Экспериментальное исследование трансмутации некоторых радиоактивных отходов с использованием пучков релятивистских протонов тема автореферата и диссертации по физике, 01.04.16 ВАК РФ

ОБЪЕДИНЕННЫЙ ИНСТИТУТ ЯДЕРНЫХ ИССЛЕДОВАНИЙ

ХЕЛЛА ХАЛЕД МОХАМЕД МАГДИ ЕЛ-ВАФАЕЙ

ЭКСПЕРИМЕНТАЛЬНОЕ ИССЛЕДОВАНИЕ ТРАНСМУТАЦИИ НЕКОТОРЫХ РАДИОАКТИВНЫХ ОТХОДОВ С ИСПОЛЬЗОВАНИЕМ ПУЧКОВ РЕЛЯТИВИСТСКИХ ПРОТОНОВ

Специальность: 01.04.16 - физика атомного ядра и элементарных

частиц

диссертации на соискание ученой степени кандидата физико-математических наук

Дубна, 2003

JOINT INSTITUTE FOR NUCLEAR RESEARCH

HELLA KHALED MOHAMED MAGDY EL-WAFAEY

EXPERIMENTAL STUDY OF TRANSMUTATION OF SELECTED RADIOACTIVE WASTE USING THE BEAMS OF RELATIVISTIC PROTONS

Speciality: 01.04.16 - Physics of Atomic Nucleus and Elementary Particles

Thesis

for the degree of Candidate of Science In Physics and mathematics

DUBNA 2003

CONTENTS

Chapter One "INTRODUCTION"

1-1 Introduction .........................................................................1

1-2 The Composition of Nuclear Waste......................................................2

1-3 The Various Management Methods for Spent Fuel....................................2

1-4 Experimental Production Rate (B-value)................................................6

1 -5 Spallation Neutrons.........................................................................6

1-6 High Energy Particle Accelerators.........................................................8

1-7 Previous Investigations......................................................................10

1-8 The Aim of the Present Work.............................................................15

Chapter Two "EXPERIMENTAL SET-UP"

2-1 Introduction.................................................................................17

2-2 General Construction for Investigation of Spallation Neutron Flux and

Transmutation Studies at Experimental Set-up GAMMA-2.........................17

Section A

2-3 Experimental Set-up GAMMA-2 with Different Targets.............................19

I-Lead Target...............................................................................19

II-Uranium/Lead Target...................................................................20

2-4 Experimental Set-up GAMMA-2 For Monitoring System (Activation

foils)..........................................................................................22

2-5 Determination of the Neutron Distribution at Different Geometries,

Energies and Different Targets using Radiochemical Sensors.......................24

2-5-1 Determination of Neutron Distribution at the Surface of Paraffin Moderator

at Different Targets and Energies using Radiochemical Sensors..................24

I- Natural Uranium Sensors.............................................................;.24

II- Lanthanum Sensors.....................................................................24

2-5-2 Experimental Set-up for Determination of Radial Distribution for Spallation

Neutrons for Different Targets and Energies using Lanthanum Sensors........24

2-5-3 Experimental Set-up for Determination of Azimuthal Distribution of Spallation Neutrons for Different Targets and Energies using 139La Sensors................24

Section B

2-6 Experimental Set-up for Investigation of Neutrons Distribution as a Function of Moderator Thickness at Different Proton Energies using Radiochemical

Sensors.........................................................................................27

2-7 Experimental Set-up for Transmutation Samples......................................28

Chapter Three "METHOD OF CALCULATIONS"

3-1 Determination of The Integral Proton Fluence by Means of Activation foils.....30

3-1-1 Interaction of Relativistic Proton with Aluminum...................................30

3-1-2 Calculation of the Integral Proton Fluence...........................................31

3-2 Calculation of the Experimental Production Rate (B-value)..........................33

3-2-1 Interactions of Spallation Neutrons with Radiochemical Sensors.................33

I- Lanthanum Sensors.....................................................................33

II- Natural Uranium sensors..............................................................33

3-2-2 Interaction of Spallation Neutrons with 1291,237Np and 239Pu.....................35

I-Interaction of Spallation Neutrons with 1291...........................................35

II-Interaction of Spallation Neutrons with 237Np.....................................36

III-Interaction of Spallation Neutrons with 239Pu.......................................36

3-2-3 Calculation of the Experimental Production Rate (B-value).......................38

Chapter Four "RESULTS AND DISSCUSSIONS"

4-1-1 Gamma Rays Measurements............................................................40

4-1-II Detection Efficiency...................................................................42

4-1 -III Determination of Beam Position and Size...................................46

4-2 Determination of Integral Proton Flux using Activation foils........................46

4-3-1 Determination of the Experimental Production Rates (B-value) and

Determination of Neutron Distribution at the Surface of Paraffin Moderator with Different Targets and Energies using Natural Uranium and Lanthanum

Sensors..................................................................................49

A- Experimental Production Rate for Lanthanum Sensors............................49

B- Experimental Production Rate for (B-value) Uranium Sensors................51

I- Experimental Production Rate for Uranium Fission Fragments and 239Np......55

4-3-II Determinations of the Experimental Production Rate and Radial

Distribution for Spallation Neutrons with Different Targets and Proton

Energies using 139La Sensors ....................................................61

4-3-III Determinations of the Experimental Production Rates (B-value) and the Azimuthal Distribution for B(140La) as a Function of Target Materials and Proton

Energies............................................................................................62

4-4 Determination of Integral Proton Fixa using 27A1 Foils................................62

4-5 Determination of Neutron Distribution as a Function of Depth Inside Paraffin Moderator for Set-up GAMMA-2 with Lead target at Different Proton

Energies using 139La Sensors............................................................63

4-6 Transmutation of Long Lived 239Pu and Radioactive Waste (129I and 237Np) using Secondary Neutrons Generated by the Interaction of Relativistic Proton

Beams at Different Energies with Lead and Uranium/Lead Target............ 66

4-6-1 Transmutation of 239Pu using Secondary Neutrons Generated in Lead

Target using Proton Beam at 0.5 and 1.0 GeV.......................................66

4-6-II Transmutation of 237Np Using Secondary Neutrons Generated in Massive

Targets:

I-Lead Target with Proton Beam at Energy 1.0 GeV

II- Uranium/Lead Target with Proton Beam at Energies 0.5 and 1.0 GeV.......73

4-6-III Transmutation of12 I Using Secondary Neutrons Generated in Massive

Targets:

I- Lead Target with Proton Beam at Energy 1.0 GeV

II-Uranium/Lead Target with Proton Beam at Energies 0,53 and 1.0 GeV....74 4-7 Determinations of Neutron Spectra at Different Proton Energies, Positions and

Depths using DCM-CEM.....................................................................76

Conclusion ....................................................................................81

Acknowledgements.............................................................................84

References........................................................................................85

CHAPTER 1

1-1 Introduction

Since the end of World War II in 1945 the few countries, which started to build up nuclear technologies have generated large amounts of nuclear waste resulting from the extraction of plutonium. Since the advent of significant commercial nuclear programs in the sixties, highly radioactive spent fuel elements are continuously being unloaded from power reactors, typically 25-30 ton per year from a 1000 MWe light water reactors, which is the most widely used reactor type. Now there are about 400 commercial nuclear power plants in operation world wide including -120 GW nuclear electric capacity operational in Western Europe and 45 GWe operational in the ex-USSR and East European countries. Although nuclear programs have been slowing down throughout the world, spent fuels are continuously stored, mainly in reactor pools, waiting for reprocessing or for final deep-underground disposal. According to OECD/NEA, by the end of last century (1992) one expects about 150000 tons of spent fuel unloaded from the commercial reactors throughout the QECD countries. As an example France, which has the most important nuclear program after the United States, will discharge about 1200 tons of spent fuels every year. France produces 70-80% of its electricity by nuclear reactors [1].

When the nuclear fuel loaded in usual light water reactors, it contains freshly enriched uranium at around 3.5% in 235U. Spent fuel elements contain almost all the radioactivity produced inside the reactor by fission, neutron capture and radioactive decay modes. This radioactivity is characterized by long-lived, highly active and high radiotoxic nuclides. The most important fission fragments, fissile material and long-lived actinides are listed in the table 1-1 as published by the International Commission on Radiation Protection [2].

Tablel-1 Data concerning the most important long-lived fission products (LLFP), fissile material and long-lived actinides in spent fuel elements as given by Ref.[2].

Nucleus Decay mode Half-Life yr Dose factor Sv/Bq Activity Bq/kg Radio-toxicity Sv/kg

99Tc 0 2.11E+5 0.78E-9 6.3E11 4.9E2

129j P 1.57E+7 0.11E-6 6.5E9 0.7E3

l35Cs P 2.30e+6 0.20E-8 4.2E10 0.8E2

237Np a 2.14e+6 O.llE-6 2.6E10 0.3E4

233U a 1 59e+5 0.25E-6..................... 3.6E11 0.9E5

238pu a 87.7 0.23E-6 6.3E14 1.4E8

Tablel-1 continued

Nucleus Decay Mode Half-Life yr Dose factor Sv/Bq Activity (Bq/kg) Radio-toxicity (Sv/kg)

239Pu a 2.41e+4 0.25E-6 6.3E12 0.6E6

240pu a 6.56e+3 0.25E-6 8.3E12 2.1E6

241 Pu a 14.3 0.47E-8 3.8E15 1.8E7

242Pu a 3.73e+6 0.24E-6 1.5E11 0.4E5

241 Am a 4.33c !-2 ; 0.20E-6 1.3E14 0.3E8

243 Am a 7.37e+3 0.20E-6 7.4E12 1.5E6

244Cm a 18.1 0.16E-6 3.0E15 0.5E9

1-2 The Composition of Nuclear Waste

At the time of discharge spent fuel elements have the following composition:

1- Uranium constitutes about 96% of the fuel unloaded from commercial power reactors. In the case of light water reactors, spent fuel contains about 0.90% enrichment in the fissile isotope 235U whereas natural uranium contains only 0.72% of this isotope.

2- Plutonium, constitutes about 1% of the weight of discharged fuel, it is a fissile material, which must be separated for future burning as actinide fuel in reactors.

3- Minor actinides constitute about 0.1% of the weight of discharged fuel. They consist of about 50 % neptunium, 47 % americium and 3 % curium. All of them are very radiotoxic.

4- Fission products (iodine, technetium, neodymium, zirconium, molybdenum, cerium, cesium, ruthenium, palladium, etc.) constitute about 2.9% of the weight of discharged fuel. At the present stage of our knowledge and our technological capacity, they are considered as the final waste form of nuclear power production, unless a specific use is found for the non-radioactive platinum metals.

1-3 The Various Management Methods for Spent Fuel

These amounts of radioactive wastes are generating very serious problems both from economic and ecological points of view. Since spent fuel elements contain very long-lived isotopes, they must be stored at least for 105 years by isolating them physically from the biosphere using successive barriers at a suitable depth in the ground, before they decay to the level of natural uranium ore. There are two parallel ways to reduce these amounts of radioactive wastes. The first one is the transmutation or the transformation of radioactive LLFP such as 99Tc, 129I and 135Cs by neutron capture and following p decay into stable or short-lived ones.

These LLFP cannot be used farther for nuclear power generation. The second method is the incineration or burning up of transuranic nuclides by means of nuclear fission induced in nuclear reactors causing energy release and emission of secondary neutrons [1,3,4].

At present time one can consider a commonly accepted idea of complex solution of the following mutually related problems: ecologically safe and commercially competitive production of energy with the simultaneous transmutation and incineration of radioactive waste using so called accelerator driven subcritical reactors [5,6].

Now one can consider that the best way for transmutation of such hazardous material to stable or short-lived nuclides needs to employ intense and extremely high thermal energy neutron fluxes (~1016 n/cm2s). For this purpose a beam of high-energy particles interacting with heavy extended targets (Pb, Bi, U or other compositions) should be used.

During the last decade intense investigations of the radiation waste transmutation (RWT) are conducted at many Laboratories and first reliable estimation have been obtained for the yield of some concrete processes for the major long-lived nuclides: 99Tc, 1291, 237Np and Pu via the following reactions:

99Tc(n,r)mI -S-* mRu (stable)

i]/2=15.8sec

n9I (n, stable)

tvl=\14d

mNp(n,f)131Np——

4/2=2.12«? hn^yr

OTQ

Pu (n,/) fission fragments

In the following a short discussion of three such experiments: TARC (CERN), GÀMMA-2 and "Energy Plus Transmutation" (LHE, JINR) is given.

1-3-1 TARC Experiment

Fig.1-1 demonstrates schematically the general view of the setup used in the experiment TARC for the investigation of the capture rate (CR) of neutrons for 99Tc.

TARC LEAD ASSEMBLY (334 tons)

Beam fiol& <0- 77.2 mm; l.oiglh 11» c-m)

Beam

AY

= 3.3 m

EE

EE

E3E

m

îïîE

Side view

èmmmn

s.e m I

View along tha baam direction

Fig. 1-1. General view of the TARC Lead assembly showing the individual lead block structure [7].

The principal idea of this experiment consists in the use of the conception of Adiabatic Resonance Crossing for transmutation when a block of pure lead (3.3x3.3x3 m3) was taken as a moderator of spallation neutrons and dense neutron "storage" medium [7]. The CR of neutrons (from 2.5 and 3.57 GeV/c proton beams) for 99Tc, ,29I and 127I were measured in different places of the lead block. So, for example, the CR for 99Tc is (2.67±0.43)xl05 per 109 protons. Similar values of CR for 129I and 127I in the same place are 26100±2600 and 14900±1500, correspondingly. Measured was also in detail the neutron fluence over 8 orders of magnitude in neutron energies from thermal up to 2 MeV. The conclusion was made that it appears possible to destroy very large amounts of 99Tc or 129I at a rate exceeding the production rate and, therefore, to reduce the existing stockpile of these two long-lived fission products.

1-3-2 JINR-Experiments

I-Program of Experimental Studies using GAMMA-2 Set-up

The experimental studies on GAMMA-2 set-up were carried out at the Laboratory of High Energies (Joint Institute for Nuclear Research, Dubna, Russia). It included the optimization of several parameters for transmutation of long-lived radioactive wastes and fissile material. The aim of experimental work using GAMMA-2 set-up is summarized in the following points:

1- Investigation of different massive targets: Cu, Pb and U

2- Investigation of the particle types and energies p, d, a and I2C

3- Studies of the effect of moderators

I-Study of the moderator thickness

II-Study of moderator types

4- Transmutation of some long-lived wastes and fissile material at different conditions

5- Investigation of the energy amplifier for transmutation samples

All details about the composition of GAMMA-2 Set-up will be discussion in the present work (Chapter 2). Some parameters and transmutation of some radioactive samples were studied

II-Program of Experimental Studies in the Frame of the Project "Energy Plus Transmutation "

Simultaneously with the GAMMA-2 project there is another large project, the so called "Energy Plus Transmutation" project, which consists of uranium/lead assembly (lead target with uranium blanket) [8-11]. It's research aims are summarized as follows:

1- Study of the heat generation and the energy cost of neutron generation.

2- Determination of neutron multiplication and balance.

3- Determination of energetic gain (power amplification coefficient).

4- Determination of transmutation cross-sections of radioactive wastes: actinides, fission fragments and activation products

5- Optimization of parameters for this electronuclear installation.

6- Practical recommendations on development of a proton type transmutation installation. 6- Data to modernize computer codes and programs to simulate electronuclear

processes

Fig. 1-2. shows that uranium blanket plus lead target

Fig. 1-2. Scheme for the uranium blanket plus lead target within set-up "Energy Plus Transmutation" installed at LHE-JINR-Dubna [9-11].

1-4 Experimental Production rate (B-value)

The experimental production rate (B-value) is defined as the total number of atoms formed during the irradiation of one gram of sample for one incident particle.

a Number of atoms formed ( X)

B( X) = --(M)

(Igram of samples) * (one bombarding ion)

The experimental production rate (B-value) is strictly empirical value, valid only for a given set-up, target, projectile, its energy and the exact position of the target.

1-5 Spallation Neutrons

The basic phenomenology of spallation reactions [12] was discovered as soon as the first accelerators capable of accelerating protons to higher energies (more than 100 MeV) became available in the late 1940's. The production of spallation neutron is described by using cascade evaporation model. According to this model, the neutron

usually generated in the heavy target materials is accomplished through the multi-stage process induced by relativistic particles. In the first the projectile looses some of its energy via the ionization process within the target medium, then the projectile will interact with the target nuclei by means of spallation reactions in which a large number of energetic fragments (n, n, p) will be produced. These energetic fragments (secondary particles) have enough energy to make further reactions. The target nuclei will loose their excitation energies by means of evaporation and fission processes. The de-excitation process will also produce more and more secondary particles. Secondary particles may escape from the target immediately after interaction between the particle and target materials or be captured by another target nucleus and transfer its energy to this nucleus. This process is called internuclear cascade. Also the excited nuclei will de-excite through evaporation and fission processes. According to the Pauli exclusion principle there is a part of nucleons, which doesn't participate in the cascade interaction because these nucleons will occupy the quantum state, which already exists. This means that the effective collision cross section will be reduced and therefore the total number of spallation neutrons will decrease as well. The neutrons, which escape from the target, are called spallation neutrons. The total number of spallation neutrons is varying according to the size and material of the target and the energy of the incident particle.

Stt.Mil

Thick large! spallation/ high-energy fission

lim ui;.:ci ^¡lUnion Ilii'll-C.lL'lL'X lisNioit

I «.ill or Ulllcr ItitlO.Mt-S ||> Alt nmli'i t

|M ritOIl

Prima r>

i>,, .

■tCtlHi'lftC'.i

■ 1 ✓ ' ■■

AT ^ "««1

m

%

o<iP.

«5So

tli.XH)

o:

1 innimi competes with high energy fission in the dc-c\ciiation of highly-excited nuclei.

Fig. 1-3 Scheme for the spallation process

1-6 High Energy Particle Accelerators

Because spallation neutrons are generated as a result of interaction between relativistic particles and massive targets, high energy particle accelerators are needed. Two accelerators are now in operation at the Laboratory for High Energies of Joint Institute for Nuclear Research, the first machine is the wellknown Synchrophasotron which accelerates protons up to Tkin~9 GeV and nuclei (including 28Si) with Z/A=l/2 up to Tkin~4 GeV/A. The new machine Nuclotron is the super-conducting synchrotron constructed over the period of 1987-1992, is intended to accelerate protons up to Tkin~12.8 GeV and nuclei (including 238U) uptoTkin~6 GeV/A for Z/A= 1/2. [13]

Ion I INJECTOR I sources.

[Place for Booster//fei

M

NUCLOTRON

ne-LiquE Fier KCU-1600J

SYNCHROPHASOTRON

<»l\

97 fas

Internal target of the SYaQ setup

Internal target & setup for first experiments at NUCLOTRON

•from

SQm

Fig. 1-4 General lay-out of the accelerator and experimental areas at the

Laboratory of High Energies[13]

1-7 Previous Investigations

During the last decade several experimental investigations were done at Laboratory of High Energies, Joint Institute for Nuclear Research to study the transmutation of radioactive and fissile materials using transmutation set-up GAMMA-2. In these investigations several parameters such as particle type, target material and particle energies were investigated simultaneously with the transmutation samples.

In 1994 B. Bisplinghoff, et al., [14] studied the experimental transmutation rates (B-values) for 139La and natural uranium radiochemical sensors. A natural copper rod (natCu) with 8 cm diameter and total length 21 cm was placed in a cylinder of paraffin with inner diameter 8 cm and the outer diameter 20 cm. The target was irradiated using 12C beams with energies of 22 GeV and 44 GeV generated by Synchrophasotron. The experimental transmutation rates for 239Np and fission fragments 140Ba and 132Te from uranium were calculated.. The neutron yield was studied using SSNTDs, for the same particle energies. Neutron spectrum for secondary neutrons emitted from the cylindrical surface of copper rod was calculated theoretically at the given energies using Monte-Carlo code.

During the last decade M. Ochs, et al., [15] used natural copper and lead targets. Two-radiochemical sensors 139La and natural uranium were used to study the neutron yield at the surface of paraffin moderator. 139La was used to determine the neutron yield around the paraffin moderator at azimuthal angles (0°, 60°, 120°, 180°, 240°, 300°). Charged particles such as 2H, 4He and 12C with energies (3.0 GeV and 7.3 GeV), (6.0 GeV and 14.7 GeV) and (18.0 GeV and 44.0 GeV) respectively were used with lead and copper targets to determine the experimental transmutation rates (B-values) for l39La, and uranium sensors. The experimental transmutation rates Bexp for 203Pb, 206Bi (lead target) and 24Na, 57Ni (copper target) were measured at different energies and different particles as a function within the target positions. A Nal sample was irradiated at the surface of paraffin moderator with 4He particles at energies 3.7 GeV. Monte Carlo code was used to calculate the neutron spectrum emitted as a result of interaction between carbon ion 12C at energies 1.5 GeV and 3.7 GeV with lead targets.

In 1997 R.Brandt, et al., [16] made a series of experiments using Synchrophasotron, using different particles and targets. Relativistic protons and carbon ions 12C with energies 44 GeV and 18 GeV respectively were used with two massive lead and uranium targets, which were surrounded by paraffin as moderator. Two different techniques were used to study the neutron yield at the top surface of paraffin moderator. The first one was consisting of a radiochemical sensor, in which one or more materials can be used. Natural uranium and 139La each of about 1 gram were used to measure the neutron yield at the top surface of moderator. The experimental production rates Bexp for

139La, 239Np and four uranium fission fragments (91Sr, 97Zr, 132Te and 133I) were determined. Bexp for 235U was found as well. The other technique used is Solid-State Nuclear Track Detectors (SSNTDs). In addition, two samples of long-lived radioactive

1-jq 037

wastes C I and "'Np) were placed at different positions on top of the paraffin moderator to study the transmutation, rate at proton energy 3.67 GeV with lead target. Neutron fluences emitted from the interaction of proton at energy 3.67 GeV with lead target were determined both theoretically and experimentally. Simulation experiment using 1.4xlOu Bq Pu/Be neutron source emitting 8.2xl06 neutron /sec and Pb target with paraffin moderator was done to investigate the neutron yield at different radius inside paraffin moderator.

M.I. Krivopustov et al., 1997 [17] carried out the first experiments on the transmutation of long-lived I and Np using relativistic protons of 3.7 GeV, which generated substantial neutron fluences in extended lead-targets. These neutrons get moderated in paraffin and are used for transmutation through the neutron capture followed by beta decay. One can estimate the transmutation cross section (n, y) in the given neutron field as cr(129I(n,y))=(10±2)barn and <y(237Np(n,y))=(140±30)barn. The experiments were carried at the Laboratory for High Energies, JINR, Dubna.

In 1996 to 1999 J.S. Wan, et al., [18] studied the transmutation of 129I and 237Np, at the LHE, JINR, Dubna using relativistic proton beam from synchrophasotron accelerator. Proton beams with energies 1.5 GeV, 3.7 GeV and 7.4 GeV interacted with Pb and U/Pb targets. The experimental transmutation rates Bexp for the transmuted

1 0 O "7 T7

samples and "'Np

were determined and the results were compared with the theoretical calculation using DCM-CEM and LAHET codes. The effective cross section for the two reactions

a(129I(n, y)130I) and cr(237Np(n, y)238Np) were measured. In addition the neutron spectrum fori.5 GeV protons was calculated using DCM-CEM and LAHET codes. Using LR-115 SSNTD the fluence of thermal and epithermal neutrons on top of the paraffin moderator were determined per one incident proton with different energies. Inside the paraffin moderator the neutron fluences were estimated using 235U and 232Th as a radiator on the Lexan.

In order to study the effect of monitor position and its type on the accuracy of the calculated proton flux, in 1998 J.S. Wan, et al., [19] used two types of activation material to study these effects. Two sets of natural copper and 27Al foils were installed at different places along the beam direction to study monitor reactions for Pb and U/Pb targets at proton energies . 1.0 GeV and 1.5 GeV. Natural copper and 27A1 have the reactions natCu (n, x) 24Na, 27Al(p, 3pn)24Na and 27A1 (n, a) 24Na. The influences of three reactions were calculated theoretically and the results were compared with the experimental results.

J.S.Wan, [20] studied the transmutation rate for two of the most long lived isotopes using secondary neutrons generated by relativistic protons with energies 1.5 GeV, 3.7 GeV and 7.4 GeV interacting with lead and uranium-lead targets. Also J.S.Wan investigated the neutron distribution at different positions at the top, inside and around the paraffin moderator for a given proton energy and targets. The neutron yield was

studied through the calculation of the experimental production rate (B-value) for two radiochemical sensors, which made from about 1 gram of 139La and natural uranium.

The experimental transmutation rates for 140La and 239Np and four uranium fission fragments was calculated. In addition to this work the neutron yield generated inside lead and uranium-lead targets was investigated with the help of the experimental transmutation rates Bexp for lead fragments (203Pb, 206Bi, 205Bi, 2®T1 and 200Pb) for several lead disks used as a target (Pb and U/Pb targets). Also the experimental transmutation rate for 239Np, 237U and uranium fission fragments (91Sr, 97Zr, 132Te and 133I) for two uranium rods used as a target were measured.

The cross section for many spallation and fission products of the two long-lived isotopes 129I and 237Np, generated through the direct interaction with relativistic protons at energy 3.7 GeV were calculated. The cross section for spallation products of 129I and spallation and fission products of 237Np were calculated theoretically using DCM/CEM code, the results were compared with the experimental values.

Beside the experimental work carried out in the LHE-JINR-Dubna, several theoretical calculations were done during the same period using different codes: LAHET code and DCM/CEM code [21-24].

In 1999 S.R Hashemi Nezhad et al., [21] used the LAHET code to study the behavior of spallation neutrons resulting from the interaction of relativistic protons with a very large thick lead target (3.3x3.3x3 m3). The space distribution of the neutron fluence and the neutron energy distribution with and without the presence of a neutron-multiplying medium (fissile material) was investigated. In this work three different cases were investigated:

1) A lead target and lead moderator without presence of neutron multiplying medium (Pb, Pb, 0) system,

2) A lead target, lead moderator with 235U neutron multiplying region (Pb, Pb, 235U) system

3) A lead target and graphite moderator without a neutron multiplying region (Pb, C, 0) system.

Transmutation rates of long-lived nuclear wastes, 99Tc and 129I were investigated with

lead target with lead and graphite moderator.

The