ML20205G459

Safety Evaluation Supporting Amend 229 to License DPR-65

ML20205G459
Person / Time
Site:	Millstone
Issue date:	03/10/1999
From:	NRC (Affiliation Not Assigned)
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ML20205G444	List: ML20205G438 ML20205G459
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NUDOCS 9904070251
Download: ML20205G459 (7)

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,panec%}t UNITED STATES y*

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NUCLEAR REGULATORY ^OMMISSION

'2 WASHINGTON, D.C. 205.

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,o SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 229 TO FACILITY OPERATING LICENSE NO. DPR-65 NORTHEAST NUCLEAR ENERGY COMPANY THE CONNECTICUT LIGHT AND POWER COMPANY THE WESTERN MASSACHUSETTS ELF ^TRIC COMPANY MILLSTONE NUCLEAR POWER STATION. UNIT NO. 2 DOCKET NO. 50-336 i

1.0 INTRODUCTION

By letter dated December 10,1998, as supplemented by letter dated February 19,1999, the Northeast Nuc! ear Energy Company, et al. (NNECO, or the licensee), submitted a license amendment request to implement changes to the Millstone Nuclear Power Station, Unit No. 2 Fir,al Scfety Analysis Report (FSAR) regarding a revised method for ensuring boron precipitation can be prevented following a loss-of-coolant sec: dent (LOCA). The supplemental submittai provided additional information that did not change the staff's proposed no significant hazards consideration determination.

2.0 BACKGROUND

Within 8 to 10 hours1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br /> fo!!owing a LOCA, if the reactor coolant system (RCS) has not been re-filled then simultaneous hot and cold jeg injection is to t;w established to provide core flushing to preclude boron precipitation. The 8 to 10 hour1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br /> time frame is used as the decision point since it provides ample time to initiate simultaneous hot and cold leg injection prior to the occurrence d boric acid precipitation. Boron precipitation can occur when reactor coolant boron concentrations increase due to liquid boiloff. This can result in increased reactor core heating due to solidified boron interfering with heat transfer from the fuel rods to the coolant.

The preferred (primary) method for hot leg injection is with one low pressure safety injection (LPSI) pump injecting by way of the shutdown cooling (SDC) system warmup and return piping, past valves 2-SI-400,2-SI-709,2-SI-651, and 2-St-652, into the RCS hot leg (see Figure 1 in the licensee's December 10,1998, submittal). Cold leg injection for the preferred method is provided by LPSI flow diverted through at least one of the four LPSI injection lines (Cee Figure 1) and high pressure safety injection (HPSI) flow to the cold legs (see Figure 2 in the licensee's December 10,1998, submittal). It the preferred method cannot be established due to a single failure,91e alternative (backup) method of simultaneous hot and cold leg c

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injection is to be used. The alternative method for hot leg injection is with HPSI flow from one HPSI pump to the charging line to the pressurizer auxiliary spray line to the pressurizer surge line to the hot leg (See Figure 2), Cold leg injection for the alternative method is accomplished by LPSI flow (See Figure 1). Adequate flow to preclude boron precipitation as well as long term cooling is provided by either the preferred LPSI or altemative HPSI hot leg injection

- methods.

A licensee evaluation for the preferred and altemative injection methods determined that both are susceptible to single failures. A LOCA coincident with a loss of a Facility Z1 power source could prevent the opening of valve 2-St-651 (See Figure 1). This would prevent the use of the LPSI pumps and the SDC system for the preferred hot leg injection method. In addition, a Facility Z1 power loss could disable HPSI pump P41 A and preclude the closing of HPSI header valves 2-SI-617,2-SI-627,2-SI-637, and 2 SI-647 (See Figure 2) which need to be j

closed to ensure adequate net positive suction head (NPSH) when using the HPSI method of hot leg injection. A Facility Z1 power loss could also preclude the opening of HPSI suction and discharge cross-connect valves 2-SI-411 and 2-St-655 (See Figure 2), respectively. The opening of these two valves is required for the use of the HPSI swing pump P418 which can be used as an operating replacement for HPSI pump P41A. A LOCA coincident with a loss of a Facility 22 altemating current (AC) power source could preclude the opening of 2-SI-652 and thus proNbit the use of the LPSI pumps and the SDC system for the preferred hot leg injection method. In addition, a Facility Z2 direct current (DC) power source loss would preclude the opening of auxiliary spray line valve 2-CH-517 and the closing of charging header supply valve 2-CH-519 (See Figure 2). Operation of these valves is required for use of the HPSI method of hot leg injection.

Since important valves in bath the preferred and attemative injection methods could be disabled by failure orloss of a single power source, the licensee has proposed plant modifications to preclude disabling these valves due to single power source faiiure concems.

The requested amendment addresses the above-identified single failure problem in the licensee's plan to prevent boron precipitation folicwing a LOCA in which the RCS is not refilled.

The amsndment provides the followine-

1. Altemate Z2 electrical power to valve 2-St-651 in the RCS hot leg injection pipe,

2. Altemate Z1 electrical power to valve 2-CH-517 in the pressurizer auxiliary spray pipe,

3. Altemate Z1 electrical power to valve 2-CH-519 in the charging system header,

4. TestJacks at the respective motor control centers for determining valve position of 2-SI-615,2-SI-625,2-SI-635, and 2-SI-645 in the cold leg injection piping, and

5. Dypass capability of the low pressure open permissive for 2-SI-651.

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,- l 3.0 EVALUATION 1

3.1 Evaluation of Electrical Considerations Millstone Unit No. 2 has various components that can be supplied from alternate sources during normal plant operation. These components are classified as Facility Z5 and are defined in the FSAR as spare units of emergency equipment that can be transferred from one power source to another. The FSAR description of spare units notes that the components can be aligned to either one of two buses depending on which redundant piece of equipment is out of service. Valves 2-SI-651,2-CH-517, and 2-CH-519 do not meet the design requirement for l

Z5 components since these valves are not installed spares. Thus, changing the power feed to these valves is not allowed during normal operation and the attemate power supplies for these i

valves are to be used only after a LOCA to mitigate various single power source failures.

As illustrated in Figure 3 of tne licensee's December 10,1998, submittal, the alternate power source for valve 2-SI-651 is provided by the Facility Z2 motor control center (MCC) 861. A spare breaker from MCC B61 is cross tied into the circuitry for valve 2-SI-651. The Facility Z1/Z2 power feeds are cross connected by way of manual disconnect switches. The manual disconnect switches are equipped with Kirk Key interlocks to ensure only one disconnect switch can be closed at a time. This type of cross connect scheme is identical to the existing scheme used for the 480-volt swing charging pump and service water strainer motors.

Additionally, alignir$g valve 2-SI-651 to its alternate power supply is annunciated in the main control room. in addition, a local control panelis installed near MCC B51 (see Figure 3) to house the motor starter and the bypass and local control switch required to open valve 2-SI-651 upon a loss of Facility Z1 power. An open permissive for SDC isolation valve 2-SI-651 prevents the opening of the valve when RCS pressure is above 280 pounds per square inch absolute (psia). This permissive is implemented by a Facility Z1 power relay that must be energized to open valve 2-St-951. During a postulated LOCA and the loss of a Facility Z1 power source, this relay may not be energized and thus prevents the valve from being opened.

Regarding this ccncern, a local control switch is installed on the local control panel to bypass the disabled permissive and allow the valve to be operated locally. Bypassing the open permissive for this valve is also annunciated in the main control room. The open permissive for the upstream vaive 2-SI-652 (See Figure 1) would continue to be available. The alarm for when valve 2-SI-651 is open and RCS pressure is above 280 psia could also be disabled upon a complete loss of Facility Z1 power although position indication for this valve would be available at the local control panel by way of Facility Z2 power. The main control room alarm for upstream valve 2-St-652, which operates the same as the disaoled alarm for valve 2-SI-l 651, would be available.

An attemate power source for valves 2-CH-517 and 2-CH-519 is provided by Facility Z1 DC Instrument Panel DV10 as illustrated in Figure 4 of the licensee's December 10,1998, submittal. A spare breaker from DV10 is cross tied into the circuitry for valves 2-CH-517 and 2-CH-519. These valves are air operated valves which require DC control power. Since these valves only require DC control power, large disconnect switches with Kirk Key interlocks are not required. The Facility Z1 DC power feed is cross connected by way of key lock switches rated to handle the control power load. The keys for these switches are captured in one position to ensure only one power source can be aligned to the valves at a time. Aligning valves 2-CH-517 and 2-CH-519 to the alternate power source is ennunciated in the main

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control room.- The disconnect switch / breaker combination provides double isolation to ensure electrical separation between Facility Z1 and Z2 power sources. The Kirk Key interlock system on the 480-volt three phase disconnect switches assures only one disconnect switch can be closed at a time. Similarly, for the DC circuitry, the key lock switches with the key removable in only one position provides an equivalent level of prutection. The alternate power feeder breakers will administratively be kept in the open position. Thus a single short circuit associated with any isolation component will not compromise the separation between the Facility Z1 and Z2 power sources.

To provide attemate power to valves 2-SI-651,2-CH-517,'and 2-CH-519, new cables and intamal wiring are provided. The new cable and wiring routings maintain the required separation. New cables and wiring which are energized during norma' operation, are routed in conduits and trays associated with the facility providing normal power. Although, these components are not classified as Z5 components (installed spare components), separation requirements for redundant power routed to the same switch are maintained.

i Diesel generator, MCC, and battery loadings are affected by the preceding electrical plant modifications. Aligning the valves to the redundant power source, changes the loading for MCC B61, DV10, Battery 201A, and both diesel generators. However, the slight increase in load does not impact the ability of any of these components to supply the required loads.

Breaker coordination for MCC B61 ar.d DV10 are not affected by the modifications. For both MCC B51 and B61, the 100 Ampere (iQ charging pump motor breaker is the most limiting i

breaker. The new breaker in MCC B61 is a 35 A breaker similar to the existing breaker in MCC B51. The new breaker in DV10 is the same size as existing oreakers in DV20 which are properly coordinated. Thus, addition of the breakers in MCC B61 and DV10 does not invalidate the existing breaker coordination calculations.

The proposed plant modi 9 cations illustrated in Figures 3 and 4 add the capability to provide either Facility Z1 or Z2 safety-related power to valves 2-SI-651,2-CH-517, and 2-CH-519.

The physical connection between the redundant power trains (that is, mechanically interlocked disconnect switdes)is consistent with the requirements of the Millstone Unit No. 2 FSAR and Safety Guide 6 " Independence Between Redundant Standby (Onsite) Power Sources and Between Their Distribution Systems." This physical connection between redundant power trains is also similar to that of the current design for the swing battery charger and swing charging pump and service water strainer motors. However, valves 2-SI-651,2-CH-517, and 2-CH-519 are not designed to be installed spare units of emergency equipment and as such they will only be aligned to the alternate power feed following a LOCA with a single failure in eithor the Facility Z1 or Z2 power distribution system.

The cables for valve 2-SI-651 will remain routed in Facility Z1 cable truys, conduits, and containment penetrations. Similarly, the cables for valves 2-CH-517 and 2-CH-519 will remain routed in Facility Z2 cable trays, conduits, and contairiment penetrations. The independence and physical separation of the redundant power systems is provided by a normally open disconnect switch and a normally open circuit breaker wired in series. With this design, ao single component failure can result in the redundant power trains being paralleled or routed together during normal operation. Multiple operator errors would be required to align valves 2-Si-651,2-CH-517, or 2-CH-519 to the alternate power eource during normal operation.

Additionally control room operators would have to disregard annunciators that indicate the

. valves are transferred to their alternate power source. The disconnect switches are mechanically interlocked as required by FSAR criteria and Safety Guide 6. The mechanical interlock ensures that the attemate feed disconnect switch cannot be closed until the primary disconnect switch is open. Thus, during normal plant operation a single failure of either the altemate breaker or disconnect switch cannot result in the cross connection of the two redundant power facilities.

When aligned to the attemate power source, the potential for routing Facility Z1 and Z2 power in the same cable trays, conduits, and containment penetrations exists. However, the ir tegrity of the cables, breakers and disconnect switches ensures that nhough the two redundant trains are routed together, both trains are protected. The new cables have been sized such that they have the required ampacity for their bads. The new breakers, B6172 and DV10 Circuit 12, and the motor starter for 2-SI-651 are sized such that they protect the cables from damage during any potential overcurrent condition. Based on a Facility Z1 or Z2 power source failure, no collateral damage is expected to exist that could impact valves 2-SI-651, 2-CH-517, and 2-CH-519. With safety-related cables, cable trays, conduits, circuit breakers, and penetrations operational and with proper breaker coordination, the alternate branch breaker Will trip prior to the alternate feeder breakers. Additionally, the isolation of all main control

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room indication and control circuitry for valve 2-SI-651, when aligned to the alternate power feed, eliminates separation concems for cables routed to the main control room.

The electrical plant modifications also provide test jacks to determine the valve position of the four LPSI injection valves 2-St-615,2-SI-625,2-SI-635, and 2-SI-645 (See Figure 1) during a loss of Facility Z1 or Z2 power. The new position indication connection jacks are added to the respective MCC and provide no control functions. The connection points are wired in paralle!

with the existing valve limit switches providing position indication.

1 The proposed electrical plant modifications ensure that single power source failures do not prevent the functional operation of long term core cooling equipment. The design for these modifications is such that there is no single failure during normal plant operation that could result in the redundant safety-related power trains being paralleled or routed in the same cable trays or conduits. The design for these modifications is also such that when the alternate power source is required during accident conditions, the electrical protective devices preclude the tripping of the redundant power train. The new electrical components, cabling, and position indication connection Jacks are designed for the rated voltages and currents. Further, the new equipment iterns are Quality Assurance Category I seismically and environmentally qualified as required and do not degrade the separation of the redundant power systems.

j The electrical design modifications as described are in conformance and are consistent with the single failure criterion, the recommendations contained in Safety Guide 6, the existing I

electrical protective device coordination scheme, and the physical separation criteria provided in the FSAR. On the basis of these findings, the staff concludes that the proposed electrical plant modifications conform to the applicable criteria and are acceptable.

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3.2 Reactor Systems Evaluation The staff's reactor systems review considered potential safety implications associated with the FSAR changes and identified the impact on a LOCA outside containment as the greatest concem. Consequently, the staff included aspects of this potential LOCA in their review and obtained further information relative to this topic from the licensee (see February 19,1999, supplemental submittal).

i The reactor systems review of the licensee's modifications deterrnined the licensee's proposed modifications to be acceptable. However, in Insert M of Attachment 3 of the Decernber 10, 1998, submittal, the licensee stated:

"When piessurizer pressure is less than 600 psia and stable with a controlled cooldown in progress, the Safety Injection Tanks (SITS) are isolated to avoid injecting nitrogen, a non-condensable gas, into the reactor coolant system (RCS)."

Isolation or venting the SITS is also included in FSAR Figure 14.6.5.3-1. On January 14,1999, the licensee documented a single failure condition involving potential inability to isolate or vent the SITS (" Emergency Core Cooling System Single Failure Vulnerat,ility," Millstone Nuclear Power Station Unit 2, LER No. 98-002-01, January 14,1999). The licensee discussed corrective actions in their February 19,1999 submital and LER 98-002-01 and stated that modifications to correct the condition will be completed prior to entry into Mode 4 from the current outage. h further stated that a review of the facility LOCA analysis will be completed prior to entry into Mode 4 from the current cutage to ensure that additional weaknesses l

relating to the single failure criterion have been identified and addressed. The staff notes that any identified design deficiencies must be corrected for the FSAR to be correct. This issue is being addressed separately and is not considered further in this safety evaluation.

The staff notes that a substantial flow passage blockage by precipitated boron would be necessary to prevent water flow to the fuel and hence to jeopardize fuel cladding integrity.

Such a condition would require a substantial quantity of precipitated boron. The operational and licensing approach is to prevent an approach to lack of cooling by not allowing boron precipitation to initiate, and to incorporate further conservatism by including additional margin in calculating the approach to the precipitation limit. The 4 percent margin is one of the assumptions used to ensure conditions are not entered where boron can begin to precSitate.

i Others include.the 1971 representation of decay heat plus 20 percent, and a boiloff model in which no boron is removed. It is the staff's engineering judgement that such conservatisms, in combination with the low probability of the LOCA of potential concern, results in a condition where not including the 4 percent margin is acceptable. Therefore, the licensee's proposal is acceptable.

3.3 Evaluation Summary TNe NRC staff performad reviews of both the electrica' and reactor systems aspects of the licensee's proposed FSAR changes. Based on the staff's review of information presented by the licensee, the ttaff finds the licensee's proposed FSAR changes to be acceptable.

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4.0 STATE CONSULTATION

in accordance with the Commission's regulations, the Connecticut State official was notified of the proposed isstance of the amendment. The State official had no comments.

5.0 ENVIRON 14 ENTAL CONSIDERATION The amendment changes requirements with respect to installation or use of a facility component located within the restricted area, as defined in 10 CFR Part 20. The NRC staff has determined that the amendment involves no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure. The Commission has previously issued a proposed finding that the amendment involves no significant hazards consideration, and there has been no public comment on such finding (64 FR 2249, January 13,1999). Accordingly, the amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9). Pursuant to 10 CFR 51.22(b) no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendment.

6.0 CONCLUSION

The Commission has concluded, based on the considerations discussed above, that: (1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public.

Principal Contributors: F. Ashe and W. Lyon Date:

March 10,1999 l

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