B.A.R.C./I-259 1 < n GOVERNMENT OF INDIA ATOMIC ENERGY COMMISSION SAFETY ASPBCTS IN PLUTONIUM HANDLING by S. Janardhanan, T. N. Krishnamurthi, S. B. Dabhadkar and S. D. Soman Health Physics Division BHABHA ATOMIC RESEARCH CENTRE BOMBAY, INDIA 1973 B.AJI.C./I-259 GOVERNMENT OF INDIA ATOMIC ENERGY COMISSION SA5BTY ASPECTS IN FTAJTONIUM HANDLING by S. Janardhanan, T.N. Krishnamurthl, S.D. Dabhadkar and S.D. Soman Health HiyBics Division BHABHA ATOMIC RESEARCH CENTRE BOMBAY, INDIA 1973 COMPEMPS fege So. 1. INTRODUCTION 1 2. RADIOLOGICAL SAFETY 1 2.1 Formation of ELutoniun iBotopes 1 2.2 Nuclear Characteristics of FLutoniua Radionuclides 2 2.3 External Hazardo 2 2.4 Internal Hazards 23 3. ENGINEERING SAFETY 31 "5.1 Glove Box for Hutoniun Handling 31 3.2 Design Safety Consideration 32 3.3 Ventilation for Hutonlum Laboratory 35 3.4 Surfaoe Finish for Plutonium Laboratory 36 3.5 Ere -commie 8 ioning Checks for Plutonium Laboratory 56 4. aONTAMINVTION EVALUATION, CONTROL AND HffiVENTION 37 4.1 Special Technique for Pu-Alr Monitoring 38 4i2 Surface and Bars onnel Monitoring 39 4.3 Decontamination 39 5. PLUTONIUM FIRE SAFETY 48 5.1 Plutonium Metal FireB . 49 5.2 Protective Measures for Hutonium Fires 50 5.3 Fire Safety in Storage, Handling and Shipment of 51 HLutonium Metal 6. CRITICALITY SAFETY . 51 6.1 Oriticality BarameterB 52 6.2 MethodB of Criticality Control 54 6.3 Safety FactorB 55 Page No. 6.4 Criticelity Data 57 6.5 Soluble Poisons 61 f, .6 Solid Poisons 61 f) .7 Pipe Intersections 61 6.8 Storage of Pu Metal, Compounds and Solution 61 6.9 Transport of Plutonium Metal, Compounds and Solution 68 6.10 Magnitude of Critieality Accident 68 6.11 Administration of Nuclear Safety 72 REFERENCES 73 Appendix-Is Design Details of a Typical Inert Atmosphere 75 Glove Box for Plutonium Handling laboratory Appendix-Hi Design Details of a Typical Normal Atmosphere 79 Glove Box and Pumehood SAFETY ASPECTS ITT PLUTONIUM HANDLING by S. Janardhanan, T.N. Krishnamurthi, S.B. Dabhadkar and S.D. Soman 1. ISTBODOCTION Jlutoniuv is being extensively used in the atoaio enorgt industry in varioua forms. Its radioactive and fissile properties •ad its biologioal behaviour present a number of basards a ad spaoial considezations mist be given to the safety problems arising in the baodling of plutooiua. Much experieooe tea been gained in this fiell at Iroabay and other laboxatories art this report compiles important safety aspeots in handling plutoniua inoluding critioaiity oonaiderationa. The safe handliqg problems could be broadly divided into the following groupst 1. Radiological safety 2. Engineering safety 5* Contamination, its evaluation,control and prevention 4* Decontamination 5* Fire hazards and control 6. Critioaiity Bafety. 2« RADIOLOGICAL SAFETY 2.1 ?o mat ion of ELutoniua Isotopes PlutonlUB is formed by neutron irradiation of Uraniu&~238. Formation of Plutonium isotopes and their daughters are shown in ohart-V '. Composition of plutonlum changes with uranium burn-up in the reactor* while at low buro-ups Pu-239 and Pu-240 are the significant plutonlum radionuolidea, at high burn-ups, plutonium isotopes from mass number 233 through 242 are generated) in quantities, significant enough to present severe hugarda during handling. 2.2 Suolear Characteristics of Plutonium Badionuolides Decay characteristics of plutonium isotopes and their daughters are shown in Table 2.1* Amongst these isotopes of plutonium,Pu-239 ie important aa it 1B the major constituent isotope in plutonium and It has a fission cross section of 746 barns for thermal neutrons, •• greater than that for U«235 (580 barns). Pu-240 la a parasitio neutron absorber for low energy neutrons• Pu-241, though produced in smaller amounts, is a better fisaile material than even Pu-239 on account of its higher thermal neutron fission cross section of 1025 barns. 2.3 External HazardB The handling of large quantities of plutonlum requires appropriate administrative control to minimise personnel exposure. The external radiation dose rate varies with the isotopio composition of plutonium* 2.3*1 Alpha particles emitted by plutonium isotopes do not constitute an external hazard because of its short range in air and body tissue (for Pu-239 alphas, range in,air is 3.68 en and range in body tissue arri water is 40 u). r37: n.?n (675 ft) p-335D) ?38JL w24V .242 n. Ciay) OCC163D) 242 CHART-1 FORMATION OF PLUTONIUM RADIONUCLIDES AND DAUGHTERS Iable-2.1 PAHIQACT3VE DECAY CHARACTERISTICS OP PKJTONIUM ISOTOPES ATO DAUGHTERS Zaotopo Radiation Yield $ Energy Specifio (MeV) activity (V) Pu-238 Alpha 100 5.49 66.4 Oamna 10-9 0.1b n 8x)0 5 0,10 2 11 3.8X10- 0.044 L-X-ray 0.017 Pu-239 Alpha too 5.U Gamma 2x10-5 0*038 11 3 0.052 2.436x10 yr» 0.062 0*12-0.20 3x10-5 0.38 L~X-raye 1.4 0.0136 2.2 0.0174 0.2 0.0205 Pu-240 Alpha 76 5.162 11 5.118 6.58x10 yre 0.23 1O~2 ' 0.044 Ir-X-raya 10 0.017 K-X-raya •tO 0.102-0.125 Pu-241 Alpha 3x10"5 4.9 13.0 yra 111.5 Beta 99.997k 0*02 Gamma 2x10"4 0*145 11 IO-5 0.10 Pu-242 Alpha 76 4.89 3.79x1O^yra 0.004 n 24 o 4.05 10-2 0.045 Ir-X-raya 10 0.017 (Tabl* 2.1 oontlmwd) laotop* Radlfttian Yl«14g( Energy Half-1 if • Specific (May) aottritj (Cl/g) U-Z37 100 .245 6.75 4aye 6.74x10 61 .059 H 35 .207 If 4 .334 Aa-241 Alpha 84 5.46 13*6 5.43 45S 3.13 37 •017 2.7 .026 it .05 •043 ti 37 .059 n .02 .099 2.2.2 Major fraction of the external dose rate originates from X-raya and gamma rays with energies below about 20 to 40 KeV. The dose due to plutooium X-rays could be significant but these weak X-rays are easily absorbed in the thinnest structural material ., The L or M X-ray activity in plutonium is quite high but these intensities can be reduced to almost zero by normal' rubber gloves. As Aaerieium-241 and uranium-237 build.up is the separated plutonium, higher energy gammas (> 40 K.eV) are emitted and gamma shielding may be required to maintain acceptable doso rates* The surface doae rate contributions from daughters of Pu-241 are a function of the Pu-241 concentration and the time since purification of plutonium. For timea much less than 14 years, the surface dose rate from Am-141 in the mixture ' is given by =» 0.2 where t is time in days since purification of plutonium and P241 is tha weight fraction of Pu-241 in the mixture. The surface dose rate contribution from U-237 in the mixture , for time a much less than 14 years is given by RadsAr . 23 P2410- e"" where pg41 and t are, aa defined earlier. The contributions from Am-241 and U-237 to the surface done rates are shown in Figure 2,1 against time since purification of Pu. U-237 contributes most to the gamma dose rate initially} however U-237 build-up reaches equilibrium in a few weeks. The 40 80 100 160 200 240 TIME IN DAYS SINCE PURIFICATION U) FIG. 2.1- SURFACE DOSE RATES FROM ?U DAUGHTERS dose rate due to Am-241 continue a to increase and just equals the U-237 dose rate at 115 days after purification. The dose rate due to Ain-241 continues to increase for many years until the parent Pu-241 can no logger maintain the build-up of Am-241 • The total X-ray and gamma radiation surface dose rate from massive plutonium can be estimated from the following equation! 980 p238 +'0.67 P259 + 14 p240 + 0.2 0 102 • 23 p2U (1 - e" ' *) where t is the time in days since purification of plutonlum and p ia the weight fractions of various pu isotopest(denoted by the subscript)* Tha surface dose rates, for massive plutonlumi from X and gamma rays with energies greater than 40 KeT? can be calculated from the equations Bem/hr - 2 p23Q + 0.056 p2jg + 0.62 p2AQ + 0.1 P24l* 102 • 23 p241 (1 - e-0' *) where p and t are, as defined earlier. An adc'ltioml source of gamma radiation from Plutonium, could be fission product contamination of Pu» however, this depends on the degree of decontamination achieved in the reprooeesing of spent fuel* Amongst the fission products, Bu, Zr, and Nb are the difficult oneB to remove. The tolerable fission product contamination level appears to be between 5 to 1.0 pCi par gram of Plutonium. 2*3»3 Beutron Emission from Plutonium Appreciable neutron dose rates are also associated with plutonium. Neutrons emitted have a wide range of energies upto tO ifeV or more. Fast neutron yields from spontaneous fission of plutonium are given in Table 2.2. For a spherical mass of plutonium, the dose rate due to fast neutron can be estimated from the equation* { 009 0<02 °» P240 * > 2 where M is the mass of Fu in grams y- la the distance in cm and p is the weight fraction of Fu isotope (denoted by subsoript) Neutron emission from plutonium in contact with light elements; due to ( <*> , n) reactione, contributes significantly to the neutron dose rates. Beutron yields from the light element-plutonium compounds, plutoolum fluoride and plutonium oxide are given in Table 2.3.