ML20207J748
| ML20207J748 | |
| Person / Time | |
|---|---|
| Site: | Quad Cities  |
| Issue date: | 07/22/1986 |
| From: | Wojnarowski J COMMONWEALTH EDISON CO. |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| 1858K, IEIN-86-025, IEIN-86-25, NUDOCS 8607290243 | |
| Download: ML20207J748 (21) | |
Text
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k Commonwealth Edison 72 West Adams Street, Chic"go, Illintis 1
V Address Reply to: Pott Offica Box 767 Chicago, Illinois 60690 0767 July 22, 1986 Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, DC 20555
Subject:
Quad Cities Station Units 1 and 2 Request for Exemption from 10 CFR 50, Appendix R for Drywell Expansion Gap NRC Docket Nos. 50-254 and 50-265
Reference:
Dear Mr. Denton:
The referenced Information Notice describes the circumstances surrounding the drywell expansion gap fire at Dresden Unit 3 and asks licensees to review the information for applicability to their facilities.
Quad cities Station has been reviewed, and it has been found that safe shutdown can be achieved and maintained in the event of an expansion gap fire; although, all Appendix R requirements are not satisfied. Since all Appendix R requirements are not met, pursuant to 10 CFR 50.12, Commonwealth Edison requests an exemption from the requirements of 10 CPR 50, Appendix R,Section III.G.3 for fire detection and fixed fire suppression in the Quad cities Units 1 and 2 drywell expansion gaps. This exemption is needed since we believe it is not possible to install the required detection and suppression system in the expansion gap.
The exemption request and supporting fire hazards analysis are provided in the enclosure to this letter. The enclosure was written to reflect plant conditions after all previously proposed modifications and final safe shutdown procedures are in place. The fire hazards analysis demonstrates that the existing and proposed fire protection features at Dresden assure that safe shutdown can be achieved and maintained in the event of a fire in the expansion gap. This satisfies the underlying purpost of Appendix R, therefore our request for exemption satisfies the special circumstance criterion in 10 CFR 50.12(a)(2)(ii), " Application of the regulation in the particular circumstances...is not necessary to achieve the underlying purpose of the rule."
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Mr. H. R. Denton July 22, 1986 In further support of our request, we believe it is virtually impossible to install effective detection and suppression in the drywell expansion gap due to the physical configuration of the gap (i.e., a two inch foam filled gap sandwiched between the steel drywell liner and at least 4 foot thick concrete). As such, we feel that installation of detection and suppression in such an area would result in undue hardship and costs that are significantly in excess of those contemplated when the regulation was adopted. This consideration falls within special circumstance 50.12(a)(2)(iii).
Based on the above discussion and the information in the enclosure, we feel our exemption request is consistent with 10 CFR 50.12 and does not compromise the underlying purpose of Appendix R.
In accordance with 10 CPR 170, a fee remittance in the amount of
$150.00 is enclosed.
If you have any questions regarding this request, please contact this office.
One signed original and five (5) copies of this letter and the enclosure are provided for your use.
Very truly yours, J. R. Wojnarowski Nuclear Licensing Administrator im cc:
R. Bevan - NRR J. G. Keppler - Region III NRC Resident Inspector - Quad Cities 1858K
QUAD CITIES 1&2 TABLE OF CONTENTS CHAPTER 8 PAGE 8.0 APPENDIX R DRYWELL EXPANSION GAP EXEMPTION REQUEST 8.0-1 8.1 DRYWELL EXPANSION GAP DESCRIPTION 8.1-1 8.2 JUSTIFICATION FOR LACK OF COMPLETE DETECTION AND SUPPRESSION IN THE EXPANSION GAP 8.2-1 8.2.1 Introduction 8.2-1 8.2.2 Fire Protection Systems 8.2-1 8.2.3 Safe Shutdown Equipment 8.2-1 8.2.4 Fire Hazards Analysis 8.2-1 8.2.5 Conclusions 8.2-4 8.2.6 References 8.2-4 O
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QUAD CITIES 1&2
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LIST OF TABLES NUMBER TITLE PAGE 8.2-1 Safe Shutdown Equipment Operated By Cables That Pass Through Unit 1 Drywell Penetrations 8.2-5 i
8.2-2 Safe Shutdown Equipment Operated By Cables That Paca Through Unit 2 Drywell Penetrations 8.2-6 4
8.2-3 Possible Effects of a Fire On Unit 1 Safe Shutdown Equipment 8.2-7 l
8.2-4 Possible Effects of a Fire On Unit 2 Safe Shutdown Equipment 8.2-9 1
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8.0 APPENDIX R DRYWELL EXPANSION GAP EXEMPTION REQUEST Per the provisions of 10CFR50.12, Commonwealth Edison Company (CECO) requests exemption from the requirements of Section III.G.3 of Appendix R to 10CFR50 that the drywell expansion gap, relying on dedicated shutdown capability, be provided with fire detection and fixed fire suppression.
Justification for the exemption is present in Section 8.2.
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QUAD CITIES 1&2
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8.1 DRYWELL EXPANSION GAP DESCRIPTION The drywell consists of a steel containment shell.
It is surrounded by a concrete shield structure.
The steel containment is a pressure vessel with a spherical lower portion and a cylindrical upper portion.
Thermal expansion, as a result of normal reactor operation or postulated accidents, will cause the steel shell to expand both radially and vertically.
To accommodate this expansion, space has been provided between the concrete shield structure and the steel shell above the foundation transition zone.
This space is a gap of approximately 2 inches and precludes any restrained thermal expansion load on the steel containment or the concrete shield.
At the foundation level, a sand pocket was used to soften the transition between the foundation and the containment vessel.
To facilitate the pouring of the concrete without reducing the required gap space during construction, prefabricated crushable polyurethane foam sheets were instal?.ed over the exterior surface of the steel containment.
Epoxy impregnated fiberglass tape was applied over all joints in the polyurethane foam, and 1/4 to 3/8-inch thick fiberglass - epoxy prefabricated cover panels were then installed over the polyurethane foam.
Once the concrete has hardened, those materials sandwiched in the annular space do not serve any design function and are no longer required.
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8.2 JUSTIFICATION FOR LACK OF COMPLETE DETECTION AND SUPPRESSION IN THE EXPANSION GAP 8.2.1 Introduction There is no detection or suppression provided in the expansion gap and it would be difficult if not impossible to provide it due to the physical. constraints.
The subsequent analysis will justify the lack
'of detection and automatic suppression throughout the gap.
8.2.2 Fire Protection Systems While no detection or suppression systems are present in the gap, fire detectors are located in the reactor building fire zones adjacent to the electrical and mechanical drywell penetrations, at the ceiling level and manual hose stations are located throughout the reactor building.
A fire in the gap can be detected by these detection systems and the fire can be extinguished by applying water through the annular gap around the penetrations using the manual hose stations.
Portable fire extinguishers are located throughout the reactor building.
8.2.3 Safe Shutdown Equipment 1
The only safe shutdown components located in the expansion gap are
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electrical conductors inside the electrical penetration assembly canisters.
Tables 8.2-1 and 8.2-2 list the safe shutdown equipment operated or associated with cables that pass through these penetrations for Units 1 and 2 respectively.
The taps for reactor level indicating switches 1( 2)-263-57A&B,
1 ( 2) -2 63-58 A& B, 1(2)-263-59 A&B and 1(2)-263-72A,B,C and D and pressure indicators (1) 2-263-60A and B are also routed through the gap in mechanical penetrations on both units.
8.2.4 Fire Hazards Analysis The 2-inch gap is filled with polyurethane sheets that are covered
' with a fiberglass cover panel.
Polyurethane is a polyester base material with a heat of combgstion of 12,000 Btu /lb, an auto-ignitign tempergture of 1000 F, and a piloted ignition temperature of 500 F to 700 F.
The 2-inch gap is separated from the drywell fire area by the steel containment shell.
Separation of the expansion gap from the rest of the reactor building is by minimum 4-feet 0-inch thick structural
" concrete that is penetrated by mechanical and electrical penetrations.
In Unit 1, the concrete wall separates the expansion gap from Fire
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~ Area RD-1.
In Unit 2, the concrete wall separates the expansion gap V
from Fire Area RB-2.
9 8.2-1
QUAD CITIES 1&2
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The electrical penetrations are three standard types:
Low Voltage Power and Control Cable Penetrations, High Voltage Power Cable Penetrations and the Shielded Cable Penetrations.
Each type of electrical penetration has the same basic configuration shown in Figure E-1.
An assembly is sized to be inserted in the penetration nozzles which are 12-inch schedule 80 steel pipe (wall thickness of 0.688 inches).
They are furnished as part of the containment structure and the design and fabrication of each assembly is in accordance with the requirements of the ASME Boiler & Pressure Code,Section III, Class B Vessel.
The assembly extends approximately 1 foot beyond the drywell wall on both sides of the penetrations. IThe drywell whll, in the vicinity of the electrical penetrations, is at least 6 feet thick.
The mechanical penetrations are of two types; those which accommodate thermal movement (hot), and those which experience relatively little thermal stress (cold).
The hot fluid line penetrations have a guard pipe between the hot line and the penetration nozzle in addition to a double-scal arrangement (see Figure E-2, Sheet 1).
This permits the penetration to be vented to the drywell should a rupture of the hot line occur within the penetration.
The guard pipes are designed to the same pressure and temperature as the fluid line and are attached to a multiple flued head fitting, a one-piece forging with integral flues or nozzles.
This fitting was designed to the ASME Pressure Vessel Code, Section
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The penetration sleeve is welded to the drywell and extends through the biological shield where it is welded to a bellows which in turn is welded to the guard pipe.
The bellows accommodates the thermal expansion of the steam pipe and drywell relative to the steam pipe.
A double bellows arrangement permits remote leak testing of the penetration seal.
The lines have been constrained at each end of the penetration assembly to limit the movement of the line relative to the containment, yet will permit pipe movement parallel to the penetration.
The penetration details of cold piping lines are shown on Figure E-2, Sheet 2.
These penetrations have a double-seal arrangement, but the guard pipe provided for the hot piping line penetrations is not provided.
There are two major concerns for a fire in the expansion gap.
- 1. Can the reactor be shut down if a fire occurs inside the gap during operation?
2.
If a fire starts in the gap and spreads to another fire area, can it affect safe shutdown capability?
The construction of the penetration assemblies makes it unlikely
(~3 that a fire in the expansion gap could prevent the electrical
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penetration assemblies from performing their function.
- However, l
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Tables 8.2-3 and 8.2-4 conservatively address the situation where the assemblies are affected.
As can be seen in the tables, shut down is not affected because of the following:
- 1. The safe shutdown valves are normally in the proper position and fault or break in the cable will not change that position.
- 2. The mechanical function of the Target Rock valve or the safety valves is not affected by an expansion gap fire, thus RPV pressure control will remain available.
- 3. Manual actions can be performed to operate valves and local operation capability is provided for pumps.
- 4. A normally closed valve is in series with another normally closed valve.
These valves are not a high/ low pressure interface and the valve does not need to be operated.
- 5. Another system is available to supply reactor water makeup that would not be affected by a fire in the gap.
Based on these reasons, if a fire occurs in the Unit 1 expansion gap, safe shutdown can be achieved and maintained using shutdown path A, while if a fire occurs in the Unit 2 expansion gap safe shutdown can be achieved and maintained using shutdown path B.
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Also routed through the gap are taps for reactor level indicating switches 1 ( 2) -2 63-5 7A& B, 1(2)-263-58A&B, 1(2)-263-59A&B, and 1(2)-263-72A,B,C and D and pressure indicators 1(2)-263-60A&B.
A fire in the gap should not prevent obtaining the reactor pressure and level for two reasons:
- 1. The amount of polyurethane around the penetration is limited.
That is, once the material has been burned away, the temperature of the penetration and that of the fluid inside will return to their ambient level, and
- 2. The taps for the Division I instruments (l(2)-263-57A and B, 1(2)-263-59A, 1(2)-263-60A and 1(2)-263-72A and C) are separated from the Division II instruments (l(2)-263-58A and B, 1(2)-263-59B, 1(2)-263-60B and 1(2)-263-72B and D) by a distance of 45 feet in Unit 1 and 29 feet in Unit 2.
Thus, at worst only one division of the instruments will be affected by the fire at any given time.
In addressing the second concern, it should be noted that the drywell is inerted during normal operation.
Thus, spread of the fire from the expansion gap to the drywell is impossible.
Since the concrete is a minimum 4-feet 0-inches thick, the only possible path for the spread of the fire to adjacent fire zones in the reactor 8.2-3
QUAD CITIES 1&2
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building is through the penetrations.
This is an unlikely event (See Reference 1).
However, if this were to occur, the ability to shut down the reactor would not be affected.
For a fire inside the Unit 1 expansion gap, shutdown path A can be used to shut down the reactor.
This is the same shutdown path that would be used for a fire in any of the fire zones in the reactor building adjacent to the expansion gap.
A similar situation exists for Unit 2:
If a fire occurred in the Unit 2 expansion gap, shut '
down can be achieved and maintained using shutdown path B.
This is the same shutdown path that can be used for a fire in any of the fire zones in the reactor building adjacent to the expansion gap.
Thus, it can be seen that if a fire were to spread from the expansion gap into the adjacent fire zones shutdown can still be achieved.
8.2.5 Conclusions This analysis justifies the exemption from complete fire detection and fixed fire suppression in the drywell steel containment expansion gaps in Units 1 and 2.
The technical basis for this justification is summarized as follows:
- 1. The expanded fire detection systems in the reactor building will alert the plant to a fire condition in the expansion gap.
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- 2. Manual suppression is readily available near the mechanical and electrical penetrations.
- 3. A safe shutdown path will be available to achieve and maintain hot and cold shutdown whether the fire remains within the expansion gap or spreads into' adjacent fire zones within the secondary containment.
8.2.6 References
- 1. " Evaluation of the Effects of the Dresden Unit 3 Polyurethane Fire," May 1986.
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(2) 8.2-4
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r^8ts 8.2-1 SAFE SHUTDOWN EQUIPMENT OPERATED BY CABLES THAT PASS THROUGH UNIT 1 DRYWELL PENETRATIONS PENETRATION SAFE SHUTDOWN NUMBER EQUIPMENT X-104F M01-0202-5B RHR CKT "B" X-100G M01-0202-5B RHR CKT "B" X-100B 1-203-3A 1-203-3B l-203-3C 1-203-3D l-203-3E M01-1001-50 M01-1001-63 RHR CKT " A" F
X-105A M01-1301-16
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1 QUAD CITIES 1&2 TABLE 8.2-2 SAFE SHUTDOWN EQUIPMENT OPERATED BY CABLES THAT PASS THROUGH UNIT 2 DRYWELL PENETRATIONS PENETRATION SAFE SHUTDOWN NUMBER EQUIPMENT X-100F M02-0202-5B RHR CKT "B" X-100D M02-0202-5B X-104A 2-203-3A 2-203-3B 2-203-3C 2-203-3D 203-3E M02-1001-50 M02-1001-63 RHR CKT " A" X-104B M02-1301-16 0
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QUAD CITIES 1&2 TABLE 8.2-3 POSSIBLE EFFECTS OF A FIRE ON UNIT 1 SAFE SHUTDOWN EQUIPMENT EQUIPMENT EFFECT M01-0202-5B The power feeds to this valve are routed through the penetration.
In order to get to cold shutdown, the valve must be opened.
After the drywell is made accessible, this valve can be manually opened.
1-203-3A A fire that affects these cables could disable the Target Rock valve.
However, the mechanical function of the valve and the safety valves will be available for RPV pressure control.
1-203-3B A fire that affects these cables could 1-203-3C disable these electromatic valves.
- However,
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1-203-3D the mechanical function of the Target Rock 1-203-3E valve and the safety valves will be available for RPV pressure control.
M01-1001-50 This valve is normally closed and must remain closed for hot shutdown.
Cables routed through the penetration supply power to the motor operator and control the limit switch.
A fault in these cables or a loss of these cables will not change the valve position.
On the other hand, in order to get to cold shutdown, the valve must be opened.
After the drywell is made accessible, this valve can be manually opened.
M01-1001-63 This normally closed valve is in series with another normally closed valve (M01-1001-60).
Since these are not on a high/ low pressure interface and since they do not need to be operated, a fire affecting these cables will not prevent achieving safe shutdown.
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TABLE 8.2-3 (Co nt ' d )
EQUIPMENT EFFECT M01-1301-16 The position of this valve will not impact on the ability to achieve safe shutduwn since the safe shutdown makeup pump system can be used for reactor water makeup.
RHR CKT "A" These cables are part of circuits associated RHR CKT "B" with various automatic RHR' system functions in response to an accident or isolationt signal which are, in turn, associated with cables that control the RHR pumps and valves.
The RHR pumps can be operated locally and necessary RHR valves can be operated manually.
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l QUAD CITIES 1&2 TABLE 8.2-4 POSSIBLE EFFECTS OF A FIRE ON UNIT 2 SAFE SHUTDOWN EQUIPMENT EQUIPMENT EFFECT M02-0202-5B The power feeds to this valve are routed through the penetration.
In order to get to cold shutdown, the valve must be opened.
After the drywell is made accessible, this valve can be manually opened.
2-203-3A A fire that affects these cables could disable the Target Rock valve.
However, the mechanical function of the valve and the safety valves will be available for RPV pressure control.
2-203-3B A fire that affects these cables could 2-203-3C disable these electromatic valves.
- However, 2-203-3D the mechanical function of the Target Rock 2-203-3E valve and.the safety valves will be available for RPV pressure control.
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M02-1001-50 This valve is normally closed and must remain closed for hot shutdown.
Cables routed through the penetration supply power to the motor operator and control the limit switch.
A fault in these cables or a loss of these cables will not change the valve position.
On the other hand, in order to get i
to cold shutdown, the valve must be opened.
After the drywell is made accessible, this valve can be manually opened.
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r-QUAD CITIES 1&2 TABLE 8.2-4 (Cont ' d )
EQUIPMENT EFFECT M02-1001-63 This normally closed valve is in series with another normally closed valve (M02-1001-60).
Since these are not on a high/ low pressure interface and since they do not need to be operated, a fire affecting these cables will not prevent achieving safe shutdown.
M02-1301-16 The position of this valve will not impact on the ability to achieve safe shutdown since the safe shutdown makeup pump system can be used for reactor water makeup.
RHR CKT "A" These cables are part of circuits associated RHR CKT "B" with various automatic RHR system functions in response to an accident or isolation signal which are, in turn, associated with cables that control the RHR pumps and valves.
The RHR pumps can be operated locally and necessary RHR valves can be O
operated manually.
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