RS-15-084, Request for Exemption from 10 CFR 50.55a, Codes and Standards, Paragrapgh (h)(2), Protection Systems

Request for Exemption from 10 CFR 50.55a, Codes and Standards, Paragrapgh (h)(2), Protection Systems

ML15097A123
Person / Time
Site:	Byron, Braidwood
Issue date:	04/06/2015
From:	Gullott D Exelon Generation Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
RS-15-084
Download: ML15097A123 (18)

Text

4300 Winfield Road Warrenville, IL 60555 Exelon Generation

630 657 2000 Office RS-15-084

10 CFR 50.12 April 6, 2015 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001 Braidwood Station, Units 1 and 2 Facility Operating License Nos. NPF-72 and NPF-77 NRC Docket Nos. STN 50-456 and STN 50-457 Byron Station, Units 1 and 2 Facility Operating License Nos. NPF-37 and NPF-66 NRC Docket Nos. STN 50-454 and STN 50-455

Subject:

Request for Exemption from 10 CFR 50.55a, "Codes and standards,"

Paragraph (h)(2), "Protection systems" In accordance with 10 CFR 50.12, "Specific exemptions," Exelon Generation Company, LLC (EGC) is requesting a permanent exemption from the requirements of 10 CFR 50.55a, "Codes and standards," Paragraph (h)(2), "Protection systems," for Braidwood Station, Units 1 and 2, and Byron Station, Units 1 and 2. Paragraph (h)(2) states: "For nuclear power plants with construction permits issued after January 1, 1971, but before May 13, 1999, protection systems must meet the requirements stated in either of IEEE [Standard] Std. 279, 'Criteria for Protection Systems for Nuclear Power Generating Stations.' or in IEEE Std. 603-1991, 'Criteria for Safety Systems for Nuclear Power Generating Stations,' and the correction sheet dated January 30, 1995." Braidwood and Byron Stations are currently committed to the requirements of IEEE Std. 279 1971. This exemption is being requested in accordance with the requirements of 10 CFR 50.12(a)(2)(ii) as the application of the regulation in this particular circumstance is not necessary to achieve the underlying purpose of the rule.

The requested exemption is limited in scope and would eliminate the requirement to meet the criteria stated in IEEE Std. 279, Section 4.17, "Manual Initiation," only for the Main Steam Isolation Valve (MSIV) bypass valves manual isolation function. This exemption is being proposed in lieu of installing a costly modification that would eliminate the non-conformance with the requirements of IEEE Std. 279. The modification would also result in a reduction in operational flexibility and would not provide an increase in safety benefit as detailed in.

EGC has discovered a discrepancy between the Updated Final Safety Analysis Report (UFSAR) and Technical Specifications (TS) regarding the description of the main steam line manual isolation function. UFSAR Section 7.3.2.2.7, "Manual Initiation of Protective Actions,"

notes that there are two "system level" main steam line manual isolation switches on the control board in the main control room; and that operating either switch will actuate all four MSIVs and

April 6, 2015 U. S. Nuclear Regulatory Commission Page 2 their associated bypass valves. This description is consistent with the requirements noted in IEEE-279, Section 4.17, "Manual Initiation." However, contrary to the UFSAR description, the information presented in the TS and TS Bases, (i.e., TS Table 3.3.2-1, "Engineered Safety Feature Actuation System Instrumentation," FUNCTION 4, "Steam Line Isolation," the associated TS Bases, and the Bases for TS 3.7.2, "Main Steam Isolation Valves (MSIVs)"),

indicates that the main steam line manual isolation switches only close the MSIVs and not the bypass valves. The associated electrical prints also show that the isolation signals from the two system level manual switches only close the MSIVs and not the bypass valves. Note that the Braidwood Station and Byron Station configurations are identical.

This issue was documented in the Braidwood Station and Byron Station Corrective Action Programs. After a thorough review, it was concluded that the MSIV bypass valves remain operable as the actual plant configuration is consistent with the TS; however, the plant configuration does not conform to the requirements of IEEE-279; and therefore, is considered non-conforming with the current licensing basis. to this letter provides the detailed basis and justification for this exemption request and addresses the exemption requirements of 10 CFR 50.12.

EGC is requesting approval of the proposed exemption by April 6, 2016.

There are no regulatory commitments in this submittal.

Should you have any questions concerning this letter, please contact Mr. Joseph A. Bauer at (630) 657-2804.

Respectfully, David M. Gullott Manager Licensing : Request for Exemption from 10 CFR 50.55a, "Codes and standards,"

Paragraph (h)(2), "Protection systems"

ATTACHMENT 1 Request for Exemption from 10 CFR 50.55a, "Codes and standards,"

Paragraph (h)(2), "Protection systems" I.

SPECIFIC EXEMPTION REQUEST In accordance with 10 CFR 50.12, "Specific exemptions," Exelon Generation Company, LLC (EGC) is requesting a permanent exemption from the requirements of 10 CFR 50.55a, "Codes and standards," Paragraph (h)(2), "Protection systems," for Braidwood Station, Units 1 and 2, and Byron Station, Units 1 and 2. Paragraph (h)(2) states: "For nuclear power plants with construction permits issued after January 1, 1971, but before May 13, 1999, protection systems must meet the requirements stated in either of IEEE [Standard] Std. 279, 'Criteria for Protection Systems for Nuclear Power Generating Stations,' or in IEEE Std. 603-1991, 'Criteria for Safety Systems for Nuclear Power Generating Stations,' and the correction sheet dated January 30, 1995." Braidwood and Byron Stations are currently committed to the requirements of IEEE Std. 279 1971. This exemption is being requested in accordance with the requirements of 10 CFR 50.12(a)(2)(ii) as the application of the regulation in this particular circumstance is not necessary to achieve the underlying purpose of the rule.

The requested exemption is limited in scope and would eliminate the requirement to meet the criteria stated in IEEE Std. 279, Section 4.17, "Manual Initiation," only for the Main Steam Isolation Valve (MSIV) bypass valves manual isolation function. This exemption is being proposed in lieu of installing a costly modification that would eliminate the non-conformance with the requirements of IEEE Std. 279. The modification would also result in a reduction in operational flexibility and would not provide an increase in safety benefit as discussed below.

Background

EGC has discovered a discrepancy between the Updated Final Safety Analysis Report (UFSAR) and Technical Specifications (TS) regarding the description of the main steam line manual isolation function. UFSAR Section 7.3.2.2.7, "Manual Initiation of Protective Actions,"

notes that there are two "system level" main steam line manual isolation switches on the control board in the main control room; and that operating either switch will actuate all four MSIVs and their associated bypass valves. This description is consistent with the requirements noted in IEEE-279, Section 4.17, "Manual Initiation," which states: "The protection system shall include means for manual initiation of each protective action at the system level..." However, contrary to the UFSAR description, the information presented in the TS and TS Bases, (i.e., TS Table 3.3.2-1, "Engineered Safety Feature Actuation System Instrumentation," FUNCTION 4, "Steam Line Isolation," the associated TS Bases, and the Bases for TS 3.7.2, "Main Steam Isolation Valves (MSIVs)"), indicates that the main steam line manual isolation switches only close the MSIVs and not the bypass valves. The associated electrical prints also show that the isolation signals from the two system level manual switches only close the MSIVs and not the bypass valves. Note that the Braidwood Station and Byron Station configuration is identical.

This issue was documented in the Braidwood Station and Byron Station Corrective Action Programs. After a thorough review, it was concluded that the MSIV bypass valves remain operable as the actual plant configuration is consistent with the TS; however, the plant configuration does not conform to the requirements of IEEE-279; and therefore, is considered non-conforming with the current licensing basis.

Page 1 of 16

ATTACHMENT 1 Request for Exemption from 10 CFR 50.55a, "Codes and standards,"

Paragraph (h)(2), "Protection systems" II.

BASIS FOR EXEMPTION REQUEST The criteria for granting specific exemptions from 10 CFR 50 regulations are stated in 10 CFR 50.12. In accordance with 10 CFR 50.12(a)(1), the NRC may grant exemptions from the requirements of 10 CFR 50, which are:

"Authorized by law, will not present an undue risk to public health or safety, and are consistent with the common defense and security."

Further, 10 CFR 50.12(a)(2) states that: "The Commission will not consider granting an exemption unless special circumstances are present." Paragraph (2)(ii) describes one of those special circumstances that is applicable to the proposed exemption request.

"Application of the regulation in the particular circumstances would not serve the underlying purpose of the rule or is not necessary to achieve the underlying purpose of the rule;"

The underlying purpose of this rule, as stated in IEEE Std. 279, Section 1, "Scope," is to:

"...establish minimum requirements for the safety-related functional performance and reliability of protection systems..."

11.1

Overview The following discussion will demonstrate why it is acceptable to permanently exempt the MSIV bypass valves manual isolation function from the requirements of 10 CFR 50.55a, "Codes and standards," Paragraph (h)(2), "Protection systems." Application of the regulation, in this particular circumstance, is not necessary to achieve the underlying purpose of the rule.

In summary, each accident scenario that requires a main steam line isolation has been reviewed. The associated single failure assumptions for each scenario were specifically evaluated. It has been concluded that the subject non-conformance with IEEE Std. 279(i.e.,

the MSIV bypass valves do not receive an isolation signal from the two "system level" main steam line manual isolation switches) has no impact on the results of the applicable accident analyses; therefore, the consequences of the analyses of record (AOR), for each applicable accident scenario, remain valid and bounding.

Information supporting these conclusions and justifying the proposed exemption is presented in the following sections:

• Section 11.2, "System Description and Design Basis Function," provides a summary of the key functions of the MSIV and MSIV bypass valves.

• Section 11.3, "Regulatory Requirement Non-Conformance," clearly describes the specific issue of non-conformance.

Page 2 of 16

ATTACHMENT 1 Request for Exemption from 10 CFR 50.55a, "Codes and standards,"

Paragraph (h)(2), "Protection systems"

• Section 11.4, "Non-Conformance Resolution Cost and System Impacts," discusses the cost, operational flexibility concerns and minimal safety benefit associated with resolving the non-conformance.

• Section 11.5, "Safety Analysis Assumptions," summarizes the accidents scenarios relying on MSIV and MSIV bypass valve closure; and the associated single failure assumptions in the current AOR.

• Section 11.6, "Exemption Request Safety Consequences," provides a discussion related to the consequences of not meeting the regulation requirements.

• Section 11.7, "Justification for Exemption," specifically addresses each criteria noted in 10 CFR 50.12(a)(1) and (a)(2).

11.2

System Description and Design Basis Function Each unit at Braidwood Station and Byron Station is a Westinghouse design, four-loop pressurized water reactor with four steam generators and associated main steam lines. Each steam line is equipped with an approximate 30-inch MSIV (i.e., 30-inch for steam lines A and D; 32-inch for steam lines B and C) and a four-inch MSIV bypass valve as shown in Figure 1, "Main Steam System, Typical Loop." Note that this figure is used for training purposes and is presented here for information only. This figure is not controlled as a design document.

The MSIVs isolate steam flow from the secondary side of the steam generators under normal and emergency conditions; specifically following a High Energy Line Break (HELB) in the main steam piping. MSIV closure terminates flow from the unaffected (i.e., intact) steam generators.

Each MSIV is located in the main steam line outside, but close to containment. The MSIVs are downstream from the Main Steam Safety Valves (MSSVs), to prevent MSSV isolation from the steam generators by MSIV closure. Closing the MSIVs isolates each steam generator from the others, and isolates the turbine, steam dump system, and other auxiliary steam supplies from the steam generators.

The MSIVs close automatically on a main steam isolation signal generated by:

• Steam Line Low Pressure,

• Steam Line High Negative Rate, or

• High-high containment pressure.

Note that the MSIVs fail as is on loss of control or actuation power.

The MSIV bypass valves allow for a slow and controlled pressurization of the main steam piping and serve to warm up the main steam piping to avoid water hammer. The MSIV bypass valves are air operated and fail closed on a loss of instrument air or loss of DC power. Although these MSIV bypass valves are normally closed at power, they receive the same automatic closure signals as their associated MSIVs. Note that the MSIV bypass valves are also containment isolation valves.

Page 3 of 16

ATTACHMENT 1 Request for Exemption from 10 CFR 50.55a, "Codes and standards,"

Paragraph (h)(2), "Protection systems" Manual Isolation Features In addition to the automatic closure signals noted above, the MSIVs and MSIV bypass valves may also be manually closed. There are four individual MSIV momentary control switches (one per loop), and four individual MSIV bypass valve control switches (one per loop), mounted on the main control board. Each switch when actuated, will isolate its respective valve. In addition, there are two manual steam line isolation "system level" switches (i.e., each switch provides an "A" and "B" train signal). Operating either switch will close all four MSIVs; however, neither system level switch will close the MSIV bypass valves. The fact that the manual system level switches do not close the MSIV bypass valves is the subject of this proposed exemption.

11.3

Regulatory Requirement Non-Conformance The main steam line isolation function is part of the engineered safety features actuation system (ESFAS) as noted in UFSAR 7.3.1.1.1, "Function Initiation," Item f. The main steam line isolation feature is designed to prevent the continuous, uncontrolled blowdown of more than one steam generator and thereby prevent an uncontrolled reactor coolant system (RCS) cooldown.

As noted above, steam line isolation is accomplished by closure of the MSIVs and their associated bypass valves initiated by an automatic signal; or the valves can be closed manually.

Based on the MSIVs and MSIV bypass valves protection function, they are subject to the requirements of 10 CFR 50.55a(h)(2) which states that protection systems must meet the requirements of IEEE Std. 279. In addition, UFSAR Section 7.3.2.2, "Compliance with Standards and Design Criteria," specifically states: "The discussion given below shows that the engineered safety features actuation system complies with IEEE Standard 279-1971..." The specific IEEE Std. 279 requirement that the MSIV bypass valves do not meet is Requirement 4.17, "Manual Initiation." Requirement 4.17 states the following (note that key text is underlined for emphasis):

The protection system shall include means for manual initiation of each protective action at the system level (for example, reactor trip, containment isolation, safety injection, core spray, etc). No single failure, as defined by the note following Section 4.2, within the manual, automatic, or common portions of the protection system shall prevent initiation of protective action by manual or automatic means. Manual initiation should depend upon the operation of a minimum of equipment.

The note in IEEE Std. 279 following Section 4.2, "Single Failure Criterion," referenced in the above paragraph, states the following:

NOTE: "Single failure" includes such events as the shorting or open-circuiting of interconnecting signal or power cables. It also includes single credible malfunctions of events that cause a number of consequential component, module, or channel failures.

For example, the overheating of an amplifier module is a "single failure: even though several transistor failures result. Mechanical damage to a mode switch would be a "single failure" although several channels might become involved."

In addition, Braidwood and Byron Stations are committed to Regulatory Guide (RG) 1.62, "Manual Initiation of Protective Actions," October 1973. This RG was issued to clarify the intent Page 4 of 16

ATTACHMENT 1 Request for Exemption from 10 CFR 50.55a, "Codes and standards,"

Paragraph (h)(2), "Protection systems" of IEEE Std. 279. RG 1.62 Section C, "Regulatory Position," Items 1 and 2 state the following (note that key text is underlined for emphasis):

1. Means should be provided for manual initiation of each protective action (e.g.,

reactor trip, containment isolation) at the system level, regardless of whether means are also provided to initiate the protective action at the component or channel level (e.g., individual control rod, individual isolation valve).

2. Manual initiation of a protective action at the system level should perform all actions performed by automatic initiation such as starting auxiliary or supporting systems, sending signals to appropriate valve-actuating mechanisms to assure correct valve position, and providing the required action-sequencing functions and interlocks.

Since the MSIV bypass valves do not receive a manual isolation signal "at the system level," the requirements of IEEE Std. 279 and the guidance in RG 1.62 are not met. Also, the existing individual MSIV bypass valves manual control switches, located on the main control board, are single train switches such that a single failure of a switch could prevent the manual initiation of the protective action (i.e., prevent closure of the MSIV bypass valve). It should be noted that the individual MSIV bypass valves manual control switches are installed for testing and can be used during startup operations.

11.4

Non-Conformance Resolution Cost and System Impacts A modification would be required to add the MSIV bypass valves to the system level main steam line isolation function to eliminate the non-conformance with the requirements of IEEE Std. 279; however, this modification (on each of four units) would be costly and would not provide an increase in safety benefit as discussed below in Section 11.6, "Exemption Request Safety Consequences." This modification would also require a TS change to reflect the addition of the MSIV bypass valves to TS Table 3.3.2-1, "Engineered Safety Feature Actuation System Instrumentation," FUNCTION 4.a, "Manual Initiation," Note (c), which currently states: "Except when all Main Steam Isolation Valves (MSIVs) are closed."

In addition, installation of this modification would limit the current operational flexibility for performing the Trip Actuating Device Operational Test (TADOT) for the Steam Line Isolation Manual Initiation Function required by TS SR 3.3.2.9. This test is performed during startup after a refueling outage and may currently be performed in MODES 2 (below the point of adding heat), 3, 4, 5 or 6. If the test is performed in MODES 2, 3, or 4, heat removal from the RCS via the Main Steam System is required. Conducting this TADOT with the current system configuration will only close the MSIVs while the MSIV bypass valves remain open providing a steam flow / heat removal path to the condenser. Addition of the MSIV bypass valves to the system level manual isolation function would result in all MSIVs and MSIV bypass valves closing during the test, completely isolating the heat removal path, causing RCS temperature control issues and probable steam relief through the steam generator PORVs. Closing both the MSIVs and bypass valves would also depressurize and cooldown the downstream main steam piping and create the potential for water hammer upon subsequent re-pressurization.

Page 5 of 16

ATTACHMENT 1 Request for Exemption from 10 CFR 50.55a, "Codes and standards,"

Paragraph (h)(2), "Protection systems" It is recognized that MSIV and MSIV bypass valve testing could be done in phases; i.e., use the system level manual switches to close the MSIVs and bypass valves separately using electrical jumpers resulting in additional and unnecessary operator burden. As can be seen, adding the MSIV bypass valves to the system level manual isolation function would significantly limit operational flexibility as the testing would need to be done with no RCS heat load in only Mode 5 or 6.

Based on the above information and the justification presented below in Section 11.6, "Exemption Request Safety Consequences," it is concluded that installing the subject modification to restore compliance with IEEE Std. 279 would result in a reduction in operational flexibility and would not provide an increase in safety benefit. In lieu of installing this modification, EGC requests this exemption from the requirements of IEEE Std. 279 for the MSIV bypass valve manual isolation function.

11.5

Safety Analysis Assumptions The current design basis of the MSIVs is established by the analysis for the large Steam Line Break (SLB) outside containment, discussed in the UFSAR, Section 15.1.5, "Steam System Piping Failure at Zero Power." The MSIV design basis is also affected by the accident analysis of the SLB events inside containment presented in the UFSAR, Section 6.2, "Containment Systems." The design precludes the blowdown of more than one steam generator, assuming a single active component failure (e.g., the failure of one MSIV to close on demand).

The accident analysis compares several different SLB events against different acceptance criteria. The large SLB outside containment upstream of the MSIV is limiting for offsite dose, although a break in this short section of main steam header has a very low probability. The large SLB inside containment at hot zero power is the limiting case for a post trip return to power. The analysis includes scenarios with offsite power available, and with a loss of offsite power following turbine trip. With offsite power available, the reactor coolant pumps continue to circulate coolant through the steam generators, maximizing the RCS cooldown. With a loss of offsite power, the response of mitigating systems is delayed. Significant single failures considered in the analysis include failure of an MSIV to close.

UFSAR Section 15.1.5.1, "Identification of Causes and Accident Description," specifically notes:

For breaks downstream of the isolation valves, closure of all valves would completely terminate the blowdown. For any break, in any location, no more than one steam generator would experience an uncontrolled blowdown even if one of the isolation valves fails to close.

UFSAR Section 6.2.1.1.3, "Design Evaluation," also notes:

Single failure in the safety grade systems required to mitigate the consequences of a spectrum of main steam line breaks inside containment were evaluated to determine the limiting set of conditions for Byron/Braidwood. One such failure is the failure of a main steam isolation valve to close.

Page 6 of 16

ATTACHMENT 1 Request for Exemption from 10 CFR 50.55a, "Codes and standards,"

Paragraph (h)(2), "Protection systems" A manual isolation of the ruptured steam generator's MSIV and MSIV bypass valve is credited during a SGTR event (i.e., item d below) for both the Offsite Dose Case and the Margin to Overfill (MTO) Case. The SGTR event is discussed in UFSAR Section 15.6.3.

The MSIVs serve only a safety function and remain open during power operation. These valves operate under the following scenarios.

a. A HELB inside containment

b. A break outside of containment and upstream from the MSIVs

c. A break downstream of the MSIVs

d. Steam Generator Tube Rupture (SGTR)

e. Other events (i.e., feedwater line break) 11.6

Exemption Request Safety Consequences Discussion As noted earlier in Section II, the underlying purpose of this rule, as stated in IEEE Std. 279, Section 1, "Scope," is to "establish minimum requirements for the safety-related functional performance and reliability of protection systems..."

Section 11.3 also previously noted that since the MSIV bypass valves do not receive a manual isolation signal "at the system level," the requirements of IEEE Std. 279 and the guidance in RG 1.62 are not met. The existing individual MSIV bypass valves manual control switches, located on the main control board, are single train switches such that a single failure of a switch could prevent the manual initiation of the protective action (i.e., prevent closure of the MSIV bypass valve).

It is important to note that an automatic main steam line isolation is credited in the AOR for events described in items a, b, c and e below. A main steam line manual isolation is not credited in these events; therefore, the non-conformance with IEEE Std. 279(i.e., the fact that the MSIV bypass valves do not receive a "system level" main steam line manual isolation signal), has no impact on the accident analysis results as this manual feature is not credited to mitigate the consequences of these events.

It is also important to note that the automatic main steam line isolation function is designed to withstand a single failure as there are two trains (i.e., "A" train and "B" train) of main steam line isolation signals generated from the solid state protection system. Therefore, the need to rely on a "system level" main steam line manual isolation during any of the events described in items a, b, c and e below would require two independent failures of the automatic isolation signal.

Based on this design, the "system level" main steam line manual isolation system is not credited in any of these events.

Page 7 of 16

ATTACHMENT 1 Request for Exemption from 10 CFR 50.55a, "Codes and standards,"

Paragraph (h)(2), "Protection systems" A manual isolation of the ruptured steam generator's MSIV and MSIV bypass valve is credited during a SGTR event (i.e., item d below) for both the Offsite Dose Case and the MTO Case.

The limiting failures for the SGTR event are a failed open steam generator PORV for the Offsite Dose Case and a failed closed steam generator PORV for the MTO Case, discussed in detail below.

The below discussion demonstrates that exempting the MSIV bypass valves from the requirements of IEEE Std. 279, Section 4.17, "Manual Initiation," (i.e., not requiring the main steam line manual isolation "system level" switches to close the MSIV bypass valves) will have no impact on the consequences associated with the subject design basis accident scenarios.

Therefore, non-compliance with IEEE Std. 279 does not affect the functional performance and reliability of the main steam isolation protection system.

Evaluation For the spectrum of main steamline breaks analyzed in UFSAR Section 15.1.5, "Steam System Piping at Zero Power," and UFSAR Section 6.2, "Containment Systems," the associated single failure analyses evaluated the consequences of a failed open MSIV. The spectrum of main steam line breaks are addressed in items a, b, c and e below.

The SGTR event single failure assumptions and accident consequences are discussed in UFSAR Section 15.6.3, "Steam Generator Tube Rupture." The limiting failures for the SGTR event are a failed open steam generator PORV for the Offsite Dose Case and a failed closed steam generator PORV for the MTO Case, discussed in item (d) below.

Each of these scenarios is evaluated below to assess the consequences of not conforming to IEEE Std. 279 with regard to the MSIV bypass valves.

a. A HELB inside containment In order to maximize the mass and energy release into containment, the analysis assumes that the MSIV in the affected steam generator remains open. For this accident scenario, steam is discharged into containment from all steam generators until the remaining MSIVs close. After MSIV closure, steam is discharged into containment only from the affected steam generator and from the residual steam in the main steam header downstream of the closed MSIVs in the unaffected loops. Closure of the MSIVs isolates the break from the unaffected steam generators.

MSIV Bypass Valve Failure Consequences For this scenario, the analysis assumes that all MSIVs and MSIV bypass valves receive an automatic closure signal (i.e., a Train A and Train B closure signal). A main steam line manual isolation is not credited in this event as two independent failures (i.e., both trains) of the automatic isolation signal must fail before needing to rely on the "system level" manual isolation signal. Failure of both trains of the automatic isolation signal would constitute a beyond design basis event; therefore, conforming to IEEE Std. 279(i.e., providing the MSIV bypass valves with a "system level" main steam line manual isolation signal), may be Page 8 of 16

ATTACHMENT 1 Request for Exemption from 10 CFR 50.55a, "Codes and standards,"

Paragraph (h)(2), "Protection systems" exempted. However, it is noted that each MSIV and MSIV bypass valve has an individual control switch should the need arise to manually isolate one or more valves.

b. A break outside of containment and upstream from the MSIVs A break outside of containment and upstream from the MSIVs is not a containment pressurization concern. The uncontrolled blowdown of more than one steam generator must be prevented to limit the potential for uncontrolled RCS cooldown and positive reactivity addition. Closure of the MSIVs isolates the break and limits the blowdown to a single steam generator.

MSIV Bypass Valve Failure Consequences For this scenario, the analysis assumes the MSIVs and MSIV bypass valves receive an automatic closure signal (i.e., a Train A and Train B closure signal). A main steam line manual isolation is not credited in this event as two independent failures (i.e., both trains) of the automatic isolation signal would need to fail before needing to rely on the system level manual isolation signal. Failure of both trains of the automatic isolation signal would constitute a beyond design basis event; therefore, conforming to IEEE Std. 279(i.e.,

providing the MSIV bypass valves with a "system level" main steam line manual isolation signal), may be exempted. However, it is noted that each MSIV and MSIV bypass valve has an individual control switch should the need arise to manually isolate one or more valves.

c. A break downstream of the MSIVs A break downstream of the MSIVs will be isolated by the closure of the MSIVs. The analysis assumes that the MSIV in the affected steam generator remains open; however, closure of the MSIVs in the unaffected steam generators isolates the break and limits the blowdown to a single steam generator.

MSIV Bypass Valve Failure Consequences For this scenario, the analysis assumes the MSIVs and MSIV bypass valves receive an automatic closure signal (i.e., a Train A and Train B closure signal). A main steam line manual isolation is not credited in this event as two independent failures (i.e., both trains) of the automatic isolation signal would need to fail before needing to rely on the system level manual isolation signal. Failure of both trains of the automatic isolation signal would constitute a beyond design basis event; therefore, conforming to IEEE Std. 279(i.e.,

providing the MSIV bypass valves with a "system level" main steam line manual isolation signal), may be exempted. However, it is noted that each MSIV and MSIV bypass valve has an individual control switch should the need arise to manually isolate one or more valves.

Page 9 of 16

ATTACHMENT 1 Request for Exemption from 10 CFR 50.55a, "Codes and standards,"

Paragraph (h)(2), "Protection systems"

d. Steam Generator Tube Rupture (SGTR)

Following a SGTR, closure of the MSIVs isolates the ruptured steam generator from the intact steam generators to minimize radiological releases.

MSIV Bypass Valve Failure Consequences For this scenario, the analysis assumes the MSIV and the MSIV bypass valve, on the ruptured steam generator, are manually closed to isolate the steam generator. Manual valve closure is necessary since an automatic steam line isolation signal is not generated by this event. Since manual valve isolation is assumed in the analysis, the consequences of the non-conformance to IEEE Std. 279(i.e., not providing the MSIV bypass valves with a "system level" main steam line manual isolation signal), are evaluated in detail below.

After the SGTR occurs, reactor coolant immediately begins flowing from the primary system into the secondary side of the ruptured steam generator causing the RCS pressure to decrease until a reactor trip occurs on Overtemperature Delta-T. The reactor trip signal closes the turbine stop valves isolating steam flow to the turbine; however, the MSIVs (and MSIV bypass valves if open) remain open as an automatic steam line isolation signal is not generated by this event.

The analysis assumes that a loss of offsite power (LOOP) occurs coincident with the reactor trip causing the reactor coolant pumps (RCPs) to trip and the main condenser to become unavailable when the circulating water pumps are lost. After the reactor trips, the core power quickly decreases to decay heat levels. The steam dump system cannot be used to dissipate the core decay heat due to the unavailable condenser. Therefore, the secondary pressure increases in the steam generators until the steam generator PORVs open.

As noted above, the analysis also assumes that operator action is taken to manually isolate the MSIV and MSIV bypass valve on the ruptured steam generator (using the single train individual valve isolation switches; not the dual train "system level" switches) as directed by Emergency Operating Procedure, B(w)EP-3, "Steam Generator Tube Rupture," since an automatic steam line isolation signal is not generated by this event.

The SGTR analysis evaluates two major consequences of concern in the following cases:

1) Offsite Dose Case: There is potential to release primary system activity through the secondary side in excess of 10 CFR 50.67, "Accident source term," limits; and

2) Margin-To-Overfill (MTO) Case: There is potential for overfilling the ruptured steam generator before the Auxiliary Feedwater (AFW) flow to the steam generator can be isolated and the break flow terminated.

Page 10 of 16

ATTACHMENT 1 Request for Exemption from 10 CFR 50.55a, "Codes and standards,"

Paragraph (h)(2), "Protection systems" Offsite Dose Case For the Offsite Dose Case, the limiting single failure assumes failure of the ruptured steam generator PORV in the full open position.

To demonstrate that conformance to IEEE Std. 279(i.e., providing the MSIV bypass valves with a "system level" main steam line manual isolation signal) may be exempted, the below discussion is presented to evaluate the consequences of having a MSIV bypass valve failing open vice a steam generator PORV.

After the ruptured steam generator is identified, Emergency Operating Procedure, B(w)EP-3, "Steam Generator Tube Rupture," directs the operator to isolate the ruptured steam generator by manually closing the MSIV and MSIV bypass valve on the ruptured steam generator (only) using the single train individual valve isolation switches; not the dual train "system level switches." The ruptured steam generator PORV is assumed to fail open at the time the MSIV is closed and release contaminated steam directly to the environment. This is the most limiting single failure from a radiological standpoint.

If the MSIV and/or MSIV bypass valve fails to close with manual operator action using the individual manual isolation switches, the "Response Not Obtained" column in B(w)EP-3 directs the operator to manually actuate main steam line isolation (using the system level switches) and manually close the MSIV bypass valves (using the individual manual isolation switches) on all steam generators. Note that the MSIV bypass valve individual manual isolation switches are used since the "system level" main steam line manual isolation switches do not send a close signal to the MSIV bypass valves (i.e., the subject of the IEEE Std. 279 non-conformance). This action serves to isolate all intact steam generators from the ruptured steam generator. The "Response Not Obtained" column continues to state that if the ruptured steam generator MSIV or MSIV bypass valve is still open, then proceed to close a number of downstream valves to isolate the ruptured steam generators steam flow path.

Supplement 1 to WCAP-10698-P-A, "Evaluation of Offsite Radiation Doses for A Steam Generator Tube Rupture Accident," specifically evaluated the dose consequences of a MSIV failure to close on the ruptured steam generator and concluded that a failed open PORV on the ruptured steam generator remains the bounding single failure, as assumed in the current AOR. Note that the failure of a MSIV bypass valve was not explicitly analyzed; however, the steam flow to the environment through an MSIV bypass valve would be significantly less than the steam flow through the analyzed MSIV failure simply due to the much smaller line size (i.e., the MSIV bypass line is 4 inches in diameter whereas the MSIV line size is approximately 30 inches in diameter); therefore, it is clear that the dose consequences of a failed open MSIV bypass valve also remain bounded by the current AOR. Based on this discussion, use of the "system level" main steam line manual isolation switches to isolate the MSIV bypass valves is not needed to successfully mitigate the consequences of the SGTR Offsite Dose Case; thus, conformance to IEEE Std. 279 may be exempted.

Page 11 of 16

ATTACHMENT 1 Request for Exemption from 10 CFR 50.55a, "Codes and standards,"

Paragraph (h)(2), "Protection systems" Margin to Overfill Case For the MTO Case, the limiting single failure assumes that one of the intact steam generator PORVs fails closed, limiting the rate of RCS cooldown.

A failure of one of the intact steam generator PORVs to open causes a reduction in the RCS cooldown rate (i.e., only two vice three intact steam generator PORVs are now available for cooldown) which consequently results in a longer time to reach the necessary RCS subcooling margin prior to initiating the RCS depressurization which prolongs the time for primary to secondary leakage. These assumptions maximize primary to secondary leakage and minimize the MTO volume in the steam generators. At the time the MTO Case is terminated, the ruptured steam generator still contains more than 50 ft3 and more than 250 ft3 of gas volume margin for Unit 1 and Unit 2, respectively.

For the MTO Case, similar to the Offsite Dose Case, the analysis assumes the MSIV and the MSIV bypass valve, on the ruptured steam generator, are manually closed to isolate the steam generator. The MTO consequences of a failed open MSIV or MSIV bypass valve on the ruptured steam generator were specifically analyzed in the Byron/Braidwood SGTR Margin to Overfill Single Failure Assessment. The analysis concluded that failure of one of the intact steam generator PORVs to open remains the bounding single failure.

As can be seen, use of the "system level" main steam line manual isolation switches to isolate the MSIV bypass valves is not needed to successfully mitigate the consequences of the SGTR MTO Case; thus, conformance to IEEE Std. 279 may be exempted.

e. Other events The MSIVs are also utilized during a feedwater line break. This event is less limiting than the above events when considering MSIV OPERABILITY.

MSIV Bypass Valve Failure Consequences For the feedwater line break event, the analysis assumes the MSIVs and MSIV bypass valves receive an automatic closure signal due to a low steam line pressure (i.e., a Train A and Train B closure signal). A main steam line manual isolation is not credited in this event as two independent failures (i.e., both trains) of automatic isolation signal would need to fail before needing to rely on the system level manual isolation signal. Failure of both trains of the automatic isolation signal would constitute a beyond design basis event; therefore, conforming to IEEE Std. 279(i.e., providing the MSIV bypass valves with a 'system level' main steam line manual isolation signal), may be exempted. However, it is noted that each MSIV and MSIV bypass valve has an individual control switch should the need arise to manually isolate one or more valves.

Page 12 of 16

ATTACHMENT 1 Request for Exemption from 10 CFR 50.55a, "Codes and standards,"

Paragraph (h)(2), "Protection systems" 11.7

Justification for Exemption As noted above, the criteria for granting specific exemptions from 10 CFR 50 regulations are stated in 10 CFR 50.12. In accordance with 10 CFR 50.12(a)(1), the NRC may grant exemptions from the requirements of 10 CFR 50, which are:

"Authorized by law, will not present an undue risk to public health or safety, and are consistent with the common defense and security."

Further, 10 CFR 50.12(a)(2) states that: "The Commission will not consider granting an exemption unless special circumstances are present." Paragraph (2)(ii) describes one of those special circumstances that is applicable to the proposed exemption request.

"Application of the regulation in the particular circumstances would not serve the underlying purpose of the rule or is not necessary to achieve the underlying purpose of the rule;"

The below discussion addresses each of these criteria.

I. This exemption request is authorized by law The proposed exemption is authorized by law in that no other law exists to preclude the latitude afforded by this exemption request should it be approved in accordance with 10 CFR 50.12.

The proposed exemption will not impact the underlying purpose of the regulation (i.e.,

10 CFR 50.55a, "Codes and standards," Paragraph (h)(2), "Protection systems"). The specific underlying purpose of this rule is to "establish minimum requirements for the safety-related functional performance and reliability of protection systems..." as stated in IEEE Std. 279, referenced in the regulation. As shown above in Section 11.6, "Exemption Request Safety Consequences," the performance and reliability of the applicable protection system are unaffected by the proposed exemption as the protection system continues to perform its design basis function.

2. This exemption request will not present an undue risk to the public health and safety As discussed above in Section 11.6, "Exemption Request Safety Consequences," an evaluation was performed to assess the consequences of not conforming to IEEE Std. 279(i.e., not requiring the manual steam line isolation "system level" switches to close the MSIV bypass valves). This evaluation clearly demonstrated that the results of the accident analysis, considering this non-conformance, remain bounded by the current analysis of record.

Therefore, this request to exempt the system level MSIV bypass valves manual isolation function from the requirements of 10 CFR 55a(h)(2), which references IEEE Std. 279, will not present an undue risk to the public health and safety.

Page 13 of 16

ATTACHMENT 1 Request for Exemption from 10 CFR 50.55a, "Codes and standards,"

Paragraph (h)(2), "Protection systems"

3. This exemption request is consistent with the common defense and security This exemption request proposes to exempt the Braidwood Station, Units 1 and 2, and Byron Station, Units 1 and 2, system level MSIV bypass valves manual isolation function from the requirements of 10 CFR 55a(h)(2), which references IEEE Std. 279. This exemption will not affect the performance or reliability of power operations of any of the subject units and will not impact the consequences of any design basis event. Therefore, this exemption request is consistent with the common defense and security.

4. Application of the regulation in this particular circumstance would not serve the underlying purpose of the rule or is not necessary to achieve the underlying purpose of the rule This request proposes to exempt the system level MSIV bypass valves manual isolation function from the requirements of 10 CFR 55a(h)(2), which references IEEE Std. 279. The underlying purpose of this rule, as stated in IEEE Std. 279, Section 1, "Scope," is to "establish minimum requirements for the safety-related functional performance and reliability of protection systems..." Section 11.6, "Exemption Request Safety Consequences," above, demonstrates that the non-conformance with IEEE-279, Section 4.17, "Manual Initiation," does not affect the functional performance and reliability of the applicable protection system (i.e., the main steam line isolation function) as the protection system continues to perform its design basis function.

Therefore, it is concluded that application of the regulation in this particular circumstance is not necessary to achieve the underlying purpose of the rule.

III.

ENVIRONMENTAL ASSESSMENT In accordance with 10 CFR 51.30, "Environmental assessment," and 10 CFR 51.32, "Finding of no significant impact," the following information is provided in support of an environmental assessment and finding of no significant impact for the proposed action. The proposed action would result in a permanent exemption from the requirements of 10 CFR 50.55a, "Codes and standards," Paragraph (h)(2), "Protection systems," for Braidwood Station, Units 1 and 2, and Byron Station, Units 1 and 2. Specifically, the requested exemption would eliminate the requirement to meet the criteria stated in IEEE Std. 279, Section 4.17, "Manual Initiation," only for the system level Main Steam Isolation Valve (MSIV) bypass valves manual isolation function.

It has been shown that the proposed exemption (i.e., not requiring the MSIV bypass valves to receive a system level manual isolation signal), will have no effect on facility operations; will not create a new or different type of accident; and has no impact on the probability or consequences of previously analyzed accidents. No changes are being made that would affect the types or quantities of any radiological effluents that may be released offsite and there is no significant increase in occupational or public radiation exposure; therefore, there are no significant radiological environmental impacts associated with the proposed exemption. In addition, the proposed exemption does not affect non-radiological plant effluents and has no other environmental impact; therefore, there are no significant non-radiological impacts associated with the proposed exemption. Based on this information, the proposed exemption will not have a significant effect on the quality of the human environment.

Page 14 of 16

ATTACHMENT 1 Request for Exemption from 10 CFR 50.55a, "Codes and standards,"

Paragraph (h)(2), "Protection systems" IV.

CONCLUSION Based on the totality of the information presented above, the proposed exemption from the requirements of 10 CFR 50.55a, "Codes and standards," Paragraph (h)(2), "Protection systems," is consistent with the criteria of 10 CFR 50.12, "Specific exemptions." Specifically, EGC has determined that, in accordance with 10 CFR 50.12(a), the proposed exemption is authorized by law, will not present an undue risk to the public health and safety, and is consistent with the common defense and security. The proposed exemption is based on special circumstances present as application of the regulation in this particular circumstance is not necessary to achieve the underlying purpose of the rule; i.e., to "establish minimum requirements for the safety-related functional performance and reliability of protection systems..." as stated in IEEE Std. 279, Section 1, "Scope." Given the proposed exemption, the main steam line isolation system design basis is maintained and the consequences of all design basis accidents remain bounded by the current analysis of record; therefore, it is concluded that the functional performance and reliability of subject protection system are unaffected by this exemption request. Lastly, it has been concluded that that the proposed exemption will not have a significant effect on the quality of the human environment.

V. REFERENCES

1. IEEE Standard 279, "Criteria for Protection Systems for Nuclear Power Generating Stations," 1971

2. Regulatory Guide 1.62, "Manual Initiation of Protective Actions," October 1973 Page 15 of 16

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