC staff is unable to confirm whether the 0-2 hour X/Q values in Table 5.1-1 actually represent the controlling X/Q values for that time period for evaluation as called for by Regulatory Positions C.3 and C.4 in

-~~-~~ ~-~~-*- _<?_~~-~~~~~-~!ly_:_ --- ---- ------- --- ------ -- ------ ----- ------ - ---- ----------------------------------------------------------------------------- -----------

Table 1 Technical Areas of Interest & Resolution Status Regarding EN-113 Dispersion Modeling Analysis of Offsite (EAB and LPZ) Impacts Need ITEM TECHNICAL ISSUE RESOLUTION for RAI 8(b1) The licensee should confirm whether 5-percent 0-2 hour overall The licensee stated that the output generated by the EN-113 No site X/Q values were estimated as part of the U1 (EAB), U2 (EAB), dispersion model includes 5-percent overall site 0-2 hour X/Q and U 1/U2 (LPZ) EN-113 model runs. values as called for by Regulatory Position C.3 in RG 1.145.

  • If not, the licensee should provide justification for not doing so . The licensee also stated that the cumulative probability
  • If so, the licensee should confirm whether the modeling results distributions of 0-2 hour X/Q values from the U1 (EAB), U2 (EAB),

from all 16 direction sectors were considered in determining and U1/U2 (LPZ) EN-113 model runs were determined using the the overall cumulative probability distribution on which results from all 16 direction sectors, consistent with Regulatory 5-percent 0-2 hour overall site X/Q values are to be based in Position C.3 in RG 1.145, and that the respective 5-percent overall accordance with Regulatory Position C.3 in RG 1.145. site 0-2 hour X/Q values were based on the corresponding

  • If the modeling results from fewer than 16 direction sectors distributions.

were included in each of those determinations, the licensee should then explain how the overall cumulative probability The NRC staff determined that that the clarifications provided by distributions were constructed and provide justification for their the licensee during the audit should be sufficient to address the comparison to the 0.5-percent sector-dependent X/Q values in NRC staff concerns.

determining the controlling 0-2 hour accident X/Q values at the EAB and outer LPZ boundary.

8(b2) The licensee should confirm whether the results from the U 1/U2 The licensee stated that intermediate, short-term X/Q values at the No (LPZ) modeling run for all 16 direction sectors were considered in LPZ were based on interpolation between the 5-percent 0-2 hour determining the intermediate, short-term accident-related X/Q overall site X/Q and the highest of the 16 sector-dependent annual values (i.e., 2-8 hours, 8-24 hours, 1-4 days, and 4-30 days) at the average X/Q values consistent with Regulatory Position C.3 in outer LPZ boundary by interpolating between the 5-percent 0-2 RG 1.145.

hour overall site X/Q and the highest of the 16 sector-dependent annual average X/Q values in accordance with Regulatory Position The NRC staff determined that that the clarifications provided by C.3 in RG 1.145. If fewer than 16 sector-dependent annual the licensee during the audit should be sufficient to address the average X/Q values were used in that determination, the licensee NRC staff concerns.

should provide justification for not doing so and address its potential effects on the interpolated intermediate, short-term accident-related X/Q values.

8(b3) Consistent with Regulatory Position C.4 in RG 1.145, the licensee The NRC staff plans to issue an RAI requesting that the licensee Yes should provide a summary of all 5-percent overall site X/Q values include the 5-percent overall site 0-2 hour X/Q values from the U1 for the U1 (EAB), U2 (EAB), and U1/U2 (LPZ) analyses equivalent (EAB), U2 (EAB), and U1/U2 (LPZ) model runs, the intermediate, to the output of the NRG-accepted PAVAN dispersion model. short-term X/Q values (i.e., 2-8 hours, 8-24 hours, 1-4 days, and 4-30 days) from the U1/U2 (LPZ) model run, and the 16 sector-dependent annual average X/Q values from the U1/U2 (LPZ) model run in the appropriate table or tables of the Technical Assessment.

Table 1 Technical Areas of Interest & Resolution Status Regarding EN-113 Dispersion Modeling Analysis of Offsite (EAB and LPZ) Impacts Need ITEM TECHNICAL ISSUE RESOLUTION for RAI 8(c) Note 2 to Table 5.1-1 of the "Diablo Canyon Power Plant Technical The licensee stated that although the worst-case downwind sector No Assessment, Revision 2," identifies the highest 0.5-percent was different for the 0-2 hour time period than for all time periods sector-dependent X/Q values for the U1 (EAB), U2 (EAB), and from 2-8 hours and longer, the highest X/Q value for any given U1/U2 (LPZ) model runs and states that "[t]he worst case time interval (i.e., 0-2 hours and the intermediate short-term downwind sector for the 0-2 hour period for all receptors is intervals from 2-8 hours, 8-24 hours, 1-4 days, and 4-30 days) northwest" and "[f]or Unit 1/2 LPZ the worst case sector for periods were used in the dose calculations, regardless of the sector in 2-8 hours and longer is southeast." The (presumably) maximum which it occurred.

sector X/Q value for the 0-2 hour time period is 180 degrees out of phase with the (presumably) maximum sector X/Q values for the The NRC staff considered the licensee's approach to be intermediate short-term accident time periods. It is not clear to the reasonable in that it meets the intent of Regulatory Position NRC staff whether this difference in maximum sectors is related to C.2.2.1 (Last Paragraph) of RG 1.145. As such, the NRC staff the issues raised in the preceding questions 8(a) and 8(b) determined that that the clarifications provided by the licensee regarding whether and how modeling results from over land and/or during the audit should be sufficient to address the NRC staff over-water receptors were considered. concerns.

Consequently, the licensee should explain how the results presented in Table 5.1-1 of the referenced Technical Assessment and as used elsewhere in the LAR implements the guidance in Regulatory Position 2.2.1 of RG 1.145 and represents the maximum sector X/Q values at the outer LPZ boundary. If not the case, then provide justification for the approach followed.

ATTACHMENT 4 Table 2 Technical Areas of Interest and Resolution Status Regarding ARCON96 Dispersion Modeling Analysis of Onsite (CR and TSC) Impacts ITEM TECHNICAL ISSUE RESOLUTION RAI 1 Issues Related to ARCON96 Dispersion Modeling Analysis 1(a) Subsection 6.4.2.3 of the UFSAR, Revision 22, refers to the The licensee reiterated that the only accident scenario analyzed for Yes following regulatory criteria with respect to the safety evaluation for LAR 15-03 submittal was the LOCA because it represented the the Technical Support Center (TSC) and its habitability: current licensing basis. However, the licensee estimated previously Supplement 1 to NUREG-0737, which in turn refers to the unanalyzed X/Q values at the TSC for accident releases from the ventilation, filtration, radiological protection, and radiation MSSVs, 10% ADVs, and an MSLB. The licensee summarized its monitoring criteria in NUREG-0696. approach for demonstrating that LOCA was still the worst-case accident scenario for dose consequences. Since the release points Section 2.6 of NUREG-0696 states that "TSC personnel shall be for these three accident scenarios are located so close together, protected from radiological hazards, including direct radiation and the highest of the modeled X/Q values was used to represent all airborne radioactivity .... under accident conditions, to the same three scenarios. The licensee performed a simplified dose degree as control room personnel." Section 8.2.1, Item (f), of assessment, based on results from RADTRAD analysis of impacts NUREG-0737 states that the TSC will be "[p]rovided with at the LPZ which covered the presumed 30-day duration of an radiological protection .... necessary to assure that radiation accident, by scaling the resultant LPZ doses using the ratio of the exposure to any person working in the TSC would not exceed 5 TSC and LPZ X/Q values. Since dispersion model calculations are rem whole body, or its equivalent to any part of the body, for the based, in part, on the distance of the receptor from a release point, duration of the accident." In addition, Section 1.3.2 of RG 1.183 this approach assumed that a TSC operator was located on the roof states that "[a]ny implementation of an AST [alternative source of the TSC at one of the air intakes and did not take into account term] .... should be supported by evaluations of all significant any reductions due to emergency air filtering.

radiological and nonradiological impacts of the proposed actions."

The licensee also indicated that a comparison was made between Section 9.0 of the "Diablo Canyon Power Plant Technical the results from a MSLB scenario to a Control Rod Ejection Assessment, Revision 2" states that "[i]n accordance with current Accident (CREA).

licensing basis, the dose to the Technical Support Center has been evaluated for the DBA [design basis accident] that has the worst The NRC staff considered the proposed approach reasonable as case radioactivity release, i.e., the LOCA [loss-of-coolant accident]." long as sufficient descriptive information is submitted documenting Section 5.2 of the referenced Technical Assessment also indicates the approach. The licensee indicated that it does not plan to that the dispersion parameter (X/Q) values selected for the dose provide dose results based on these additional evaluations.

consequence assessments are intended to support bounding analyses for an accident that occurs at either unit and that they take The NRC staff plans to issue an RAI requesting that the licensee into consideration the various release points-receptors applicable to update the Technical Assessment and UFSAR, as appropriate, with each accident to identify the bounding X/Qs. a thorough explanation of the approach used, including X/Q modeling results at the TSC receptors for MSSV, 10% ADV, and Receptors associated with the Control Room (CR) are located MSLB release scenarios, determination of the ratios of these results closer to potential accident releases from Main Steam Safety to the X/Q values estimated at the LPZ, and a relative comparison Valves (MSSVs), 10% Atmospheric Dump Valves (ADVs), and due of the estimated doses based on these ratios to the doses for the to a Main Steam Line Break (MSLB) at Units 1 and 2 than to TSC assumed controlling LOCA scenario. The RAI will also request for receptors. However, dispersion modeling results for MSSV, ADV,

Table 2 Technical Areas of Interest and Resolution Status Regarding ARCON96 Dispersion Modeling Analysis of Onsite (CR and TSC) Impacts ITEM TECHNICAL ISSUE RESOLUTION RAI and MSLB release scenarios range from a factor of about 2 higher ARCON96 model input and output files for these additional model to almost a factor of 10 higher (particularly at the CR Center runs.

receptor location), depending on averaging time, compared to LOCA-related release points I scenarios. Section 8.0 of the referenced Technical Assessment estimates the total effective dose equivalent to the TSC operator to be 4.1 rem compared to the 5 rem regulatory limit.

Based on this information, it is not clear that the LOCA-related release scenarios represent the highest potential dose to TSC occupants. Therefore, the licensee should either provide additional regulatory and technical justification for retaining only the LOCA-related release scenarios as the licensing and design bases for radiological impacts at the TSC, or perform additional ARCON96 dispersion modeling runs to estimate X/Qs at the TSC receptors due to accident releases from the MSSVs, ADVs, and MSLB scenarios at Units 1 and 2 and update any subsequent dose calculations.

1(b) If bounding X/Q values for a given release scenario and dose The NRC staff plans to issue an RAI requesting that the licensee Yes calculation are selected from the corresponding ARCON96 annotate any tables in the UFSAR and Technical Assessment to modeling results associated with a given unit (as appears to be the indicate the unit from which a bounding X/Q was obtained and used case in Chapter 15 of the UFSAR and Section 7 of the referenced as input to a dose calculation for a given release scenario.

Technical Assessment), then the licensee should annotate the tables to indicate the unit from which the X/Q values were obtained.

2 Issues Related to ARCON96 Dispersion Modeling Analysis 2(a) Subsection 2.3.5.2.2 of the UFSAR, Revision 21, as proposed to be The licensee acknowledged misinterpretation of 95th-percentile Yes revised on December 17, 2015 (ADAMS Accession wind speed for the purpose of determining the ratio of the expected No. ML16004A363), and Section 5.2 of the "Diablo Canyon Power vertical velocity of releases from MSSVs and 10% ADVs to that Plant Technical Assessment, Revision 2," under the headings 95th-percentile wind speed value in order to justify use of "Energetic Releases" and "Vertically-Oriented Releases," identifies deterministic reduction factor applied to modeled X/Q values for accident releases from the MSSVs and 10% ADVs as "energetic" in those release scenarios.

terms of exit velocity. The context of those discussions is to justify the application of a deterministic reduction factor to modeled onsite The licensee indicated that 95th-percentile 10-m wind speed was X/Q values based on Regulatory Position C.6 in RG 1.194 to about 11.0 m/sec for the modeled 5-year POR rather than 1 m/sec sources with these characteristics. as currently stated in Technical Assessment. Ratio of expected vertical velocity of MSSV and 10% ADV releases to 95th-percentile The vertical velocity of MSSV and 10% ADV releases is stated to wind speed at 10-m decreases from 95, as currently stated, to be at least 95 times larger than the 95th-percentile wind speed of 1 about 8.6.

Table 2 Technical Areas of Interest and Resolution Status Regarding ARCON96 Dispersion Modeling Analysis of Onsite (CR and TSC) Impacts ITEM TECHNICAL ISSUE RESOLUTION RAI m/sec and approximately 5 times larger than the highest observed 10-m wind speed (i.e., 18.9 m/sec) within the modeled 5-year Met The NRC staff plans to issue an RAI requesting that the licensee data base. Plume rise from MSSVand 10% ADV releases is also update any related discussions in the UFSAR and Technical stated to be enhanced by 11 m at the (presumed) 95th-percentile Assessment to correct:

wind speed of 1 m/sec due to the large vertical velocities. (a) the 95th-percentile 10-meter wind speed value to be consistent with the guidance in Note 13 at Paragraph 1 (Sentence 3) of Note 13 at Paragraph 1 (Sentence 3) of Regulatory Position C.6 of Regulatory Position C.6 of RG 1.194; RG 1.194 states "[a]s used here, 95th-percentile wind speed is that (b) the ratios of the expected vertical velocity of MSSV and 10%

wind speed that is not exceeded more than 5 percent of the time." ADV releases to corrected 95th-percentile 10-meter (m) wind It appears that the licensee interpreted this note incorrectly and that speed; and wind speeds greater than 1 m/sec occur more than 5 percent of the (c) the corrected 95th-percentile 10-m wind speed as it appears to time at the DCPP site. Therefore, the licensee should correct the have been used in estimating enhancement to plume rise of the 95th-percentile wind speed value to be consistent with the MSSV and 10% ADV releases.

referenced guidance and as that value appears to have been used in estimating plume rise enhancement from MSSV and 10% ADV releases.

2(b) Given the general tendency of wind speed to increase with height To address this concern, the licensee also determined Yes and the stated release heights for the MSSVs and 10% ADVs (i.e., 95th-percentile 76-m wind speed to be 12.1 m/sec for the modeled 27.1 and 26.5 m, respectively}, confirm the appropriateness of 5-year POR and ratio of expected vertical velocity of MSSV and using unadjusted wind speed data from the 10-m level of the onsite 10% ADV releases to 95th-percentile 76-m wind speed to be about Met tower to determine the 95th-percentile wind speed value or 7.8. For both levels, revised ratio is still greater than threshold provide the technical basis for and propose adjustments to the value of 5 in Regulatory Position C.6 of RG 1.194 below which resulting value or other alternative approach. allows reduction factor to be applied.

The NRC staff plans to issue an RAI requesting that the licensee confirm the appropriateness of using unadjusted wind speed data from the 10-m level of the onsite Met tower to determine the 95th-percentile wind speed value or provide the technical basis for and propose adjustments to the resulting value or other alternative approach.

Table 2 Technical Areas of Interest and Resolution Status Regarding ARCON96 Dispersion Modeling Analysis of Onsite (CR and TSC) Impacts ITEM TECHNICAL ISSUE RESOLUTION RAI 2(c) It is reasonable to expect that wind speeds at the indicated release The NRC staff concern covered possibility that the deterministic No heights and in the layer of air above (through which the plume reduction factor of 5 might not apply based on the re-calculated would rise) would be higher than those measured at the 10-m level. 95th-percentile wind speed and the ratio of the expected vertical If it is determined that the ratio of the MSSV and 10% ADV exit velocity of MSSV and 10% ADV releases to the 95th-percentile velocities to the appropriate 95th-percentile wind speed value is 10-m wind speed (or a value adjusted for a higher elevation).

less than the threshold value of 5 in the cited guidance, that allows Based on discussions with the licensee, it was determined that that for the X/Q reduction factor of 5 to be applied, then revise the the ratios based on the 95th-percentile 10- and 76-m wind speeds applicable ARCON96 modeled X/Q values and subsequent dose are both greater than the threshold value of 5.

calculations accordingly.

The NRC staff determined that the information provided by the licensee was sufficient to address the NRC staff concern and no further action is warranted.

3 Issues Related to ARCON96 Dispersion Modeling Analysis 3(a) The minimum cross-sectional area of the reactor building identified The licensee confirmed that a value 2745 (2744.5) sq-m was used No in Subsections 2.3.4.7 (Paragraph 5) and 2.3.5.2 (Paragraph 1) of to account for building wake effects in the ARCON96 modeling the UFSAR, Revision 22, pertaining to the analysis of offsite analysis of onsite X/Q values at the CR and TSC receptors. The impacts at the EAB and outer LPZ boundary, is 1600 sq-m and is licensee also indicated that value of 1600 sq-m for the minimum designated as the variable "A." However, the 16 sector-specific cross-sectional area of the containment buildings is a value entered values entered on Card 10 for the variable "A" for the Unit 1 (EAB), in the plant meteorological computer for its X/Q calculations Unit 2 (EAB), and Unit 1 I Unit 2 (LPZ) EN-113 model runs is "2745" (possibly for emergency response purposes, although the licensee (units of measure are not specified). was unsure of its purpose or history) but was not the value used for design basis X/Q calculations. The licensee stated that the use of a Further, Section 5.1 (Paragraph 3, for the variable "A," and containment building cross-sectional area of 2745 sq-mis Paragraph 7) in the "Diablo Canyon Power Plant Technical Report, conservative (i.e., a smaller area) compared to the actual larger Revision 1" and the later "Diablo Canyon Power Plant Technical cross-sectional area of all the other structures directly adjacent to Assessment, Revision 2" does not specify the building each containment building.

cross-sectional area used for the offsite impact modeling analysis.

In addition, Subsection 2.3.5.2.1 (Paragraph 3) of the UFSAR, The NRC staff determined that the information provided by the Revision 21, as proposed to be revised on December 17, 2015 licensee during the audit was sufficient to address the NRC staff (ADAMS Accession No. ML16004A363), no longer specifies the concerns and no further action is warranted. The concern that building cross-sectional area used for this offsite impact analysis. modeled cross-sectional area for the Containment Building represents a non-conservative change to this element of the current Similarly, Subsection 2.3.5.2.2 (Paragraph 1) of the UFSAR, licensing basis has previously been addressed under EN-113 Item Revision 21, as proposed to be revised on December 17, 2015, 6(a1 ).

indicates that input data to the ARCON96 dispersion model consists, in part, of release characteristics that include the "building area affecting the release." Subsection 2.3.5.2.2 (Paragraph 7, third bulleted item) also states that "[t]he applicable structure Table 2 Technical Areas of Interest and Resolution Status Regarding ARCON96 Dispersion Modeling Analysis of Onsite (CR and TSC) Impacts ITEM TECHNICAL ISSUE RESOLUTION RAI relative to quantifying building wake effects on the dispersion of the releases is based on release I receptor orientation relative to the plant structures." Comparable text also appears in Section 5.2 (Paragraph 2 and the third bulleted item of Paragraph 8) of the referenced Technical Assessment.

The licensee should explain the rationale and basis for the potentially non-conservative change to this element of the licensing basis by assuming a building cross-sectional area of 2745 sq-m compared to the value of 1600 sq-m in the referenced revisions of the UFSAR subsections.

3(b) None of the three different building cross-sectional areas used in The licensee agreed to update UFSAR and Technical Assessment. Yes the ARCON96 model input files - that is, 2744.5, 215.5, and 530.4 sq-m representing the Unit 1 and Unit 2 Containment Buildings, The NRC staff plans to issue an RAI requesting that the licensee Refueling Water Storage Tanks (RWSTs), and Fuel Handling update the UFSAR and Technical Assessment by identifying the Buildings (FHBs), respectively - appear to be specified in the cross-sectional areas of the Containment Buildings, RWSTs, and referenced UFSAR or Technical Assessment (Report) text, nor is FHBs for Units 1 and 2 as input to the ARCON96 dispersion the determination of those values explained. The building modeling analysis (and for the Containment Buildings in the case of cross-sectional area input to the EN-113 and selected ARCON96 the EN-113 modeling analysis). This information represents part of dispersion model runs (i.e., for the Unit 1 and 2 containment (or, in the case of the cross-sectional area for the Containment buildings) is essentially the same numerically. The output files for Buildings, a possible change to) the licensing basis associated with the ARCON96 model runs specify the units of measure for the the dispersion analyses that support the LAR.

building (cross-sectional) area as square meters.

The licensee will also be requested to update the Technical The licensee should explain the determination of each of the three Assessment by explaining how the respective cross-sectional areas building cross-sectional areas input to the various ARCON96 were determined (e.g., identification of the applicable structures or dispersion modeling runs including identification of the applicable portions of structures considered, building dimensions (e.g., width, structures or portions of structures, building dimensions (e.g., width, height, and, if applicable, the method of handling portions of height, and, if applicable, the method of handling portions of irregularly-shaped structures), and cross-references to the irregularly-shaped structures), and cross-references to the applicable plant drawings on which the preceding information is applicable plant drawings on which the preceding information is based). The NRC staff notes that some of this information was based. available in one of the calculations reviewed during the audit.

Table 2 Technical Areas of Interest and Resolution Status Regarding ARCON96 Dispersion Modeling Analysis of Onsite (CR and TSC) Impacts ITEM TECHNICAL ISSUE RESOLUTION RAI 3(c) The DCPP, Units 1 and 2, containment buildings and RWSTs are The licensee presented an image of power block area that included No cylindrical structures with domed tops. The projected widths of the FHB showing it as a continuous structure across both units and these structures alone, as seen by a given downwind receptor, with the extent of the entire FHB within the area covered by the should be the same except for the different structural widths larger Auxiliary Building. The licensee indicated that only a portion regardless of the release-receptor orientation. However, the FHBs of the entire FHB structure (i.e., for either Unit 1 or Unit 2) was used appear to be rectangular-shaped structures and the orientations to determine the projected width and building cross-sectional area between a potential release point, on or affected by the wake of the (input to the ARCON96 modeling runs) to account for building wake applicable FHB, and receptor pairing varies along with the projected effects where the dispersion of certain release scenarios were width of the building wake. assumed to be affected by the FHB wake. Projected width for a given unit was taken on the diagonal of that portion of the The same building cross-sectional area is input for several of the applicable FHB.

ARCON96 modeling runs used to evaluate accident releases from or affected by the wake of a FHB. The statements in the earlier The NRC staff considers use of cross-sectional area from only that referenced UFSAR and Technical Assessment (Report) text (i.e., portion of the FHB associated with a given unit (i.e., a relatively

"[t]he applicable structure relative to quantifying building wake smaller area), compared to the larger cross-sectional area of all the effects on the dispersion of the releases is based on release I other structures directly adjacent to the FHB, to generally be a receptor orientation relative to the plant structures") appears to be conservative approach. Further, based on the past experience, the inconsistent with the fact that the projected width of the building NRC staff believes that ARCON96 is not necessarily sensitive to wake for the FHB is the same for different release-receptor cross-sectional area at wind speeds associated with higher X/Q orientations. values.

The licensee should clarify the text in UFSAR Subsection 2.3.5.2.2 The NRC staff determined that the information provided by the and Section 5.2 of the Technical Assessment (Report) by licensee was sufficient to address the NRC staff concerns and no expanding the discussion to include any limitations on the further action is warranted.

referenced statements and the rationale for using the same building cross-sectional area for the FHB-related scenarios. If necessary, the licensee should also revise any affected ARCON96 modeling runs, subsequent dose calculations, and any other related discussions and summary tables.

4 Issues Related to ARCON96 Dispersion Modeling Analysis 4(a) Subsection 2.3.5.2.2 (Paragraph 1) of the UFSAR, Revision 21, as The NRC staff plans to issue an RA requesting that the licensee Yes proposed to be revised on December 17, 2015 (ADAMS Accession correct the statement in the referenced UFSAR subsection (and No. ML16004A363), indicates that input data to the ARCON96 Technical Assessment, if applicable) regarding the proper direction dispersion model consists, in part, of "various receptor parameters orientation between receptor locations and release points to be (e.g., distance and direction from release to control room air entered into the ARCON96 dispersion model input files (i.e., from intake ... )." However, Section 2.3.4 of Revision 1 to the receptor to the release point).

NUREG/CR-6331, which implements (with qualification) the guidance in RG 1.194, calls for the direction from the intake to the Table 2 Technical Areas of Interest and Resolution Status Regarding ARCON96 Dispersion Modeling Analysis of Onsite (CR and TSC) Impacts ITEM TECHNICAL ISSUE RESOLUTION RAI source to be entered into the ARCON96 model. The revised ARCON96 model input files, provided with the RAI responses of April 21, 2016, appear to have correctly-entered directions from the various intake locations associated with the Unit 1 and Unit 2 CRs and the TSC to the various release points assumed for the accident scenarios evaluated.

Consistent with the referenced regulatory guidance, the licensee should correct the statement in the proposed Revision to UFSAR Subsection 2.3.5.2.2 regarding the proper direction orientation between receptor locations and release points to be entered into the ARCON96 dispersion model input files.

4(b) The ARCON96 dispersion model requires receptor-to-source Based on discussions during the audit, the receptor-to-source No orientations to be specified with respect to True North as Appendix orientations specified in the Technical Assessment were reviewed A to the "Diablo Canyon Power Plant Technical Assessment, and found to be within 1-2 degrees azimuth of those determined by Revision 2," acknowledges (also indicating that there is a 23-degree the NRC staff rather than as reported. The licensee's re-checked clockwise offset between Plant North and True North). Based on a orientations were: dccase07 (was 354°, should be 348°); dccase17

+/- 5 degree tolerance limit and using Figure A-1 of the referenced (was 140°, should be 146°); dccase18 (was 105°, should be 118°);

Technical Assessment, the NRC staff identified four dcfhc11 (was 112°, should be 121°).

receptor-to-source orientations that need to be verified:

  • dccase07 - Control Room Center (Point 9) to U1 Plant Vent It was also found that the receptor (center of Control Room at roof (Point 1) specifies 354° as the direction to source. The NRC elevation) associated with the receptor-to-source orientations for staff's check shows an orientation of about 347°. the first two cases differs by 6 degrees azimuth from those
  • dccase17 - Control Room Center (Point 9) to U2 Plant Vent specified previously in LAR 15-03. This difference reflects the (Point 2) specifies 140° as the direction to source. The NRC limitations of accuracy of orientation measurements from drawings, staff's check shows an orientation of about 147°. and is nearly within the +/- 5 degree azimuth tolerance used by
  • dccase18 - U1 Control Room Emergency Intake (Point 5) to U2 NRC staff. The licensee noted that this receptor is meant to be Refueling Water Storage Tank Vent (Point 8) specifies 105° as representative of general Control Room in-leakage and therefore the direction to source. The NRC staff's check shows an not a precise location like an air intake, but is a general location orientation of about 120°. chosen to represent possible multiple points of entry. As such, and taking into context the use made of this receptor in the dose
  • dcfhc11 - U1 Control Room Emergency Intake (Point 5) to U2 consequence analysis, the licensee does not consider a 6-degree Fuel Handling Building (Point 15) specifies 112° as the direction azimuth difference to be critical.

to source. The NRC staff's check shows an orientation of about 122°. In addition, it was determined that the receptor-to-source orientations associated with the 3rd and 4th cases are different by The licensee should confirm the indicated receptor-to-source 13 degrees and 9 degrees azimuth, respectively, from those orientations and, if necessary, correct and update any affected specified previously in LAR 15-03. The licensee indicated that Table 2 Technical Areas of Interest and Resolution Status Regarding ARCON96 Dispersion Modeling Analysis of Onsite (CR and TSC) Impacts ITEM TECHNICAL ISSUE RESOLUTION RAI ARCON96 modeling runs, subsequent dose calculations, and/or review of Tables 7.2-5 and 7.3-3 of the Technical Assessment any other related discussions and summary tables in the UFSAR indicates that X/Q values associated with the emergency intakes and elsewhere in the LAR submittal as necessary. In addition, are approximately 1 to 2 orders of magnitude less than the other Figure A-1 in the referenced Technical Assessment and UFSAR XIQ values used in the analysis, lending credence to the argument Figure 2.3-5 should be updated to illustrate and specify the offset that the dose consequences associated with these pathways are between Plant North (already shown) and True North (not minimal, and that any minor change in the X/Q values due to provided). orientation correction will have no impact on the reported dose consequences in the Control Room following a LOCA or a fuel handling accident in the Fuel Building, respectively.

The NRC staff considered licensee's explanation for first two cases and agrees that accuracy for determining orientations from drawings has limitations. More importantly, X/Q values in Table 7.3-3 of Technical Assessment suggest that Plant Vent releases to Control Room Center are not the controlling scenario.

With respect to third and fourth cases, NRC staff agreed that although modeled orientations are incorrect, impacts to U1 Control Room Emergency Intake have nearly the lowest X/Qs (as pointed out by staff) among all scenarios. So, correction of modeling runs for these cases not necessary.

Finally, licensee pointed out that Figure 5.1-1 shows and text in Chapter 5 of Technical Assessment identifies the offset between Plant and True North.

The NRC staff was of the opinion that the implications of orientation discrepancies are minimal and information on Plant North and True North offset is available. Therefore, the NRC staff determined that the information provided by the licensee was sufficient to address the NRC staff concerns and no further action is warranted.

5 Issues Related to ARCON96 Dispersion Modeling Analysis There appears to be a minor discrepancy between one of the The NRC staff plans to issue an RAI requesting that the licensee Yes revised ARCON96 dispersion model input files provided with the correct the typographical error in the Technical Assessment for the RAI responses of April 21, 2016, and the scenario tables in building area entered for Case 9 by changing it to "0.0" from Appendix A of the "Diablo Canyon Power Plant Technical "2744.5" sq-m.

Assessment, Revision 2." Specifically, a building area of 2744.5 sq-m is listed for Case 9 of the summary titled "Unit 1 MSSVs I 10%

ADVs I MSL Break Releases to CR Receptors." The entry should Table 2 Technical Areas of Interest and Resolution Status Regarding ARCON96 Dispersion Modeling Analysis of Onsite (CR and TSC) Impacts ITEM TECHNICAL ISSUE RESOLUTION RAI be "0.0" consistent with the entries for Cases 1 and 17 under that summary table and the entries for Cases 6, 14, and 22 under the comparable summary table for Unit 2.

No model runs were made for these particular scenarios because of the energetic nature of these releases and the proximity of the release points to the normal CR air intake of the same unit consistent with the guidance in RG 1.194. However, the licensee should confirm this apparent discrepancy and, if necessary and for consistency with these other cases, correct the typographical error for the building area entered for Case 9 by changing it to "0.0" from "2744.5" sq-m.

NOTE: The RAls expected to be issued as a result of the audit were issued on September 7, 2016 (ADAMS Accession No. ML16251A091 ).

E. Halpin If you have any questions, please contact me at 301-415-3016 or via e-mail at Balwant.Singal@nrc.gov.

Sincerely,

/RA/

Balwant K. Singal, Senior Project Manager Plant Licensing Branch IV-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-275 and 50-323

Enclosure:

Audit Report cc w/encl: Distribution via Listserv DISTRIBUTION:

PUBLIC RidsNrrLAJBurkhardt Resource LPL4-1 R/F RidsNrrPMDiabloCanyon Resource RidsACRS_MailCTR Resource RidsRgn4MailCenter Resource RidsNrrDorllpl4-1 Resource BHarvey, N RO/DSEA/RH M 1/RMOT RidsNrrDraArcb Resource MMazaika, NRO/DSEA/RHM 1/RMOT RidsNroDsea Resource KBucholtz, NRR/DRA/ARCB ADAMS Access1on No.: ML16279A343 U It Summarv by memo dated s eptem ber 26, 2016

  • Ad.

OFFICE NRR/DORL/LPL4-1/PM NRR/DORL/LPL4-1 /LA NRR/DRA/ARCB/BC NAME BSingal JBurkhardt US hoop DATE 10/24/16 10/20/16 10/26/16 OFFICE NRO/DSEA/RHM1/RMOT/TL NRR/DORL/LPL4-1 /BC NRR/DORL/LPL4-1 /PM NAME BHarvey* RPascarelli BSingal DATE 09/26/16 10/27/16 10/27/16 OFFICIAL RECORD COPY

Retrieved from "https://kanterella.com/w/index.php?title=ML16279A343&oldid=2626948"