ML19347D024
| ML19347D024 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 02/27/1981 |
| From: | Crouse R TOLEDO EDISON CO. |
| To: | Reid R Office of Nuclear Reactor Regulation |
| References | |
| TASK-2.B.1, TASK-TM 692, TAC-44364, NUDOCS 8103100559 | |
| Download: ML19347D024 (4) | |
Text
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Docket No. 50-346 TOLEDO License No. NPF-3 EDISON Serial No. 692 a -.< p case
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February 27, 1981 b $,m Director of Nuclear Reactor Regulation Attention:
Mr. Robert W. Reid, Chief Operating Reactors Branch No. 4 Division of Licensing United States Nuclear Regulatory Commission Washington, D.C.
20555
Dear Mr. Reid:
A previous Toledo Edison letter dated January 30, 1981 (Serial No. 582) discussed installation of a Reactor Coolant High Point Vent System for the Davis-Besse Nuclear Power Station Unit 1 (DB-1).
This was in response to your letters of September 13, and October 30, 1979 concerning implemen-tation of lessons learned from the Three Mile Island, Unit 2 (TMI-2) incident. Toledo Edison proposed that vents would be installed and include a flow detection device to provide the control room with flow /no flow indication.
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This letter is to identify a revision in the method of flow indication for the pressurizer and hot leg vents. The design now provides solenoid operated valves with stem operated limit switches that provide positive "0 PEN" or " CLOSED" position switches for indicating lights in the control room. This is in lieu of the previously indicated flow switches with
" FLOW /NO FLOW" lights. The attachment is the Reactor Coolant High Point Vents System design criteria revised to reflect this design. Figure 1 reflects the revised conceptual drawing.
In a letter to Mr. D. G. Eisenhut dated December 30, 1980 (Serial No. 670) concerning Clarification of TMI Action Plan Requirements (NUREG 0737)
Toledo Edison committed to installation of vents during the first refueling outage after January 1, 1982 (item II.B.1).
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DB-1 NRC Resident Inspector p THE TCLECO ECTSON COMPANY ED: SON PLAZA _ 300 MADISCN AVENUE TOLEDO, CHlO 43S52 810810 0 W
o' Docket No. 50-346 License No. NPF-3 Serial No. 692 February 27, 1981 Page One of Three REACTOR C00LAN HIGH POINT VENTS SYSTEM DESIGN CRITERIA (Revision 1)
The proposed Reactor Coolant System (RCS) High Point Vent System provides vents on each of the two hot legs and on the pressurizer. Each vent line will be controlled by two valves from the control room using individual handswitches and each valve will have positive position indication in the control room. The two hot leg vent lines will have restrictive orifices sized such that-the flow rate will not exceed the RCS makeup system capability. The vent on the pressurizer shall also be designed and sized such that the inadvertent opening of both valves could not cause the RCS to depressurize when all pressurizer heaters are energized.
The vents will be routed to the containment atmosphere in an unobstructed area. A conceptual drawing (Figure 1) of the system is provided. The circled areas indicate the changes necessary to the existing RCS.
The vent on each hot leg will be controlled by two solenoid operated valves. The valves will be nuclear Class 1 and will be seismically and environmentally qualified to the criteria of the DB-1 FSAR. The valves will be powered from Class 1E power supplies. The two valves on loop 1 line will receive channel'1 AC and channel 1 DC power, respectively. The two' valves on loop 2 will receive channel 2 AC and channel 2 DC power,
-respectively. The AC valves will utilize control penetrations, while the DC valves will utilize power penetrations through the containment vessel. Also,-the channel 1 AC control circuits and power circuits between the motor control centers and the valves will be separated from the channel 1 DC circuits. The same will be done for the channel 2 circuits. Therefore, all cabling will be kept separate for all four valves._ This will be'done to maintain channel separation and to prevent the possibility of hot shorts causing inadvertent opening of both of these vents..The valves will fail closed on loss of power.
- The high point vent from the pressurizer will be installed as shown on
- Figure 1.
Existing valve HV-239A is presently powered from a channel 2 Class 1E supply. Existing valve HV-200 is presently powered from a non-1E supply, but will be modified to be powered from a channel 2, Class IE supply. All power circuits between the motor. control centers and the valves and all control wiring for HV-200 and HV-239A will be separated to prevent the possibility of hot shorts inadvertently opening both valves. To utilize the high point vent on the pressurizer, these valves
.would be opened from'the control room.
All taps for the new vent lines and all associated valving and instru-
- mentation will be located above-the maximum credible water level in the containment vessel and v111'be protected against damage from adjacent systems.
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9 Docket No. 50-346 License No. NPF-3 Serial No. 692 February 27, 1981 Page Two of Three As discussed in the Davis-Besse Unit 1 FSAR, Section 6.2.5, the fla=ma-bility limit (4%) for hydrogen generated in accordance with Regulatory Guide 1.7 is not reached until 37 days after the postulated accident.
The FSAR analysis assumes that all the hydrogen from the metal-water reaction is released from the Reactor Coolant System to the containment in the first 2 minutes after the accident. Therefore, it is concluded that this analysis envelopes the case where hydrogen could be released into the containment over a longer period of time due to 2CS high point venting.
The system design as described above has considered the effects of single failures, interaction with adjacent systems that could cause missiles, water levels in the containment vessel after a LOCA and fire.
The high point vent valves are located so that they will not be affected by missiles or high water level. The separation assures that a fire would not cause inadvertent opening of a vent path, or failure of a vent path if needed. The electrical design assures that a single failure, including interruption of a power supply or hot shorts, will neither prevent the ability to vent through at least one high point vent nor cause the inadvertent opening of'any high point vent. Redundancy of one reactor coolant loop vent is provided by the other hot leg vent.
The primary vent path for the pressurizer is the installed Pilot Operated Relief Valve (PORV). The additional pressurizer vent described here will provide a back-up capability for that path.
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