ML18039A500

Proposed Tech Specs Re Use of Containment Overpressure for ECCS Pump Net Positive Suction Head Analyses

ML18039A500
Person / Time
Site:	Browns Ferry
Issue date:	09/04/1998
From:	TENNESSEE VALLEY AUTHORITY
To:
Shared Package
ML18039A499	List: ML18039A498 ML18039A500
References
NUDOCS 9809150303
Download: ML18039A500 (8)

Text

ENCLOSURE 2 TENNESSEE VALLEY AUTHORITY BROWNS FERRY NUCLEAR PLANT (BFN)

UNITS 2 AND 3 PROPOSED LICENSE AMENDMENT MARKED PAGES I. AFFECTED PAGE LIST The following Amendment 16 Updated Final Safety Analysis pages have been revised. A revision bar has been placed in the right hand margin to indicate where the changes occurs Pacae Section 5.2-7 5.2.3.3.1 General Description 6.5-15 6.5.5 Potential Plugging of Emergency Core Cooling System Suction Strainers (Units 2 and 3)

Table

6. 5-7 RHR and CS Pump NPSH Cases With Credit For 3 PSIG Overpressure Response 9809'150303 980904 PDR ADOCK 05000260 P PDR

The system to establish and maintain a controlled pressure differential between the drywell and pressure suppression chamber during normal operations is described in paragraph 5.2.3.9.

The toroidal suppression chamber is designed to the same material and code requirements as the steel drywell vessel. All attachments to the torus are by full penetration welds.

The HWWV can mitigate a severe accident that would cause the pressure of the torus to exceed 56 psig. The HWWV connects the torus of each unit to a common header which discharges in the stack via a 14" pipe.

During each refueling and each shutdown for required maintenance inside the containment, the containment is purged to restore a normal air atmosphere and to reduce the amount of gaseous and airborne radioactivity present. These purges are accomplished through the ventilation purge connections and are normally passed through a containment purge filter train (HEPA and charcoal filters) before release through the normal reactor building ventilation system. A vent from the primary containment is provided which will normally be closed, but which will permit the vent discharge to be routed to the Standby Gas Treatment System so that release of gases from the primary containment is controlled, and so that eNuents are filtered and monitored before dispersal through the stack.

A 30-inch suction header with a wall thickness of 1/2-inch minimum circumscribes th'e suppression chamber at El, 525 feet 4 inches. Four 30-inch tees are used to connect the suction header to the suppression chamber. The suction header is supported vertically and horizontally by brackets attached to the 16 cradles.

Four strainers on connecting lines between the suction header and the suppression chamber have been provided. izi o e s nn ctin ew s ve a a tion at tie ton ofth fou

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The suction header and its connecting pipes are designed, constructed, tested, and inspected in accordance with the same requirements as the suppression chamber. Additional safety is provided by locating the four connecting pipes in unused portions of the suppression chamber so that they will not be directly, subjected to the water jet issuing from the downcomers. The suction header is designed to accommodate a temperature differential between itself and.the suppression chamber. Hydraulic snubbers are used to support the suction header to provide seismic supports that will prevent any abrupt lateral movement, due to earthquake, but will not offer resistance to relatively slow thermal 5.2-7

6.5.3.4 Alternate 0 eratin Mode Considerations The impact of alternate operating modes on LOCA results is evaluated by analyzing the limiting LOCA case at such operating conditions as: Increased Core Flow (ICF),

Maximum Extended Load Line Limit (MELLL), and Final Feedwater Temperature Reduction (FFWTR)." For ICF and FFWTR, the impact on LOCA results is negligible. The Appendix K PCT at MELLLcore flow conditions is approximately 20'F higher, which is insignificant relative to the PCT margin available at the rated core flow conditions, with respect to the 2200'.F limit.

6.5.4 Emer enc Core Coolin S stems Redundanc The design criterion of preventing peak cladding temperatures greater than 2200'F is satisfied across the entire spectium of possible liquid or steamline break sizes even in the event of the loss of normal auxiliary power combined with a single failure. It is concluded that the redundant capability of the ECCS is sufficient for all size line breaks up to and including the design basis break.

The individual functions of the ECCS also meet the design criteria over various ranges of break sizes in the nuclear system. Their integrated performance provides adequate and timely core cooling over the entire spectrum of loss-of-coolant accidents up to and including the design basis loss-of-coolant accident even with concurrent loss of offsite AC power. It is concluded that safety design basis 1 is satisfied.

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Insert A:

Four strainers on connecting lines between the suction header and the suppression chamber have been provided.

For Units 2 and 3, the strainers are a stacked disk design having a large surface area to accommodate debris that may be generated by the dynamic forces in a LOCA and other debris that may be resident in the containment such as sludge and paint chips. The Unit 2 and 3 strainer design is governed by debris generation assumptions in accordance with the Boiling Water Reactor Operating Group Utility Resolution Guidance for ECCS Suction Strainer Blockage (GE NED0-32686, RO, Dated November 1, 1996). The strainers are designed to provide acceptable head loss while saturated with reflective metal insulation from primary system piping combined with other debris.

On Unit 1 only, sizing of the strainers and connecting pipes was conservatively based on the assumption that at least one of the four strainers was completely plugged during the postulated accident. In addition, the curves surface and location of the strainer minimize the possibility of clogging.

Insert B:

Add the Followin Pro osed Section to UFSAR Cha ter 6:

6.5.5 Potential Plu in of Emer enc Core Coolin S stem Suction Strainers (Units 2 and 3)

NRC Bulletin 96-03 concerns the potential for inadequate NPSH for ECCS pumps resulting from accumulated debris on the ECCS suction strainers during the recirculation phase of a LOCA. As part of the resolution of this issue, a high capacity passive stacked disk strainer is installed on the ring header. The strainer design is governed by the debris generation calculations in accordance with the Boiling Water Utility Resolution Guidance (BWROG) (URG) (GE NED0-32686, RO, Dated November 1, 1996) for ECCS Suction Strainer Blockage.

The primary insulation type on, the drywell piping systems is reflective metal insulation (RMI) of both aluminum and stainless steel. The suction strainers provide adequate NPSH margin with a saturated thickness of foils of either aluminum or stainless steel insulation. The debris generation calculations utilize BWROG URG assumptions and assume worst case debris loading during a postulated accident. Debris captured by the strainer during a E2-4

postulated LOCA will increase the pressure drop across the strainers.

The low pressure ECCS systems are designed to provide adequate NPSH for the pumps during the full range of post accident operation and containment pressure and temperature response. Credit is taken for 3 psi above atmospheric in the primary containment air space and it is assumed that operators take manual control of ECCS systems at 10 minutes after an accident to reduce flow to the minimum required. Table 6.5-7 provides the NPSH values and system configurations Containment pressure response analyses evaluated the suppression pool temperature and suppression chamber airspace pressure responses for the limiting short-term and long-term LOCA events with respect to available NPSH for the RHR and CS pumps. Input assumptions maintain the overall conservatism in the evaluation by maximizing the suppression pool temperature and minimizing the suppression chamber airspace pressure, and, therefore; minimize the available NPSH. These analyses show that at least 3 psi overpressure would be present in accident conditions when it is needed to offset the effect of debris on the strainers.

Table 6.5-7 provides a computation of limiting plant condition descriptions and NPSH at the pump for these selected analyzed conditions.

E2-5

PROPOSED TABLE 6.5-7 RHR AND CORE SPRAY PUMP NPSH CASES WITH CREDIT FOR 3 PSIG OVERPRESSURE RHR PUMP PUMP CS PUMP PUMP NPSH NPSH NPSH SPRAY CORE SPRAY NPSH AVAILABLE 1nitial ECCS RHR PUMP FLOW CONDITION 2 pumps on one 11,000 gpm (x2) 30'HR RHR PUMP FLOW RATE REQUIRED (FEET)

AVAILABLE PUMP FLOW (FEET) 32.05'ORE CONDITION 2 pumps on PUMP FLOW RATE 3,125 gpm 27'S REQUIRED (FEET)

(FEET) 35.77/

Start-Maximum flo loop at maximum 22,000 gpm each loop 8 (x4) =

limited by flow limited by plus 10, 000 gpm design flow 12,500 gpm orifices in one orifices and 2 (x2) =20, 000 gpm RHR loop and pumps on one Total Flow design flow in loop at design 42,000 gpm other RHR and CS flow loops. (in LPCI Mode)

Suppression Pool at 95F At 10 minutes, 2 pumps on one 11,000 gpm (x2) pumps on 3125 GPM LPCI maximum flow loop at maximum 22,000 gpm each loop 8 (x4) ~

in one RHR Loop, flow limited by plus 10, 000 gpm design flow 12,500 GPM CS at normal orifices and 2 (x2) ~20, 000 gpm 30'4'2.74'6.

design flow. pumps on one Total Flow 27'7'6.54'3.56I Suppression Pool loop at design 42, 000 gpm at 150'F flow (in LPCI Mode)

Long Term ECCS 2 pumps on one 6,500 gpm 89' 2 puIILps on 3125 gpm pump flows at pea loop at design (x2)=13,000 gpm one loop at (x2) =

suppression flow design flow 6250 gpm chamber (Containment temperatures cooling)

(177 F) 1 No credit taken for overpressure at time ~ 0 seconds.

2. Assumes 3 psig overpressure at time ~600 seconds