ML20247H454
| ML20247H454 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 09/14/1989 |
| From: | Michael Ray TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| RTR-REGGD-01.097, RTR-REGGD-1.097 NUDOCS 8909190344 | |
| Download: ML20247H454 (12) | |
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.s-TENNESSEE VALLEY AUTHORITY CH ATTANOOGA. TENNESSEE 37401 SN 1578 Lookout Place SEP 141189
.U.S. Nuclear Regulatory Commission ATTN:. Document Control Desk Washington, D.C.
20555 Gentlemen:
-In the Matter of
)
Docket Nos. 50-327 Tennessee Valley Authority
)
50-328 SEQUOYAH NUCLEAR PLANT (SQN) - RESPONSE TO NRC QUESTIONS CONCERNING SQN'S l
REGULATORY GUIDE (RG) 1,97 COMMITMENTS
References:
1.
TVA' letter to NRC dated March 15, 1982 2.
TVA letter to NRC dated December 28, 1988, "Sequoyah Nuclear Plant (SQN) - Regulatory Guide (RG) 1.97, Postaccident Monitoring (PAM) Instrumentation - Request for Additional Information" This letter provides additional information in response to 12 NRC questions regarding SQN's compliance with RG 1.97.
TVA's response to each question was discussed during a July 10, 1989, telephone conference call among NRC, SQN Nuclear Engineering, and SQN Site Licensing staffs.
TVA'is currently in the process of finalizing SQN's RG 1.97 program. Should additional NRC questions arise that would impact the acceptance of SQN's l
current program as outilned in this letter and the referenced letter, please I
notify SQN's Regulatory Licensing Staff so that any changes can be incorporated into SQN's program. TVA intends to submit SQN's finalized RG 1.97 program before the end of 1989. contains the additional information in response to 12 NRC questions regarding SQN's RG 1.97 program. contains a commitment associated with TVA's response to Question 4 from Enclosure 1.
Please direct questions concerning this issue to D. V. Goodin at l
(515) 843-7734.
Very truly yours, TENNESSEE VALLEY AUTHORITY Managbr, Nuclear Licensing and Regulatory Affairs Enclosures cc: See page 2 8909190344 890914
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- DR ADOCK 0500 7
An Equal opportunity Employer
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~ SEP 141989 U.S. Nuclear Regulatory Commission cc (Enclosures):
Ms. S. C. Black, Assistant Director for Projects TVA Projects Division U.S. Nuclear Regulatory Commission One White Flint, North 11555 Rockville. Pike-
'Rockville, Maryland. 20852 h
Mr. B. A. Wilson,. Assistant Director for Inspection Programs TVA Projects Division.
U.S. Nuclear Regulatory Commission Region II 101 Marietta Street. NW, Suite 2900 Atlanta, Georgia 30323 i
NRC Resident Inspector Sequoyah Nuclear Plant 2600 Igou Ferry Road Soddy Daisy, Tennessee 37379 e
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ENCLOSURE 1 1.
NRC Ouestion - Recording of Catenory 1 Variables The licensee did not discuss the recording of Category 1 variables. We are unable to conclude that recording is provided to meet the recommendations of Regulatory Cuide (RG) 1.97 for each Category 1 variable. The licensee should verify that recording is provided for each Category 1 variable.
Should any Category 1 variable not presently be recorded, the licensee should cor.mit to provide recording capability for that variable.
TVA Response Category 1 analog variables will be recorded by the Technical Support Center (TSC) computer.
In addition to the TSC computer, the following Category 1 variables will also be monitored by nondivisional trend recorders to increase reliability:
Reactor Coctant System (RCS) Hot Leg Water Temperature RCS Cold Leg Water Temperature RCS Pressure l
Steam Generator (SG) Pressure Pressurizer Level SG Level (Wide Range)
Neutron Flux Core Exit Temperature The TSC computer and nondivisional trend recorders will be qualified to meet Category 2 requirements and will be isolated from the Class IE instrument loops associated with Category 1 variables by qualified isolators. TVA does not consider the trend recorders or the trending function performed by the TSC computer to be critical for accident mitigation, and therefore, Category 1 qualification is unnecessary.
However, TVA acknowledges that the trending equipment will enhance the operator's ability to cope with mitigating various design basis accidents, and for this reason, the trending equipment was appropriately qualified to Category 2 requirements.
Note:
Category 1 variables will be monitored in the main control room by redundant Class IE indicators.
The TSC computer is designed to meet the following minimum trending requirements for Category 1 variables:
1.
Automatic trending from the start of the accident.
2.
Sampling rate will be sufficiently small to ensure adequate data resolution for accident transients.
3.
Sufficient data storage capacity.
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-3 2.
NRC Cuestion - Containment Sump Water Level - Waerow Range The licensee has not identified the range of the containment sump water level instrumentation. The licensee should identify the range of this instrumentation in accordance with the requirements of Supplement No. 1 of NUREG-0737, Section 6.2, or install containment cump water level instrument ation with a range that is in accordance with the criteria of RG 1.97.
TVA Response RG 1.97 recommends that instrumentation be provided to monitor the water level in the containment sump.
SQN does not have any narrow-range level instrumentation located in the containment sump. However, level instrumentation is provided by the reactor building floor and equipment drain sump and the reactor building auxiliaty floor and equipment drain sump. These sumps are located outside the crane wall inside lower containment at the same elevation (679.78) as the containment sump used for recirculation.
The reactor building floor and equipment drain sump is designed to collect RCS leakage that originates outside the crane wall. The sump is 77 inches deep. The level instrumentation associated with the reactor building floor and equipment drain sump is designed to provide both high-and low-level alarms in the main control room (MCR) (LA-77-125A and B and LA-77-126k and B).
The actual level is measured by LT-77-125 and 126, which have spans of 0 to 64 inches, and the level is monitored in the MCR l
by the plant process computer.
The reactor building auxiliary floor and equipment drain sump (also known as the pocket sump) is located within the reactor building floor and equipment drain sump and is designed to collect RCS leakage that originated inside the crane wall. This sump is provided with two MCR level indicators (L1-77-410 and 411).
The actual level is measured by LT-77-410 and 411, which have spans of 0 to 37 inches. This sump has a high-level alarm to alert the operator to start the reactor building auxiliary floor and equipment sump pumps. The sump contents are pumped to the reactor building floor and equipment drain sump, and the control logic automatically stops the pumps on low level.
TVA believes that the level instrumentation associated with the reactor building floor and equipment drain sump and the reactor building auxiliary floor and equipment drain semp provides level instrumentation to meet the intent of RG 1.97 for narrow-range Invel of the containment sump. These level instruments were o:rginally installed to detect RCS leakage.
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NRC Ouestion - Radiation Exposure Rate l
The licensee did not provide any information concerning radiation exposure rate instrumentation. The licensee should provide the radiation exposure rate instrumentation information required by Section 6.2 of Supplement No. 1 of NUREG-0737.
TVA Response RG 1.97, Revision 2, includes exposure rate monitors as Type E (Category 2) variables. These monitors are required to have a range of 10-1 Rem per hour (R/hr) to 104 R/hr and are to be located inside buildings or areas where access is required to service equipment important to safety. The area monitors are intended for use in detection l
of significant releases, release assessment, and long-term surveillance.
1 RG 1.97, Revision 2, also included radiation exposure rate monitors with ranges of 10-1 R/hr to 104 R/hr as Type C variables (these monitors were to be installed inside buildings or areas in direct contact with primary containment where penetrations and hatches were located). This variable was removed from RG 1.97 in Revision 3 and will not be addressed further.
monitoring instrumentation does not include installed high-range exposure rate monitors as Type E variables. The intended objectives of such instrumentation will be achieved in a different manner than that described in RG 1.97.
The following paragraphs describe how SQN's program is designed to monitor radiation exposure rates.
l A large number of useful missions outside the MCR during accident j
conditione may be postulated. These missions would be for activities, such as equipment maintenance, grab sample acquisition, and laboratory analyses of grab samples, that might enhance accident mitigation.
Exposure rates encountered on these missions would vary over a wide range. This variability arises from the fact that most high exposure cates outside the containment during accident conditions would be attributable to contained sources and, therefore, be strong functions of q
distance from the sources.
Because of the wide exposure rate
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variability, the installation of even a large number of high-range j
exposure rate monitoring instruments at selected locations on projected i
mission routes might not contribute substantially either to the planning of missions for accident mitigation purposes or to the minimization of dose equivalent to personnel performing the missions.
Based on the above considerations, the SQN radiation monitoring system design uses portable high-range exposure rate instruments in lieu of installed high-range exposure rate monitors. Crews attempting missions outside the MCR following an accident would include Radiological Control personnel provided with high-range exposure rate instrumentation. As listed in TVA's December 1988 submittal, the range of the Type E portable j
instrumentation available for this purpose is 10-3 R/hr to 104 R/hr, which is consistent with the range required for area exposure rate monitoring.
Additionally, the TVA radiation monitoring system presently includes 28 normal-range area monitors, each with a range from 10-1 MR/hr to 104 HR/hr.
These monitors are located throughout the plant in areas where personnel access is common. Although the area monitors are not required to be within the scope of the environmental qualification program and they are not included in the postaccident monitoring (pAM) program, monitors located outside the primary containment and other locations of high postaccident exposure rates can be expected to remain on scale and to continue to provide exposure rate indication with required accuracy during accident conditions. The monitors that remain on scale will provide useful input to MCR personnel for assessment of plant exposure rate levels during accident conditions. This assessment would be a factor in a decision as to whether or not missions outside the MCR would be attempted.
In summary, the SQN position on high-range accident monitoring is that high-range exposure rate instrumentation will not be installed and that high-range monitoring will be provided by portable monitoring instrumentation that meets the RG 1.97 required range.
4.
NRC Ouestion - Boric Acid Charning Flow The licensee has provided boric acid charging flow instrumentation with a range of 0 to 150 gallons per minute (gal / min). The boric acid charging pumps each with a flow of 75 gal / min operate in parallel. The licensco states that the flow is less than 150 gal / min because of, pump characteristics and system head losses. The licensee has not shown that when the instrument system inaccuracies are accounted for, the boric acid charging flow readout will remain on scale for full flow and not confuse the operator should the instrumentation fail high. The licensee should document that this instrumentation will remain on scale and readable under all system operating conditions.
TVA Response The boric acid transfer pumps are identical, two per unit (100 percent redundant) centrifugal type, two-speed pumps, with constantly rising head (to shutoff) characteristic curves, rated at 75 gal / min at 235 feet. One pump of each pair is aligned with one boric acid tank and runs continuously at low speed to provide recirculation through the boron injection tank and the boric acid tank.
The second pump serves as a standby pump and is aligned with the third boric acid tank (shared tank between the units) also recirculating boric acid solution through the third tank.
Normal operation of the reactor makeup control activates the
running pump to high speed to provide boric acid solution as required.
If emergency boration is required, manual actuation of the running pump or the standby pump will be required.
The normal and emergency boration flow from the boric acid transfer pumps discharges into the suction header of the charging pumps.
If the standby pump is desired, the operator must locally align the valving to put the pump in line.
If the operator decides to use both boric acid transfer pumps, discharge flow will be administrate.ively controlled to well within the capability of the installed flow indication instrumentation. contains TVA's commitment for implementing administrative control of emergency boration
-flow rates.
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NRC Ouestion - SG Level - Wide Ranne The instrumentation provided by the licensee does not meet the seismic qualification and class 1E power supply criteria of RG 1.97.
Also, the licensee has stated that this instrumentation is required by Function Restoration Guideline procedure FR-H.S.,
The licensee has identified SG 1evel narrow range as the Type A variable to perform this function. This appears to be an inconsistency. The licensee should upgrade the SG level wide-range instrumentation to meet the Category 1 criteria of RG 1.97 and declare the appropriate Type A variables.
TVA Response SG wide-range level instrumentation will be upgraded to Type A, Category 1 criteria. One level channel per SG will be provided (four channels total).
TVA's finalized program submittal will reflect this change.
6.
WRC Ouestion - Auxiliary Feedwater (AFW) Flow The licensee has identified AFW flow as a Type A variable. However, the licensee has not identified the number of channels per SG or redundancy in power supplies. The licensee states that, for a SG tube rupture, AFW valve position and narrow-range SG 1evel can be used to identify and isolate a faulted SG instead of AFW flow instrumentation. The licensee should provide additional documentation in support of the use of SGs as heat sinks by using a combination of level and AFW flow instrumentation.
TVA Response In accordance with RG 1.97, Section 1.3.1.8, "Within each redundant division of a safety system, redundant monitoring channels are not needed except for SG level instrumentation in two-loop plants." SQN is a four-loop plant, and the design basis for the AFW system is that the system must be capable of providing 440 gal / min to two SGs for a loss of primary or secondary coolant accident.
In other words, the plant's only requirement is that two loops be available for accident mitigation.
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. If a secondary line break were to occur on one SG loop and a single failure of an AFW flow channel is assumed to occur on another loop, SQN will still have two fully functional loops available for cooldown.
In reality, however, three loops are intact and available for heat removal.
The only event that would require redundant flow instruments on each SG loop is an SG tube rupture (SGTR) event. However, for this event TVA elected to use diverse methods of detecting a faulted SG.
Method 1 consists of monitoring SG level for increasing icvel with no AFW flow.
This method is adequate because, if the operator is initially unaware of an SGTR event, it will become apparent once he acknowledges a high SG level alarm on the affected SG.
Under these conditions, the AFW level control valves for the affected SG will automatically throttle close; and the operator can only conclude that, with no AFW flow and increasing SG level, an SGTR event must have occurred. Method 2 relles on AFW valve position in lieu of AFW flow to detect the faulted SG.
The operator will verify that flow to the suspected SG is isolated and then will observe the SG.
The power supplies for the SG level indicators and the AFW valve position indicators will be arranged so that no single failure will result in the loss of both SG level indication and AFW valve position indication for any SG loop.
These diverse methods provide the redundance needed to detect an SGTR event.
7.
NRC Question - Condensate Storage Tank Water Level The licensee has not provided Category 1 instrumentation to monitor the condensate storage tank (CST) water level. The licensee has provided Cater 9ry 2 instrumentation for this variable, with no justification for this 8 viation.
Should another water source be the primary source of AFW, it should be identified and verified to be monitored by Category 1 instrumentation. The licensee should document the primary source of AFW.
The licensee should provide documentation that verifies that the primary source of AFW is monitored by Category 1 instrumentation.
TVA Response The safety-grade source of AFW for SQN is the essential raw cooling water (ERCW) system.
The status of this supply of water is provided by the ERCW to AFW valve position, rather than CST level, and will be monitored by existing Category 1 instruments. The valve position status will also be monitored by the TSC computer.
TVA's finalized program submittal will include this clarification for CST water level.
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8.
NRC Ouestion - Hinh-Level Radioactive Liquid Tank Level RG 1.97 recommends Category 3 control room instrumentation to monitor the high-level radioactive liquid tank level. The licensee has provided instrumentation located in the auxiliary building. An alarm is also provided; however, its location and function are not mentioned. The l
licensee should provide justification for this deviation from the recommendations of RG 1.97.
TVA Response The "High-Level Radioactive Liquid Tank Level" variable is monitored locally by measuring the level in the tritiated drain collector tank (TDCT), which is used to collect drains from containment.
The drains from containment are automatically isolated on a containment isolation signal or a high radiation signal.from the process radiation monitoring system.
In the event of an accident, the containment isolation valves controlling the drains from containment can only be opened after the operator has reset the containment isolation signal and manually opens the containment isolation valves from the MCR.
If the drains were isolated because of high radiation, the valves can only bo opened if the operator manually blocks the high radiation signal.
Since the drains will be automatically isolated under accident or high radiation and
. deliberate operator action must be taken to reopen the isolation valves, the potential for overfilling the TDCT is very unlikely. Because of these dcsign features, MCR level indication for PAM purposes is deemed unnecessary.
9.
NRC Question - Radioactive Gas Holdup Tank Pressure RG 1.97 recommends Category 3 control room instrumentation to monitor the radioactive gas holdup tank pressure. The licensee has provided instrumentation located in the auxiliary building. An alarm is also provided; however, its location and function are not mentioned. The licensee should provide justification for this deviation from the recommendations of RG 1.97.
l TVA Response The gaseous waste processing system consists of a collection header into which various sources of waste gas discharge. Two waste gas compressors (100 percent redundant units) pressurize the waste gas, and a series of tanks (nine tanks total) stores the pressurized gas for decay.
The components or systems that nay vent to the collection header are:
degassing of the reactor coolant and purging of the volume control tank prior to cold shutdown, displacing of cover gases caused by liquid accumulation in the tanks connected to the vent header, purging of some equipment, sampling and gas analyzer operation, and boron recycle operation.
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_8 The equipment serves both units.
One compressor starts automatically when the pressure increases to 2 psis in the header; the other compressor is on standby.
All gas sources to the waste gas collection header are controlled from the MCR.
The waste gas compressor discharges through,a self-contained pressure regulator and an individual gas decay tank pressure isolation valve. Two tanks are selected by the radwaste operator in the local waste processing panel to store gas:
one is selected for receiving gas and the other for standby; when the tank in service is pressurized to 100 psig, the flow is automatically switched to the standby tank, and an alarm on the local control panel alerts the radwaste operator to select a new standby tank.
MCR indication for PAM purposes is not necessary because:
(a) Each tank is equipped with a safety valve for overpressure protection.
(b) All gas sources to t.he waste collection header are controlled from the MCR.
(c) Local operat ion is required to fill the tanks.
Indication and control of this system are provided on local panels.
10.
NRC Ouestion - Accident Sampling RG 1.97 recommends sampling and onsite analysis capability for RCS, containment sump, emergency core cooling system pump room sprays, other auxiliary. building sump liquids, and containment air. The licensee has not provided the information required by Section 6.2 of Supplement 1 of NUREG-0737. The licensee should provide the required information, identify any deviation from RG 1.97, and provide supporting justification or alternatives for those deviations.
TVA Response NRC has previously approved TVA's postaccident sampling system capability in Supplements 2 and 5 to the safety evaluation report for SQN.
NRC authorized operation of SQN's installed postaccident sampling system and provided the associated safety evaluation by letter dated April 24, 1984.
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NRC Ouestion - Airborne Radiohalonens and Particulate (Portable Sampling with Onsite Analysis capability)
TVA's 1982 submittal did not address airborne radiohalogens and particulate.
TVA should provide information indicating how TVA's PAM program complies with RG 1.97 requirements for these variables.
TVA Response These variables are in TVA's 1988 submittal (see Reference 2) and were inadvertently omitted from TVA's 1982 submittal. TVA's 1988 submittal supercedes the 1982 submittal.
TVA will comply with the range and category classification as specified in RG 1.97 Since detailed implementation of these variables is in the development stage, TVA's finalized program submittal will contain a description of how TVA's PAM program complies with RG 1.97 requirements for these variables.
12.
NRC Ouestion - Plant and Environs Radioactivity (Portable Instrumentation)
TVA's 1982 submittal did not address plant and environs radioactivity.
I TVA shoul< provide information indicating how TVA's PAM program complies with RG 1.97 requirements for these variables.
TVA Response These variables are in TVA's 1988 submittal (see Reference 2) and were inadvertently omitted from TVA's 1982 submittal.
TVA's 1988 submittal supercedes the 1982 submittal.
TVA will comply with the range and category classification as specified in RG 1.97.
Since detailed implementation of these variables is in the development stage, TVA's finalized program submittal will contain a description of how TVA's PAM progrem complies with RG 1.97 requirements for these variables.
l ENCLOSURE 2 l contains 12 WRC questions regarding SQN's compliance with RG 1.97, "Postaccident Monitoring Instrumentation." NRC, by question 4 requested that TVA ensure that boric acid flew instrumentation remains on scale for full flow and not confuse the operator should the instrumentation fail high. The following provides TVA's commitment for administratively controlling boric acid flow to ensure that this instrumentation remains on scale and readable under all system operating conditions.
TVA will revise Abnormal Operating Instruction 34, " Emergency Boration," and Emergency Instruction ES-0.1, " Reactor Trip Response," to ensure that the
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operator limits emergency boration flow rate to less than full scale (150 gal / min).
These procedures will be revised by December 1, 1989.
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