ML19350D074
| ML19350D074 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 04/06/1981 |
| From: | Hukill H METROPOLITAN EDISON CO. |
| To: | Reid R Office of Nuclear Reactor Regulation |
| References | |
| TLL-637, NUDOCS 8104130253 | |
| Download: ML19350D074 (8) | |
Text
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Metropolitan Edison Company Post Office Box 480 II Middletown, Pennsylvania 17057 Writer's Direct Dial Number April 6,1981 TLL 637 Office of Nuclear Reactor Regulation Attn:
R. W. Reid, Chief Operating Reactors Branch No. 4 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 Analysis of the Boron Dilution Event This lett.er and attachments are in response to discussions held with Mr. D.
DiIanni of your staff concerning the notential for boron dilution events.
Specifically, the pathways for a boron dilution event have been reviewed using the drained down RCS volume and the 15 minute criteria reouired by SRP 15.4.6 for hot and cold shutdown modes. Our response concludes that there are no dilution patfiways with significant flow rate which could be established through a single failure or operation error which would completely eliminate the shutdown margin. Therefore, no further response is required.
Sincerely, I
kill Director, TMI-l HDH:DGF:1ma Attachments cc:
L. Barrett B. J. Snyder e
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BACKGROUND A review of the plant systems and procedures has been performed to determine the potential pathways for a moderator dilution event. The purpose of this review and evaluation is to determine if a possible moderator dilution event exists with a closed Reactor Coolant System (RCS) in a drained down state, which was not previously considered and would cause a loss of shutdown margin. Four general pathways have been identified. The Makeup and Puri-fication System, Liquid Waste Disposal System, Reactor Building Spray System, and leakage through seals and/or packing.
Q CLUSION The conclusion of this review is that there are no dilution pathways with significant flowrates which could be established through a single failure or operator error during cold shutdown.
Furthermore, the nomally available shutdown margin would not be lost even in the unlikely event of multiple failures leading to the establishment of a significant dilution pathway.
DISCUSSION The Reactor Building Spray System dilution path via the Decay Heat Removal System has been studied for a full RCS and the method for precluding this dilution event is considered acceptable by the NRC (Letter to R. C. Arnold from Rober;t W. Reid, Chief ORB #4, dated December 31,1979). This method is equally applicable during drained down conditions and therefore need not be addressed further in this context.
During drained down conditions, the systems which indirectly interface with the RCS through seals, motor coolers, or packings are either shutdown or create a,-atential for such small dilution rates as to be insignificant.
Dilution evnts of this nature occur slow enough that operator action to terminate or compensate for deboration can be made based on periodic boron samples and/or the control room instrumentation.
The Makeup & Purification System provides one possible pathway for injection to the RCS of unborated water from the makeup tank, but only through an ex-tensive valve lineup. Under drained down conditions, or any cold shutdown condition, administrative measures are applied which prevent injection of water from the makeup system. These include racking out the breakers for the makeup pumps, closing their associated makeup valves V217, V16A, V168, V16C and V16D, and opening their respective breakers. Also, injection of unborated water from the makeup tank would terminate with greater than 2.0% shutdown margin remaining.
(See Attachment I for details).
In view of this, any likelihood of injection from the makeup tank during cold shutdown is very small and even if it would occur during drained down conditions, would not l
result in a loss of the shutdown margin.
Since the Decay Heat Removal System is normally in operation when the RCS is in cold shutdown, this system provides another possible pathway by which un-l borated water from an RC Bleed Tank in the Liquid Waste Disposal System could 1
be added 1.0 the RCS.
However, this would also require an extensive valve
lineup (See Attachment II). Although highly unlikely, if injection of unborated water from an RC Bleed Tank to the RCS were to occur, the conse-quences are even less severethan addition from the makeup tank resulting in an even larger shutdown margin remaining.
All calculations were performed using a conservative volume for the drained down RCS and the applicable sections of the NRC Standard Review Plan.
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Attat.hment I Consequences of the addition of unborated water to the RCS from the makeup tank during RCS drained down conditions:
Using initial conditions as follows:
BOC-5 (worst casg for dilutions reactivity effect) 1.
2.
Temperature - 68 F 3.
Pressure - Atmospheric 4.
Volume of contained water - 20,070 gallons.
5.
RCS baron concentration - 1356 ppm 6.
Makeup tank volume - 4500 gallons 7.
All rods in 8.
Complete mixing of all unborated water additions The analysis is based on the maximum moderatorcoefficient, Beginning-of-Core life doppler coefficient and initial RCS boron concentration at cold shut-down. Both the moderator coefficient and boron conces.tration values us6d are conservative.
A reactivity balance at these initial conditions and assuming the worst case stuck rod reveal the initial shutdown margin as follows:
Core excess %ho
+16.466 Rod worth (gps 1-7)
- 5.32 boron worth (at 1366 ppm) -18.79 stuck ryd worth
+ 1.657 Net Rho
- 5.99% AK/K Injection of 4500 gallons of unborated water to the RCS at this time will reduce the shutdown margin as follows:
Ci =.817 ci New boron concentration = 200 0 00
=.817 (1266) 1116 ppm
=
Core excess Rho
+16.466 Rod worth (gpsi-7)
- 5.32 boron worth (at 1116 ppm) -15.35 stuck rod worth
+ 1.657
- 2.55% AK/K For additional conservatism, Gp 8 worth is removed from the balance to get a final shutdown margin of:
-2.42% AK/K
-2.55% + 0.135%
=
Therefore: an injection of 4500 gallons of unborated water to this volume of water in the RCS at the above conditions will leave greater than 2% shutdown margin remaining to preclude criticality.
In addition, administrative measures are used to prevent injection from the makeup system at cold shutdown. These include racking out the breakers for the makeup pumps, closing makeup valves V217, V16A, V168, V16C and V16D, and
2-Attachment I opening th1ir respective breakers.
In view of the above, any likelihood of injection from the makeup tank during shutdown is very small and even if it would occur, would not result in criti-cality or loss of the shutdown margin.
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Attachment II Pathway from "A" RC Bleed Tank to D. H. Pump "A suction WDL-V164 +
WDL-V340 +
WSL-V23 +
WDL-P6A + WDL-V343 +
WDL-V32 +
WDL-V38 +
WDL-V51 +
SF-V43 +
SF-44 +
DK-V50 +
DH-VISA +
DH-P1A k
Valve Lineup for D. H. Pump A from A R.C. Ble'edtank Closed valves Open Valves WDL-V26 WDL-V23 WDL-V29 WDL-V32 WDL-V24 SF-V44 WDL-V25 SF-V43 WDL-V35 WDL-V51 WDL-Vil WDL-V38 adjust to 150 gpm WDL-V33 WDL-V39 WDL-V40 WDL-V68 WDL-V69 WDL-V70 WDL-V71 WDL-V41 WDL-V42 WDL-V43 WDL-V44 SF-V56 SF-V45 5F-V46 SF-V47 i
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Attachment III Since the Decay Heat System is nonnally in operation with the RCS in cold shutdown, this system provides a pathway by which unborated water could be added to the RCS. The Decay Heat Removal System draws water directly from the "B" Hot leg of the RCS to the suction on the two Decay Heat Pumps through two Decay Heat Remeval Coolers and returns it through the core flood inlet nozzles.
It is possible to intentionally lineup one of the RC Bleed Tanks to the "A" Decay Heat Pump suction, thereby establishing a path for unborated water to be added to the RCS from a RC Bleed Tank.
If this pathway is established i
during Decay Heat Removal System with the RCS in a drained down condition, a boron dilut.fon event will occur. However, as shown below, a more than adequate shutdown margin will remain.
The following initial conditions and calculations form the bases for this determination:
1.
B00-5 (worst casg for dilutions reactivity effect) 2.
Temperature - 68 F 3.
Pressure-Atmospheric 4.
Volume of contained water - 20.070 gallons 5.
RCS baron concentration - 1366 ppm 6.
All rods in 7.
Maximum possible flow from bleed tank - 150 gpm 8.
Indication of waste transfer pump operation in Control Room commences 15 minute time interval for operator action.
In-dication of RC Bleed Tank level is also available.
9.
Complete mixing of all water addi.tions underthese initial conditions at cold shutdown, and accounting for the worst case stuck rod, the initial shutdown margin is shown as:
Core excess Rho
+16.466 Rod worth (gpsi-7)
- 5.32 boron worth (at 1366 ppm) -18.79 stuck rod worth
+ 1.657 Net Rho
- 5.99 % AK/K Injection of 2250 gallons of demineralized water results in a new boron concentration of:
.899 ci Ci Cf
=
=
2007 250
.899 (1366) 1228 ppm New boron concentration
=
=
Thus, the final shutdown margin is determined to be:
Core excess Rho
+16.466 Rod worth (gpsi-7)
- 5.52 boron worth (at 1228 ppm) -16.89 stuck rod worth
+ 1.657 Net Rho
- 4.097, aK/K
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2-Attachment III For additional conservatism, Gp 8 worth is removed from the balance to get
- a final shutdown margin of:
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3.95% t.K/K 4.09% +. 0.135%
= -
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