ML19309F061
| ML19309F061 | |
| Person / Time | |
|---|---|
| Site: | 05000550 |
| Issue date: | 04/21/1980 |
| From: | Quirk J GENERAL ELECTRIC CO. |
| To: | Teh-Chiun Su Office of Nuclear Reactor Regulation |
| References | |
| MFN-082-80, MFN-82-80, NUDOCS 8004280422 | |
| Download: ML19309F061 (13) | |
Text
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UbW G E N E R A L h. E L E CT R I C NUCLEAR POWER SYSTEMS DIVISION GENERAL ELECTRIC COMPANY,175 CURTNER AVE., SAN JOSE, CALIFORNIA 95125 MFN-082-80 1
April 21, 1980 U. S. Nuclear Regulatory Commission Division of Systems Safety Containment Systems Branch Washington, D. C. 20555 Attention:
T. M. Su
Dear Nelson:
SUBJECT:
Low-Low Set Relief Function Attached are excerpts from GESSAR II, submitted to the USNRC on bbrch 31, 1980 which define the Low-Low Set Relief function of the Nuclear Boiler System in the BWRG. The information is being provided in this supplementary letter in order to facilitate completion of the Staff's review on this subject.
The attached information is unchanged from that which was pre-sented to the Staff in a meeting in Bethesda, >bryland, February 8, 1980.
Sincerely, (Manager J.
. Quirk BWR Standardization l
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GESSAR II 238 NUCLEAR ISLAND Rev. 0 033180 5.2.2.2.3.1 Safety / Relief Valve Capacity (Continued) high flux scram is described in Figure 5.2-5.
Also shown in Figure 5.2-5 is the parametric relationship between peak vessel (bottom) pressure and safety / relief valve capacity for the generator load rejection with a coincident closure of the turbine bypass valves and direct scram, which is the most severe transient when direct scram is considered.
Pressures shown for flux scram will result only with multiple failure in the redundant direct scram system.
l The time response of the vessel pressure to the MSIV transient-with-flux scram and the generator load rejection with a coinci-dent closure of the turbine bypass valves and direct scram for 10 valves is illustrated in Figure 5.2-6.
This shows that the pressure at the vessel bottom exceeds 1250 psig for less than 5 seconds which is not long enough to transfer any appreciable amount of heat into the vessel metal which was at a temperature
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well below 550*F at the start of the transient.
5.2.2.2.3.2 Low-Low Set Relief Function In order to assure that no more than one relief valve reopens following a reactor isolation event, two Automatic Depressuriza-tion System (ADS) safety / relief valves and four non-ADS valves are providea with7cweropeningwdvlosing-setpoints.
These setpoints override the normal setpoints following the initial opening of the relief valves and act to hold open these valves longer, thus preventing reopening of more than one valve subse-quently.
This system logic is referred to as the low-low set j
relief logic and functions to ensure that the containment design basis of one safety / relief valve operating on subsequent actuations is met.
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22A7000 GESSAR II Rev. 0 238 NUCLEAR ISLAND 033180 5.2.2.2.3.2 Low-Low Set Relief Function (Continued)
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The results using the above assumptions are shown in the reactor Vessel pressure transient curve (Figure 5.2-8).
Despite the conservative input assumptions which tend to maximize the pres-sure peaks on subsequent actuations, there is a 65-psi margin for avoiding the second pop of more then one valve.
The system is single-failure proof since a failure of one of the low-low set valves still gives a 42-psi margin for avoiding multiple value actuations.
The safety / relief valves are balanced, spring-loaded, and pro-vided with an auxiliary power-actuated device which allows opening of the valve even when pressure is less than the safety-set pressure of the valve.
Previous undesirable performance on operating BWRs was associated principally with multiple stage These newer, power-operated pilot operated safety / relief valves.
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safety / relief valves employ significantly fewer moving parts wetted by the steam and are therefore considered an improvement over the ones previously used.
5.2.2.2.3.3 Pressure Drop in Inlet and Discharge Pressure drop on the piping from the reactor vessel to the valves is taken into account in calculating the maximum vessel pres-Pressure' drop in~~the~~ discharge ~ piping to the suppression sures.
pool is limited by proper discharge line sizing to prevent back-pressure on each SRV from exceeding 40 percent of the valvo inlet pressure, thus assuring choked flow in the valve orifice and no reduction of valve capacit3 due to the discharge piping.
Each SRV has its own separate discharge line.
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5.2-13 i
GESSAR II 22A7000 23R NUCLEAR ISLAND Rev. 0 033180 Table 5.2-2 NUCLEAR SYSTEM SAFETY / RELIEF VALVE SETPOINTS.
Set Pressures and Capacities ASME Rated Capacity at 103%
Relief Spring Spring Set Pressurd Low-Low Set Relief No.*
Set Pressure of Pressure (lb/hr Set Pressure No. of Setpoint Valves (psig) each)
(psig)
Valves Open/Close 8
1165 895,000 6
1180 9^6,000 5
1190 913,000 1103**
1 1033/926 1
1113**
1 1073/936 9
4 1113/946
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- Eight of the safety relief valves serve in the automatic depressurization function.
- Closing setpoint is 100 psi below opening setpoint 5.2-83
GESSAR II 22A7000 238 NUCLEAR ISLAND Rev. 0 033180
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iOO RELIEF VALVE OPENING CHARACTERtSTICS E
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OJ 11 Tihet immel 11 = Tie 8E AT VIMICH PRESSURE EXCEEDS THE VALVE SET PRESSURE Figure 5.2-7.
Power-Actuated and Safety-Action Valve Lift Characteristics 5.2-105
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,!!! %Il i 4 dii i \\\\\\\\$QO ii' i 'd' il'8 l!! I:"'!8 I'!'I! ill-d! i \\\\'\\\\$\\NW + 1 i i li f li t i l I i i i i l hi: ~ did W$ i 17 i i iiil! l'i'y i A I I i j r-' - j ~ Ei l l i gl I ' ' IU! I II.3I I l [sil!il!!!!!!iili !'sW!I !!iii n!!ir 'hil'i!,!!!' GESSAR II 22A7000 238 NUCLEAR ISLAND Rev. 0 033180 O's 7.3.1.1.1.2.C Aut '.natic Depressurization System Instrumentation and :ontrols (Cont inued) alarm setting is enough above normal rated power drywell ambient temperatures to avoid spurious alarms, yet low enough to give early indication of safety / relief valve leakage. c3 Setpoints Refer to Table 7.3-2 for instrument ranges and Chapter 16 for setpoints and margin. Discussions on instru-ment accuracy may be found in Topical Report NEDO-21617-A. 10. Parts of System Not Required for Safety The non-essential portions of the ADS include the annunciators and the computer. Other instrumentation considered f non-safety-related are those indicators which are provided for operator information, but are not essential to correct operator action. D. Pressure Relief Function of the Safety / Relief Valves The nuclear pressure relief system is designed to pre-vent overpressurization of the nuclear system that could lead to the failure of the reactor coolant pressure boundary. Details of ~ the design bases are discussec in Subsection 5.2.2. Pressure relief of the nuclear boiler system (Figure 7.3-3) is by power actuation of all the safety-relief valves (SRV), including the valves used in the automatic depressurization function. The safety-relief function (Figure 7.3-3) consists of redundant reactor pressure instrument channels arranged in sepa-rated logics that control separate soldnoid-operated air pilots on (}h each valve. These pilot valves control the pneumatic pressure \\- applied to an air cylinder operator. Accumulators are included 7.3-19 _ _ _ _ _ = _ _ - _ x,... e GESSAR II 22A7000 238 NUCLEAR ISLAND Rev. 0 033180 7.3.1.1.1.2.D Automatic Depressurization System Instrumentation ? and Controls (Continued) with the control equipment to store the pneumatic energy for relief valve operation. Each valve (including those with ADS function) has on'c accumulator. The safety / relief valves are initiated by reactor vessel pressure. Cables from the sensors for vessel pres-sure lead to two separate logic cabinets (ADS cabinets) where the redundant logics are formed. Separate station batteries power the electrica'l control circuitry. The power supplies for the redundant logics are separated to limit the effects of electrical failures. Electrical elements in the control system energize to cause the relief valves to open. The elementary diagram for the automatic depressurization system is shown in Figure 7A.3-2 and contains logic for the SRV actuation system. All power supplies, separation, etc., are identical to, and shared with ADS. 1. Initiating Circuits Reactor pressure is detected by four pressure trans-ducers (two for each division), which are located in the contain-ment. The logic requires a two-out-of-two trip on vessel pressure to prevent inadvertent SRV actuation. The logic is arranged such that no single failure will prevent SRV actuation or cause more tha_n one SRV to inadvertently actuate. 2. Logic and Sequencing Two initiation signals are used for SRV actuation. Two-out-of-two reactor vessel pressure is required to initiate the safety / relief valves. High vessel pressure indicates the need for SRV actuation to prevent nuclear steam overpressure. After receipt of the initiation signal, each of the two solenoid pilot air valves on each safety-relief valve is ener-g i z.ed. Either or both solenoid actuations' allow pneumatic pressure 7.3-20 GESSAR II 22A7000 238 NUCLEAR ISLAND Rev. 0 033180 O 7.3.1.1.1.2.D Automatic Depressurization System Instrumentation and Controls (Continued) from the accumulator to act on the air cylinder operator. The air cylinder operator holds the relief valve open. Lights in the main control room indicate when the solenoid-operated pilot valves are energized to open a safety / relief valve. The SRVs remain open until system pressure drops below the high pressure setpoint. Manual system level initiation of the SRVs is accom-plished by a control switch in the Division 1 portion of the main control room panel or by a control switch in the Division 2 portion of the main control room panel. Two redundant SRV trip systems are provided in two divisional cabinets. 3. Bypasses and Interlocks (Low-Low Setpoint Logic) To ensure that no more than one relief valve reopens following a reactor isolation event, a portion of the auto-matic depressurization system safety / relief valves and non-ADS valves is provided with switchover lower opening and closing set-points. These setpoints override the normal setpoints following the initial opening of the relief valves and act to hold open these ~ ' ~" valves longer, thus prevent'ing more Ehan a single valve from reopen-ing subsequently. This system logic is referred to as the low-low relief logic (LLS) and functions to ensure that the containment design basis of one safety / relief valve operating on subsequent actuations is met. This logic is armed from the existing pressure sensors of the second normal relief setpoint group. When reactor pressure reaches this level, low-lo.w set logic automatically seals itself into control of the selected valves and actuates the annun-ciator. This logic remains sealed in until manually reset by the gx operator. \\-) 7.3-21 l GESSAR II 22A7000 238 NUCLEAR ISLAND Rev. 0 033180 7.3.1.1.1.2.D Automatic Depressurization System Instrumentation l and Controls (Continued) Since the (LLS) valves will have already opened along with the others in their setpoint group, the low-low set logic' acts to hold them open past their normal reclose point until the pressure decreases to a predetermined " low-low" setpoint. Thus, these valves remain open longer than the other safety / relief valves. This extended relief capacity assures that no more than one valve will reopen a second time. Also, the seal-in logic prc-vides the first two low-low set valves with new reopening setpoints which are lower than their original S/R setpoints. These two valves provide redundancy in case of a single valve failure. The low-low set logic is designed with the same redundancy and single failure criteria as the safety-relief logic (i.e., no single electrical failure will: (1) prevent any low-low set valve f rom opening, (2) cause inadvertent seal-in of low-low set logic, or (3) cause more than one valve to inadvertently open or stick open). The valves associated with low-low set are arranged in three independent secondary setpoint groups or ranges (low, medium, and high). The " low" and " medium" pressure ranges consist of one valve each, having both " reopen" and "reclose" setpoints independently and uniquely adjustable. These are set considerably lower than their normal SRV setpoints. The remaining LLS valves are simultaneously controlled by the "high" range sensors which have an independently adjustable "reclose" setpoint. The normal SRV opening setpoint is retained for this valve group through reclose is extended in the low-low set operating mode. The sensors are arranged in two trains for each division. These conform to Safety Relief logics A and E for Divi-sion 1 and B and F for Division 2. The single-failure criterict. is maintained because two-out-of-two logic trains (per divisions l i l 7.3-22 GESSAR II 22A7000 238 N" CLEAR ISLAND Rev. 0 033180 ( 7.3.1.1.1.2.D Automatic Depressurization System Instrumentation and Controls (Continued) 1 1 are required to open the valves and one-out-of-two in each division acts to reclose them. The low range sensors which control the first valve are placed in logic E[F] and the medium range sensors ) which control the second valve are placed in logic A[B]. The highest pressure sensors, which are used for arming and sealing in low-low set logic, act on three or more valves simultaneously. Therefore, these are also arranged in redundant two-out-of-two (A E)+B F) logic to maintain " single failure proof" integrity. 4. Redundancy and Diversity The SRV logic is initiated by high reactor pressure. The initiating circuits and logic are designed with built-in redun-dancy explained in the circuit description of this section. No diversity is provided. 5. Actuated Devices All relief valves are actuated by three methods: a) Automatic action resulting from the logic chains in either Division 1 or Division 2 trip system actuating; b) Manual action by the operator; and c) Mechanical actuation as a result of high reac-tor pressure. 6. Separation SRV logic is a Division 1 and Division 2 system, } except that only one set of relief valves is supplied. Each relief valve can be actuated by either of two solenoid pilot valves 7.3-23 GESSAR II 22A7000 238 NUCLEAR IS LAND Rev. 0 0.1 11 A' 7.3.1.1.1.2.D Automatic Depressurization System Instrumentation ) and Controls (Continued) supplying air to the relief valve air piston operators. One of the solenoid pilot valves is operated by Logic A and the other is oper4ted by Logic B. Logic circuitry, manual controls and instru-mentation are mounted so that Division 1 and Division 2 separation is maintained. Separation from Divisions 3 and 4 is likewise maintained. 7. Testability The SRV system has two complete logics, one in Division 1 and one in Division 2. Either one can initiate depres-surization. Each logic has two trains, both of which must operate to actuate the SRV. The SRV instrument channels signals are tested by cross-comparison between the channels which bear a known rela-tionship to each other. Meters indicating for each instrument channel are mounted in the logic cabinets. The logics are tested by pre-programmed automatic pulse testing. The instrument channel setpoints may be verified by introducing a test signal to move the signal toward trip. The setpoint is verified by observing the meter and the indicator light on the output of the instrument chan-nel trip device. Testing does not interfere with automatic opera-tion if required by an initiation signal. 8. Environmental Considerations The solenoid valves and their cables and the safety / relief valve operators are the only control and instrumentation equipment for the SRV system located inside the drywell. Equipment located outside the drywell will also operate in their normal and accident environments. C 7.3-24 l ~ GESSAR II 22A7000 238 NUCLEAR ISLAND Rev. 0 033180
- 3 7.3.1.1.1.2.D Automatic Depressurization System Instrumentation
-) and Controls (Continued) 9. Operational Considerations The SRV instrumentation and controls are required for normal plant operations to prevent nuclear system overpressure. When depressurization is required, it will be initiated automati-cally by the circuits described in this section. A temperature element is installed on the safety-relief valve discharge piping several feet from the valve body. The temperature element is connected to a multipoint recorder in the control room to provide a means of detecting SRV leakage during plant operation. When the temperature in any safety / relief valve discharge pipeline exceeds a preset value, an alarm is sounded in the control room. The alarm setting is far enough above normal (rated power) drywell ambient temperatures to avoid spurious O alarms, yet low enough to give early indication of significant safety / relief valve leakage. 10. Parts of System Not Required for Safety The non-essential portions of the SRV function include the annunciators and the computer. Other instrumentation considered'non-safety related ars Ehose indicators which are pro-vided for operator information, but are not essential to correct operator action. 7.3.1.1.1.3 Low Pressure Core Spray Instrumentatisn..nd Controls A. System Identification The low pressure core spray (LPCS) system will supply gs sufficient cooling water to the reactor vessel to adequately cool the core following a design basis loss-of-coolant accident. 7.3-25 9