ML20190A067

July 7, 2020, Teleconference Regarding Safety Chilled Water System License Amendment Request - Comanche Peak Talking Points

ML20190A067
Person / Time
Site:	Comanche Peak
Issue date:	07/08/2020
From:	Dennis Galvin Plant Licensing Branch IV
To:	Peters K Vistra Operations Company
Galvin D
References
EPID L-2020-LLA-0137
Download: ML20190A067 (6)

Text

JULY 7, 2020, TELECONFERENCE R E G A R D I N G NRC OBSERVATIONS ON THE JUNE 24, 2020, LICENSE AMENDMENT REQUEST TO MAKE A ONE-TIME CHANGE TO TECHNICAL SPECIFICATION 3.7.19, "SAFETY CHILLED WATER" VISTRA OPERATIONS C O M P A N Y L L C COMANCHE PEAK UNIT 1 AND 2 DOCKET NOS. 50-445 AND 50-446 By , Safety Chilled Water|letter dated June 24, 2020]] (Agencywide Documents Access and Management System (ADAMS) Accession No. ML20176A281), Vistra Operations Company LLC (the licensee) submitted a license amendment request (LAR) for Nuclear Regulatory Commission (NRC) approval for an amendment to the facility operating license for the Comanche Peak Nuclear Power Plant, Units 1 and 2 (Comanche Peak). The proposed amendment would revise Technical Specification (TS) 3.7.19, "Safety Chilled Water," Condition A, "One safety chilled water train inoperable," to add new required action A.2 with a 7-day completion time. This one- time change is to allow the replacement of the Comanche Peak Unit 2 Safety Chiller 2-06 compressor. The Nuclear Regulatory Commission (NRC) staff is conducting an acceptance review of the LAR and has identified the following observations/potential issues.

• The LAR enclosure states in several places that the proposed 7-day completion time for required action A.2 is based on a deterministic evaluation supplemented with risk insights.

LAR Enclosure Section 3.3, "Equipment Response to Loss of Cooling,"

addresses the deterministic evaluations related to loss of cooling to the engineered safety features equipment rooms. The conclusion of Section 3.3 states "These analyses demonstrated that on a loss of room cooling there is sufficient time to take corrective or compensatory actions to maintain acceptable room temperatures." However, Section 3.3 does not provide details to support the conclusion such as heat up rates, equipment qualification temperatures, the time to heat up to these temperatures, and the compensatory actions that are planned, including the capability to implement them within the required time periods.

o Discuss the basis for the conclusion that there is sufficient time to take corrective or compensatory actions to maintain acceptable room temperatures, including providing appropriate details. Also, discuss if the calculations were done for one train or both trains of the safety chilled water system.

The method of Interference Theory reviewed existing design and vendor documentation and data to estimate the probability that a given pump and motor would operate during its PRA mission time (24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />) if room cooling became unavailable. PWROG-18027-NP concludes that the use of Interference Theory to develop heat-up related probabilities is

acceptable. A summary of the major elements is;

• Reviewed existing room heat-up calculations in support of equipment survivability.

• Evaluated mechanical and electrical equipment qualification packages to determine the most limiting components.

• Evaluated lubricants used in these pieces of equipment and determined their maximum operating temperatures.

• Performed room heat-up calculations for each pump room that plot heatup rate as a function of time, for three sets of boundary conditions, to develop a correlation in support of the conditional probability calculations.

• Performed a statistical analysis of the temperature and the heat-up rates of the pump rooms to develop lognormal probability density functions for the pump rooms.

• The results of the statistical analysis are applied as conditional probabilities, given the failure of the room cooling system components or their supports.

An overview of the process used is as follows:

• Analyze the relevant components (pumps, batteries, chargers, switchgear) for the limiting sub-components and failure modes (vendor input required).

• Develop heat-up curves for the compartments containing the equipment, including all heat sources.

• Generate parameters for probability densities (PDFs) of allowable and actual component temperatures.

• Integrate for the region of failure to develop corresponding probabilities.

The conclusion of these reviews was; Lubricants testing showed that they would be suitable for service after remaining at 275°F for much longer than the PRA mission time.

For the pumps, non-metallic components such as gaskets and O-rings were found to have limiting operating temperatures of 250°F or less. Meaning the pumps have a low probability of failure at 122°F (approaching zero) and their reliability above 250°F is questionable.

Motor bearings were the most temperature limiting components. All motor bearings were either split sleeve type (periodically inspected and replaced as necessary) or ball bearings. For all of the bearings evaluated, the maximum bearing temperature at which the pump motor could operate, without loss of function, was approximately 250°F (169ºF ambient temperature with a heat rise of 81ºF).

Each pump room was simulated in a computer code called Compare Mod 1-A and heat-up curves were generated for three representative pump-specific initial ambient temperatures. Both trains were analyzed individually as each train is 100% capacity.

In accordance with calculation ME-CA-0000-3169-01, CCW Pump 1-01 Room 198, CCW Pump 1-02 Room 205, CCP 1-01 Room 200, CCP 1-02 Room 201, MDAFW Pump 1-01 Room 73 and MDAFW Pump 1-02 had the following

results on loss of room cooling:

Initial Pump Rooms Room Temp. (ºF) CCWP 1-01 CCWP 1-02 CCP 1-01 CCP 1-02 MDAFWP 1-01 MDAFWP 1-02 74 186 168 169 173 199 204 87 199 181 181 186 211 217 104 215 197 198 202 228 234 Room Temperatures at 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> (ºF)

• LAR Attachment 4, Figure 1, "Safety Chilled Water System," provides a flow diagram of the safety chilled water system flow diagram indicates an additional chilled water supply and return line tie-ins with trains A and B, with a blocked valve from Unit 2.

o Discuss the function of these additional chilled water supply and return line tie-ins.

These cross-connect valves are in the design to cross-connect safety chilled water between the units. One set of cross-connect valves is available to transfer the supply of safety chilled water to the fan coil units for the Spent Fuel Pool Heat Exchanger and Pump rooms. Either unit is capable of providing safety chilled water for these fan coil units.

The other set of cross-connect valves allows safety chilled water from one unit to be provided to the other unit Residual Heat Removal (RHR) Pump and Component Cooling Water (CCW) Pump room fan coil units for room cooling.

These cross-connects when used make the affected train on both units inoperable.

Both sets of cross-connect valves are controlled in accordance with ODA-403, Operations Department Locked Component Control procedure. In accordance with ODA-403 these valves are control based on two criteria; Criterion 2 - Sharing of Structures, Systems, and Components 2.1 This applies to safety related components which cross-connect units.

Two single-failure proof automatic isolation components or one locked in position component shall be used for separation.

To deviate a criterion 2.1 component from its secured position the following is required; An engineering review should be performed, taking into account the safety implications for both units, prior to the component's deviation. In cases where the prints contain notes which allow the locked components to be repositioned to supply common equipment from the off-normal unit, the engineering review has already been done and is reflected on the prints.

Criterion 4 - Safety Related Flowpaths 4.1 Technical Specifications require either frequent surveillance of valve position or locking the valves. Locking the valves reduces exposure (ALARA) and reduces the time required to verify valve positions.

• Enclosure, Section 3.6, "Assumptions and Compensatory Measures,"

identifies compensatory measures for severe weather after entry into TS 3.7.19 proposed required action A.2 and after 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> have elapsed. The compensatory measure addresses the issuance of a Severe Thunderstorm Warning or Tornado Warning and identifies actions to be taken within 6

hours and 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />. The NRC staff notes that weather warnings, compared to watches, indicate that the weather event is occurring or is imminent and that severe thunderstorm warnings or tornado warnings do not typically last 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />.

Enclosure, Section 3.6, states that Comanche Peak would not enter the one-time extended COMPLETION TIME if severe weather is anticipated. The NRC staff notes that this is one of the recommended compensatory measures for other allowed outage time extensions (see NUREG-0800, "Standard Review Plan," Branch Technical Position 8-8, "Onsite (Emergency Diesel Generators) And Offsite Power Sources Allowed Outage Time Extensions").

o Given that Comanche Peak has proposed the recommended severe weather compensatory measure and the typically short-term nature of severe thunderstorm warnings or tornado warnings, discuss the function of the compensatory measure upon issuance of warnings.

This compensatory measure was added as a contingency in the case when a severe thunderstorm or tornado warning are not short-term. The reasoning behind this measure is the challenge to offsite AC power sources due to the severe weather. As long as the offsite AC power sources remain viable there is no need to shutdown the affected unit. CPNPP would not enter the one time 7 day action requirement until the severe weather warning is cancelled for Somervell County.

APLC

• LAR Enclosure Section 3.3 mentions that the licensee has evaluated the loss of room cooling on engineered safety features equipment and cites the Updated Final Safety Analysis Report (UFSAR). The identified sections in the UFSAR do not provide information about the evaluations for loss of room cooling and the resulting insights.

The following FSAR section is what the Enclosure is referring to when discussing the loss of cooling water to vital components. Since, Safety Chilled Water, Component Cooling Water, and Station Service Water are all redundant, the loss of any one train does not cause a loss of safety function.

7.4.2.3.2 Loss of Cooling Water to Vital Equipment Cooling water for safety-related systems is supplied by the Safety Chilled Water System (Section 9.4F), the Component Cooling Water System (Section 9.2.2),

and the Station Service Water System (Section 9.2.1). Each of these systems is redundant; therefore, the loss of any one cooling loop or instrumentation associated with that loop will not degrade the safety-related equipment serviced by the system. Also see the analyses presented in Sections 9.4F, 9.2.1 and 9.2.2 and Tables 9.2-1 and 9.2-5.

Use of the word analysis in the last sentence of the preceding paragraph would be better worded as information vice analysis as the information supports that there are two independent 100% capacity trains of safety chilled water.

Either train satisfies the safety function requirements. The analysis documents referenced above look at each train separately.

LAR Enclosure Section 3.5.2, "Development and Use of PRA Insights,"

states that the loss of heating, ventilation, and air conditioning (HVAC) evaluations demonstrated that "in several areas analyzed the temperature reached following a loss of HVAC would allow components to continue to function with some higher likelihood and in other areas additional time would be available to take risk mitigating actions."

Please see preceding response regarding loss of room cooling.

LAR Enclosure Section 3.5.3, "Avoidance of Risk Significant Plant Configurations," states that "the dominant impact of the above scenarios on critical safety functions is the loss of heat removal from the Steam Generators due to failure of all the auxiliary feedwater pumps (random or induced) or loss of room cooling to the motor driven pumps."

o Discuss the loss of HVAC evaluation performed by the licensee and the insights from that evaluation.

Please see preceding response regarding loss of room cooling.

o Based on risk insights available to the NRC staff, the failure of the motor-driven auxiliary feedwater (AFW) pumps and failure of the component cooling water (CCW) pumps due to loss of room cooling appear to be dominant contributors to the sequences of interest for the proposed LAR.

However, the risk management actions in LAR Enclosure Sections 3.5.3 and 3.6 do not include actions to provide alternate room cooling (e.g.,

pre-staging diesel driven fans) for the rooms containing motor-driven AFW pumps and CCW pumps. Discuss the rationale for not including the risk management actions to provide alternate room cooling for the rooms containing motor-driven AFW pumps and failure of the CCW pumps.

Alternate room cooling could and would be provided if the loss of room cooling analysis had a different outcome. Based on the analysis the RHR pump rooms would be the rooms that would have the least amount of time before the pumps would be secured or damaged if not secured. Based on the preceding response regarding loss of room cooling there is sufficient time to either restore a train of safety chilled water or alternate room cooling. CPNPP believes the mitigative actions to protect the OPERABLE train of safety chilled water mechanically and electrically provide the best compensatory measures available. If there is no loss of all AC power but a loss of the operating train of safety chilled water, then the Primary Plant Ventilation System would still be cooling the areas adjacent to the pump rooms (halls and corridors) and opening the pump room doors and possibly increasing the supply of cooled air would provide additional time to implement alternate cooling.

• Based on risk insights available to the NRC staff, the loss of CCW initiator is a dominant contributor for the licensee's plant risk. As mentioned above, the loss of room cooling can impact the availability of the CCW pumps. LAR Enclosure Section 3.6 identifies protection of the Unit 2 CCW pumps as a risk management action. However, LAR Enclosure Section 3.5.3 states that the CCW crosstie configuration will be prohibited. Discuss how prohibiting CCW crosstie is an effective risk management action for the proposed change.

CPNPP first line of defense will be to protect the unaffected train (Train A) components and not perform any activities that would challenge those components. The procedural guidance to cross-connect CCW is provided in an off-normal procedure that could be used as an option if needed. The cross-unit option makes the Unit 1 train that is cross-connected to Unit 2 inoperable. A better statement is that the option of cross-connecting CCW trains between units was not included in the risk insights. All off-normal and emergency procedures could be implemented based on the conditions.

• Based on risk insights in LAR Enclosure Section 3.5.3, loss-of-offsite power is the dominant sequence for the proposed configuration. It is unclear whether the risk insights were developed with credit for the existing diverse and flexible coping (FLEX) strategies. Clarify whether FLEX strategies were credited in developing the risk insights presented in LAR Enclosure Section 3.5.3 or whether those strategies are uncredited defense-in-depth measures.

FLEX strategies were not used in developing the risk insights for extending the COMPLETION TIME. FLEX components could be used if the cause for the loss of the OPERABLE safety chilled water train is all AC power is lost and an ELAP is declared. FLEX equipment is provided in extreme circumstances that are not designed to maintain the ability to restart the units so they would only be used to protect the health and safety of the public.

STSB

• If during the work on the "B" train of the safety chilled water system, train "A" of a supported system becomes inoperable (e.g. failure of a containment spray pump supported by train "A" of the safety chilled water system},

potentially resulting in a loss of function, discuss actions to be taken as mandated by TS 5.5.15, "Safety Function Determination Program (SFDP)."

CPNPP first line of defense will be to protect the unaffected train (Train A) components and not perform any activities that would challenge those components. But if a supported system became inoperable on the protected train that would result in a Loss of Safety Function then the supported system LCO would be entered. Specifically, for a loss of both trains of Containment Spray, Unit 2 would enter LCO 3.0.3 and ensure the following;

a. MODE 3 within 7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br />;

b. MODE 4 within 13 hours1.50463e-4 days <br />0.00361 hours <br />2.149471e-5 weeks <br />4.9465e-6 months <br />; and

c. MODE 5 within 37 hours4.282407e-4 days <br />0.0103 hours <br />6.117725e-5 weeks <br />1.40785e-5 months <br />.