Total MSLB accident: effect of stronger density reactivity feedback

In this application, we keep the "mox" beta value .005 and attempt to simulate, in addition, a "mox-representative ?" density feedback effect by scaling the reference core / Lstrvg /rog values by a factor 1.2.
This would bring the density reactivity coefficient at vm= 1.0e-3 and 1.3e-3 to .41e-3*1.2 and .35e-3*1.2, respectively.

The consequences of this larger density effect are severe: compared (chart 01 to chart 05) with rtvsym_4 case, q2c peak increases from 850e6 to 1300e6 and u2c7 peak from 850 K to 1050 K, the peaks occurring at 200 s, ie at end sg voiding phase, thus more than 100 s later than the q2c peak!
At u2c7 peak time, core is critical and almost stationary (f2c=q2c) .

The symmetrical mslb accident is characterized by boiling in the major upper part of the core and concomitant shifting of power profile towards the bottom and a resulting high fqc there.

As soon as the sg's are completely voided from their liquid water, boiling extends to the whole core, which results in a rapid reactivity and power drop.

As pressure increases again, thanks to primary water expansion, core boiling disappears and a permanent, zero power, higher temperature condition establishes.

The sg feed water is evaporated in the bottom of the first sg nodes to extract the primary pump power and any residual power.

Surprisingly, the effect of boration does not seem to be critical during the dangerous phases of the accident.

If the auxiliary feed water flow wyan in the sg is not low enough, the core cannot be shutdown to zero power at the outcome of the accident: in that case, one should refrain from the "fireman reaction" of bringing more water to the sg, but on the contrary, restrain the feed flow in order to force temperature increase of primary water, which is the main mechanism for shutting down the core, SI boration playing a subsidiary, too late, long term effect.

In the course of the accident both primary and sg pressures drop down rapidly.
As pressu refills, primary pressure increases again. Controlling long term pressure evolution is an issue of post accident management

Obviously, the previous findings are tentative and deserve to be confirmed by using more realistic neutronic tables.
If they do,they highlight the remarkable capacity of the pwr system of self recovering, thanks to the sole action of intrinsic core reactivity and spatial redistribution feedback, from a severe mslb, even in the incredible case of failure of all fast sg insolation valves.