ML20205J115
| ML20205J115 | |
| Person / Time | |
|---|---|
| Site: | Beaver Valley |
| Issue date: | 10/21/1988 |
| From: | Sieber J DUQUESNE LIGHT CO. |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| NUDOCS 8810310307 | |
| Download: ML20205J115 (7) | |
Text
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i Nr.Nbw w wrreota October 21, 1988 l
U. S. Nuclear Regulatory Commission I
Attnt Document Control Desk Washington, DC 20555 f
Reference:
Beaver Valley Power Station, Unit No. 1 i
Docket No. 50-334, Ltcense No. DPR-66 j
NRC Inspection 88-03-04 1
Gentlement During Inspection 88-08, selected Emergency Operating Procedures I
(EOPs) were exercised on the Beaver Valley Power Station Simulator.
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One specific procedure step alerts the operator to terminate containment spray should the containment pressure approach 8.9 psia j
(a limiting containmont design consideration).
At this point in the L
procedure, the NRC Inspector asked the operator if at 8.9 psia, the low head safety injection (LHSI) pumps would have adequate net L
positive suction head (NPSH).
Since plant design assures that under
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all
- analyzed, worst case accident scenarios sufficient LHSI NPSH t
- exists, operators are not required nor directed to take actions
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rylated to this condition under these accident scenarios.
This issue was carried as Open Item 88-08-04, and DLCo indicated i
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that an Engineering evaluation would be provided to verify that t
adequate LHSI NPSH exists.
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A review of the preliminary evaluation was conducted by the NRC l
l with suggestions that we add such additional information to the
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emergency operating procedure to alert tue operators of containment conditions that would cause a loss of NPSH to the LHSI pumps.
j We have reviewed the engineering evaluation to determine if it
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could provide meaningful information for the operators for EOP use.
l It is our conclusion that the transient bounding analysis curves developed provide no real benefit to the accident management process.
The reasons for this are enumerated below, i
i 1.
The transient curves are based on licensing grade f
calculations to meet FSAR worst case assumptions.
The results are thus very conservative and show that fundamental design considerations assure adequate NPSH under all
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scenarios.
l 6910310307 831021 9
PDR ADOCK 05000334 l
O PDC f 1 i
I
1
- Benvor Volloy Pcwor Station, Unit No. 1 j
Docket No. 50-334, License No. DPR-66 Page 2 i
j 2.
If action were required to be taken on the conservative bases and results of the licensing calculations, the operators could be prematurely and unnecessarily influenced to reduce LHSI flow or terminate Quench Spray.
This would clearly have unfavorable consequences to the overall j
accident management strategy.
These consequences include:
Reduced sump pH control and iodine scavenging effects.
A reduction in sump cooling and the consequent results on assuring maintenance of containment subatmospheric conditions.
Potential reduction of RWST volume transfer with consequent effects on the long-term recirculation phase.
3.
- Finally, contingency actions are provided in the E0P's to address loss of the LHSI function for any reason.
In
- summary, the use of TSAR licensing basis analysis results in the EOP's must be approached with caution.
The inherent conservatism of these analyses can result in taking unnecessarily restrictive action to the detriment of the overall accident management process.
Attached for your review is the analysis showing that adequate NPSH exists for all analyzed scenarios and combinations of limiting parameters.
Should ycu have any questions regarding this subject, please contact my office.
Very truly yours, G d.ha-
- 3. D. Sieber
('Vice President Nuclear Group Attachments cc:
Mr. J. Beall, Sr. Resident Inspector Mr. W. T. Russell, NRC Region I Administrator Mr. P. Tam, Project Manager Director, Safety Evaluation & Control (VEPCO)
ATTACHMENT 1 d
BEAVER VALLEY POWER STAT 20N UNIT NO. 1 LOW HEAD SAFETY INJECTION PUMPS -
NET POSITIVE SUCTION HEAD j
h PURPOSE I
The purpose of this analysis is to show that advouato not positive suction head exists for all credible scenarios and combinations of limiting parameters.
BACKGROUND i
The Reactor Containment Building at Beaver Valley Unit No. 1 is of sub-atmospheric cesign.
The basic criteria for acceptable Design Basis Accident Analyses include Itmlting peak pressure to less than the design pressure of 45 psig and returning the i
containment pressure to a sub-atmospheric condition within one (1) hour following an accident.
The Containment Depressurization System consists of two (2) Quench Spray Pumps and four (4) Recirculation Spray Pumps. The Quenen Spray Pumps take suction t
from the Refueling Water Storage Tank (RWST) and deliver water to spray rings inside i
containment.
Two headers are provided off of the Quench Spray Header tu the containment sump for NPSH consideration.
These pumps start automatically from a containment pressure signal of 8 psig. The Recirculation Spray Pumps take suction t
from the containment sump and deliver water to spray headers through spray coclers.
l The spray coolers use river water to provide long term cooling for the ECCS and Containment Depressurization Systems.
The major component of the ECCS System include the High Head Safety Injection Pumps.
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Low Head Safety Injection Pumps, and the Accumulators.
Following a DBA, the LHSI and HHSI pumps take suction from the RWST during the injection phase. khen a preset level is reached on the RWST, the LHS! pump suction is automatically transferred to l
the containment sump.
It is during this recirculation phase that the NPSH of the LHS! pumps is at its minimum.
LHSI pVMP NPSH l
The LHS! pumps are located outside the Containment Building and take suction from the containment sump during recirculation mode via an innerconnecting pipe. The available net positive suction head is calculated from the following:
f s
f (1)
NPSHA*PC + P g - Py - P$t Where:
PC=
Containment pressure
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l PSH =
Pump suction static head due to height of water in containmr.t sump.
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Py =
Varur pressure of water entering p u'rp (vapor pressure l
corresponding to sump temperature) l P(=
Head loss in LHS!
pump suction piping, screens nd pump l
can.
(Varies with pump flow).
l 1
l
- a
ATTACHMENT &
BEAVER VALLEY POWER STATION UNIT NO. 1 i
LOW HEAD SAFETY INJECTION PUMPS -
t NET POSITIVE SUCTION HEAD In order to calculate the minimum available NPSH: we must find conditions which minimize containment pressure and sump level while maximizing sump temperature and pump flaw.
Sensitivity analyses were performed to establish worst case conditions for type of analysis, in., peak pressure, depressurization time, LHS! NPSH, and i
recir. " u en spray pump NPSH, The conditions examined wert break location, break
- size, ni failure, and RWST and river water temperat.n s.
Additionally, initial a
conditiona for centainment pressure and ternperature de chosen at the limiting condition which is conservative for the particular analysis.
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For the specific concern of LHS! NPSH, the sensitivity analysis shows that the worst case conditions are a pump suction double ended rupture w',th minimum safeguards, For this case, the limiting combination for a high RWST temperature snd river water l
temperature yields the minimum NPSH available.
Initial containn.6nt air partial l
pressure is set at the minimum value of 8,9 psia ind initial containment tempe ature is set at the maximum of 105'F, This combination results in the minimum possible air mass in containment which results in lower containment pressures during the transient.
The analyses also show that the most limitir9 point in time is at the I
1 switchover point or when the LHS! pumps !nitially take suction from the sump.
The 1
available NPSH increases from this point. This is dae to tne fact that following l
switchover, the sump level continues to increas? c a result of continued quench spray.
Additionally, the sump temperature continues tv decrease due to heat removal l
through recirculation spray coolers and the addition of quench sprays.
The l
j containment pressure may also be decreasing from this point, however, the effects of I
the sump temperature and level are more significant and, thercio*e, available NPSH
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l increases, i
Examining each term of equation (1) with respect to the limiting canditions
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established provides useful in,ight into onderstanding th relative effects.
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PC-Containment Pressure i
As stated, the worst ca;' conditions in general would be those t.hich f
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result in the lowest cotssinment preisure at the point of minimum j
NPSH.
The containment pressure is directly related to containment temperature, ie.,
containment total pressure can N, determined from t
i i
the containment temperature when initial air paitici pressure is i
j
- known,
- t. owe r containment atmospheric temperatures yield lower l
pressures.
This would require that minimum values he used for RWST i
and river water temperatures.
- However, the sensitivity analyses indicate that higher RWST and river wator temperatures are more limiting.
This is due to the fact that the available hPSH is more sensitive to sump temperature changes since the,apor pressure of sump
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water varies significantly more than containment pressure in the
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temperature ranges of interest, Containment pressure is minimized for i
the conditions by assumption of low initial att partial pressure and l
I high initial temperature, f
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ATTACHMENT 1 BEAVER VALLEY POWER STATION UNIT NO. 1 LOW HEAD SAFETY INJECTION PUMPS -
NET POSITIVE SUCTION HEAD Py -
Sump Vapor oressure The vapor pressure of the containment sump water is maximized through various conditions and assumptions in the analysis.
The sump temperature has the most significant effect on available NPSH.
Essentially, all of the limiting conditions are based on maximizing l
sump temperature.
The break location, single failure, and break size generally provide the highest relative energy distribution to the sump.
Additionally, the assumption of maximum RWST and river water temperatures maximizes heat addition via quench spray and minimizes heat removal via the spray coolers.
Also for this case, spray thermal effectiveness is set at 100% in order to reduce containment pressure and increase heat transfer to the sump.
Pg-Pump Suction Static Head S
The pump suction static head is basically fixed since the switchover actuation is taken from a level setpoint on the RWST.
An equivalent volume of water will be available regardless of the :ime at which switchover occurs.
The volume is conservatively criculated by assum'ng the RWST level is at the switchover setpoint plus the level instrument uncertainty.
PSL -
Pump Suction Head Loss The pump suction head loss has been calculated and includes losses through the sump screens, suction piping and pump casing.
This loss is relatively insensitive to all conditions except pump flow and to a lesser degree sump temperature.
The containment sump vapor pressure is the major variant and therefore, the limiting conditions tend to be those which have the effect of maximizing sump temperature.
Containment pressure can be a limiting factor if it is low while sump temperatures are relatively high.
This would decouple the two parameters which is not a credible thermodynamic assumption.
However, the capabilities of tha recirculation spray coolers est&hlish a lower limit of containment pressures for a given range of sump temperatures.
These pressures remstent the minimum long term pressure achievable, based on recirculation spray temperoture.
(Refer to Figure 1).
Figure 1 shows the minimum ca.n.oinment pressure required to maintain adequate NPSH
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for the LHSI pumps based nn ' rip temperature.
This curve is based on a LHS! pump flow of 3200 gpm. The LHSI pump flow is limited to a maximum of 3200 by cavitating i
venturis installed in the discharge piping.
The curve is also based on the sump level at the switchover point.
Sump isvels in excess of this level at later times in the transient will cause the curve to snift downward.
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ATTACHMENT 1 BEAVER VALLEY POWER STATION UNIT NO. 1 LOW HEAD SAFETY INJECTION PUMPS -
NET POSITIVE SUCTION HEA0 Also shown in Figure 1 is the results of several limiting transients which cover the range of river water temperatures and single failures. The points plotted represent conditions at switchover or the most limiting point for NPSH. The results indicate that for the most limiting conditions, adequate containment pressure is maintained to provide required NPSH for the LHSI pumps over the range of. river water temperatures.
Sump temperatures for the normal safeguards case are much lower and sufficient margin exists for LHSI NPSH.
To address the specific question as to whether adequate NPSH is maintained for the LHSI pumps at 8.9 psia, the following justification is presented. The maximum sump temperature which maintains NPSH at 8.9 psia is 167'F.
For this sump temperature and a river water temperature of 320F a recirculation spray temperature can be calculated.
TRS = TSUMP - RHX (TSUMP -TRW)
Where RHX =.6461 Therefore:
TRS = 167
.6461 (167-32)
TRS = 79.8'F The containment air partial pressure is then PCA = 8.9 539.78 565 PCA = 8.503 The containment total pressure is PT=PCA + Py Where Py = Vapor pressure corresponding to the containment temperature PT = 8.503 +.5 PT = 9.0 psia l
The minimum attainable containment pressure for a sump temperature of 167'F is l
greater than 8.9 psia.
Acceptable results are demonstrated by the analyses which show adequate NPSH over the range of river water conditions with all other parameters and assumptions set to yield the most conservative results.
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/N REGUIFIED NPSH @ 3200 GPM 4100 110 120 130 140 150 160 170 180 190 Transient Results at Switchover E
PSDER, MIN ESF, 55 RWST, 80 RIVER O) Additional analyses have indicated an adequate LHSI NPSH for River Water temperatures g
PSDER, MIN ESP, 55 RWST, 32 RIVER up to 90*F.
A HLDER, NORM ESP, 45 RWST, 32 RIVER FIGURE 1 Minimum Attainable Long Term Containment Pressure
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