ML20207L729
| ML20207L729 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 10/07/1988 |
| From: | Mroczka E NORTHEAST NUCLEAR ENERGY CO., NORTHEAST UTILITIES |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| A06837, A6837, NUDOCS 8810170417 | |
| Download: ML20207L729 (5) | |
Text
NORTHEAST UTILITIES o., m omc.. s.*n sua e.mn conr.acu
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October 7, 1988 Docket No. 50-336 A06837_
Re:
10CFR50, Appendix R U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D.C.
20555
Reference:
(1)
W. V. Johnston lettar to E. J. Hroczka "Inspection Report No. 50-33e/87 16," dated September 25, 1987.
Gentlemen:
Millstone Nuclear Power Station, Unit No. 2 Additional Information Regarding Inspection Report No. 50-336/87-16 Main Control Room Fire Detection Panel Reference (1) transmitted to Northeast Nuclear Energy Company (NNECO) the results of a special team safety inspection conducted at Hillstone Unit No. 2 on July 13 17, 1987.
During that inspection, NNECO committed to provide the Staff with the design details of the supervision of the fire alarm system.
Specifically, the inspection team's concern was that a simple break or grcund fa 'It could rer. der any of the fire alarm systems inoperable without a trouble ala,m being transmitted to the control room to correct the condition.
Provided in Attachment I is NNEC0's response to the Staff's request for additional information which concludes that a trouble or fire alarm will be transmitted to the control room if a simple break or ground fault were to occur.
Should you have any questions, please contact us.
Very truly yours, NORTHEAST NUCLEAR ENERGY COMPANY d@Mw[
E. Jr Mroczka g
Senior *Vice President cc:
W. T. Russell, Region 1 Administrator
/g D. H. Jaffe, NRC Project Manager, Millstone Unit Nos. 2 and 3 W. J. Raymond, Senior Resident Inspector, Hillstone Unit Nos.1, 2 and 3 DN[
6 Q
)
e Docket No. 50 336 A06837 i
Attach:nent I Main Control Room Fire Detection Panel October 1988
-.- - - - - -. - - =_ - -.- - -
Attachment !
A06837/Page 1 Main Control Room Qre Detection Panel General Descriotion:
l The Main Control Room Fire Detection Panel (C 26) consists of a Pyr A-Larm multi-zone fire and smoke detector system with remote control panel inputs.
j 4
j This fire panel monitors 67 individual zones / areas and remote pWis.
t l
These 67 individual zones monitor such things as valve position, water flow switches, water main pressure switches, heat and smoke detectors and remote control panels.
The main fire panel also provides some control outputs such i
i, as pump starts, valve operation and damper operation.
i The main fire panel has alarm /troi,ble override cut out switches which allows i
the resetting of the main control board annunciator to prevent any future main fire panel alarms from being masked, but still provides alarm / trouble j
indication on the main fire panel.
If a trouble signal was present and an alarm condition was present, the alarm signal will override the trouble signal.
t Theory of Ooeration:
l The Main Fire Panel (C 26) is a multi zone input device.
All zone inputs are basically a field contact status change.
In a normal condition (no fire / trouble alarm) each zone outputs 220 volts DC across a 91K ohm supervisory resistor.
This combination produces a very lov supervisory l
l current (2.4 mA).
When a fire condition exist, the field contact closes and I
places the 12K ohm resistor aad 91K ohm resistor in parallel which causes an i
j increase in current flow (approximately 20 mA).
It is this increase in current flow which the zone electronics sense and provides the resulting fire 3
alarm.
I Each remote control panel monitors up to four zones in a particular area, any l
one of which will cause a common fire or trouble alarm on the zone to which it I
is connected.
The remote panels operate using the same principle as the main j
fire panel by monitoring detection / actuation circuits using a supervisory current.
i Figure I shows a typical schematic of the main and remote fire panels, The j
panels consist of five control relays.
Relay K1 is the detection relay, i
Relays K2 and K3 are supervisory relays for detection and actuation circuits, respectively.
Relay K4 provides alarm functions and relay K5 provides trouble alarm functions.
Relays K2 and K3 are normally energized, Kl K4, and K5 are l
normally deenergized.
Upon activation of a detection device, relay K1 energizes which in turn energizes the release device and K4 relay which provides a local alarm and a main fire panel alarm.
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l Relays K2 and K3 (supervisory relays) provide supervision for loss of power and open circuits.
The main fire panel receives its power from the Instrument AC bus which is fed
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from a safety related bus.
The remote paaels are fed from the plant's DC j
- buses, i
i
Attachment I A06837/Page 2 l
Suoervision f
The main fire panel monitors and alarms (trouble alarm) for the condition o loss of power and break in the detector wiring between the detecto A single ground (one leg or panel) and the main fire panel.the detector legs are grounded (ground fau one side of the line grounded) in a sensor wil This is based on the a fire and provide a fire alarm.
t circuit analysis that showed a single ground will slightly increase detec o sensor to detect sensor will thus still generate a fire A double ground on a detector (one in current.
An actuated monitoring ble alarm, with a single ground present.each leg) will act like a short and ei alarm.
The recent addition of three new remote fire panels utilizing th? Pyrotr System 3 and the Ansul Autopulse 2000 are supervised for low /no po shorts and grounds.
These panels will which they are connected to alarm as a "trouble alarm" when a trouble condition is detected.
Conclusion A simple break or ground fault will not render any of the fire alarm syste inoperable without a trouble or fire alarn being transmitted to the co room fire panel.
Attachment I A06837/Page 2 Spervi sion The main fire panel monitors and alarms (trouble abrm) for the condition of loss of power and break in the detector wiring between the detector (or remote panel) and the main fire panel.
The main fire panel will not alarm if one of
'he detector legs are grounded (ground fault).
A single ground (one leg or one side of the line grounded) in a sensor will not affect the ability of the sensor to detect a fire and provide a fire alarm.
This is based on the circuit analysis that showed a single ground will slightly increase detector monitoring current.
An actuated sensor will thus still generate a fire alarm, with a single ground present.
A double ground on a detector (one in each leg) will act like a short and either generate a fire alarm or trouble al arm, The recent addition of three new remote fire panels utilizing the Pyrotronics System 3 and the Ansul Autopulse 2000 are supervised for low /no power, opens, t
shorts and grounds.
These panels will cause the main fire panel zones to which they are connected to alarm as a "trouble alarm" when a trouble condition is detected.
Conclusion A simple break or ground fault will not render any of the fire alarm systems inoperable without a trouble or fire alarm being transmitted to the control room fire panel.
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