Hydrogen fix for Japanese reactors

[Fermi2]

Explain how Radiolytic Decomposition of water occurs during this event...

[Xenon_Free]

Low reactor water level, beta, alpha, gamma decomposition of water is as follows:

H2O > H + OH

H + H > H2

OH + OH > H2O2

H2O2 + OH > HO2 + H2O

HO2 + OH > H2O + O2

And

HO2 + HO2 > H2O2 + O2

And

H2O2 + HO2 > H2O + OH + O2


XF

[HeavyD]

I always thought the radiolytic decomposition of water was the action of a neutron flux breaking down water into separate hydrogen and oxygen molecules.

So in a major LOCA scenario, assuming the reactor is scrammed, wouldn't the vast majority of the neutron flux be gone?  Realizing of course there is still some residual flux due to the small amount of ongoing fission, but still.

I admit it has been quite some time since I sat and thought about the ins and outs of reactor physics and the interaction of the various radiation fluxes on matter, so I could be confusing things here.

[Xenon_Free]

That's true, neutrons contribute far more to the radiolytic decomposition than gamma.  However, it still occurs with gamma and add to that the low water level there is still a contribution from neutrons which will remain at higher energies for a longer period of time.  So their contribution would remain significant.

XF

[HydroDave63]

Boiling water reactors use high purity water as the neutron moderator and primary coolant in the production of steam. In an operating BWR, most of the radiolysis occurs in the high flux core region. Under normal operating conditions, the core contains an average steam void of ~30% and the core radial average void fraction increases from 0 at core inlet to ~70% at the top of the core.

A brief overview of radiation chemistry in the BWR coolant has been reported by The radiation energy generated in the reactor core and absorbed in the coolant is mainly attributed to fast neutrons and gamma rays; the contributions from thermal neutron and beta particles are relatively small.

The core average total neutron dose rate is estimated at 1.5×10⁹ R/hr and the total gamma dose rate is estimated at 3.1×10⁸ R/hr for a 50 W/cm3 power density standard plant. The total radiation dose rate in the core region

http://www.nap.edu/openbook.php?record_id=9263&page=125

[Cellman]

I can see that you would get some oxygen from radiolysis of water. I was under the impression that most of the H2 comes from the Zircalloy oxidation reaction scavenging the oxygen from the water molecule. This would leave the hydrogen, but the oxygen would not be released to containment in gaseous form. Thanks for the discussion so far.

[spentfuel]

Incorrect, BWR Mark 1 Containments are inerted to 97% Nitrogen concentration minimum by Tech Specs. Last I checked 3% Oxygen was not breathable.

Thanks for the correction at least I did learn something I was not aware of.  I have only made two BWR power entries,  one at VBWR and one at the Ferry.  I guess that was why we wore air packs at the Ferry 

I thought we were just being over conservative 

And by the by I was half correct 

I would add that the H2 generation at Fuk was also due to hydrolysis from the addition of salt water or at least thats what I recall

but I will admit I could be half wrong

sf

[Xenon_Free]

I can see that you would get some oxygen from radiolysis of water. I was under the impression that most of the H2 comes from the Zircalloy oxidation reaction scavenging the oxygen from the water molecule. This would leave the hydrogen, but the oxygen would not be released to containment in gaseous form. Thanks for the discussion so far.

That seems correct.  Btw, I did not state that there would be a tremendous amount of O2, just that it would be developed.  Any that would accumulate can be removed by the recombiners.  I am not sure what BZ wants to debate.

XF

[HeavyD]

I, for one, learn new stuff everyday I read these types of discussions.

As a retired Navy nuke, I realize that what we spent years operating are vastly different; in operation, response time and the affect various transients have on the plant to name just a few areas.

As a tried and true nuke geek, I love nuclear power.  Working in QA, there are times when I miss being involved in operating the plant.  However, my days of working shift work are long gone 

Kudos to the operators, and it is good to see that I still remember some stuff

[RDTroja]

I am not sure what BZ wants to debate.

He doesn't really want to. His idea of debate is "The Great and Powerful Bz has spoken!"

[HydroDave63]

He doesn't really want to. His idea of debate is "The Great and Powerful Bz has spoken!"

The first 8 seconds...

[Fermi2]

You realize in these conditions radiolysis doesn't really occur right?

[Xenon_Free]

Because of hydrogen suppression, or low LET gamma?  I covered the later and the former needs some type of recirculation flow to truly be effective, which will not be occurring since the reactions and steam formation is happening as fast as you add the water.

Interested to see what you've got though.

XF

[Xenon_Free]

Interesting read on accident sequence with some specific focus on radiolysis of water.

http://pbadupws.nrc.gov/docs/ML0716/ML071620344.pdf

Check out pages 2-7 to 2-10, they describe pieces of what I have been describing pretty well.  This is on the NRC website.  I admit I have not yet gotten through the whole thing.

XF