ML19260C873
| ML19260C873 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 01/30/1980 |
| From: | Crouse R TOLEDO EDISON CO. |
| To: | Reid R Office of Nuclear Reactor Regulation |
| References | |
| TASK-2.B.1, TASK-TM TAC-44364, NUDOCS 8002060317 | |
| Download: ML19260C873 (4) | |
Text
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TOLEDO Docket No. 50-346 EDISON License No. NPF-3 acuac P Cacuse Serial No. 582 u,>,,,
January 30, 1980 h*",Qm, Director of Nuclear Reactor Regulation Attention:
Mr. Robert N. Reid, Chief Operating Reactors Branch No. 4 Division of Operating Reactors United States Nuclear Regulatory Commission Washington, D. C. 20555
Dear Mr. Reid:
Attached is the preliminary design description and criteria for the proposed reactor coolant high point vent system for the Davis-Besse Nuclear Power Station, Unit 1 (DB-1).
This submittal is in partial response to your letters of September 13 and October 30, 1979 concerning implementation of lessons learned f rom the Three Mile Island, Unit 2 (TMI-2) incident. The proposed system consists of a vent at the top of each reactor coolant hot leg as well as a pressurizer vent.
These would be operable from the control room. Criteria details are provided in the attachment to th.s latter.
Af ter evaluation of the ability to insure venting of gases that could prevent natural circulation, it was determined that a reactor vessel head vent provided no advantages for a Babcock and Wilcox nuclear steam supply system beyond those achieved by the proposed loop vents. The loop vents are physically located at the high point of each reactor coolant hot leg.
Therefore the DB-1 reactor coolant vent system design does not include a reactor vessel head vent.
It is currently projected that the pressurizer and hot leg vents could be installed at Davis-Besse during the refueling outage currently scheduled for the spring of 1981. This is considered to complete the response to the " Category A" concern addressed as item "(e)" in your letter of September 13, 1979.
Very truly yours, RPC:TJM:ces Attachment 1933 093 5
THE TCLEDO EDISON COMPANY EDISCN PLAZA 300 MADISCN AVENUE TCLE00. CHtO 43652 800206o 317
Docket No. 50-346 License No. NP F-3 Serial No. 582 January 30, 1980 Page One of IVo REACTOR COOLANT HIGH P9 INT VENTS SYSTEM DESIGN CRITERIA 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 con-trolled 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 be approximately one half inch nominal diameter, 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 below 2000 psi when all pressurizer heaters are energized. The vents will be routed to the containment atmosphere in an unobstructed area (which will provide adequate mixing).
Each ven t line will include a flow detection device to provide control room flow /no flow indication. A conceptual drawing of the system is provided as an attachment to this description. The circled areas indicate the changes necessary to the existing RCS.
A vent on the top of the reactor vessel head is not required for the following reason:
The RCS has the ability to vent all gases that may impede natural circula-tion through high point vents installed on the hot legs. Any accumulation of gases that is sufficient to fill the reactor vessel below the hot leg nozzles can be vented via the hot leg vents due to the free path available from the reactor vessel to these vents.
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 quali-fled to the criteria of the DB-1 FSAR. The valves will be powered from Class IE 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 f rom 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 f ail closed upon interruption of power. The hot leg vent lines will tap off the existing manual vent lines from the RCS loops to the containment vent header. These existing lines tap off the RCS hot legs at the high point directly above each steam generator. The new taps will be downstream of the first existing globe valve RC 42 (RC44), which will be locked open to ensure a flow path.
A new manual valve will be added in each line downstream of existing valve RC43 (RC45) to provide RCS isolation by two valves f rom the containment vent header. A new manual valve will also be added in each nitrogen inlet line upstream of existing valve NN69 (NN68) to provide similar isolation for the nitrogen system. All these new valves will be nuclear Class 1 valves and will be seismically and environmentally qualified as above.
The high point vent lines to the containment atmosphere will be routed to ensure a suitable mounting location for the solenoid valves.
1933 094
Docket No. 50-346 License No. NP F-3 Serial No. 582 January 30, 1980 Page TVo of Two The high point vent from the pressurizer will tap off the existing pressurizer vent header downstream of the two existing motor-operated valves RV-239A and HV-200.
The new vent line will include a normally open manual valve and is a nuclear Class 2 line, because it is downstream of the second valve on the vent header for isola-tion from the RCS.
A normally closed manual valve will be added immediately downstream of the new vent line tap to provide isolation for the existing line to the containment vent header.
Existing valve HV-239A is powered from a channel 2 Class IE supply.
Existing valve HV-200 is powered from a non-IE 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
- g. point vent on the pressurizer, these valves would be opened from the cont.ol room.
All taps for the new vent lines and all associated valving and Lastrume..tation will be located above the maximum credible water level in the containment vessel and will be protected against damage from adjacent systems.
As discussed in the Davis-Besse Unit 1 FSAR, Section 6.2.5, the flammnbility limit (4%) for hydrogen generated in accordance with Regulatory Guide 1.7 is not reached until 37 days af ter 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 af ter the accident. There fo re, 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 RCS high point ventin g.
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 thay 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 f ailure 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.
1933 095
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