ML20030B335
| ML20030B335 | |
| Person / Time | |
|---|---|
| Site: | Maine Yankee |
| Issue date: | 07/31/1981 |
| From: | Garrity J Maine Yankee |
| To: | Clark R Office of Nuclear Reactor Regulation |
| References | |
| FMY-81-118, JHG-81-168, NUDOCS 8108060342 | |
| Download: ML20030B335 (2) | |
Text
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%CU (207; 623-3521 July 31, 1981
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6 United Stated Nuclear Regulatory Commission f tp/
3 Washington, D.C.
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W Attention: Office of Nuclear Reector Regulation h
,UG ()3 Jggj 5 Division of Licensing m_
Operating Branch #3 q
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M. Robert A. Clark, Chief c
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Reference:
a) License No. DPR-36 (Docket No. 50-309)
Q Q..\\g b) USmC Letter to MYAPCO dated April 13, 1981
Subject:
Flooding of Safety-Related Equipment in the Turbine Building
Dear Sir:
Your letter, Reference (b), requested that Maine Yankee provide information relative to the potential flooding of safety-related equipment in the turbine building as a result of a failure of the circulating water piping or expansion joint.
In response to your request, Maine Yankee offers the following information.
The circulating water piping in the Maine Yankee turbine building is all located on the ground floor, Elevation 21'.
This elevation of the turbine building contains numerous openings such as roll-up doors to the outside, wall ventilation louvers to the outside, doorways leading to non-safety related areas, etc. Although many of these openings are watertight, it is difficult to envision any significant flooding depth due to the number of openings available.
The gound floor of the turbine building is a normally manned area. Virtually all plant personnel utilize this area as a major passage route between the various departmental areas such as Maintenance, I&C, HP, Chemistry, Administration, etc. Auxiliary operators and Security personnel make their rounds throughout this area. Any significant leakage from the circulating water system in this area would be readily apparent to any of these personnel passing through the turbine building.
The circulating water piping on the outlet of the condenser is always under a negative pressure due to the siphon created by its discharge to the diffuser seal pit.
Thus, failure of this piping can be disregarded as it would only lead to air intake into the system.
This reduces the amount of piping subject to the postulated failure by a factor of two.
The design of the Maine Yankee circulating water system utilizes a vacuum priming system which enables the circulating water pump discharge to reach the pl full elevation of the condenser in addition to removing disolved gases. Any g
significant leakage from the circulating water piping would result in a loss p
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a MAINE YANKEE ATOMIC POWER COMPANY United Stated Nuclear Regulatory Commission Page 2 Attn: Office of tOclear Reactor Regulation July 31, 1981 l
of system vacuum. The alarm associated with the vacuum priming system, coupled with other indications and alarms such as decreasing condenser vacuum and alarm, condenser vacuum differential, fluctuating circulating water pump amperage, etc., would all provide the control room operators with an immediate awareness of the situation.
Regardless of the aforementioned, Maine Yankee has evaluated the flooding of the turbine building under two different situations. First, a more or less credible situation was considered which results in a flooding rate of 10,000 gal / min. Using conservative area / volume calculations of the turbine building at Elevation 21'; and assuming zero leakage through any of the many turbine building openings, a water level rise of about 0.5" per minute was calculated. The only safety-related equipment in the turbine building proper at these elevations are the Component Cooling pumps. The motors for these pumps are located more than 22" above the floor of the building. At the postulated rate, flooding would have to continue for about 45 minutes, unnoticed, with no operator action and no leakage out of the building, before the Component Cooling pump motors will be affected. Failure to detect and correct this situation is not considered credible.
The second situation considered was a bounding catastrophic complete open-ended break of a circulating water inlet line with a flooding rate of 110,000 gpm. Although this potential accident results in a flooding rate over 10 times faster than the previous situation, it is felt that a situation of this magnitude would not go unnoticed for more than a few seconds given the number of people normally in the area and the number of alarms and indications available to the Control Room operators.
Maine Yankee believes there is ample time for assessment and corrective action (such as opening doors to let out water) by the operators in order to prevent the flooding of safety-related equipment.
However, in light of today's regulatory climate, we recognize that these assurances may not satisfy the staff, so Maine Yankee is prepared to consider the installation of a passive opening in the turbine building wall opposite the circulating water inlet piping to relieve the consequences of an unlikely complete severence of a circulating water pipe. Maine Yankee will agree to install this passive opening only upon commission approval and agreement that complete resolution of this issue has been achieved. Again though, it is felt that the circumstances described above without the passive opening in the turbine building are sufficient to mitigate the consequences of a circulating water system leak in the turbine building.
We trust this information is satisfactory; however, should you require further details please contact us.
Very truly yours, MAINE YANKEE ATOMIC POWER COMPANY f
John H. Garrity, Director Nuclear Engineering and Licensing JHC/plb
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