ML20041A541
| ML20041A541 | |
| Person / Time | |
|---|---|
| Site: | Wolf Creek, Callaway  |
| Issue date: | 02/12/1982 |
| From: | Petrick N STANDARDIZED NUCLEAR UNIT POWER PLANT SYSTEM |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| SLNRC-82-09, SLNRC-82-9, NUDOCS 8202220273 | |
| Download: ML20041A541 (5) | |
Text
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pnCENED SNUPPS Stenderdized Nuclear Unit
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FED 1'91982" -11 Po-se risai sv.t.,n 5 Choke Cherry Road g Jg;;g t@Lt pf FM Nicholas A. Petrick 8
Rodville, Meryland 20850 g
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- Executive Director (301) 8664010
/
February 12, 1982 SLNRC 82- 09 FILE: 0278 SUBJ:
Safe Shutdown with a Postulated.
Fire in the Control Room Mr. Harold R. Denton, Director /
Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, D. C.
20555 Docket Nos:
STN 50-482 and STN 50-483
Dear Mr. Denton:
In September _1981, during a meeting between SNUPPS and the NRC, the NRC stated its position regarding design requirements to mitigate the effects of postulated fires in the control room.
In response to that position, SNUPPS is in the process of implementing design changes which.will iso-late one train of controls and required instrumentation on the auxiliary shutdown panel from the control room. This will provide the capability to take the plant to safe (hot) standby from the auxiliary shutdown panel following a postulated fire in the control room.
Additionally, the auxil-iary shutdown panel is constructed in two sections, which will be separa-ted by a three-hour rated fire wall. This will ensure the capability to-take the plant to safe shutdown for any postulated fire at the auxiliary shutdown panel.
These design modifications are described in further detail in the enclo-sure to this letter.
This letter is intended to serve to close outstand-ing issue #10 in the Callaway SER.
We believe these design modifications meet the NRC's stated position.
Your prompt review and comments are requested because modifications are-being implemented into the plant design.
Appropriate changes will be made in the next revision to the SNUPPS FSAR.
Very truly yours,
_k thCQ Nicholas A. Petrick FS/mtkRLS4bil 0
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DESIGN
SUMMARY
Isolation of Safe (Hot) Standby Equipment from Control Room a
===1.
Background===
The SNUPPS control room is located at elevation 2047'6" in the Control Building (ref: FSAR Figure 1.2-25).
The control room contains the control boards, operators' console, and, in an area behind the main control board, equipment cabinets containing protection system and process equipment racks. Safety-related electrical cabling within the control room is assigned to four separation groups, which are physically separated in accordance with Regulatory Guide 1.75.
Outside of the control room safety-related cabling and equipment are grouped into two safety trains, with each train containing cabling and equipment of two safety-related separation groups. The two safety trains are physically separated by 3-hour rated fire barriers or, in a few cases, by lesser rated oarriers or distance (ref:
FSAR Appendix 9.58).
The auxiliary shutdown panel (ASP) is located in the north east corner of the Auxiliary Building one level below the control room at Elevation 2026 (ref: FSAR Figure 1.2-12).
The ASP is subdivided into two separate sections; one is associated with instrumentation and con-trol circuits used for controlling safe shutdown equipment in train A and the other is associated with instrumentation and control circuits used for controlling safe shutdown equipment in train B.
The two sec-tions of the ASP are electrically and physically separated and are associated with the same safety-grade circuits that serve their respec-tive trains.
Each section of the ASP is enclosed by a 3-hour rated fire wall, floor and ceiling.
The initial design of the SNUPPS control room and ASP considered the occurrence of a severe " exposure" fire in the control room or ASP room to be nat credible.
This was based on consideration of the small amounts of flammable material present in each area, stringent access controls, and continuous occupancy of the control room.
In September 1981, during a meeting between SNUPPS and the NRC, the NRC stated its position regarding design requiremants to mitigate the effects of postulated fires in the control room.
In response to that position, SNUPPS is in the process of implementing design changes which will isolate one train of controls and required instrumentation on the auxiliary shutdown panel from the control room.
2.
iiodifications for Postulat_ed Exposure Fires a) Fire at Auxiliary Shutdown Panel (ASP)
A three-hour, fire-rated wall is to be provided between the two sections of the ASP. This provides assurance that a postulated fire in one remote shutdown panel area will not disable the other shutdown train.
To allow access to the panels and operator viewing of the panels, two doors are provided in the wall.
The doors are also fire-rated; one is located in the panel front area and the other in the panel rear area.
The daors will normally be closed. They may be open when control is transferred to the ASP.
b) Fire in Control Room Controls and instrunentation in Train B (one section of ASP) are to be isolated from the control room in the following manner.
(1) Train B (panel RPil8B) has been chosen as the most advan-tageous train for isolation because this panel contains controls for the turbine-driven auxiliary feedwater pump.
This panel contains equipment in separation groups 2 and 4.
(2) New process and auxiliary relay panels will provide iso-lation for the related control and instrument circuits of Train B.
These panels are located in ESF switchgear room No. 2 (a seismic, category 1 area at elevation 2000' of the Control Building (ref:
FSAR Figure 1.2-24). These i
process panels are seismically and environmentally quali-fied.
(3) Normally, digital (on-off) control circuits are opera-tional from both the control room and ASP, whereas analog (modulating) control circuits are lined-up to be opera-tional from the control room.
In the event the control room must be abandoned, the control room circuits are iso-lated, and control allowed only from the ASP.
The trans-fer operation to the ASP is initiated via hand operated transfer switches provided in all control circuits between ASP Train B and the main control room. These transfer switches are located at the auxiliary shutdown panel.
To reenergize the main control room circuits, it is necessary to go to auxiliary relay panel and reset the individual transfer relays for the digital (on-off) circuits.
The modulating circuits are reset from the auxiliary shutdown panel.
In addition, duplicate fuses are provided in related motor control centers, switchgear, and control panels such that the control circuitry in the control room and ASP are separately fused.
Therefore, in the event that a fire in one location blows its related fuse, the control circuit, when transferred to the other location, would be connected to a separate fuse.
The indicating lights related to the controls discussed above at each location are continously connected to their respective fuses. This allows continous light operation to provide the operator with system status prior to transfer of control.
(4) For instrument circuits, the new process panels contain power supplies and signal conditioning equipment to pro-vide isolated outputs to the main control room process racks and the ASP. One set of process panels is provided.
to isolate the balance of plant (80P) instruentation.
Another process panel is provided to isolate and house the NSSS instr uentation.
The combination of the two process panels provides isola-tion for the following instrumentation on the ASP required for hot shutdown.
a.
Steam Generator B Wide Range Level ( AE-LI-502A) b.
Steam Generator B Aux. Feed Flow ( AL-FI-38) c.
Steam Generator B Atmos. Relief Control ( ABPIC-28) d.
Steam Generator B Aux. Feed Control Vlv (TD) (AL-HK-108) e.
Steam Generator D Wide Range Level (AE-LI-504A) f.
Steam Generator D Aux. Feed Flow ( AL-FI-18) g.
Steam Generator D Atmos. Relief Control ( AB-PIC-48) h.
<* Jam Generator D Aux. Feed Control Viv (MD) (AL-HK-5B) 1.
noxiliary Feedpump Speed Control (FC-HIK-3138)B)
- j. Auxiliary Feed Suction Pressure (MD) (AL-PI-248) k.
Auxiliary Feed Suction Pressure (TD) (AL-PI-268) 1.
Pressurizer Level (BB-LI-4608) m.
Wide Range Reactor Coolant T -Loop 4 (BB-TI-443A)
(new indication at ASP resulUing from NRC ICSB review) n.
Wide Range Reactor Coolant T -Loop 2 (BB-TI-423X)
C o.
Reactor Coolant Pressure (No. later)
(5) The process panels provided for the modifications discussed above have the same test capability as that provided for the criginal safety related process panels in the main control room.
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