Talk:Decay heat

Performed a partial rewrite. Since decay heat is a very significant issue for nuclear reactor safety, I will probably be revisiting this article, as well as others that should know about decay heat.--Burzum 07:09, 31 December 2005 (UTC)

Good! I shall read with interest (though I'm no great expert in this area). Just to warn you that the last 'Nuclear Technology' topic I contributed to, got a 'too technical' tag slapped on it Bob aka Linuxlad 16:44, 31 December 2005 (UTC)

Edit request: "This results in 13 MeV" --> "This results in 23 MeV"

I disagree. 10 MeV of neutrinos (of the 23 MeV total for beta decay) are not deposited in the core. This results in only 13 MeV being deposited in the core.--Burzum 00:08, 16 June 2006 (UTC)

Even the 13 MeV may be high - does this include decays with long halflife that are unlikely to happen while the fuel is still in the reactor? --JWB (talk) 18:00, 20 May 2008 (UTC)

Yes. But this isn't an issue. Decays of nuclides with exceptionally long half-lives do not deposit a significant amount of energy. And the long and steady power history ensures that the 13 MeV number is reasonable since these nuclides will build up to a steady state inside the reactor. Before the reactor shuts down, it is still producing 6.5% of its power from decay heat. The rest comes from induced fission. After it shuts down and the induced fission rate is made negligible, the only heat production will be from the same decay heat. This previously steady state value will then decrease because no more radioactive nuclides are being produced as fission products. Cheers.--Burzum (talk) 03:53, 9 September 2008 (UTC)

I changed the definition of T_subscript_S to the correct definition as stated in reference [3]. The equation is number (3) of reference [3]. 68.35.150.245 (talk) 02:13, 9 January 2011 (UTC) Mike McNaughton, mcnaught@unm.edu

title

Decay heat = Decay energy. May be change article title on “residual heat” (delayed heat; afterheat; shutdown heat)? Especially article about it. Hullernuc (talk) 14:49, 23 March 2011 (UTC)

I'd say no. I recently toured Callaway Nuclear plant, and they talked of "decay heat", not residual heat. "Residual heat" also implys that no further heat is being produced by nuclear reaction, which is not what is being discussed on this page. Brad (talk) 16:48, 30 September 2013 (UTC)

Error in the Reference 3

In the current version, the approximation for the decay heat is suggested:

${\frac {P}{P_{0}}}=0.066\left(\left(\tau -\tau _{s}\right)^{-0.2}-\tau ^{-0.2}\right)$

Where $P$ is the decay power, $P_{0}$ is the reactor power before shutdown, $\tau$ is the time since reactor start and $\tau _{s}$ is the time of reactor shutdown measured from the time of startup (in seconds).

The last statement, in the parenthesis, about unit of measurement, is not supported by the PDF [3] cited. The cite [3] now refers to http://www.nuceng.ca/papers/decayhe1b.pdf ; there, the text just after the formula reads:

where P is the decay power, P₀ is the nominal reactor power, τ is the time since reactor startup and τ_s is the time of reactor shutdown measured from the time of startup. The above expressions are valid for times between 10 seconds and 100 days (8.6 x 10⁸ seconds) after shutdown.

The units of time are not specified there; so, the right hand side of the equation has dimension "time power minus one fifth". The left hand side of the expression is dimensionless. Therefore, the formulas (1),(2),(3) in [3] are just wrong.

However, if one looks for any indication to the units of measurement, trying to give some meaning to the formulas (1)-(5), then one should look to the text after equation (5) that refers to one specific case ( τ_s= 10 years ) confirming that τ_s and τ are dimensional quantities.

If the nuclear engineers cannot perform even the trivial dimensional analysis,
then we should not wonder that the reactors do explode. dima (talk) 08:29, 4 April 2011 (UTC)

Perhaps the dimensional factor has been absorbed into the 0.066 figure. What else does this figure do, after all? I agree that dimentional analysis is greatly neglected, and would save many a physicist and engineer from embarassement when done in all equations, term by term. SBHarris 22:50, 3 August 2012 (UTC)

Please add calculation method

Please add calculation method for determining the heat of radioactive decay in Watts per kg from half life and decay energy (MeV) of any radioactive isotope.Mollwollfumble (talk) 18:14, 3 August 2012 (UTC)

What for? It won't help you here, where many, many radioisotopes are involved. You can see the calculations for decay with time at radioactive decay. For converting decay energy to watt/kg, you simply have to convert one kg to number of atoms N, and then find decay rate dN/dt = N (ln2/half life). If you use N as the atoms in a kg, and half live in sec, this gives the decay rate (in seconds) per kg. Multiply decay energy to give MeV/kg/sec, and then divide by MeV/J to give J/sec/kg, which is watts/kg. SBHarris 22:48, 3 August 2012 (UTC)