RBG-46226, License Amendment Request for One-Time Extension of the Drywell Bypass Test Interval

License Amendment Request for One-Time Extension of the Drywell Bypass Test Interval

ML040540445
Person / Time
Site:	River Bend
Issue date:	02/16/2004
From:	King R Entergy Operations
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
LAR 2004-02, RBG-46226
Download: ML040540445 (62)

Text

Entergy Operations, Inc.

River Bend Station

'-Entergy 5485 U. S. Highway 61N St. Francisville. LA 70775 Fax 225 635 5068 RBG-46226 February 16, 2004 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555

SUBJECT:

License Amendment Request One-time Extension of the Drywell Bypass Test Interval (LAR 2004-02)

River Bend Station, Unit 1 Docket No. 50-458 License No. NPF-47

REFERENCES:

Letter from Mr. J. C. Roberts to USNRC Dated May 12, 2003 - One-time Extension of the Integrated Leak Rate Test and Drywell Bypass Test for Grand Gulf Nuclear Station

Dear Sir or Madam:

Pursuant to 10 CFR 50.90, Entergy Operations, Inc. (Entergy) hereby requests an amendment for River Bend Station, Unit 1 (RBS) to change Technical Specification (TS) 3.6.5.1.3 regarding drywell bypass leakage. The change would allow for an extended interval (15 years) for performance of the next drywell bypass leakage test. In accordance with recent practice for similar submittals, this request is made for a one-time extension of the interval.

This request is made on a risk-informed basis as described in Regulatory Guide 1.174. The attached technical justification for this request provides a risk evaluation using a methodology that has been found acceptable for other similar requests.

The proposed change has been evaluated in accordance with 10 CFR 50.91 (a)(1) using criteria in 10 CFR 50.92(c) and it has been determined that this change involves no significant hazards considerations. The bases for these determinations are included in the attached submittal. The TS bases changes are provided for information only.

The proposed change does not include any new commitments.

RBS has identified this change as affecting activities planned during the upcoming refueling outage and on that basis requests approval of this proposed change by September 17, 2004.

The requested approval date and implementation period will enable RBS to optimize refueling outage planning and activities. This request will save critical path time in the refueling outage FoIl

RBG-46226 Page 2 of 2 and permit the deferral of the drywell bypass test until a subsequent outage. Once approved, the amendment shall be implemented within 60 days. This request is similar to a request from Grand Gulf Nuclear Station currently under consideration by the NRC. Although this request is neither exigent nor emergency, your prompt review is requested.

If you have any questions or require additional information, please contact Bill Brice at 601-368-5076.

I declare under penalty of perjury that the foregoing is true and correct. Executed on February 16, 2004.

Sincerely, ick ng Director, Nuclear Safety Assurance River Bend Station, Unit I RJK//WBB Attachments:

1. Analysis of Proposed Technical Specification Change

2. Proposed Technical Specification Changes (mark-up)

3. Changes to Technical Specification Bases Pages - For Information Only cc: Mr. Bruce S. Mallett U. S. Nuclear Regulatory Commission Region IV 611 Ryan Plaza Drive, Suite 400 Arlington, TX 76011 NRC Senior Resident Inspector P. 0. Box 1050 St. Francisville, LA 70775 U.S. Nuclear Regulatory Commission Attn: Mr. Michael K. Webb MS O-7D1 Washington, DC 20555-0001 Louisiana Department of Environmental Quality Office of Environmental Compliance Attn: Mr. Prosanta Chowdhury Surveillance Division P. 0. Box 4312 Baton Rouge, LA 70821-4312

RGB-46226 bcc: File No.: G9.5, G9.42 File: RBF1-04-0001 File: LAR 2004-02

Attachment 1 RGB-46226 Analysis of Proposed Technical Specification Change to RBG-46226 Page 1 of 53

1.0 DESCRIPTION

This letter is a request to amend Operating License(s) NPF-47 for River Bend Station, Unit 1 (RBS).

The proposed changes will revise the Operating License to change the Technical Specification (TS) regarding drywell bypass leakage testing (DWBT) frequency. The change would allow for an extended interval (15 years) for performance of the next DWBT. In accordance with recent practice for similar submittals, this request is made for a one-time extension of the interval.

2.0 PROPOSED CHANGE

The proposed change will revise the Operating License to change Technical Specification (TS) Surveillance Requirement (SR) 3.6.5.1.3 regarding drywell bypass leakage testing (DWBT). The change would allow for an extended interval (15 years) for performance of the next DWBT. This would allow the test to be performed on the same frequency as the Integrated Leak Rate Test (ILRT) which was already approved for a one-time 15 year frequency. This is consistent with current practice. Approval of this amendment would allow sufficient time to allow for an expected regulatory action that would extend testing frequencies for the ILRT and the DWBT.

RBS proposes to revise TS SR 3.6.5.1.3 by adding an exception to the Frequency requirement of 120 months that states:

...except that the next drywell bypass leak rate test performed after the June 24, 1994 test shall be performed no later than June 23, 2009.

In summary, the proposed change would represent a one-time deferral of the DWBT by up to five additional years. A marked-up modification to a Technical Specification Bases associated with this change is included in Attachment 3 for information only.

3.0 BACKGROUND

RBS is a General Electric Boiling Water Reactor (BWR) design plant. It is a BWR-6 with a Mark ill containment. The drywell is enclosed within the primary containment and is designed to divert the energy released during a design basis large break loss of coolant accident (LOCA). The drywell communicates with the primary containment through a series of horizontal vents in the drywell wall. The vents are covered both inside and outside the drywell by water from the annular shaped suppression pool. The pool forms a seal between the drywell and the primary containment. During a LOCA, blowdown from the reactor coolant system will uncover these vents allowing flow to the primary containment through the suppression pool water. The suppression pool serves as a heat sink for the energy released during a large break LOCA. The drywell contains the reactor coolant system and other high energy piping systems. This design also allows much of the high energy auxiliary systems to be located inside the primary containment. This is discussed further in Section 6.2 of the RBS Updated Final Safety Analysis Report (USAR).

to RBG-46226 Page 2 of 53 Several tests are done to ensure the integrity of the containmentldrywell function, including both the ILRT and the DWBT. Testing frequencies for the ILRT are performance-based as allowed by 10 CFR 50, Appendix J, Option B. The DWBT is also on a performance-based interval with a current maximum testing frequency of 120 months as required by TS.

ILRTs and DWBTs for BWR6/Mark IlIl plants have been required of operating nuclear plants to ensure the public health and safety in the event of an accident that would release radioactivity into the containment. Conservative design and construction practices have led to very few ILRTs or DWBTs exceeding their required acceptance criteria. The NRC has allowed the extension of test frequency from three times in ten years to once in ten years based on performance. The changes were based for the most part on NUREG 1493, "Performance Based Containment Leak-Test Program," dated September, 1995. The NUREG stated that an interval between ILRTs of up to twenty years would contribute an imperceptible increase in risk. The DWBT has been historically associated with the ILRT frequency because the plant line-ups are similar and the same equipment is used to perform both tests. The ILRT test interval has already been extended on a one time basis to once in 15 years.

RBS has performed several DWBTs during the period of its Operating License. The two most recent DWBTs were performed in August, 1992 and June, 1994. These tests were successful and on this basis, RBS currently has a ten-year interval in which to perform the next DWBT. Without this change, RBS, utilizing provisions allowing an interval extension of up to 15 months, would plan to perform the next DWBT during the upcoming outage in October, 2004.

Entergy is aware of the discussion between the NRC and NEI concerning a possible permanent extension of the ILRT intervals. The one-time change requested here will defer the immediate need for the DWBT and should permit consideration of any agreements reached on the generic change.

4.0 TECHNICAL ANALYSIS

The RBS DWBT and ILRT require similar equipment and are performed using similar procedures. Because of these similarities, both tests have been performed on the same test frequency. However, the NRC has recently approved a change to allow the ILRT test interval to be extended on a one time basis to once in 15 years. Since the similarities of the tests remain, it is desirable to maintain both tests on the same frequency by extending the DWBT similarly on a one time basis to 15 years.

The DWBT verifies that pre-existing drywell bypass leakage does not exceed the maximum allowed leakage. The DWBT acceptance criterion in the Tech Specs is <10% of the analyzed design limit. The design bypass limit is used to establish the timing of automatic actuation of containment unit coolers following a LOCA. The unit coolers effectively control the containment pressure to less than its design limit (15 psi) by removing heat from the containment environment. The DWBT thus affects the likelihood of suppression pool bypass in the level 1 and 2 PSA analyses.

An evaluation of extending the RBS DWBT surveillance frequency from once in 10 years to once in 15 years has been performed using a slightly modified version of the method used by to RBG-46226 Page 3 of 53 Grand Gulf Nuclear Station (GGNS) to support their DWBT one time extension. The GGNS evaluation was based on the ILRT methodologies previously accepted by the NRC. The RBS evaluation assumed that the DWBT frequency was being adjusted in conjunction with the ILRT frequency, which has already been extended to once in 15 years. Three cases (a base case and two sensitivity cases) have been constructed in this analysis. The case descriptions are provided in Section 4.3.2 A summary of the results from all cases is provided in Section 4.7. The comparisons of the three risk metrics used in this calculation (the total dose risk, Large Early Release Frequency (LERF) and Conditional Containment Failure Probability (CCFP)) are summarized in Tables 4.7-1 through 4.7-3.

4.1 Inputs and Assumptions Even though the methodologies used for the ILRT extension do not directly address the DWBT, it is judged that a similar methodology can be used to address the impact of extending the DWBT with a few additional considerations and assumptions.

4.1.1 PRA Model The current RBS Level 1, Revision 3B, PRA model was used for this evaluation. Although the precise methods used in the RBS ILRT submittals were not used for this analysis, some of the Level 1 and Level 2 PRA results from that analysis were utilized in the DWBT analyses when they were determined to be applicable. Based on the RBS Level 1 PRA model, Revision 3B results, the baseline total CDF value is 4.26E-6/yr.

4.1.2 DWBT and ILRT Test Intervals The base case for the evaluation is the original commitment interval of 3 tests in 10 years.

The current interval for DWBT is now 1 test in 10 years. Note that RBS has already received approval for a one-time extension of the ILRT interval to 1 in 15 years.

4.1.3 Containment Leakages for EPRI Accident Classes The maximum containment leakage for EPRI Class 1 (the EPRI containment failure classes are defined in the next section) sequences is 1 La based on the previously approved methodology.

The maximum containment leakage for EPRI Class 3a sequences is 10 La based on the previously approved methodology.

The maximum containment leakage for EPRI Class 3b sequences is 35 La based on the previously approved methodology. EPRI Class 3b is conservatively categorized as LERF based on the previously approved methodology Containment leakage due to EPRI Classes 4 and 5 are considered negligible based on the previously approved methodology.

to RBG-46226 Page 4 of 53 EPRI Classes 2 and 6 are defined for large containment isolation failure and other isolation failures, respectively. Both classes would have large containment leakages due to the isolation failures; however, they are not affected by the ILRT/DWBT interval extension.

Class 7 is defined as severe accident. Typically a containment leakage of 100 La is conservatively assumed.

Because EPRI Class 8 sequences are containment bypass sequences, potential releases are directly to the environment. However, the containment structure does not impact the release magnitude.

4.1.4 DWBT Data and Characterization of DWBT Leakages Since the start of commercial operation, RBS has performed five full DWBTs. Base drywell leakage (DWLb) is assumed to be 800 scfm, which bounds all the RBS DWBT results (see Table 4.1-1 below).

Table 4.1-1 RBS Drywell Bypass Leakage Test Results Test Leakage Date Rate SCFM Dec- 602 87 Jun- 141 89 Nov- 345 90 Aug- 754 92 Jun. 41 942 The characterization of increased leakage associated with DWBTs was based on the ILRT methodologies. That is, the leakage for a small pre-existing leak is assumed to be less than 10 DWLb (or 8000 scfm) and the leakage for a large pre-existing leak is assumed to be less than 35 DWLb (or 28,000 scfm). This is considered conservative. Even though the drywell design differential pressure is 25 psid, the limiting sustained differential pressure between the drywell and the containment is 3.1 psi resulting from a small steam line break inside the drywell. On the other hand, a large line break on the reactor coolant system would generate a higher internal drywell pressure but rapidly depressurize the reactor vessel, thus quickly terminating the blowdown. The drywell bypass test pressure of 3 psid is based on the pressure difference caused by a small line break. The leakage flow associated with the allowable bypass leakage area (ARvK) of 1.0 ft2 corresponds to 40,110 scfm, which bounds the assumed leakage for a large pre-existing leak.

to RBG-46226 Page 5 of 53 4.1.5 Credit of Availability of Containment Unit Cooler Containment pressure is controlled to its design pressure as long as the containment unit coolers operate. Since the leakage for both DWBT leakage categories is below the design value of 40,110 scfm, the assumption will be made that as long as containment unit coolers operate, there will be no impact on the containment's existing leakage category. Also, the timing of containment unit cooler operation will not be adversely impacted with this assumption.

If containment unit coolers do not operate, the assumption is that any increased drywell leakage above DWLb will lead to containment failure. This assumption results in an increase in the frequency of EPRI Class 7 sequences rather than Class 3a or 3b. This is considered a conservative assumption, since not all accident sequences without unit coolers will lead to containment failure. Also RBS Level 1 PRA calculations show that it would take approximately 16 hours1.851852e-4 days <br />0.00444 hours <br />2.645503e-5 weeks <br />6.088e-6 months <br /> to reach the containment failure pressure (53.7 psia) without any containment heat removal system. Operator actions performed according to the Emergency Operating Procedures (EOPs) such as containment venting would further delay the time to containment failure. Therefore, the additional frequency of EPRI Class 7 sequences likely does not contribute to the LERF because of the time duration involved. However, for simplicity and consistency with the GGNS DWBT extension submittal, the additional frequency of EPRI Class 7 sequences was conservatively assumed to be LERF.

4.1.6 Credit for Availability of Reactor Depressurization In the base case, no credit for the availability of reactor pressure vessel (RPV) depressurization was taken. However, if the RPV can be successfully depressurized before vessel breach, there will be no concern associated with drywell bypass through the pre-existing drywell leakage path since there will be no driving force for the postulated bypass leakage flow. This statement is consistent with the discussion in RBS USAR section 6.2 on the severity of large and small line breaks on reactor coolant system. Also, drywell bypass is not a concern for transient initiated events as there is no steam release into the drywell. The total contribution from transient or loss of offsite power (LOSP) initiating events is greater than 99% of the total core damage frequency (CDF). Therefore, for severe accident scenarios that are not initiated by LOCA-type events, depressurization of the vessel and the subsequent release of steam to the suppression pool effectively remove the potential for significant drywell bypass following vessel failure.

RPV depressurization will release a large amount of heat into the suppression pool, which poses a challenge to the containment heat removal systems. However, the thermal hydraulic calculations supporting the RBS accident sequences development has already considered the limiting case for the heat addition into the containment suppression pool. Moreover, the containment pressurization will take a long period of time before failure occurs if no containment heat removal system is available, which then would not result in large early releases to the environment.

Therefore, the availability of RPV depressurization could be credited for mitigating the impact of increased drywell bypass. This is evaluated in Case 3 as a sensitivity.

to RBG-46226 Page 6 of 53 4.1.7 Accident Doses The DWBT extension analysis baseline accident doses are based on those utilized in the ILRT extension analyses, which was based on RBS Level 1 PRA Model Revision 3. No significant impact on the accident dose rates was expected for the model changes between Revision 3 and the interim model Revision 3B.

4.2 Methodologies RBS has already received NRC approval for the one time extension on the ILRT interval, which was based on a methodology similar to the approved Crystal River ILRT methodology.

While the RBS method was tailored to the RBS specific PSA definitions and analysis, a sensitivity study as part of the RBS ILRT analysis had also been performed to show the difference in results between the RBS method and the Crystal River method.

For the analysis of this one-time extension on the RBS DWBT interval, the previously approved RBS ILRT method is not followed. This is due to the additional complexity associated with consideration of the DWBT. The GGNS DWBT methodology, which was modified from both the approved Crystal River ILRT method and the NEI interim guidance ILRT method, is used in this analysis. The DWBT extension evaluation methodology derived from the NEI Interim Guidance ILRT methodology will be called the Modified NEI Interim Guidance Method.

Since the GGNS DWBT methodologies were modified from the existing ILRT methodologies, both the ILRT and DWBT methodologies are discussed in the following sections.

4.2.1 The NEI Interim Guidance ILRT Method EPRI developed the alternate methodology for NEI in order to provide interim guidance to licensees for developing uniform risk impact assessments supporting one-time extensions of ILRT surveillance intervals. This guidance improves on previous methods in three areas.

These areas include:

• a more realistic treatment of the increase in probability of leakage,

• more correct treatment and additional data for determining the probability of leaks detectable by ILRT, and

• the inclusion of provisions for utilizing NUREG-1 150 dose calculations.

This methodology incorporates the following steps.

1) Quantify the baseline (nominal three year ILRT interval) risk in terms of frequency per reactor year for the EPRI accident classes of interest.

2) Determine the containment leakage rates for applicable cases, 3a and 3b.

3) Develop the baseline population dose (man-rem) for the applicable accident classes.

to RBG-46226 Page 7 of 53

4) Determine the population dose rate (man-rem/year) by multiplying the dose calculated in step 3 by the associated frequency calculated in step 1.

5) Determine the change in probability of leakage detectable only by ILRT, and associated frequency for the new surveillance intervals of interest. Note that with increases in the ILRT surveillance interval, the size of the postulated leak path and the associated leakage rate are assumed not to change, however the probability of leakage detectable only by IRLT does increase.

6) Determine the population dose rate for the new surveillance intervals of interest.

7) Evaluate the risk impact (in terms of population dose rate and percentile change in population dose rate) for the interval extension cases.

8) Evaluate the risk impact in terms of LERF.

9) Evaluate the change in conditional containment failure probability.

4.2.2 Containment Failure Classes EPRI TR-1 04285 identifies eight classes of containment failure. Per the NEI interim guidance, Class 3 is divided into two parts for this analysis. The classes along with a summary description are listed in Table 4.2-1.

Table 4.2-1 Containment Failure Classes from EPRI TR-104285 Class Number Description Containment intact: accident sequences do not lead to failure; not affected by changes to ILRT leak testing frequencies.

2 Failure of isolation system to operate from common cause or power failure; 3a Small pre-existing leak in containment structure or liner; identifiable by ILRT; affected by ILRT testing frequency.

3b Large pre-existing leak in containment structure or liner; identifiable by ILRT; affected by ILRT testing frequency.

4 Type B tested components fail to seal; not affected by ILRT testing frequency.

Type Ctested components fail to seal; not affected by ILRT leak testing frequencies.

6 Failure to isolate due to valves failing to stroke closed; not affected by ILRT 7 Failure induced by severe accident phenomena; not affected by ILRT testing frequency.

8 Containment Bypass; not affected by ILRT testing frequency (ISLOCA, MSIV leakage)

The RBS ILRT evaluation grouped the containment failures into the above eight classes in order to be consistent with previous submittals. The frequency, person-rem (or man-rem) and to RBG-46226 Page 8 of 53 person-rem/yr for the given accident classes from the original ILRT analysis are listed in Table 4.2-2. Although the total CDF value in Table 4.2-2 was based on the Revision 3 PRA model which differs from the Revision 3B model CDF used in this evaluation, the percentages of the accident class contributions, the included Source Term Categories (STCs) and their characteristics in each accident class are not expected to have significantly changed between the Revision 3 and Revision 3B PRA models.

Table 4.2-2 RBS Accident Classes Class STCs Included Frequency  % Freq Person- Person-  % Risk in Class Frqec rq Rem Remn/yr

1. No failure 60,18, 6, 72 1.01 E-06 10.69% 6.92E+05 6.99E-01 0.35%

2. Large Isolation 52 (LG) 1.35E-09 0.01% 2.16E+08 2.92E-01 0.15%

Failure 3a. Small Preexisting Liner N/A NIA N/A N/A N/A N/A Breach 3b. Large 22b, 23b, 34b, Preexisting Liner 76b, 35b, 77b, N/A N/A N/A N/A N/A Breach 35La

4. Small Isolation Not currently N/A Failure Noted N/A N/A N/A N/A N/A (Type B Test)evlaeN/NANANA

5. Small Isolation Not currentlyN/

(TypueCTet evaluated N/A N/A N/A N/ANA 6.p ConTanent)

6. ContainFient 52 (SM) 1.07E-06 11.32% 4.90E+07 5.24E+01 26.35%

7. Severe 54, 50, 22, 23, Accident 34,76, 35,77, 7.37E-06 77.98% 1.98E+07 1.46E+02 73.15%

Accident97, 31, 104

8. Bypass Included above N/A N/A N/A N/A N/A Total 9.45E-06 100.00% N/A 1.99E+02 100.00%

to RBG-46226 Page 9 of 53 4.2.3 DWBT Methodology The primary difference in the methodology used to evaluate the extension of the DWBT is in the determination of the conditional probability of an existing drywell leak. The same failure frequencies, accident doses, consequence calculations, and acceptance criteria will be used.

The analysis will be performed assuming that both the ILRT and the DWBT are on the same frequencies.

With the Mark IlIl containment, the drywell is completely enclosed by the outer containment.

As such, drywell leakage does not leak directly to the environment but is further mitigated by the outer containment leakage barrier. Because of this 'dual" containment, there are several possible leakage path combinations that must be considered. The drywell can be intact (base leakage assumed), it can have a small pre-existing failure (10 times base leakage), or it can have a large pre-existing failure (35 times base leakage). The probability of each of these drywell failure categories is assumed to be the same as the equivalent categories for the ILRT evaluations. This results in at least nine combinations of drywell and containment leakage sizes. See the figure below.

A Normal I A', La DWLb B B', 10La 1ODWLb RPV C I C, 35La 35DWLb Drywell Boundary _4 Containment Boundary For GGNS, the assignment of each of these combinations to an original containment failure category depends on the consideration of the availability of the containment spray system, which has similar effects in reducing the containment pressure as the containment unit coolers at RBS. If containment sprays are available, the combination of drywell and containment leakage is categorized based on the containment leakage category. If containment sprays are not available, the combination of drywell and containment leakage is assumed to result in containment failure (Class 7) except for the combinations with base drywell bypass leakage. The combinations with base drywell leakage (DWLb) are assumed to to RBG-46226 Page 10 of 53 have the same categories as the base case ILRT evaluation. Table 4.2-3 summarizes the classification of combinations into the EPRI accident classes.

Table 4.2-3 DWBT and ILRT Leakage Combination Accident Classes Leakage Combinations DW Bypass Containment EPRI Class Leakage Leakage Assignment AA' 1DWLb 1 L, 1 AB' 1 DWLb 10 La 3a AC' 1 DWLb 35 La 3b BA'1 CS Available 10 DWLb 1 La I BA'2 CS Not Available Note 1 Note 1 7 BB'1 CS Available 10 DWLb 10 La 3a BB'2 CS Not Available Note 1 Note 1 7 BC'1 CS Available 10 DWLb 35 La 3b BC'2 CS Not Available Note I Note 1 7 CA'1 CS Available 35 DWLb I La 1 CA'2 CS Not Available Note I Note 1 7 CB'1 CS Available 35 DWLb 10 La 3a CB'2 CS Not Available Note 1 Note 1 7 CC'1 CS Available 35 DWLb 35 La 3b CC'2 CS Not Available Note 1 Note 1 7 Note 1: Containment failure assumed to occur.

The probability for each combination in Table 4.2-3 is determined by multiplying the conditional probabilities for DWBT and ILRT category by each other. For those cases where containment spray is a factor the probability of the combination of DWBT and ILRT is multiplied by the probability that containment spray is available or is not available as applicable.

The other change in the methodology to address the DWBT is the need to increase the containment failure due to phenomenology class (Class 7) frequency for the extended test frequencies. This is done in a manner similar to the method applied to Class 3a and 3b. That is, the Class 1frequency is also adjusted downward for the Class 7 frequency increase in order to maintain the same total CDF. The DWBT frequency extension will be evaluated using the NEI Interim Guidance methodology's conditional leak size probabilities.

The remaining portions of the DWBT methodologies are identical to that of alternate ILRT methodology.

to RBG-46226 Page 11 of 53 4.3 DWBT Extension Evaluation Although RBS has already received approval of the one-time extension on ILRT interval to 1 in 15 years, the case descriptions in the following sub-sections still denote the test interval of 1 in 10 years as "current" and the test interval of 1 in 15 years as "proposed" for consistency with the GGNS methodology.

4.3.1 Modifications to GGNS DWBT Methodology The GGNS methodology for DWBT extension evaluation is used in this analysis. The main modifications to the GGNS methodology are as follows:

• RBS credits the containment unit coolers to mitigate the adverse effects of the increased drywell leakages instead of the containment spray credited in the GGNS evaluation. Containment spray has dual functions by reducing the containment pressure and scrubbing the fission products from the containment atmosphere while containment unit coolers were designed mainly to reduce containment pressure.

However, the GGNS method does not credit the containment spray for scrubbing.

Thus the effects of crediting containment unit coolers and containment spray are the same.

• The RBS base case for DWBT extension evaluation uses EPRI Class 1 frequency to calculate the Class 3a, Class 3b and additional Class 7 frequencies. The GGNS method base cases used the total CDF for the calculation, which was conservative since more Class 1 frequencies would be re-categorized into Class 3a, 3b or Class 7 frequencies. Such a conservative approach was not considered to be appropriate for the RBS evaluation. Since the RBS Class 1 frequency only consists of about 10% of the total CDF, the calculated Class 3a, 3b and additional Class 7 frequencies will always exceed the Class 1 frequency if the total CDF was used for the calculations.

Since it is assumed that the total CDF does not change with the increased DWBT/ILRT leakages, in order to maintain total CDF, some of the CDF contributions from more severe classes such as Classes 2, 6 or 7 would have to be re-categorized to Class 3a or 3b, which was not considered appropriate.

For the calculation of conditional probabilities of combined DWBT/ILRT leakage, the drywell leakage probabilities are calculated in a manner to maximize the impact of the increased drywell leakage due to the DWBT interval extension. For example, the drywell leakage probability for leakage combinations CA', CB' and CC' with a test interval of 1 in 15 years is calculated as 0.02 (probability for large DWBT leakages using the industry data)

• 5 (probability increase factor for changing the test interval from 3 in 10 years to 1in 15 years) =

0.1. The drywell leakage probability for leakage combinations BA', BB', and BC' with a test interval of 1 in 15 years is then calculated as (1 - 0.1) = 0.9. Multiplying the 3a probability for small DWBT leakages using the industry data (0.292) times the probability increase factor for changing the test interval from 3 in 10 years to 1 in 15 years (5) would result in a probability of 1.46. This probability would exceed the total possible probability of 1. This method maximizes the impact on LERF since the 3b category is increased by the maximum amount while still ensuring that the total probability does not exceed 1.

to RBG-46226 Page 12 of 53 4.3.2 RBS DWBT Extension Evaluation Cases For the RBS DWBT extension evaluation, a base case and 2 sensitivity cases have been constructed. Table 4.3-1 lists the descriptions of the three cases. More detailed discussions for these cases are included in Sections 4.4 through 4.6.

Cases #2 and #3 were constructed to address an NRC Request for Additional Information (RAI) on the GGNS extension submittal to use the DWBT leakage probabilities calculated from the industry data. Although RBS had no DWBT failure in its plant history, the failure probabilities were evaluated with a plant-specific base leakage rate (i.e., 800 scfm for RBS) on the industry DWBT data without considering the differences among the plant designs and operation histories. To reduce the extra conservatism introduced by the using of the industry data, Case #3 credited the RPV depressurization along with crediting the containment unit coolers.

Table 4.3-1 RBS DWBT Extension Evaluation Case Descriptions Case Descriptions Case Frequency Baserof UsdfrCrediting CrdtnReco ase ofu rce sed fo Class 1 Containment Depressurization Case? DWBT Cass3a,7 Frequency Unit Coolers Dpesrzto Data Calculations 1 Base as ILRT Class 1 Rev. 3B X 2 Sensitivity Industry Class 1 Rev. 3B Data 3 SniiiyIndustry Class I Rev. 3B3 X X Senitiity Data 4.3.3 Frequencies and Accident Dose Rates for the Containment Failure Classes The frequencies and accident dose rates used in this analysis are listed in Table 4.3-4. It is reasonable to assume that the frequency fractions for the containment failure classes with Rev. 3B model are similar to the ones with Rev. 3. This simplification removed the burden to do a full-scope Level 2 PRA model update for an interim Level 1 model such as Rev. 3B.

to RBG-46226 Page 13 of 53 Frequencies The baseline total CDF value for Level 1 Rev. 3B PRA model is 4.26E-6/yr. The frequencies in Column "Frequency with Rev. 3B Model" in Table 4.3-4 are calculated by multiplying this baseline CDF value with the corresponding frequency fractions from Table 4.2-2.

Accident Dose Rates Based on RBS USAR Section 2.1.3.1 through 2.1.3.4, the expected 2030 populations are listed as follows.

Table 4.3-2 RBS USAR Expected 2030 Populations Locations Population Reference LPZ 1613 USAR Section 2.1.3.4 10 Mile Radius 42770 USAR Section 2.1.3.1 50 Mile Radius 1491919 USAR Section 2.1.3.2 The Person-Rem (or Man-Rem) values for containment failure classes were based on the RBS Design Basis Accident (DBA) LOCA doses and were consistent with other DWBT/ILRT submittals. The accident dose rates without containment failure were conservatively assumed to be the DBA LOCA dose (about 3 Rem whole body at the Low Population Zone (LPZ)). For this calculation, the dose rates listed in Table 4.3-3 were used.

For more conservatism, the population within the 10 mile radius was assumed to be concentrated at the 5 mile radius. Half of the population within 50 mile radius was assumed to be concentrated at the 10 mile radius and the other half was assumed to be on the 30 mile radius.

to RBG-46226 Page 14 of 53 Table 4.3-3 RBS DBA LOCA Dose Rates Location Dose Rates Comment (Rem)

LPZ 3From the RBS ILRT Analysis. Based on the DBA LOCA dose rates. DBA LOCA LPZ dose is approximately 3 Rem whole body.

5 Mile 0.9 From the RBS ILRT Analysis. Based on the DBA LOCA dose rates. Calculated as 30% of LPZ dose.

10 Mile 0.33 From the RBS ILRT Analysis. Based on the DBA LOCA dose

. rates. Calculated as 11% of LPZ dose.

30 Mile 0.09 0rates. From the RBS ILRT Calculated as Analysis.

3% of LPZBased dose. on the DBA LOCA dose Therefore, the no-containment-failure Class 1 Person-Rem (Man-Rem) was calculated as:

Class 1 Person-Rem = 3

• 1613 + 0.9 * (42770-1613) + 0.33 * (1491919-42770) /2 + 0.09 *

(1491919-42770) /2

= 3.46E5 Since Class 3a and Class 3b were assumed to have a leakage of 10 La and 35 La, the Person-Rem values were calculated as:

Class 3a Person-Rem= Class 1 Person-Rem

• 10 = 3.46E6 Class 3b Person-Rem= Class 1 Person-Rem

• 35 = 1.21 E7 The Class 6 or Class 7 Person-Rem was assumed to be 100 x (Class 1 Person-Rem):

Class 6 Person-Rem = Class 1 Person-Rem

• 100 = 3.46E7 Class 7 Person-Rem = Class 1 Person-Rem

• 100 = 3.46E7 Although the Class 6 Person-Rem value in the RBS ILRT Submittal is slightly higher than the above value, the total dose contribution from Class 6 and Class 7 in this analysis is much higher than the total contribution in the RBS ILRT Submittal. The Class 2 Person-Rem value was obtained from the RBS ILRT Submittal.

to RBG46226 Page 15 of 53 Table 4.3-4 Frequencies and Accident Dose Rates Frequency Class F with Person-Rem Frequency Rev. 3B Model

1. No failure 10.69% 4.55E-07 3.46E+05

2. Large Isolation Failure 0.01% 6.08E-10 2.16E+08 3a. Small Preexisting Liner Breach N/A N/A 3.46E+06 3b. Large Preexisting Liner Breach N/A N/A 1.21 E+07

4. Small Iso Failure (Type B Test) N/A N/A N/A

5. Small Iso Failure (Type C Test) N/A N/A N/A

6. Containment Isolation Failure 11.32% 4.82E-07 3.46E+07

7. Severe Accident 77.98% 3.32E-06 3.46E+07

8. Bypass N/A N/A N/A Total 100.00% 4.26E-6 NIA 4.3.4 DWBT Data Assessment With the limited DWBT data, the DWBT leakage probabilities were assumed to be the same as the ones used in the ILRT extension evaluation methodologies for the base case. This approach is considered to be appropriate since no DWBT failure has occurred at RBS during its plant history.

to RBG-46226 Page 16 of 53 Table 4.3-5 Baseline Drywell Leakage Probabilities in DWBT Evaluation DWBT Extension Evaluation DW Leakage Probability - DW Leakage Probability -

Method Small Leakage Large Leakage Modified NEI Interim Guidance 2.7E-2 2.7E-3 Per the NRC's RAI on the GGNS extension submittal, the drywell leakage probabilities derived from the industry data are also used as a sensitivity case in the DWBT extension.

A limited set of data is available for Mark IlIl plants. Data from other BWR containment types (e.g., Mark il's) is not considered applicable because of the differences in drywell configuration and free volume. A summary of Mark IlIl drywell bypass leakage test results categorized in accordance with the RBS DWBT extension evaluation leakage assumptions is provided in the following table.

to RBG-46226 Page 17 of 53 Table 4.3-6 A Summary of the Mark III DWBT Results DWBT Leakages Total Plant Small Large Tests PlantI 0 0 6 Plant 2 6 0 7 Plant 3 1 0 6 Plant 4 0 0 5 Total 7 0 24 The test results were classified as 'Small" if the leakage was greater than the base DWB leakage (DWLb) assumed in the RBS DWBT evaluation (800 scfm) but less than 10 x DWLb.

Results would have been classified as "Large" if the test leakage had been greater than 10 x DWLb (8000 scfm). It should be noted that none of the above test results were considered failures of the drywell bypass test as there was considerable margin in each of the tests. The above is a categorization of the test results in relation to the assumed base leakage and the 3a and 3b leakage categories.

A review of all the DWBT results for the domestic Mark IlIl plants leads to the conclusion that the maximum observed leakage rate, 2599 scfm, is well within the leakage rate assigned for Category 3b leakage (28,000 scfm) and that the majority of the leakage rate results (17 of 24) are represented by the value assigned to Category 1. (The RBS maximum DWBT result is only 754 scfm)

Even though the data is sparse, an estimate of the Category 3a and 3b probabilities can be calculated using the data. Using a Chi Squared upper bound (95% confidence) value is not considered to be appropriate since it will give a bounding value that is not representative of RBS operation. The use of the mean for the 3a Category (7/24 = 0.292) is considered more appropriate for a realistic evaluation. Since there have been no Category 3b occurrences, the Jeffreys non-informative is more appropriate for the 3b Category. Use of the Jeffreys non-informative is based on the following justification from the NEI Interim Guidance.

'Application of the Jeffreys non-informative prior is one of a number of statistical analysis approaches to estimating probabilities when no failures have been experienced. The approach was used in NUREG-1150 and more recently in NUREG/CR-5750.

NUREG/CR-5750 is now the preferred source of initiating event data, which also involves rare event approximations. The selected approach is more conservative than many of the referenced approaches. (See for example Lipow, M. and Welker, E. "Estimating the Exponential Failure Rate From Data With No Failure Events", Proceedings of the 1974 to RBG-46226 Page 18 of 53 Annual Reliability and Maintainability Symposium, Los Angeles CA January 29-31, 1974.)

The principle exception being the Chebychev upper bound. However, the Chebychev upper bound is specifically selected when a 95% confidence interval is desired.

Regulatory Guide 1.174 decision criteria are designed for use with mean values rather than upper bound estimates. We believe, given the information available at this time, that the Jeffreys non-informative prior provides a reasonable balance between conservatism in light of uncertainty and yet meets the intent of Regulatory Guide 1.174. Further, application of the Jeffreys non-informative prior is consistent with NUREG-1 150, a reference applied in this interim guide and previous ILRT documents related to this question, namely EPRI TR-1044285 and NUREG-1493."

The Category 3b probability is calculated below using the Jeffreys non-informative prior.

Category 3b Leak Probability= Numberof Occurrences(0)+ 12 Number of Tests + 1

_(0)+

= 24+= 2.OE - 02 24+1 To summarize, the base Category 3a leak probability based on the industry data is estimated as 2.92E-01 and the Category 3b leak probability is estimated as 2.OE-02. These values are considered conservative but are used along with the Modified EPRI Interim Guidance Method to perform a sensitivity analysis. This is documented in the following sections.

4.3.5 Availability of Containment Unit Cooler The availability of a containment unit cooler (UC) was determined using the RBS Level 1 Revision 3B PRA model. The inadequate containment cooling by unit coolers gate in the fault tree model was solved and the resulting cutsets were delete-termed from the overall Revision 3B PRA results cutset file to obtain the cutsets which do not have events which would fail the unit coolers. The unit coolers would be available for each of these cutsets. The total frequency for these cutsets is 5.26E-7/year. Therefore, the probability that a unit cooler is available is determined as follows:

PUC Available = Frequency of cutsets with UC available/Overall CDF

= 5.26 E-7 / 4.26E-6

= 12.34%

The probability that containment UC is not available is:

PUC Unavailable = 1 - PUC Available

= 87.66%

These values were used in the determination of combined leakage probabilities. They are conservative since there is no consideration of the recovery of containment unit coolers. The UC availability strongly depends on the Div I and 11diesel generator power after loss of offsite to RBG-46226 Page 19 of 53 power (LOSP) and the standby service water system (SSW), which are the dominant contributors to RBS core damage frequencies.

4.3.6 Availability of Containment Unit Cooler or Reactor Depressurization The availability of containment unit cooler (UC) or reactor depressurization (DEP) was determined in a similar manner as the availability of containment unit cooler in the previous section. A gate was developed for inadequate containment cooling provided by unit coolers and the failure of reactor depressurization. This gate was solved with the appropriate flag files and the resultant cutset was saved. This cutset file was then delete-termed from the overall Revision 3B total CDF cutset to obtain a file representing the RBS core damage frequency with either a containment unit cooler or depressurization available. This cutset file includes cutsets that do not have events which would fail both containment unit coolers and reactor depressurization.

The probability that a containment unit cooler or reactor depressurization is available is determined as follows:

PUC or DEP Available

= Frequency of cutsets with UC or DEP available/Overall CDF

= 3.53E-6 / 4.26E-6

= 82.96%

The probability that both UC and DEP is not available is:

PUC and DEP Unavailable

= 1 - PUC or DEPAvailabfe

= 17.04%

4.4 Case 1: Base Case with Modified NEI Interim Guidance Method This base case was performed with the Modified NEI Interim Guidance Method.

4.4.1 Frequency Calculations The method of combining the probability of DWBT leakage and the probability of containment leakage has been discussed in Section 4.2.3 for the GGNS DWBT methodology.

The conditional probability of the different combinations of DWB and ILRT leakage are calculated using a probability of 2.7E-2 for a small leak and 2.7E-3 for a large leak. The probability that a containment unit cooler is available is also factored in for certain combinations.

The probability increase factor from the baseline interval (3 in 10 years) to the current interval (1 in 10 years) and the proposed interval (1 in 15 years) are 3.33 and 5.0 respectively based on the NEI Interim Guidance Methodology. The probability increase factors are calculated as follows:

to RBG-46226 Page 20 of 53

• Probability Increase Factor from base to current = (Current Interval / 2) / (Base Interval

12) = (10*12 / 2) / (36 1 2) = 3.33

• Probability Increase Factor from base to proposed = (Proposed Interval / 2) / (Base Interval / 2) = (15*12 / 2)/(36/2) = 5.0 The following tables calculate the conditional probabilities of the combined leakage for the baseline, current and proposed DWBT intervals. The frequencies of Classes 3a, 3b, and 7 are then calculated with the total contribution from different leakage combinations.

Table 4.4-1 Conditional Probability of Combined Leakage for Baseline Interval (Case 1)

Bypass LDW CTMT DW Prob CTMT Combined Class Combinations Leakage Leakage Prob of UC Leakage Prob Assign-Leakag Probment A' 1DWWLB 1 La 0.97 NA 0.97 9.41 E-01 1 AB' 1 DWLB 10 La 0.97 NA 2.7E-02 2.62E-02 3a AC' 1 DWLB 35 La 0.97 NA 2.7E-03 2.62E-03 3b BA'1 UC Available 2.7E-02 12.34% 0.97 3.23E-03 1 BA'2 UC Not Available 10DWLB 1 La 2.7E-02 87.66% 0.97 2.30E-02 7 BB'1 UC Available 2.7E-02 12.34% 2.7E-02 9.OOE-05 3a BB'2 UC Not Available 10 DWLB 101La 2.7E-02 87.66% 2.7E-02 6.39E-04 7 BC'1 UC Available 2.7E-02 12.34% 2.7E-03 9.00E-06 3b C'2 BC2 C o Aaiabe10 DWLB UCNotAvailable 35 La 32.7E-02 87.66% 2.7E-03 6.39E-05 7 CA'1 UC Available 2.7E-03 12.34% 0.97 3.23E-04 1 35 DWLB 1 La CA'2 UC Not Available 2.7E-03 87.66% 0.97 2.30E-03 7 CB'1 UC Available 2.7E-03 12.34% 2.7E-02 9.OOE-06 3a CB'2 UC Not Available 35 DWLB 10 La 2.7E-03 87.66% 2.7E-02 6.39E-05 7 CC'1 UC Available 2.7E-03 12.34% 2.7E-03 9.OOE-07 3b 35 DWLB 35 La CC'2 UC Not Available 2.7E-03 87.66% 2.7E-03 6.39E-06 7 The overall baseline conditional probabilities for Classes 3a, 3b and 7 are then calculated as follows:

• Class 3a Probability = 2.62E-2 + 9.OOE-5 + 9.OOE-6 = 2.63E-2

• • Class 3b Probability = 2.62E-3 + 9.OOE-6 + 9.OOE-7 = 2.63E-3

• • Change in Class 7 Probability = 2.30E-2 + 6.39E-4 + 6.39E-5 + 2.30E-3 + 6.39E-5 +

6.39E-6 = 2.60E-2 to RBG-46226 Page 21 of 53 The baseline frequencies for Classes 3a, 3b and 7 are calculated by multiplying the overall conditional probabilities with the non-containment-failure (NCF) Class 1 frequency.

• Class 3a Frequency = 2.63E-2

• 4.55E-7 = 1.20E-8

• Class 3b Frequency = 2.63E-3

• 4.55E-7 = 1.20E-9

• Change in Class 7 Frequency = 2.60E-2

• 4.55E-7 = 1.19E-8 Table 4.4-2 Conditional Probability of Combined Leakage for Current Interval (Case 1)

DW DWCTMTEPRI Leakage Bypass WCTM Prob Leakage CTMT Combined Class Combinations Bypassa CTMLeakagePo of UC Leakag Prob Assign-LeakgePob eakge robment AA' 1 DWLB I La 0.90 NA 0.90 8.12E-01 1 AB' I DWLB 10 La 0.90 NA 9.OE-02 8.11E-02 3a AC' 1 DWL 8 35 La 0.90 NA 9.OE-03 8.11 E-03 3b BA'1 UC Available 9.0E-02 12.34% 0.90 1.OOE-02 1 10 OWL 8 1 La BA'2 UC Not Available 9.OE-02 87.66% 0.90 7.11 E-02 7 BB'1 UC Available 9.0E-02 12.34% 9.0E-02 1.00E-03 3a BB'2 UC Not Available 10 OWL 8 10 La 9.OE-02 87.66% 9.OE-02 7.1OE-03 7 BC'1 UC Available 9.OE-02 12.34% 9.OE-03 1.OOE-04 3b 10 OWL 8 35 La BC'2 UC Not Available 9.OE-02 87.66% 9.OE-03 7.10E-04 7 CA'1 UC Available 9.OE-03 12.34% 0.90 1.00E-03 1 35 OWL 8 1 La CA'2 UC Not Available 9.OE-03 87.66% 0.90 7.11 E-03 7 CB'1 UC Available 9.OE-03 12.34% 9.OE-02 1.OOE-04 3a CB'2 UC Not Available La 9.OE-03 87.66% 9.OE-02 7.10E-04 7 CC'1 UC Available 9.OE-03 12.34% 9.OE-03 1.00E-05 3b CC2 C Not Available35 DWLB 35 La 9.OE-03 87.66% 9.OE-03 7.1OE-05 7 The overall current case conditional probabilities for Classes 3a, 3b and 7 are then calculated as follows:

• Class 3a Probability = 8.11 E-2 + 1.OOE-3 + 1.OOE-4 = 8.22E-2

• Class 3b Probability = 8.11 E-3 + 1.OOE-4 + 1.OOE-5 = 8.22E-3

• Change in Class 7 Probability = 7.11 E-2 + 7.1 OE-3 + 7.1 OE-4 + 7.11 E-3 + 7.1 OE-4 +

7.1OE-5 = 8.68E-2 The current case frequencies for Classes 3a, 3b and 7 are calculated by multiplying the overall conditional probabilities with the non-containment-failure (NCF) Class 1 frequency.

to RBG-46226 Page 22 of 53

• Class 3a Frequency = 8.22E-2

• 4.55E-7 = 3.74E-8

• Class 3b Frequency = 8.22E-3

• 4.55E-7 = 3.74E-9

• Change in Class 7 Frequency = 8.68E-2

• 4.55E-7 = 3.95E-8 Table 4.4-3 Conditional Probability of Combined Leakage for Proposed Interval (Case 1)

EPRI Leakage DW CTMT DW Prob CTMT Combined Class Combinations Bypass Leakage of UC Leakage Prob Assign-LaaeLeakage Prob Prob ment A' 1DWLB I La 0.85 NA 0.85 7.25E-01 1 AB' 1 DWLB 10 La 0.85 NA 1.4E-01 1.15E-01 3a AC' I DWLB 35 La 0.85 NA 1.4E-02 1.15E-02 3b BA'1 UC Available 1.4E-01 12.34% 0.85 1.42E-02 1 BA'2 UC Not Available 1.4E-01 87.66% 0.85 1.01 E-01 7 BB'1 UC Available 1.4E-01 12.34% 1.4E-01 2.25E-03 3a BB'2 UC Not Available 10 DWLB 10 La 1.4E-01 87.66% 1.4E-01 1.60E-02 7 BC'1 UC Available 1.4E-01 12.34% 1.4E-02 2.25E-04 3b BC'2 UCBC'Not Nt U Available valale10 DWLB 35 La 1.4E-01 87.66% 1.4E-02 1.60E-03 7 CA'1 UC Available 1.4E-02 12.34% 0.85 1.42E-03 I 35 DWLB 1 La CA'2 UC Not Available 1.4E-02 87.66% 0.85 1.01 E-02 7 CB'1 UC Available 1.4E-02 12.34% 1.4E-01 2.25E-04 3a CB'2 UC Not Available 3 DWLB 10 La 1.4E-02 87.66% 1.4E-01 1.60E-03 7 CC'1 UC Available 1.4E-02 12.34% 1.4E-02 2.25E-05 3b CC'2 C Not Available WLB 35 La 1.4E-02 87.66% 1.4E-02 1.60E-04 7 The overall proposed case conditional probabilities for Classes 3a, 3b and 7 are then calculated as follows:

• Class 3a Probability = 1.15E-1 + 2.25E-3 + 2.25E-4 = 1.174E-1

• • Class 3b Probability = 1.15E-2 + 2.25E-4 + 2.25E-5 = 1.174E-2

• Change in Class 7 Probability = 1.01 E-1 + 1.60E-2 + 1.60E-3 + 1.01 E-2 + 1.60E-3 +

1.60E-4 = 1.30E-1 to RBG-46226 Page 23 of 53 The proposed case frequencies for Classes 3a, 3b and 7 are calculated by multiplying the overall conditional probabilities with the non-containment-failure (NCF) Class 1 frequency.

• • Class 3a Frequency = 1.174E-1

• 4.55E-7 = 5.35E-8

• Class 3b Frequency = 1.174E-2

• 4.55E-7 = 5.35E-9

• Change in Class 7 Frequency = 1.30E-1

• 4.55E-7 = 5.93E-8 The class frequencies for different DWBT intervals are summarized in the following table.

Class 2 and Class 6 frequencies were kept the same as the original ones without considering the DWBT intervals. Class 1 and Class 7 frequencies were calculated as following:

• Class 1 Frequency = Original NCF Freq - (Class 3a + Class 3b + Change in Class 7)

• Class 7 Frequency = Original Class 7 + Change in Class 7 Table 4.4-4 Class Frequencies for Different DWBT Intervals (Case 1)

Class 3 in 10 I in 10 1 in 15

1. No failure 4.30E-07 3.75E-07 3.37E-07

2. Large Isolation Failure 6.08E-10 6.08E-10 6.08E-10 3a. Small Preexisting Liner Breach 1.20E-08 3.74E-08 5.35E-08 3b. Large Preexisting Liner Breach 1.20E-09 3.74E-09 5.35E-09

4. Small Iso Failure (Type B Test) N/A N/A N/A

5. Small Iso Failure (Type C Test) N/A N/A N/A

6. Containment Isolation Failure 4.82E-07 4.82E-07 4.82E-07

7. Severe Accident 3.33E-06 3.36E-06 3.38E-06

8. Bypass N/A N/A N/A Total Frequency 4.26E-06 4.26E-06 4.26E-06 4.4.2 Accident Dose Rate Calculations As indicated before, the evaluation of the DWBT extension will use the accident dose estimates from the evaluation of the ILRT extension. The detailed calculation and a summary of the accident release (person-rem) and the risk (person-rem/year) calculated for each class is contained in Table 4.4-5 and Table 4.4-6.

to RBG-46226 Page 24 of 53 Table 4.4-5 Detailed Accident Release and Risk Calculations (Case 1)

Class 1 - Person-RemNr Calculation Base Case 1 in 10 1 in 15 Person-Rem 3.46E+05 3.46E+05 3.46E+05 Frequency 4.30E-07 3.75E-07 3.37E-07 Person-RemNr 1.49E-01 1.30E-01 1.17E-01 Class 2 - Person-RemNr Calculation Base Case I in 10 1 in15 Person-Rem 2.16E+08 2.16E+08 2.16E+08 Frequency 6.08E-10 6.08E-10 6.08E-10 Person-RemNr 1.31 E-01 1.31 E-01 1.31 E-01 Class 3a Person-RemNr Calculation Base Case I in 10 I in 15 Person-Rem 3.46E+06 3.46E+06 3.46E+06 Frequency 1.20E-08 3.74E-08 5.35E-08 Person-RemNr 4.14E-02 1.30E-01 1.85E-01 Class 3b Person-RemNr Calculation Base Case 1in 10 I in 15 Person-Rem 1.21 E+07 1.21 E+07 1.21 E+07 Frequency 1.20E-09 3.74E-09 5.35E-09 Person-Rem/Yr 1.45E-02 4.53E-02 6.48E-02 to RBG-46226 Page 25 of 53 Class 6 Person-RemNr Calculation Base Case 1 in10 1 in 15 Person-Rem 3.46E+07 3.46E+07 3.46E+07 Frequency 4.82E-07 4.82E-07 4.82E-07 Person-RemNr 1.67E+01 1.67E+01 1.67E+01 Class 7 Person-RemNr Calculation Base Case DIin15 in10 Person-Rem 3.46E+07 3.46E+07 3.46E+07 Frequency 3.33E-06 3.36E-06 3.38E-06 Person-Rem/Yr 1.15E+02 1.16E+02 1.17E+02 Change in Class 7 Person-Rem/Yr Calculation Base Case 1in 10 1in 15 Person-Rem 3.46E+07 3.46E+07 3.46E+07 Frequency 1.19E-08 3.95E-08 5.93E-08 Person-Rem/Yr 4.1OE-01 1.37E+00 2.05E+OO to RBG-46226 Page 26 of 53 Table 4.4-6 Summary of Accident Release and Risk Calculations (Case 2)

Class Base 1 in 10 1 in 15

1. No failure 1.49E-01 1.30E-01 1.17E-01

2. Large Isolation Failure 1.31 E-01 1.31 E-01 1.31 E-01 3a. Small Preexisting Liner Breach 4.14E-02 1.30E-01 1.85E-01 3b. Large Preexisting Liner Breach 1.45E-02 4.53E-02 6.48E-02

4. Small Iso Failure (Type BTest) N/A N/A N/A

5. Small Iso Failure (Type CTest) N/A N/A N/A

6. Containment Isolation Failure 1.67E+01 1.67E+01 1.67E+01

7. Severe Accident 1.1 5E+02 1.16E+02 1.17E+02

8. Bypass N/A N/A N/A TOTAL Person-RemlYr: 1.324E+02 1.335E+02 1.342E+02 Change from BaseLine Person- 1.06E+00 1.80E+00 Rem/yr:

Change from I in 10 to 1 in 15: 7.46E-01

% increase from Base: lI0.80% 1.36%

% Change from 1 in 10 to 1 in 15: 0.56%

ILRT/DWBT Contribution 0.35% 1.16% 1.71%

4.4.3 Changes in LERF and CCFP Calculations The change in LERF for extending the DWBT interval is the increase due to the change in the large pre-existing leak class, Class 3b, and the increase in the portion of Class 7 due to DWBT. As in the previous evaluations, the Class 3a leak size is too small to be considered a LERF. This increase is documented below.

to RBG-46226 Page 27 of 53 Table 4.4-7 Change in LERF (Case 1)

Base 1 in 10 1 in 15 Class 3b Frequency 1.20E-09 3.74E-09 5.35E-09 Change in Class 7 Frequency 1.19E-08 3.95E-08 5.93E-08 Total LERF 1.30E-08 4.32E-08 6.46E-08 Change from Base 3.02E-08 5.16E-08 Change from 1 in 10 to I in 15 2.14E-08 The change in CCFP is considered to be the change in containment failure probability given an accident. This can be calculated as follows:

CCFP = 1 - (Frequency of NCF) / CDF Frequency of NCF = Class 1 frequency + Class 3a frequency The calculations for each DWBT option are summarized below.

Table 4.4-8 Change in CCFP (Case 1)

Class Freq I Class Freq 3a NCF Freq Total CDF ChangeCag CCFP from base from frombase Current Baseline 4.30E-07 1.20E-08 4.42E-07 4.26E-06 89.62%

1 in 10 3.75E-07 3.74E-08 4.12E-07 4.26E-06 90.33% 0.71%

1 in 15 3.37E-07 5.35E-08 3.91 E-07 4.26E-06 90.83% 1.21% 0.50%

4.4.4 Summary of Results Table 4.4-9 provides a summary of the results for the extension of the DWBT frequency (in conjunction with the ILRT extension).

Table 4.4-9 Summary of DWBT Extension Evaluation Case 1 Results 3 In 10yr 1 in 10yr 1 in 15yr Total Risk 132.4 133.5 134.2 DWBT/ILRT Risk Contribution (%) 0.35% 1.16% 1.71%

% Change from Base 0.80% 1.36%

to RBG-46226 Page 28 of 53 3 in 10yr I in 10yr 1 in 15yr

% Change from Current 0.56%

LERF value due to DWBT/ILRT 1.30E-08 4.32E-08 6.46E-08 Change from Base 3.02E-08 5.16E-08 Change from Current 2.14E-08 CCFP 89.62% 90.33% 90.83%

Change from Base 0.71% 1.21%

Change from Current 0.50%

Based on the above results, the extension of the DWBT (in conjunction with an extension of the ILRT) surveillance interval from either the baseline interval (3 in 10 years) or the current interval (once in 10 years) to once in 15 years does not pose a significant increase in risk to the public. The LERF value is within Region 3 of Regulatory Guide 1.174 (very small) guidance and is considered acceptable.

4.5 Case 2: Sensitivity Case with Modified NEI Interim Guidance Method and Industry DWBT Data This sensitivity case was performed with the Modified NEI Interim Guidance Method to address the impact of using the industry DWBT data per NRC request during the GGNS submittal review.

4.5.1 Frequency Calculations The method of combining the probability of DWBT leakage and the probability of containment leakage has been discussed in Section 4.2.3 for the GGNS methodology.

The conditional probability for each of the different combinations of DWB and ILRT leakage is calculated using the following probabilities:

• A probability of 0.292 for a small drywell leak and 0.02 for a large drywell leak by using the Mark IlIl DWBT historical data (see the details in Section 5.1.4);

• A probability of 2.7E-2 for a small containment leak and 2.7E-3 for a large containment leak to RBG-46226 Page 29 of 53 The probability that a containment unit cooler is available is also factored in for certain combinations.

The probability increase factor from the baseline interval (3 in 10 years) to the current interval (1 in 10 years) and the proposed interval (1 in 15 years) are 3.33 and 5.0 respectively based on the NEI Interim Guidance Methodology.

The following tables calculate the conditional probabilities of the combined leakage for the baseline, current and proposed DWBT intervals. The frequencies of Classes 3a, 3b, and 7 are then calculated with the total contribution from different leakage combinations.

Table 4.5-1 Conditional Probability of Combined Leakage for Baseline Interval (Case 2)

DW DWCTMTEPRI Leakage Byas CTMT DWaag Prob CTMTag Combined Class Combinations Bypassage Leakage ofoUC Leakage Prob Assign-Leakge Pob eakge robment AA 1 DWLB 1 La 0.69 NA 0.97 6.68E-01 1 AB' I DWLB 10 La 0.69 NA 2.7E-02 1.86E-02 3a AC' I DWLB 35 La 0.69 NA 2.7E-03 1.86E-03 3b BA'l UC Available 2.9E-01 12.34% 0.97 3.49E-02 1 10ODWLB 1ILa BA'2 UC Not Available 2.9E-01 87.66% 0.97 2.48E-01 7 BB'1 UC Available 2.9E-01 12.34% 2.7E-02 9.72E-04 3a 10 DWLB 10 La BB'2 UC Not Available 2.9E-01 87.66% 2.7E-02 6.90E-03 7 BC'1 UC Available 2.9E-01 12.34% 2.7E-03 9.72E-05 3b BC'2 UC Not Available La 2.9E-01 87.66% 2.7E-03 6.90E-04 7 CA'1 UC Available 2.0E-02 12.34% 0.97 2.40E-03 I 35 DWLB 1La CA'2 UC Not Available 2.OE-02 87.66% 0.97 1.70E-02 7 CB'1 UC Available 2.OE-02 12.34% 2.7E-02 6.67E-05 3a 35 DWLB 10 La CB'2 UC Not Available 2.OE-02 87.66% 2.7E-02 4.73E-04 7 CC'I UC Available 2.OE-02 12.34% 2.7E-03 6.67E-06 3b 35 DWLB 35 La CC'2 UC Not Available 2.0E-02 -87.66% 2.7E-03 4.73E-05 7 The overall baseline conditional probabilities for Classes 3a, 3b and 7 are then calculated as follows.

• • Class 3a Probability = 1.86E-2 + 9.72E-4 + 6.67E-5 = 1.96E-2

• Class 3b Probability = 1.86E-3 + 9.72E-5 + 6.67E-6 = 1.96E-3

• • Change in Class 7 Probability = 2.48E-1 + 6.90E-3 + 6.90E-4 + 1.70E-2 + 4.73E-4 +

4.73E-5 = 2.73E-1 to RBG-46226 Page 30 of 53 The baseline frequencies for Classes 3a, 3b and 7 are calculated by multiplying the overall conditional probabilities with the non-containment-failure (NCF) Class 1 frequency.

• Class 3a Frequency = 1.96E-2

• 4.55E-7 = 8.93E-9

• Class 3b Frequency = 1.96E-3

• 4.55E-7 = 8.93E-10

• Change in Class 7 Frequency = 2.73E-1

• 4.55E-7 = 1.24E-7 Table 4.5-2 Conditional Probability of Combined Leakage for Current Interval (Case 2)

DW DWCTMTEPRI Leakage DW CTMT DW Prob CTMT Combined Class Combinations Bypass Leakage Lekg of UC Leakage Prob Assign-Leakge Pob eakge robment AA I DWLB 1La 0.00 NA 0.90 O.OOE+00 1 AB' 1 DWLB 10 La 0.00 NA 9.OE-02 O.OOE+00 3a AC' I DWLB 351La 0.00 NA 9.OE-03 O.OOE+00 3b BA'1 UC Available 9.3E-01 12.34% 0.90 1.04E-01 1 BA'2 UC Not Available 10DWLB 1La 9.3E-01 87.66% 0.90 7.37E-01 7 BB'1 UC Available 9.3E-01 12.34% 9.0E-02 1.04E-02 3a BB2 UC Not Available 10 DWLB 10 La 9.3E-01 87.66% 9.OE-02 7.36E-02 7 BC'1 UC Available 9.3E-01 12.34% 9.0E-03 1.04E-03 3b BC'2 UC Not Available 10 DWLB 35 La 9.3E-01 87.66% g.oE-03 7-36E 03 CA'1 UC Available 6.7E-02 12.34% 0.90 7.41 E-03 1 CA'2 UC Not Available 35 DWLB 1La 6.7E-02 87.66% 0.90 5.27E-02 7 CB'1 UC Available 6.7E-02 12.34% 9.OE-02 7.41 E-04 3a CB'2 UC Not Available 35 DWLB 10 La 6.7E-02 87.66% 9.OE-02 5.26E-03 7 CC'1 UC Available 6.7E-02 12.34% 9.OE-03 7.41 E-05 3b CC'2 UC Not Available La 6.7E-02 87.66% 9.OE-03 5.26E-04 7 The overall current case conditional probabilities for Classes 3a, 3b and 7 are then calculated as follows.

• Class 3a Probability = 0.0+ 1.04E-2 + 7.41 E-4 = 1.11E-2

• Class 3b Probability = 0.0 + 1.04E-3 + 7.41 E-5 = 1.11E-3

• • Change in Class 7 Probability = 7.37E-1 + 7.36E-2 + 7.36E-3 + 5.27E-2 + 5.26E-3 +

5.26E-4 = 8.77E-1 to RBG-46226 Page 31 of 53 The current case frequencies for Classes 3a, 3b and 7 are calculated by multiplying the overall conditional probabilities with the non-containment-failure (NCF) Class 1 frequency.

• Class 3a Frequency = 1.11E-2

• 4.55E-7 = 5.06E-9

• Class 3b Frequency = 1.11 E-3

• 4.55E-7 = 5.06E-10

• Change in Class 7 Frequency = 8.77E-1

• 4.55E-7 = 3.99E-7 Table 4.5-3 Conditional Probability of Combined Leakage for Proposed Interval (Case 2)

EPRI Leakage DW CTMT DW Prob CTMT Combined Class Combinations Bypass Leakage of UC Leakage Prob Assign-LaaeLeakage Prob Prob ment A' 1 DWL 9 1 La 0.00 NA 0.85 O.OOE+00 1 AB' 1 DWLB 10 La 0.00 NA 1.4E-01 O.OOE+00 3a AC' I DWLB 35 La 0.00 NA 1.4E-02 O.OOE+00 3b BA'1 UC Available 9.OE-01 12.34% 0.85 9.46E-02 1 BA'2 UC Not Available 9.OE-01 87.66% 0.85 6.72E-01 7 BB'1 UC Available 9.OE-01 12.34% 1.4E-01 1.50E-02 3a BB'2 UC Not Available 10 OWLB 10 La 9.OE-01 87.66% 1.4E-01 1.07E-01 7 BC'1 UC Available 9.OE-01 12.34% 1.4E-02 1.50E-03 3b BC'2 UC Not Available 10 OWL 8 35 La 9.0E-01 87.66% 1.4E-02 1.07E-02 7 CA'1 UC Available 1.0E-01 12.34% 0.85 1.05E-02 1 CA'2 UC Not Available 1.OE-01 87.66% 0.85 7.46E-02 7 CB'1 UC Available 1.0E-01 12.34% 1.4E-01 1.67E-03 3a CB'2 UC Not Available 35 OWL 8 10 La 1.0E-01 87.66% 1.4E-01 1.18E-02 7 CC'1 UC Available 1.0E-01 12.34% 1.4E-02 1.67E-04 3b CC'2 UC Not Available 35 OWL 8 35 La 1.OE-01 87.66% 1.4E-02 1.18E-03 7 The overall proposed case conditional probabilities for Classes 3a, 3b and 7 are then calculated as follows.

• • Class 3a Probability = 0.0 + 1.50E-2 + 1.67E-3 = 1.67E-2

• • Class 3b Probability = 0.0 + 1.50E-3 + 1.67E-4 = 1.67E-3

• • Change in Class 7 Probability = 6.72E-1 + 1.07E-1 + 1.07E-2 + 7.46E-2 + 1.18E-2 +

1.18E-3 = 8.77E-1 The proposed case frequencies for Classes 3a, 3b and 7 are calculated by multiplying the overall conditional probabilities with the non-containment-failure (NCF) Class 1 frequency.

to RBG-46226 Page 32 of 53

• • Class 3a Frequency = 1.67E-2

• 4.55E-7 = 7.59E-9

• Class 3b Frequency = 1.67E-3

• 4.55E-7 = 7.59E-10

• Change in Class 7 Frequency = 8.77E-1

• 4.55E-7 = 3.99E-7 The class frequencies for different DWBT intervals are summarized in the following table.

Class 2 and Class 6 frequencies were kept the same as the original ones without considering the DWBT intervals. Class 1 and Class 7 frequencies were calculated as follows:

• Class 1 Frequency = Original NCF Freq - (Class 3a + Class 3b + Change in Class 7)

• Class 7 Frequency = Original Class 7 + Change in Class 7 Table 4.5-4 Class Frequencies for Different DWBT Intervals (Case 2)

Class 3in 10 I in l 1 in 15

1. No failure 3.21 E-07 5.06E-08 4.78E-08

2. Large Isolation Failure 6.08E-10 6.08E-10 6.08E-10 3a. Small Preexisting Liner Breach 8.93E-09 5.06E-09 7.59E-09 3b. Large Preexisting Liner Breach 8.93E-10 5.06E-10 7.59E-10

4. Small Iso Failure (Type B Test) N/A N/A N/A

5. Small Iso Failure (Type C Test) N/A N/A N/A

6. Containment Isolation Failure 4.82E-07 4.82E-07 4.82E-07

7. Severe Accident 3.45E-06 3.72E-06 3.72E-06

8. Bypass N/A N/A N/A Total Frequency 4.26E-06 4.26E-06 4.26E-06 4.5.2 Accident Dose Rate Calculations As indicated before, the evaluation of the DWBT extension will use the accident dose estimates from the evaluation of the ILRT extension. The detailed calculation and a summary of the accident release (person-rem) and the risk (person-rem/year) calculated for each class is contained in Table 4.5-5 and Table 4.5-6.

to RBG-46226 Page 33 of 53 Table 4.5-5 Detailed Accident Release and Risk Calculations (Case 2)

Class I - Person-RemNr Calculation Base Case I in 10 1 in 15 Person-Rem 3.46E+05 3.46E+05 3.46E+05 Frequency 3.21 E-07 5.06E-08 4.78E-08 Person-RemNr 1.11 E-01 1.75E-02 1.66E-02 Class 2 - Person-Rem/Yr Calculation Base Case I in 10 1 in 15 Person-Rem 2.16E+08 2.16E+08 2.16E+08 Frequency 6.08E-10 6.08E-10 6.08E-10 Person-Rem/Yr 1.31 E-01 1.31 E-01 1.31 E-01 Class 3a Person-RemNr Calculation Base Case I in 10 1 in 15 Person-Rem 3.46E+06 3.46E+06 3.46E+06 Frequency 8.93E-09 5.06E-09 7.59E-09 Person-RemlYr 3.09E-02 1.75E-02 2.63E-02 Class 3b Person-RemNr Calculation Base Case I in 10 1 in 15 Person-Rem 1.21 E+07 1.21 E+07 1.21 E+07 Frequency 8.93E-10 5.06E-10 7.59E-10 Person-Rem/Yr 1.08E-02 6.13E-03 9.19E-03 to RBG-46226 Page 34 of 53 Class 6 Person-RemIYr Calculation Base Case I in 10 1 in 15 Person-Rem 3.46E+07 3.46E+07 3.46E+07 Frequency 4.82E-07 4.82E-07 4.82E-07 Person-Rem/Yr 1.67E+01 1.67E+01 1.67E+01 Class 7 Person-Rem/Yr Calculation Base Case 1 in 10 I in 15 Person-Rem 3.46E+07 3.46E+07 3.46E+07 Frequency 3.45E-06 3.72E-06 3.72E-06 Person-RemNr 1.19E+02 1.29E+02 1.29E+02 Change in Class 7 Person-RemNr Calculation Base Case 1 in 10 1 in 15 Person-Rem 3.46E+07 3.46E+07 3.46E+07 Frequency 1.24E-07 3.99E-07 3.99E-07 Person-Rem/Yr 4.31 E+00 1.38E+01 1.38E+01 to RBG-46226 Page 35 of 53 Table 4.5-6 Summary of Accident Release and Risk Calculations (Case 2)

Class Base I in 10 1 in 15

1. No failure 1.11 E-01 1.75E-02 1.66E-02

2. Large Isolation Failure 1.31 E-01 1.31 E-01 1.31 E-01 3a. Small Preexisting Liner Breach 3.09E-02 1.75E-02 2.63E-02 3b. Large Preexisting Liner Breach 1.08E-02 6.13E-03 9.19E-03

4. Small Iso Failure (Type B Test) N/A N/A N/A

5. Small Iso Failure (Type C Test) N/A N/A N/A

6. Containment Isolation Failure 1.67E+01 1.67E+01 1.67E+01

7. Severe Accident 1.19E+02 1.29E+02 1.29E+02

8. Bypass N/A N/A N/A TOTAL Person-Rem/Yr: 1.363E+02 1.457E+02 1.457E+02 Change from BaseLine Person-Rem/yr 9.40E+00 9.41 E+00 Change from 1 in 10 to 1 in 15: 1.09E-02

% increase from Base: 6.90% 6.90%

% Change from 1 in 10 to 1 in 15: 0.01%

ILRT/DWBT Contribution 3.19% 9.50% 9.51%

4.5.3 Changes in LERF and CCFP Calculations The change in LERF for extending the DWBT interval is the increase due to the change in the large pre-existing leak class, Class 3b, and the increase in the portion of Class 7 due to DWBT. As in the previous evaluations, the Class 3a leak size is too small to be considered a LERF. This increase is documented below.

to RBG-46226 Page 36 of 53 Table 4.5-7 Change in LERF (Case 2)

Base 1 in 10 I in 15 Class 3b Frequency 8.93E-10 5.06E-10 7.59E-10 Change in Class 7 Frequency 1.24E-07 3.99E-07 3.99E-07 Total LERF 1.25E-07 4.OOE-07 4.OOE-07 Change from Base 2.74E-07 2.75E-07 Change from I in 10 to 1in 15 2.53E-10 The change in CCFP is considered to be the change in containment failure probability given an accident. This can be calculated as follows:

CCFP = 1 - (Frequency of NCF) / CDF Frequency of NCF = Class 1 frequency + Class 3a frequency The calculations for each DWBT option are summarized below.

Table 4.5-8 Change in CCFP (Case 2)

Class I Class 3a ChangeCag Freq Freq NCF Freq Total CDF CCFP Change from frombase Current Baseline 3.21 E-07 8.93E-09 3.30E-07 4.26E-06 92.25%

1 in 10 5.06E-08 5.06E-09 5.57E-08 4.26E-06 98.69% 6.44%

1 in 15 4.78E-08 7.59E-09 5.54E-08 4.26E-06 98.70% 6.44% 0.01%

4.5.4 Summary of Case 2 Results Table 4.5-9 provides a summary of the results for the extension of the DWBT frequency (in conjunction with the ILRT extension) for Case 3.

to RBG-46226 Page 37 of 53 Table 4.5-9 Summary of DWBT Extension Evaluation Case 2 Results 3 in 10yr 1 in 10yr I in 15yr Total Risk 136.3 145.7 145.7 DWBT/ILRT Risk Contribution (%) 3.19% 9.50% 9.51%

% Change from Base 6.90% 6.90%

% Change from Current 0.01%

LERF value due to DWBT/ILRT 1.25E-07 4.OOE-07 4.00E-07 Change from Base 2.74E-07 2.75E-07 Change from Current 2.53E-10 CCFP 92.25% 98.69% 98.70%

Change from Base 6.44% 6.44%

Change from Current 0.01%

Based on the above results, the extension of the DWBT (in conjunction with an extension of the ILRT) surveillance interval from the current interval of once in 10 years to once in 15 years does not pose a significant increase in risk to the public. The LERF value is within Region 3 of Regulatory Guide 1.174 (very small) guidance and is considered acceptable.

On the other hand, the extension of the DWBT (in conjunction with an extension of the ILRT) surveillance interval from the baseline interval of 3 in 10 years to once in 15 years would result in relatively larger increases in all three risk metrics. However, the change in LERF still falls into the small range as defined by RG 1.174. As shown in the calculations for the current and proposed case conditional probabilities for combination of leakage in Section 4.5.1, all the NCF Class 1 frequency has been virtually turned into the change in Class 7 frequency except that 12.34% of the Class 1 frequency remains Class 1 by crediting containment unit cooler availability. This is very conservative due to the conservative drywell leakage probabilities estimated from the industry data and the embedded conservatism in the GGNS methodology.

4.6 Case 3: Sensitivity Case with Modified NEI Interim Guidance Method, Industry DWBT Data and Crediting Reactor Depressurization to RBG-46226 Page 38 of 53 This sensitivity case was performed with the Modified NEI Interim Guidance Method to address the impact of using the industry DWBT data per NRC request. The availability of either a containment unit cooler or reactor depressurization was credited for this sensitivity case.

4.6.1 Frequency Calculations The method of combining the probability of DWBT leakage and the probability of containment leakage has been discussed in Section 4.2.1 for the GGNS methodology.

The conditional probability of the different combinations of DWB and ILRT leakage are calculated using the following probabilities:

• A probability of 0.292 for a small drywell leak and 0.02 for a large drywell leak by using the Mark IlIl DWBT historical data (see the details in Section 5.1.4);

• A probability of 2.7E-2 for a small containment leak and 2.7E-3 for a large containment leak The probability that a containment unit cooler or reactor depressurization is available is also factored in for certain combinations.

The probability increase factor from the baseline interval (3 in 10 years) to the current interval (1 in 10 years) and the proposed interval (1 in 15 years) are 3.33 and 5.0 respectively based on the NEI Interim Guidance Methodology.

The following tables calculate the conditional probabilities of the combined leakage for the baseline, current and proposed DWBT intervals. The frequencies of Classes 3a, 3b, and 7 are then calculated with the total contribution from different leakage combinations.

to RBG-46226 Page 39 of 53 Table 4.6-1 Conditional Probability of Combined Leakage for Baseline Interval (Case 3)

DW CTT DW Prob CTMT Cmi EdPCas Leakage Combinations Bypass LCeakae Leakage of UC Leakage PCrombined Cassi LaaeLeakage Prob or DEP Prob Prbesint AA' 1 DWLB I La 0.69 NA 0.97 6.68E-01 1 AB' 1 DWLB 10 La 0.69 NA 2.7E-02 1.86E-02 3a AC' I DWLB 35 La 0.69 NA 2.7E-03 1.86E-03 3b BA'1 UC or DEP Available 2.9E-01 82.96% 0.97 2.35E-01 1 10 DWL 8 1 La BA'2 UC&DEP Not Available 2.9E-01 17.04% 0.97 4.82E-02 7 BB'1 UC or DEP Available 2.9E-01 82.96% 2.7E-02 6.53E-03 3a 10 DWLB 10 La BB'2 UC&DEP Not Available 2.9E-01 17.04% 2.7E-02 1.34E-03 7 BC'1 UC or DEP Available 2.9E-01 82.96% 2.7E-03 6.53E-04 3b BC'2 UC&DEP Not Available 2.9E-01 17.04% 2.7E-03 1.34E-04 7 CA'1 UC or DEP Available 2.OE-02 82.96% 0.97 1.61 E-02 1 35 DWLB 1 La CA'2 UC&DEP Not Available 2.OE-02 17.04% 0.97 3.31 E-03 7 CB'1 UC or DEP Available 2.OE-02 82.96% 2.7E-02 4.48E-04 3a 35 DWL 8 10OLa CB'2 UC&DEP Not Available 2.OE-02 17.04% 2.7E-02 9.20E-05 7 CC'1 UC or DEP Available 2.OE-02 82.96% 2.7E-03 4.48E-05 3b CC'2 UC&DEP Not Available 2.OE-02 17.04% 2.7E-03 9.20E-06 7 The overall baseline conditional probabilities for Classes 3a, 3b and 7 are then calculated as follows.

• • Class 3a Probability = 1.86E-2 + 6.53E-3 + 4.48E-4 = 2.56E-2

• • Class 3b Probability = 1.86E-3 + 6.53E-4 + 4.48E-5 = 2.56E-3

• . Change in Class 7 Probability =4.82E-2 + 1.34E-3 + 1.34E-4 + 3.31 E-3 + 9.20E-5 +

9.20E-6 = 5.31 E-2 The baseline frequencies for Classes 3a, 3b and 7 are calculated by multiplying the overall conditional probabilities with the non-containment-failure (NCF) Class 1 frequency.

• e Class 3a Frequency = 2.56E-2

• 4.55E-7 = 1.16E-8

• Class 3b Frequency = 2.56E-3

• 4.55E-7 = 1.16E-9

• • Change in Class 7 Frequency = 5.31 E-2

• 4.55E-7 = 2.42E-8 to RBG-46226 Page 40 of 53 Table 4.6-2 Conditional Probability of Combined Leakage for Current Interval (Case 3)

DW CTT DW Prob CTMT Cmi edPCas Leakage Combinations Bypass CTMT Leakage of UC Leakage pCrobined Cassign Leakage Leakage Prob or DEP Prob mebAsint AA I DWLB 1 La 0.00 NA 0.90 O.OOE+00 I AB' I DWLB 10 La 0.00 NA 9.OE-02 O.OOE+00 3a AC' 1 DWLB 35 La 0.00 NA 9.OE-03 O.OOE+00 3b BA'1 UC or DEP Available 9.3E-01 82.96% 0.90 6.98E-01 1 10 OWLB 1 La BA'2 UC&DEP Not Available 9.3E-01 17.04% 0.90 1.43E-01 7 BBMUC or DEP Available 9.3E-01 82.96% 9.OE-02 6.97E-02 3a 10 OWL 8 10 La BB'2 UC&DEP Not Available 9.3E-01 17.04% 9.OE-02 1.43E-02 7 BC'1 UC or DEP Available 9.3E-01 82.96% 9.OE-03 6.97E-03 3b BC'2 UC&DEP Not Available 9.3E-01 17.04% 9.OE-03 1.43E-03 7 CA'1 UC or DEP Available 6.7E-02 82.96% 0.90 4.98E-02 1 CA'2 UC&DEP Not Available 6.7E-02 17.04% 0.90 1.02E-02 7 CB'1 UC or DEP Available 6.7E-02 82.96% 9.OE-02 4.98E-03 3a 35 OWL 8 10 La CB'2 UC&DEP Not Available 6.7E-02 17.04% 9.OE-02 1.02E-03 7 CC'1 UC or DEP Available 6.7E-02 82.96% 9.0E-03 4.98E-04 3b 35 DWLB 35 La CC'2 UC&DEP Not Available 6.7E-02 17.04% 9.0E-03 1.02E-04 7 The overall current case conditional probabilities for Classes 3a, 3b and 7 are then calculated as follows.

• Class 3a Probability = 0.0 + 6.97E-2 + 4.98E-3 = 7.47E-2

• Class 3b Probability = 0.0 + 6.97E-3 + 4.98E-4 = 7.47E-3

• Change in Class 7 Probability = 1.43E-1 + 1.43E-2 + 1.43E-3 + 1.02E-2 + 1.02E-3 +

1.02E-4 = 1.70E-1 The current case frequencies for Classes 3a, 3b and 7 are calculated by multiplying the overall conditional probabilities with the non-containment-failure (NCF) Class 1 frequency.

• Class 3a Frequency = 7.47E-2

• 4.55E-7 = 3.40E-8

• Class 3b Frequency = 7.47E-3

• 4.55E-7 = 3.40E-9

• Change in Class 7 Frequency = 1.70E-1

• 4.55E-7 = 7.76E-8 to RBG-46226 Page 41 of 53 Table 4.6-3 Conditional Probability of Combined Leakage for Proposed Interval (Case 3)

DW CTT DW Prob CTMT Cmi edPCas Leakage Combinations Bypass LCeTaMkTage Leakage of UC Leakage PCrombined Cassign LaaeLeakage Prob or DEP Prob mebAsint AA' 1 DWLB I La 0.00 NA 0.85 O.OOE+00 1 AB' I DWLB 10 La 0.00 NA 1.4E-01 O.OOE+00 3a AC' I DWLB 35 La 0.00 NA 1.4E-02 O.OOE+00 3b BA'1 UC or DEP Available 9.OE-01 82.96% 0.85 6.36E-01 I 10ODWLB 1ILa BA'2 UC&DEP Not Available 9.OE-01 17.04% 0.85 1.31 E-01 7 BB'1 UC or DEP Available 9.OE-01 82.96% 1.4E-01 1.01 E-01 3a BB'2 UC&DEP Not Available 9.OE-01 17.04% 1.4E-01 2.07E-02 7 BC'1 UC or DEP Available 9.OE-01 82.96% 1.4E-02 1.01 E-02 3b BC'2 UC&DEP Not Available 9.OE-01 17.04% 1.4E-02 2.07E-03 7 CA'1 UC or DEP Available 1.OE-01 82.96% 0.85 7.06E-02 1 35 DWLB 1 La CA'2 UC&DEP Not Available 1.OE-01 17.04% 0.85 1.45E-02 7 CB'1 UC or DEP Available 1.OE-01 82.96% 1.4E-01 1.12E-02 3a 35 OWL 0 10 La CB'2 UC&DEP Not Available 1.OE-01 17.04% 1.4E-01 2.30E-03 7 CC'1 UC or DEP Available 1.OE-01 82.96% 1.4E-02 1.12E-03 3b CC'2 UC&DEP Not Available 1.OE-01 17.04% 1.4E-02 2.30E-04 7 The overall proposed case conditional probabilities for Classes 3a, 3b and 7 are then calculated as follows.

• • Class 3a Probability = 0.0 + 1.01E-1 + 1.12E-2 = 1.12E-1

• Class 3b Probability = 0.0 + 1.O1E-2 + 1.12E-3 = 1.12E-2

• Change in Class 7 Probability = 1.31E-1 + 2.07E-2 + 2.07E-3 + 1.45E-2 + 2.30E-3 +

2.30E-4 = 1.70E-1 The proposed case frequencies for Classes 3a, 3b and 7 are calculated by multiplying the overall conditional probabilities with the non-containment-failure (NCF) Class 1 frequency.

• Class 3a Frequency = 1.12E-1

• 4.55E-7 = 5.1OE-8

• Class 3b Frequency = 1.12E-2

• 4.55E-7 = 5.10E-9

• Change in Class 7 Frequency = 1.70E-1

• 4.55E-7 = 7.76E-8 to RBG-46226 Page 42 of 53 The class frequencies for different DWBT intervals are summarized in the following table.

Class 2 and Class 6 frequencies were kept the same as the original ones without considering the DWBT intervals. Class 1 and Class 7 frequencies were calculated as follows:

• • Class 1 Frequency = Original NCF Freq - (Class 3a + Class 3b + Change in Class 7)

• • Class 7 Frequency = Original Class 7 + Change in Class 7 Table 4.6-4 Class Frequencies for Different DWBT Intervals (Case 3)

Class 3 in 10 1 in 10 I in 15

1. No failure 4.18E-07 3.40E-07 3.22E-07

2. Large Isolation Failure 6.08E-10 6.08E-10 6.08E-10 3a. Small Preexisting Liner Breach 1.16E-08 3.40E-08 5.10E-08 3b. Large Preexisting Liner Breach 1.16E-09 3.40E-09 5.10E-09

4. Small Iso Failure (Type B Test) N/A N/A N/A

5. Small Iso Failure (Type C Test) N/A N/A N/A

6. Containment Isolation Failure 4.82E-07 4.82E-07 4.82E-07

7. Severe Accident 3.35E-06 3.40E-06 3.40E-06

8. Bypass N/A N/A N/A Total Frequency 4.26E-06 4.26E-06 4.26E-06 4.6.2 Accident Dose Rate Calculations As indicated before, the evaluation of the DWBT extension will use the accident dose estimates from the evaluation of the ILRT extension. The detailed calculation and a summary of the accident release (person-rem) and the risk (person-rem/year) calculated for each class is contained in Table 4.6-5 and Table 4.6-6.

to RBG-46226 Page 43 of 53 Table 4.6-5 Detailed Accident Release and Risk Calculations (Case 3)

Class I - Person-RemNr Calculation Base Case I in10 I 1in15 Person-Rem 3.46E+05 3.46E+05 3.46E+05 Frequency 4.18E-07 3.40E-07 3.22E-07 Person-Rem/Yr 1.45E-01 1.18E-01 1.1IE-01 Class 2 - Person-RemNr Calculation Base Case I in10 I in 15 Person-Rem 2.16E+08 2.16E+08 2.16E+08 Frequency 6.08E-10 6.08E-10 6.08E-10 Person-Rem/Yr 1.31 E-01 1.31 E-01 1.31 E-01 Class 3a Person-Rem/Yr Calculation Base Case 1in 10 Iin15 Person-Rem 3.46E+06 3.46E+06 3.46E+06 Frequency 1.16E-08 3.40E-08 5.1OE-08 Person-Rem/Yr 4.03E-02 1.18E-01 1.77E-01 Class 3b Person-RemNr Calculation Base Case 1in10 Iin 15 Person-Rem 1.21 E+07 1.21 E+07 1.21 E+07 Frequency 1.16E-09 3.40E-09 5.1OE-09 Person-RemNr 1.41 E-02 4.12E-02 6.18E-02 to RBG-46226 Page 44 of 53 Class 6 Person-RemlYr Calculation Base Case I Iin 10 in15 Person-Rem 3.46E+07 3.46E+07 3.46E+07 Frequency 4.82E-07 4.82E-07 4.82E-07 Person-RemNr 1.67E+01 1.67E+01 1.67E+01 Class 7 Person-Rem/Yr Calculation Base Case l in 10 I in15 Person-Rem 3.46E+07 3.46E+07 3.46E+07 Frequency 3.35E-06 3.40E-06 3.40E-06 Person-Rem/Yr 1.16E+02 1.18E+02 1.18E+02 Change in Class 7 Person-Rem/Yr Calculation Base Case in 10 I in15 Person-Rem 3.46E+07 3.46E+07 3.46E+07 Frequency 2.42E-08 7.76E-08 7.76E-08 Person-Rem/Yr 8.37E-01 2.69E+00 2.69E+00 to RBG-46226 Page 45 of 53 Table 4.6-6 Summary of Accident Release and Risk Calculations (Case 3)

Class Base 1 in 10 1 in 15

1. No failure 1.45E-01 1.18E-01 1.11 E-01

2. Large Isolation Failure 1.31 E-01 1.31 E-01 1.31 E-01 3a. Small Preexisting Liner Breach 4.03E-02 1.18E-01 1.77E-01 3b. Large Preexisting Liner Breach 1.41 E-02 4.12E-02 6.18E-02

4. Small Iso Failure (Type B Test) N/A N/A N/A

5. Small iso Failure (Type C Test) N/A N/A N/A

6. Containment Isolation Failure 1.67E+01 1.67E+01 1.67E+01

7. Severe Accident 1.16E+02 1.18E+02 1.18E+02

8. Bypass N/A N/A N/A TOTAL Person-Rem/Yr: I 1.329E+02 l 1.348E+02 1.349E+02 Change from BaseLine Person-Rem/yr 1.93E+00 2.OOE+00 Change from 1 in 10 to 1 in 15: 7.30E-02

% increase from Base: r 1.45% 1.50%

% Change from 1 in 10 to 1 in 15: 0.05%

ILRT/DWBT Contribution l 0.67% l 2.11% 2.17%

4.6.3 Changes in LERF and CCFP Calculations The change in LERF for extending the DWBT interval is the increase due to the change in the large pre-existing leak class, Class 3b, and the increase in the portion of Class 7 due to DWBT. As in the previous evaluations, the Class 3a leak size is too small to be considered a LERF. This increase is documented below.

to RBG-46226 Page 46 of 53 Table 4.6-7 Change in LERF (Case 3)

Base I in 10 1 in 15 Class 3b Frequency 1.16E-09 3.40E-09 5.1OE-09 Change in Class 7 Frequency 2.42E-08 7.76E-08 7.76E-08 Total LERF 2.53E-08 8.10E-08 8.27E-08 Change from Base 5.56E-08 5.73E-08 Change from 1 in 10 to I in 15 1.70E-09 The change in CCFP is considered to be the change in containment failure probability given an accident. This can be calculated as follows:

CCFP = 1 - (Frequency of NCF) / CDF Frequency of NCF = Class 1 frequency + Class 3a frequency The calculations for each DWBT option are summarized below.

Table 4.6-8 Change in CCFP (Case 3)

Clas 3aChange 1 las fromg CFarss CFrsesq3aFreqNCF Freq FreqCurrent Total CDF CCFP from base Baseline 4.18E-07 1.16E-08 4.30E-07 4.26E-06 89.91%

1 in 10 3.40E-07 3.40E-08 3.74E-07 4.26E-06 91.21% 1.31%

1 in 15 3.22E-07 5.10E-08 3.73E-07 4.26E-06 91.25% 1.35% 0.04%

4.6.4 Summary of Case 3 Results Table 4.6-9 provides a summary of the results for the extension of the DWBT frequency (in conjunction with the ILRT extension) for Case 3.

to RBG-46226 Page 47 of 53 Table 4.6-9 Summary of DWBT Extension Evaluation Case 3 Results 3in 10yr I in 10yr 1 in 15yr Total Risk 132.9 134.8 134.9 DWBT/ILRT Risk Contribution (%) 0.67% 2.11% 2.17%

% Change from Base 1.45% 1.50%

% Change from Current 0.05%

LERF value due to DWBT/ILRT 2.53E-08 8.10E-08 8.27E-08 Change from Base 5.56E-08 5.73E-08 Change from Current 1.70E-09 CCFP 89.91% 91.21% 91.25%

Change from Base 1.31% 1.35%

Change from Current 0.04%

Based on the above results, the extension of the DWBT (in conjunction with an extension of the ILRT) surveillance interval from the current interval of once in 10 years to once in 15 years does not pose a significant increase in risk to the public. The LERF value is within Region 3 of Regulatory Guide 1.174 (very small) guidance and is considered acceptable.

4.7 Results Summary Tables 4.7-1 through 4.7-3 provide a summary of all the DWBT extension evaluation cases.

to RBG-46226 Page 48 of 53 Table 4.7-1 Summary of DWBT Extension Evaluation Results (Total Risk)

Total Risk (Person-Rem/yr) DWBT/ILRT Contribution %Change from Case Base

____ ___ ___ ___ ____ ___ C hange from Base Current Proposed Base Current Proposed Current Proposed Current (3 in 10) (1 in 10) (1 in 15) (3 in 10) (1 in 10) (1 in 15) (1 in 10) (1 in 15) 1 132.4 133.5 134.2 0.35% 1.16% 1.71% 0.80% 1.36% 0.56%

2 136.3 145.7 145.7 3.19% 9.50% 9.51% 6.90% 6.90% 0.01%

3 132.9 134.8 134.9 0.67% 2.11% 2.17% 1.45% 1.50% 0.05%

Table 4.7-2 Summary of DWBT Extension Evaluation Results (LERF)

LERF due to DWBT/ILRT Change from Base Case # _ _ _ _ _ _ __ Change from Base Current Proposed Current Proposed Current (3 in 10) (1 in 10) (1 in 15) (1 in 10) (1 in 15) 1 1.30E-08 4.32E-08 6.46E-08 3.02E-08 5.16E-08 2.14E-08 2 1.25E-07 4.OOE-07 4.OOE-07 2.74E-07 2.75E-07 2.53E-10 3 2.53E-08 8.10E-08 8.27E-08 5.56E-08 5.73E-08 1.70E-09 to RBG-46226 Page 49 of 53 Table 4.7-3 Summary of DWBT Extension Evaluation Results (CCFP)

CCFP Change from Base Case# Change from Current Base Current Proposed Current Proposed (3 in 10) (1in 10) (1in 15) (1 in 10) (1 in 15) 1 89.62% 90.33% 90.83% 0.71% 1.21% 0.50%

2 92.25% 98.69% 98.70% 6.44% 6.44% 0.01%

3 89.91% 91.21% 91.25% 1.31% 1.35% 0.04%

5.0 Monitoring Drywell Leakage On January 29, 1996, the NRC issued an amendment to the RBS (Amendment 87 to Facility Operating License No. NPF-47 Docket No. 50-458) that revised the TS SR 3.6.5.1.3 to allow a performance-based drywell bypass leakage surveillance test. Per the NRC request, RBS committed to qualitatively assess the leaktightness of the drywell once each operating cycle.

The assessment is performed once each cycle. It involves trending drywell pressure vs.

containment pressure. Because of normal air system leakage in containment, RBS must periodically vent the containment. By trending drywell pressure changes vs. containment pressure changes and observing the time it takes for the pressure to recover, a gross evaluation of drywell integrity is determined. This assessment provides reasonable assurance that the drywell can perform its safety function; that is, remain operable.

6.0 Conclusion An evaluation of extending the RBS DWBT surveillance frequency from once in 10 years to once in 15 years has been performed using the modified GGNS DWBT evaluation methodologies which were based on the ILRT methodologies. This evaluation assumed that the DWBT frequency was being adjusted in conjunction with the ILRT frequency, which has already been extended to once in 15 years at RBS. Three cases, one base case and two sensitivity cases, have been analyzed. The case descriptions are provided in Section 4.3.2.

A summary of the results from all cases is provided in Section 4.7.

The change from the current interval (1 in 10 years) to the proposed one (1 in 15 years) is not risk significant based on the guidance of Regulatory Guide 1.174. The resulting changes in the three risk metrics are summarized as follows:

to RBG-46226 Page 50 of 53

• The maximum total dose risk percentage change for Cases 1 through 3 is 0.56%.

• The maximum LERF change due to DWBT/ILRT interval extension for Cases 1 through 3 is 2.14E-8/yr.

• The maximum CCFP change due to DWBT/ILRT interval extension for Cases 1 through 3 is 0.50%.

The most realistic case is Case 1 with the modified NEI interim guidance method. Based on the Case 1 results, the change from the baseline interval (3 in 10 years) to the proposed one (1 in 15 years) is not risk significant with the resulting changes in the three risk metrics as follows:

• The total dose risk percentage change for Case 1 is 1.36%.

• The LERF change due to DWBT/ILRT interval extension for Case 1 is 5.16E-8/yr.

• The CCFP change due to DWBT/ILRT interval extension for Case 1 is 1.21 %.

Therefore, the results from these analyses indicate that the proposed extension of the DWBT frequency has a minimal impact on plant risk and is acceptable.

7.0 REGULATORY ANALYSIS

7.1 Applicable Regulatory Requirements/Criteria The proposed changes have been evaluated to determine whether applicable regulations and requirements continue to be met.

Entergy has determined that the proposed changes do not require any exemptions or relief from regulatory requirements, other than the TS, and do not affect conformance with any General Design Criterion (GDC) differently than described in the Updated Safety Analysis Report (USAR.)

The requirement to perform a drywell bypass leakage rate test is derived from 10 CFR 50.36.

10 CFR 50.36(c)(3), "Surveillance requirements," requires the inclusion in the TS, "tests, calibrations or inspections to assure that the necessary quality of systems and components is maintained, that facility operation will be with safety limits, and that the limiting conditions for operation will be met."

10 CFR 50.36(c)(5), "Administrative controls," requires that "provisions relating to organization and management, procedures, recordkeeping, review and audit, and reporting necessary to assure operation of the facility in a safe manner" will be included in the TS. The Appendix J Testing Program is included in this section. 10 CFR 50, Appendix J, Option B,Section V.B, "Implementation" requires that the implementation document used to develop a performance-based leakage testing program be included by general reference in the TS.

As the proposed change is for test interval extensions, Entergy is justifying the request on a risk-informed basis in accordance with Regulatory Guide (RG) 1.174, "An Approach for Using Probabilistic Risk Assessment in Risk-Informed Decisions on Plant-Specific Changes to the Licensing Basis." The proposed change has been found to satisfy the key principles identified in RG 1.174 for risk-informed changes. Those principles are:

to RBG-46226 Page 51 of 53

• the change satisfies current regulations

• the change is consistent with the defense-in-depth philosophy

• the change maintains sufficient safety margins

• the increase in risk is small and is consistent with the NRC Safety Goal Policy Statement

• the impact of the proposed change will be monitored using performance measurement strategies (as a part of the current performance-based testing program).

7.2 No Significant Hazards Consideration Entergy Operations, Inc. has evaluated whether or not a significant hazards consideration is involved with the proposed amendment(s) by focusing on the three standards set forth in 10 CFR 50.92, 'Issuance of amendment," as discussed below:

Entergy Operations, Inc. is proposing to revise the River Bend Station (RBS) Administrative Technical Specifications regarding drywell bypass testing. The proposed change will revise the improved RBS Technical Specification (TS) SR 3.6.5.1.3 regarding drywell bypass leakage testing (DWBT). The change would allow for an extended interval for performance of the DWBT. The effect of this request will be a one-time extension of the interval between tests from 10 years to 15 years.

Entergy Operations, Inc. has evaluated whether or not a significant hazards consideration is involved with the proposed amendments by focusing on the three standards set forth in 10 CFR 50.92, "Issuance of amendment," as discussed below:

1. Does the proposed change involve a significant increase in the probability or consequences of an accident previously evaluated?

Response: No.

The proposed amendment to TS SR 3.6.5.1.3 adds a one-time extension to the current interval for the DWBT. The current interval of ten years, based on past performance, would be extended on a one-time basis to 15-years from the date of the last test. The proposed extension to the DWBT cannot increase the probability of an accident since there are no design or operating changes involved and the test is not an accident initiator. The proposed extension of the test interval does not involve a significant increase in the consequences since analysis has shown that, the proposed extension of the DWBT frequency has a minimal impact on plant risk. Therefore, the proposed change does not involve a significant increase in the probability or consequences of an accident previously evaluated.

2. Does the proposed change create the possibility of a new or different kind of accident from any accident previously evaluated?

Response: No.

to RBG-46226 Page 52 of 53 The proposed extension to the interval for the DWBT does not involve any design or operational changes that could lead to a new or different kind of accident from any accidents previously evaluated. The tests are not being modified, but are only being performed after a longer interval. The proposed change does not involve a physical alteration of the plant (no new or different type of equipment will be installed) or a change in the methods governing normal plant operation. Therefore, the proposed change does not create the possibility of a new or different kind of accident from any previously evaluated.

3. Does the proposed change involve a significant reduction in a margin of safety?

Response: No.

An evaluation of extending the DWBT surveillance frequency from once in 10 years to once in 15 years has been performed using methodologies based on the ILRT methodologies. This evaluation assumed that the DWBT frequency was being adjusted in conjunction with the ILRT frequency. This analysis used realistic, but still conservative, assumptions with regard to developing the frequency of leakage classes associated with the DWBT. The results from this conservative analysis indicates that the proposed extension of the DWBT frequency has a minimal impact on plant risk and therefore, the proposed change does not involve a significant reduction in a margin of safety.

Based on the above, Entergy concludes that the proposed amendment(s) present no significant hazards consideration under the standards set forth in 10 CFR 50.92(c), and, accordingly, a finding of 'no significant hazards consideration" is justified.

7.3 Environmental Considerations The proposed amendment does not involve, (i) a significant hazards consideration, (ii) a significant change in the types or significant increase in the amounts of any effluent that may be released offsite, or (iii) a significant increase in individual or cumulative occupational radiation exposure. Accordingly, the proposed amendment meets the eligibility criterion for categorical exclusion set forth in 10 CFR 51.22(c)(9). Therefore, pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the proposed amendment.

8.0 PRECEDENCE This request is similar to a request from Grand Gulf Nuclear Station currently under consideration by the NRC as referenced below.

to RBG-46226 Page 53 of 53

9.0 REFERENCES

Letter from Mr. J. C. Roberts to USNRC Dated May 12, 2003 -- One-time Extension of the Integrated Leak Rate Test and Drywell Bypass Test for Grand Gulf Nuclear Station.

Attachment 2 RGB-46226 Proposed Technical Specification Changes (mark-up) to RGB-46226 Page 1 of2 Drywell 3.6.5.1 SURVEILLANCE REQUIREMENTS (conflnued)

SURVEILLANCE FREQUENCY

SR 3.6.5.1.3 Verify bypass leakage Is less than or equal to the -- NOTE -

bypass leakage limit. SR 3.0.2 Is not applicable for However, during the first unit startup following extensions > 12 bypass leakage testing performed in accordance months with this SR, the acceptance criterion is s 10% of the drywell bypass leakage limit.

24 months following 2 consecutive tests with bypass leakage greater than the bypass leakage limit until 2 consecutive tests are less than or equal to the bypass leakage limit AND 48 months following a test with bypass leakage greater than the bypass leakage limit AND

=ns eT_ .

120 monthsD RIVER SEND 3.6-61 Amendment No. 84,87 to RGB-46226 Page 2 of2 Insert A

...except that the next drywell bypass leak rate test performed after the June 24, 1994 test shall be performed no later than June 23, 2009.

Attachment 3 RBG-46226 Changes to Technical Specification Bases Pages For Information Only to RGB-46226 Page 1 of 1 Drywell B 3.6.5.1 BASES SURVEILLANCE SR 3.6.5.1.3 REQUIREMENTS (continued) The analyses in Reference 1 are based on a maximum drywell bypass leakage. This Surveilance ensures that the actual drywell bypass leakage is less than or equal to the acceptable NJk design value of 1.0 ft. As left drywell bypass leakage, prior to the first startup after performing a required drywell bypass leakage test. Isrequired to be s 1 0%of the drywell bypass leakage limit. At all other times between required drywell leakage rate tests, the acceptance crIteria Is based on design Ah- At the design A/+4 the containment temperature and pressurization response are bounded by the assumptions of the safety analysis. This surveillance Is performed a' least once every 10 years on a performance basedrequen 9 he frequency is consistent with the c mIg the es, risk of high radiation exposure, and the IS .?C b e Cf°v 't remote possibility that sufficient component failures will occur such that 6OC'oj-jc 'l i L q.s 1the dryWell bypass leakage lmit will be exceeded. If during the eS' performance of this required Surveilance the drywell bypass leakage rate U

LX 7 o e ad aoD1is greater than the drywall bypass leakage limit, the Surveillance 31uJ

/ Frequency IsIncreased to every 48 months. If during the performance of the subsequent consecutive Surveillance the drywell bypass leakage rate is less than or equal to the drywell bypass leakage limit, the 10 year Frequency may be resumed. If during the performance of two consecutive Surveillances the drywell bypass leakage Is greater than the drywell bypass leakage limit, the Surveillance Frequency Is Increased to at least once every 24 months. The 24 month Frequency Is maintained untl during the performance of two consecutive Surveillances the drywell bypass leakage rate is less than or equal to the drywell bypass leakage limit. at which time the 10 year Frequency may be resumed. For two Surveillances to be considered consecutive, the Surveillances must be performed at least 12 months apart. Since the frequency Is performance based, the Frequency was concluded to be acceptable from a reliability standpoint.

SR 36,5.1.4 The exposed accessible drywell Interior and exterior surfaces are Inspected to ensure there are no apparent physical defects that would prevent the drywall from (continued)

RIVER BEND B 3.6-120 Revision No. 2.4