ML19296B183
| ML19296B183 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee File:NorthStar Vermont Yankee icon.png |
| Issue date: | 08/09/1979 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19296B182 | List: |
| References | |
| NUDOCS 8002200222 | |
| Download: ML19296B183 (7) | |
Text
Enclosure 1 Date: August 9, 1979 Reviewer:
L. Derderian RESOLUTION OF INCOMPLETE ITEMS - STATUS VERMONT YANKEE Licensee Staff Evaluation Response Due 3.1.1 In-Situ Tests Ongoing 3.1.3 Hose Station Calculations Complete 3.1.4 Water Suppression Systems Information 1/15/80 Late 3.1.5 Foam Suppression Systems Complete 3.1.6 Gas Suppression Systems Information 2/25/80 3.1.8 Fire Barrier Penetrations Information 2/25/80 3.1.13 Portable Ventilation Equipment Ongoing 3.1.14 Air Breathing Apparatus Information 1/15/80 Late 3.2.1 Protection of Essential Power Sources Complete 3.2.2 Flame Retardant Coatings Complete 3.2.3 Fire Water Loop Ongoing 3.2.4 Primary Containment Analysis Requi rement 30 days 3.2,5 Gas Suppression Systems Complete 3.2.6 Radiological Consequences of Fires Complete 3.2.7 Administrative Controls Requirement 30 days 3.2.8 Shutdown Capability Ongoing L 2. 7 aca2200.;f
3.0 EVALUATION The following provides our evaluation of the incomplete items.
Numbers in parenthesis following each heading refer to the Sections of our previously issued SER which address these incomplete items.
3.1 Protection of Essential Power Sources (3.2.1)
Our SER noted that the licensee would review the electrical power distribution system and routing of non-essential load cables connected to essential power sources required for safe shutdown to verify that the integrity of redundant power supplies is not dependent upon operation of isolation devices operated by fault currents resulting from fire damage.
The licensee's submittal dated January 30, 1978, indicated that this review has identified three cases where the integrity of redundant power supplies is dependent upon operation of isolation devices operated by fault currents resulting from fire damage. Two of these are non-essential cables fed from motor control centers which do not supply safe shutdown loads.
Fire induced faults on these cables, if not cleared by the load supply breakers would be cleared by the main feed breaker.
The opening of the main feed breaker would not affect safe shutdown.
In the third case, Train "B" cables are in the same tray with a non-essential cable from a train "A" motor control center which prov' 'es power to safe shutdown loads.
If the load supply breakei for these cables failed to clear fire induced faults, the power to safe shutdown equipment connected to these buses could be lost.
The requirement for not depending on fault current actuated devices to assure the integrity of redundant power supplies is found in Revision 1 to Regulatory Guide 1.75.
This guide applies to plants whose construction permits are issued on or after February 1, 1974. Appendix A to BTP 9.5-1 includes the divisional cable separation guidelines of Regulatory Guide 1.75, i.e., the 3' horizontal and 5' vertical separation distance required between redundant cable trays.
It was not intended to backfit all the requirements of Regulatory Guide 1.75.
Because Vermont Yankee's construction permit was issued in November 1966, it need not be backfitted to these requi rements.
Reasons for not requiring such a backfit are:
(1) breakers are designed for the express purpose of providing protection against faults; (2) the coordination of breakers (that is, the sizing and timing of sequential breakers in a zoned protection system) is such as to cause the load breaker to open at a much lower current value than the main feed breaker and in a shorter time, thus preventing the loss of the loads fed by the same main breaker and bus; (3) the fire induced simultaneous faulting of a number of load cables to produce sufficiently high currents of sufficient duration to cause a main breaker to open is highly unlikely due to the short time required for a breaker to clear faults in comparison with the slower time progressed nattrc of a fire; and (4) in the unlikely event a main feed breaker were to open because of a load line fault, the breaker could be closed to provide power to the remaining loads once the failed breaker has been cleared manually,
,. Based on the above stated reasons and the fire protection provided for these cables, we conclude that further separation of these cables for the purpose of protecting against loss by the described failure of fault actuated devices is not required.
3.2 Flame Retardant Coatings (3.2.2)
Our SER noted that the use of flame retardant coatings on electrical cables in trays and risers in the switchgear room has been recommended by the staff and that the licensee would evaluate the impact of flame retardant coatings on cable derating to determine if sufficient design margin exists to use this method to improve the fire resistance of electrical cables.
The licensee's submittal dated January 30, 1978, indicated that the application of a fire retardant coating to all electrical cables routed in cable trays in the switchgear room is not feasible because there is no derating margin.
The licensee has previously committed to install an automatic C02 suppression system which is actuated by smoke detectors.
By letter dated September 14, 1979, the licensee agreed to coat the cables in cable trays at divisional crossovers. The cables will be coated for a minimum distance of 5 feet beyond the nearest redundant division cables. A fire stop will be provided in any conduit connecting one safety train to another.
In addition, where conduit containing safety related cable from one division crosses cable trays containing safety related cable from a redundant division, fire r tardant coatings which extend to a minimum of 2-1/2 feet beyond the conduit crossing will be provided. He has agreed to add coatings at redundant divisional crossovers and to show capability to achieve and maintain shutdown conditions independent of the switchgear room.
We accept the proposed application of flame retardant coatings at the crossovers of redundant divisions as a means of slowing the progress of a fire in the switchgear room.
3.3 Primary Containment Analysis (3.2.4)
Our SER noted that the fire hazards analysis for the primary containment was not completed and the adequacy of the fire protection features could not be evaluated.
. Tbt containment is not presently inerted although it is anticipated that inerting may be necessary in the future to satisfy other requirements.
However, the licensee has indicated via telecon that the modifications he proposes are dependent on the outcome of the staff's decision on inerting. The area between the biological shield and containment wall contains support equipment including recirculation pumps, motors, and auxiliaries. Combustibles consist of 50 gallons of lube oil in each of the recirculation pumps. The motors are equipped with sensors for oil and bearing temperature. Armoflex ombustible pipe insulation is installed in the containment.
The fire protection for the containment consists of containment sprays, temperature sensors, and oil level alarms. There are no fire detection systems. The air temperature is, however, detected by RTD's. Because of the lack of detection, the concentration of cables near pumps and penetration areas, limited access, and the probable loss of some nuclear instrumentation and rod position cabling, the licensee by letters dated January 30, 1978 and September 14, 1979, proposed the following modifications:
1.
A means for early detection of oil fires inside the containment.
2.
A collection system for small oil leaks from each reactor recirculation pump motor.
3.
Fixed (manual) suppression for oil fires at each reactor recirculation pump motor (density of.3 gpm/sq. ft.).
4.
Replacement of all combustible "armoflex" insulation with non-combustible insulation.
We accept replacement of combustible insulation with non-combustible insulatioa; however, the fire protection does not meet minimum requirements for BWR containments. We will require the following:
Standpipe and hose stations shall be outside the drywell with adequate lengths of hose to reach any location inside the drywell with an effective hose stream.
The Reactor Recirculation Pump lubrication system shall be protected by either an oil collection system, or an automatic fire suppression system.
Oil collection systems shall be capable of collecting lube oil from all potential pressurized and unpressurized leakage sites in the reactor recirculation pumps' lube oil systems and drain the oil to a vented closed container.
Requirements for a flame arrestor in the vent shall be determined on the basis of flash point characteristics of the oil involved.
Leakage points to be protected shall include lift pump and piping, overflow lines, lube oil cooler, oil fill and drain lines and plugs, flanged connections on oil lines and lube oil reservoirs where such features exist on the reactor recirculation pumps. Leakage shall be collected and drained to a closed container that can hold the entire lube oil system i nventory. The drain line shall be large enough to accommodate the largest potential oil leak.
To provide adequate protection for an SSE, one of the following should be provided:
a.
The lube oil system components whose failure could result in leakage should be designed to withstand an SSE without leakagc; and, the dropping of oil collection system components during an SSE should not cause loss of operability of safety-related equipment; or b.
The oil collection system should be designed to withstand an SSE and continue to be able to collect and drain leakage that may occur during an SSE.
In this case the oil collection system should be adequate to collect oil from any external lube oil piping not designed to withstand an SSE, in addition to leakage from points identified above.
If an automatic fire suppression system is selected, either the automatic and manual fire suppression system or the lube oil system components whose failure could result in leakage should be designed to withstand an SSE.
All of the above requirements are now included in Appendix R to 10 CFR Part 50 which became effective on We, therefore, expect that the licensee will conform to these requirements.
Subject to conformance to these requirements, these items are satisfactorily resolved.
. 3.4 Gas Suppression Systems (3.2.5)
Our SER noted that the licensee would provide the description for the actuation of automatic C02 systems including those interlock features incorporated to disable the system when personnel would be working in the area.
The licensee's submittal, dated September 14, 1979, indicated that both the switchgear room and the cable vault systems will operate in a similar manner upon actuation of ionization detectors.
Upon the receipt of each of three successive alarms, an output signal is sent from a counting module to initiate a preprogrammed, sequential response function. The first detector alarm will sound local bells and an alert signal at the main and local control panels. The second detector alarm will automatically close all associated fire dampers and shutdown room exhaust fans.
The third detector alarm will automatically trip the CO2 System and provide local and remote indication that the CO2 System has been activated.
Both detection and trip systems are to be electrically supervised including the abort switches.
Backup CO2 suppression for the cable vault is actuated directly from a pull station and a directional valve.
Both systems will have a 30 second evacuation time delay and alarm for personnel safety.
In addition, override abort switches will be provided to enable local fire fighting.
Use of these switches will be strictly controlled via fire fighting training and procedures.
We have reviewed the proposed system with particular attention to the location, spacing, number of detectors, and actuation logic. The location of the detectors is reasonable. The detectors are located on the ceiling in a deep beamed area.
There are two detectors per deep beamed area.
The system requires three detectors to alarm before actuation of the system occurs. With this logic, the respoase time for actuation may be too long because of the ceiling obstructions thus allowing a deep seated fire to propagate.
The detection system has the flexibility to provide one, two, or three detectors in the actuation logic. The licensee via telecon on January 14, 1980, indicated the actuation mechanism will be changed to provide two detectors in the actuation logic in place of three detectors.
We find that the design of the gas suppression systems is acceptable.
.... 3.5 Radiological Consequences of Fires (3.2.6)
Our SER noted that the licensee would evaluate the radiological consequences of fires in the radwaste and advanced off-gas building.
By letters dated January 30, 1978 and September 14, 1979, the licensee provided analysis concerning the radiological consequences of fires and proposes special training for fire fighting in the Radwaste and A0G building areas is adequate to assure that personnel will not be unduly exposed to radiation during fire fighting operations in these areas.
We conclude that the radiological effects of a fire cannot be more severe than those the licensee has considered in other accident analysis. The fire protection for this area is acceptable.