TCM IMPLEMENTATION OF BURNUP CREDIT IN SPENT FUEL MANAGEMENT SYSTEMS

V. FAJMAN

Department of Nuclear Materials, State Office for Nuclear Safety, Prague, Czech Republic

Abstract

The paper tries to describe the existing legislative and administrative requirements for the Spent Fuel Facilities licensing in the Czech Republic concerning the Burnup Credit Implementation. It also briefly mentions recent situation in the Spent Fuel Management and the future tasks connected with BUC.

1. INTRODUCTION

Nuclear power represents a significant source of Czech Republic electricity production. The four WWER 440 units at NPP Dukovany contribute to the electricity production in Czech Republic by about 215%. NPP Temelín will increase the ratio of nuclear power on total electricity production about 40%. In May ’99, after long evaluations based both on economical and safety features of the Temelín project, the Czech government decided positively about the completion of NPP Temelín. The first fuel assembly was loaded in the core of NPP Temelín Unit 1 in July 2000.

Spent Fuel from the WWER 440 NPP Dukovany after discharging from reactors spends from five to six years cooling period in NPP's at reactor pools. This spent fuel is than stored in a dry interim storage - Interim Spent Fuel Storage Facility (ISFSF) at Dukovany using dual - transport and storage CASTOR - 440/84 casks. The ISFSF Dukovany was commissioned in January 1997. ISFSF consists of a light storage building and its capacity is approximately 600 Mg of heavy metal (60 casks). Its storage capacity could cover spent fuel arisings from the operation of NPP Dukovany only until the year 2005. A storage facility will be built next to the existing one. This facility will also use dual-purpose metallic casks- for storage and transport. The bid has not been finished yet, but there are shortlisted three vendors: GNB, SKODA and Transnucleaire. The initial conditions for these cask licensing were set according usual conservative practice (fresh fuel, fresh water) without Implementation of Burnup Credit (BUC).

2. REGULATION ON SPENT FUEL STORAGE LICENSING

Parliament of the Czech Republic passed new act in January 1997 under No. 18/1997 Coll., on Peaceful Utilization of Nuclear Energy and Ionizing Radiation (the Atomic Act) [1]. The Act was developed with the objective to re-codify utilization of nuclear energy and ionizing radiation, and, especially to modify so far insufficiently regulated issues such as radioactive waste management, liability for nuclear damage, emergency preparedness.

State guarantees safe disposal of all radioactive waste, and a Radioactive Waste Repositories Authority has been set up for this purpose by the Ministry of Industry and Trade. Activities of the Authority are financed from nuclear account with main income represented by payments from radioactive waste generators. This act also establishes the basic principles of spent fuel safe management. The Atomic act does not predict whether to reprocess or dispose the spent

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fuel. According to this law spent fuel is not considered the waste, but both the operator and the State Office for Nuclear safety have right to declare spent fuel the waste.

The Atomic Act authorized the SÚJB, and in some specific cases - also other State Administration Bodies, to issue a set of implementing regulations (full text of the regulations can be found in the SÚJB Website www.sujb.cz).

In order to license a spent fuel storage facility there is a complex procedure which can be seen the in Figure 1. Such procedure includes EIA process and According Czechoslovak Act No.

50/1976 Coll., on Civil Construction [2] there are three stages of the licensing process of any construction with a nuclear facility:

1. Siting permit, 2. Construction permit, 3. Operational permit.

The power to issue respective permits is in the hands of a local Construction Authority.

But for each step an approval shall be issued by the SUJB. Basic condition to SUJB approval represents SAR evaluation. Initial, Preliminary and Pre – operational (final) SARs shall be gradually submitted to the SUJB. The contents of them as well as requirements are set by the Atomic Act.

More detailed safety requirements are set namely by Regulation No 195/1999 Coll on Requirements on Nuclear Installations, which in its §47 (Irradiated and Spent Nuclear Fuel Handling and Its Storage) requires.

The installation for the handling with the irradiated and spent nuclear fuel and its storage, and for the handling and storing the other substances containing the fissile products and radioactive substances shall be designed in a such way, in order that it may be possible:

1. To prevent with reserve the achievement of criticality even under conditions of the most effective deceleration of neutrons (optimum moderation) by area arrangement or by other physical means and procedures, and by this to prevent:

1.1. The exceeding the 0.95 value of effective coefficient of multiplication of neutrons under the assumed accident situations (including the flooding by water),

1.2. the exceeding the 0.98 value of effective coefficient of multiplication of neutrons under the conditions of optimum moderation,

2. To assure the sufficient remove of residual heat under normal and abnormal operations and under accident conditions,

3. To assure the capability for performance of periodic inspections and tests, 4. To prevent the fall of irradiated fuel during the transport,

5. To reduce to the minimum the possibility of fuel damage, i.e. namely to prevent the exposure of irradiated element or fuel set to the non-allowable load during the handling, 6. To prevent the fall of heavy objects on the fuel set, i.e. the objects with the mass greater

than the mass of fuel set is,

7. To enable the storage of damaged fuel elements or damaged fuel sets at the constructions and operational units, the part of which is a nuclear reactor,

8. To assure the radiation protection of nuclear installation personnel, 9. For wet storage with a water charge to assure

9.1. The check-up of chemical composition and of radioactivity of all water, inside of which the irradiated fuel is stored or in which there is a handling with it, 9.2. The monitoring and controlling the height of water level in the spent fuel pool

and the leakage detection.

From the text above could be easily derived that no explicit rules for BUC implementation exist in the CR. Anyway the licensing process has been until now based on conservative approach, without BUC.

3. IMPLEMENTATION OF CRITICALLITY EVALUATIONS IN THE STORAGE SYSTEMS AND THE FUTURE TASKS

During licensing Interim Spent Fuel Storage Facility (ISFSF) at Dukovany the requirement on maintaining subcriticality naturally belonged to basic safety criteria. For the SAR consideration the fresh fuel its maximum allowed enrichment 3,6% U235, in fresh water were calculated. Upon the SUJB request were calculated the situations taking into an account optimum moderation, namely the decreasing density of water. No credit was taken for BUC.

During licensing Spent Fuel Pools at Reactors – NPP Dukovany was the situation almost the same as above (ISFSF). There was only one exemption. Partial credit was allowed for one (not compacted yet) upper rack (for emergency unloading) the validity of this decision was limited until re-racking. The SUJB decision was conditioned - prior to its eventual use was necessary to calculate subcriticality and the result consult with the regularor.

Because there appeared several indications, especially from the cask vendors to ask for the future storage-transport cask licenses with the BUC implementation, the intensive studying of the BUC issue in the CR has started. SUJB opened a state supported research project, with the goal to prepare the metrology and detailed safety criteria for the evaluation of BUC in transport and storage systems. The team of experts at the Nuclear Research Institute Rez realizes this project.

4. CONCLUSIONS

Existing experience in the field of the BUC implementation can be briefly summarized as follows:

1. Conservative approach based No significant experience with the BUC yet, 2. Next transport/storage cask to be licensed – indication of the licensee – BUC, 3. A state programs focused on BUC (namely the regulatory aspects) started this year.

REFERENCES

[1] CZECHOSLOVAK ACT No. 18/1997 Coll. on Peaceful Utilization of Nuclear Energy and Ionizing Radiation (the Atomic Act) and on Amendments and Additions to Related Acts January 24, 1997.

[2] CZECHOSLOVAK ACT No. 50/1976 Coll. on Civil construction, April 27, 1976.

[3] REGULATION No 195/1999 Coll. on Requirements on Nuclear Installations for Assurance of Nuclear Safety, Radiation Protection and Emergency Preparedness, July, 1997.

CURRENT APPLICATIONS OF ACTINIDE-ONLY BURNUP CREDIT