TSTF-07-22, TSTF-478, Revision 2, BWR Technical Specification Changes That Implement the Revised Rule for Combustible Gas Control.

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TSTF-478, Revision 2, BWR Technical Specification Changes That Implement the Revised Rule for Combustible Gas Control.
ML071920140
Person / Time
Site: Technical Specifications Task Force
Issue date: 07/10/2007
From: Gambrell R, Joseph Messina, Millar D, Yates B
Babcock & Wilcox, BWR Owners Group, Combustion Engineering, PWR Owners Group, Technical Specifications Task Force
To:
Document Control Desk, Office of New Reactors
References
TSTF-07-22, TSTF-478, Rev 2
Download: ML071920140 (36)
v • d • e


Text

TECHNICAL SPECIFICATIONS TASK FORCE TSTF A JOINT OWNERS GROUP ACTIVITY July 10, 2007 TSTF-07-22 PROJ0753 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001

SUBJECT:

TSTF-478, Revision 2, "BWR Technical Specification Changes that Implement the Revised Rule for Combustible Gas Control"

REFERENCE:

Letter from T. Kobetz (NRC) to the TSTF, "Denial Of TSTF-478, Revision 1,

'BWR Technical Specification Changes that Implement the Revised Rule for Combustible Gas Control'," dated May 8, 2007.

Dear Sir or Madam:

Enclosed for NRC review is Revision 2 of TSTF-478, "BWR Technical Specification Changes that Implement the Revised Rule for Combustible Gas Control."

In the referenced letter, the NRC provided a Safety Evaluation which accepted three of the five changes in TSTF-478 and rejected two of the changes. The attached revision of TSTF-478 includes only the three accepted changes.

Any NRC review fees associated with the review of TSTF-478 should continue to be billed to the Boiling Water Reactor Owners Group.

We request that the Traveler changes applicable to BWR/4 plants be made available under the Consolidated Line Item Improvement Process. The Traveler changes applicable to BWR/6 plants only affect the Technical Specifications Bases and their adoption does not require a plant-specific license amendment request.

11921 Rockville Pike, Suite 100, Rockville, MD 20852 Phone: 301-984-4400, Fax: 301-984-7600 Email: tstf@excelservices.com Administered by EXCEL Services Corporation

TSTF 07-22 July 10, 2007 Page 2 Should you have any questions, please do not hesitate to contact us.

Bert Yates (PWROG/W) John Messina (BWROG)

Dana Millar (PWROG/CE) Reene' Gambrell (PWROG/B&W)

Enclosure cc: Tim Kobetz, Technical Specifications Branch, NRC Ross Telson, Technical Specifications Branch, NRC Matthew Hamm, Technical Specifications Branch, NRC

BWROG-98, Rev. 2 TSTF-478, Rev. 2 Technical Specification Task Force Improved Standard Technical Specifications Change Traveler BWR Technical Specification Changes that Implement the Revised Rule for Combustible Gas Control NUREGs Affected: 1430 1431 1432 1433 1434 Classification 1) Technical Change Recommended for CLIIP?: Yes Correction or Improvement: Improvement NRC Fee Status: Not Exempt Benefit: Retires Equipment Industry

Contact:

John Messina, (330) 384-5878, jmessina@firstenergycorp.com See attached.

Revision History OG Revision 0 Revision Status: Closed Revision Proposed by: BWROG Revision

Description:

Original Issue Owners Group Review Information Date Originated by OG: 10-May-04 Owners Group Comments (No Comments)

Owners Group Resolution: Superceeded Date: 17-May-04 OG Revision 1 Revision Status: Closed Revision Proposed by: BWROG Revision

Description:

Complete replacement of Revision 0. Revised title. In addition to the original change to eliminate CAD, added changes to Primary Containment Oxygen Concentration, Primary Containment and Drywell Hydrogen Ignitors, Drywell Cooling System Fans, and Drywell Purge System.

Owners Group Review Information Date Originated by OG: 12-Aug-04 Owners Group Comments (No Comments)

Owners Group Resolution: Approved Date: 06-Oct-04 TSTF Review Information TSTF Received Date: 06-Oct-04 Date Distributed for Review 06-Oct-04 OG Review Completed: BWOG WOG CEOG BWROG 10-Jul-07 Traveler Rev. 3. Copyright (C) 2006, EXCEL Services Corporation. Use by EXCEL Services associates, utility clients, and the U.S. Nuclear Regulatory Commission is granted. All other use without written permission is prohibited.

BWROG-98, Rev. 2 TSTF-478, Rev. 2 OG Revision 1 Revision Status: Closed TSTF Comments:

TSTF approved in principle at the August 25 TSTF meeting. BWROG chairman to provide additional editorial comments. To redistribute to BWROG TSICC for confirmation.

TSTF Resolution: Superceeded Date: 06-Feb-05 OG Revision 2 Revision Status: Closed Revision Proposed by: BWROG Revision

Description:

Various editorial improvements.

Owners Group Review Information Date Originated by OG: 07-Feb-05 Owners Group Comments (No Comments)

Owners Group Resolution: Approved Date: 21-Mar-05 TSTF Review Information TSTF Received Date: 21-Mar-05 Date Distributed for Review 21-Mar-05 OG Review Completed: BWOG WOG CEOG BWROG TSTF Comments:

(No Comments)

TSTF Resolution: Approved Date: 23-Apr-05 NRC Review Information NRC Received Date: 25-Apr-05 NRC Comments:

NRC provided RAI on 11/9/06. TSTF responded on 2/7/07. In response to RAI #3, the TSTF stated that they would withdraw the change to NUREG-1434 (BWR/6), Specification 3.6.3.2, to delete Required Action B.2.

Final Resolution: Superceded by Revision TSTF Revision 1 Revision Status: Closed Revision Proposed by: TSTF Revision

Description:

NRC provided RAI on 11/9/06. TSTF responded on 2/7/07. In response to RAI #3, the TSTF stated that they would withdraw the change to NUREG-1434 (BWR/6), Specification 3.6.3.2, to delete Required Action B.2.

This revision makes that change.

TSTF Review Information 10-Jul-07 Traveler Rev. 3. Copyright (C) 2006, EXCEL Services Corporation. Use by EXCEL Services associates, utility clients, and the U.S. Nuclear Regulatory Commission is granted. All other use without written permission is prohibited.

BWROG-98, Rev. 2 TSTF-478, Rev. 2 TSTF Revision 1 Revision Status: Closed TSTF Received Date: 07-Feb-07 Date Distributed for Review 07-Feb-07 OG Review Completed: BWOG WOG CEOG BWROG TSTF Comments:

(No Comments)

TSTF Resolution: Approved Date: 20-Feb-07 NRC Review Information NRC Received Date: 20-Feb-07 Date of NRC Letter: 08-May-07 Final Resolution: NRC Rejects: TSTF to Revise TSTF Revision 2 Revision Status: Active Revision Proposed by: BWROG Revision

Description:

Pursuant to the May 8, 2007 letter from the NRC, TSTF-478, Revision 2, is revised to include only the following changes:

Delete the BWR/4 Containment Atmosphere Dilution System Specification, Delete Required Action B.1 of the BWR/4 Drywell Cooling System Fans Specification, and Revise the BWR/6 Drywell Purge System Bases.

The TSTF-478, Revision 1, changes regarding Primary Containment Oxygen Concentration and Primary Containment and Drywell Hydrogen Igniters are removed from TSTF-478, Revision 2.

Owners Group Review Information Date Originated by OG: 11-Jun-07 Owners Group Comments (No Comments)

Owners Group Resolution: Approved Date: 28-Jun-07 TSTF Review Information TSTF Received Date: 28-Jun-07 Date Distributed for Review 28-Jun-07 OG Review Completed: BWOG WOG CEOG BWROG TSTF Comments:

(No Comments)

TSTF Resolution: Approved Date: 10-Jul-07 NRC Review Information NRC Received Date: 10-Jul-07 10-Jul-07 Traveler Rev. 3. Copyright (C) 2006, EXCEL Services Corporation. Use by EXCEL Services associates, utility clients, and the U.S. Nuclear Regulatory Commission is granted. All other use without written permission is prohibited.

BWROG-98, Rev. 2 TSTF-478, Rev. 2 TSTF Revision 2 Revision Status: Active Affected Technical Specifications Bkgnd 3.6.3.1 Bases Drywell Cooling System Fans NUREG(s)- 1433 Only S/A 3.6.3.1 Bases Drywell Cooling System Fans NUREG(s)- 1433 Only Appl. 3.6.3.1 Bases Drywell Cooling System Fans NUREG(s)- 1433 Only Ref. 3.6.3.1 Bases Drywell Cooling System Fans NUREG(s)- 1433 Only Action 3.6.3.1.A Bases Drywell Cooling System Fans NUREG(s)- 1433 Only Action 3.6.3.1.B Drywell Cooling System Fans NUREG(s)- 1433 Only Action 3.6.3.1.B Bases Drywell Cooling System Fans NUREG(s)- 1433 Only 3.6.3.3 CAD System NUREG(s)- 1433 Only Change

Description:

Deleted 3.6.3.3 Bases CAD System NUREG(s)- 1433 Only Change

Description:

Deleted Bkgnd 3.6.3.2 Bases Drywell Purge System NUREG(s)- 1434 Only S/A 3.6.3.2 Bases Drywell Purge System NUREG(s)- 1434 Only Appl. 3.6.3.2 Bases Drywell Purge System NUREG(s)- 1434 Only Ref. 3.6.3.2 Bases Drywell Purge System NUREG(s)- 1434 Only Action 3.6.3.2.A Bases Drywell Purge System NUREG(s)- 1434 Only Action 3.6.3.2.B Bases Drywell Purge System NUREG(s)- 1434 Only 10-Jul-07 Traveler Rev. 3. Copyright (C) 2006, EXCEL Services Corporation. Use by EXCEL Services associates, utility clients, and the U.S. Nuclear Regulatory Commission is granted. All other use without written permission is prohibited.

TSTF-478, Rev. 2 1.0 Description The Nuclear Regulatory Commission (NRC) has revised 10 CFR 50.44 to amend its standards for combustible gas control in light-water-cooled power reactors. The Commission eliminated the design basis loss of coolant accident (LOCA) hydrogen release from 50.44 and consolidated the requirements for hydrogen and oxygen monitoring to 50.44, while relaxing safety classifications and licensee commitments to certain design and qualification criteria. TSTF-447, Elimination of Hydrogen Recombiners and Change to Hydrogen and Oxygen Monitors, implemented the majority of the Technical Specification (TS) changes resulting from this rule change. Specifically, TSTF-447 provided model changes to permit the NRC to efficiently process amendments to remove requirements for hydrogen recombiners, and hydrogen and oxygen monitors from TS. TSTF-447 was approved for adoption using the Consolidated Line Item Improvement Process (CLIIP) on September 25, 2003, and many Boiling Water Reactors (BWR) have submitted TS changes to adopt the TSTF.

During the comment period for the 50.44 rule change, the Industry commented that BWRs with Mark I Containment designs either use a Containment Atmospheric Dilution (CAD) System or Hydrogen Recombiners, and that both systems would no longer be required under the revised standards for combustible gas control. However, since the proposed rule change to 50.44 and the associated model safety evaluation did not specifically address elimination of the CAD System specification, the Industry agreed to request elimination of the CAD system separate from TSTF-447.

Subsequently, an additional inconsistency between the revised 50.44 rule and the BWR Improved Standard Technical Specifications (ISTS) was discovered. Namely, BWR/4 Specification 3.6.3.1, Drywell Cooling System Fans, contains a Required Action to "Verify by administrative means that the hydrogen control function is maintained." The alternate hydrogen control functions (e.g., hydrogen recombiners or CAD systems) are intended to control a design basis LOCA hydrogen release. These functions are eliminated from the TS consistent with the 10 CFR 50.44 rule change that eliminated the design basis hydrogen release. The TS requirements for hydrogen recombiners were previously deleted by TSTF-447 and the CAD system requirements are proposed to be deleted by this Traveler. Therefore, this Traveler corrects the ISTS by eliminating the subject alternate hydrogen control function found acceptable in TSTF-447.

2.0 Proposed Change BWR/4 Specification 3.6.3.3, CAD system, and the associated Bases, are deleted from the BWR/4 ISTS. Note that the Specification is deleted and not relocated to licensee control. There are no subsequent specifications which must be renumbered. There are no reference changes required in other specifications due to this deletion.

BWR/4 Specification 3.6.3.1, Drywell Cooling System Fans, is revised to eliminate Required Action B.1. Subsequent Required Actions are renumbered. The Bases are revised to reflect this change and other changes required by the 50.44 rule change.

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TSTF-478, Rev. 2 BWR/6 Specification 3.6.3.2, Drywell Purge System, Bases are revised to eliminate references to Design Basis Accidents while adding references to accidents.

3.0 Background

In the revised 10 CFR 50.44 rule, the Commission eliminated the requirements for hydrogen recombiners and hydrogen purge systems, and relaxed the requirements for hydrogen and oxygen monitoring equipment to make them commensurate with their risk significance.

Installation of hydrogen recombiners and/or vent and purge systems originally required by 50.44 (b)(3) was intended to address the limited quantity and rate of hydrogen generation that was postulated from a design basis LOCA. In the basis for the rule change, the Commission found that this hydrogen release is not risk significant because the design basis LOCA hydrogen release does not contribute to the conditional probability of a large release up to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> after the onset of core damage. In addition, the Commission found that these systems were ineffective at mitigating hydrogen releases from risk significant accident sequences that could threaten containment integrity.

The Commission noted that the regulatory analysis for the rulemaking found the cost of maintaining the recombiners exceeded the benefits of retaining them to prevent containment failure sequences that progress to the very late time frame. The Commission further noted that the "NRC believes that this conclusion would also be true for the backup hydrogen purge system even though the cost of the hydrogen purge system would be much lower because the system also is needed to inert the containment".

While the rule change was broad in its implications, the TS changes that were approved by the NRC (TSTF-447) in association with the rule change were relatively narrow and only addressed containment gas monitoring instrumentation requirements and the elimination of the hydrogen recombiner TS. Other justifiable TS changes were identified prior to and subsequent to the completion of the rule change. However, revision of the rule change package to address these other issues would have delayed the rule change, so the Industry and the NRC agreed to address the other ISTS changes related to the 50.44 rule change in a separate Traveler.

TSTF-478, Revisions 0 and 1, contained additional changes related to post-accident hydrogen control. In a letter dated May 8, 2007 (Reference 4), the NRC stated that three of the five changes in TSTF-478, Revision 1, were acceptable but that two were denied. Revision 2 of TSTF-478 contains only the three changes in TSTF-478, Revision 1, that the NRC found acceptable.

4.0 Technical Analysis Elimination of the CAD System As a result of the requirements originally imposed by 10 CFR 50.44, BWRs with Mark I containment designs either installed hydrogen recombiners or CAD systems to meet requirements for hydrogen control. To ensure that a combustible gas mixture does not occur, oxygen concentration is kept < 5.0 volume percent (v/o), or hydrogen concentration is kept Page 2

TSTF-478, Rev. 2

< 4.0 v/o. Hydrogen recombiners work to reduce the combustible gas concentration in the primary containment by recombining hydrogen and oxygen to form water vapor. The CAD System functions to maintain combustible gas concentrations within the primary containment at or below the flammability limits following a postulated loss of coolant accident (LOCA) by diluting hydrogen and oxygen with nitrogen.

The following is an excerpt from the BWR/4 NUREG-1433 containing the TS BASES for BWRs with Mark I Containments who use hydrogen recombiners or CAD systems. By comparing these discussions side by side, it is evident that the two systems accomplish the same function, but accomplish the task via different systems.

BWR-4 Hydrogen Recombiner BASES (B BWR-4 CAD BASES (B 3.6.3.3) 3.6.3.1)

BACKGROUND BACKGROUND The primary containment hydrogen recombiner The CAD System functions to maintain eliminates the potential breach of primary combustible gas concentrations within the containment due to a hydrogen oxygen reaction primary containment at or below the and is part of combustible gas control required flammability limits following a postulated loss by 10 CFR 50.44, "Standards for Combustible of coolant accident (LOCA) by diluting Gas Control Systems in Light-Water-Cooled hydrogen and oxygen with nitrogen. To ensure Reactors" (Ref. 1), and GDC 41, "Containment that a combustible gas mixture does not occur, Atmosphere Cleanup" (Ref. 2). The primary oxygen concentration is kept < [5.0] volume containment hydrogen recombiner is required percent (v/o), or hydrogen concentration is to reduce the hydrogen concentration in the kept < 4.0 v/o.

primary containment following a loss of coolant accident (LOCA). The primary The CAD System is manually initiated and containment hydrogen recombiner consists of two independent, 100% capacity accomplishes this by recombining hydrogen subsystems. Each subsystem includes a liquid and oxygen to form water vapor. The vapor nitrogen supply tank, ambient vaporizer, remains in the primary containment, thus electric heater, and connected piping to supply eliminating any discharge to the environment. the drywell and suppression chamber volumes.

The primary containment hydrogen recombiner The nitrogen storage tanks each contain is manually initiated since flammability limits [4350] gal, which is adequate for [7] days of would not be reached until several days after a CAD subsystem operation.

Design Basis Accident (DBA).

The CAD System operates in conjunction with The primary containment hydrogen recombiner emergency operating procedures that are used functions to maintain the hydrogen gas to reduce primary containment pressure concentration within the containment at or periodically during CAD System operation.

below the flammability limit of 4.0 volume This combination results in a feed and bleed percent (v/o) following a postulated LOCA. It approach to maintaining hydrogen and oxygen is fully redundant and consists of two 100% concentrations below combustible levels.

capacity subsystems. Each primary containment hydrogen recombiner consists of an enclosed blower assembly, heater section, Page 3

TSTF-478, Rev. 2 reaction chamber, direct contact water spray gas cooler, water separator, and associated piping, valves, and instruments. The primary containment hydrogen recombiner will be manually initiated from the main control room when the hydrogen gas concentration in the primary containment reaches [3.3] v/o. When the primary containment is inerted (oxygen concentration < 4.0 v/o), the primary containment hydrogen recombiner will only function until the oxygen is used up (2.0 v/o hydrogen combines with 1.0 v/o oxygen). Two recombiners are provided to meet the requirement for redundancy and independence.

Each recombiner is powered from a separate Engineered Safety Feature bus and is provided with separate power panel and control panel.

The process gas circulating through the heater, the reaction chamber, and the cooler is automatically regulated to [150] scfm by the use of an orifice plate installed in the cooler.

The process gas is heated to [1200]_F. The hydrogen and oxygen gases are recombined into water vapor, which is then condensed in the water spray gas cooler by the associated residual heat removal subsystem and discharged with some of the effluent process gas to the suppression chamber. The majority of the cooled, effluent process gas is mixed with the incoming process gas to dilute the incoming gas prior to the mixture entering the heater section.

SAFETY ANALYSIS SAFETY ANALYSES The primary containment hydrogen recombiner To evaluate the potential for hydrogen and provides the capability of controlling the bulk oxygen accumulation in primary containment hydrogen concentration in primary following a LOCA, hydrogen and oxygen containment to less than the lower flammable generation is calculated (as a function of time concentration of 4.0 v/o following a DBA. following the initiation of the accident). The This control would prevent a primary assumptions stated in Reference 1 are used to containment wide hydrogen burn, thus maximize the amount of hydrogen and oxygen ensuring that pressure and temperature generated. The calculation confirms that when conditions assumed in the analysis are not the mitigating systems are actuated in exceeded. The limiting DBA relative to accordance with emergency operating Page 4

TSTF-478, Rev. 2 hydrogen generation is a LOCA. procedures, the peak oxygen concentration in primary containment is < [5.0] v/o (Ref. 2).

Hydrogen may accumulate in primary containment following a LOCA as a result of Hydrogen and oxygen may accumulate within either: primary containment following a LOCA as a result of either:

A metal steam reaction between the zirconium fuel rod cladding and the reactor coolant or A metal water reaction between the zirconium Radiolytic decomposition of water in the fuel rod cladding and the reactor coolant or Reactor Coolant System. Radiolytic decomposition of water in the Reactor Coolant System.

To evaluate the potential for hydrogen accumulation in primary containment The CAD System satisfies Criterion 3 of 10 following a LOCA, the hydrogen generation is CFR 50.36(c)(2)(ii).

calculated as a function of time following the initiation of the accident. Assumptions 1. Regulatory Guide 1.7, Revision [2].

recommended by Reference 3 are used to maximize the amount of hydrogen calculated.

The calculation confirms that when the mitigating systems are actuated in accordance with emergency procedures, the peak hydrogen concentration in the primary containment is <

4.0 v/o (Ref. 4).

The primary containment hydrogen recombiners satisfy Criterion 3 of 10 CFR 50.36(c)(2)(ii).

3. Regulatory Guide 1.7, Revision [1].

From the above, it is easily seen that the hydrogen recombiners and CAD system perform the exact same function for post-LOCA gas control. Considering that the 10 CFR 50.44 rule change allowed for elimination of hydrogen recombiners for post-LOCA gas control, it follows directly that the rule change basis would likewise allow for the elimination of CAD systems.

Hence, it is concluded that CAD systems no longer meet the criteria for retention in the TS and may be removed from the plant.

Certain statements in the amended rule may have influenced judgments on the disposition of the CAD system. Statements refer to the "backup purge system" which is not a system used in BWRs with Mark I Containments who have CAD systems. Some BWRs with Mark III Containment designs have a non-safety backup purge system. The backup purge system referred to in the amended rule is believed to be the CAD system; however, the CAD system is not used for purging or for inerting activities. The CAD system is only used for post-accident addition of nitrogen. A totally separate system is used in BWRs for the initial nitrogen inerting of the Page 5

TSTF-478, Rev. 2 containment and BWRs who have CAD systems also have separate system which may be used for purging/controlled venting as part of severe accident management strategies.

In addition, there appear to be judgments in the rule consideration that the cost to maintain the CAD system is not significant. In reality, the cost of maintaining the CAD system is significant at BWRs and exceeds the reported cost of maintaining the recombiners.

As part of the Commissions regulatory analysis for the proposed rulemaking cost and benefit calculations were performed for recombiners. The total benefits calculated are $21,300 which when compared with operating costs led to the conclusion that recombiners could be eliminated to reduce unnecessary regulatory burden. Concerning the "backup hydrogen purge system" (CAD), the regulatory analysis states:

The issue of eliminating the requirement for safety grade purge/vent systems is not specifically analyzed in this regulatory analysis because the staff believes that the above conclusion would also be true for the backup hydrogen purge system. The cost is expected to exceed the estimated benefit of $21,320 as calculated in Appendix A of this document.

In addition, the benefit would not be as great because the hydrogen purge system does not prevent a release.

The regulatory analysis referred to information provided by the BWR Owners Group topical report NEDO-33033 titled "Regulatory Relaxation for the H2/O2 Monitors and Combustible Gas Control System," July 2001, for annual cost burden for recombiners and monitors. The BWR Owners report also includes annual cost for maintaining the CAD system. The report notes that the typical yearly cost to maintain a BWR CAD system is approximately $200k. The major costs include:

  • Vendor support $15k
  • Maintenance, planning, and scheduling $25k
  • System and design engineering $80k
  • Component replacements and repairs $75k The above yearly costs when compared to the maximum present worth benefits calculated in the Commissions regulatory analysis would support elimination of the CAD system to reduce unnecessary regulatory burden.

With respect to the potential benefits of maintaining CAD for severe accidents, the BWR Emergency Procedures conclude that use of CAD is of little benefit in responding to most events, due to its limited capacity. In fact, for the likely scenario of a degraded core that generates significant hydrogen, use of CAD can be detrimental to event mitigation as it overpressurizes the containment during containment flooding scenarios, forcing containment venting that would otherwise not be warranted.

From these discussions, it is clear that the change to 10 CFR 50.44 eliminated the basis for considering the CAD system to meet 10 CFR 50.36(c)(2)(ii). The Safety Evaluation reached the same conclusion for the hydrogen recombiner system and allowed that system to be deleted from Page 6

TSTF-478, Rev. 2 the TS and allows the equipment to be eliminated from the plant. This Traveler deletes the CAD system from the TS and allows the equipment to be eliminated from the plant.

Elimination of the Drywell Cooling System Fans Required Action to Verify the Hydrogen Control Function Required Action B.1 of BWR/4 TS 3.6.3.1 requires verification that the hydrogen control function is maintained if both drywell cooling system fans were inoperable. This Action may be deleted because, consistent with the basis for the changes to 10 CFR 50.44, the probability of the occurrence of an accident that would generate hydrogen in the amounts capable of exceeding the flammability limit is low during the 7 day period of mixing system unavailability.

The 50.44 rule change eliminated the DBA hydrogen control requirements and the recombiner TS requirements. TSTF-447 eliminated the Required Action B.1 Bases statement describing which systems provide the alternate DBA hydrogen control capabilities, but the Action itself was unchanged. BWR/4 TS 3.6.3.1, Required Action B.1, needs to be deleted since the action was related to maintaining an alternate DBA function (i.e., the hydrogen recombiners) which has been eliminated. Alternate methods of managing a severe accident hydrogen release are addressed through the Severe Accident Management Guidelines.

Bases Revisions for the Drywell Purge System The Drywell Purge Systems (BWR/6 TS 3.6.3.2) ensure a mixed atmosphere for combustible gas control as required by 10 CFR 50.44 (b)(1). A mixed atmosphere helps prevent localized accumulation of hydrogen following a Design Basis Accident (DBA) LOCA. Localized concentration in amounts exceeding the flammability limits could impact safety related structures or components relied upon to mitigate a DBA. More recent studies have shown, however, that the hydrogen release postulated from a DBA LOCA is not risk significant because it is not large enough to lead to early containment failure. The revised rule effective October 16, 2003, eliminated the design basis LOCA hydrogen release from 10 CFR 50.44, but retained the requirement for all containment types to have the capability for ensuring a mixed atmosphere.

Since the DBA LOCA hydrogen release was eliminated from 10 CFR 50.44, the system is not needed to mitigate a design basis accident and therefore no longer satisfies Criterion 3 of 10 CFR 50.36(c)(2)(ii). However, the system requirements are retained in accordance with Criterion 4.

The Applicable Safety Analysis section of the TS Bases for BWR/6 TS 3.6.3.2 is revised to state that the LCO meets Criterion 4 instead of Criterion 3.

5.0 Regulatory Analysis 5.1 No Significant Hazards Consideration The TSTF has evaluated whether or not a significant hazards consideration is involved with the proposed generic change by focusing on the three standards set forth in 10 CFR 50.92, "Issuance of amendment," as discussed below:

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TSTF-478, Rev. 2

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

Response: No.

The Containment Atmosphere Dilution (CAD) system is not an initiator to any accident previously evaluated. The Required Actions taken when a drywell cooling system fan is inoperable are not initiators to any accident previously evaluated. As a result, the probability of any accident previously evaluated is not significantly increased. The CAD system and drywell cooling system fans are used to mitigate the consequences of an accident. However, the revised 10 CFR 50.44 no longer defines a design basis accident (DBA) hydrogen release and the Commission has subsequently found that the DBA loss of coolant accident (LOCA) hydrogen release is not risk significant. In addition, CAD has been determined to be ineffective at mitigating hydrogen releases from the more risk significant beyond design basis accidents that could threaten containment integrity. This is similar to the Staffs conclusion relative to hydrogen recombiners. Therefore, elimination of the CAD system will not significantly increase the consequences of any accident previously evaluated. The consequences of an accident while relying on the revised Required Actions for drywell cooling system fans are no different than the consequences of the same accidents under the current Required Actions. As a result, the consequences of any accident previously evaluated is not significantly increased.

Therefore, the proposed changes do 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.

No new or different accidents result from utilizing the proposed change. The changes do not involve a physical alteration of the plant (i.e., no new or different type of equipment will be installed) or a change in the methods governing normal plant operation, except for the elimination of the CAD system. The CAD system is not considered an accident precursor, nor does its existence or elimination have any adverse impact on the pre-accident state of the reactor core or post accident confinement of radionuclides within the containment building from any design basis event. In addition, the changes do not impose any new or different requirements. The changes to the Technical Specifications do not alter assumptions made in the safety analysis, but reflect changes to the safety analysis requirements allowed under the revised 10 CFR 50.44. The proposed changes are consistent with the revised safety analysis assumptions.

Therefore, the proposed changes do 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?

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TSTF-478, Rev. 2 Response: No.

The Commission has determined that the DBA LOCA hydrogen release is not risk significant and is not required to be assumed in the plants accident analyses. The proposed changes reflect this new position and, in light of the remaining plant equipment, instrumentation, procedures, and programs that provide effective mitigation of and recovery from reactor accidents, including postulated beyond design basis events, does not result in a significant reduction in a margin of safety.

Therefore, the proposed changes do not involve a significant reduction in a margin of safety.

Based on the above, the TSTF concludes that the proposed change presents 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.

5.2 Applicable Regulatory Requirements/Criteria The proposed changes revise the ISTS to reflect changes in the applicable regulatory requirements and criteria in 10 CFR 50.44.

In conclusion, based on the considerations discussed above, (1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Commissions regulations, and (3) the approval of the proposed change will not be inimical to the common defense and security or to the health and safety of the public.

6.0 Environmental Consideration A review has determined that the proposed change would change a requirement with respect to installation or use of a facility component located within the restricted area, as defined in 10 CFR 20, or would change an inspection or surveillance requirement. However, the proposed change 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 change 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 change.

7.0 References

1. Notice of Proposed Rulemaking, Federal Register: August 2, 2002 (Volume 67, Number 149), Proposed Rules, Page 50374-50383, Combustible Gas Control in Containment.
2. Final Rule, Federal Register: 68 FR 54141 (Volume 67, Number 149), September 16, 2003, Combustible Gas Control in Containment.

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TSTF-478, Rev. 2

3. Letter from Thomas H. Boyce (NRC) to Technical Specification Task Force dated October 1, 2003, approving TSTF-447, Revision 1, "Elimination of Hydrogen Recombiners and Change to Hydrogen and Oxygen Monitors."
4. Letter from Timothy Kobetz (NRC) to Technical Specification Task Force dated May 8, 2007, "Denial of TSTF-478, Revision 1, 'BWR Technical Specification Changes that Implement the Revised Rule for Combustible Gas Control'."

Page 10

TSTF-478, Rev. 2

[Drywell Cooling System Fans]

3.6.3.1 3.6 CONTAINMENT SYSTEMS 3.6.3.1 [Drywell Cooling System Fans]

LCO 3.6.3.1 Two [drywell cooling system fans] shall be OPERABLE.

APPLICABILITY: MODES 1 and 2.

ACTIONS CONDITION REQUIRED ACTION COMPLETION TIME A. One [required] [drywell A.1 Restore [required] [drywell 30 days cooling system fan] cooling system fan] to inoperable. OPERABLE status.

B. Two [required] [drywell B.1 Verify by administrative 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> cooling system fans] means that the hydrogen inoperable. control function is AND maintained.

Once per 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> thereafter AND B.12 Restore one [required] 7 days

[drywell cooling system fan]

to OPERABLE status.

C. Required Action and C.1 Be in MODE 3. 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> associated Completion Time not met.

BWR/4 STS 3.6.3.1-1 Rev. 3.0, 03/31/04

TSTF-478, Rev. 2 CAD System 3.6.3.3 3.6 CONTAINMENT SYSTEMS 3.6.3.3 Containment Atmosphere Dilution (CAD) System LCO 3.6.3.3 Two CAD subsystems shall be OPERABLE.

APPLICABILITY: MODES 1 and 2.

ACTIONS CONDITION REQUIRED ACTION COMPLETION TIME A. One CAD subsystem A.1 Restore CAD subsystem to 30 days inoperable. OPERABLE status.

B. [ Two CAD subsystems B.1 Verify by administrative 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> inoperable. means that the hydrogen control function is AND maintained.

Once per 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> thereafter AND B.2 Restore one CAD 7 days ]

subsystem to OPERABLE status.

C. Required Action and C.1 Be in MODE 3. 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> associated Completion Time not met.

BWR/4 STS 3.6.3.3-1 Rev. 3.0, 03/31/04

TSTF-478, Rev. 2 CAD System 3.6.3.3 SURVEILLANCE REQUIREMENTS SURVEILLANCE FREQUENCY SR 3.6.3.3.1 Verify [4350] gal of liquid nitrogen are contained in 31 days the CAD System.

SR 3.6.3.3.2 Verify each CAD subsystem manual, power 31 days operated, and automatic valve in the flow path that is not locked, sealed, or otherwise secured in position is in the correct position or can be aligned to the correct position.

BWR/4 STS 3.6.3.3-1 Rev. 3.0, 03/31/04

TSTF-478, Rev. 2

[Drywell Cooling System Fans]

B 3.6.3.1 B 3.6 CONTAINMENT SYSTEMS B 3.6.3.1 [Drywell Cooling System Fans]

BASES BACKGROUND The [Drywell Cooling System fans] ensure a uniformly mixed post accident primary containment atmosphere, thereby minimizing the potential for local hydrogen burns due to a pocket of hydrogen above the flammable concentration.

The [Drywell Cooling System fans] are an Engineered Safety Feature and are designed to withstand a loss of coolant accident (LOCA) in post accident environments without loss of function. The system has two independent subsystems consisting of fans, fan coil units, motors, controls, and ducting. Each subsystem is sized to circulate [500] scfm.

The [Drywell Cooling System fans] employ both forced circulation and natural circulation to ensure the proper mixing of hydrogen in primary containment. The recirculation fans provide the forced circulation to mix hydrogen while the fan coils provide the natural circulation by increasing the density through the cooling of the hot gases at the top of the drywell causing the cooled gases to gravitate to the bottom of the drywell. The two subsystems are initiated manually since flammability limits would not be reached until several days after a LOCAan accident. Each subsystem is powered from a separate emergency power supply. Since each subsystem can provide 100% of the mixing requirements, the system will provide its design function with a worst case single active failure.

The [Drywell Cooling System fans] use the Drywell Cooling System recirculating fans to mix the drywell atmosphere. The fan coil units and recirculation fans are automatically disengaged during a LOCAan accident but may be restored to service manually by the operator. In the event of a loss of offsite power, all fan coil units, recirculating fans, and primary containment water chillers are transferred to the emergency diesels. The fan coil units and recirculating fans are started automatically from diesel power upon loss of offsite power.

APPLICABLE The [Drywell Cooling System fans] ensure a mixed atmosphere for SAFETY combustible gas control as required by 10 CFR 50.44 (b)(1). The [Drywell ANALYSES Cooling System fans] were originally designed to help mitigate the potential consequences of hydrogen generation following a Design Basis Accident (DBA) loss of coolant accident (LOCA). However, more recent studies have shown that the hydrogen release postulated from a DBA LOCA is not risk significant because it is not large enough to lead to early containment failure. The revised rule effective October 16, 2003, eliminated the design basis LOCA hydrogen release from 10 CFR 50.44 but retained the requirement for all containment types to have the capability for ensuring a mixed atmosphere in order to prevent local BWR/4 STS B 3.6.3.1-1 Rev. 3.0, 03/31/04

TSTF-478, Rev. 2

[Drywell Cooling System Fans]

B 3.6.3.1 accumulation of detonable gases that could threaten containment integrity or equipment operating in a local compartment.

APPLICABLE The [Drywell Cooling System fans] provide the capability for reducing the SAFETY local hydrogen concentration to approximately the bulk average ANALYSES concentration following an accident a Design Basis Accident (DBA). The limiting DBA relative to hydrogen generation is a LOCA.

Hydrogen may accumulate in primary containment following a LOCAan accident as a result of:

a. A metal steam reaction between the zirconium fuel rod cladding and the reactor coolant or BWR/4 STS B 3.6.3.1-2 Rev. 3.0, 03/31/04

TSTF-478, Rev. 2

[Drywell Cooling System Fans]

B 3.6.3.1 BASES APPLICABLE SAFETY ANALYSIS (continued)

b. Radiolytic decomposition of water in the Reactor Coolant System.

To evaluate the potential for hydrogen accumulation in primary containment following a LOCAan accident, the hydrogen generation as a function of time following the initiation of the accident is calculated.

Conservative assumptions recommended by Reference 1 are used to maximize the amount of hydrogen calculated.

The Reference 2 calculations show that hydrogen assumed to be released to the drywell within 2 minutes following a DBA LOCA raises drywell hydrogen concentration to over 2.5 volume percent (v/o).

Nnatural circulation phenomena result in acceptably small a gradient concentration differences in the drywell and of less then 0.5 v/o in the drywell and less than 0.1 v/o in the suppression chamber. Even though this gradient is acceptably small and no credit for mechanical mixing was assumed in the analysis, two [Drywell Cooling System fans] are [required]

to be OPERABLE (typically four to six fans are required to keep the drywell cool during operation in MODE 1 or 2) by this LCO.

The [Drywell Cooling System fans] satisfy Criterion 43 of 10 CFR 50.36(c)(2)(ii).

LCO Two [Drywell Cooling System fans] must be OPERABLE to ensure operation of at least one fan in the event of a worst case single active failure. Each of these fans must be powered from an independent safety related bus.

Operation with at least one fan provides the capability of controlling the bulk hydrogen concentration in primary containment without exceeding the flammability limit.

APPLICABILITY In MODES 1 and 2, the two [Drywell Cooling System fans] ensure the capability to prevent localized hydrogen concentrations above the flammability limit of 4.0 v/o in drywell, assuming a worst case single active failure.

In MODE 3, both the hydrogen production rate and the total hydrogen produced after a LOCAan accident would be less than that calculated for an accident in MODE 1 or 2the DBA LOCA. Also, because of the limited time in this MODE, the probability of an accident requiring the [Drywell Cooling System fans] is low. Therefore, the [Drywell Cooling System fans] are not required in MODE 3.

BWR/4 STS B 3.6.3.1-3 Rev. 3.0, 03/31/04

TSTF-478, Rev. 2

[Drywell Cooling System Fans]

B 3.6.3.1 BASES APPLICABILITY (continued)

In MODES 4 and 5, the probability and consequences of a LOCAan accident are reduced due to the pressure and temperature limitations in these MODES. Therefore, the [Drywell Cooling System fans] are not required in these MODES.

ACTIONS A.1 With one [required] [Drywell Cooling System fan] inoperable, the inoperable fan must be restored to OPERABLE status within 30 days. In this Condition, the remaining OPERABLE fan is adequate to perform the hydrogen mixing function. However, the overall reliability is reduced because a single failure in the OPERABLE fan could result in reduced hydrogen mixing capability. The 30 day Completion Time is based on the availability of the second fan, the low probability of the occurrence of a LOCA an accidentthat would generate hydrogen in amounts capable of exceeding the flammability limit, and the amount of time available after the event for operator action to prevent exceeding this limit, and the availability of the Containment Atmosphere Dilution System.

B.1 and B.2

REVIEWERS NOTE-----------------------------------

This Condition is only allowed for units with an alternate hydrogen control system acceptable to the technical staff.

With two [Drywell Cooling System fans] inoperable, the ability to perform the hydrogen control function via alternate capabilities must be verified by administrative means within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />. The alternate hydrogen control capabilities are provided by the [Primary Containment Inerting System or one subsystem of the Containment Atmosphere Dilution System]. The 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> Completion Time allows a reasonable period of time to verify that a loss of hydrogen control function does not exist.

REVIEWERS NOTE-----------------------------------

The following is to be used if a non-Technical Specification alternate hydrogen control function is used to justify this Condition: In addition, the alternate hydrogen control system capability must be verified once per 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> thereafter to ensure its continued availability.

BWR/4 STS B 3.6.3.1-4 Rev. 3.0, 03/31/04

TSTF-478, Rev. 2

[Drywell Cooling System Fans]

B 3.6.3.1 BASES ACTIONS (continued)

[Both] the [initial] verification [and all subsequent verifications] may be performed as an administrative check by examining logs or other information to determine the availability of the alternate hydrogen control system. It does not mean to perform the Surveillances needed to demonstrate OPERABILITY of the alternate hydrogen control system. If the ability to perform the hydrogen control function is maintained, Ccontinued operation is permitted with two [Drywell Cooling System fans]

inoperable for up to 7 days. Seven days is a reasonable time to allow two

[Drywell Cooling System fans] to be inoperable because the hydrogen control function is maintained and because of the low probability of the occurrence of a LOCA an accident that would generate hydrogen in amounts capable of exceeding the flammability limit and due to post-accident natural circulation forces that promote mixing.

C.1 If any Required Action and associated Completion Time cannot be met, the plant must be brought to a MODE in which the LCO does not apply.

To achieve this status, the plant must be brought to at least MODE 3 within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. The allowed Completion Time of 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> is reasonable, based on operating experience, to reach MODE 3 from full power conditions in an orderly manner and without challenging plant systems.

SURVEILLANCE SR 3.6.3.1.1 REQUIREMENTS Operating each [required] [Drywell Cooling System fan] for 15 minutes ensures that each subsystem is OPERABLE and that all associated controls are functioning properly. It also ensures that blockage, fan or motor failure, or excessive vibration can be detected for corrective action.

The 92 day Frequency is consistent with the Inservice Testing Program Frequencies, operating experience, the known reliability of the fan motors and controls, and the two redundant fans available.

BWR/4 STS B 3.6.3.1-5 Rev. 3.0, 03/31/04

TSTF-478, Rev. 2

[Drywell Cooling System Fans]

B 3.6.3.1 BASES SURVEILLANCE REQUIREMENTS (continued)

[ SR 3.6.3.1.2 Verifying that each [required] [Drywell Cooling System fan] flow rate is

[500] scfm ensures that each fan is capable of maintaining localized hydrogen concentrations below the flammability limit. The [18] month Frequency is based on the need to perform this Surveillance under the conditions that apply during a plant outage and the potential for an unplanned transient if the Surveillance were performed with the reactor at power. Operating experience has shown these components usually pass the Surveillance when performed at the [18] month Frequency.

Therefore, the Frequency was concluded to be acceptable from a reliability standpoint. ]

REFERENCES 1. Regulatory Guide 1.7, Revision [31].

2. FSAR, Section [6.2.5].

BWR/4 STS B 3.6.3.1-6 Rev. 3.0, 03/31/04

TSTF-478, Rev. 2 CAD System B 3.6.3.3 B 3.6 CONTAINMENT SYSTEMS B 3.6.3.3 Containment Atmosphere Dilution (CAD) System BASES BACKGROUND The CAD System functions to maintain combustible gas concentrations within the primary containment at or below the flammability limits following a postulated loss of coolant accident (LOCA) by diluting hydrogen and oxygen with nitrogen. To ensure that a combustible gas mixture does not occur, oxygen concentration is kept < [5.0] volume percent (v/o), or hydrogen concentration is kept < 4.0 v/o.

The CAD System is manually initiated and consists of two independent, 100% capacity subsystems. Each subsystem includes a liquid nitrogen supply tank, ambient vaporizer, electric heater, and connected piping to supply the drywell and suppression chamber volumes. The nitrogen storage tanks each contain [4350] gal, which is adequate for [7] days of CAD subsystem operation.

The CAD System operates in conjunction with emergency operating procedures that are used to reduce primary containment pressure periodically during CAD System operation. This combination results in a feed and bleed approach to maintaining hydrogen and oxygen concentrations below combustible levels.

APPLICABLE To evaluate the potential for hydrogen and oxygen accumulation in SAFETY primary containment following a LOCA, hydrogen and oxygen generation ANALYSES is calculated (as a function of time following the initiation of the accident).

The assumptions stated in Reference 1 are used to maximize the amount of hydrogen and oxygen generated. The calculation confirms that when the mitigating systems are actuated in accordance with emergency operating procedures, the peak oxygen concentration in primary containment is < [5.0] v/o (Ref. 2).

Hydrogen and oxygen may accumulate within primary containment following a LOCA as a result of:

a. A metal water reaction between the zirconium fuel rod cladding and the reactor coolant or
b. Radiolytic decomposition of water in the Reactor Coolant System.

The CAD System satisfies Criterion 3 of 10 CFR 50.36(c)(2)(ii).

BWR/4 STS B 3.6.3.3-3 Rev. 3.0, 03/31/04

TSTF-478, Rev. 2 CAD System B 3.6.3.3 BASES LCO Two CAD subsystems must be OPERABLE. This ensures operation of at least one CAD subsystem in the event of a worst case single active failure. Operation of at least one CAD subsystem is designed to maintain primary containment post-LOCA oxygen concentration < 5.0 v/o for 7 days.

APPLICABILITY In MODES 1 and 2, the CAD System is required to maintain the oxygen concentration within primary containment below the flammability limit of 5.0 v/o following a LOCA. This ensures that the relative leak tightness of primary containment is adequate and prevents damage to safety related equipment and instruments located within primary containment.

In MODE 3, both the hydrogen and oxygen production rates and the total amounts produced after a LOCA would be less than those calculated for the Design Basis Accident LOCA. Thus, if the analysis were to be performed starting with a LOCA in MODE 3, the time to reach a flammable concentration would be extended beyond the time conservatively calculated for MODES 1 and 2. The extended time would allow hydrogen removal from the primary containment atmosphere by other means and also allow repair of an inoperable CAD subsystem, if CAD were not available. Therefore, the CAD System is not required to be OPERABLE in MODE 3.

In MODES 4 and 5, the probability and consequences of a LOCA are reduced due to the pressure and temperature limitations of these MODES. Therefore, the CAD System is not required to be OPERABLE in MODES 4 and 5.

ACTIONS A.1 If one CAD subsystem is inoperable, it must be restored to OPERABLE status within 30 days. In this Condition, the remaining OPERABLE CAD subsystem is adequate to perform the oxygen control function. However, the overall reliability is reduced because a single failure in the OPERABLE subsystem could result in reduced oxygen control capability.

The 30 day Completion Time is based on the low probability of the occurrence of a LOCA that would generate hydrogen and oxygen in amounts capable of exceeding the flammability limit, the amount of time available after the event for operator action to prevent exceeding this limit, and the availability of the OPERABLE CAD subsystem and other hydrogen mitigating systems.

BWR/4 STS B 3.6.3.3-3 Rev. 3.0, 03/31/04

TSTF-478, Rev. 2 CAD System B 3.6.3.3 BASES ACTIONS (continued)

B.1 and B.2

REVIEWERS NOTE-----------------------------------

This Condition is only allowed for plants with an alternate hydrogen control system acceptable to the technical staff.

With two CAD subsystems inoperable, the ability to perform the hydrogen control function via alternate capabilities must be verified by administrative means within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />. The alternate hydrogen control capabilities are provided by the [Primary Containment Inerting System or one hydrogen recombiner and one Drywell Cooling System fan]. The 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> Completion Time allows a reasonable period of time to verify that a loss of hydrogen control function does not exist.

REVIEWERS NOTE-----------------------------------

The following is to be used if a non-Technical Specification alternate hydrogen control function is used to justify this Condition: In addition, the alternate hydrogen control system capability must be verified once per 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> thereafter to ensure its continued availability.

[Both] the [initial] verification [and all subsequent verifications] may be performed as an administrative check by examining logs or other information to determine the availability of the alternate hydrogen control system. It does not mean to perform the Surveillances needed to demonstrate OPERABILITY of the alternate hydrogen control system. If the ability to perform the hydrogen control function is maintained, continued operation is permitted with two CAD subsystems inoperable for up to 7 days. Seven days is a reasonable time to allow two CAD subsystems to be inoperable because the hydrogen control function is maintained and because of the low probability of the occurrence of a LOCA that would generate hydrogen in amounts capable of exceeding the flammability limit.

With two CAD subsystems inoperable, one CAD subsystem must be restored to OPERABLE status within 7 days. The 7 day Completion Time is based on the low probability of the occurrence of a LOCA that would generate hydrogen in the amounts capable of exceeding the flammability limit, the amount of time available after the event for operator action to prevent exceeding this limit, and the availability of other hydrogen mitigating systems.

BWR/4 STS B 3.6.3.3-3 Rev. 3.0, 03/31/04

TSTF-478, Rev. 2 CAD System B 3.6.3.3 BASES ACTIONS (continued)

C.1 If any Required Action cannot be met within the associated Completion Time, the plant must be brought to a MODE in which the LCO does not apply. To achieve this status, the plant must be brought to at least MODE 3 within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. The allowed Completion Time of 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> is reasonable, based on operating experience, to reach MODE 3 from full power conditions in an orderly manner and without challenging plant systems.

SURVEILLANCE SR 3.6.3.3.1 REQUIREMENTS Verifying that there is [4350] gal of liquid nitrogen supply in the CAD System will ensure at least [7] days of post-LOCA CAD operation. This minimum volume of liquid nitrogen allows sufficient time after an accident to replenish the nitrogen supply for long term inerting. This is verified every 31 days to ensure that the system is capable of performing its intended function when required. The 31 day Frequency is based on operating experience, which has shown 31 days to be an acceptable period to verify the liquid nitrogen supply and on the availability of other hydrogen mitigating systems.

SR 3.6.3.3.2 Verifying the correct alignment for manual, power operated, and automatic valves in each of the CAD subsystem flow paths provides assurance that the proper flow paths exist for system operation. This SR does not apply to valves that are locked, sealed, or otherwise secured in position, since these valves were verified to be in the correct position prior to locking, sealing, or securing.

A valve is also allowed to be in the nonaccident position provided it can be aligned to the accident position within the time assumed in the accident analysis. This is acceptable because the CAD System is manually initiated. This SR does not apply to valves that cannot be inadvertently misaligned, such as check valves. This SR does not require any testing or valve manipulation; rather, it involves verification that those valves capable of being mispositioned are in the correct position.

BWR/4 STS B 3.6.3.3-3 Rev. 3.0, 03/31/04

TSTF-478, Rev. 2 CAD System B 3.6.3.3 BASES SURVEILLANCE REQUIREMENTS (continued)

The 31 day Frequency is appropriate because the valves are operated under procedural control, improper valve position would only affect a single subsystem, the probability of an event requiring initiation of the system is low, and the system is a manually initiated system.

REFERENCES 1. Regulatory Guide 1.7, Revision [2].

2. FSAR, Section [ ].

BWR/4 STS B 3.6.3.3-5 Rev. 3.0, 03/31/04

TSTF-478, Rev. 2

[Drywell Purge System]

B 3.6.3.2 B 3.6 CONTAINMENT SYSTEMS B 3.6.3.2 [Drywell Purge System]

BASES BACKGROUND The [Drywell Purge System] ensures a uniformly mixed post accident containment atmosphere, thereby minimizing the potential for local hydrogen burns due to a pocket of hydrogen above the flammable concentration.

The [Drywell Purge System] is an Engineered Safety Feature and is designed to operate following a loss of coolant accident (LOCA) in post accident environments without loss of function. The system has two independent subsystems, each consisting of a compressor and associated valves, controls, and piping. Each subsystem is sized to pump [500] scfm. Each subsystem is powered from a separate emergency power supply. Since each subsystem can provide 100% of the mixing requirements, the system will provide its design function with a worst case single active failure.

Following an accident LOCA, the drywell is immediately pressurized due to the release of steam into the drywell environment. This pressure is relieved by the lowering of the water level within the weir wall, clearing the drywell vents and allowing the mixture of steam and noncondensibles to flow into the primary containment through the suppression pool, removing much of the heat from the steam. The remaining steam in the drywell begins to condense as steam flow from the reactor pressure vessel ceases, the drywell pressure falls rapidly. Both drywell purge compressors start automatically 30 seconds after a LOCA signal is received from the Emergency Core Cooling System instrumentation, but only when drywell pressure has decreased to within approximately

[0.087] psi above primary containment pressure. This ensures the blowdown from the drywell to the primary containment is complete. The drywell purge compressors force air from the primary containment into the drywell. Drywell pressure increases until the water level between the weir wall and the drywell is forced down to the first row of suppression pool vents forcing drywell atmosphere back into containment and mixing with containment atmosphere to dilute the hydrogen.

BWR/6 STS B 3.6.3.2-1 Rev. 3.0, 03/31/04

TSTF-478, Rev. 2

[Drywell Purge System]

B 3.6.3.2 BASES APPLICABLE The [Drywell Purge System] ensures a mixed atmosphere for combustible SAFETY gas control as required by 10 CFR 50.44 (b)(1). The [Drywell Purge ANALYSES System] was originally designed to help mitigate the potential consequences of hydrogen generation following a Design Basis Accident (DBA) loss of coolant accident (LOCA). However, more recent studies have shown that the hydrogen release postulated from a DBA LOCA is not risk significant because it is not large enough to lead to early containment failure. The revised rule effective October 16, 2003, eliminated the design basis LOCA hydrogen release from 10 CFR 50.44, but retained the requirement for all containment types to have the capability for ensuring a mixed atmosphere in order to prevent local accumulation of detonable gases that could threaten containment integrity or equipment operating in a local compartment. The [Drywell Purge System] provides the capability for reducing the SAFETY drywell hydrogen concentration to approximately the bulk average ANALYSES primary containment concentration following an accidenta Design Basis Accident (DBA). The limiting DBA relative to hydrogen generation is a LOCA.

Hydrogen may accumulate in primary containment following a LOCAan accident as a result of:

a. A metal steam reaction between the zirconium fuel rod cladding and the reactor coolant and
b. Radiolytic decomposition of water in the Reactor Coolant System and drywell sump.

To evaluate the potential for hydrogen accumulation in primary containment following a LOCAan accident, the hydrogen generation as a function of time following the initiation of the accident is calculated.

Conservative Evaluation assumptions recommended by Reference 1 are used to determine the timing of the actions to mitigate the event maximize the amount of hydrogen calculated.

[ Based on a conservative assumption used to calculate the hydrogen concentration versus time after a LOCA, the hydrogen concentration in the primary containment would reach [3.5 v/o about 6 days] after the LOCA and [4.0 v/o about 2 days] later if no hydrogen mixing and recombiner were functioning (Ref. 2). ]

The [Drywell Purge System] satisfies Criterion 3 4 of 10 CFR 50.36(c)(2)(ii).

LCO Two [drywell purge] subsystems must be OPERABLE to ensure operation of at least one primary containment [drywell purge] subsystem in the event of a worst case single active failure. Operation with at least one BWR/6 STS B 3.6.3.2-2 Rev. 3.0, 03/31/04

TSTF-478, Rev. 2

[Drywell Purge System]

B 3.6.3.2 OPERABLE [drywell purge] subsystem provides the capability of controlling the hydrogen concentration in the drywell without exceeding the flammability limit.

APPLICABILITY In MODES 1 and 2, the two [drywell purge] subsystems ensure the capability to prevent localized hydrogen concentrations above the flammability limit of 4.0 v/o in the drywell, assuming a worst case single active failure.

In MODE 3, both the hydrogen production rate and the total hydrogen produced after a LOCAan accident would be less than that calculated for the DBA LOCAan accident in MODE1 or 2. Also, because of the limited time in this MODE, the probability of an accident requiring the [Drywell Purge System] is low. Therefore, the [Drywell Purge System] is not required in MODE 3.

BWR/6 STS B 3.6.3.2-3 Rev. 3.0, 03/31/04

TSTF-478, Rev. 2

[Drywell Purge System]

B 3.6.3.2 BASES APPLICABILITY (continued)

In MODES 4 and 5, the probability and consequences of a LOCAan accident are reduced due to the pressure and temperature limitations in these MODES. Therefore, the [Drywell Purge System] is not required in these MODES.

ACTIONS A.1 With one [drywell purge] subsystem inoperable, the inoperable subsystem must be restored to OPERABLE status within 30 days. In this Condition, the remaining OPERABLE subsystem is adequate to perform the drywell purge function. However, the overall reliability is reduced because a single failure in the OPERABLE subsystem could result in reduced drywell purge capability. The 30 day Completion Time is based on the availability of the second subsystem, the low probability of a LOCAan accident that would generate hydrogen in amounts capable of exceeding the flammability limit, and the amount of time available after the event for operator action to prevent hydrogen accumulation from exceeding this limit.

B.1 and B.2

REVIEWERS NOTE-----------------------------------

This Condition is only allowed for units with an alternate hydrogen control system acceptable to the technical staff.

With two [drywell purge] subsystems inoperable, the ability to perform the hydrogen control function via alternate capabilities must be verified by administrative means within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />. The alternate hydrogen control capabilities are provided by [one division of the hydrogen ignitors]. The 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> Completion Time allows a reasonable period of time to verify that a loss of hydrogen control function does not exist.

REVIEWERS NOTE-----------------------------------

The following is to be used if a non-Technical Specification alternate hydrogen control function is used to justify this Condition: In addition, the alternate hydrogen control system capability must be verified once per 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> thereafter to ensure its continued availability.

BWR/6 STS B 3.6.3.2-4 Rev. 3.0, 03/31/04

TSTF-478, Rev. 2

[Drywell Purge System]

B 3.6.3.2 BASES ACTIONS (continued)

[Both] the [initial] verification may [and all subsequent verifications] may be performed as an administrative check by examining logs or other information to determine the availability of the alternate hydrogen control system. It does not mean to perform the surveillances needed to demonstrate OPERABILITY of the alternate hydrogen control system. If the ability to perform the hydrogen control function is maintained, continued operation is permitted with two [drywell purge] subsystems inoperable for up to 7 days. Seven days is a reasonable time to allow two

[drywell purge] subsystems to be inoperable because the hydrogen control function is maintained and because of the low probability of the occurrence of a LOCAan accident that would generate hydrogen in amounts capable of exceeding the flammability limit.

C.1 If any Required Action and the required Completion Time cannot be met, the plant must be brought to a MODE in which the LCO does not apply.

To achieve this status, the plant must be brought to at least MODE 3 within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. The allowed Completion Time of 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> is reasonable, based on operating experience, to reach MODE 3 from full power conditions in an orderly manner and without challenging plant systems.

SURVEILLANCE SR 3.6.3.2.1 REQUIREMENTS Operating each [drywell purge] subsystem for 15 minutes ensures that each subsystem is OPERABLE and that all associated controls are functioning properly. It also ensures that blockage, compressor failure, or excessive vibration can be detected for corrective action. The 92 day Frequency is consistent with Inservice Testing Program Frequencies, operating experience, the known reliability of the compressor and controls, and the two redundant subsystems available.

[ SR 3.6.3.2.2 Verifying that each [drywell purge] subsystem flow rate is [500] scfm ensures that each subsystem is capable of maintaining drywell hydrogen concentrations below the flammability limit. The 18 month Frequency is based on the need to perform this Surveillance under the conditions that apply during a plant outage and the potential for an unplanned transient if the Surveillance were performed with the reactor at power. Operating experience has shown that these components usually pass the Surveillance when performed at the [18] month Frequency. Therefore, the Frequency was concluded to be acceptable from a reliability standpoint. ]

BWR/6 STS B 3.6.3.2-5 Rev. 3.0, 03/31/04

TSTF-478, Rev. 2

[Drywell Purge System]

B 3.6.3.2 BASES REFERENCES 1. Regulatory Guide 1.7, Revision [13].

2. FSAR, Section [6.2.5].

BWR/6 STS B 3.6.3.2-6 Rev. 3.0, 03/31/04

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