ML20085J782
| ML20085J782 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 04/30/1995 |
| From: | STONE & WEBSTER ENGINEERING CORP. |
| To: | |
| Shared Package | |
| ML20085J781 | List: |
| References | |
| NUDOCS 9506230018 | |
| Download: ML20085J782 (27) | |
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April 1995 4 MILLSTONE NUCLEAR POWER STATION UNIT 2 ENCLOSURE BUILDING PURGE SYSTEM AND ENCLOSURE BUILDING FILTRATION SYSTEM DESIGN EVALUATION ,
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l STONE & WEBSTER ENGINEERING CORPORATION BOSTON, h1ASSACHUSETTS
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9506230018 950606 6 DR ADOCK 0500
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. lI. INTRODUCTION An operational review'has been conducted by the Unit 2 Engineering Department on the Enclosure = ?
Building Purge, Exhaust and Filtration Systems resulting in the generation of a f_W Event Report
- (LER 94-040-01), Plant Information Report (PIR 2-95-126) and an Engineering Work Request regarding the aforementioned systems ability to meet the single failure criteria and control releases to the
environment. :
The enclosure building purge fan (F-23) supplies air to the enclosure building to nuintain acceptable l environmental limits for equipment and personnel and when containment' cleanup is required. The i enclosure building purge fan (F-23) discharges through air operated damper AC-1 which is controlled and ,
> monitored from the Unit 2 main control board (COI). AC-1 presently receives a safety-related facility -i
! CIAS initiation signal to close on a containment isolation signal. [
The main exhaust fans (F-34A, 34B, and 34C) take suction from a common exhaust plenum for several [
. plant areas including the Enclosure Building. At least one fan is running during normal operation with .j an additional fan started to exhaust air from the enclosure building when the purge supply fan (F-23) is ;
running. Main exhaust air-operated isolation damper AC-11 which is controlled and monitored from the !
Unit 2 control board (COI), isolates the exhaust plenum from the enclosure building. Air operated i damper (AC-11) receives a safety related facility 2 CIAS signal to close on a containment isolation signal. ,.
The enclosure building filtration system exhaust fans (F-25A and F-25B) take suction from the EBFS !
plenum. One of the exhaust fans (F-25A or F-25B) is required to maintain a negative pressure in the enclosure building during an accident condition. Both exhaust fans (F-25A and F-25B) receive a safety-related EBFAS signal to start on a containment isolation signal.
This evaluation will document the review of the design basis for the enclosure building filtration system 4 and its associated systems, discuss potential design concerns, provide recommendations to alleviate l concerns and provide a recommended course of action. l II. LICENSING / DESIGN BASIS :
1 The licensing commitments for the Enclosure Building Filtration System (EBFS) are provided in l Sections 6.7 and 8.7 of MNPS-2 FSAR.
The design basis for the Enclosure Building Filtration System (EBFS) as specified in Technical Specification 3/4.6.5 is to maintain the Enclosure Building Filtration Region (EBFR) below 0.25 in.W.G.
negative pressure, within 60 seconds, following initiation of the Containment Isolation Actuation Signal (CIAS). However, FSAR Section 6.7 states that the negative pressure of 0.25 in. W.G. must be obtained within 110 seconds. This apparent discrepancy should be reconciled.
, . The system is designed to comply with the following design basis and licensing commitments:
- Each of the two EBFS redundant trains, with design flow of 9,000 cfm, is capable of maintaining the design basis negative pressure. In the event of mechanical failure of the Containment Purge Supply damper AC-1 to close, both trains, with a total design flow of 13,900 cfm, are required to operate.
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- Following an initiation of CIAS, the EBFS is automatically isolated from the interfacing non-safety related systems by closure of a safety related isolation damper AC-11, and from the !
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Enclosure Building Purge System supply fan F-23 by a safety related damper AC-1. The EBFS l exhausts the EBFR through the Unit I stack to outside atmosphere.
- Both redundant trains of the EBFS system must be available whenever the reactor plant is in !
Modes 1 through 4.
- The following are Unit 2 Design Basis Operability Criteria for safety-related and non-safety-related equipment: l k
- 1. Prior to initiation of CIAS signals, all systems' are +. 64 under normal plant i operation. ,
- 2. At the time of CIAS initiation, non-safety related equipment which interfaces with safety-related systems or equipment will continue to run with power available or de-energize if ,
power is not available. Safety-related equipment will receive actuation signals to operate. 4
- 3. Following CIAS initiation, a signal failure of safety-related systems or components is postulated. [
i The following Northeast Utilities organizations were contacted to discuss several topics associated with the design and licensing of the EBFS system: !
- Discussions were conducted with Unit 2 Engineering (Design Engineering and Technical Support) concerning the existence of any design / licensing documents other than listed in Section IV. They l suggested adding the Technical Specification to Section III.
Unit 2 Engineering is not aware of any other documents. l i
- Radiation Engineering was contacted concerning the impact of the bypass of post-LOCA '
containment atmosphere directly to the Unit 2 stack resulting from a failure of AC-11 to close.
Radiation Engineering stated that the bypass of this magnitude (approximately 0.01 % of the EBFS l design flow) would have minimal impact on the offsite dose and limits would not be exceeded.
(Refer to Section V.B.2 for a description of the modifications to damper AC-8.) ;
- Licensing was contacted and asked if they were aware of any Failure Mode and Effect Analysis performed for EBFS system, in particular, evaluation of a single failure of dampers AC-1 and i AC-11 and its impact on EBFS capability to perform its safety functions.
Licensing stated that they were not aware of these types of analysis being performed for EBFS 1 and its components, to verify this they will initiate search of licensing documentation files.
- Configuration Management Group was contacted to discuss the Design Basis Documents associated with EBFS and whether there is any additional information they may have which impacts the design of the EBFS. They stated that amendments to the FSAR as listed in Section V.A.5 address questions related to the EBFS.
III. EVALUATION OF DESIGN BASIS During our design evaluation of the purge and enclosure building filtration systems the following was noted:
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. 1. . Purge fan (F-23) air-operated isolation damper (AC-1) is controlled and monitored from the Unit 2 control board (COI). It presently receives a safety-related facility 1 CIAS initiation signal to close. With the failure of facility 1 train (electrical), AC-1 will fail to close and EBFS exhaust faa (F-25A) will fail to start, it appears a mechanical failure of the damper could be tolerated as it can be assumed that power ;
would be available to both EBFS exhaust fans (F-25A or F-25B). Both fans running will provide sufficient capacity to achieve the required negative pressure within the specified time period.
Upon cursory review, this evaluation appears sound.
- 2. The main exhaust air operated isolation damper (AC-11) is controlled and monitored from the Unit 2 control board (COI). It presently receives a safety-related facility 2 CIAS signal to close.
If the damper were to mechanically fail open, this would establish a flow path for a potential release of radioactive material to the Unit 2 stack and potentially degrade the ability of the EBFS exhaust fans (F-25 A or F-25B) to perform their required function of achieving a negative pressure in the enclosure building within the prescribed time period as stated in the FSAR and other design basis documents. We could find no indication that these conditions have been evaluated (see Section IV.A).-
- 3. With respect to the AC-11 design, the loss of facility 2 train will cause AC-11 to remain open and EBFS fan (F-25B) will fail to start. We could find no indication that these conditions have been evaluated (see Section IV A).
W. DOCUMENTS REVIEWED A. Unit 2 FSAR
- 1. FSAR Section 6.7, ENCLOSURE BUILDING FILTRATION SYSTEM.
- 2. FSAR Section 8.7, WIRE, CABLE, AND RACEWAY FACILITIES.
- 3. FSAR Section 9.9, PLANT VENTILATION SYSTEMS.
- 4. Technical Specification 3/4.6.5 " Secondary Containment - Enclosure Building Filtration i System."
- 5. Amendments 16 and 27 to FSAR, Questions 6.15.1 through 6.15.4 Questions and responses con'.ained in these amendments pertain to the capability of EBFS to achieve and maintain the enclosure building under 0.25 in. W.G. negative pressure.
The technical evaluations to substantiate the responses are included in Unit 2 design basis documents.
B. Unit 2 Design Basis Documentation Package
- 1. Design Basis Documentation Package, VENTILATION SYSTEMS, Section 3.1.2, ;
Enclosure Building Filtration System (EBFS).
- 7 3
"- C. Unit 2 System Descriptions
- 1. System Description M2-OP-PRI-2314G, Rev.1, Enclosure Building Filtration System
- 2. System description M2-OP-SEC-2314, Rev. O, Radioactive Discharge Ventilation Systems D. Licensee Event Report (LER 94-040-01)
E. Plant Information Report (PIR-2-95-126) f F. Unit 2 Calculations
- 1. The following calculations were reviewed to determme the design basis infiltration for EBFR:
1 1.1 Calculation IK21-18,11/28/69, " Pressure in EBFR-Transient Conditions" This calculation determined inleakage to the EBFR.
1.2 Calculation 1K215,6/6/73, "EBFR-Inleakage" This calculation revised and updated calculation 1K21-1 with the latest test data.
The inleakage to the EBFR at 0.25 in.W.G. is calculated to be 3,175 cfm.
This inleakage is greater than 2,560 cfm listed in FSAR (6/6/88), Section 6.7, j Page 6.7 8. This greater inleakage does not invalidate analysis presented in Section 6.7.4.1 for capability of EBFS, with both fans F-25A and F-25B operating, and a failure of isolation damper AC-1 to close, to maintain EBFR below design basis negative pressure of 0.25 in.W.G. The total flow of 10,960 cfm (as indicated in Item 5, p.6.7-8) would increase to 9,363m + 3,175 =
12,538 cfm. This is less than the EBFS capacity of 13,900 cfm with F-25A and F-25B operating in parallel. However, with the single EBFS fan operating, the inleakage into EBFR is 3,538 cfm greater than the exhaust capability of the singe EBSF fan.
(1) See review of calculation 1K12 'i in 2.2 below
- 2. The following calculations were reviewed to determine the design basis capacity for the i EBFS fans F-25A and F-25B:
2.1 Calculation 1K21-5, 6/6/73, "EBFR-Inleakage" This calculation determined fan capacity to be 6,000 cfm at 6 in.W.G. Buffalo Forge fan size 445 BL, operating at 1,889 RPM was selected.
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.i 2.2 Calculation 1K21-1,10/23/74, " Enclosure Building Filtration System" This calculation nxxlified performance parameters for EBFS fans based on as-built conditions. The fan speed was increased to 2525 RPM resulting in improved fan performance as follows:
Single fan operation 9,150 cfm at 10.4 in.W.G. l Two fan operation 13,900 cfm at 12.45 in.W.G. 1 These parameters correspond to the design basis fan performance listed in FSAR l 6.7 at 9,000 cfm and 10.4 in.W.G. for single fan and 13,900 cfm and 12.5 in.
W.G. for two fans operating in parallel.
2.3 Calculation 1K12-1,11/20/73, " Containment and Enclosure Building Purge System.
This calculation detennines pressure loss for the supply side of the purge system. l At design basis flow of 32,000 cfm the system pressure loss is 2.92 in.W.G.. ;
Upon shutdown of the supply fan F-23 and failure of damper AC-1 to close, the ,,
flow into the EBFR, with enclosure building at design basis 0.25 in.W.G., would be:
32,000 cfm x (0.25/2.92)" = 9,363 cfm l G. Piping and Instrumentation Diagrams The following Piping and Instrumentation Diagrams were reviewed to determine compliance of mechanical components, to isolate the EBFS from interfacing non-safety related systems, with i the design basis single failure criterion:
- 1. P&lD 25203-26028 " Containment and Enclosure Building Ventilation", Sh.1 of 5
- 2. P&ID 25203-26028 " Containment and Enclosure Building Ventilation", Sh.2 of 5
- 3. P&ID 25203-26028 " Containment and Enclosure Building Ventilation", Sh.3 of 5
- 4. P&ID 25203-26028
- Containment and Enclosure Building Ventilation", Sh.4 of 5
- 5. P&lD 25203-26028
- Containment and Enclosure Building Ventilation", Sh.5 of 5 H. Unit 2 Logic Diagrams The following logic diagrams were reviewed to verify current operation:
- 1. 25203-28128 Sh.15 Main Exhaust Fans (F-34A,34B, and 34C)
- 2. 25203-28128 Sh.16 Containment Purge Supply Fan (F-23)
- 3. 25203-28128 Sh. 31 A Enclosure Building Purge Isolation Damper (AC-1) !
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- 4. 25203-28128 Sh. 31C Enclosure Building Arge Exhaust Damper (AC-8) ;
- 5. 25203-28128 Sh. 34 Enclosure Building P.trge Supply Damper (AC-3)
- 6. 25203-28128 Sh. 35 Containment and Enclesure Building Exhaust Damper (AC-11) I
- 7. 25203-28128 Sh. 41 Enclosure Building Filtration Fans (F-25A and' 25B) and l Discharge Damper (EB-52) l
)
- 8. 25203-28128 Sh. 37 Enclosure Building Filtration Motor Operated Damper (EB-40 r and EB-50) ,
- 9. 25203-28128 Sh. 38 Enclosure Building Filtration Air Operated Damper (EB-41 and .
EB-51)
- 1. Unit 2 Elementary Diagrams The following elementary diagrams were reviewed to verify current operation and consistency with logics: ;
1, 25203-32022 Shs. A through E Control Switch Developments l
- 2. 25203-32022 Sh.10 Containment Purge Supply Fan (F-23) 3, 25203-32022 Shs.11,12, and 13 Main Exhaust Fans (F-34A,34B, and 34C)
- 4. 25203-32022 Shs. 21 and 22 Enclosure Building Filtration Fans (F-25A and ;
25B) :
5, 25203-32022 Sh. 29 Purge Fan Isolation Damper (AC-1) !
- 6. 25203-32022 Sh. 34 Enclosure Building Filtration Discharge Damper l (EB-52) l
- 7. 25203-32022 Sh. 50 Enclosure Building Filtration System Air !
Operated Damper (EB-41)
- 8. 25203-32022 Sh. 35 Enclosure Building Filtration System Air Operated Damper (EB-51)
]
- 9. 25203-32022 Sh. 36 Containment and Enclosure Building Exhaust Damper (AC-11)
- 10. 25203-32022 Sh. 53 Enclosure Building Filtration System Motor Operated Damper (EB 40) e 11. 25203 32022 Sh. 37 Enclosure Building Filtration System Motor Operated Damper (EB-50)
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. 12. 25203-32022 Sh. 46 Enclosure Building Purge Supply Damper I (AC-3)
- 13. 25203-32022 sh. 48 Enclosure Building Purge Exhaust Damper (AC-8) ,
J. Unit 2 Specifications
- 1. 7604-M-506, Rev. 9, ' Containment and Safeguards Ductwork" f
- 2. 7604-M-534, Rev. 7, " Enclosure Building Filter System"
- 3. 7604-M-526, Rev. 6. " Heating and Ventilation Ductwork"
{
V. MODIFICATIONS l Operability issues related to these modifications will not be discussed as pan of this repon. They will !
be addressed in the Notes of Conference of the Technical Meeting of April 6,1995.
l The following modifications were identified to alleviate concerns described in Section III:
A. Any one of the following modifications would address isolation of EBFS from the purge supply !
system:
t
- 1. Provide discharge damper AC-1 with both a Facility 1 CIAS initiation and a facility 2 !
CIAS initiation thereby ensuring a closure of AC-1 with a postulated electrical failure.
l NOTE: The damper and its associated solenoid valves are located in an area adjacent l' to nonseismic equipment. This issue should be evaluated.
The following activities are required to implement this modification:
- Procure and install new safety related solenoid valve (NP-1) and identify a new power source for the solenoid
- Install new conduit, control and power cabic :
- Modify existing instrument tubing
- Revise P&ID, logic and elementary diagrams ;
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- Develop new wiring diagram i
- Revise all applicable licensing and design basis documents
- Determine if existing control switch (HS 8050) on COI can be modified for two train operation to control both solenoid valves or provide a new control switch.
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- The following constructability and material reviews have been conducted to date:
- Based on a recent walkdown, it appears the existing control switch for AC-1, located on Unit 2 control board CO1, can be modified to allow installation of adder decks and a barrier for separation of the Z1 and Z2 electrical circuits at the switch. Separation for the new Z2 power source can be maintained by the use of flex conduit. The availability of spare fused Z2 circuits would have to be verified. A review of the ESAS panel (RCO2C) would have to be conducted to determine the availability of spare Z2 CIAS contacts. It appears a new limit switch would be required. Mounting this switch would be difficult due to the accessibility to the damper. There is sufficient room and access space for ,
installation of the new solenoid valve, next to the existing solenoid valves, and to modify the instrument air tubing. The availability of spare cables should be !
reviewed as the walkdown identified interferences and the possible requirements !
for core borings associated with running new cables. The difficulty of cable . l installation will be considerable. Imad time for delivery of the safety-related .I solenoid valve is undetermined. The site personnel are investigating available - [
stores on site. !
- 2. Provide a new safety-related counterweighted, gravity isolation damper in the ventilation j duct upstre/.m of purge fan (F-23). This damper would close and isolate the flow path' ;
automaticrily when a low flow condition exists, thereby ensuring redundancy for AC-1. )
Note: Succesful implementation of the gravity damper modification is contingent upon verification of fan F-23 performance. Calculation 1K12-1, dated 11-20-73, j indicates purge supply system pressure loss to be 2.92 in W.G. at 32,000 cfm. l This provides margin of 0.68 in. W.G. between calculated pressure loss and fan ,
design pressure of 3.6 in. W.G. However, drawing No. 25203-29644 indicates :
actual flow as 28,379 cfm.- Installation of the gravity damper will introduce !
. additional pressure loss of 0.5 in. W.G., further reducing this flow. This l reduction of flow could be potentially compensated by increasing fan F-23 speed ;
until full motor horsepower is utilized. if increase of the fan speed would not i give satisfactory results, increase in the enclosure building and containment purge j time should be addressed. ;
I To verify that the closure time of the gravity damper upon trip of fan F-23 is )
acceptable, the coastdown time of fan F-23 should be calculated. The time i should correspond to fan pressure decay from full operating pressure to damper
]
closing pressure. '
Review of Specification 7604-M-526 indicate that this modification will be based on the premise that it would be acceptable for the gravity damper to be installed in non-seismic ductwork. The precedence of this arrangement is set by location of safety-related damper AC-11 in non-seismic ductwork.
The following activities are required to implement this modification:
1
- Procure a new safety-related gravity damper
- Modify existing ductwork to accept new damper 300s9 B33
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'- * ' Revise ductwork drawings -
- Revise all applicable licensing and design basis documents ,
i The following constructability and material reviews have been conducted to date:
(
- There is sufficient space in the ductwork upstream of the purge H&V unit (F-23) and adequate construction access for installation of the new gravity damper.
- Iead time for delivery of safety-related gravity damper is approximately 1 15 weeks.(unexpedited) and could have an impact on startup of Unit 2 if ;
implementation of this option would extend into warm weather period. .;
- 3. - Modify the actuator for air-operated damper AC-3 frem fail open to fall close. Install !
a mechanical stop on the damper to prevent the damper from fully closing thereby !
,' ensuring a relief path for potential containment leakage. Change control and power l sources from facility 1 to facility 2 to ensure isolation of the purge air system by :
providing redundancy for damper AC-1. j NOTE: Review of Specification 7604-M-526 indicates that the purge system ductwork -
is of non-seismic construction. Damper AC-3 is installed in this non-seismic -
ductwork. ..
l 4
As mentioned in V.A.2, location of damper AC-11 establishes the precedence j
, for acceptability of this arrangement. !
i The following activities are required to implement this modification: i
- Modify existing damper - install mechanical stop i
- Modify existing damper operator !'
- Revise all applicable licensing and design basis documents
- Revise P&lD, logic and elementary diagrams
- Revise wiring diagram
- Install new conduit, control and power cable
- Assess the separation concerns for control switch HS 8081 (changing from facility 1 to facility 2)
The following constructability and material reviews have been conducted to date:
- The control switch and all associated electrical components for AC-3 would have to be rewired and barriers installed to change from Z1 to Z2 control and power circuits. A review of the ESAS panel (RC02C) will have to be conducted to determine the availability of spare Z2 CIAS contacts. Based on a recent see om
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walkdown, the difficulty to run new power and control cable will be considerable and worst than modification A1. i
- The lead time for damper AC-3 modification is undetermined and could have an impact on Unit 2 startup ifimplementation of this option would extend into warm weather.
B. Any one of the following modifications would address isolation of EBFS from the main exhaust system:
- 1. Provide an additional air-operated isolation damper in series with AC-11. This damper would be automatically isolated with a facility 1 CIAS initiation or manually from the main control board and would provide redundancy for AC-11.
NOTE: Review of Specification 7604-M-526 indicates that the Main Exhaust System ductwork is of non-seismic construction. Damper AC-11 is installed in this .
non-seismic ductwork. Acceptability of this arrangement and its conformance -
to the Unit 2 design basis would have to be verified.
Response to Question 6.15.4 (FSAR Amendment 16), addressing inward flow through damper AC-11 should be evaluated. It appears that under certain ,
conditions of operation, fans F-34A, B or C running, there could be some .
outleakage through damper AC-11.
The following activities are required to implement this modification:
- Procure and install a new safety-related air-operated damper with a safety-related ,
solenoid (NP-1) ,
- Procure new control switch and indicating lights
- Identify new power source
- Install new conduit, control and power cable f
- Provide tubing installation detail
- Revise control board layout drawing
- Make modifications to control board (CO1)
- Revise P&lD e Develop new logic, elementary, and wiring diagrams
- Revise all applicable licensing and design basis documents i
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- Assess whether the existing modulating / isolation damper. AC-11 should be replaced as part of this modification based on its present condition The following constructability and material reviews have been conducted to date:
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- There is sufficient space on the vertical run of the purge nhaust ductwork to install a new damper (AC-11A) and, if required, to install upgraded existing damper AC-11.
- Based on a recent walkdown, mounting a new control switch and indicating lights
, . for the new AC-11A damper would noi present any significant problems. A review of the CO1X panel still has to be performed to determine the availability of spare contacts for this modification. A review of the ESAS panel (RCO2B) would also have to be conducted to determine the availability of spare Z1 CIAS contacts. The availability of spare cables should be reviewed as the walkdown - )
identified interferences and the possible requirements for core borings associated with running new cables. The difficulty of cable installation will be moderate.
- approximately 15 weeks (unexpedited) after receipt of the purchase order by.
vendor and could have an impact on Unit 2 startup if implementation of this
[
option would extend into warm weather period.
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- 2. Modify the actuator for air operated damper AC-8 from fail open to fail close. The damper will close instead of open on a facility 1 CIAS initiation to provide redundancy for AC-11. In the event of the failure of Facility 2 to close AC-11, AC-8 will close on a Facility 1 signal, thereby isolating the exhaust system from the Enclosure Building, allowing only the leakage from the containment isolation valves to exit unfiltered to the Unit 2 stack.
Install a mechanical stop on the damper to prevent the damper from fully closing, thereby ensure a relief path for potential containment leakage.
NOTE: This modification is based on the acceptability of safety-related damper (AC-8) being installed in nonseismic ductwork (similar to damper AC-11). This modification is also based on the premise that the main exhaust fans are off or a flow path to the plenum is established from alternate locations.
The following activities are required to implement this modification:
.l
- Modify existing damper - install mechanical stops
- Modify existing damper operator
- Revise all applicable licensing and design basis documents ,
- Revise P&ID, logic, elementary and wiring diagrams
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The following constructability and material reviews have been conducted to date:
I.
- Control switch for AC-8 would have to be rewired and wiring at the limit switch would have to be nodified.
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- The lead time for AC-8 actuator modification is undetermined and could have an impact on Unit 2 startup if implementation of this option would extend into warm weather.
l VI. OPTIONS l
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! The following options were identified to implement the modifications described in Section V:
l Option 1
- 1. Description l Option 1, illustrated on Attachment 1, adds a new air-operated damper (AC-11A) in l series with existing damper AC-Il and adds a new safety-related solenoid valve and a j safety-related facility 2 signal for damper AC-1.
i l Ontion 2
- l. Description l 1
Option 2, illustrated on Attachment 2, would add a new air-operated damper AC-11 A, as described under Option 1, and a new safety-related, counterweighted, gravity damper upstream of the purge H&V unit.
Qption 3
- 1. Description !
Option 3, illustrated on Attachment 3, would provide new gravity damper, as described under Option 2, and change damper AC-8 from fail open to fail close.
Ontion 4
- 1. Description Option 4, illustrated on Attachment 4, would change damper AC-8 from fail open to fail close and change damper AC-3 from fail open to fail close and from opening on CIAS facility I signal to closing on CIRS facility 2 signal.
3CDet 800 as 12
.- i Ontion 5 l
- 1. Description ;
Option 5, illustrated on Attachment 5, would change operation of damper AC-8 as in Option 3 and modify damper AC-1 as described in Option 1.
- VH.
SUMMARY
AND RECOMMENDATIONS This report has provided an independent evaluation of the design of the enclosure building purge and t filtration systems. Electrical failure of AC-1 and AC-11, and mechanical failure of AC-11 may not have !
been evaluated in the original design.
In the event Unit 2 Engineering determines that the physical modifications are required, we recommend the addition of a safety-related gravity damper to alleviate the purge supply system isolation concern and l
the modification of enclosure building purge exhaust damper AC-8 from fail open to fail close to alleviate the purge exhaust system isolation concern.
This modification, Option 3, is illustrated in Attachment 3. In the technical meeting on April 6,1995, with Unit 2 Engineering, this Option was the consensus choice in consideration of plant impact, :
operation, and economics. Operability issues and impact on outage schedule will be addressed in the j April 6,1995, Meeting Notes. 6 The following technical issues must be addressed prior to implementing this option:
- Acceptability of the containment enclosure building atmosphere bypass through the open damper AC-11 to the Unit 2 stack would have to be documented by review of offsite dose calculations. i
- Fan curve and operating wheel speed, utilizing full motor horsepower of 40 hp for fan F-23, would have to be obtained from the fan manufacturer to confirm the fan has sufficient capacity l i
to compensate for pressure loss associated with the new gravity damper.
- Negative pressure at no flow conditions in the main exhaust pressure and enclosure building ductwork between the plenum and damper AC-8 with fans F-34A, B, or C running would have to be addressed. Licensing basis for assuming that non safety related main exhaust fans F-34A, B, and C will trip upon receipt of non-safety related no flow signal must be documented. !
- Data for the fan-motor assembly mass modulus of inertia (WK2) would have to be obtained and coastdown time of fan-motor assembly calculated.
i
- In accordance with the precedent established with the damper AC-11 design, it is acceptable to
- install the new seismic dampers in nonseismic ductwork.
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- Complete the review with the licensing group to confirm that all commitments associated with the design basis (e.g., FSAR questions / answers) are disclosed.
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.. Attachment 2 -
Page 1 of 2
) i ACTION PLAN 1 l
AC-01 & 11 PROBLEM RESOLUTION 1 l
Action Item Due Date
- 1. Place order for 2AC-01 A. !
1A. Resolve seismic design issue - F-23 ducting. !
IB. Re-analyze single failure possibilities with '
proposed new design. !
IC. Calculate set point for AC-01 A, F-23 and electrical load analysis check. Need fan curve and to evaluate coast down. I ID. Verify. set point AC-Ol A, with respect to Enclosure !
Building design . draw down. '
1 E. Develop specifications for purchase AC-01 A.
1F Negotiate with suppliers to lead time down. ' ,
- 2. Place order for. 2AC-08 i 2A. RAC complete preliminary calculation work to allow 2 AC-08 L 2B. LLRT read out on leakage after accident vs. no pressure.
2C. CH 14 review to ensure no other problem with AC-08 closing -
calculations, building spec., FSAR,DBDP questions i etc. l 2D. Re-analyze single failure possibilities with proposed new design.
2E. Re-analyze AC-08 ducting for new heavier !
damper and seismic design. i 2 F. Develop specifications for purchase AC-08 2G. Negotiate with suppliers to lead time down.
- 3. Fabricate test and deliver 2AC-01 l 3A. Preliminary design sketches I
3B. Test plan meeting with preliminary design 3C. Get Operations and Management concurrence for i proposed test plan.
3D. Test AC-01 A for set point and closure at factory.-
3E. Approve manufacturers drawings release i fabrication. !
- 4. Fabricate test and deliver 2AC-08 ,
4A. Preliminary design sketches I 4B. Test plan meeting with preliminary design l 4C. Get Operations and Management concurrence for proposed test plan. !
4D. Get conceptual re-wiring for AC-08 and finalize j retest methodology. -
4 E. Witness test of damper AC-08 at factory.
4F. Approve manufacturers drawings release i fabrication. !
i
.. . Attachment 2 Page 2 of 2 '
ACTION PLAN AC-01& 11 PROBLEM RESOLUTION s
l Action Item Due Date
- 5. B/J to fail AC-01, AC-11 shut.
- 6. Complete PDCR.
6A. Complete test plan.
6B. Design Seismic - new hangers for and duct work as necessary. ,
6C. AC-08 control board DCN out PDCR risk release to do board work.
- 7. Implementation.
7A. Install AC-08.
7B. Test AC-08 7C. Retest EBFS vacuum to Enclosure Building. !
7D. Retest Enclosure Building for vacuum after AC- i 01A Installed.
7E. Flow test and balance F-23 after AC-01 A installed.
7 F. Install Hangers. ;
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SECONDARY 70 mti 2 5C" CONTAINMENT Ac-e ENCLOSURE I F-t i I l OPENS j ( ON CIAS I
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,'N PLENtM AC-Il F-344 5 F-28 I F-34BI AC-3 -
- CLOSES *, y.g i F-34c) , ow CIAS g--g optus -
ON CIAS mtr 1
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2 TACE CONTAINMENT
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. ' '. PURGE H&v j
\, UNIT D ' !
' ' AC-1 EB-4C n F-in : rn0u )
- CLOSESg F-23 OUTSIDE F-25A l
F-Il *GN F- agg g CIAS, j ON CIAS i
4 i AC-7 AC-8 F-258 -
M AC-6 AC-4 EBFS FANS START ON EBFAS ENCLOSURE BUILDING CONTAINMENT VENTILATION 2AC-01 AND 2AC-11 PROBLEMS PAGE l 0F 2 ATTACMdENT 131
i SECONDARY To uMIT 2 CONT AINM ENT STACK - AC-8 ENCLOSU RE j i (Z-li OPENS ON CIAS f' .
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\ j PLENUM g AC-Il F-34A , (Z-2) AC-3 t-F-34BI . CLOSES l F-34Cl \ ON CIAS *.
(Z-il OPENS *K
.~...J ON CIAS TO IT 1 AC-57
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AC-1 l (Z-1) . FROM EB-4C '. CLOSES F-23 OUTSIDE F-25A (Z-Il l0N {ASl AIR ON CIAS
, AC-7 AC-6
. 4 F-258 -
M AC-4 AC-5 EBFS FANS START ON EBFAS ENCLOSURE BUILDING CONTAINMENT VENTILATION 2AC-01 AND 2AC-11 PROBLEMS PAGE 10F 2 ATTACHWENT (3)
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CHANct 10 m SECONDARY To mIT 2 \ CLOSE m \. CONT AINMENT SC" '
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. F-Il ENCLOSURE
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0eENS j [ **%.. _ ,,/ 0N CIAS PLENUM l AC-Il l F-34A F-21 #C-3 -
F-34B I CLOSES g_g F-34Cl DN CIAS OPENS -
S,* y 1 CONTAINMENT PURGE FROM.
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f* . OUTSIDE WIT . Arn k
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EB-4C a Eii CLOSES F-23 *
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F-25A F-l l ON CIAS y.21 STOPS ON CIAS ( NEW SAFETY RELATEDI COUNTER BALANCED '*
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'**--..,**j GRAVITY DAMPER s
AC-7 AC-8 i
F-258 -
AC-G AC-4 EBFS FANS START ON EBFAS ENCLOSURE BUILDING CONTAINMENT VENTILATION 2AC-01 AND 2AC-11 SOLUTIONS PAGE 2 0F 2 ATTACHMENT (3)
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Page 1 of 1 April 28,1995 Attachment (4)
Evaluation of Proposed Solutions Problem Proposed Solution Attributes j e c r *t4 ' n w o,;p!'iri p g ; p y Constructability Operability Scope to be Overall .
Completed by Mode 4 Evaluation 2AC-01 (A) Add F-2 CIAS signal + Difficult Requires Cable & Conduit + Control Room Work can't be Control Room Work POOR to 2AC-01 from Control Room to Enclosure done on-line. and B/J for AC-01 bldg.
- ESAS Retest needs
+ Main board additions on 2 boards additional Facility 2 outage 2 AC-01 (B) Add Gravity Counter + Good Access + Install any time before too B/J to fail AC-01 GOOD balanced damper to F-23 + No Electrical hot (July) shut suction - Retest-on-line
+ Flow balance F-23/ main Exhaust
All work and retest on-line 2 AC-01 (C) 2AC-03 to shut on + Difficult
Same issues as for (A) above + Control Room IOORER CIAS + Cable & Conduit Control Room to + Need Rad assess Calculation work Enclosure (worse than A) for LLRT leakage - B/J to shut AC-
- Traced out - Lots of Staging 01
+ Main Board additions 2 AC- 11 (D) Cause 2AC-08 to + Change out operator and damper + Rad analysis LLRT leakage
- B/J to fail 2AC- GOOD close with facility-1 2AC-08 2AC-06 and 07 11 shut CIAS + Minor Switch rewire at Control + Retest looks like can be + Rewire Switch at Board done at power Main Board
- No ESAS retest 2 AC- 11 (E) Add 2AC-II A + Have space - Main board work by Mode 4 + Main board work POOR additional isolation + Add damper Can't do Elect. Retest while + Install access damper to close on +
Should be able to do at power if operating (ESAS) door for fire facility 1 CIAS install blank now + Can close fire damper when damper
+ Need cable / conduit from Control do installation instead of Room to Enclosure blJg. Not as bad blank as A.
- Can't retest after S/U
+ Main board work e e g- %
9
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D . REVIEWED BY Northeast Y ' A D. pp
,, ' gM Utilities System M.S.K.
s.o.w*
Mcv 25, 1995 '
NE45-SAB-225 M.Lv. M-eIHO TO: T. Doyle g s
FROM: S.D. Weerakkody- . 3594 J.K. Rothert-P . 5689 MD*
SUBJECT:
The Single Failures of EBFS and Their Impact on Public Safety OVERALL CONCLUSION:
The PRA Section has investigated the public safety and cost / benefits associated with the single failures of EBFS at MP2.
Our overall conclusions are provided below.
- 1. The public safety impact associated with these single failures are negligible, as demonstrated by the results of the cost-benefit analysis we performed. When dollar equivalents of 1000$ per averted person-rem are used, the benefit of eliminating these single failures amounts to 3S/ year, or approximately $60 over the remainder of the plant life.
- 2. Not withstanding the above cost-benefit analysis, PRA recognizes the significance of maintaining the functionality ,
of EBFS for design basis events. Therefore, we would l recommend use of " negligible risk significance" as a basis l to not perform expensive fixes and recommend the following I compensatory actions to maintain functionality, in light of the single failures:
a) AC-11: Revision of procedure (s) to trip fans F-34A/B/C or manually close 2AC-08 in the case of a stuck open AC-11 post LOCA.
b) AC-01: Revision of procedure (s) to manually start F-25A (if motive power is available) post LOCA. However, ,
we would like to note that the risk significance l of this single failure is much less significant when compared with the risk significance of 2AC-
- 11. !
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SDW/JKR: cms i
i c: R.W. Wells S.A. Sudigala R. Crandall M.S. Kai ;
R.P. Necci l C. Bouchard :
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Distribution: NDS !
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