LR-N17-0034, Salem Generating Station, Units 1 & 2, Revision 29 to Updated Final Safety Analysis Report, Section 11.3, Gaseous Waste System
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11.3 GASEOUS WASTE SYSTEM The Gaseous Waste System (GWS) provides controlled handling and disposal of gaseous wastes generated during plant operation. The system also supplies hydrogen and nitrogen to primary systems' components as required during normal operation. The system is designed to minimize exposure to plant personnel and the general public, in accordance with Nuclear Regulatory Commission (NRC) regulations. In this section, the system is described and evaluated. 11.3.1 Design Objectives Design objectives for the GWS are the following: 1. To provide sufficient capacity and storage to process and store the volume of gaseous effluent expected for a period of 45 days 2. To provide cover gas for the liquid holdup tanks 3. To assure that releases of radioactive gaseous wastes are kept as low as practicable. 4. To maintain releases below the limits set by 10CFR20 5. To assure that exposures to the public are maintained below the design objective of lOCFRSO Appendix I The design criteria for the GWS are as follows: The facility design shall include those means necessary to maintain control over the plant radioactive gaseous effluents. Appropriate holdup capacity shall be provided for retention of gaseous effluents, particularly where unfavorable environmental conditions can be expected to require operational limitations upon the release of radioactive effluents to the environment. In all 11.3-1 SGS-UFSAR Revision 6 February 15, 1987 cases, the design for radioactivity control shall be justified 1) on the basis of 10CFR20 requirements, for both normal operations and for any transient situation that might reasonably be anticipated to occur and 2) on the basis of I 10CFR50, 67 dosage level limits for potential reactor accidents of exceedingly low probability of occurrence. Gaseous waste facilities are designed so that discharge of effluents are in accordance with applicable governmental regulations. Radioactive gases entering the GWS are collected in tanks to allow for decay and isotopic analysis. The system design and operation is directed toward minimizing releases to unrestricted areas. Discharge streams are appropriately monitored and safety features are incorporated to preclude releases in excess of the limits of 10CFR20. Radioactive gases are pumped by compressors through a manifold to one of the gas decay tanks where they are held for a suitable period of time to allow for decay. Cover gases in the Nitrogen Blanketing System can be reused to minimize gaseous wastes. intermittently at During normal operation, decayed gases are discharged a controlled rate from these tanks through the moni tared plant vent. The system is provided with discharge controls. 11.3.2 System Description During plant operations, gaseous wastes will originate from the following: 1. Degassing reactor coolant discharge to the Chemical and Volume Control System (CVCS) 2. Displacement of cover gases as liquids accumulate in various tanks 11.3-2 SGS-UFSAR Revision 23 October 17, 2007 * *
- 3. Miscellaneous equipment vents and relief valves 4. Sampling operations and automatic gas analysis for hydrogen and oxygen in cover gases. The GWS consists of two waste gas compressors and four waste decay tanks. During normal operation, the GWS supplies nitrogen to plant components. Two liquid nitrogen storage tanks, each with a self contained (ambient) vaporizer are supplied. One storage tank and its vaporizer is used at a tLme to supply the operating headers for both units. The pressure regulator in the operating header of each unit is set for 100 psig discharge. Each operating header is backed up by a nitrogen (gaseous) cylinder manifold with a pressure regulator set at 90 psig. When the operating header is below 100 psig, an alarm will alert the operator. The backup header will come into service automatically at 90 psig to assure a continuous supply of gas. After the operating header has been switched over to the standby liquid nitrogen storage tank, and the operating header pressure restored to 100 psig, the flow from the backup header will drop to zero. In addition to use as a backup nitrogen supply to the Waste Disposal System (WDS), the nitrogen (gaseous) cylinder manifold also supplies high pressure nitrogen gas for recharging accumulators. A hydrogen cylinder manifold is included in the Gaseous Waste Disposal System. It serves as a backup supply for hydrogen feed to the volume control tank. Normal feed is from the bulk hydrogen Control System. Most of the gas received by the WDS during normal operation is cover gas displaced from the eves holdup tanks as they fill with liquid. Since this gas must be replaced when the tanks are emptied during processing, facilities are provided to return gas from the decay tanks to the holdup tanks. A backup supply from the nitrogen header is provided for makeup if return flow from the gas decay tanks is not available. To avoid the possibility of hydrogen combustion in the vent header system while gas is being displaced from holdup tanks to the vent header, components discharging to the vent header system are restricted to those 11.3-3 SGS-UFSAR Revision 6 February 15, 1987 containing no air or aerated liquids and the vent header itself is designed to operate at a slight positive pressure (0.5 psig minimum to 4.0 psig maximum) to prevent in leakage. out leakage from the system is minimized with Saunders patent diaphragm valves, bellows seals, self-contained pressure regulators and soft-seated packless valves throughout the radioactive portions of the system. Gases vented to the vent header flow to the waste gas compressor suction header. One of the two compressors is in continuous operation with the second unit instrumented to act as backup for peak load conditions or failure of the first unit. From the compressors, gas flows to one of four gas decay tanks. The control arrangement on the gas decay tank inlet header allows the operator to place one tank in service and to select one tank for backup. When the tank in service becomes pressurized to 92 psig, a pressure transmitter automatically closes the inlet valve to that tank, opens the inlet valve to the backup tank and sounds an alarm to alert the operator so he may select a new backup tank. Pressure indicators are provided to aid the operator in selecting the backup tank. Gas held in the decay tanks can either be returned to the eves holdup tank or discharged to the atmosphere if it has decayed sufficiently for release. Generally, the last tank to receive gas will be the first tank emptied back to the holdup tanks which permits the maximum decay time before releasing gas to the environment. However, the header arrangement at the tank inlet gives the operator the option to fill, reuse or discharge gas to the environment simultaneously without restriction by operation of the other tanks. During degassing of the reactor coolant prior to a cold shutdown, for example, it may be desirable to pump the gas purged from the volume control tank into a particular gas decay tank and isolate that tank for decay rather than reuse the gas in it. This is done merely by aligning the control to open the inlet valve to the 11.3-4 SGS-UFSAR Revision 15 June 12, 1996 desired tank and closing the outlet valve to the reuse header. Simultaneously, one of the other tanks can be opened to the reuse header if desired, while another is discharged to atmosphere. Before a tank is discharged to the environment, it is sampled and analyzed to determine and record the activity to be released, and then discharged to the plant vent at a controlled rate, and monitored for gross activity. During operation, gas samples are drawn automatically from the gas decay tanks and automatically analyzed to determine their hydrogen and oxygen content. There should be no significant oxygen content in any of the tanks, and an alarm will warn the operator if any sample shows 2 percent or higher by volume of oxygen. This allows time to take required action before the combustible limits of hydrogen-oxygen mixtures are reached. Another tank is placed in service while the operator locates and eliminates the source of oxygen. The system is controlled from a central panel in the Auxiliary Buildings. Malfunction of the system is alarmed in the Auxiliary Building, and annunciated in the Control Room. Building. All system equipment is located in the Auxiliary The Unit 1 & Unit 2 auxiliary feedwater storage tanks are provided with a nitrogen purge/blanket system in order to control the dissolved oxygen concentration in the water. Each nitrogen purge/blanket system is provided with a dedicated nitrogen source. The GWS process flow diagrams are shown on Plant Drawings 205240 and 205340. 11.3-5 SGS-UFSAR Revision 27 November 25, 2013 11.3.3 system Design Gas Decay Tanks Four welded carbon steel tanks per unit are provided to contain waste gases (hydrogen, nitrogen, and fission gases). Each tank conforms to ASHE Boiler and Pressure Vessel Code Section III, Class c. Design data are as follows: 3 volume, each (ft } Design pressure (psig) Design temperature (°F) Operating pressure {psig) Operating temperature (°F) Type Waste Gas Compressors 525 150 180 0 -92 50 -150 Vertical cylinder There are two waste gas compressors per system to provide continuous removal of gases discharged to the vent header. Only one unit is normally in operation. The second unit is provided for backup during peak load conditions, such as when degassing the reactor coolant or for service when the first unit is down for maintenance. The compressors are water sealed, rotary, positive displacement units in which the water is used to displace and compress the gas being moved. Each compressor has a capacity of 40 cfm at 105 psig. The seal water is cooled, in a heat exchanger, by the component cooling water. Makeup water for the seal is supplied to the compressor suction from the Component Cooling System. Each compressor contains a mechanical seal to minimize leakage of seal water. The compressor discharges a mixture of waste gas and water into the separator. In the separator, the water is centrifuged out of the mixture and is accumulated in the bottom of the separator. 11.3-6 SGS-UFSAR Revision 15 June 12, 1996 The discharge from the separator is saturated at the discharge pressure and temperature of the gas. At 40 cfm, 105°F cooling water and 105 psig discharge, water vapor carryover is based on the following inlet conditions: Saturated N2 Saturated N2 65% by Volume N2 and 35% H2 65% by Volume N2 and 35% H2 Inlet Temperature Vapor Carryover 0.87 l.b/min 0.352 1b/min 0.019 lb/min 0.355 lb/min In order to assure that there will be sufficient pressure to circulate seal water at startup, the compressor discharge control valve on the separator is set to open at 50 psig. Proper water level in the separator is maintained by means of a liquid high level transmitter and a low level alarm and makeup switch. The liquid level transmitter actuates the high level drain valve. If the water level falls below the low level cutoff point, the low level switch opens the water makeup valve and water is introduced to the compressor through the inlet. Design data for the compressor are as follows: 11.3-7 SGS-UFSAR Revision 13 June 12, 1994 Compressor Number per unit Type Design flow rate, N2 (at 140°F, 2 psig) cfm Design pressure (psig) Design temperature (°F) Normal operating pressure (psig) Suction Discharge Normal operating temperature (°F) Compressor Motor H.P .. RPM volts Phase Cycle Rise Ambient temperature Dripproof Enclosure Class B Powerhouse insulation Nitrogen Manifold 2 Liquid piston rotary type 40 150 180 o.s -4.0 0 -92 70 -130 25 3500 460 3 60 90°C 40°C A supply header from the Liquid Nitrogen System supplies nitrogen gas to purge the vapor spaces of various components, to reduce hydrogen concentrations or replace fluid in emptying tanks. Pressure controllers ( I-PIA-1066) which. switch from the normal bulk supply to a backup gaseous cylinder header, assure a continuous flow of gas. Pressure regulator 1-PCV-1043 in the backup header is set at 90 psig which is lower than the 100 psig 11.3-8 SGS-UFSAR Revision 15 June 12, 1996 in the operating header. When the operating header supply from one bulk tank is exhausted, the discharge pressure of this header will fall below the setpoint pressure of the backup header. will come into service automatically. This system has the additional function of supplying N2 at 800 psi to the accumulator in the Safety Injection System. If the need ever arises, this pressurized gas will inject borated liquid from the accumulators into the reactor coolant loops. Design data for the manifold are as follows: Type Automatic switching dual header Number per unit 1 Number of separate headers per package 2 Number of cylinders per header 18 Design flow rate, scfm 40 Design delivery pressure, psig 100 Station Bulk Lpw Pressure Nitrogen Supply A station bulk low pressure {LP) nitrogen supply package has been added to the above system to provide additional capability. Two liquid nitrogen storage tanks, each with a self-contained vaporizer are supplied. One storage tank and its vaporizer are used at a time to supply the operating headers for both units. Design data are as follows: 11.3*9 SGS-UFSAR Revision 13 June 12. 1994 Type Argon Operating pressure (Max) Design pressure (Max) Design temperature Empty weight Hydrogen Manifold Vertical cylindrical, Double walled 55,866 scf 69,030 scf 67,470 scf 245 psig 249 psig 4,400 lbs A dual manifold serves as a backup to the Bulk Hydrogen System to supply hydrogen to the volume control tank and to maintain the hydrogen partial pressure as hydrogen dissolves in the reactor coolant. A pressure controller (1-PIA-1065) which automatically switches from the normal system to the backup system, assures a continuous supply of gas. The operation of the backup header is essentially the same as for the Nitrogen Manifold System. Design data are as follows: Type Automatic switching Number per unit 1 Number of separate headers per package 2 Number of cylinders per header 6 11.3-10 scs .. uFsAR dual header Revision 6 February 15, 1987 Design flow rate, scfm 30 Design delivery pressure, psig 100 Gas Analyzer Redundant gas analyzers, one in each Salem Unit and both cross-connected, are provided in accordance with the recommendations of NUREG-0472 to automatically monitor the concentrations of oxygen and hydrogen in the system, in order to indicate when the accumulation of these gases approaches an explosive mixture. Upon indication by alarm that the oxygen level is approaching a hazardous level, provisions must be made to either isolate the component or purge with nitrogen to the GWS. The gas analyzer has sui table connections for sampling when necessary from the following components: Waste gas to plant vent Reactor coolant drain tank Spent resin storage tank Gas decay tanks (2 points) eves holdup tanks Boric acid evaporator and gas stripper Volume control tank Pressure relief tank Gas decay tank samples are analyzed continuously to ensure that the oxygen concentration remains less than or equal to 2 percent. Separate feed lines with calibration gases are provided for analyzer calibration purposes. The 11.3-11 SGS-UFSAR Revision 20 May 6, 2003 I I high-span calibration gas is nominally 4% oxygen, and low-span calibration gas is nominally 1% oxygen. The balance of the calibration mixtures consists of nitrogen, except for small amounts of hydrogen {between 1% and 2.5%). mixture allows calibration of the analyzer to the profile expected The gas in the sample stream at alarm conditions. follows: Design data for the analyzers are as Oxygen Hydrogen Recorder printout (chart} By partial pressure measurement 0-5% o2 Range By partial pressure measurement 0-25% H2 Range Waste Gas Decay Tank: every 3 minutes Sequential sampling (cover gas): each point All major equipment in the Gaseous Radwaste D1sposal System is located outside of the Reactor Containment Building in the Auxiliary Building 1 Elevation 64 feet and 122 feet. Limiting Condition for Operation a) A minimum of one radioactive gaseous effluent oxygen monitoring instrumentation channel(s) shall be OPERABLE with their alarm/trip set points set to ensure that the limits of Technical Specification 3.11.2.5 are not exceeded during waste gas holdup system operation. b) With a radioactive gaseous effluent oxygen monitoring instrumentation channel alarm/trip set point less conservative than condition {a) above, declare the channel inoperable and continue operation of the waste gas holdup system provided that grab samples are collected at least once per 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> and analyzed within the following 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />. c) With less than the minimum number of radioactive gaseous effluent oxygen monitoring instrumentation channels OPERABLE, continue operation of the waste gas holdup system provided that grab samples are collected at least once per 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> and analyzed within the following 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />. Exert best efforts to return the instrument to OPERABLE status within 30 days and, if unsuccessful, develop an Action Plan, approved by the Operation Director, to return the channel(s) to OPERABLE. 11.3-12 SGS-UFSAR Revision 23 October 17, 2007
- Surveillance Requirements OPERABILITY of each radioactive gaseous effluent oxygen monitoring instrumentation channel during waste gas holdup system operation shall be demonstrated by the performance of: a) CHANNEL CHECK at least daily. b) CHANNEL CALIBRATION at least quarterly, including the use of standard gas samples containing a nominal: 1. One volume percent oxygen, balance nitrogen and 2. Four volume percent oxygen, balance nitrogen c) CHANNEL FUNCTION TEST at least monthly. Piping Gas piping is mainly carbon steel with stainless steel piping in some sections installed as part of modifications. Piping connections are welded except where flanged connections are necessary to facilitate equipment maintenance. Valves exposed to gases are either carbon steel or stainless steel. Isolation valves are provided to isolate each piece of equipment for maintenance, to direct the flow of waste through the system, and to isolate storage tanks for radioactive decay. Relief valves are provided for tanks containing radioa,_cti ve wastes if the tanks might be over-pressurized by improper operation or component malfunction. Codes and Standards Additional information is presented in Table 11.2-3 for system piping, valves and compressors. 11.3.4 Operating Procedures The gaseous wastes processed by this system consist primarily of hydrogen stripped from reactor coolant during boron recycle and degassing operations and nitrogen from the various tank _cover gases and from the, degassing qperation. These gases are discharged to the vent header which feeds the suction of the waste gas compressors. One of the two waste gas compressors will be operating with the other ,.J:..
- compressor being on standby. The operating compressor maintains a vent header pressure of 0.5 to 4.0 psig. If the vent header pressure rises to 4 psig, the standby compressor automatically energizes. The compressors can be used to: 1) pump gas to the waste decay tanks; 2) transfer gas between tanks; and 3) pump gas directly to the eves holdup tanks. 11.3-13 SGS-UFSAR Revision 23 October 17, 2007
'l'o pump gas to the gas decay tanks 1 the operator selects two tanks at the auxiliary control panel No. 104: one to receive gas, and one for standby. When the tank in-service is pressurized to 92 psig, flow is automatically switched to the standby tank and an alarm alerts the operator to select a new standby tank. The decay tank being filled is sampled automatically by the gas analyzer and an alarm will alert the operator to a high oxygen content. The tank must then be isolated and the operator is required to direct flow to the standby tank and select a new standby tank. As the liquid in the CVCS holdup tanks is processed by the boric acid evaporator, gas must be provided as cover gas to replace the processed liquid. The cover gas may be provided from any of the gas decay tanks or from the nitrogen supply. The gas decay tank supplying the returning cover gas is selected manually at the auxiliary control panel No. 104 by opening the appropriate valve in the return line header. To maximize total residence time for gas decay in the system, the last tank filled should be the first tank returned as cover gas. A backup supply of gas to the holdup tanks is provided from the bulk nitrogen header for makeup when return flow is not available from the decay tanks. Before a gas decay tank is discharged to the plant vent for release to atmosphere, a sample must be taken to determine activity concentration of the gas and total activity inventory in the tank. Total tank activity inventory is determined from the activity concentration and pressure in the tank. To release the gas, the appropriate local manual stop valve is opened to the plant vent and the gas discharge modulating valve is opened at the auxiliary control panel. If the Plant Vent Radiation Monitor detects high activity during release, the modulating valve automatically trips closed. To reopen the valve, the switch must first be reset by returning it to the closed posit ion. The valve can then be repositioned. The equipment which connects with the vent header system is limited in number. Under normal operating conditions no air is permitted to enter the vent header. During maintenance operations air could enter the boric acid evaporator vent condenser or the waste evaporator vent condenser. During maintenance operations on either of these pieces of equipment, the valve on the equipment discharge line to the vent header is closed. When maintenance operatj.ons are completed, and prior to opening the valves, the equipment is filled with nitrogen to purge the air. During discharge, the nitrogen purge is continued. No fluids can get into the vent header. 11.3-14 SGS-UFSAR Revision 23 October 17, 2007
- The maximum allowable release rate of gaseous radioactivity is specified in the Offsite Dose Calculation Manual. A record of all releases is kept. 11.3.5 Performance Tests Periodic inspection of waste gas compressors shall be done in accordance with the manufacturer's technical manual. 11.3.6 Estimated Releases HISTORICAL NOTE: The radiological release values originally contained in this section were calculated in support of initial licensing and have been deleted. Off-site releases during normal plant operations are controlled by the Radioactive Effluent Control Program. Several sources of potential release of gaseous radioactivity to the environment have been identified. Each is discussed separately below. Gas Decay Tanks Gaseous wastes consist primarily of hydrogen stripped from coolant discharged to the eves holdup tanks during boron dilution, nitrogen and hydrogen gases purged from the eves volume control when degassing the reactor coolant, and nitrogen from the closed gas blanketing system. The gas decay tank capacity will permit adequate time to allow for decay of waste gas activity release based on 1-percent defective fuel clad, and 34 23 MWt power with daily load reductions to 50-percent power for several hours. 11.3-15 SGS-UFSAR Revision 29 January 30, 2017 Containment Purging Purging of the containment will take place infrequently, on the order of two to three times a year per unit, to keep concentrations of radioactive gases in the containment within specified limits to allow plant personnel to enter the containment periodically for maintenance and inspection. Section 9.4 describes the methods employed to minimize release to the environment from containment purging. Diaphragm valves are used in the GWS vent header to eliminate steam leakage. All pipe connections in the vent headers are welded. Therefore, there will be no effect on the annual release of gaseous radioisotopes. 11.3.7 Release Points Release points are shown on the system flow diagrams (Plant Drawings 205240 and 205340). 11.3.8 Dilution Factors See Section 11.3.9. 11.3.9 Estimated Doses The radiological release doses originally contained in this section were calculated in support of initial licensing and have been deleted. Off-site doses during normal plant operations are controlled by the Radioactive Effluent Control Program and the ODCM. 11.3-16 SGS-UFSAR Revision 27 November 25, 2013