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pressure loss

A loss-of-pressure-control accident (LOPA) is a mode of failure for a nuclear reactor that involves the pressure of the confined coolant falling below specification. Most commercial types of nuclear reactor use a pressure vessel to maintain pressure in the reactor plant. This is necessary in a pressurized water reactor to prevent boiling in the core, which could lead to a nuclear meltdown. This is also necessary in other types of reactor plants to prevent moderators from having uncontrolled properties.
Pressure is controlled in a pressurized water reactor to ensure that the core itself does not reach its boiling point in which the water will turn into steam and rapidly decrease the heat being transferred from the fuel to the moderator. By a combination of heaters and spray valves, pressure is controlled in the pressurizer vessel which is connected to the reactor plant. Because the pressurizer vessel and the reactor plant are connected, the pressure of the steam space pressurizes the entire reactor plant to ensure the pressure is above that which would allow boiling in the reactor core. The pressurizer vessel itself may be maintained much hotter than the rest of the reactor plant to ensure pressure control, because in the liquid throughout the reactor plant, pressure applied at any point has an effect on the entire system, whereas the heat transfer is limited by ambient and other losses.

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  1. P

    Heating Pressure Loss

    Hi all, This pressurised system was installed about eleven years ago, and most of the existing radiators were replaced. For some years, the system has slowly lost pressure. I have put a sticking plaster over this by injecting a leak sealer into it, then re-pressurising, which works for a...
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  2. C

    Cast Iron Radiator Pressure Problems

    Hello, I am hoping to gain some advice following encountering several issues which I'm struggling to determine the magnitude of in my central heating system. I had 8 new cast iron radiators installed in December and since then my Vokera 28 Compact boiler has been dropping pressure on a regular...
  3. T

    Water pressure issue, sometimes results in our taps `sucking`

    We live in a row of 4 terrace houses running perpendicular to a main road, we are the end terrace furthest from the road. We often lose water pressure and sometimes we get no flow of water at all (particularly annoying when showering). When the water stops, the taps sound like they are drawing...
    • Theeonlywaddy
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  4. B

    Combi Boiler Pressure Loss

    I hope somebody can help us. Our oil Worcester combination boiler powers an old cottage with 17 radiators. We have major pressure loss. One radiator was feed by a pipe within the concrete floor but I have now replumbed that to be above ground. So all pipes are visible. We were told by the...
  5. W

    Pressure loss from sealed system stops when open/closing a zone with 'a leak'

    Hello all, Seeking any input on a matter that seems to defy logic and common sense. Sealed system Oil fired boiler (newish) feeding a large farmhouse from an annex with a good quality install/ pump etc that seems to be doing the job. The system is losing 1 bar per day for a long time. I...
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  6. P

    Air getting in to sealed system ... !!

    I am collecting air in one downstairs radiator which requires bleeding once per week and a small amount on the auto bleed valve on the hot water side of the system. However, there is no pressure drop until I bleed the rad which then drops about 0.1 bar. The system was flushed couple of months...
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  7. F

    System pressure loss

    I'm an amateur with an interest in plumbing - installed 2 systems in the 60s and 70s and modified others for self and family until banned in 1991. Current problem relates to daughter's system. She had an Ideal Logic 35kw combi installed under Government scheme some 8 or so years ago. At the same...
  8. N

    Air accumulating in system. No pressure loss.....

    Hello, I'm hoping someone can help... I have a system boiler (Worcester Bosch 18i - Unvented) in my garage. I am having to bleed top towel rad in house and magnaclean next to boiler daily. Air is getting into the system. I have no loss in pressure. I have removed the lower level rads in house...
  9. Windy

    Pressure loss on gas pipe (BS 6891 pipe sizing)

    Hi, I'm doing my ACS and have an issue with pressure loss calculations!! sample question : "what would the pressure loss per meter be on copper tube of 15mm feeding a 12kw (gross) gas hotplate" I can't for the life of me get the correct answer..... I nett the hotplate 10.81kw divide that...
  10. P

    MegaFlo again. Pressure loss

    Hi there - I am convinced that my 25 yr old Megaflo is providing less hot water pressure than it used to. I have reset the bubble several times but it doesn't seem to help. But the shower pressure is not bad and I can live with it. But then yesterday I got up earlier than usual (before the HW...
  11. L

    Potterton Combi Boiler Frequent Pressure Loss in Winter only

    Hi, My Potterton Heatmax Boiler is nearly 10 years old, but has been serviced regularly and the Pressure Release Valve was recently replaced. It frequently loses pressure throughout Winter, when the heating is in use. During Summer months, it's fine! All radiators are all heating up to HOT and...
  12. J

    INTERMITTENT WATER PRESSURE LOSS

    Re: Domestic c/h with Vaillant ecoTEC plus 837 boiler. For the past 12 months or so, boiler water pressure has intermittently dropped from the normal operating pressure of 1.8bar to 0.3bar overnight, indicated by fault code F75. I would re-pressurise the system and monitor pressure for a...
  13. R

    Very slight pressure loss

    Hey guys I have a quick question I hope you all can help with I have Ariston class he evo 30 boiler it’s just over a year old we got 3 new tads fitted a few weeks ago as old ones were rusting at the top valves anyway we had a small leak in the pipe going into the new one which my heating...
  14. D

    Mystery pressure loss on WB 24i

    Hey folks, got a weird one here. CH system has been isolated and is not dropping ( gas test, acoustics, gauge on radiator ) Its a brand new worcester bosch 24i and is fitted with a snorkel/vertical extension outside, this is spurting and abnormal amount of water when the boiler runs, the...
  15. R

    Combi sudden pressure loss.

    Hi, my 80 year old mum has a combi boiler that suddenly loses pressure. She lives 70 miles away and having problem diagnosing fault. It happens irregularly and suddenly so dont think it is leak. Expansion tank and prv has been changed by a local plumber. I think it might be dumping water out the...
  16. G

    Need to restart Glowworm 30hxi after water pressure loss

    Hi guys. The water pressure got too low and my boiler switched itself off (actually, it stopped heating and was making a whirring noise and there may have been a flashing light, I turned it off quickly). I have brought water pressure back up to about 1 bar and am attempting to reset following...
  17. D

    Boiler Pressure Loss

    Hi, Boiler has been losing pressure for a couple of weeks and just got round to having a look. Seems to be a leak on the cold water feed into the boiler. On the attached photo is two taps and it’s the top one that’s leaking. Easy enough to depressurise the system, kill the lower tap and...
  18. N

    Central heating pressure loss

    Hi I have a ideal logic 30kw system boiler runnong central heating and underfloor heating and an invented tank. The boiler has always lost pressure to a degree but now it's worse than ever. I've fitted isolators downstairs so I can turn that off and it still loses pressure. With the UFH isolated...
  19. M

    Pressure loss through the pipework

    I have recently read a couple of posts on here that specify that the pressure loss from the meter to the applicate can be a max on 1.5 mbar. I always understood it to be 1.0 mbar. Has it changed without my knowledge? I am due to resit my assessment soon so it was a while ago. Mark.
  20. B

    Magnaclean / pressure loss

    Has anyone ever heard of pressure loss (requiring repeated top-ups) on combi systems after fitting on a Magnaclean ? I've not had chance to look at the installations yet but seemingly the same problem on a couple of systems.
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