* Corresponding author. Fax: #36-1-395-9165. E-mail address: grosz@power.szfki.kfki.hu (T. Gro H sz) Physica B 276}278 (2000) 214}215 Thermo-hydraulic test of the moderator cell of LH  cold neutron source at BNC T. Gro H sz*, T. Hargitai, V.A. Mityukhlyaev, L. Rosta, A.P. Serebrov, A.A. Zaharov Research Institute for Solid State Physics and Optics, KFKI H-1525, Budapest 114, P.O.B. 49, Hungary AEKI Atomic Energy Research Institute, H-1525, Budapest 114, P.O.B. 49, Hungary St. Petersburg Nuclear Physics Institute, 188350 Gatchina, Leningrad district, Russia Abstract Thermo-hydraulic experiment was carried out in order to test the performance of the direct cooled liquid hydrogen moderator cell to be installed at the research reactor of the Budapest Neutron Center (BNC). Two electric heaters up to 300 W each imitated the nuclear heat release in the liquid hydrogen as well as in the construction material. The test moderator cell was also equipped with temperature gauges to measure the hydrogen temperature at di!erent positions as well as the inlet and outlet temperatures of cooling He gas. The hydrogen pressure in the connected bu!er volume was also controlled. At 140 W expected total heat load the moderator cell was "lled with liquid hydrogen within 4 h. The heat load and hydrogen pressure characteristics of the moderator cell are also presented.  2000 Elsevier Science B.V. All rights reserved. Keywords: Cold neutrons; Neutron sources; Neutron instruments 1. Introduction The Cold Neutron Source (CNS) implementation pro- ject at the Budapest Research Reactor is close to comple- tion. Before assembling and commissioning the CNS, we tested the heat-removal capacity of the direct cooled liquid hydrogen moderator cell [1]. Checking of the cooling performance of double-walled moderator cell as cold He gas cooled heat exchanger was especially impor- tant because the size of cell and therefore the expected heat load has been slightly increased compared to the original project parameters (see Table 1). 2. Tests and results Two electric heaters were mounted into the full-size test moderator cell in order to imitate the nuclear heat release in the liquid hydrogen and in the cell walls, and both could be regulated up to 300 W. The test cell was equipped with temperature gauges to measure the hydro- gen temperature at three positions in the middle, at median level near the wall and close to the top of the cell. Also, the inlet and outlet temperatures and pressures of cooling He gas as well as the hydrogen pressure were controlled. The test cell was mounted into a high vacuum case and connec- ted to a hydrogen bu!er volume and to the KGU-150/4.5 He refrigerator system operating at PNPI, Gatchina and providing up to 600 W cooling power at 15 K temperature. At the beginning of the experiment the test was cooled down from ambient temperature until completely "lled with liquid hydrogen without electric heat load. The stationary state was reached in 2 h and identi"ed by the hydrogen temperatures inside the cell and the pressure of the hydrogen gas remaining in the bu!er volume. The electric heat load was increased in 10}20 W steps. The e!ect of heat load in the hydrogen and in the cell walls was investigated separately as well as combined in 1 : 2 proportion, which is close to the ratio of expected radi- ation heat loads, respectively. 0921-4526/00/$ - see front matter  2000 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 2 6 ( 9 9 ) 0 1 2 4 4 - 2