ML20217N815
| ML20217N815 | |
| Person / Time | |
|---|---|
| Site: | Seabrook  |
| Issue date: | 03/02/1998 |
| From: | Feigenbaum T NORTH ATLANTIC ENERGY SERVICE CORP. (NAESCO) |
| To: | |
| Shared Package | |
| ML20217N811 | List: |
| References | |
| NUDOCS 9803090230 | |
| Download: ML20217N815 (4) | |
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This License Amendment Request is submitted by North Atlantic Energy Service Corporation I
pursuant to 10CFR50.90. The following information is enclosed in support of this License Amendment Request:
Section 1 Introduction and Safety Assessment for Proposed Change Section ll Markup of Proposed Change Section ill Retype of Proposed Change Section IV Determination of Significant Hazards for Proposed Change Section V Proposed Schedule for License Amendment issuance and Effectiveness e
Section VI EnvironmentalImpact Assessment Sworn and Subscribed before me this c$d day of
.1998 Nddl Ted C. Feigenbaum/
' g Notary Public Executive Vice President and Chief Nuclear Officer 9003090230 98030A ~
PDR ADOCK 05000443 P
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Section I Introduction and Safety Assessment for the Proposed Change 1
i Page1
I.
INTRODUCTION AND SAFETY ASSESSMENT OF THE PROPOSED CHANGE I
A.
Introduciks License Amendment Request (LAR) 98-01 proposes a change to Seabrook Station Technical Specification (TS) Surveillance Requirement TS 4.5.2b.1 to exclude the prescriptive requirement to vent the operating Chemical Volume and Control System (CVCS) centrifugal charging pump (CCP) casing.
i Mandatory venting of the operatinn, CCP is unnecessary since the CCPs are desigt.ed and installed to be self-venting, particularly when operating under dynamic conditions.
B.
Background And Description of Proposed Change TS 4.5.2 currently states:
"Each ECCS subsystem sht.Il be demonstrated OPERABLE:
- b. At least once per 31 days by:
- 1) Verifying that the ECCS piping is full of water by venting the ECCS pump casings and accessible discharge piping high points,"
North Atlantic's past practice of not manually venting the operating CCP, by crediting the dynamic venting of the pump in operation, was considered to be in compliance with TS 4.5.2b.1 requirements.
The idle CCP has been, and still is, routinely vented per the requirements of TS 4.5.2b.l. Because of recent industry experience North Atlantic has determined that its past practice of crediting dynamic venting has not been in literal compliance with TS 4.5.2b.l. This has been reported in Licensee Event Report (LER) 98-001-00.
North Atlantic proposes to revise TS 4.5.2b.1 as follows:
" Verifying that the ECCS piping is full of water by venting the ECCS pump casings (excluding the operating centrifugal charging pump) and accessible discharge piping high points,"
C.
Safety Assessment of the Proposed Change The CVCS centrifugal charging pumps perform several functions, Normally, to return conditioned letdown flow back to the reactor coolant system (RCS) and inject e
j seal water into the reactor coolant pump (RCP) No. I seals.
Supply borated water to the RCS for emergency boration.
Supply high head safety injection (HHSI) flow during Emergency Core Cooling System (ECCS) actuation.
The CCPs are an 11 stage, multi-diffuser type IJ, horizontal barrel case, centrifugal pumps manufactured by Pacific Pumps. These pumps have no installed pump casing vent (s). Since the design of the pump has top mounted suction and discharge nozzles its unlikely that gasses, of any significance, can accumulate inside the pump during periods of pump operation or when the pump is secured. Any gasses that may be introduced into the pump casing would not accumulate in the casing area (s), but would be carried with the fluid being pumped, through the pump, back into the system. The pump vendor manual Page 2
i t
i identifies that the pump design does not include casing vents, since the pumps have top mounted suction and discharge nozzles which allow gasses in the pump to escape through the pump nozzles.
He CCPs are located in the Primary Auxiliary Building (PAB) at elevation 13'- 11 1/2". The pump suction is normally aligned to the volume control tank (VCT) which operates at a minimum 17 psig overpressure. The VCT is located in the PAB at elevation 64'. The VCT elevation and overpressure provide the CCP pumps with a nominal 21 psig suction pressure. Plant design allows CCP pump venting j
through the discharge piping to a high point vent valve directly over each pump assembly. The idle CCP casing is vented through its associated high point vent per the requirements of TS 4.5.2b.l.
)
Considering that any gasses that may be introduced into an operating pump would be carried by the fluid j
being pumped, accumulation of gasses within the pump casing is not credible, therefore, venting of the
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operating pump is unnecessary. Furthermore, the accumulation of gasses at the high point vent valve j
during pump operation is not credible either; since operating system pressure (~ 2500 psig) would keep i
gasses in solution and the flow (~ 100 gpm, normally) through the 4 inch discharge piping is sufficient to sweep away non-condensable gasses. Gasses in solution would either be carried to the RCS via the normal charging path and/or recirculated via the minimum flow recirculation piping to the VCT outlet piping back to the CCP suction piping. The potential for gasses to be stripped from the recirculation fluid due to the pressure reduction of the recirculation flow orifices back to the CCP suction has not been observed at Seabrook Station. The recirculation flow orifices are fourteen stage design that show no indication of being susceptible to gas stripping. Therefore, opening a vent valve on piping under dynamic conditions, i.e., high velocity, high pressure, would be ineffective in removing gasses since there are no accumulated gasses to be vented. In addition, venting of piping under high system pressures poses a significant risk to personnel safety.
Currently, North Atlantic is manually venting both CCPs on a 31 day frequency, as required by TS 4.5.2b.l. This is accomplished by manually venting the idle CCP through the discharge piping to a high point vent valve directly over the pump assembly. The operating CCP is presently vented through its recirculation line to the vapor space of the VCT. This method of venting does not allow visual confirmation of the presence of air / gas because the VCT cannot be accessed, however, it is a high point in the system which allows the gasses to be vented. Additionally, North Atlantic does not believe it is appropriate to swap CCPs once every 31 days for the sole purpose of statically venting the CCP which had been previously in operation. North Atlantic's present practice of swapping pumps is performed quarterly
(~90 days). This is to minimize pump startup/ shutdown cycles and accelerated wear / fatigue loading on pump components. Swapping of the pumps to meet current TS 4.5.2b.1 requirements will increase the number of pump startup/ shutdown cycles, thus, potentially decreasing pump availability and longevity. As a result, considering that venting of the CCP under dynamic conditions is considered ineffective, North Atlantic believes that routine venting of the operating CCP is unnecessary.
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