ML20059L881
| ML20059L881 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 09/18/1990 |
| From: | Shelton D TOLEDO EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 1836, NUDOCS 9010020110 | |
| Download: ML20059L881 (5) | |
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- 9 e-TOLEDO EDISDN A Cent.erer Wgy Carew l
Document Number 50-346 DONALo C SHELTON i
%ce Premdeft-Nurier License Number NPF-3
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Serial Number 1836 September 18, 1990 United States Nuclear Regulatory Commission Document Control Desk Vashington, D.C.
20555 Subj ec t :
Feed and Blud Modification Summary f
Gentlemen:
Toledo Edison made a long term commitment in a November 4, 1985, submittal (letter Serial Number 1207) to enha. ace the existing primary system feed and bleed capability at the Davis-Besse Nuclear Power Station (DBNPS), Unit Number 1.
The original commitment, based upon a preliminary evaluation, involved installation of Reactor Coolant System (RCS)-blevdown valves.
In subsequent k
submittals-(letter Serial Numbers 1382, 1526 and 1656 dated June 25, 1987, August 8, 1988 and May 5,.1989, respectively), the original blowdown valve approach was modified because detailed analysis could not fully support viability of the method.
As a result, in order to achieve an effective method of feed and bleed cooling capability, RCS makeup (MU) system flov enhancements and upgrade modifications were made during the fifth and sixth refueling-outages. This letter is being submitted for your information to srnmarize the modifications which have he n made to provide enhanced feed and bleed cooling capability at the DBNPS.
Feed and bleed cooling would be required only in a beyond-det:ign basis event involving loss of p,imary to secondary heat transfer (e.g.,' loss of both main feedvater pumps, loss,f both turbine driven auxiliary feedvater pumps, and loss'of-the motor dt'ivet. feedvater pump).
The previously existing feed and bleed cooling capability cequired use of the Pilot Operated Relief Va:.'ve (PORV), RCS Pressurizer coo, safety valves, and both MU pumps. The r.pgraded makeup system provides incret sed flow capability and train independence. As a result, feed and bleed cooling capability vill not be lost upon a failure of either a MU pump or the PORV.
Components necessary to support feed and. bleed cooling have been upgraded to be functional following a seismic event and a loss of offsite power.
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THE TOLEDO ED SON COMPANY EDISON PLAZA 300 MADISON AVENUE TOLEDO. OHIO 43652 l
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S;ric1 Numb 2r 1836 Page 2 Feed and bleed cooling can be manually initiated from the control room; however, subsequent compensatory action outside the control room may bn required in order to maintain feed and bleed: capability (i.e., operator action in response to a loss of DC Train No. 2 power or of the MU pump room cooler).
Sufficient time has been shown to be available for operators to respond l
vithout interrupting the feed and bleed functions.
Other hazards such as fires, internal or external missiles, and high energy line breaks / critical cracks have not been postulated to occur concurrent with the need for feed and bleed cooling.
Feed and bleed cooling is considered to be successful if the fluid level inside the reactor vessel is sufficient to maintain the core covered with vater (or a two phase mixture) until normal heat removal methods can be reestablished. Analytical results indicate that successful feed and b1beci cooling vill be attained with the following minimum equipment combinations:
1.
Two makeup pumps and the RCS Pressurizer code safety valves.
2.
One makeup pump operating in piggyback with a Low Pressure Injection pump, RCS Pressurizer code safety valves, and the PORV.
i Vith the worst case (one makeup pump) combination, analysis indicates that minimum collapsed reactor vessel fluid level vill be 11.6 feet, as measured against the 12-foot core height. This level is considered to be acceptable because steam voids within the 11guld vill increase the mixture height to above the top of the core. Although the analysis assumes that feed and bleed cooling would not be initiated until ten minutes following the time when the RCS hot leg reaches 600*F, procedures currently direct that feed and bleed be initiated immediately if only one MU pump is available and primary to secondary heat transfer cannot be established through the steam generators.
The analysis also does not take credit for an anticipatory reactor trip which would conserve RCS inventory for sor transients, such as those involving loss of both main feedvater pumps.
Two MU pumps in operation would provide approximately twice the injection flow rate, resulting in a substantially greater margin.
In addition, actual test results indicate that the system flow capability is currently slightly greater than the analyzed flow capability. Therefore, actual minimum reactor vessel fluid levels in a feed l
and bleed scenario should be higher than analytical results.
Fifth Refueling Outage Modifications As provided in Toledo Edison's May 5, 1989, submittal (Letter Serial Number 1656), the following flow enhancements were completed during the fifth refueling outage 1.
A reduction in system flow usistance was accomplished. This included installation of new injection and suction piping and valves for MU pump No. 1 (previously, the system consisted of common suction and injection headers for both pumps). High. flow resistance in MU Train No. 2 due to throttle valve MU-32 was reduced by installation of a motor operated bypass valve around this valve.
A discharge piping cross-tie with motor. operated dual isolation valves was also added.
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Discharge head-flow capability of the MU pumps was increased by-rerouting the pumps' suction from directly off the Borated Vater Storage Tank to the High Pressure Injection (HPI) pumps' suction lines. This permitted the suction pressure to be boosted by the Lov Pressure Injection (LPI) pumps via the already existing LPI to HPI pig;f ack piping.
b 3.
Solenoid valves were added to the minimum recirculation lines on eacF MU pump. This permits control room isolation of recirculation flow to maximize injection flow when necessary.
4.
The PORV power source was reconfigured to be supplied from the essential DC Distribution Panel, D2N. The solenoid coil on the PORV was environmentally qualified for_the Containment atmosphere as calculated for the feed and bleed scenario.
5.
The Safety Features Actuation System (SFAS) signal was removed from-the Containment isolation valve on MU-injection line No. 2 (License Amendment Number 112). This ensures continued availability of feed and bleed cooling once it is initiated.
6..
The 4160 VAC LPI-MU beaker interlock vas modified. A MU pump vas previously tripped when the associated LPI pump was running on a bus being supplied by an Emergency Diesel Generator. The MU pump vill no longer be tripped if an SFAS level 3. actuation (i.e., high containment pressure or low-low RCS pressure) occurs and the LPI pump is already running. This ensures continued availability of feed and bleed cooling once it is initiated.
7.
Class lE isolation circuitry was added between the MU pump 3-vay suction valves and the common MU tank level interlock circuits.
8.
The Reactor Coolant Pump seal injection and MU flow test line was relocated from MU Train No. 2 discharge to the discharge cross-tie between MU trains.
9.
Flow indication on each train was upgraded with dual range digital meters.
Sixth Refueling Outage Modifications During the sixth refueling outage, the system was primarily upgraded to provide single failure and seismic protection.
Modifications and analysis completed during the sixth refueling outage. included:
1.
KU system piping required to support feed and bleed cooling was-evaluated to be seismic class 1.
Vhere possible, existing electrical cables, conduits, and components which are required to support feed and bleed cooling were determined to be acceptable by application of Seismic Qualification Utility Group (SOUG) criteria.
New cable runs
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and those which could not be seismically qualified by application of
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Page 4 SOUG criteria vere remounted or_ rerouted in seismic category I (S/I) cable trays and conduits.
This work required extensive rerouting of cables, some of which had been located in the turbine building.
Toledo Edison believes that the completed vork provides adequate assurance that the system vill remain functional following a design basis earthquake.
2.
Essential Component Cooling Vater (CCV) was provided to both MU pumps. This modification provides each MU pump with its own safety grade cooling vater supply.-
3.
The flow indication circuitry for MU Train No. 2 was upgraded to noclear safety-related "0".
(Train No. 1 flow indication was installed as "0" during the fifth refueling outage).
4.
Circuitry required to manually open the PORV was upgraded to "0".
As part of this work, the power supply associated with the indicating-lights was transferred to an essential 120 VAC instrument distribution panei.
In addition, cable size for the PORV solenoid power was increased to reduce voltage drop. This should ensure that the PORV vill open even with the degraded battery voltage which might occur if the battery charger associated'vith essential DC Distribution Panel D2N is lost.
5.
Check valve HU169 in MU Train No. 2 discharge piping was replaced with a check valve design having lever frictional losses. -Although testing following the fifth refueling outage demonstrated acceptable flow, the previously installed MU169 substantially reduced the available flow margin in MU Train No. 2.
Testing was conducted following replacement of MU169 and demonstrated improved performance.
6.
The MU pumps are located in a common room which is cooled by a single air conditioning unit.
As part of single failure protection, Toledo Edison explored several options for replacing, supplementing, or upgrading this cooler. None of the options was able to meet all design criteria and space constraints within'the room. Therefore, i
Toledo Edison undertook an effort to qualify equipment within the HU pump room which is necessary'to support feed and bleed cooling. This l
approach required calculation of the room temperature profile which vould result without an operating room cooler.
Four pressure switches which control part of the HU pump lube oil pump motor control logic were replaced to ensure that they would-continue to function in the elevated room temperature environment. The existing AC povered MU pump bearing oil pump. motors were found not to be qualiffed for operation in elevated temperatures.
While an attempt was made to replace these motors with qualified components during the j
sixth refueling outage, the replacement motors did not arrive'at the plant.in sufficient time for installation without adverse restart schedule impact. Therefore, as indicated in a previo's submittal (letter Serial Number 1656), environmentally qualified AC povered bearing lube oil pump motors vill be installed during the seventh refueling outage. The remaining components which are necessary for feed and bleed cooling, except for the MU pump motor bearings, vere 4
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evaluated and determined to be capable of' continued operation in the postulated environment without operator action.
Environmental qualification studies shoved that the MU pump motor bearings are the most temperature sensitive components remaining within the MU pump room. Because the bearings cannot be upgraded without substantial additional modifications, compensatory operator action has been weified to limit room heatup in the event of a loss of the room j
sler. This action is needed thirty minutes following loss of the cooler and has been incorporated in plant emergency procedures.
It is the intent of Toledo Edison to maintain the components necessary to support feed and bleed cooling in accordance with Augmented Quality, "A0",
requirements. New components within the feed and bleed system vere generally purchased and installed in accordance with nuclear safety-related "0" requirements. Where feasible, from a parts availability and schedule standpoint, these items vill be maintained with "0" replacement parts.
It is also the intent of Toledo Edison to monitor MU pump performance through existing Technical Specification surveillance tests'(or other periodic tests) to ensure that feed and bleed capability is maintained; however, Technical Specification operability is not dependent upon adequate feed and bleed capability.
Should system degradation occur such that successful feed and bleed cooling may be compromised, corrective action vill be taken to ensure success of the feed and bleed capability at the earliest opportunity commensurate with outage scheduling and parts availability.
Vith the exception of qualification / replacement of the AC povered MU pump i
bearing oil pump motors mentioned above, Toledo Edison considers that modifications made during the fifth and sixth refueling outages satisfy all previous commitments with respect to enhancing feed and bleed capability at I
the Davis-Besse Nuclear Power Station.
i If you have any questions, please contact Mr.
R.' V. Schrauder, Manager -
Nuclear Licensing, at (419) 249-2366.
Very t
- yours, RMC/mmb cci P. M. Byron, DB-1 NRC Senior Resident Inspector A. B. Davis, Regional Administrator, NRC Region III M. D. Lynch, DB-1 NRC Senior Project Manager Utility Radiological Safety Board-1 i
.