Druck-Materie 20b.qxd - JUWEL - Forschungszentrum Jülich

More documents

Recommendations

Info

state. Conversely, the monatomic hydrogen in the presence of ortho-hydrogen molecules may catalyze the relaxation to the para state. Finally, there are indications that a fourth species, triatomic hydrogen, is also present in irradiated hydrogen, presumably resulting from the combination of monohydrogen with ordinary dihydrogen. [5] This trihydrogen is unstable, and can act as a means of “storing” monohydrogen. Thus the ortho:para equilibrium balance in the presence of ionizing radiation may be significantly different from the balance in the absence of radiation. Measurements of the neutronic performance of cold moderators are inconclusive as to the relative concentrations of ortho- and para-hydrogen. [1–4, 6–8] Our goal is to provide a basis for understanding the evolution of the ortho/para state of liquid hydrogen in the practical circumstance of a radiation environment. Section 2 describes the mathematical models for the kinetics of liquid hydrogen in such a radiation environment. Section 3 applies the model to the Spallation Neutron Source liquid hydrogen moderators, and surveys possible effects of the pulsed nature of source and the circulating nature of the hydrogen loop. Section 4 describes further work we see as necessary. 2. KINETICS MODEL In an unirradiated liquid hydrogen system, the ortho-para hydrogen distribution can be characterized [9] by in which no (np) represents the density of ortho- (para-) hydrogen in the system (we work in units of moles of diatomic hydrogen per cubic centimeter), Kop (Kpo) represents the rate constant for ortho-to-para (para-to-ortho) spontaneous spin-exchange conversion, and Cop (Cpo) represents the rate constant for ortho-to-para (para-to-ortho) catalyzed conversion. The coefficients are related in that as is necessary to reach eventual equilibrium at the ortho-hydrogen fraction with a similar equation for Cop and Cpo. Milenko et al. [9] report detailed measurements of ortho-para conversion providing values for Kop as functions of temperature and pressure. The catalytic conversion coefficients will depend completely on the details of the system, such as the material, surface area, and surface preparation of the container, etc., and we consider a broad range of values in our analysis. Based on the results of irradiation studies conducted in support of the NERVA program, we extend the above mathematical model to include the radiolytic evolution of monatomic and triatomic hydrogen radicals in the hydrogen system, the slow spontaneous dissociation the triatomic hydrogen radicals into additional monatomic hydrogen (and e-H2), the orthopara conversion catalyzing effects of the monatomic hydrogen, and the recombination of the monatomic hydrogen into n-H2. [10] In mathematical terms, this can be expressed as 52
where nH 3 (nH) is the molecular density of triatomic (monatomic) hydrogen, and we introduce additional conversion coefficients and parameters as shown in Table 1. We quote values for 20 K and 14.9 bar as typical for cold moderator applications. Obviously, specific systems may have somewhat different values, but they will likely be similar. 2.1 Equilibrium Levels Equation 7 can easily be solved for for the concentration of trihydrogen at equilibrium to give giving the result that equilibrium trihydrogen levels are directly proportional to the energy deposition rate. At Ė = 1 W/cm 3 , the equilibrium level is 1.66 × 10 −4 moles per cubic centimeter, which implies that 6.7 × 10 −3 of all hydrogen nuclei are in the trihydrogen species. 53
Page 1 and 2:
ACoM - 6 6th 6 International Worksh
Page 3 and 4:
Forschungszentrum Jülich GmbH Inst
Page 5: Preface These are the Proceedings o
Page 8 and 9: List of participants, cont’d. Kü
Page 10 and 11: Pepe M. 43 Petriw S. 43 Picton D.J.
Page 12 and 13: Experimental background, results an
Page 14 and 15: • Light water ice as H(H2O) at T
Page 16 and 17: In Table 2 a survey is given about
Page 18 and 19: sigma-T in barns/molecule Figure 4.
Page 20 and 21: 2.3 Liquid water Compared to the so
Page 22 and 23: presented. The corresponding experi
Page 24 and 25: 3.2 Gaseous hydrogen and deuterium
Page 26 and 27: Rho(Omega) normalised 160 140 120 1
Page 28 and 29: elatively free and can also suffer
Page 30 and 31: Figure 16. Heat Capacity for Solid
Page 32 and 33: o-D2 and p-H2 at 5K for an ucn ener
Page 34 and 35: Figure 22. UCN Upscattering Rates i
Page 36 and 37: ho(omega) normalised 40 35 30 25 20
Page 38 and 39: derived from Walker [52]. The neutr
Page 40 and 41: Since there is only a small gain of
Page 42 and 43: 7. CALCULATION OF SCATTERING LAW DA
Page 44 and 45: For the validation of these data se
Page 46 and 47: [36] Nielsen, M.: Phonons in Solid
Page 48 and 49: 2. THE CASE OF MOLECULAR SOLIDS An
Page 50 and 51: γ r ( 0) ≅ 2 2 2 T erf e ( ) / 2
Page 52 and 53: 4. PRELIMINARY APPLICATION Solid Me
Page 54 and 55: [5] Meeting on Moderator Concepts a
Page 58 and 59: Note that the equilibrium trihydrog
Page 60 and 61: para hydrogen system under irradiat
Page 62 and 63: [12] T. E. Fessler and J. W. Blue,
Page 64 and 65: tion of neutron intensities, partic
Page 66 and 67: varied between calculations but the
Page 68 and 69: 5. THE OPTIMISATION OF MULTIPLY GRO
Page 70 and 71: Figure 7. A comparison of time dist
Page 72 and 73: 4.8 cm hydrogen slab in front of a
Page 75 and 76: ACoM - 6 6 th Meeting of the Collab
Page 77 and 78: the moderator is annealed every 12
Page 79 and 80: The method requires two additional
Page 81 and 82: ABSTRACT ACoM - 6 6 th Meeting of t
Page 83 and 84: Heat transfer processes across phas
Page 85 and 86: 3. TWO-PHASE FLOW PATTERN IN THE MO
Page 87 and 88: continuous phase dominating, and a
Page 89 and 90: Also the velocity pattern has chang
Page 91 and 92: Figure 8. Methane pellets concentra
Page 93 and 94: ACoM - 6 6 th Meeting of the Collab
Page 95 and 96: sample volume and the nominal densi
Page 97 and 98: The results presented in this paper
Page 99: Table 10. Summary of energy transfe
Page 102 and 103: 2. EXPERIMENTAL Methane hydrate was
Page 104 and 105: Figure 4. Energy levels of methane
Page 106 and 107:
102
Page 108 and 109:
phase transitions from phase II to
Page 110 and 111:
After melting phase I in the cryost
Page 112 and 113:
4. SOLID PHASES OF MESITYLENE-D0 AN
Page 114 and 115:
G(ν) [a.u.] 8 6 4 2 Phase II Phase
Page 116 and 117:
112
Page 118 and 119:
A not quite as perfect cold spectru
Page 120 and 121:
2.2 Inelastic neutron scattering Th
Page 122 and 123:
Figure 4. Inelastic spectra at the
Page 124 and 125:
3.2 Moderator performance The resul
Page 126 and 127:
122
Page 128 and 129:
Figure 2. The methane pelletizer, m
Page 130 and 131:
Figure 5. The cryogenic hopper fill
Page 132 and 133:
128
Page 134 and 135:
ture
Page 136 and 137:
The charging device scheme could be
Page 138 and 139:
Table 1. Data of irradiation of met
Page 140 and 141:
5. METHODS OF PROCESSING OF RAW EXP
Page 142 and 143:
of radicals, that is, before a burp
Page 144 and 145:
6.2 Condition for thermally stimula
Page 146 and 147:
Table 4. Estimated values of an ene
Page 148 and 149:
• Nine spontaneous burps were obs
Page 150 and 151:
APPENDIX Some useful relations and
Page 152 and 153:
APPENDIX. Graphs of burps. 148
Page 154 and 155:
150
Page 156 and 157:
152
Page 158 and 159:
154
Page 160 and 161:
2. EXPERIMENTAL SETUP Fig. 1 will g
Page 162 and 163:
All these parameters are kept const
Page 164 and 165:
4. CONCLUSIONS We demonstrated that
Page 166 and 167:
JESSICA (Juelich Experimental Spall
Page 168 and 169:
The moderator system consists of th
Page 170 and 171:
to change the temperatures and to p
Page 172 and 173:
168
Page 174 and 175:
supplied from the high pressure bom
Page 176 and 177:
10 9 10 8 10 7 10 6 Para35%[Experim
Page 178 and 179:
174
Page 180 and 181:
2. TIME OF FLIGHT SPECTRA AND ENERG
Page 182 and 183:
When applying this transformation t
Page 184 and 185:
data were analyzed in more detail.
Page 186 and 187:
182
Page 188 and 189:
First of all, we should conclude th
Page 190 and 191:
The equation (a) may also describe
Page 192 and 193:
Even at h=0.01 mm which is too smal
Page 194 and 195:
model and some consequences of its
Page 196 and 197:
methane and 0.7-1.5% for water ice
Page 198 and 199:
case: the sample of infinite size.
Page 200 and 201:
196
Page 202 and 203:
198
Page 204 and 205:
200
Page 206 and 207:
202
Page 208 and 209:
204
Page 210 and 211:
206
Page 212 and 213:
208
Page 214 and 215:
210
Page 216 and 217:
Phase Diagram of the CH4-H20 system
Page 218 and 219:
Reaction Chamber for Hydrate Produc
Page 220 and 221:
Analysis: X-ray diffraction pattern
Page 222 and 223:
Comparison with non-hydrate forming
Page 224 and 225:
Mechanical Tests: Apparatus 220
Page 226 and 227:
Morphology of Indium Jacket 222
Page 228 and 229:
Schriften des Forschungszentrums J
Page 230 and 231:
Schriften des Forschungszentrums J
show all

Druck-Materie 20b.qxd - JUWEL - Forschungszentrum Jülich

Create successful ePaper yourself

Delete template?

Save as template?