ML20237A262
| ML20237A262 | |
| Person / Time | |
|---|---|
| Site: | Pilgrim |
| Issue date: | 12/08/1987 |
| From: | Bird R BOSTON EDISON CO. |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| 87-196, NUDOCS 8712140368 | |
| Download: ML20237A262 (10) | |
Text
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h wsrwemsw Executwe Ofhces 800 Boylston Street Boston, Massachusetts 02199 December 8, 1987 Ralph G. Bird BECo 87-196 Senior Vice President - Nuclear U. S. Nuclear Regulatory Commission Document Control Desk Hashington, DC 20555 License DPR-35 Docket 50-293 CONTROL ROOM FLOOR
Dear Sir:
This letter provides information and an evaluation to resolve Item A on page 4 of Inspection Report 87-39.
This item relates to a 1981 exemption from 10CFR50 Appendix R requirements for Control Room fire suppression at Pilgrim Nuclear Power Station (PNPS) that was based, in part, on a three-hour fire rating for the Control Room floor.
A recent Boston Edison inspection of penetration seals in the Cable Spreading Room (CSR) ceiling / Control Room floor at PNPS found some of the seals do not meet a three-hour rating and others could not be inspected from below. He have evaluated the barrier (see Attachment) and determined that it provides adequate protection both to the Control Room (primarily as a smoke barrier) 4 and to the CSR (as a Halon gas barrier). The attached evaluation includes a background discussion; descriptions of the Control Room, the CSR, and the barrier between them; and details of existing fire protection features, particularly those that have been added since the 1981 exemption was issued.
Based on this evaluation, we conclude the barrier satisfies Appendix R and the 1981 exemption is still valid.
Since this is an Appendix R issue, it must be resolved before PNPS restart.
21.W
. G. Bird
Attachment:
Engineering Evaluation - Cable Spreading Room Ceiling Fire Barriers SA2MBas! SAS$ga bA\\
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BOSTON EDISON COMPANY
' U.S. Nuclear Regulatory Commission December 8, 1987 Page 2 cc: Mr. R. H. Hessman, Project Manager Division of Reactor Projects I/II' Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission 7920 Norfolk Avenue Bethesda, MD 20814 U.S. Nuclear Regulatory Commission, Region I 631 Park Avenue King of Prussia, PA 19406 Senior NRC Resident Inspector Pilgrim Nuclear Power Station i
JJ/jr/1403
ATTACHMENT l
i to BECo Letter 87-196 ENGINEERING EVALUATION CABLE SPREADING ROOM CEILING FIRE BARRIERS (Barriers 195.601 A, B)
This evaluation demonstrates the existing Cable Spreading Room (CSR) ceiling at the Pilgrim Nuclear Power Station (PNPS) adequately protects the Control Room from a fire in the CSR with existing levels of fire protection. The following sections discuss the background of the issue, describe the configuration of the fire barrier and other fire protection features, analyze the ceiling requirements and capabilities, and present conclusions.
1.
SUMMARY
Combustible loading in the CSR is primarily cable insulation, most e
of which is of a type that has been tested to prove its fire-inhibiting characteristics. Most of the cable, including all of the non-fire-retardant cable, has been coated with a fire-retardant coating.
The CSR has a total-flooding Halon system with automatic actuation from a cross-zoned smoke detection system and a connected reserve.
Alternate safe shutdown systems have been installed at PNPS independent of both the Control Room and the CSR.
The alternate systems, complete with de hiled emergency operating procedures, are available for use in the event of a fire in either or both rooms.
The alternate systems exceed the requirements of Appendix R, both in redundancy and in plant functions provided, Although the Control Room and the CSR are listed as separate e
Appendix R fire areas, a major fire in either area would disable the safe shutdown components in the other, regardless of the fire barrier between them.
The Control Room floor /CSR ceiling is a twelve-inch-thick slab of l
concrete. Other than some penetration seals and a small amount of l
uncoated structural steel, the concrete floor is capable of achieving a three-hour rating.
Structural steel under the Control Room floor /CSR ceiling has been covered with a fire-resistant coating at all accessible points; the j
remaining uncoated steel has been found acceptable in an SER.
Although some of the penetrations are not three-hour rated, they all provide a level of protection commensurate with the barrier's Appendix R requirements.
Therefore, the Control Room floor /CSR ceiling provides adequate fire protection to the Ccantrol Room and the CSR.
Due to congestion under the CSR ceiling, upgrading the penetration seals would require disruption of many circuits, some of which are safety-related, with extensive impact on time and resources and a potential negative impact on safety. _ _ _ _ _ _ _ _ _ _ _ _ _
2.
BACKGROUND The Cable Spreading Room ceiling separates the Control Room from the Cable Spreading Room. Appendix A to Branch Technical Position 9.5-1 (Reference 6.1) required both of these rooms to be separated from each other and other plant areas by rated fire barriers; therefore, the CSR ceiling was included in Boston Edison Company's (BECo's) 1977 Fire Protection System Evaluation (FPSE) (Reference 6.2).
The fire protection Safety Evaluation Report (SER) (Reference 6.3) included the CSR ceiling with the statement:
"Three-hour rated fire barriers are provided to separate the cable spreading room from the remainder of the plant" (page 5-14).
The SER noted the presence of unprotected structural steel under the CSR ceiling, but also noted that the C02 suppression system in th9 Cable Spreading Room (since upgraded to a Halon system) could mitigate fire exposure to the beams.
The SER also provisionally accepted the less-than-three-hour cable penetration seals 1
based on a BECo commitment to modify or replace them with seals that have a demonstrated fire rating equivalent to that of the barrier or to provide an analysis to demonstrate acceptability of lower-rated seals, based on test results and the completed fire hazards analysis.
The CSR ceiling was included as a fire barrier in the BECo Appendix R Fire Hazards Analysis (FHA) (Reference 6.4).
The acceptability of the ceiling as an Apptadix R barrier was based on its previous acceptance in the Appendix A SER (though it does not separate redundant safe shutdown j
systems).
On March 18, 1981, BECo requested an exemption from the Appendix R requirement to Install a fixed fire suppression system in the PNPS Control Room (Reference 6.5).
The exemption request was based primarily on operator ability to shut down the plant from outside the Control Room.
BECo also pointed out that the Control Room must be continuously occupied (providing in effect a continuous fire watch) and listed design features contributing to Control Room fire protection (smoke detectors in panels, breathing air system for operators, Flamemastic coating on CSR cables, water hose station outside the room, and removal of the stove from the nearby kitchen).
Finally, BECo cautioned that a fixed water suppression system in the Control Room could reduce safety by damaging control equipment and interfering with the operators.
When the exemption was granted (Reference 6.6), the exemption document's safety evaluation section accepted the arguments in the request, but added:
"The licensee has also confirmed that:... - The Control Room is separated from high risk areas by 3-hour fire rated barriers." BECo's exemption request was not based on this statement, but on the fire protection features listed above.
BECo recently evaluated the CSR ceiling after a comprehensive penetration l
seal inspection program found some deficient penetration seals, and others that were not accessible and could not be inspected.
This evaluation demonstrates the existing fire barrier and associated fire protection features, particularly those added since the exemption was issued, provide adequate protection for the Control Room.
It is based on Generic letter 86-10 (Reference 6.7), which states:,,,,,,,,,,.
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The term " fire area" as used in Appendix R means an area sufficiently bounded to withstand the hazards associated with the fire area and, as necessary, to protect important equipment within the fire area from a fire outside the area. In order to meet the regulation, fire area boundaries need not be completely sealed with floor-to-ceiling and/or wall-to-wall boundaries. Where fire boundaries... are not wall-to-wall or floor-to-ceiling boundaries with all penetrations sealed to the fire rating required of the boundaries, licensees must l
perform an evaluation to assess the adequacy of fire area boundaries in their plants to determine if the boundaries will withstand.the hazards associatea with the area and protect important equipment within the area from a fire outside the area.
This analysis must be performed by at least a fire protection engineer and, if required, a systems engineer. Although not required, licensees may submit their evaluations for Staff review and concurrence.
In any event, these analyses must be retained by the licensee for subsequent NRC audits.
3.
DESCRIPTION 3.1 Area Configuration The CSR (Fire Area 3.2) is located on the 23'-0" elevation of the Radwaste and Control Building. Halls, floors, and ceiling consist of heavy concrete and cont. rete masonry unit construction.
The fire barrier comprises the ceiling of the CSR and is a 12"-thick reinforced concrete slab supported by steel beams and columns. All accessible portions of the structural steel are covered with a fire-resistant coating.
The cei ing has approximately 250 holes, t
typically six inches in diametc., through which pass approximately 650 penetrations containing cable and/or conduit.
Directly under the ceiling is a dense congestion of wble trays and conduits that prevents access to the underside of nany of the penetrations.
The Control Room (Fire Area 3.1) is located on the 37'-0" elevation of the Radwaste hnd Control Building, directly above the CSR.
The Control Room and its peripheral r? oms are separated from the remainder of the plant by heavy coscrete and concrete masonry unit barriers.
The fire barrier discussea L: this evaluation is the portion of the Control Room floor that is common with the CSR ceiling.
3.2 Combustible Loading Duetoitsfunction,theCSRcontainsalargaamoungofcable.
Its combustible loading is approximately 120,000 BTU /ft, for an equivalent fire severity of approximately one and one-half hours.
The effects of this combustible loading are mitigated by the following features:
Although PNPS was built before the issuance of the IEEE-383 standard for cable insulation flammability, most of the cable in the CSR is insulated with the same materials and is of the same design as cables that have later been tested and shown to inhibit flame propagation. - -_ -
Most of the cabling in the CSR, including all of the o
non-flame-retardant cable, is coated with Flamemastic fire-retardant coating.
Administrative procedures prohibit stored combustibles and control ignition sources in the CSR.
I Halon system operation requires a room with low air leakage.
Therefore, a fire would quickly become ventilation-controlled, and its temperature would be significantly lower than that predicted by the standard time-temperature curve.
2 The Control Room's moderate combustible loading ( 70,000 BTU /ft )
consists primarily of Class A combustibles, such as papers, carpeting, cables, and plastic components associated with the control cabinets. Although included as a combustible in the FHA, the Control Room carpeting has been tested and is rated Class I.
Cables from the CSR are routed through floor penetrations directly into the control cabinets.
3.3 Fire Protection Systems CSR fire suppression is provided by a total-flooding Halon 1301 system that is automatically actuated by cross-zoned smoke detectors.
In addition to automatic actuation, the Halon system can be manually actuated at pull stations, or by operating pneumatic releases on the Halon bottles in the adjacent switchgear room.
The Halon system was tested and found to maintain a minimum of 61. Halon concentration in the CSR for ten minutes. There is an extended discharge feature that adds Halon to the room after the normal initial discharge, and there is a connected reserve that can provide an additional full Halon discharge.
The system was designed to extinguish postulated fires in the CSR.
It was installed in 1983-84 with the purpose of improving CSR fire suppression capability over the then-installed C02 system.
In accordance with the 1981 exemption, the Control Room has no fixed fire suppression system but has fire detectors installed in six of the control cabinets.
For manual firefighting, hose stations and portable fire extinguishers are mounted in or near both the CSR and the Control Room.
The PNPS fire brigade has been trained in the use of this equipment.
3.4 Safe Shutdown Components Both the CSR and the Control Room contain numerous safe-shutdown components.
Although the Appendix R analysis treats the two rooms as separate fire areas, they cannot function independently. A design-basis fire in either room would have the same safe-shutdown effect as a fire in both rooms.
In response to Appendix A, BECo installed alternate safe shutdown capability independent of both the Control Room and the CSR.
In response to Appendix R, BECo made improvements to the alternate shutdown system.. _ _
The alternate shutdown system providas control for redundant trains of equipment, and for additional functions (High Pressure Coolant Injection and Reactor Core Isolation Cooling) beyond those required for safe shutdown.
BECo has issued a detailed emergency operating procedure for achieving shutdown from the alternate panels.
The same equipment and procedure are used for a fire in either the Control Room or the CSR.
The alternate shutdown capability was accepted in a November 1983 SER (Reference 6.8).
3.5 Penetrations As stated in Section 3.1, there are approximately 250 holes through the CSR ceiling fire barrier.
They are typically 6" diameter openings whose purpose is to pass cables and cable-bearing conduit between the rooms.
The openings were initially sealed as described in Appendix II of BECo's 1977 FPSE:
a 2" base of "Minit foam" or mineral fiber to approximately 8" e
below the top of the penetration (Control Room side) an additional 4-6" of "Minit foam" on top of the base e
at least 1" of cementitious grout or 1/8" of Flamemastic from e
the foam layer to the top of the penetration.
The Fire Protection SER required the penetration seals to be upgraded to equal the fire rating of the fire barrier they penetrate.
BECo implemented this requirement by performing IEEE-634 fire tests on various seal configurations and by upgrading the penetrations under Plant Design Change 81-05.
In 1987, BECo performed field verification of fire barrier penetrations at PNPS.
The verification team found that:
Some of the CSR ceiling penetrations could not be inspected from underneath because of the congestion of cable trays and conduits under the ceiling.
A small number of penetrations were found to have deficiencies on the CSR side (e.g., missing Kaowool or foam) such that their three-hour rating is no longer valid.
The worst case appears to be a penetration with no foam material, only the top grout.
This configuration provides some fire resistance but does not have a specific fire rating.
The penetration seals were inspected from the Control Room side and were found to be acceptable. Also, the Halon system discharge test in the CSR exhibited no significant Halon leaks into the Control Room, indicating that the penetrations are effectively gas and smoke tight.
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3.6 Structural Steel Steel columns and beams support the CSR ceiling / Control Room floor.
BECo's 1977 FPSE reported that the structural steel under the CSR ceiling was not fireproofed. The Appendix A SER noted the then-existing 002 system (which has since been upgraded to Halon) as a mitigating measure.
In later correspondence (Reference 6.9), BECo committed to protect the accessible structural steel in the CSR (some cannot be coated due to obstructions or other lack of access) and to minimize combustible loading around the unprotected steel.
This commitment was accepted in an October 7,1980 SER (Reference 6.10). Most of the steel is now protected with a fire-retardant coating.
According to Generic Letter 86-10 (Reference 6.11), Appendix R does not require further protection of structural steel in existing fire barriers that were approved in an Appendix A SER. The existing unprotected portions of structural steel, therefore, do not preclude acceptance of the CSR ceiling as an adequate Appendix R fire barrier.
4.
ANALYSIS This analysis focuses on a CSR fire challenging the fire barrier from beneath.
Propagation of a Control Room fire downward into the CSR is not considered to be a credible event, for several reasons:
The Control Room is continuously occupied, so any fire in the room would be detected and extinguished rapidly.
The Control Room has only moderate combustible loading.
Fire propagation downward is not considered credible, given the nature of the combustion process where cooler air comes from below and flame and hot gases propagate upward.
Safe shutdown panels in the Control Room are provided with smoke detectors for rapid fire detection.
The following CSR design features reduce the likelihood of a fire in the CSR and mitigate the effects of a fire should one begin:
Cable insulation is the principal combustible in the CSR, and most of the CSR cable is insulated with materials that have been shown to inhibit ignition and flame propagation.
Most of the original plant CSR cables, including all of the non-flame-retardant cables, have been coated with Flamemastic.
Transient combustibles and hot work in the CSR are controlled by administrative procedures.
Access to the CSR is controlled through the plant security system, reducing ignition potential by limiting personnel access.
The CSR has a fixed Halon 1301 fire suppression system, automatically actuated by cross-zoned smoke detectors.
In addition to providing a Halon concentration of 6% for ten minutes, the system has an extended discharge feature and a j
connected reserve.
The system will effectively suppress postulated fires in the CSR before they could affect the structural steel or the penetrations.
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All the penetrations, including those that could not be o
inspected from beneath, have been determined by Control Room-side inspection to be effective smoke and gas barriers.
These features act to prevent a fire from propagating between the two l
areas before it is extinguished.
They also contribute to keeping the l
Control Room habitable in the event of a fire in the CSR.
In the event that a CSR fire were not suppressed, it could eventually propagate to the Control Room. A CSR fire involving cable insulation, however, would be slow to develop and low in intensity due to l
fire-retardant coatings and limited ventilation.
Control Room operators l
would have ample time to react to the fire due to CSR fire detection and annunciation.
The fire rating of the subject barrier does not impact the ability to shut down the plant safely after a design basis fire in either the l
Control Room or the CSR. Whether or not a fire penetrates the ceiling bairier from one room to the other, operators can still shut the plant down from the alternate shutdown panels outside the Control Room following detailed emergency operating procedures.
Upgrading the CSR ceiling penetration seals is not practical, nor is it advisable for safety maximization. Upgrading the seals would require access to the underside of the penetrations since the tops of the penetrations are located inside the Control Room panels and are generally sealed with at least an inch of solid grout.
The area under the CSR ceiling is congested with conduits and cable trays, many containing i
safety-related circuits. Access to the penetrations for upgrading would require disruption of many of these circuits.
The disruption and l
subsequent restoration of the circuits would require extensive time and I
effort and could result in cable damage, potentially reducing plant safety.
l 5.
CONCLUSIONS Based on this evaluation, BECo concludes that the barrier between the Control Room and the CSR provides adequate protection for the Control Room, that defense-in-depth is not compromised, and that upgrading the l
barrier penetration seals is neither necessary nor advisable.
6.
REFERENCES 6.1 Appendix A -) Branch Technical Position APCSB 9.5-1, " Guidelines for Fire Protection for Nuclear Power Plants Docketed Prior to July 1, 1976", NRC Office of Nuclear Reactor Regulation, August 23, 1976.
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6.2 Fire Protection System EvA.luation. Pilarim Station 600 Unit #1, Boston Edison Company, dated March 1, 1977 (submitted March 7, 1977).
l 6.3 Safety Evaluation Reoort by the Office of Nuclear Reactor Regulation S_upportina Amendm3nt No. 35 to Facility Goerating License No.
DPR-35.... transmitted by letter from T. A. Ippolito (NRC) to G.C.
Andognini (BECo), December 21, 1978.
6.4 Pilarim Ng lear Power Station Unit #1 Fire Protection AnalysiL_
10CFR50 - Accendix R, Boston Edison, submitted June 25, 1982. l
6.5 BECo letter #81-59 to D. G. Eisenhut (NRC), " Status of Boston Edison Effort in Meeting the Schedular Requirements of Appendix R to 10 CFR Part 50", March'18, 1981.
6.6 Letter from H. R. Denton (NRC) to A. V. Morisi (BECo), transmitting exemption to Section III.G.3 of 10CFR50 Appendix R. November 10, 1981.
6.7 Generic Letter 86-10. " Implementation of Fire Protection Requirements", NRC Office of Nuclear Reactor Regulation, April 24, 1986,' Enclosure 2. " Appendix R Questions and Answers", page 4, Question 3.1.2.
6.8 Letter from D. B. Vassallo (NRC) to H. D. Harrington (BECo), " Safety Evaluation for Appendix R to 10CFR Part 50, Items III.G.3 and II.L",
November 2,'1983.
6.9 BECo letter #79-58 to T. A. Ippolito (NRC), March 14, 1979.
6.10 Letter from T. A. Ippolito (NRC) to A. V. Moriti (BEco), October 7, 1980.
6.11 GL 86-10 (op. cit.), Enclosure 2, page 9, Question 3.3.2.
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