ML17191B472
| ML17191B472 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 10/01/1999 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML17191B471 | List: |
| References | |
| NUDOCS 9910120182 | |
| Download: ML17191B472 (6) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 174 TO FACILITY OPERATING LICENSE NO. DPR-19 AND AMENDMENT NO. 170 TO FACILITY OPERATING LICENSE NO. DPR-25 COMMONWEAL TH EDISON COMPANY DRESDEN NUCLEAR POWER STATION. UNITS 2 AND 3 DOCKET NOS. 50-237 AND 50-249
1.0 INTRODUCTION
By letter dated May 20, 1999, as supplemented by letters dated September 8, September 16, and September 20, 1999, Commonwealth Edison Company (ComEd, the licensee) requested a license amendment for Dresden Nuclear Power Station, Units 2 and 3. The proposed license amendment would change the Technical Specifications (TSs) to revise the minimum water level in the suppression chambE!r, and to clarify the Containment Cooling Service Water (CCSW)
System requirements as a support system for the Control Room Emergency Ventilation System (CREVS). The September 8, September 16, and September 20, 1999, submittals provided clarifying information that did not change the initial proposed no significant hazards consideration determination.
This Safety Evaluation only addresses the proposed change to the CCSW requirements. The change to the suppression chamber water level is unrelated to the CCSW change and will be addressed in a separate licensing action.
2.0 EVALUATION The proposed TS change is to TS 3/4.8.A, "Containment Cooling Service Water," but the primary impact is on the control room (CR) habitability system. The control room heating, ventilation and air conditioning (HVAC) receives cooling water from CCSW an.d service water (SW). These systems are described below.
System Design
The CR habitability systems are designed to ensure that control room operators are able to remain in the control room, operate the plant safely under normal conditions, and maintain the plant*in a safe'condition under accident conditions. The habitability systems consist of systems and equipment which protect the control room operators against such postulated releases as radioactive materials, toxic gases, and smoke. The Dresden CREVS, which includes the safety-related train of CR HVAC, is described in Sections 6.4 and 9.4 of the Updated Final
. Safety Analysis Report (UFSAR). The Dresden CR is shared between Units 2 and 3.
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J I The control room habitability systems are designed so that radiation exposure of control room personnel does not exceed limits of NUREG-0800, "Standard Review Plan" (SRP) 6.4, or 1 O CFR Part 50, Appendix A, General Design Criterion (GDC) 19. GDC 19 and SRP 6.4 require adequate radiation protection to permit access to and occupancy of the CR under accident conditions without personnel receiving exposures in excess of 5 rem whole body or its equivalent to any part of the body for the duration of the design-basis accident (OBA).*
The CR HVAC system consists of two independe~t HVAC subsystems sharing some common ductwork: one multizone subsystem (Train A) and one single zone subsystem (Train B). The system was modified to meet the intent of NUREG-0737, "Clarification of TMI Action Plan Requirements," Action Item 111.D.3.4, "Control Room Habitability." The system design relies on non-safety related (NSR) components to provide redundancy in CR cooling.
Train A is the primary temperature control and air distribution subsystem for the control room emergency zone. Train A is NSR and is used during normal operation. CR cooling is provided by two, 50 percent capaCity, 45-ton chilled water compressors which are NSR and are not normally aligned to receive power from an emergency diesel generator (EOG). The cooling, water for Train A is from SW. Train A can be operated in the event of a loss of offsite power (LOOP) if the 4-kV nonessential switchgear i~ backfed.
Train B of CR HVAC is the safety-related (SR) portion of the system and is used as a backup for Train A Train B is initiated if Train A is out-of-service, or in the accident-response modes of CREVS. CR cooling is provided by a single, 90-ton compressor. Cooling water is normally provided by the SW system; however, upon a loss of SW operators manually align Unit 2
- CCSW to cool the compressor. The air distribution from each train is aligned through the use of air-operated isolation dampers. These dampers fail to the Train B mode since Train B is powered from a Unit 2 emergency bus and is available in the event of a LOOP.
CREVS is not modeled in the Dresden probabilistic risk assessment b~sed individual plant examination (IPE).. The Dresden IPE states that because of the redundant supplies of cooling water and because of procedural controls, loss of main control room ventilation is judged to have an insignificant impact on modeled equipment failure rates or on modeled human error probabilities (HEPs). Loss of control room ventilation is not expected to lead to control room evacuation or either an automatic or manual reactor scram. In response to the staff's questions about the CR HVAC being a support system for other systems that are needed to prevent core damage, Com Ed stated that most of the safety-significant switchgear is not located in the CR envelope. Instead, the switchgear is located in open areas of the plant where the temperatur.e is not expected to exceed 120 degrees Fahrenheit. Therefore, loss of ventilation in these areas was not warranted as a support system based initiator for the Dresden IPE. Furthermore, neither modification of HEPs (due to temperature concerns) nor addition of HVAC basic events to relevant fault trees was warranted. By letter dated October 2, 1997, the staff determined that ComEd's response was sufficient and that the Dresden IPE met the intent of Geril=lric Letter 88-20.
The CCSW system is a SR, open loop cooling water system consisting of four CCSW pumps and associated valves, piping, controls and instrumentation for each unit. The CCSW system provides cooling water for the containment cooling heat exchangers during both accid.ent and non-accident conditions. The system piping is arranged in two separate loops, each with two pumps and a heat exchanger. At the heat exchanger, heat is transferred from the low pressure coolant injection (LPCI) subsystem to the CCSW system. During normal plant operation, the CCSW system is not operating. Following an accident or other plant evolution which requires containment heat removal, the CCSW system is manually started. The Unit 2 CCSW pumps are powered from 4 kV buses 23 and 24. These buses are manually back-fed from EDGs which can supply the necessary loads in the event of a LOOP. Four CCSW pumps are located in the turbine buildings, Two of the four CCSW pumps (pumps B and C) are located in a single, common watertight vault for flood protection. To prevent the CCSW pump motors from overheating, the vault has two vault coolers. The cooling water for each vault cooler is provided from its respective CCSW pump discharge. Only Unit 2 CCSW loops provide a SR source of wciter to the SR control room HVAC condensers.
SW is a NSR open system designed to provide strained river water for various plant equipment.
The system consists of five pumps, three strainers, and a common distribution header. Two SW pumps are provided on each unit and the fifth shared pump is used as a backup. Normally, two pumps and one strainer for each unit are in operation, while the fifth pump and one strainer are in standby. The system is cross-tied between Units 2 and 3. The SW pumps are powered by 4 kV buses 23(33) and 24(34). The 2/3 SW pump can be powered by either Unit 2 or Unit 3.
There are no automatic features for the SW pumps. In the event of a loss of all AC' power, the operator can manually start a SW pump on EOG power after securing a safe shutdown of a unit (no emergency core cooling in operation). SW is not necessary for a safe shutdown of the units, but it is needed to attain a normal cold shutdown condition. The SW system provides the normal source of cooling water to both the SR and NSR trains of CR HVAC.,
In summary, the CR HVAC that supports CREVS is a single train system (Train B) with no redundant SR equipment. Support systems include NSR cooling water to the compressor, which is normally provided from SW from Unit 2 and/or Unit 3. Either subsystem of Unit 2
. CCSW can be aligned to provide a SR source of cooling water for CREVS. Electrical power for*
CREVS and for CCSW pumps 2C and 20 is provided by SR bus 24-1 that is normally fed by the Unit 2 EOG upon loss-of-power. Electrical power for CCSW pumps 2A and 28 is provided by SR bus 23-1 that is normally fed by the Unit 2/3 EOG upon loss-of-power. The SW pumps, which are not normally aligned to the EDGs, are not immediately available on either unit, so that
- Unit 2 CCSW is used in the event of a LOOP. If needed, the SW pumps and/or Train A of CR HVAC can be run from the EDGs if emergency core cooling system (ECCS) loads are not required.
In 1983, the staff reviewed Dresden's CR habitability against the criteria in SRP Sections 2.2.1, 2.2.2, 2.2.3 and 6.4, and Regulatory Guides 1. 78 and 1.95. By letter dated May 11, 1983, the staff approved the CREVS design as meeting the intent NUREG-0737, Item 111.D.3.4. At that time, no TSs were added related to the cooling function of CREVS.
Technical Specifications for CREVS As a result of findings by a Diagnostic Evaluation Team inspection performed by the NRC staff at Dresden in 1987, ComEd decided that both Dresden and its sister site, Quad Cities Nuclear Power Station (Quad Cities) needed att~ntion focused on their TS.
ComEd initiated the Technical Specification Upgrade Program (TSUP) for both Dresden and Quad Chies Stations. The licensee evaluated the then-current TSs for both Dresden and Quad Cities against the Standard Technical Specifications (STS) contained in NUREG-0123, "Standard Technical Specifications General Electric Plants BWR/4." The licensee proposed numerous improvements such as clarifying requirements, changing the TS to make them more understandable and to eliminate interpretation, and deleting requirements that were no longer considered current. ComEd updated both the Dresden and Quad Cities TS based on the STS contained in NUREG-0123. ihe final amendment related to TSUP was approved by the staff by letter dated June 28, 1996.
During the TSUP, ComEd adopted TS related to the cooling function of CREVS. ComEd modeled the s;:iecifications for safety-related service water (CCSW at Dresden and Residual Heat Removal Service Water (RHRSW) at Quad Cities) after NUREG:-0123, and kept the wording the same between Dresden and Quad Cities.
Specification 3.8.A for Ores.den and Quad Cities are similar in that Dresden's CCSW and Quad Cities RHRSW perform the containment cooling functions for their respective stations. At Quad Cities, RHRSW is also needed to perform the Decay. Heat Removal function. Furthermore, like Dresden's CCSW system, the Quad Cities RHRSW provides backup cooling to CREVS; however, at Quad Cities the cooling water comes from one train of RHRSW from each unit, whereas at Dresden the cooling water can only be supplied from the Unit 2 CCSW. Com Ed modeled TS 3/4.8.A for both stations after the Quad Cities system configuration.
Currently, Dresden TS 3.8.A requires four CCSW pumps in two operable CCSW trains when a unit is in Modes 1, 2, or 3. During irradiated fuel movement and operations with the potential to drain the reactor vessel (Mode*), TS 3.8.A requires "the subsystem(s) associated with subsystems/loops and components required OPERABLE by Specification 3.8.D (CREVS)."
TS 3.8.A defines a subsystem as (1) two operable CCSW pumps; and (2)' an operable flow path through a LPCI heat exchanger and to the associated safety-related equipment. This TS structure implies that two pumps and one LPCI heat exchanger need to be operable during Mode* to support CREVS. According to Com Ed, this TS structure overstates the CCSW requirements in support of CREVS when Unit 2 is in Mode
- and does not adequately describe the system requirements in Modes 1, 2 and 3.
Evaluation of Proposed Change Com Ed proposed to revise TS 3/4.8.A to clarify the CCSW requirements as follows: (1) two.
CCSW subsystems, each comprised of two CCSW pumps, a LPSI heat exchanger, and a flow path to the associated safety-related equipment, is required to be OPERABLE in Modes 1, 2 and 3 to support containment cooling; and (2) any one of the t.our Unit 2 CCSW pumps and the associated flow path is required to be OPERABLE in Modes 1, 2, 3 and
- to support CREVS. In addition, TS 3/4.8.A, Action 2, was revised to clarify that the actions in TS 3/4.8.D, "Control Room Emergency Ventilation System," are followed if the Unit 2 CCSW pump is inoperable in
~odes 1, 2, 3 or*.
The staff reviewed the proposed change and the design of the Dresden systems. The staff determined that, for containment cooling support, the proposed TS meets the system requirements for CCSW and is, therefore, acceptable. For CREVS support the staff determined that the proposed TS meets the system requirements with the following
- Clarifications:
CCSW Minimum Flow Requirements: In response to the staff's questions, ComEd stated that the minimum flow to support long-term operation of a CCSW pump is 350 gpm, or 10 percent of design flow through a CCSW pump. Since the CREVS refrigeration control unit (RCU) only uses 121 gpm, other flow paths are needed for a CCSW pump to support the CREVS function. If a flow path through the LPCI heat exchanger is not available, ComEd stated that sufficient flow is achieved through use of other flow paths, including the CCSW pump vault coolers. Since the CCSW pump vault coolers are only available on CCSW pumps 2B and 2C, CCSW pumps 2A and 2D can only support CREVS if a flow path is available through the LPCI heat exchanger. In the September 16, 1999, submittal, ComEd stated that the Dresden UFSAR will be revised to clearly reflect the flowpath and minimum flow requirements of CCSW in support of CREVS. Any future changes to the UFSAR will be subject to the requirements of 1 O CFR 50.59 and will be submitted to the NRC in accordance with the requirements of 1 O CFR 50. 71 (e). The staff finds this to be an acceptable level of control for these system requirements.
Division I Power: In their submittal, ComEd proposed that any one of the four CCSW pumps 2A, 2B, 2C, or 2D may be used to meet TS requirements for CREVS. CCSW pumps 2C and 2D and CREVS are in electrical Division II. CCSW pumps 2C and 2D are, therefore, the pumps that are electrically associated with the CREVS subsystem and components required OPERABLE by TS 3.8.D. CCSW pumps 2A and 2B are in electrical Division I. If pumps 2A or 2B are the source of cooling for CREVS, the RCU function could be lost if either Division I or Division II power is lost whereas, if pumps 2C
- or 2D are used, only a-loss of Division II power would cau!)e the RCU to be lost. The.
station blackout (SBO) system as describ.ed in UFSAR Section 9.5.9 is a NSR independent source of additional onsite emergency AC power. Each unit has a diesel driven SBO EDG which is. connectable to each units' SR 4kv bus. To compensate for any increased chance that the CREVS RCU could be lost due to a loss of power to pumps 2A or 2B, ComEd stated on September 27, 1999, that they would verify SBO availability, including connectability, whenever 2A or 2B CCSW pumps are the CCSW supply for CREVS TS 3.8.D OPERABILITY. ComEd also stated that the UFSAR will be revised to reflect that the 2A or 2B CCSW pumps are dependent on SBO availability when only pumps 2A or 2B are credited for TS 3.8.D OPERABILITY. Ariy future changes to the UFSAR will be subject to the requirements of 10 CFR 50.59 and will be submitted to the NRC in accordance with the requirements of 10 CFR 50.71(e). The staff finds thi$ to be an acceptable level of control for these system requirements.
The staff reviewed the system configurations and the operator actions that are required post-accident to align the CREVS CR HVAC. The staff determined that, with the proposed changes to the TSs, the CREVS availability and operation will be consistent with design that was originally approved by the staff by letter dated May 11, 1983. The staff finds that the proposed changes to TS 3.8.A reflect the design of the Dresden CCSW system and provide an
.,, acceptable level of redundancy in the CR HVAC function. The staff finds the proposed changes to TS 3.8.A and the associated Bases to be acceptable.
3;0 STATE CONSULTATION In accordance with the Commission's regulations, the Illinois State official was notified of the proposed issuance of the amendments. The State official had no comments.
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4.0 ENVIRONMENTAL CONSIDERATION
The amendments change a requirement with respect to the installation or use of a facility component located within the restrictecf area as defined in 10 CFR Part 20. The NRC staff has determined that the amendments involve no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure. The Commission has previously issued a proposed finding that the amendments involve no significant hazards consideration, and there has been no public comment on such finding (64 FR 46426). Accordingly, the amendments meet the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9). Pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendments.
5.0 CONCLUSION
The Commission has concluded, based on the considerations discussed above, that: (1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Commission's regulations,* and (3) the issuance ofthe *amendments will not be* inimical to the.
common defense and security or to the health and safety of the public.
Principal Contributor: S. Bailey Date:
October 1, 1999