ML20151H630
| ML20151H630 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 04/12/1983 |
| From: | Harold Denton Office of Nuclear Reactor Regulation |
| To: | Heltemes C NRC OFFICE FOR ANALYSIS & EVALUATION OF OPERATIONAL DATA (AEOD) |
| References | |
| AEOD-E304, NUDOCS 8305040727 | |
| Download: ML20151H630 (1) | |
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OP,AB r/f NRC PDR APR 121983 L PDR PRC NSIC T. Ippolito H. Centon/E. Case D. Eisenhut/R. Purple MEMORANDUM FOR: C. J. Heltemes, Director F. Miraglia/L. Berry Office for Analysis and Evaluation G. Holahan of Operational Data D. Pickett M. Garver (NRR #83-74)
FROM: Harold R. Denton, Director E. Jordan i
Office of Nuclear Reactor Regulation J. Tay1or OELD
SUBJECT:
AEOD ENGINEERING EVALUATION REPORT AEOD/E 304 We have received your engineering evaluation report AE0D/E 304, " Investigation of Backflow Protection in Common Equipment and Floor Drain Systems to Prevent Flooding of Vital Equipment in Safety-Related Compartments." The report centers on design flaws in the Calvert Cliffs Auxiliary building drainage system which empties onto the floor of the turbine building condenser pit.
, If the turbine building is flooded to the design flood level, water can be t
postulated to back up through the floor drain systems and flood the safety related service water pumps in the auxiliary building.
The report concludes that older operating plants that have not been designed or upgraded to the licensing criteria of SRP Section 9.3.3 may not be adequately protected from flooding due to water backflow through equipment and floor drain systems. Your recommendation is that this topic be included with the other generic issues in the Unresolved Safety Issue (USI) Topic A-17,
" Systems Interaction in Nuclear Power Plants."
We plan on addressing this generic issue by using the guidelines of NRR Office Letter No. 40, " Management of Proposed Generic Issues." This procedure requires the Safety Program Evaluation Branch to develop an assessment of the priority ranking of this issue. The SPEB assessment will be forwarded to you, the originator, and the other NRR divisions for comment. After the SPE3 priority assessment has been received and commented upon, an appropriate j course of action will be developed by the responsible division.
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MEMORANDUM FOR: Harold R. Denton, Director /
Office of Nuclear Reactor Regulation FROM: C. J. Heltemes, Director Office for Analysis and Evaluation of Operational Data
SUBJECT:
Engineering Evaluation Report, INVESTIGATION OF BACKFLOW PROTECTION IN COMMON EQUIPMENT AND FLOOR DRAIN SYSTEMS TO PREVENT FLOODING 0F VITAL EQUIPMENT IN SAFETY-RELATED COMPARTMENTS Enclosed is a recent engineering evaluation report concerning backflow pro-tection for equipment and floor drain systems. This report concludes that backflow protection has not been addressed for the older operating units, i.e., units not designed or upgraded to the current licensing criteria of SRP, section 9.3.3.
AE00 believes that this subject should be reviewed and recommends that this topic be included with the other generic issues in the Unresolved Safety Issue (USI), Topic A-17, SYSTEMS INTERACTIONS IN NUCLEAP. POWER PLANTS.
If you should have questions concerning this report or this recommendation, contact Ted Cintula on extension 24494.
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C eltames Director 0 e for Analysis and Evaluation of Operational Data i
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AE00 ENGINEERING EVALUATION REFORT* .
UNIT: Calvert Cliffs Units 1 & 2 EE REPORT NO. AE0D/E304 DOCKET NO.: 50-317 & 318 DATE: March 11, Iw.s LICENSEE: Baltimore Gas & Electric Co. EVALUATOR / CONTACT: Theodore C. Cintula NSSS/AE: Combustion Engineering, Inc./Bechtel Corp. l
SUBJECT:
INVESTIGATION OF BACKFLOW PROTECTION IN COMMON EQUIPMENT AND FLOOR DRAIN SYSTEMS TO PREVENT FLOODING 0F VITAL EQUIPMENT IN SAFETY-RELATED COMPARTMENTS EVENT DATE: November 5,1981
SUMMARY
On November 5,1981, Bechtel Corporation, the architect-engineer, notified the licensee for Calvert Cliffs Unit 1 and 2 that the watertight integrity of the service water pump rooms at both units could be-impaired because check 4
valves had not been installed in the floor drain system whicn drains by gravity to the turbine condenser pit in the turbine building. Without these check valves, the operability of the service water pumps for both units could not be assured in the event of a circulating water conduit break in the tur'ine o building (a nonsafety area). As a temporary corrective measure, the licensee
- sesled some of the ficor drains with inflatable plugs and modified the remain-
- ing drain lines by' installing check valves to prevent potential backflow.
As part of the evaluation, we investigated the NRC requirements on the
- protection of safety-related equipment from possible backflow in the i floor drainage system. We concluded that this topic is not being addressed ,
as a safety issue for older operating plants.
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- This report supports on-going AE00 and NRC activities and does not represent the position or requirements of the responsible NRC program office.
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DISCUSSION On November 11, 1981, the DAILY REPORT-REGION I carried a " prompt report" from !
Calvert Cliffs Units 1 and 2 indicating the licensee had been notified that the l watertight integrity of the service water pump rooms in both units could be impaired because check valves had not been installed in the floor drain system :
which drains by gravity to the turbine condenser pit in the turbine building.
Without these check valves, the operability of the service water pumps for both units could not be assured in the event of a circulating water conduit break in the turbine building of that unit, This event was subsequently reported as LERs 81-79 and 81-47 for Units 1 and 2 respectively. The LERs state that Bechtel Corporation, the architect-engineer, notified the licensee that they consider the system design basis used to establish the watertight integrity of the service water pump room to be invalid since the service water pump room floor drains are connected without isolation to the turbine condenser pit.
Although the elevation of the service water pump room floor is twelve feet above the turbine condenser pit floor, the water level in the turbine building following the breaking of a circulating water conduit would have resulted in backflow through the floor drains and simultaneous flooding of the service water pump rooms in both Units 1 & 2 to a depth of 15 feet. Although the increase in water level would have been detected and annunciated by nonsafety grade instrumentation in'the turbine pit and safety grade instrumentation in the service water pump room, there would not have been any way to stop the inflow of water into the service water pump room following a design basis flood.
As somea temporary corrective of the floor drains measure with inflatableto resume power plugs operation, (which are stillthe in utility) place sealed and the remaining drain lines were modified by installing check valves to prevent potential backflow into the safety-related rooms. A review of other drain lines within the plants did not reveal a similar situation.
The LERs for Calvert Cliffs were submitted in accordance with technical specification 3.7.10., titled " WATERTIGHT DOORS". The licensee co'nsidered the violation of watertight integrity for the service water pump room due to improper drain line design to be comparable to the inoperability of the watertight doors to this room.
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FINDINGS The service water system at Calvert Cliffs Units 1 and 2 each have three pumps and serve bot'h safety (the conts.inment cooling units and the emergency diesel generator heat exchangers) and nonsafety equipment. The three service water pumps for each unit are located in a single room and Unit 1 and 2 service water systems can be cross-connected by spool pieces to allow the Unit 1 system to backup Unit 2 and vice-versa. However, Unit 1 and 2 share a common turbine building, so both of tne service water pump rooms would be simultaneously affected by a circulating conduit break in the turbine building if backflow protection was not provided.
A loss of service water flow yould affect the four containment air coolers for each unit, and assuming both service water pump rooms are flooded, all of the three emergency diesel generators at the site (the emergency diesel generator heat exchangers are cooled by the service water system). If containment
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- cooling is lost, heat removal from the containment following a LOCA can be accomplished with the containment spray system which uses the refueling water tank as a coolant source. However, if the failure of the circulating water conduit occurred as a result of a seismic event which simultaneously resulted in a loss of offsite power, then both units would have experienced a total loss of AC (plant blackout) since cooling for the emergency diesels would be lost. The impact of such a failure on safe shutdown was r.ot discussed in the LERs by the licensee.
The design flood level of the turbine building is +18 feet. The finished grade of the plant site is +45 feet, high enough so outside flooding interactions with the turbine building were not considered in the Final Safety Analysis Reports (FSAR). The service water pump room floor is at an elevation of +3 feet (with the service water pump platfonn at +6 feet). Therefore, the design flood could have resulted in 15 feet of water in the service water pump rooms. There are redundant high level switches in each service water pump room; these switches are waterproof, testable, seismic class 1, and actuate an alann in the control room.
Since the technical specifications at Calvert Cliffs did not address the equip-ment and floor drainage systems, an LER search was undertaken to see if, ar.d how, licensees had reported similar defects within these systems. A fairly generalized cut set was used for the search and it obtained over 1000 reports.
There were no reports similar to Calvert Cliffs, that is, no LERs on missing or faulty drainage system backflow protection devices or of backflow through drainage systems that resulted in a loss of safety-related equipment.
An examination of the FSARs of other Combustion Engineering (CE) plants indicated that potentially radioactive drainage is required to be isolated from nonradioactive drainage systems; however, the potential interactions within nonradioactive drainage systems were not specifically addressed. The exception was the FSAR for San Onofre 2 and 3, which are newer vintage plants; it states in Section 9.3.3.1 that drainage from engineered safety feature equipment rooms is configured to prevent flooding of engineered safety features equipment by drainage piping backflow. In their piping and instrinentation di'agram, a check valve and butterfly valve, installed in series, are shown in the drain line between the auxiliary building (the location of the service water pump room) sump and the Unit 2/3 turbine building stnp.
In view of the inconsistency in Ne'FSARs for the older and the newer vintage designs, we decided to survey some other sources to see whether the topic of backflow protection in the floor drainage system for safety-related equipment was considered in the design of older plants.
Th.e guidance provided in the Standard Review Plan (SRP), Section 9.3.3. " Equip-ment and Floor Drainage Systems" (EFDS), is quite clear in expressing the need for protection for safety-related equipment from possible backflow of the floor drainage system. Dr.e of several examples states:
System capability to prevent drain or flood water from backing up in the drainage system into areas housing safety-related equipment has
- been incorporated. Statements in the SAR that this capability is provided are acceptable.
The SRP, however, applies only to the newer vintage of plant designs.
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- The Systematic Evaluation Program (SEP) lists the safety-related topics under review for eleven of the older light water reactors that do not have technical specifications commensurate with the Standard Technical Specifications. The basic purpose of the SEP, begun in 1978, is to reconfim the safety of older nuclear power plants. The review compares the as-built plant with current licensing criteria and determines whether there is need for change between current technical positions on safety issues and those that existed when a particular plant was licensed. Although the SEP addresses compartment flooding, it does not include a topic pertaining to backflow protection of drain lines in safety-related rooms; therefore, in this regard, these systems are not being studied (and possibly upgraded) in accordance with SRP section 9.3.3.
In reviewing other sources of information to see if the potential interaction of compartment drain lines was previously considered in plant designs, we found that flooding of critical equipment was considered in 1972 because of an operational event at Quad Cities. At that time, Unit 1 experienced a rupture of an expansion bellow in the circulating water system (a low energy nonsafety system) and the resultant flooding caused some degradation to engineered safety feature equipment. As a result of this event, a generic review titled " Flood of Equipment Important to Safety" was initiated. This issue was tracked as topic 3-18 in the REGULATORY LICENSING - STATUS
SUMMARY
REPORT (the " Pink" Book) and was applicable to all operating plants as of 03/01/74. Calvert Cliffs 1 and 2, holders of construction pemits at this 1,
time, were not included with the 39 operating units as a recipient of the generic letter. Calvert Cliffs, and other plants being evaluated for construction pemits or operating licenses, were to have this probits evaluated as part of their safety evaluation for the license. l Topic 3-18 was phased out before all plants could be evaluated and licensees who did not respond with sufficient infomation to prepare an adequate Safety Evaluation Report (SER) for topic 3-18 were assigned to NRR Generic Technical Issue B-11, SUBCOMPARTMENT STANDARD PROBLEMS. The SERs issued under B-11 to complete the topic 3-18 program were titled SUSCEPTIBILITY OF l l
SAFETY-RELATED SYSTEMS TO FLOODING FROM FAILURE OF NON-CATEGORY 1 SYSTEMS.
These reports which were issued for San Onofre 1, Yankee Rowe, Indian Pt. 2 and Surry 1 and 2, and were to consider all sources of potential flooding that might adversely affect the perfomance of safety-related equipment required for safe shutdown. However, examination of several of these later SERs did not indicate any directed attention to drain line problems or of backflow protection. No SER was issued for Calvert Cliffs since it was not part of the topic 3-18.
The successor to the " Pink" Book is the " Aqua" Book; it is titled UNRESOLVED SAFETY ISSUES. Its most relevant subject to drain line backflow protection is topic A-17 SYSTEMS INTERACTIONS IN NUCLEAR POWER PLANTS. According to the task manager for topic A-17, backflow protection of drain lines will not be covered as part of this program or as part of the other generic issues of this publi-cation. Additional work in topic A-17 is now being perfomed under TMI Action Plan, Item II-C-3, SYSTEMS INTERACTION. The systems interaction program is directed toward identifying hidden deficiencies in properly designed systems that may create a safety hazard, rather than identifying improperly designed systems. Thus, the design adequacy of equipment and floor drainage systems would rcmain the resoonsibility of the chartered technical branches; pressably, this is a reference to SRP, Section 9.3.3, which, by our observation, has not been, implemented for the older plants.
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. 5-In May,1978, IE issited Circular No. 78-06, titled P0TENTIAL COMMON MODE FLOODING 0F ECCS EQUIPMENT ROOMS AT BWR FACILITIES. This circular resulted from a design review at Hatch 1, where the equipment drain system did not have !
isolation valves within the piping between the corner rooms. With this design, i in the event of a postulated pipe break of sufficient size to flood the sump pumps in any one room, the other ECCS corner rooms would also be subject to flooding via the equipment drain system. One of the recommendations of this circular was:
lhe specific design and installation for floor and equipment drains should be reviewed to verify that a flood in any one room or location would not result in flooding equipment in other ECCS equipment rooms or in areas at a lower elevation.
The circular was issued to all holders of reactor operating licenses and construction permits. No written response to this circular was necessary, so, it is not clear what action, if any, was taken by Calvert Cliffs at this time.
CONCLUSIONS From our study, we are led to the conclusion that the subject of potential damage to redundant safety equipment as a result of backfinw through the equipment and floor drain system has not been addressed for thi. older operating plants, i.e., units not designed to standards of SRP section 9.3.3. Both completed and existing safety improvement programs, as shown by an LER search, reviews of the SEP, SERs, and various generic topics, do not seem to address updating this subject to current licensing criteria. IE Circular No. 78-06, was too specialized to be relevant to the problem discovered at Calvert Cliffs. It covered ECCS equipment rooms in lieu of the more generalized. topic of safety-related compart-ments and flooding of areas at a lower elevation instead of backflow protection.
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