ML20078J378

Proposed Tech Specs Reducing Leak Rate Test Pressure for Safety Related ADS Nitrogen Receiving Tanks from 385 Psig to 365 Psig

ML20078J378
Person / Time
Site:	Nine Mile Point
Issue date:	11/14/1994
From:	NIAGARA MOHAWK POWER CORP.
To:
Shared Package
ML20078J353	List: ML20078J348 ML20078J374 ML20078J378
References
NUDOCS 9411210184
Download: ML20078J378 (5)

Text

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EMERGENCY CORFmCOOLING SYSTEMS l 1

ECCS - OPER ATING i

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SURVEILLANCE REQUIREMENTS 4.5.1 (Continued) e) Performing a leak rate toct for the safety related ADS accumulator pneumatic supply system (including special emergency tube trailer supply piping) up to SRV actuators / operators. With the SRV's actuated by either of the ADS solenoids and with ADS accumulators at 178 psig and with ADS nitrogen receiving tanks at 365 psig (high pressure alarm), the leakage rates j shall not exceed the following limits:

1. For the ADS SRV actuators, supply header and accumulators, and the nitrogen receiving tank for the SRV's 2 MSS *PSV 121,126 & 127, maximum allowable leakage is 3 SCFH.

2. For the ADS SRV actuators, supply header and accumulators, and the nitrogen receiving tank for the SRV's 2 MSS *PSV 129,130,134,&

137, maximum allowable leakage is 4 SCFH.

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l NINE MILE POINT - UNIT ? 3/4 5-6 Amendment No.

9411210184 941114 PDR ADOCK 05000410 p PDR

s ATTACHMENT B NIAGARA MOHAWK POWER CORPORATION LICENSE NO. NPF-69 DOCKET NO. 50-410 l Snecific Information and No Stanificant Hazards Consideration Analysig _

BACKGROUND The Nine Mile Point Unit 2 (NMP2) Automatic Depressurization System (ADS) is designed to provide automatic depressurization of the reactor vessel by activating seven (7) safety /

relief valves (SRV). These valves vent steam from the reactor vessel to the suppression pool in the event the High Pressure Core Spray System (HPCS) cannot maintain reactor  ;

water level following a loss of coolant accident. The ADS reduces reactor pressure so that flow from the Low Pressure Core Spray System (LPCS) and the low pressure coolant injection (LPCI) mode of the Residual Heat Removal System (RHR) can inject to and cool l the core. This limits fuel cladding temperature during small break loss of coolant I accidents. in the ADS mode, each of the ADS SRVs is opened by compressed nitrogen l from its respective accumulator (located in Primary Containment) via a solenoid valve. The )

accumulators are supplied from two nitrogen receiving tanks (located inside Secondary Containment) which are supplied from a bank of high-pressure nitrogen storage tanks located outside of the Reactor Building. The ADS receiving tanks provide an inventory of nitrogen to make up for system leakage and maintain the accumulators charged for five days after initial actuation of the ADS. The nitrogen receiving tanks also provide for one additional sustained SRV actuation during the five days. This five day capability is maintained without taking credit for any makeup from the high pressure nitrogen storage tanks.

In order to maintain a sufficient inventory, the initial pressure of the nitrogen receiver tanks must be at least 334 psig and the leakage for receiving tanks 2lAS *TK4 (supplies 3 ADS SRVs) and 2lAS*TK5 (supplies 4 ADS SRVs) must be less than or equal to 3 SCFH and 4 SCFH, respectively. The ability of the nitrogen receiving tanks to perform their design function is currently verified by Surveillance Requirement 4.5.1.e.2.e), which requires leak rate testing at 385 psig. This pressure corresponds to the highest pressure that can occur in the nitrogen receiving tank without the knowledge of the operator (via the high pressure alarm) and is based upon the high pressure alarm setpoint of 380 psig plus 5 psig for instrument inaccuracies. As designed, the high pressure alarm was intended to alert the operator of an impending overpressure condition and relief valve lift. However, the system was modified to install a rupture disk in series with and upstream of the relief valve. The modification allowed for a constant leak tightness of the system as pressure approached the lift pressure of the relief valve.

Previous surveillance tests have caused several rupture disks to burst at pressures below the manufacturer's stated burst pressure. These disk failures have added to the outage work scope because the disks required replacement and retesting. After consultation with the manufacturer, it was determined that the rupture disks should not be operated at pressures in excess of 367 psig for the rupture disks installed on the nitrogen receiving Page 1 of 4

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i tanks. At pressures approaching the burst pressure, plastic deformation occurs that can

, reduce the burst pressure of the rupture disk. By reducing the high pressure alarm i setpoint to 360 psig, the highest pressure that can occur in the nitrogen receiving tank l without the operators' knowledge is 365 psig. 1 DESCRIPTION OF PROPOSED CHANGE Current SURVEILLANCE REQUIREMENT 4.5.1.e.2.e) e) Performing a leak rate test for the safety related ADS accumulator pneumatic supply system (including special emergency tube trailer supply piping) up to SRV actuators / operators. With the SRV's actuated by either of the ADS solenoids and with ADS accumulators at 178 psig and with ADS nitrogen receiving tanks at 385 psig (high pressure alarm), the leakage rates shall not exceed the following limits:

Proposed SURVEILLANCE REQUIREMENT 4.5.1.e.2.e) l l

e) Performing a leak rate test for the safety related ADS accumulator l pneumatic supply system (including special emergency tube trailer supply l piping) up to SRV actuators / operators. With the SRV's actuated by either of the ADS solenoids and with ADS accumulators at 178 psig and with ADS nitrogen receiving tanks at 365 psig (high pressure alarm), the leakage rates i shallnot exceed the following limits:

I EVALUATION 1

The proposed change from 385 psig to 365 psig is needed to prevent potential degradation of the rupture disk located on each ADS nitrogen receiving tank during performance of the surveillance requirement. The lower end of the operating pressure band is 340 psig and is determined by the minimum design pressure of 334 psig plus the 5 psig instrument inaccuracy. In order to maintain a reasonable operating pressure band of 20 psig, the upper end of the operating pressure band is 360 psig. The manufacturer's recommended maximum operating pre.ssure for the rupture disks is 360 psig. With the nitrogen receiving tank high pressure alarm set at 360 psig, the maximum pressure that can occur in the tank without the operators' knowledge is 365 psig (due to instrument inaccuracies). The manufacturer was consulted concerning the 365 psig test pressures and concurred that it was within the tolerance of the rupture disk operating pressure after instrument conservatisms were removed (367 psig maximum). To maintain consistency with the current Surveillance Requirement, the proposed test pressure is 365 psig and corresponds to the new maximum value for the high pressure alarm setpoint.

The proposed test pressure of 365 psig is well above the design minimum nitrogen receiving tank pressure of 334 psig and bounds the upper end of the operating pressure range. Therefore, the surveillance leakage test will continue to verify the ability of the receiving tanks to perform their design function by verifying the ADS accumulator pneumatic supply system actualleakage is bounded by the calculated leakage. The 365 Page 2 of 4

psig test pressure will also prevent approaching the rupture disk burst pressure and

. prevent disk degradation. In addition, the proposed change to the leak test pressure still satisfies the requirements of TMI Issue ll.K.3.28.

CONCLUSION The ADS is required to effect or support the safe shutdown of the reactor. This is accomplished by the blowdown of steam from a group of seven designated ADS SRVs to the suppression poof. The operation of the ADS SRVs,in conjunction with the LPCI mode of RHR and/or the LPCS System, functions as an alternative to the HPCS for protection against fuel cladding damage during a small break loss-of-coolant accident. The blowdown of steam by these SRVs depressurizes the reactor allowing injection by the low-pressure makeup sources.

In the event the nitrogen gas supply from the high pressure nitrogen gas storage tanks is lost, a minimum nitrogen pressure of 334 psig in the ADS nitrogen receiver tanks assures a five-day supply of nitrogen to the ADS accumulators, The proposed change to Surveillance Requirement 4.5.1.e.2.e) would decrease the leak rate test pressure of the ADS nitrog;n receiver tanks from 385 psig to 365 psig. The proposed test pressure remains well above the design minimum pressure of 334 psig and bounds the upper end of the operating pressure band. Therefore, the surveillance test continues to ensure that the actualleakage of the safety related ADS accumulator pneumatic supply system is bounded by the leakage assumptions contained in the system design. In addition, the surveillance test continues to ensure that the ADS nitrogen receiver tanks are capable of providing a five-day supply of nitrogen to the ADS accumulators.

The effect of the proposed change has been evaluated and found to have no impact on system reliability or performance. Based upon these considerations, there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner. Issuance of the proposed amendment is consistent with the common defense and security.

NO SIGNIFICANT HAZARDS C_QNSIDERATION ANALYSIS 10 CFR 50.91 requires that at the time a licensee requests an amendment,it must provide to the Commission its analysis, using the standards in Section 50.92 about the issue of no significant hazards consideration. Therefore,in accordance with 10 CFR 50.91 and 10 CFR 50.92, the following analysis has been performed:

Ihe coeration of Nine Mile Point Unit 2. In accordance with the oronosed umendment, will not involve a slanificant increase in the gobability or conseopences of an accident geviousiv ev_pluated.

The ADS is required to effect or support the safe shutdown of the reactor. This is accomplished by the blowdown of steam from a group of seven designated ADS SRVs to the suppression pool. The proposed change to the test pressure does not affect any accident precursors. Therefore, the proposed change cannot increase the probability of an accident previously evaluated.

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In the event the nitrogen gas supply from the nitrogen gas storage tanks is lost, a

. minimum' nitrogen pressure of 334 psig in the ADS nitrogen receiver tanks assures a five-day supply of nitrogen to the ADS accumulators. The proposed change to Surveillance Requirement 4.5.1.e.2.e) would decrease the leak rate test pressure of the ADS nitrogen receiver tanks from 385 psig to 365 psig. Since the proposed test pressure remains well above the design minimum pressure of 334 psig, the surveillance test continues to ensure that the actualleakage of the safety related ADS accumulator pneumatic supply system is bounded by the leakage assumptions contained in the system design. In addition, the surveillance test continues to ensure that the ADS nitrogen receiver tanks are capable of providing a 5-day supply of nitrogen to the ADS accumulators. Therefore, the proposed change does not significantly increase the consequences of a previously evaluated accident.

Ihe coeration of Nine ' Mile Point Unit 2, in accordance with the orocosed amendment, will nqt create the oossibility of a new or different kind of accident from any accident oreviousiv evaluated. -

The proposed leak rate test pressure of 365 psig for the ADS nitrogen receiver tanks is above the minimum design pressure to assure a 5-day supply of nitrogen is available to the ADS accumulators if makeup from the high pressure nitrogen gas storage tanks is lost.

With the proposed change, the ADS will continue to perform its safety function of effecting and supporting the safe shutdown of the reactor. The nitrogen receiving tank test pressure is not a precursor for any new or different accident and the change does not offect the operation of the system in any way.

Accordingly, the proposed change does not create the possibility of a new or different kind of accident from any accident previously evaluated, r

l Ihg ooeration of Nine Mile Point Unit 2, in accordance with the orooosed amendment, will  !

Dat involve a sianificant reduction in a marain of safety.

l The operation of the ADS SRVs,in conjunction with the LPCI mode of RHR and/or the  ;

LPCS system, functions as an alternative to the HPCS for protection against fuel cladding l

damage upon a small break loss-of-coolant accident. The blowdown of steam by these l SRVs depressurizes the reactor, allowing injection by the low-pressure coolant injection j sources. With the proposed change, the ADS will continue to perform its intended safety 4

function of effecting and supporting the safe shutdown of the reactor as an alternate to i the HPCS. The proposed test pressure of 365 psig remains well above the minimum acceptable pressure for the nitrogen receiver tanks of 334 psig. Therefore, the change will not involve a significant reduction in the margin of safety.

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