Text

Technical Specifications B.4.17., Steam Generator (SG) Tube Integrity, LTOP Orifice-Key Design Features, and Additional Information
	ML16083A565
Person / Time
Site:	Diablo Canyon
Issue date:	03/23/2016
From:	Gerfen P; Pacific Gas & Electric Co
To:	; Office of Nuclear Reactor Regulation
Shared Package
ML16084A588	List: DCL-16-028, Technical Specifications B.4.17., Steam Generator (SG) Tube Integrity, LTOP Orifice-Key Design Features, and Additional Information; ML16083A564;
References
	DCL-16-028
	Download: ML16083A565 (32)
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Steam Generator (SG) Tube Integrity B 3.4.17 BASES APPLICABLE The PORV setpoints in the PTLR will be updated when the revised PIT SAFETY limits conflict with the LTOP analysis limits. The PIT limits are ANALYSES periodically modified as the reactor vessel material toughness (continued) decreases due to neutron embrittlement caused by neutron irradiation.

Revised limits are determined using neutron fluence projections and the results of examinations of the reactor vessel material irradiation surveillance specimens. The PTLR discusses these examinations.

The failure of one Class I PORV is assumed to represent the worst case, single active failure.

RCS Vent Performance With the RCS depressurized, analyses show a vent size of 2.07 square inches is capable of mitigating the allowed LTOP transient. The capacity of a vent this size is greater than the flow of the limiting transient for the LTOP configuration, no Sl pumps, ~one ECCS CCP OPERABLE, and the NCP aligned to the LTOP orifice when it is capable of injecting into the RCS , maintaining RCS pressure less than the maximum pressure on the PfT limit curve.

The RCS vent size will be re-evaluated for compliance each time the PIT limit curves are revised based on the results of the vessel material surveillance.

The RCS vent is passive and is not subject to active failure. The pathway from the RCS to the vent is also considered to be passive.

The vent is considered to connect directly to the RCS. If the pathway includes devices with the potential to block the pathway, these devices must be secured to avoid blocking the vent. A PORV may be used as RCS vent if it is blocked opened by mechanical means with a vent size of at least 2.07 square inches. The associated block valve must be fully opened with the control power removed (Ref. 10).

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

This LCO requires that the LTOP System is OPERABLE. The LTOP LCO System is OPERABLE when RCS coolant input and pressure relief capabilities are within limits established in the LCO. Violation of this LCO could lead to the loss of low temperature overpressure mitigation capability and violation of the PTLR limits as a result of an operational transient.

To limit the coolant input capability, the LCO requires that a ma.*imum of zerono Sl pumps, and one CCP the NCP aligned to the LTOP orifice, and a maximum of one ECCS CCP (except during pump swap operations) be capable of injecting into the RCS, and all accumulator discharge isolation valves be closed and immobilized when accumulator pressure is greater than or equal to the maximum RCS pressure for the existing RCS cold leg temperature allowed in the PTLR.

(continued)

Steam Generator (SG) Tube Integrity B 3.4.17 BASES LCO Note 1 allows two charging pumpsECCS CCPs and the NCP aligned to (continued) the LTOP orifice to be made capable of injecting for s 1 hour1.157407e-5 days 2.777778e-4 hours 1.653439e-6 weeks 3.805e-7 months during pump swap operations. One hour provides sufficient time to safely complete the actual transfer and to complete the administrative controls and surveillance requirements associated with the swap. The intent is to minimize the actual time that more than one centrifugal charging pump is physically capable of injection .The intent is to minimize the time when the maximum flow could be more than the combined flow from the NCP aligned to the LTOP orifice and one ECCS CCP are physically capable of injecting.

Note 2 states that the accumulator may be unisolated when the accumulator pressure is less than the maximum RCS pressure for the existing temperature, as allowed by the PIT limit curves. This Note permits the accumulator discharge isolation valves Surveillance to be performed only under these pressure and temperature conditions.

The elements of the LCO that provide low temperature overpressure mitigation through pressure relief are:

a. Two RCS Class I PORVs as follows:

A Class 1 PORV is OPERABLE for LTOP when its block valve is open, its lift setpoint is set to the limit required by the PTLR and testing proves its ability to open at this setpoint, and motive power is available to the two valves and their control circuits.

OR

b. A depressurized RCS and an RCS vent.

An RCS vent is OPERABLE when open with an area of~ 2.07 square inches.

Either of these methods of overpressure prevention is capable of mitigating the limiting LTOP transient.

The LCO is modified by a Note that permits the NCP aligned to the LTOP orifice and two ECCS CCPs capable of injecting into the RCS for one hour for pump swap operation.

APPLICABILITY This LCO is applicable in MODE 4 when any RCS cold leg temperature is s LTOP arming temperature specified in the PTLR, in MODE 5, and in MODE 6 when the reactor vessel head is on and the vessel head closure bolts are not fully de-tensioned. RCS overpressure protection is not required in MODE 6 with the reactor vessel head closure bolts fully de-tensioned. The head is considered to be fully detensioned when all the nuts on the reactor head studs are backed off at least 0.3 inches (0.5 +/- 0.2 inches). This will provide adequate margin for pressure relief capability for a maximum ECCS injection flow when LTOP restrictions are no longer in place. A minimum of three equally spaced nuts will be retained to prevent head cocking, tilting, or separation of the upper internals from the fuel assemblies, if the head is to remain on the flange detensioned for any extended period of time.

Steam Generator (SG) Tube Integrity 8 3.4.17 (continued)

Steam Generator (SG) Tube Integrity B 3.4.17 BASES APPLICABILITY The pressurizer safety valves provide overpressure protection that (continued) meets the Reference 1 PIT limits above the limiting temperature specified in the PTLR. When the reactor vessel head is off, overpressurization cannot occur.

The PTLR provides the operational PIT limits for all MODES.

LCO 3.4.1 0, "Pressurizer Safety Valves," requires the OPERABILITY of the pressurizer safety valves that provide overpressure protection during MODES 1, 2, 3, and MODE 4 above LTOP arming temperature specified in the PTLR.

Low temperature overpressure prevention is most critical during shutdown when the RCS is water solid, and a mass or heat input transient can cause a very rapid increase in RCS pressure when little or no time is available for operator action to mitigate the event.

ACTIONS A Note prohibits the application of LCO 3.0.4.b to an inoperable LTOP system. There is an increased risk associated with entering MODE 4 from MODE 5 with LTOP inoperable and the provisions of LCO 3.0.4.b, which allow entry into a MODE or other specified condition in the Applicability with the LCO not met after performance of a risk assessment addressing inoperable systems and components, should not be applied in this circumstance.

A.1 and B.1 With one or more Sl pumps or two ECCS CCPs capable of injecting into the RCS, or the NCP not aligned to the LTOP orifice (when it is capable of injecting into the RCS) , RCS overpressurization is possible.

To immediately initiate action to restore restricted coolant input capability to the RCS reflects the urgency of removing the RCS from this condition.

C.1. D.1. and D.2 An unisolated accumulator requires isolation within 1 hour1.157407e-5 days 2.777778e-4 hours 1.653439e-6 weeks 3.805e-7 months . This is only required when the accumulator pressure is at or more than the maximum RCS pressure for the existing temperature allowed by the PIT limit curves.

If isolation is needed and cannot be accomplished in 1 hour1.157407e-5 days 2.777778e-4 hours 1.653439e-6 weeks 3.805e-7 months , Required ACTION D.1 and Required ACTION D.2 provide two options, either of which must be performed in the next 12 hours1.388889e-4 days 0.00333 hours 1.984127e-5 weeks 4.566e-6 months . By increasing the RCS temperature to > LTOP arming temperature specified in the PTLR, an accumulator pressure of 600 psig cannot exceed the PIT limits if the accumulators are fully injected. The second option to depressurize the accumulators below the PIT limits from the PTLR also gives this protection.

The Completion Times are based on operating experience that these activities can be accomplished in these time periods and on engineering evaluations indicating that an event requiring LTOP is not likely in the allowed times.

(continued)

Steam Generator (SG) Tube Integrity B 3.4.17 BASES ACTIONS E.1 (continued)

In MODE 4 when any RCS cold leg temperature iss LTOP arming temperature specified in the PTLR, with one required RCS Class I PORV inoperable, the RCS Class I PORV must be restored to OPERABLE status within a Completion Time of 7 days. Two RCS Class I PORVs are required to provide low temperature overpressure mitigation while withstanding a single failure of an active component.

The Completion Time considers the facts that only one of the RCS Class I PORVs is required to mitigate an overpressure transient and that the likelihood of an active failure of the remaining valve path during this time period is very low.

E1 The consequences of operational events that will overpressurize the RCS are more severe at lower temperature (Ref. 7). Thus, with one of the two RCS Class I PORVs inoperable in MODE 5 or in MODE 6 with the head on and the vessel head closure bolts not fully de-tensioned, the Completion Time to restore two valves to OPERABLE status is 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months .

The Completion Time represents a reasonable time to investigate and repair several types of relief valve failures without exposure to a lengthy period with only one OPERABLE RCS Class I PORV to protect against overpressure events.

G.1 The RCS must be depressurized and a vent must be established within 8 hours9.259259e-5 days 0.00222 hours 1.322751e-5 weeks 3.044e-6 months when:

a. Both required RCS Class I PORVs are inoperable; or

b. A Required Action and associated Completion Time of Condition A, B, D, E, or F is not met; or

c. The LTOP System is inoperable for any reason other than Condition A, B, C, D, E, or F.

The vent must be sized ~ 2.07 square inches to ensure that the flow capacity is greater than that required for the worst case mass input transient reasonable during the applicable MODES. This action is needed to protect the RCPB from a low temperature overpressure event and a possible brittle failure of the reactor vessel.

The Completion Time considers the time required to place the plant in this Condition and the relatively low probability of an overpressure event during this time period due to increased operator awareness of administrative control requirements.

(continued)

Steam Generator (SG) Tube Integrity 8 3.4.17 BASES (continued)

SURVEILLANCE SR 3.4.12.1. SR 3.4.12.2. and SR 3.4.12.3 REQUIREMENTS To minimize the potential for a low temperature overpressure event by limiting the mass input capability, a maximum of zerono Sl pumps and one ECCS CCP are verified capable of injecting into the RCS and the accumulator discharge isolation valves are verified closed and their breakers open. Verification that each accumulator is isolated is only required when accumulator isolation is required as stated in Note 1 to the LCO. Further, CCP 3 must be realigned for LTOP operation the NCP alignment to the LTOP orifice when it is capable of injecting into the RCS is also verified during LTOP conditions.

The Sl pumps and one ECCS CCP are rendered incapable of injecting into the RCS for example, through opening the DC knife switch supplying the pumps breaker's control power or removing the power from the pumps by racking the breakers out under administrative control or by isolating the discharge of the pump by closed isolation valves with power removed from the operators or by a manual isolation valve secured in the closed position.

An alternate method of providing low temperature overpressure protection may be employed to prevent a pump start that could result in an injection into the RCS. An inoperable pump may be energized for test or for accumulator fill provided the discharge of the pump is isolated from the RCS by closed isolation valve(s) with power removed from the valve operator(s), or by manual isolation valve(s) sealed in the closed position. The Surveillance Frequency is based on operating experience, equipment reliability, and plant risk and is controlled under the Surveillance Frequency Control Program.

SR 3.4.12.4 Not Used SR 3.4.12.5 The RCS vent of;;:; 2.07 square inches is proven OPERABLE by verifying its open condition.

The Surveillance Frequency is based on operating experience, equipment reliability, and plant risk and is controlled under the Surveillance Frequency Control Program.

(continued)

Steam Generator (SG) Tube Integrity 8 3.4.17 BASES SURVEILLANCE SR 3.4.12.5 (continued)

REQUIREMENTS Any passive vent path arrangement need only be open when required to be OPERABLE. This Surveillance is required to be performed if the vent is being used to satisfy the pressure relief requirements of LCO 3.4.12.b.

SR 3.4.12.6 The Class I PORV block valve must be verified open every 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months to provide the flow path for each required Class I PORV to perform its function when actuated. The valve must be remotely verified open in the main control room. This surveillance is performed if the PORV satisfies the LCO.

The block valve is a remotely controlled, motor operated valve. The power to the valve operator is not required removed, and the manual operator is not required locked in the inactive position. Thus, the block valve can be closed in the event the PORV develops excessive leakage or does not close (sticks open) after relieving an overpressure situation.

The Surveillance Frequency is based on operating experience, equipment reliability, and plant risk and is controlled under the Surveillance Frequency Control Program.

SR 3.4.12.7 Not Used SR 3.4.12.8 The SR Note states that the SR is not required to be performed until 12 hours1.388889e-4 days 0.00333 hours 1.984127e-5 weeks 4.566e-6 months after decreasing any RCS cold leg temperature to s LTOP arming temperature specified in the PTLR.

The SR may be performed prior to reaching ~ LTOP arming temperature and must be current (within 31 days) to meet this surveillance requirement. If not performed prior to reaching LTOP temperature, the test must be performed within 12 hours1.388889e-4 days 0.00333 hours 1.984127e-5 weeks 4.566e-6 months after entering the LTOP MODES. The 12 hour1.388889e-4 days 0.00333 hours 1.984127e-5 weeks 4.566e-6 months allowance considers the unlikelihood of a low temperature overpressure event during this time.

Following the initial SR, while remaining in the Applicable LTOP MODE, the SR will be performed thereafter on each required Class I PORV to verify and, as necessary, adjust its lift setpoint. The COT will verify the setpoint is within the PTLR allowed limits in the PTLR. PORV actuation could depressurize the RCS and is not required.

The Surveillance Frequency is based on operating experience, equipment reliability, and plant risk and is controlled under the Surveillance Frequency Control Program.

(continued)

Steam Generator (SG) Tube Integrity 8 3.4.17 BASES SURVEILLANCE SR 3.4.12.9 REQUIREMENTS Performance of a CHANNEL CALIBRATION on each required Class I (continued)

PORV actuation channel is required to adjust the whole channel so that it responds and the valve opens within the required range and accuracy to known input.

The Surveillance Frequency is based on operating experience, equipment reliability, and plant risk and is controlled under the Surveillance Frequency Control Program.

REFERENCES 1. 10 CFR 50, Appendix G.

2. Generic Letter 88-11 .

3. Not Used

4. FSAR, Chapter 5.

5. 10 CFR 50, Section 50.46.

6. 10 CFR 50, Appendix K.

7. Generic Letter 90-06.

8. Not Used

9. ASME Code Case N-514.

10. AR A0625429

11. AR A0589860

12. Diablo Canyon Power Plant Pressure and Temperature Limits Report -

13. Letter from NRC, dated January 3, 2013: \f\lolf Creek Generating Station Interpretation of Technical Specification Limiting Condition for Operation 3.4 .12, "Low Temperature Overpressure Protection (LTOP) System" (TAG No. Me9037)PG&E Letter DCL-16-028. License Amendment Request 16-02. "License Amendment Request To Revise Technical Specification 3.4.12. "Low Temperature Overpressure Protection (LTOP) System"." dated March 2016.

Enclosure Attachment 4 PG&E Letter DCL-16-028 L TOP Orifice- Key Design Features

Enclosure Attachment 4 PG&E Letter DCL-16-028 L TOP Orifice - Key Design Features Introduction There have been many positive displacement pump (PDP) failures reported in the industry, such as cracking of the pump block, vibration induced weld cracks in the nearby pipe, degassing in the chemical and volume control system and the emergency core cooling system, etc. The root cause was that the PDP suction stroke causes a significant depressurization of the hydrogen (H 2) saturated process fluid from the volume control tank resulting in gas coming out of solution in the PDP. The subsequent discharge stroke generated pressure pulses (water hammer) as the pump piston pushed through the H2 voids. PG&E replaced the PDP pump with a non-safety-related centrifugal charging pump (CCP), called the normal charging pump (NCP), during the Unit 1 Fourteenth Refueling Outage in 2007 and during the Unit 2 Fourteenth Refueling

_Outage (2R14) in 2008.

Flow Characteristics of PDP and NCP The flow range for the PDP was 99 gallons per minute (gpm) to 102 gpm; flowrate was fairly constant near 100 gpm for all the reactor coolant system (RCS) operating pressure conditions. However, the flowrate for a typical CCP is solely dependent on its discharge pressure according to the pump performance curve. The NCP performance curve measured in 2R14 is shown in Figure 1. From the results presented in Figure 1, it could be observed that the runout flow of the NCP is about 200 gpm.

Flow Choking Orifice (L TOP Orifice)

As a centrifugal pump discharge pressure decreases, the pump flow increases. When RCS is depressurized, the NCP would provide much more flow than the PDP to the RCS and could raise the low temperature overpressure (LTOP) transient concern. In order to limit the flow addition to the RCS, PG&E designed and installed a LTOP flow choking orifice (called the LTOP orifice) to limit the flow to less than 120 gpm. The LTOP orifice design takes advantage of the fact that the flow velocity has a vector property. Thus, by the arrangement of two opposing flow jets, the associated fluid kinetic energy cancels out, whereas the potential energy (in term of the local static pressure) is boosted to alleviate the cavitation concern associated with the typical orifice design.

The LTOP orifice drawing is shown in Figure 2.

Performance of LTOP Orifice: Wyle Lab Test Results An LTOP orifice performance test was conducted at Wyle lab to demonstrate its flow choking capabilities. The lab results are presented in Figure 3. From the results Page 1 of6

Enclosure Attachment 4 PG&E Letter DCL-16-028 presented in Figure 3, it can be observed that LTOP orifice limits the flow to less than 120 gpm.

Performance of L TOP Orifice: Acceptance Criteria The minimum LTOP orifice flow resistance maximizes the LTOP injection flow. This maximum injection flow is conservatively assumed in the LTOP transient analysis to challenge the RCS pressure. This LTOP orifice flow resistance as a function of the flowrate was incorporated into surveillance acceptance criteria as shown in Figure 4.

Performance of L TOP Orifice: Flow Alignment The LTOP orifice was installed in NCP discharge bypass piping. During plant shutdown, as well as during plant start-up, once the RCS pressure reaches the LTOP condition, the LTOP orifice charging bypass-line will be opened, and then the main discharge line will be isolated. This will direct the NCP flow through the LTOP orifice to limit the RCS charging flow.

Conclusion Based on the LTOP performance test conducted at Wyle Lab and in the field at DCPP, it is concluded that under LTOP conditions, when the NCP is aligned to the LTOP orifice, the NCP flow would be limited to less than 120 gpm (into the RCS) and would remain bounded by the LTOP analysis of record.

Page 2 of 6

Enclosure Attachment 4 PG&E Letter DCL-16-028 Figure 1: Normal Charging Pump (NCP) - Performance Curve 7000 6000 5000 g 4000

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0 25 50 75 100 125 150 175 200 225 250 Flow (gpm)

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Page 3 of6

Enclosure Attachment 4 PG&E Letter DCL-16-028 Figure 2: LTOP Orifice - Design Drawing 2'-0' 2' s¥4* IW 6' 6!il" C:ONCENTR I C SWAGE J'/,' CONCENTRIC SWAGE NCPPLE A NIPPLE S 3" MIN. 6" l'llN. 3" <MIN.l 2 ISOO* SOCkET WELDED RF' F'LANGE 4' MIN.

Page 4 of6

Enclosure Attachment 4 PG&E Letter DCL-16-028 Figure 3: L TOP Orifice - Pressure Drop -vs- Flow Rate (Wyle Lab Test Results) 1000 - - - - - - - - - - -* - - - - - - - - - * .-

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Page 5 of 6

Enclosure Attachment 4 PG&E Letter DCL-16-028 Figure 4: NCP aligned to LTOP Orifice -Acceptance Criteria 700 600

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Page 6 of6

Enclosure Attachment 5 PG&E Letter DCL-16-028 Additional Information

Enclosure Attachment 5 PG&E Letter DCL-16-028 Additional Information In Reference 1, Wolf Creek Nuclear Operating Corporation (WCNOC) submitted a license amendment request (LAR) to revise Technical Specification (TS) 3.4.12, "Low Temperature Overpressure Protection (LTOP) System," to reflect the mass input transient analysis that assumes an emergency core cooling system (ECCS) centrifugal charging pump (CCP) and the normal charging pump (NCP) capable of injecting into the reactor coolant system (RCS) during the TS 3.4.12 Applicability.

In Reference 2 and Reference 3, the Nuclear Regulatory Commission (NRC) requested for additional information (RAI) to complete the review of Reference 1.

The purpose of this attachment is to specifically address the RAI questions from References 2 and 3. Additional information that is pertinent to the current LAR is provided to the paraphrased NRC RAI questions below.

NRC RAI Question 1 from Reference 2 (ML13030A062):

({Please explain whether the mass input analysis of record addresses the ability to have three charging pumps capable of injecting into the RCS as could be allowed by the proposed Note to Technical Specification 3.4. 12."

Additional Information from PG&E:

The proposed Diablo Canyon Power Plant (DCPP) TS 3.4.12 is structured similar to WCNOC's TS and the DCPP LTOP analysis is also similar in that it analyzed a maximum flow associated with one ECCS CCP along with the NCP being capable of injecting into the RCS. The proposed DCPP TS Notes and administrative controls allow for up to one hour to perform a swap of safety-related ECCS CCPs, which is justified as a reasonable time frame in the NRC approved TSTF-285. This is considering the small likelihood of an LTOP event during this brief period and the other operator actions that would be readily available during the controlled evolution such as stopping any pump that inadvertently starts.

Procedure and administrative controls are discussed on Page 7.

NRC RAI Question 2 from Reference 2 (ML13030A062):

({Please provide a detailed summary of the mass input analysis that supports the LAR. Please include a description of the significant inputs to the analysis, explain how the RETRAN code was used (i.e., by referencing an NRC-approved methodology), provide key plots of the results, characterize any significant modeling assumptions, and explain how the results conform to the applicable acceptance criteria."

Page 1 of 16

Enclosure Attachment 5 PG&E Letter DCL-16-028 Additional Information from PG&E:

The DCPP LTOP analysis methodology using the RETRAN code is described in detail in Section 4.3, Provision 3 of Reference 5. This includes a listing of the significant analysis input assumptions and describing how the LTOP analysis is consistent with the NRC-approved methodology in WCAP-14040-NP-A. Therefore, this section will focus on providing key plots of the results, and a summary of the results explaining how the results conform to the applicable acceptance criteria.

Introduction The design basis mass injection event is defined as the initiation of the maximum injection flow capability for the applicable mode of operation into a water solid RCS with letdown isolated. Figure 1 plots a typical RCS pressure response for a LTOP mass injection event. The RCS pressure increases to the power operated relief valve (PORV) setpoint, however, due to instrument uncertainty and delays associated with the PORV opening time, the RCS pressure will continue increasing until the PORV has opened enough for the relief capacity to equal the mass injection capability. Consistent with WCAP-14040-NP-A, this maximum pressure above the PORV setpoint is labeled the RCS pressure overshoot as shown in Figure 1. As the PORV reaches full open, the relief capacity exceeds the mass injection capability and the RCS pressure begins decreasing and eventually reaches the PORV reset or close setpoint. However, similar to the overshoot, the RCS pressure continues decreasing below the reset value due to the instrument uncertainty and delays associated with the PORV closing time.

Consistent with WCAP-14040-NP-A, this minimum pressure value below the PORV setpoint is labeled the RCS pressure undershoot as shown in Figure 1.

The DCPP LTOP analysis methodology evaluates the limiting three pump configurations and mass injection capability that are allowed per the TS and administrative controls within the LTOP range of operation. The DCPP LTOP lift setpoint for the pressurizer PORV is established at a constant value and is currently set to 435 pounds per square inch, gage (psig). The maximum RCS overshoot that can occur for each mass injection case is determined and compared to the applicable Appendix G Pressure and Temperature (PIT) limits in the pressure and temperature limits report (PTLR) that protect the reactor vessel from potential brittle fracture. The LTOP analysis methodology then calculates the minimum RCS temperature at which the RCS Pressure Overshoot for a given mass injection configuration remains bounded.

The corresponding LTOP RCS temperature administrative limit accounting for PIT instrument uncertainties is then calculated to establish when a more restrictive mass injection pump configuration must be implemented to protect the LTOP limits. These LTOP administrative temperature limits are then updated into the DCPP PTLR and applicable operating procedures. The following section describes in detail how the LTOP mass injection results are generated and used to establish the LTOP administrative limits for the current DCPP PTLR which bounds a reactor vessel neutron fluence up to 27 effective full power years (EFPY).

Page 2 of 16

Enclosure Attachment 5 PG&E Letter DCL-16-028 LTOP Evaluation of Mass Injection Cases As described above, the LTOP orifice was designed to ensure that the total maximum mass injection capability with the NCP remains bounded by the original NRC approved LTOP mass injection analysis with the positive displacement pump (PDP)

(Reference 4). Therefore, the current LTOP mass injection analysis and calculated RCS overshoot based on the PDP still bounds the NCP operation with the LTOP orifice such that no new mass injection analysis is required to support this LAR. The mass injection flows listed in Table 1 are the original mass injection flows based on the PDP as approved by the NRC in Reference 4. These flow rates were calculated based on a conservatively bounding combination of maximum pump performance curves and minimum system line resistances. These flow cases have now been relabeled to be applicable for the NCP, since they conservatively bound the mass injection capability of the NCP providing flow through the LTOP orifice. The CCP and NCP flow are modeled as evenly distributed to each of the four RCS loops.

LTOP Administrative Actions and RCS Temperature Limits with Uncertainties Eight mass injection cases were analyzed to establish the RCS temperature limits associated with various LTOP administrative actions during plant shutdown and plant start-up conditions. Note that the NCP is always injecting through the LTOP orifice as required, and Reactor Coolant Pump (RCP) seal injection flow is provided to all operating RCPs. The analysis results for eight mass injection events are listed in Table 2 and Table 3. The LTOP administrative actions and the corresponding RCS temperature limits are listed in Table 4.

Table 2 summarizes the peak relative RCS pressure results for the pressurizer, reactor vessel, and RCS hot leg locations along with the RCS pressure overshoot result for each of the LTOP mass injection cases currently evaluated. The limiting LTOP peak pressure and RCS pressure overshoot results are established with respect to the reactor vessel peak pressure value.

Table 3 lists the LTOP analysis peak pressure results for each mass injection case corresponding to the reactor vessel peak pressure values listed in Table 2. Note that the Case C-6 with an open RCS vent is not listed in Table 3, since there is no RCS overpressure condition requiring uncertainty evaluation for this case.

Since the measurement uncertainties for the RCS pressure and the RCS temperature are independent, they may be statistically combined using the sum of the squares methodology. However, while the pressure error [plus/minus 31 pounds per square inch (psi)] has a constant 31 psi effect on the PIT curve limit, the temperature error (plus/minus 9°F) has a significantly greater effect on the Appendix G PIT limit curve as temperature increases. Therefore, Table 3 lists the total statistical error for each mass injection case as evaluated at the applicable section of the Appendix G PIT limit curve Page 3 of 16

Enclosure Attachment 5 PG&E Letter DCL-16-028 which conservatively bounds the mass input peak pressure and corresponding RCS temperature. Since the LTOP analysis peak pressure was originally calculated assuming a constant 32 psi pressure uncertainty on the PORV setpoint, this value is subtracted from the total statistical PIT error to determine the final PIT pressure limit listed in Table 3. The final PIT temperature limit in Table 3 is then determined by interpolating the Appendix G PIT limits at the value corresponding to the final PIT pressure limit.

The final PIT temperature limits in Table 3 represent the calculated temperature limits for performing the LTOP administrative actions to limit mass injection capability, RCP operation, and have an open RCS vent path. Table 4 lists the LTOP administrative actions and the corresponding RCS temperature limits (conservatively rounded values) that are currently listed in the DCPP PTLR effective to 27 EFPY, and which have been incorporated into the plant operating procedures. The basis for each administrative action is summarized below:

Action 1 - Enable LTOP TS 3.4.12 is applicable when any RCS cold leg temperature is less than or equal to the LTOP arming temperature that is specified in the PTLR (Reference 5). One of the two ECCS CCPs will be disabled and the NCP discharge will be aligned to the LTOP orifice, prior to entering the LTOP range of operation.

Action 2 -Block Sl Signal and ECCS Flow Paths When LTOP is first enabled, the safety injection (SI) signal and ECCS valves associated with the ECCS CCP are still in service. Therefore, the most limiting mass injection case in this LTOP range assumes that the NCP (via the LTOP orifice) and one ECCS CCP are both injecting through the four ECCS cold leg flow paths, with RCP seal injection flow to all four RCPs. The total mass injection flow rates as a function of the RCS pressure for this ECCS injection Case A are listed in Table 1. The peak pressure results from this ECCS injection case establish the minimum LTOP administrative RCS temperature limit for Action 2 at which the Sl signal and charging system ECCS flow path must be blocked.

Action 3 - Disable Second Charging Pump After the ECCS flow path is isolated, the most limiting mass injection flow is Case 8, which has the NCP aligned to the LTOP orifice and one ECCS CCP injecting simultaneously into both the normal and the alternate charging paths. This is conservative since DCPP plant procedures specify that only one charging injection path (normal charging or alternate) can be used at a time in the LTOP range. Table 1 summarizes the maximum mass injection flow rates versus RCS pressure for the ECCS CCP and the NCP. The peak pressure results from this mass injection case establish the minimum LTOP administrative RCS temperature limit Action 3 at which only one Page 4 of 16

Enclosure Attachment 5 PG&E Letter DCL-16-028 CCP (either the ECCS CCP or the NCP, but not both) is permitted to be operating at a time.

Actions 4, 5, 6, and 7 With only one charging pump allowed, the most limiting mass injection flow is Case C-1, which is one ECCS CCP injecting into both the normal and the alternate charging path, since this represents significantly more flow than the NCP injecting by itself through the LTOP orifice. Table 1 summarizes the Case C-1 maximum mass injection flow rates versus RCS pressure for one ECCS CCP. The peak pressure results from this CCP charging injection Case C-1 establish the minimum LTOP administrative RCS temperature limit at which all four RCPs may be operated.

The number of operating RCPs determines the dynamic pressure drop between the peak pressure which occurs at the bottom of the RCS vessel and the RCS hot leg where the LTOP pressure transmitter is located. Since the DCPP PORV actuation parameters (setpoint, delay time, and stroke time) are all constant throughout the LTOP range, the dynamic pressure drop translates into a direct increase in the RCS peak pressure overshoot. The maximum mass injection flow capability versus RCS pressure remains the same for the next four mass injection for cases (i.e., C-1 through C-4) as listed in Table 1 for one ECCS CCP. However, as the RCS temperature and the corresponding Appendix G PIT limit continue to decrease, the number of operating RCPs must be restricted to ensure the LTOP PORV parameters adequately protect the resulting peak pressure at the bottom of.the RCS vessel. The next four mass injection cases (i.e., C-1 through C-4) evaluate the peak pressure results for one ECCS CCP mass injection with 4, 3, 2, and 1 RCPs operating. These cases then determine the minimum LTOP administrative RCS temperature limits for Actions 4, 5, 6, and 7 to restrict the number of operating RCPs to 3, 2, 1, and 0, respectively. Actions 4, 5, 6, and 7 are summarized below:

Action 4 - Stop 1 of 4 RCPs Mass injection study - Case C-1 establishes the RCS temperature limit for Action 4 to stop one RCP and restrict operation to a maximum of 3 RCPs. In this mass injection study, the following charging flow rates were analyzed:

One ECCS CCP injecting into both the normal and alternate charging flow paths with 4 RCPs running.

Page 5 of 16

Enclosure Attachment 5 PG&E Letter DCL-16-028 Action 5 - Stop 2 of 4 RCPs Mass injection study- Case C-2 establishes the RCS temperature limit for Action 5 to stop a second RCP and restrict operation to a maximum of 2 RCPs. In this mass injection study, the following charging flow rates were analyzed:

One ECCS CCP injecting into both the normal and alternate charging flow paths with 3 RCPs running.

Action 6- Stop 3 of 4 RCPs Mass injection study - Case C-3 establishes the RCS temperature limit for Action 6 to stop a third RCP and restrict operation to a maximum of 1 RCP. In this mass injection study, the following charging flow rates were analyzed:

One ECCS CCP injecting into both the normal and alternate charging flow paths with 2 RCPs running.

Action 7- Stop 4 of 4 RCPs Mass injection study- Case C-4 establishes the RCS temperature limit for Action 7 to stop the fourth and the last RCP and restrict operation to no RCPs. In this mass injection study, the following charging flow rates were analyzed:

One ECCS CCP injecting into both the normal and alternate charging flow paths with 1 RCP running.

Action 8 - Establish RCS Vent The next mass injection case C-5 evaluates the same Case C (one ECCS CCP) mass injection through the normal and alternate paths with all RCPs secured. The results for this case then determine the minimum RCS temperature at which the LTOP PORV instrument uncertainties and opening delay time can still maintain the peak pressure overshoot below the Appendix G PIT limit curve. This then establishes the minimum LTOP administrative RCS temperature limit at which an open RCS vent path must be established since the automatic actuation of the PORV no longer provides adequate overpressure protection.

Final Mass Injection Study One additional final mass injection case C-6 is then evaluated to establish that with the required open RCS vent flow path size; there is no credible LTOP event which could challenge the Appendix G pressure limit such that no additional administrative actions are required in the LTOP range. In additio*n, TS 3.4.12 is not applicable once the Page 6 of 16

Enclosure Attachment 5 PG&E Letter DCL-16-028 reactor vessel head closure bolts are fully de-tensioned. In this mass injection study, the following charging flow rates were analyzed:

One ECCS CCP injecting into both the normal and alternate charging flow paths with 0 RCPs running and an open RCS vent flow path.

NRC RAI Question 1 from Reference 3 (ML13116A075):

Please provide a safety basis for the exception(s) to the safety analysis. This basis may include procedural controls, operator training, and related considerations, which ensure that the likelihood of an initiating event, which could cause the actuation of the two emergency core cooling system centrifugal charging pumps (CCPs) along with the normal CCP, remains minimal. The basis may also include similar considerations that show that the consequences of such a simultaneous actuation are reasonably mitigated.

Additional Information from PG&E:

Administrative and procedural controls for swapping ECCS CCPs are described in this section. Administrative and procedural controls for aligning the NCP to the LTOP orifice are also described in this section.

(A) Administrative and procedural controls for swapping ECCS CCPs The LTOP System controls RCS pressure at low temperatures so the integrity of the reactor coolant pressure boundary (RCPB) is not compromised by violating the Pff limits of 10 CFR 50, Appendix G.

Limiting Condition for Operation (LCO) 3.4.3, "RCS Pressure and Temperature (PIT)

Limits," requires administrative control of RCS pressure and temperature during heatup and cooldown to prevent exceeding the PTLR limits. Further, the proposed changes to LCO 3.4.12, "Low Temperature Overpressure Protection (LTOP) System," require the NCP to be aligned to the LTOP orifice (when it is capable of injecting into the RCS) during LTOP conditions.

DCPP Operating Procedure OP L-5, "Plant Cooldown From Minimum Load to Cold Shutdown," and OP L-1, "Plant Heatup From Hot Shutdown to Hot Standby,"

administratively control the availability of equipment that provides the methods of mass injection and pressure relief. These procedures control mass injection and pressure relief by directing the use of procedure OP 0-32, "Control of Refueling Tags," and applying administrative clearance on the appropriate equipment.

LCO 3.4.3 currently provides RCS overpressure protection by having a maximum coolant injection limitation and adequate pressure relief capacity. Limiting coolant input requires all Sl pumps and one ECCS CCP incapable of injection into the RCS and Page 7 of 16

Enclosure Attachment 5 PG&E Letter DCL-16-028 isolating the accumulators. Alignment of these ECCS pumps can be found in OP L-5, during shutdown and the realignment can be found in OP L-1, step 6.1.3.h for startup.

The NCP aligned to the LTOP orifice when it is capable of injecting into the RCS and a maximum of one ECCS CCP shall be capable of injecting into the RCS, in MODE 4, 5, and 6 when any RCS cold leg temperature is less than or equal to the LTOP arming temperature and the vessel head is tensioned.

However, CCPs in excess of the above limitations can be momentarily capable of injection into the RCS while swapping in-service CCPs. Note 1 of the proposed T.S. 3.4.12 allows the NCP aligned to the LTOP orifice and two ECCS CCPs to be made capable of injecting for less than or equal to 1 hour1.157407e-5 days 2.777778e-4 hours 1.653439e-6 weeks 3.805e-7 months during pump swap operations.

One hour provides sufficient time to safely complete the transfer and the administrative controls and surveillance requirements associated with the swap. The intent is to minimize the actual time that more than the combined flow from the NCP aligned to LTOP orifice and more than one ECCS CCP is physically capable of injection. This condition is acceptable based on the operator's attentiveness to RCS pressure during the pump swap over.

In addition, the following attributes and administrative controls provide additional margin to safety:

The LTOP System for pressure relief consists of two Class I PORVs with reduced lift settings or a depressurized RCS and an RCS vent of sufficient size.

One RCS Class I PORV has adequate relieving capability to prevent over-pressurization from the allowable coolant input capability specified by TS 3.4.12.

Two RCS Class I PORVs are required for redundancy providing ?dditional assurance of adequate pressure relief. OP L-5 requires arming both PORVs for low temperature overpressure protection when RCS wide range average temperature (WR Tave) is less than the PTLR upper limit (i.e., currently 350°F) and the lowest loop RCS wide range cold leg temperature (WR Tcold) is greater than the PTLR lower limit (i.e., currently 283°F).

The analog signals that would provide an ECCS actuation signal, except high containment pressure, are blocked below the PTLR limit (i.e., currently 1915 psig and Engineered Safety Feature Actuation System Interlock-Pressurizer Pressure, P-11, actuated) per OP L-5. This provides further assurance that an inadvertent start of an ECCS pump does not occur. This procedure specifies the steps necessary for ensuring that the safety injection pumps and one ECCS CCP are made incapable of injecting into the RCS for the TS 3.4.12 mode of applicability. Specifically, procedures OP L-5 via OP 0-32 and STP M-15, "Integrated Test of Engineered Safeguards and Diesel Generators," are used to close the discharge valves of the Sl and CCPs to prevent them from injecting.

Page 8 of 16

Enclosure Attachment 5 PG&E Letter DCL-16-028 When transferring charging pumps, OP B-1A:V, "CVCS- Transfer Charging Pumps,"

cautions against performing the pump transfer during solid plant operations because of the potential for rapid RCS pressure changes. In addition, the procedure reminds operators that the period of time that two charging pumps are operable is limited to one hour. The one hour time limit is tracked by use of a clearance point recorded in Appendix 3 of OP 0-32, "Control of Refueling Tags." In the event that the one hour time limit is exceeded, operators would initiate action to verify the NCP is aligned to the LTOP orifice and a maximum of one ECCS CCP is capable of injecting into the RCS, in accordance with T.S. 3.4.12.

The proposed LCO 3.4.12 Note 1 time window (one hour) of exposure is minimal. The likelihood of an operator error leading to an ECCS actuation or an inadvertent start of ECCS CCP during this one-hour window is remote. The procedure requirements exist in OP L-1, OP L-5, OP 0-32, and OP B-1A:V that provide instructions for pump swap operations. During this time window, there are at least two pressure relief devices (normally the PORVs) available for overpressure protection. The one-hour time limit allowed by the proposed LCO 3.4.12 Note 1 provides sufficient time to safely complete the transfer and to complete the administrative controls associated with pump swap operations.

(B) Aligning of NCP to the LTOP orifice under LTOP conditions (both during plant shutdown and plant start-up conditions)

The aligning of the NCP to the LTOP orifice is controlled by multiple procedures of which the OP L series procedures provide the high level direction. These procedures

direct the use of OP 0-32, "Control of Refueling Tags," which specifies and tracks the specific equipment configuration by use of administrative clearance points. Other procedures, such as STP M-15, "Integrated Test of Engineered Safeguards and Diesel Generators," and OP B-1 A:V can be used to achieve the LTOP orifice alignment if the associated equipment is being tested or swapped and operating procedure OP B-1A:V may be used for the specific steps to swap charging pumps.

The following sections describe the sequence of controlling plant equipment for a plant shutdown and for a plant startup that will be implemented after this license amendment request is approved by the NRC. Currently, only one CCP (i.e., the NCP aligned to the LTOP orifice or one ECCS CCP) is allowed to operate in the LTOP range of operation.

During plant shutdown:

During plant shutdown, with RCS WR Tave less than 350°F and greater than the PTLR lower limit of 283°F, OP L-5, "Plant Cooldown from Minimum Load to Cold Shutdown," directs both Sl pumps be disabled in accordance with STP M-15 or OP 0-32. One ECCS CCP is verified to be operable and then the other ECCS CCP is disabled in accordance with STP M-15 or OP 0-32. LTOP is then activated per OP L-5 by verifying that RCS pressure is less than 425 psig, the Page 9 of 16

Enclosure Attachment 5 PG&E Letter DCL-16-028 low set-point protection is then "cut-in" for PORVs PCV-455C and PCV-456 and the NCP alignment to the LTOP orifice is placed in service per OP 0-32.

Goold own continues to 174°F where the remaining operable ECCS charging pump is blocked from injecting into the ECCS flow path in accordance with OP L-6, "Cold Shutdown/Refueling." A second CCP (either the other ECCS CCP or the NCP) must be disabled when the RCS temperature is less than or equal to 161°F. A vent path of greater than or equal to 2.07 inches squared must be established when the RCS temperature is less than or equal to 96°F and the reactor head must be fully de-tensioned before the RCS temperature is less than 60°F.

During plant start-up:

The start-up sequence is initiated with OP L-6 with the reactor vessel head in place. A vent path is verified via an open PORV and the LTOP circuit is verified to be cut-in with refueling tags installed per OP 0-32. This includes the NCP alignment to the LTOP orifice. The refueling tags ensure that the accumulator isolation valves are closed and that both Sl pumps and one ECCS charging pump are disabled. In addition, either the second EGGS CCP or the NCP must be disabled until the RCS temperature is greater than 161°F. Reactor coolant heat-up commences using Residual Heat Removal (RHR) pumps and RCPs while ensuring that heat-up limits are satisfied per OP L-1. To prepare for entering Mode 4 (highest RCS WR Tave exceeds 200°F), one ECCS CCP is returned to service and the NCP is verified to be available. When Mode 4 is entered, operators transition from OP L-6 to OP L-1 and when the lowest WR Tcold reaches greater than 283°F, a one hour clock will start for CCP operability.

The NCP shall be made OPERABLE and at least two ECCS CCPs shall be OPERABLE prior to exceeding one hour. This includes closing the LTOP orifice isolation valve and reestablishing the normal flow path for the NCP.

Following the return to normal service of the ECCS CCPs and the NCP, the low set-point protection circuit is cut-out for PORVs PCV-455C and PCV-456. Since the maximum RHR temperature of 350°F is above the LTOP maximum, the RHR pump may be removed from service either before or after LTOP is disabled based on operational preference.

References

1. WCNOC Letter WO 12-0066, from R. A. Smith, to NRC, "Docket No. 50-482:

License Amendment Request to revise Technical Specification 3.4.12, 'Low Temperature Overpressure Protection (LTOP) System,"' dated November 21, 2012 (ML12334A406)

2. NRC Letter from C. F. Lyon, toM. W. Sunseri, WCNOC, "Wolf Creek Generating Station - Request for Additional Information Re: Revision to Page 10 of 16

Enclosure Attachment 5 PG&E Letter DCL-16-028 Technical Specification 3.4.12, 'Low Temperature Overpressure Protection (LTOP) System' (TAC NO. MF0309)," dated February 1, 2013 (ML13030A062)

3. NRC Letter from C. F. Lyon, toM. W. Sunseri, WCNOC, "Wolf Creek Generating Station - Request for Additional Information Re: Revision to Technical Specification 3.4.12, 'Low Temperature Overpressure Protection (LTOP) System,' (TAC NO. MF0309)," dated April30, 2013 (ML13116A075)

4. NRC Letter from D. Holland, to G. M. Rueger, DCPP, "Diablo Canyon Power Plant, Unit No. 1 (TAC No. MB5796) and Unit No. 2 (TAC No. MB5797) -

Issuance of Amendment Revising Technical Specification 5.6.6- Reactor Coolant System Pressure Temperature Limits Report," dated May 13, 2004 (M L041400243)

5. PG&E Letter DCL-02-079, "License Amendment Request 02-04, Revision of Technical Specification 5.6.6- Reactor Coolant System Pressure and Temperature Limits Report," dated July 31, 2002 (ML022200120)

6. TSTF-285 Rev. 1, "Charging Pump Swap LTOP Allowance," dated April 28, 1999 Page 11 of 16

Enclosure Attachment 5 PG&E Letter DCL-16-028 Table 1: DCPP LTOP Mass Injection Cases RCS Case A Case 8 Case C Pressure (psig) One ECCS CCP One ECCS CCP [C-1 to C-5]

and NCP Charging and NCP Charging One ECCS CCP Flow (gpm) Flow Charging Flow (gpm) (gpm)

[NOTE 1] [NOTE 2] I [NOTEs 3 and 4]

0.0 595.2 473 418 100.0 582.8 463 408 200.0 571.2 454 400 300.0 559.4 446 390 400.0 547.6 437 381 500.0 535.7 428 372 600.0 523.9 419 362 700.0 512 409 352 800.0 500.1 401 343 900.0 486.1 391 332 1000.0 472.2 381 322 Notes:

1. The NCP is injecting through the LTOP orifice into the four ECCS cold leg flow paths, and one ECCS CCP is also injecting into the four ECCS cold leg flow paths simultaneously.

2. The NCP is injecting through the LTOP orifice into both the normal and alternate charging flow paths, and one ECCS CCP is also injecting into both the normal and alternate charging flow paths simultaneously.

3. One ECCS CCP is injecting into both the normal and alternate charging flow paths with 4 RCPs running.

4. Case C consists of five sub-cases C-1 to C-5.

Page 12 of 16

Enclosure Attachment 5 PG&E Letter DCL-16-028 Table 2: Peak Pressure Results for L TOP Mass Injection Events Pressurizer Reactor RCS Hot RCS Case Mass Injection Case Description RCPs Pressure Vessel Leg Pressure (PSIA) Pressure Pressure Overshoot i(PSIA) (PSIA) (PSID) (1)

A One ECCS CCP and NCP Charging (z) 4 590.6 653.5 581.9 203.5 8 One ECCS CCP and NCP Charging<3 J 4 567.3 630.1 558.5 180.1 C-1 One ECCS CCP Charging<4 ) 4 556.2 618.7 547.1 168.7 C-2 One ECCS CCP Charging<4 J 3 547.2 597.5 547.8 147.5 C-3 One ECCS CCP Charging<4 ) 2 546.4 582.2 548.4 132.2 C-4 One ECCS CCP Charging<4 J 1 545.8 573.6 548.6 123.6 C-5 One ECCS CCP Charging<4 J 0 534.2 559.4 549.7 109.4 C-6 On~ ECCS CCP Charging w/ RCS 0 176.7 200.5 190.8 N/A vent(s)

Notes:

1. RCS Pressure Overshoot is defined with respect to PORV lift setpoint = 450 psia.

=

[RCS Pressure Overshoot Reactor Vessel Pressure (psia) minus 450 (psia)].

2. The NCP is injecting through the LTOP orifice into the four ECCS cold leg flow paths, and one ECCS CCP is also injecting into the four ECCS cold leg flow paths simultaneously.

3. The NCP is injecting through the LTOP orifice into both the normal and alternate charging flow paths, and one ECCS CCP is also injecting into both the normal and alternate charging flow paths simultaneously.

4. One ECCS CCP is injecting into both the normal and alternate charging flow paths.

5. One ECCS CCP is injecting into both the normal and alternate charging flow paths with an open RCS vent (one pressurizer PORV removed).

Page 13 of 16

Enclosure Attachment 5 PG&E Letter DCL-16-028 Table 3: LTOP Mass Injection PIT Limits with Uncertainty LTOP Total Final PIT Final PIT Analysis Statistical PIT Pressure Temperature MASS INJECTION CASE<2> Peak Error< 1> Limit <3> Limit Pressure (psi) (psia) (oF)

(psi a)

Case A: CCP (ECCS ) I NCP 653.5 36.6 658.1 173.3 Case 8: ECCS CCP I NCP 630.1 35.0 633.1 160.3 Case C-1: ECCS CCP - 4 RCPs 618.7 34.3 621.0 152.9 Case C-2: ECCS CCP - 3 RCPs 597.5 33.1 598.6 136.8 Case C-3: ECCS CCP - 2 RCPs 582.4 32.4 582.8 122.6 Case C-4: ECCS CCP - 1 RCPs 573.8 32.1 573.9 113.1 Case C-5:ECCS CCP- 0 RCPs 560.7 31.7 560.4 95.6 Notes:

1. Statistical combination of 31 psi pressure and 9°F temperature uncertainty on Appendix G Pff Curve.

2. Case C-6 with an open RCS vent is not listed in this table since there is no RCS overpressure condition requiring uncertainty evaluation.

3. Since the calculated LTOP analysis peak pressure already includes a conservative 32 psi uncertainty on pressure, the final Pff pressure limit is adjusted by the net uncertainty effect based on the total statistical Pff error minus 32 psi.

Page 14 of 16

Enclosure Attachment 5 PG&E Letter DCL-16-028 Table 4: DCPP PTLR LTOP Administrative Actions and RCS Temperature Limits for 27 EFPY< 1 H2>

LTOP Administrative Actions RCS (during a plant shutdown)(3) Temperature (oF)

Action 1. LTOP Enable - Disable one ECCS CCP and 283(4) align NCP through LTOP orifice Action 2. Block Sl signal and ECCS flow paths (s) 174 Action 3. Disable second charging pump 161 i.e., Operate either the NCP aligned to LTOP orifice or one ECCS CCP (but not both)

Action 4. Stop 1 of 4 RCPs 153 Action 5. Stop 2 of 4 RCPs 137 Action 6. Stop 3 of 4 RCPs 123 Action 7. Stop 4 of 4 RCPs 114 Action 8. Establish RCS Vent (6) 96

1. These LTOP administrative actions and associated RCS temperature limits will become applicable only after this LAR is approved and implemented. Currently, only one CCP (i.e., the NCP aligned to LTOP orifice or one ECCS CCP) is allowed to operate in the LTOP range of operation.

2. 27 EFPY Appendix G 0°F/hour cooldown curve with 10 percent relaxation per ASME Code Case N-514. All temperatures limits have been rounded to the next largest whole value.

3. The LTOP administrative actions will be implemented in reverse order during a plant startup, at the applicable RCS temperature limits. During a plant startup, the LTOP administrative actions will implement the opposite actions when compared to a plant shutdown (e.g. , stop 4 of 4 RCPs becomes start 1 of 4 RCPs).

4. This LTOP arming temperature is specified in the PTLR (Reference 5). It is calculated as a function of the reactor vessel material properties as described in PTLR Section 2.2.1. TS 3.4.12 is applicable when any RCS cold leg temperature is less than or equal to LTOP arming temperature.

5. The ECCS flow paths to the RCS cold legs are blocked by closing the ECCS injection motor operated valves and physically removing power to the operators.

6. Action 8 is the last LTOP administrative action, during a plant shutdown. After establishing the required RCS vent, no additional LTOP administrative actions are required for overpressure protection. In addition, TS 3.4.12 is not applicable once the reactor vessel head closure bolts are fully de-tensioned.

Page 15 of 16

Enclosure Attachment 5 PG&E Letter DCL-16-028 Figure 1 - DCPP LTOP Mass Input Typical RCS Pressure Transient 550 ~--------------------------------------------------------------------------~

500 +---------------~~----r---~---------------+------~r---------------~----~

u; E:

(1)

I..

~ 450 t/)

(1)

I..

a.

Cl) ------------------- * -----~-------------------------------

0 a:::

PORV Setpoint =435 psig Undershoot 400 ._----~~--------------------------------------------------------------------~

._----------~------------~------------~----------~------------~----------~

350 30 35 40 45 50 55 60 Time (Seconds )

Page 16 of 16

Steam Generator (SG) Tube Integrity B 3.4.17 BASES APPLICABLE The PORV setpoints in the PTLR will be updated when the revised PIT SAFETY limits conflict with the LTOP analysis limits. The PIT limits are ANALYSES periodically modified as the reactor vessel material toughness (continued) decreases due to neutron embrittlement caused by neutron irradiation.

Revised limits are determined using neutron fluence projections and the results of examinations of the reactor vessel material irradiation surveillance specimens. The PTLR discusses these examinations.

The failure of one Class I PORV is assumed to represent the worst case, single active failure.

RCS Vent Performance With the RCS depressurized, analyses show a vent size of 2.07 square inches is capable of mitigating the allowed LTOP transient. The capacity of a vent this size is greater than the flow of the limiting transient for the LTOP configuration, no Sl pumps, ~one ECCS CCP OPERABLE, and the NCP aligned to the LTOP orifice when it is capable of injecting into the RCS , maintaining RCS pressure less than the maximum pressure on the PfT limit curve.

The RCS vent size will be re-evaluated for compliance each time the PIT limit curves are revised based on the results of the vessel material surveillance.

The RCS vent is passive and is not subject to active failure. The pathway from the RCS to the vent is also considered to be passive.

The vent is considered to connect directly to the RCS. If the pathway includes devices with the potential to block the pathway, these devices must be secured to avoid blocking the vent. A PORV may be used as RCS vent if it is blocked opened by mechanical means with a vent size of at least 2.07 square inches. The associated block valve must be fully opened with the control power removed (Ref. 10).

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

This LCO requires that the LTOP System is OPERABLE. The LTOP LCO System is OPERABLE when RCS coolant input and pressure relief capabilities are within limits established in the LCO. Violation of this LCO could lead to the loss of low temperature overpressure mitigation capability and violation of the PTLR limits as a result of an operational transient.

To limit the coolant input capability, the LCO requires that a ma.*imum of zerono Sl pumps, and one CCP the NCP aligned to the LTOP orifice, and a maximum of one ECCS CCP (except during pump swap operations) be capable of injecting into the RCS, and all accumulator discharge isolation valves be closed and immobilized when accumulator pressure is greater than or equal to the maximum RCS pressure for the existing RCS cold leg temperature allowed in the PTLR.

(continued)

Steam Generator (SG) Tube Integrity B 3.4.17 BASES LCO Note 1 allows two charging pumpsECCS CCPs and the NCP aligned to (continued) the LTOP orifice to be made capable of injecting for s 1 hour1.157407e-5 days 2.777778e-4 hours 1.653439e-6 weeks 3.805e-7 months during pump swap operations. One hour provides sufficient time to safely complete the actual transfer and to complete the administrative controls and surveillance requirements associated with the swap. The intent is to minimize the actual time that more than one centrifugal charging pump is physically capable of injection .The intent is to minimize the time when the maximum flow could be more than the combined flow from the NCP aligned to the LTOP orifice and one ECCS CCP are physically capable of injecting.

Note 2 states that the accumulator may be unisolated when the accumulator pressure is less than the maximum RCS pressure for the existing temperature, as allowed by the PIT limit curves. This Note permits the accumulator discharge isolation valves Surveillance to be performed only under these pressure and temperature conditions.

The elements of the LCO that provide low temperature overpressure mitigation through pressure relief are:

a. Two RCS Class I PORVs as follows:

A Class 1 PORV is OPERABLE for LTOP when its block valve is open, its lift setpoint is set to the limit required by the PTLR and testing proves its ability to open at this setpoint, and motive power is available to the two valves and their control circuits.

OR

b. A depressurized RCS and an RCS vent.

An RCS vent is OPERABLE when open with an area of~ 2.07 square inches.

Either of these methods of overpressure prevention is capable of mitigating the limiting LTOP transient.

The LCO is modified by a Note that permits the NCP aligned to the LTOP orifice and two ECCS CCPs capable of injecting into the RCS for one hour for pump swap operation.

APPLICABILITY This LCO is applicable in MODE 4 when any RCS cold leg temperature is s LTOP arming temperature specified in the PTLR, in MODE 5, and in MODE 6 when the reactor vessel head is on and the vessel head closure bolts are not fully de-tensioned. RCS overpressure protection is not required in MODE 6 with the reactor vessel head closure bolts fully de-tensioned. The head is considered to be fully detensioned when all the nuts on the reactor head studs are backed off at least 0.3 inches (0.5 +/- 0.2 inches). This will provide adequate margin for pressure relief capability for a maximum ECCS injection flow when LTOP restrictions are no longer in place. A minimum of three equally spaced nuts will be retained to prevent head cocking, tilting, or separation of the upper internals from the fuel assemblies, if the head is to remain on the flange detensioned for any extended period of time.

Steam Generator (SG) Tube Integrity 8 3.4.17 (continued)

Steam Generator (SG) Tube Integrity B 3.4.17 BASES APPLICABILITY The pressurizer safety valves provide overpressure protection that (continued) meets the Reference 1 PIT limits above the limiting temperature specified in the PTLR. When the reactor vessel head is off, overpressurization cannot occur.

The PTLR provides the operational PIT limits for all MODES.

LCO 3.4.1 0, "Pressurizer Safety Valves," requires the OPERABILITY of the pressurizer safety valves that provide overpressure protection during MODES 1, 2, 3, and MODE 4 above LTOP arming temperature specified in the PTLR.

Low temperature overpressure prevention is most critical during shutdown when the RCS is water solid, and a mass or heat input transient can cause a very rapid increase in RCS pressure when little or no time is available for operator action to mitigate the event.

ACTIONS A Note prohibits the application of LCO 3.0.4.b to an inoperable LTOP system. There is an increased risk associated with entering MODE 4 from MODE 5 with LTOP inoperable and the provisions of LCO 3.0.4.b, which allow entry into a MODE or other specified condition in the Applicability with the LCO not met after performance of a risk assessment addressing inoperable systems and components, should not be applied in this circumstance.

A.1 and B.1 With one or more Sl pumps or two ECCS CCPs capable of injecting into the RCS, or the NCP not aligned to the LTOP orifice (when it is capable of injecting into the RCS) , RCS overpressurization is possible.

To immediately initiate action to restore restricted coolant input capability to the RCS reflects the urgency of removing the RCS from this condition.

C.1. D.1. and D.2 An unisolated accumulator requires isolation within 1 hour1.157407e-5 days 2.777778e-4 hours 1.653439e-6 weeks 3.805e-7 months . This is only required when the accumulator pressure is at or more than the maximum RCS pressure for the existing temperature allowed by the PIT limit curves.