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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. S

    Boiler pressure loss🙄

    I have an 8 year old Potterton HE Gold combi boiler losing pressure. I have isolated the central heating to leave just water heating and it is fine. As soon as the central heating is introduced the pressure drops to zero within an hour. I have had floor boards etc up but cannot find a leak...
  2. ArifP569

    Pressure loss when UFH called for

    Hello all, hoping someone could help me with this, Boiler pressure is 1.5 bar, but when we turn on UFH pressure drops to 1 bar. then when we turn off UFH, pressure on boiler goes back up to 1.5 bar?? any help much appreciated
  3. M

    Non uniform pressure loss in Greenstar 30i

    Dear All, I hope you might be able to point me in the right direction with an issue I have with a 3 year old Greenstar 30i boiler, last serviced in Oct ‘22, with new pipe work all around the house at time of boiler install. We have separate circuits upstairs and down and a water cylinder. At...
  4. M

    Repeated complete pressure loss

    Can it be anything other than a leak? The reason I ask is that I have had 4 plumbers/heating engineers out over the past 3 months and none are able to figure this out. System boiler powering a mixture of radiators and UFH. No detectable leaks by the rads, by the manifolds or really anywhere in...
  5. A

    Ideal Combi Logic+ C24 Losing pressure

    Hello guys! I had an Ideal Combi Logic+ C24 fitted in August 2021 in my mid terraced house and I started noticing that it was losing pressure during winter 2021. I had the first engineer sent by Ideal in March 2022 when the pressure was going down very fast, I could see the gauge going down...
  6. C

    Struggling to repressurise my boiler and heating system

    Hi folks - new here and looking for a bit of advice. I've got a British Gas 532/i boiler which is struggling for pressure - around 0.5 bar. Heating works fine through most of the house just struggles to get to the very top rooms. I don't think any bleeding is necessary, and I cannot find a...
  7. A

    Worcester Bosch Greenstar 30 CDi - Pressure loss

    Hi all, Recently moved into a new house and noticed the Greenstar boiler has low pressure on the dial. Quick Google suggests using a key, valves, or fill loop to increase the pressure. Only problem being is I don't have either of those things. Any help would be appreciated. Cheers.
  8. R

    URGENT Pressure loss in new loft (unvented cylinder)

    Hello. I need some urgent advice re water pressure in an unvented system. A few months back, I had my gravity fed system + boiler changed to an unvented cylinder + system boiler. The water pressure following the swap was incredible. We were originally talking about putting in a mains booster...
  9. E

    What boiler pressure loss is ok over time?

    My Ideal boiler pressure gauge pointer shows about 0.85 when cold (about 1.8 when the heating is on). 10 weeks ago the readings were 1.0 when cold and 2.0 when hot. Clearly there is a loss in pressure over time. I can see no leak on any radiator or near the boiler. Is this pressure drop of...
  10. Elraoak

    Pressure Loss (new EV, PRV and dosed with F4)

    Have a large CH system, not sure the volume but a mix of column radiators and UFH means it's probably 250L or more. Runs on a Vaillant Ecotec 630 that's been OK for 7 years, but recently started losing pressure (needs topping up weekly). Had a new EV (old one was full of water apparently)...
  11. M

    Greenstar CDI, Pressure loss, not HE

    I am a retired gas engineer. Corgi and Domestic Electrics + Building Surveyor. I have a Greenstar CDI 35kw that I fitted in my own home 15 years ago, serviced regularly, no issues till now. Suddenly its losing full pressure in approx 2 hours. I have concrete floors with buried copper pipe but...
  12. R

    Help... no gas coming through meter or regulator

    My daughter has just moved into her first rental house with gas stove and hot water in Melbourne. The meter (pictured) definitely has gas connected to the regulator. But gas is not getting to the stove or water heater. The previous tenant had turned the gas tap off at the meter but it's on now...
  13. H

    Pressure loss in Heating System post fitting new Expansion Tank

    Hi, hope someone can help me with a heating pressure loss problem. My valiant boiler has been loosing pressure over the last few months, resulting in me having to top up the water every week or so. Managed to get a boiler engineer to visit who diagnosed a faulty expansion tank. (Water evident at...
  14. M

    pressure loss and air in ground floor rad and top foor towel rad

    Hi Towel rad in bathroom needs bleeding every few days and now noticed a small rad downstaris also has air in it regularly. Pressure drops every few days and needs topping up. I've tested with a flame for corrosion and it's clear, tried leak sealer and checked for weaping rad connections . I...
  15. P

    Bosch Worcester Gr8300iw 30 C pressure loss and temperature

    Have just moved home and had a Worcester Bosch Greenstar Life Gr8300iw 30 C installed. It has a thermostat which I had turned down low overnight (but not that low, 18 degrees C) and found the pressure had dropped to something like 0.3 bar the next morning. I topped it up but since then the same...
  16. MancAnt

    Bosch Worcester Junior 28I pressure loss

    Hi all, anyone give any advice regarding our Bosch Worcester Junior 28I .... I have to keep re pressuring it every two weeks ( drops to 0.6- I put it back upto 1.2 and then it drops after 2 weeks). Expansion vessel was re-pressured earlier this year by the installer . It is in warranty until the...
  17. R

    Pressure loss warmflow

    Hi all first post in this forum and hopefully someone can advise. I have a warmflow external oil Combi boiler approx 4 years old. Problem I'm having is this time of year when we start using the heating I am intermittently loosing all pressure on boiler and needing to refill, it has worked fine...
  18. E

    pressure loss pressure gain

    Hi all I have a Halstead combi boiler in the loft about 12 years old, every week I have to raise my pressure back up as it nears zero, this has been ongoing for around six months. I have recently started putting my heating on, when I turns it on I get an error code 3 for a few seconds, then...
  19. A

    Shower pump activating for a few seconds when no demand

    Hi everyone. I recently had to replace my shower pump and increase the size of the cold water storage. Since moving to a gravity fed pump the pump is activating with no demand for a few seconds. The pump is now connected to all outlets in the house but I am concerned it will burn out if it...
  20. M

    Isolating boiler to test if hex is causing pressure loss

    If Isolating a boiler to determine if the leak is on the pipework or the boiler. If pressurising to 1.5bar then isolating the flow and return for an overnight test. Is it still acceptable to use the combi boiler for hot water? Expansion vessel located in the boiler.
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