Or you can depressurize and use the same portable pump to inject to *RPV* instead of the more complex setup you describe.
The issue here, is that you have to assume the plant has already gone 8+ hours without electricity. In this case, a blowdown of the reactor has the potential to result in damage to the containment as the HCTL (heat capacity temperature limit) of the suppression pool will be exceeded. You CANNOT blow down a BWR type reactor when you are above the HCTL, as the potential to damage the containment is not acceptable. In these cases, the best thing to do is to keep running RCIC, and work on cooling your suppression pool through venting and feed and bleed, and ultimately portable heat exchangers. Once you are below the HCTL and can blow down again, or you have manually and slowly blown down the reactor to a level where low pressure pumps can handle injection at a sufficient rate, then you can transition to using your portable pumps for core cooling. Damaging containment is NOT an acceptable response.
RCIC is useful for delaying the meltdown. Useful, but not enough.
RCIC will run as long as you can maintain the suppression pool relatively cold. If you vent containment and feed/bleed replacement suppression pool water, you can run RCIC indefinitely. There are several BWRs who would use their RCIC system for days in the 80s in order to shorten the time between restarts if there was an equipment failure, something which is not acceptable anymore.
I want to have a system which pretty much *guarantees* to prevent meltdowns. Which means passive, power-independent system. Which means it should be gravity-fed. Which means very low pressure. Which means it can't inject water into pressurized PCV or RPV. Which means they need to be depressurized in order to allow this water to go in.
Pretty much the ESBWR design. Take a look at it. The problem is you are limited based on the size of your initial pools (which is limited based on the design and cost of the structural loading on your containment, as the pools are all seismic class 1).
Are filters being installed on vent lines?
Mark I containment plants are upgrading their existing hardened vents, and Mark II containment plants are installing them. Mark III plants already have MANY containment venting systems. With regards to filters, this is a regulatory issue in the US right now. The industry wants to be required to have decontamination factor goals, which is consistent with NRC policy and direction right now, and allows for the greatest flexibility using equipment already available while avoiding unintended consequences. This is the same position that ACRS (Advisory committee for reactor safeguards) has, and is a position the NRC staff also agrees is a feasible approach. The staff however suggests installing mandatory filters as filters meet the commission's intent of a prompt action which could have a net benefit. There's a lot going on in this area and I think there's more information out there than I can give justice to right now. The short answer though is that the industry has a lot of concerns, many of which are NOT cost related, that have to do with the fact that filters are only applicable in roughly 3-4 out of 8 scenarios where containment venting or release is required, and that the installation of filters for beyond design basis events can REDUCE the reliability of the containment system during required design basis events. There are very large cost increases associated as well which were not accounted for in the backfit analysis, and there is no generic/common approach for plants to do this. Anyways.....the industry is putting together plants which will achieve decontamination factors on the order of 1000 to 10000 using FLEX equipment. This is a political issue at the moment and I really don't want to get into more than that.
Do you have battery-backed lighting? Individual batteries in each light, or what?
Emergency lighting is a fire-code thing. I can't speak for all plants, but at the plant I'm at now, and the few I've been at, emergency lights have individual lighting packs. The lights are separated into "normal" emergency lighting, and b.5.b emergency lighting, which is accredited for beyond design basis events where there are explosions and other significant site damage. Only b.5.b lighting would be assumed to function during a Fukushima-like event. There are b.5.b storage lockers with credited lights and equipment for operators to use in the event that all normal and emergency lighting and systems are lost. The emergency lights have their own backup batteries, and there are reserve batteries on site.
Do your operators now know how to open the vent? Did they practice it? Without electricity
YES! I even know the procedure number off the top of my head (and will not state it here because it may point back to my plant). Our extensive damage mitigating procedures, part of our b.5.b plan and 9/11 terrorist attack response plan includes things such as black starting the diesel generators with no control power, cooling the plant using a variety of crazy methods, running RCIC without electricity, AND, using credited b.5.b portable battery packs which are above ground in seismically qualified lockers and going to the SRV penetrations and hooking the batteries up to the appropriate connections to cause the SRV to actuate. These tasks have been "simulated", and are very clearly laid out in the procedure. The procedure includes a list of all SRVs, which contacts you have to wire to in order to read suppression pool temperature. Which contacts you have to wire up in order to energize each individual SRV, preferred energization order based on plant conditions, how to identify if the lift was successful, and how long the battery is expected to maintain the valve open. In a Fukushima like event, we would disable the relief mode of the SRVs (the air/power operated mode), and activate the ADS backup air supply, which will give us more lifts without having to install portable air bottles, but the options for installing portable air bottles or compressors do exist and are detailed in the extensive damage mitigation guidelines. We also have a remote shutdown panel with a select number of SRVs, and wiring up any power source to the RSP can allow lifting those valves without having to open up a penetration.
With regards to emergency procedures, the EOPs (emergency operating procedures), are high level guidelines/procedures for how to achieve critical safety objectives. The SAGs (severe accident guidelines) are even higher level goals to achieve critical safety objectives if core damage is a possibility. The EDMGs (extensive damage mitigation guidelines), are unique ways to meet those goals without using normal equipment or operating procedures, and assuming significant site damage. The new Fukushima/FLEX procedures further expand upon that and include very extended duration events. In other words EOPs/SAGs = goals, EDMGs and FLEX = extra means to fulfill those goals, should normal means become unavailable. All procedures are trained on by operators in the simulator and are part of their initial licensing and requalifications.
Do you have gravity-feed water sources?
BWR series plants do not have this. The AP1000 and ESBWR are the only two plants I know of that utilize some form of gravity fed source.
The more I learn here, the scarier it looks. Safety relief valves need something (compressed air) to work? *Safety* valves? Really? Why? It's not possible to have valves which are actuated solely by the pressure they are intended to relieve??
The valves are SAFETY-RELIEF valves. The SAFETY mode is spring operated, and requires no electricity or pressure to function. These valves are sequenced to lift against spring pressure as reactor pressure exceeds the relief mode setpoints. This is what prevents the reactor from exceeding its 1375 PSI ASME code limit post event with no power or ADS air.
The RELIEF mode is power actuated utilizing a pneumatic air supply. The RELIEF mode is the mode in which the plant's safety systems will automatically lift to limit pressure. The relief mode setpoints are below the safety mode setpoints. The operators can manually lift the valve in relief mode, and can also disable the relief mode, for each valves. Typically, if the instrument air supply to the containment is isolated or disabled for any reason, the operators will turn off the relief mode on all SRVs and allow the safety mode to actuate in order to preserve accumulator air for a blowdown, if required. Once the operators get a handle on the situation and are ready to blow down, they will either actuate ADS (which automatically lifts several valves in relief mode) or they will manually lift valves. The SRVs have enough air for a specific number of rated lifts against containment design pressure. Once lifted, if DC power is continuously applied, the valves will stay open for quite a while, as the leakage from the accumulators is rather low. For extended events, a means to assure recharging the accumulators may be vital to success. There are other ways to blowdown the reactor should the SRVs be all failed, but those means require AC power to be restored to some plant systems, while the SRVs only require DC power and pre-charged instrument air.
