he secondary loop. Describe how thermal energy is transferred from the reactor core to rotate the turbines, and explain how this dual-loop design contributes to radiation safety.","markscheme":"- Explains that high-pressure water in the primary loop absorbs thermal energy directly from the nuclear fission occurring inside the reactor core M1\n- Explains that this hot primary water passes through a heat exchanger (steam generator), transferring its thermal energy to water in the secondary loop to produce high-pressure steam without the two fluids physically mixing M1\n- States that this high-pressure steam in the secondary loop is directed to rotate the turbine, and the isolation between loops ensures radioactive contaminants from the core are contained within the primary loop and do not reach the turbines or the external environment A1","marks":3,"order":0,"markingRubric":null,"explanation":{"methods":[{"id":"energy_transfer_and_containment","label":"Trace energy and containment","steps":[{"type":"text","order":1,"title":"Heat the primary water","content":"A PWR has two separate water loops: the **primary loop** and the **secondary loop**.\n\nInside the **reactor core**, nuclear fission releases energy. High-pressure water in the primary loop absorbs this thermal energy directly from the core. This clear link from fission to heating the primary water earns **M1**.","highlights":[{"text":"primary loop","location":"specification"},{"text":"secondary loop","location":"specification"},{"text":"reactor core","location":"specification"}]},{"type":"text","order":2,"title":"Transfer energy across","content":"The hot water in the primary loop flows through a heat exchanger, also called a steam generator. There, it transfers thermal energy to water in the **secondary loop**.\n\nThe two water supplies do **not** mix. The secondary-loop water becomes high-pressure steam. Explaining this transfer and separation earns **M1**.","highlights":[{"text":"primary loop","location":"specification"},{"text":"secondary loop","location":"specification"}]},{"type":"text","order":3,"title":"Drive turbines safely","content":"The high-pressure steam in the secondary loop is sent to rotate the turbines. Keeping the loops separate confines radioactive contamination to the primary loop, so it does not travel to the turbines or outside the power station.\n\nThis links the turbine rotation to the radiation-safety advantage, earning **A1**.","highlights":[{"text":"rotate the turbines","location":"specification"},{"text":"secondary loop","location":"specification"}]}]}],"generatedAt":"2026-07-22T09:52:39.680Z","modelVersion":"gpt-5.6-terra+diagrams-1","explanationVersion":"v3"},"options":[]}],"options":[],"explanation":null,"firstAttemptFullMarks":null},{"id":"7c5d1aac-95f3-4656-ba93-50f6cd95000d","revisionId":"5400e57e-abd1-4faa-8460-c9d8d1e63361","questionNumber":null,"questionType":"LA","specification":"In a pressurized water reactor (PWR), liquid water serves a dual purpose as both the coolant and the moderator. During a hypothetical accident, a breach in the cooling system causes a rapid drop in pressure, causing the liquid water inside the reactor core to instantly flash into low-density steam.","difficulty":7,"difficultyBand":"medium","totalMarks":3,"sourceTitle":null,"calculatorUse":null,"parts":[{"id":"f17d195a-3f00-4e95-a709-129332ccaf95","label":null,"content":"Explain how this sudden change in the state of the water affects the rate of nuclear fission inside the reactor.","markscheme":"- Identifies that steam has a much lower density than liquid water, meaning there are far fewer water molecules (or hydrogen nuclei) per unit volume in the core to act as a moderator. M1\n- Explains that fast-moving neutrons released from fission are less likely to collide with moderator nuclei, meaning they are not slowed down to thermal speeds. M1\n- Concludes that these fast neutrons are significantly less likely to be captured/absorbed by Uranium-235 nuclei, causing the rate of nuclear

Radiation safety and nuclear energy

Question 13

Radiation safety and nuclear energy Questions

Radiation safety and nuclear energy

Question 13

Radiation safety and nuclear energy Questions