ML20199C302
| ML20199C302 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 06/16/1986 |
| From: | Tiernan J BALTIMORE GAS & ELECTRIC CO. |
| To: | Thadani A Office of Nuclear Reactor Regulation |
| References | |
| GL-83-37, NUDOCS 8606180062 | |
| Download: ML20199C302 (5) | |
Text
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BALTIMORE GAS AND ELECTRIC CHARLES CENTER P. O. BOX 1475 BALTIMORE, MARYLAND 21203 JOSEPH A.TIERNAN Vict PRESIDENT-NUCLEAR ENERGY June 16,1986 U. S. Nuclear Regulatory Commission Office of Nuclear Reactor Regulation Washington, D. C. 20555 ATTENTION:
Mr. Ashok C. Thadani, Director PWR Project Directorate #8 Division of PWR Licensing-B
SUBJECT:
Calvert Cliffs Nuclear Power Plant Unit Nos.1 & 2; Docket Nos. 50-317 & 50-318 Control Room Ventilation
REFERENCES:
(a)
NRC letter from Mr. D. H. Jaffe (NRC), to Mr. 3. A. Tiernan (BG&E), dated April 11, 1986 Gentlemen:
Reference (a) requested information regarding the performance of the control room ventilation system. Enclosure (1) provides our response to the four items mentioned in your request.
Should you have any further questions regarding this response, we will be pleased to discuss them with you.
Very truly yours, JAT/MTF/MGP/ dim Enclosures cc:
D. A. Brune, Esquire
- 3. E. Silberg, Esquire D. H. Jaffe, NRC T. Foley, NRC 8606180062 860616 PDR ADOCK 05000317 gdf P
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ENCLOSURE (1)
RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION CONCERNING CONTROL ROOM VENTILATION ITEM 1 The basis for the temperature limitation of 104 F in the control room is equipment qualification. The location where this temperature is measured is important. BG&E should detail how the location they have selected adequately represents the point of maximum vulnerability for safety grade instrumentation and equipment during normal operation of the non-safety grade chiller system, during operation of the safety grade system and during a loss of ventilation or loss of chiller event.
Response
Our control room instrumentation cabinet design is quite open with several continuously open walkways and an open grating on top providing free communica-tion of air between the cabinets and the open areas of the control room. As evidence of the extent of air circulation, a temperature survey performed by Argonne National Laboratory during an onsite review of control room habitability in September 1985 did not indicate any significant temperature anon.alies within the cabinets. We do intend, however, to conduct a temperature survey inside the control room cabinets during the months when the air conditioning heat load is highest, July and August. The results of the survey will be evaluated and a follow-up response to this item will be provided to the NRC by October 31,1986.
When evaluating the survey results, we do not intend to postulate a loss of control room ventilation event. The operation of the air handling units is independent of the cooling units and we have never experienced a complete loss of ventilation in the control room; therefore, a loss of ventilation event is not considered credible.
ITEM 2 In accordance with Generic Letter 83-37, the staff's position is that a Technical Specification is necessary to periodically verify the leaktightness of the control room.
The Technical Specification for testing the leaktightness of the control room should be consistent with the test requirements specified in the sample Technical Specification provided by Generic Letter 83-37.
Response
The test requirement specified in the sample Technical Specification provided by Generic Letter 83-37 concerning verification of leaktightness is not applicable to our control room design. Our control room ventilation system is an isolation with filtered recirculation type, but it is not a pressurized system. Therefore, it is not possible or meaningful to verify that the system maintains a positive 1/8 inch water gauge pressure.
An evaluation of control room inleakage was recently performed and submitted to the NRC. The purpose of this evaluation was to determine the inleakage rate on a one-time basis to be used in the control room dose calculation during the design
ENCLOSURE (1)
RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION CONCERNING CONTROL ROOM VENTILATION basis radiological accident. The control room ventilation system design does not facilitate periodic inleakage testing and we feel that such testing would be a major burden without commensurate safety benefit. Our position appears consistent with Standard Review Plan Section 6.4, Control Room Habitability, which does not require periodic inleakage testing for our control room design unless the assumed inleakage rate is less than.06 volume changes per hour. We assume an inleakage rate of approximately.4 volume changes per hour.
ITEM 3 For the normal supply isolation damper, how does BG&E ensure that GDC-19 criteria is met in the event of a single failure of these dampers.
Response
All control elements associated with the operauw of the supply isolation dampers are arranged in a manner such that failure of a single element will place the dampers in a " fail safe" mode. The dampers are maintained in their normally open position by air pressure. Failure of a solenoid or other controlling device causes loss of control air pressure to the damper's piston operator and the damper fails closed.
Louvered dampers are installed immediately downstream of the normal supply isolation dampers. These dampers are piston operated and opened by increasing air pressure. Failure of a solenoid or other controlling device would also cause a loss of control air pressure and the louvered dampers would fail closed. Both the louvered and normal supply isolation dampers close on receipt of a high radiation signal. If a mechanical failure prevents the normal supply isolation damper from fully closing upon demand, the louvered dampers would close restricting the amount of air inleakage during a desi;;n basis accident. Thus, the requirement of GDC-19 is met.
The operating linkages for the louvered dampers are attached to the blade by a bracket. Bracket failures were discovered in November 1985 (LER 85-14). Through research and discussions with the vendor, newer design brackets are available and will be installed on these dampers. The newer bracket is a more rigorous design.
Installation will reduce the probability of failure, thus increasing the reliability of the louvered dampers to close upon demand.
ITEM 4 The cooling requirement for the control room is 116.5 tons while the capacity of the safety grade control room chiller unit is to be 96 tons.
During the period from July 16,1980, through September 11, 1980, a total of five incidents occurred (LERs80-034, 80-038,80-039, 80-049, and 80-051), in which the safety grade control room chillers tripped. In one case, a total loss of HVAC was experienced. In four of these LERs, the licensee stated that the system design was being reevaluated for additional _
ENCLOSURE (1)
RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION CONCERNING CONTROL ROOM VENTILATION cooling capacity and for reliability of the cooling portions of the control room HVAC system. BG&E's resolution to the problem was to install a new,220 ton, non-safety grade chiller unit to cool the control room during normal operation. However, if the plant is required to operate the safety grade chiller unit for any reason such as during a loss of offsite power event, the system would still be susceptible to those same potential trips which were experienced in 1980 since nothing has been done to upgrade the safety grade chillers. Provide a justification as to why an upgrade of the safety grade chiller unit is not required.
Response
The assertion by the NRC that we have experienced a total loss of control room Heating, Ventilation and Air Conditioning (HVAC) is incorrect. The air handling units remained OPERABLE during these events. In addition, the assertion that nothing has been done to upgrade the safety grade refrigerant system is also incorrect. As discussed below, modifications have been made and reported to the NRC.
The LERs referred to concerned the following two causes:
o Three reported compressor trips due to high head pressure, and o
Two reported compressor trips due to defective or misadjusted uni-pressure valves.
Investigation of the cause of the problems reported in the LERs showed that they all related to one problem source, the uni-pressure valves. Originally there were three such valves in each system. They were difficult to calibrate and keep in adjustment. If the valve malfunctioned it allowed more hot gas to bypass to the coil or compressor, seriously reducing system capacity and causing compressor trip on high head pressure. These valves were replaced with a more conventional hot-gas by-pass valve arrangement and the problems described in the LERs were eliminated. This modification was completed in August 1980 and was reported in revisions to the LERs of concern (all revisions dated August 19, 1983).
In addition, an oil separator was installed in the hot gas discharge line of each compressor to assure retention of oil in the compressor for adequate lubrication.
This increased reliability of the system.
This modification was completed in June 1983. Completion of these two modifications has reduced the susceptibility of the system to trips such as those experienced in 1980; there have been no loss of control room cooling events since 1980.
In order to maintain a comfort temperature of 75 F in the Control Room, approximately 116.5 tons of cooling is necessary. The safety grade refrigerant system has the capacity (96 tons) to maintain Control Room temperatures approximately 83-85 F (with outside air temperature at 95 F) which is well below the Technical Specification limit of 104 F. The addition of the 220 ton non-safety grade chilled water system provides adequate cooling to maintain 75 F and allows the safety grade refrigerant system to essentially remain in standby instead of -
ENCLOSURE (1)
RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION CONCERNING CONTROL ROOM VENTILATION constantly running. The safety grade refrigerant system is periodically tested to verify it can maintain control room temperature below 104 F without the chilled water system operating.
Completion of these three modifications has increased the reliability of the Control Room Ventilation System to provide adequate cooling during all accident situations. Therefore, additional upgrading of the safety grade refrigerant systems is not considered necessary.
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