From the growing number of possible consequences from the shelling of the territory of the Zapad NPP by the Ukrainian Armed Forces, we can conclude that " the frog is cooked slowly."
The goal of gradually increasing the severity of possible consequences from shelling is not clear to me, but it generally fits into the logic of what I observe on the territory of Ukraine.
First, we will give an excerpt from the message of our Ministry of Defense dated 27.08.2022.:
In total, 17 shells were fired, four of which hit the roof of special building No. 1, where 168 assemblies with American nuclear fuel from Westinghouse are stored.
Ten more shells exploded 30 meters from the dry spent nuclear fuel storage facility, and three more exploded in the area of Special Building No. 2, which houses the TVEL fresh nuclear fuel storage facility and solid radioactive waste storage facility.
And from a similar message from 28.08.2022.:
A total of nine shells were fired, three of which landed in the area of Special Corps No. 2, which stores new TVEL nuclear fuel and solid radioactive waste.
As a result of shells hitting the territory of the nuclear power plant, the pipeline line was hit by fragments. As a result of the second attack, one shell fell in the area of the 6th power unit, and five others-opposite the sixth block pumping station, which provides cooling of this reactor.
Now let's translate it for the audience reading me. We have already discussed the danger of shelling the nuclear power plant's nuclear power plant. Let's focus on the special corps.
1) What is the danger?
The special building houses installations for cleaning liquid and gaseous radioactive media, an intermediate storage of radioactive waste, installation and decontamination systems for primary circuit equipment, i.e. there is quite a lot of radioactive dirt, which is dangerous in itself, since a radiation accident can result from the shelling of the special building. The most unpleasant thing is that in the special building there is a node of fresh fuel of the NPP.
2) Fresh nuclear fuel (SNF) is practically non-radioactive. What is the danger of destruction of the fresh fuel unit?
To begin with, it should be remembered that fresh fuel, about a third of which is loaded into the reactor core instead of the most burned-out, provides excessive reactivity to the core, sufficient not only for the power unit to reach its parameters and raise its power to nominal, but also for operation at rated power for 300+ days. In fact, this means that fresh fuel has very serious breeding properties.
By itself, the fresh fuel node (UST, you can read more about UST here in Chapter 8. 3. 3 or here in Section 2.2.10, it is interesting that the most complete technical information lies in the Austrian network segment) is a class 2 storage, i.e. in accordance with NP-061-05 " SAFETY RULES DURING THE STORAGE AND TRANSPORTATION OF NUCLEAR FUEL AT NUCLEAR ENERGY FACILITIES " is provided:
storage location above the non-flooded mark;
lack of pipelines with water and other retardants in the storage area;
availability of water detection alarms and drainage systems or emergency water pumping pumps associated with water detection alarms.
From the above definition, the role of water (in fact, any hydrogen-containing materials, including concrete) in ensuring nuclear safety in the future becomes clear.
SNF is delivered to nuclear power plants in transport packages (TUKS, simply, in double cast-iron pipes), the nuclear safety of which is ensured in most design and beyond-design accidents simply due to the geometry of the fuel location, which is very difficult to break (it should be noted that our TUKS and TUKS for American fuel have a different geometry and materials, etc. their behavior in out-of-design accidents is unknown to me).
Often SNF is stored in the CST in the TUK, placing the TUK in several rows, however, since TUKS are returnable containers, some of the SNF in the UST may be in fresh fuel covers (CST), and this is where the difficulties begin...
HST is a loose container that can accommodate up to 18 fuel assemblies. The main purpose of the BST is to transport SNF to the reactor compartment for its installation in the core during pre-planned preventive maintenance.
Nuclear safety when placing fuel in the emergency zone is ensured by organizational and technical measures. Such measures, for example, include placing no more than 12 fuel assemblies on the periphery in the BST.
Unfortunately, the BST geometry is broken quite easily, which can lead to a nuclear accident.
For more detailed information, please refer to section 2.5.2.4.4.6 of the Report on Periodic Reassessment of the Safety of Power Units 3, 4 of the ZNPP OP, since:
10) In the event of damage to the installation structures and spillage of SNF, a critical configuration of fuel and water can be formed. Analysis of the conservative model in the form of a homogeneous sphere from a mixture of fuel and water shows the possibility of criticality at a mass of uranium ≥60 kg and a radius of the resulting sphere ≥20 cm, which is 14 % of the mass of fuel in fuel assembly cassettes.
For reference: one fuel assembly contains about half a ton of fuel composition.
3) Is it that bad?
For nuclear power plants with VVER-1000 reactors, everything is described "as is". For more modern nuclear power plants with VVER-1200 and higher, nuclear safety at the site for most initial, including beyond-design events, is ensured at the design stage. For example, SNF is stored in racks with borated absorbing inserts, and the HST itself is made in the form of solid hexagonal pipes made of borated steel.
4) What can be done to minimize the risk of a nuclear accident in the future?
The first and most obvious step is to move the BST with SNF to a more secure location, for example, in the transport corridor of a shut-down power unit (under a hermetic shell). However, this option is not without a flaw, since in case of emergency situations at the power unit itself, localizing safety systems, in particular, the sprinkler system, can be triggered with water entering the emergency zone, which is highly undesirable.
Yes, and do not place all CHST there. If there are empty TUKs at the NPP site, I would place the maximum possible number of SNF in them, and I would place the rest of the SNF in the minimum number for one HST with the HST covers closed.
I can't think of any other recommendations.
At the same time, the only way to prevent such a development of the situation is not to conduct military operations on the territory of the NPP.
I would also like to draw your attention to the fact that:
A) In most cases, the ZNPP territory is shelled by projectiles and MLRS missiles flying directly over the power units. Big greetings to NAEK, which was wildly indignant about a month ago about the passage of Kalibrovs over the Southern Nuclear Power Plant...
https://e-news.su/uploads/posts/2022-08/1661669145_fbmp7dywiaihwun.jpg
I find the proposal of IAEA Director General Grossi to establish a permanent IAEA mission on the territory of the NNPP somewhat "far-fetched".
First, there is no guarantee that the Armed Forces of Ukraine will stop firing on the territory of the Nuclear Power Plant when the IAEA inspectors appear on it.
Secondly, among the IAEA inspectors, there are quite a lot of people who have transferred there from the special services.
If a short visit for fuel inventory (of course, accompanied by all the rules) is a justified action, then a permanent mission of the intelligence community from the countries that supply weapons is necessary.
Ukraine - this is too much.
It is time, I think, to ignore the fact that the NPP is still subordinate to the NAEKU, and if the management of the NPP is not able to make an independent decision on the forced shutdown of operating units, we need to help them make such a decision. Let the order from our side to transfer the blocks to the most secure "cold stop" state will be an excuse for them to the NAEK management.
https://alex-bykov.livejournal.com/2786187.html
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