ML20093M672
| ML20093M672 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 10/18/1984 |
| From: | Hukill H GENERAL PUBLIC UTILITIES CORP. |
| To: | Stolz J Office of Nuclear Reactor Regulation |
| References | |
| 5211-84-2256, NUDOCS 8410230120 | |
| Download: ML20093M672 (6) | |
Text
GPU Nuclear Corporation Nuclear
- ,ome
- r8o s
Middletown, Pennsylvania 17057-0191 717 944 7621 TELEX 84 2386 Writer's Direct Dial Number:
October 18, 1984 5211-84-2256 Office of Nuclear Reactor Regulation Attn:
J. F. Stolz, Chief Operating Reactors Branch No. 4 Division of Licensing U.S. Nuclear Regulatory Commission Washington, D. C.
20555
Dear Sir:
Three Mile Island Nuclear Station, Unit 1 (TMI-1)
Operating License No. DPR-50 Docket No. 50-289 Plant Shielding - DHR System Option Attached is the information concerning our alternate Decay Heat Removal System configuration which was requested during our discussion on September 6,1984 of GPUN letter of July 27, 1984 (5211-84-2179). This evaluation shows that simultaneous suction from the Decay Heat Dropline and the Reactor Building sump does not produce entrained air in the DH suction piping because the RB sump acts as a surge volume ensuring that the water level in the dropline is above the inlet to the suction at all times.
Sincerely,
\\
. D.
t' kill i
Director, TMI-1 HDH/LWH/MRK/lr/0ll6A Attachment cc:
J. Van Vliet 8410230120 841018 PDR ADOCK 05000289 P
PDR Q0 I U (t A
GPU Nuclear Corporation is a subsidiary c,f the General Public Utilities Corporation l
=
7~
Simultaneous Suction On Decay Heat Dropline And Reactor Building Sump BACKGR0'ND U
..The DHR System is used.as a method of controlling boron concentration in the core following an accident. -Of.the three methods for controlling boron precipitation outlined by Babcock & Wilcox (Ref.1), the following two methods were found to be acceptable-by:the NRC and were adopted at TMI-1:
-1)
Gravity drain from the_ decay heat dropline to the reactor building i
sump through' the LPI string not in operation and continue low
, pressure injcction through the operable string.
2)-
_ Forced circulation with' Hot Leg Injection via the auxiliary pressurizer, spray line.
The first mode utilizes either DH string to provide a letdown path from the RCS hot leg.with the water ultimately being pumped back i.o the core flood
.line. xIn order to establish this flow path, the dropline must be aligned to
--the RB Sump by opening _DH-V1, 2, 3 and one of the suction cross connect valves, DH-V12 A or B,'and. respective sump isolation valve DH-V6 A & B.
DH-V1, 2, 3 and 6 are motor operated valves which are operated from the i
' control room; DH V12 A & B are local, manually operated valves. Post accident
' radiation-levels have been' calculated to be sufficiently high to potentially preclude-local operation of these valves.
The second Boron Control. Mode requires that the 'A' DH string be operable or that the cross: connect from theB' DH string be open in order to inject to the Hot Leg via the pressurizer.- The-path to the pressurizer is established by opening the DH-V64 and RC-V4 valves and closing the RC-V3 valve. Operation
~of RC-V3 and RC-V4 valves is from the control room; DH-V64 is operated by a-local handwheel' and could be made inaccessible due to post accident radiation
-levels.
LIn order to ensure that control of boron precipitation is possible, post LOCA,
~
~
GPUN.has proposed that the~following changes be'made:
1)
Lock open DH-V12B to provide for a letdown path to the RB sump from the DH dropline without the need to enter a high radiation area.
2):
Installation of a remote operator (reach' rod) on DH-V64 to allow for operation of this valve from a shielded location.
DISCUSSION The' proposed so.lution to the problem.of plant shielding with respect to DH system operation during emergency operating conditions, including long term boron precipitation control as outlined above, were proposed to the NRC in GPUNC letter 5211-84-2179, dated July 27,1984 (Reference 2).
c m._ _.._,___ _.., - -,.,
~
~ These methods were also discussed briefly on September 6,1984, with representatives of the NRC. GPUN was requested to provide further information concerning the effect on DH system operation by taking suction from the RB sump and the DH drop 11ne simultaneously.
This alignment can result from failure of the DH-V6A valve to open upon switching LPI Modes from the BWST as a source of water to recirculation from the RB sump (as discussed in Attachment 2 of Reference 2). This failure effectively eliminates the 'A' DH pump from operation in the recirculation mode, since its suction line is closed.
Low pressure injection would continue in this case through the 'B' string in the recirculation mode. Boron control would be established by opening the DH dropline to allow for letdown flow from the hot leg.
The sketch in Figure 1 shows the flow path and relative elevations of the DH pump, RB sump, and RCS hotleg.
As shown in Figure 1, the dropline comes off the bottom of the "B" hot leg at elevation 312'-6".
The connection with the decay heat pump suction is a " tee" at elevation 263'-0" (labeled PT A). Since this is a common point between two flow paths, the pressure at this point is determined from the hydraulic conditions in the two paths. The Bernoulli Theorem can be applied to the evaluation of either path. That is:
HEL1 + 144 P1 + vi 2 = HEL2 + 144 Pg +
+hL p
2g p
8 1
2 for either of thw two paths.
Looking first at the drop line path:
HEL1=
Elevation of water in the
=h drop line (since line may not be full, this must he treated as a variable).
P1 Pressure in the "B" hot leg
=PRB
=
which is assumed to be equal to the reactor building pres-sure since this operation will not occur until at least 24 i
hours following the accident.
l p1 Density of recirculation
=PRCS
=
l water.
v1 Velocity of water within
= vDL
=
dropline.
HEL2 Elevation of PT A.
=hA
=
i P2 Pressure at PT A.
=PA
=
dropline.
I i
1 v2 Velocity of water within
=-vDL
=
drop line.
P 2 Density of recirculation
=P
=
RCS water.
hl Frictional loss in the drop
=0
=
line. Assumed to be Zero since the flow through this line will be small.
- Thus, or, solving for h:
h + 144 PRB + vg 2=hA + 144 PA + VE 2+0 P
RCS 2g RCS 2g h=hA + 144 (PA-PRB)
(1)
PRCS Now, looking at the ECCS recircultion pathway, HEL1 Elevation of water in
=hRB
=
the reactor building.
Conservatively assumed to be the RB floor elevation.
P1 Pressure in the reactor
=PRB
=
building.
Vi Velocity at the sump
=0
=
surface.
HEL2 Elevation at point A.
=hA
=
P2 Pressure at point A.
=PA
=
P 1 Density of recirculation
= PRCS
=
l water.
l l
P 2 Density of recirculation
=P
=
ges
- water, i
r V2 Velocity in the suction
= 7.1 FT/SEC
=
pipe at point A.
Based on: Recirculation l
f'ow = 3000 gpm pipe cross sectional area =
0.94 Ft2 l
hl Frictional loss in suction
= 3.0 Ft
=
line. Based on:
ht = fLv2 + hs + K.y2 D2g 2g
- Where, Lf_=
Piping resistance
= 2.73 D
hs frictional loss through
= 0.23 Ft
=
screen.
K entrance resistance
= 0.78
=
or, ht
-(2.73 + 0.78) v2 + 0.23
=
2g-
- Thus, hRB + 144PRB + 0 m hA + 144PA + V2 2 + 3.0 P
PRCS RCS 2g or, 144(PA-PRB) = hRB - hA - V2 2 - 3.0 (2)
PRCS 2g Substituting equation (2) into equation (1) gives:
4 h=hA+hRB - hA - V2 2 - 3.0 2g h=hRB - V2 2 - 3.0 2g h = 280'-0" --0.78' - 3.0' = 277.2 Ft.
CONCLUSION:
l The results of this calculation gives a dynamic head of 14.2 Ft. (277.2' -
l 263') at the point where the dropline enters the decay heat pump suction line. This is determined to be sufficient to maintain the suction piping t
flooded and free of entrained air. The reactor butiding sump in this case i
functions as a surge volume, ensuring that the water level in the dropline is above the inlet to the suction at all times.
l This calculation is considered conservative since it assumes the water level in the reactor vessel is below the RCS hot leg nozzle.
In fact, whenever the L
water level in the reactor vessel exceeds EL 312'-6", water will flow down the i
dropline and into the suction line as the head in the dropline exceeds the pressure at PT A.
This will continue until a hydraulic equilibrium is achievad between the level in the dropline and the level in the sump.
Similarly, if the drop 11ae is empty when the RB sump valves are opened, water from the sump will fill the line up to the equilibrium level calculated above.
l
REFERENCES:
1.
Topical report 10103A, Rev. 3 "ECCS Analysis of B&W 177 FA Lowered l
Loop NSS".
l 2.
GPUN letter No. 5211-84-2179 to NRC, Dated July 27, 1984.
_ _... _., ~. - _ _ _
s
'B' Hotleg EL-314-0 l
DH-V1
(
h EL302'-0"
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i Reactor Building N
DH-V3 EL291'-6" 12"Dil Dropline DH-V12A U"~'
O Reactor Building s
- EL 281'-0" l
i l
Ml
-EL 274 '-10" EL 274 _
- 6B DH-VISB 9
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-EL 263 '-0" 14" DH Suction EL 263' -6" l
DH-Pump
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