JustinConrad_NUC350_M3A3

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M3A3: Loss of Reactor Coolant Accident Introduction: This activity is designed to reinforce the module reading material by allowing you to observe and analyze both a PWR and BWR simulator response to loss of reactor coolant accident. Your observation and associated analysis exercise will be focused on the emergency safeguards equipment designed to mitigate such an accident. Instructions: Prior to attempting this lesson, ensure that you have completed the module reading assignments pertaining to both the BWR and PWR Emergency Core Cooling Systems This form includes supplemental reading material, instructions for the simulator lesson, and provides space to complete assignment requirements. You will complete the assignment by submitting this form for grading via the M3A3 assignment folder. Requirements for M3A3: o Lesson Part B: Step 7 o Lesson Part C: Step 12 Lesson Part A: Supplemental Reading Pressurized Water Reactor Simulator: Engineered Safety Feature Systems-Reactor Coolant Injection The following reading material provides a description of the Reactor Coolant Injection systems and components that are modeled on the Pressurized Water Reactor student simulator. You should complete this reading prior to moving on to Part B of the simulator lesson. Engineered Safety Feature Systems-Reactor Coolant Injection High-Pressure Coolant Injection System (HPCIS) Overview The HPCIS consists of two distinct injection systems, the Boron Injection System (BIS) and the Safety Injection System (SIS). The high-pressure coolant injection system plays an integral role in meeting the emergency core cooling and shutdown requirements. Emergency core cooling delivers borated water to the reactor coolant system (RCS) in the event of the following type accident conditions: Loss-of-coolant accident (LOCA), including a pipe break or spurious relief or safety valve lifting in the RCS which cause a discharge larger than that which can be made up by the normal makeup system, up to the largest pipe in the RCS. Rupture of a control rod drive mechanism causing a rod cluster control assembly ejection accident.
Pipe breaks and spurious relief or safety valve lifting in the secondary system, up to and including the instantaneous circumferential rupture of the largest pipe in the secondary system. A steam generator tube failure. The high-pressure coolant injection system is primarily used for a small RCS break, steam generator tube failure, secondary system breaks, or transients where the RCS pressure remains high for an extended period of time. System Description The Boron Injection System (BIS) consists of an injection tank and associated piping, valves, and instrumentation. The driving forces used to sweep the borated water from the Boron Injection Tank (BIT) into the reactor coolant system are the centrifugal charging pumps in the Chemical and Volume Control System (CVCS). The BIS is initially filled with a solution of boric acid from the Refueling Water Storage Tank (RWST). A sparger is inserted at the BIT inlet so that incoming fluid will not pass through without mixing with and forcing out the boric acid in the tank. There are two parallel normally closed, motor-operated gate valves at the entrance and exit of the BIT which isolate it from the Centrifugal Charging Pumps (CCP) and RCS during normal operation. These valves are interlocked to open on a Safety Injection (SI) signal. The BIS supplies a boric acid solution to provide negative reactivity to totally counteract the positive reactivity due to the cooldown of the RCS following a main steam line break. The Safety Injection System (SIS) consists of two safety injection pumps, mini-flow orifices, associated piping, valves, and instrumentation to take suction from either the RWST or the Residual Heat Removal (RHR) pump discharge and deliver to either the RCS cold legs or the RCS hot legs. The safety injection pumps have the capability of supplying borated water to all cold leg injection headers of the RCS during the injection process. The safety injection pumps are driven by electric motors powered by the Class 1E emergency buses. Each pump is designed to provide adequate flow at its specified discharge pressure such that, in conjunction with the remaining ECCS pumps, sufficient flow is available to maintain the core in a coolable geometry following a LOCA or a main steam line break. The following screen simulator screen depicts the High Pressure Coolant Injection system and its components. This screen will be valuable to you in completing the lesson assignment.
Accumulator Safety Injection System (ASIS) Overview The accumulator safety injection system (ASIS) plays an integral role in meeting the emergency core cooling requirements. The system consists of four accumulator tanks and associated piping, valves, and instrumentation required for operation control. The specific function of the ASIS is to deliver borated water from the accumulator tanks to the RCS cold legs during loss of coolant injection. When the RCS pressure falls below the gas pressure within the accumulator tanks, injection by the accumulator injection system will automatically begin. Description The ASIS system is designed to operate in case of an intermediate or larger break in the RCS where the pressure in the RCS drops below the nitrogen cover gas pressure in the tank. The accumulator tanks are located within containment. In the worst of these cases, rapid depressurization of the RCS occurs and the reactor core is completely uncovered. The system is completely passive and rapid injection of the contents of the tanks occurs as soon as the RCS pressure drops below the cover gas pressure. Each of the four accumulator tanks discharges its water containing 2300-2500 ppm Boron through a separate line into the associated RCS cold leg. Each of the discharge lines contains two check valves and one normally open motor-operated valve. The minimum volume in each tank is such that only the contents of three tanks are necessary to provide sufficient liquid to initiate refill of the reactor vessel and recovery of the core following a large RCS break. The core is completely recovered in a short time with the sequenced flow delivered from the boron injection system, high head safety injection system, and the residual heat removal system in conjunction with the accumulator safety injection system . The accumulator tank pressure is provided by a supply of nitrogen gas located outside the reactor building. The nitrogen gas pressure can be adjusted during normal operation; however, the
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accumulators and the reactor building are normally isolated from the nitrogen supply. Each accumulator tank is supplied with a relief valve to protect against over pressurization. The accumulator safety injection system requires no actuation signal or emergency power to operate after a LOCA. When the RCS pressure drops below the nitrogen cover gas pressure of approximately 46kg/cm2 (650 psig), accumulator injection begins. The nitrogen pressure will force the borated water in the accumulator tanks into the RCS rapidly, to initiate refilling of the reactor vessel. Major Components Accumulator Tanks (4) High Pressure Discharge Line Tank Connection Lines The following screen simulator screen depicts the Accumulator Safety Injection System and its components. This screen will be valuable to you in completing the lesson assignment. Residual Heat Removal System (RHR) Overview The RHR system consists of two separate trains of equal capacity, each independently capable of meeting the safety design bases. The residual heat removal system (RHRS) plays an integral role in meeting the emergency core cooling and shutdown requirements. The specific functions of the RHRS are to provide low head safety injection to the cold legs of the reactor coolant system and long term heat removal following a loss-of-coolant accident (LOCA). Additionally, the RHR system is utilized to remove decay heat and sensible heat from the core and RCS during planned plant cooldown and refueling
operations. A secondary function of the RHRS is to transfer refueling water between the refueling water storage tank (RWST) and the refueling cavity as required for refueling operations. Description Each RHR train includes one pump, one heat exchanger and the associated piping, valves, and instrumentation required for operational control. For normal plant planned cooldown and refueling operations, the RHR system is placed in operation approximately four hours after reactor shutdown is initiated. The RHR system reduces the temperature of the reactor coolant to 60°C (140°F) within the design basis of 20 hours following reactor shutdown. During normal plant operation, when the plant is at power, the RHR system is aligned to automatically respond upon receipt of a safety injection (SI) signal. Following an accident, the pumps take water from the RWST and inject it into the reactor vessel via the safety injection system cold leg injection header, once the RCS pressure drops below that of the RHR pump shutoff head . When RWST Lo-Lo level setpoint is reached, the suction source of water for the RHR pump is automatically switched to the containment recirculation sump. To assure the RHR pumps do not overheat or vibrate while RCS pressure remains above the RHR pump shutoff head pressure in a post-Design Basis Accident (DBA) scenario, a mini-flow return line is provided from the downstream side of each RHR heat exchanger to the pump suction lines. A motor- operated gate valve located in each miniflow line automatically assures that the RHR pump discharge flow is greater than the pump minimum flow requirements. An orifice is provided in each miniflow line to restrict the flow returning to the pump suction. Major Components RHR Pumps- The two pumps are vertical, single-stage, centrifugal units with mechanical seals to prevent reactor coolant leakage to the atmosphere. RHR Pump Motors-The pump motors are 373 Kw (500 horsepower), 1500 RPM with a 5 sec start time, powered by Class 1E emergency buses. RHR Heat Exchangers- The heat exchangers are of the shell and U-tube type. The tubes are seal welded to the tube sheet. RHR Heat Isolation Valve Encapsulation Tanks- The tanks are made of austenitic stainless steel and have a capacity of approximately 5.8 m3 (1542 gallons). The following screen simulator screen depicts the Residual Heat Removal System and its components. This screen will be valuable to you in completing the lesson assignment.
(Material obtained from: Keymaster, Generic PWR Simulator, Training Guide, April 2016, Western Services Corporation, Frederick, Maryland.) Lesson Part B: Loss of Reactor Coolant Accident-Pressurized Water Reactor Introduction: In this activity you will observe the changing conditions in the Reactor Coolant System, as well as the response of the Engineered Safety Feature Injection Systems, include the High-Pressure Coolant Injection System (HPCIS), Accumulator Safety Injection System (ASIS), and the Residual Heat Removal System (RHR). For the purpose of this lesson, you will be focusing only on reactor coolant system parameters and the Engineered Safety Feature Injection Systems. Step 1 Log onto the student simulator at http://3keystudent.ws-corp.com/
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Step 2 On the “Welcome to Generic PWR Simulator” screen click on the “Generic PWR” yellow box. (The simulator should open and an “Lesson Selection” box will appear.) Step 3 In the “Lesson Selection” box you should see a drag down box titled “Lesson”. Click on the “down arrow” to open up the list of available lessons. Next, click on Module 3: Medium Break LOCA
Step 4 In “Lesson Selection” box click on “Enter”. (The lesson should now load. This may take a few moments. When the lesson loads an “Overview Page” screen will appear.) Step 5 An “ITS” window should now appear in front of the Overview Page. NOTE: This lesson requires you to observe the response of Reactor Coolant System parameters as well as the response of the Engineered Safety Feature Injection Systems. You may find it easier to run the lesson a few times in order to obtain the necessary information to complete the lesson. You are allowed to run the lesson as many times as needed.
Step 6 On the “ITS Panel” screen click on green arrow to start the lesson. The loss of coolant accident will commence 60 seconds after you click “Run” Step 7 Assignment Requirement Utilizing the data available on the simulator “Overview” screen, answer the following questions: 1. Describe the trend and overall change in Reactor Coolant System water inventory (Pressurizer Level and Reactor Vessel Level). For the rupture I saw a loss in level of about 12 inches per minute and was fairly constant. ` 2. Describe the trend and overall change in Reactor Coolant System pressure. The pressure loss was not as sever due to the pressurizer acting as a surge volume and pressurizer heater turned on which helped fight against the pressure loss. Once the pressurizer emptied there was a sudden drop in pressure due to the lack of no make up water, but pressure stabilized due to a bubble formation in the core and the addition of the High-Pressure Coolant Injection system. 3. Describe the response of the High-Pressure Coolant Injection System (HPCIS),
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Accumulator Safety Injection System (ASIS), and the Residual Heat Removal System (RHR) and associated components. Your description should include when and why equipment actuated and whether or not the specific systems injected coolant and why? The HPCIS actuated around the 5:32 with pressure reading approximately 1750 psig mark due to low level and high temperature as well as the RHR system to start removing heat with the regenerative heat exchangers. Make up water was not added through HPCIS due to the maximum pressure to inject water is 1500 psig. Boron was injection was successfully commenced via the boron injection tank by the CCP into the cold legs of the reactor loop indicated by boron concentration increasing. At this time the ASIS remained in standby due to the accumulators charge of 600 psig and unable to overcome primary pressure. At 21:45 primary pressure dropped to 1544 psig which is significant since the HPCIS was able to overcome primary pressure and inject cooling water into the primary, but primary pressure continued to drop. At 1500 psig the simulator kicked me out in total of five times. The highest core temperature I saw was around 561 F which no fuel damage is expected, and the ASIS system will not be effective until pressure falls below 600 psig.
Step 8 This part of the lesson is now over. Exit the simulator.
Lesson Part C: BWR: Reactor Vessel Medium Size Break Introduction: In this lesson you will observe a “crack” opening at the Reactor Vessel bottom, resulting in a medium sized loss of coolant accident. The plants safety system will detect the condition, which will automatically activate the plants Emergency Core Cooling system. Prior to attempting this lesson, ensure that you have completed the module reading assignments pertaining to BWR Emergency Core Cooling Systems. Step 1 Accept the terms of use in Module 0. Step 2 Download the Advanced_BWR_Simulator.zip [ZIP file, 3907KB]. The link is located in M1A3. Step 3 Unzip the downloaded zip file in your local computer. (in Windows, you may right click the file and then select “Extract All” from the menu) Step 4 Enter the Conventional BWR_Simulator folder and locate the BWR_V3.EXE application. Step 5 To start the Simulator, run the PBWR.exe file by double-clicking on it. If you see a Security Warning window, click on the Run button to continue. Step 6 You will see the landing screen. The screen allows you to start with different level of power output. We will use the default selection, Full Power. Step 7 Click anywhere on ‘BWR simulator” screen Step 8 A “popup” screen will appear asking “Load Full Power IC?”. Click OK Step 9 On the lower right corner of the Plant Overview Screen click RUN Step 10 On the lower right corner of the screen click on “Malf” Step 11 A “popup” screen will appear. Click on “Reactor Vessel Medium Size Break LOCA-
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800Kg/s”. NOTE: This lesson requires you to observe the response of various parameters as well as the plants ECCS system response. You may find it easier to run the lesson a few times in order to obtain the necessary information to complete the lesson. You are allowed to run the lesson as many times as needed. Step 12 Assignment Requirement Describe the response of the following parameters and systems throughout the event: Reactor Power (%) Initial power was 99.6% until scram was inserted Neutron power went to appoximatly 0%. While the thermal power had an initial decrease with the scram but did not go to 0 due to the residual heat in the core, but continued to decrease as heat was removed from the core Break flow Break flow decreased but never went to zero since water was being added to the core.
Reactor pressure Pressure initial increased due to a loss of steam flow out of the reactor and went above 7474 kPa, but as cooling and depressurization took place it decreased accordingly. Reactor water level Water level went down as expected with a rupture in the system once level reached approximately 11 the rate slowed and level reached 6. when pressure was decreased spray flow increased and level increased to 14.1. Reactor Coolant temp Was a continuous decrease Steam flow from dome Went to zero upon turbine trip and main steam stop closure however steam was released via SRV to the suppression pool. Fuel temp Was a continuous decrease Feedwater flow Feed flow decreased to zero
ECC activation: Note which ECC system is activated: ADS, RCIC, HPCF, LPCF and the respective flow rates. The highest spray flow observed around 800 Highest flow from SRV 1000 Step 13 The simulator lesson is now over. Exit the simulator. NOTE As stated up front in the introduction, this form includes instructions to navigate through the simulator lesson and provides space to complete any assignment requirements. You must complete the assignment by submitting this form for grading via the M3A3 assignment folder.
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